Barrington and Lirk [1] and Saporito et al [2] make many valid arguments with regard to pressure monitoring during regional anaesthesia. However, I would like to dispel the implicit assumption that because injection line pressure is not an accurate reflection of needle-tip pressure, it is not useful. Being a positive pressure system, in-line pressure is equal or higher than the needle-tip pressure. If we are guided by in-line pressure, we err on the side of lower and therefore, safer needle-tip pressure.

There is one scenario where in-line pressure is equal to needle-tip pressure and that is when there is no flow, assuming a patent fluid system. The in-line pressure at which flow starts, that is, the "opening pressure", will then be a reasonably accurate (if safer) reflection of needle-tip pressure.  

As one of the authors of a paper [3] cited in the editorial [1], I regularly use the clinically improvised pressure gauge we described, which is a three-way tap with an air-filled 1 ml syringe inserted between the needle and the syringe, in my practice as an orthopaedic anaesthetist. I apply the principles described above, with the added bonuses of high availability, low cost and quick construction.  

M. Lim

Cardiff and Vale University Health Board,

Cardiff, Wales.

Email: mnj.lim@gmail.com

No external funding and no conflicts of interest declared.

References

1. Barrington MJ, Lirk P. Reducing the risk of neurological complications after peripheral nerve block: what is the role of pressure monitoring? Anaesthesia 2019; 74: 9-12.  

2. Saporito A, Quadri C, Kloth N, Capdevila X. The effect of rate of injection on injection pressure profiles measured using in‐line and needle‐tip sensors: an in‐vitro study. Anaesthesia 2019; 74: 64–8.

3. Patil J, Ankireddy H, Wilkes A, Williams D, Lim M. An improvised pressure gauge for regional nerve blockade/anesthesia injections: an initial study. Journal of Clinical Monitoring and Computing 2015; 29: 673–9.

Whilst we agree with the recommendations made in recent papers [1-2], we are surprised that the one airway device which has already fulfilled the suggested criteria has been omitted. The Tulip® airway was originally designed as a Guedel airway replacement and research was completed through a series of pre-defined development process steps from bench top testing, through Medicines and Healthcare products Regulatory Agency (MHRA) applications, Council of Europe (CE) marking, International Standards Organisation (ISO) and Food and Drug Administration (FDA) certification, and then multiple published manikin studies which concluded in a level 1 randomiosed controlled trial in humans [3-8]. These successful studies also produced the first direct comparative man and manikin results known, which showed very close, statistically significant correlation. We think that this is the first time an airway device has been introduced which fulfils the proposed guideline protocols for any such new airway device.

The question that arises is that if a new device produces statistically significant results and follows a logical, published development process, what happens next? The clinical application of any new airway device must involve independent research by anaesthetists and allied medical and para-medical practitioners, otherwise new airway devices will be overlooked as adjuncts for advancing patient safety.

P. N. Robinson

A. Shaikh

Northwick Park Hospital,

Harrow, UK.

Email: pnrfmt@msn.com

No external funding declared. Dr. Shaikh is the inventor and patent owner of the Tulip^(R) device.

References

1. Ahmad I, El-Boghdadly K. From evidence based on practice to evidence-based practice; time for a difficult airway management strategy. Anaesthesia 2019; 74: 135-9.
2. Pandit JJ, Popat MT, Cook TM, Wilkes AR, Groom P, Cooke H, Kapila A, O'Sullivan E. The Difficult Airway Society 'ADEPT' guidance on selecting airway devices: the basis of a strategy for equipment evaluation. Anaesthesia 2011; 66: 726-37.
3. Robinson NP, Shaikh A. An ADEPT apology. Anaesthesia 2012; 67: 432-33.
4. Harrison S, Robinson NP, Shaikh A, Yentis SM. Manikin evaluation of the Tulip – a new supraglottic airway. Anaesthesia 2009;64: 807.
5. Kynoch M, Saini R, Robinson PN,  Shaikh A, Hasan M, Vaughan D.  Randomised crossover comparison of the Tulip airway compared with the Guedel airway for inexperienced users in a manikin. Anaesthesia 2013; 68: 317.
 6. Murashima K, Ozaki M. New supraglottic airway device Tulip is easy to insert: a manikin study. Anesthesia and Analgesia 2011; 112: S05. 
7. Robinson PN, Shaikh A, Sabir NM, Vaughan DJA, Kynoch M, Hasan M. A pilot study to examine the effect of the Tulip^® oropharyngeal airway on ventilation immediately after mask ventilation following the induction of anaesthesia. Anaesthesia 2014; 69: 707-11.

We congratulate Whittaker et al. for their work with the Global Capnography Project (GCAP) [1]. Given the likely physical and personnel infrastructures involved, it is a significant achievement to not only provide robust monitoring but also to show follow up with the participants.

Our hospital has an established link with a plastic surgical unit in Accra, Ghana. Ghana is 31 points higher on the Human Development Index than Malawi [2]. In December 2018, we undertook an anaesthetic seminar in Accra for 27 individuals from 10 hospitals who varied from medical officers to consultant anaesthetists. Despite 20 having access to capnography, 13 felt uncomfortable managing an airway at least once a month. Sixteen had previously seen an aspiration under anaesthesia and 26 a failed intubation. Worryingly, 7 had previously seen a failed ventilation or aspiration causing mortality. It is evident, therefore, that airway issues are paramount even in this relatively fortunate cohort. A monitor is only as good as the person watching and reacting to it.

We were impressed by the simplicity of the teaching involved in GCAP and are sure that airway training was included, but think that improvements will truly occur when local, world or specialist societies who have expertise in airway management, link and produce an additional standardised simple airway training package. Our teaching involved reinforcing simple measures looking at airway assessment, aspiration risk and simple airway strategies, including bougies, laryngoscopy and laryngeal mask airways, and endotracheal tubes ('ABLE'). Simple surgical airway techniques via a highly effective low-cost manikin were taught according to Difficult Airway Society guidelines [3,4]. For 10 candidates, this was the first time they had undergone any formal airway training. Nineteen felt “much better prepared” to manage a difficult airway following the course, and the remaining candidates felt “better prepared”. All candidates would recommend a similar course to colleagues. Such training increases local status for anaesthesia and can help promote teamwork. This GCAS project is an important initiative. We feel that combining it with a simple airway management teaching package may help ensure that airway management for many can move from uncertainty to competence and capability although the difficulty of this task should not be underestimated.

M. Basler

A. Capek

Glasgow Royal Infirmary,

Glasgow, UK.

D. Kwami

M. Karbo

Korle Bu Hospital,

Accra, Ghana.

Email: michael.basler@ggc.scot.nhs.uk

No external funding and no conflicts of interest declared.

References

1. Jooste R, Roberts F, Mndolo S, Mabedi D, Chikumbanje S, Whitaker DK, O'sullivan EP. Global Capnography Project (GCAP): implementation of capnography in Malawi–an international anaesthesia quality improvement project. Anaesthesia 2019; 74: 157-65.

2. Anand, S, Sen, A, 1994. Human Development Index: Methodology and Measurement. Human Development Report Office Occasional Paper No.12. United Nations Development Programme, New York. 

3. Frerk C, Mitchell VS, McNarry AF, et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults. British Journal of Anaesthesia 2015; 115: 827-48.

4. Willers J, Harries M, Young P0042 Development of a bleeding thyroid phantom to increase fidelity of an emergency tracheostomy simulation. BMJ Simulation and Technology Enhanced Learning 2015; 1: A8.

We would like to thank the authors for their interesting and thought-provoking publication of their case series of awake breast surgery using a combination of regional techniques, as well as their hard work in delivering a novel service to breast cancer patients [1].

At Aneurin Bevan University Health Board (ABUHB), we have also been providing a comparable service for the last two years, which we formulated following direct discussions with the authors at Guy’s and Thomas’ NHS Foundation Trust.

We have provided an awake breast surgery service for patients with breast cancer, who would otherwise be unsuitable for general anaesthesia. These are largely frail, elderly patients and possess multiple significant comorbidities placing them in a high-risk category. Comparable to the authors’ case series, a total of 23 awake breast surgeries have been performed over this two-year period, 16 of which have been audited.

Our regional anaesthetic recipe for these surgeries is modified from that presented in the authors’ original article, quoting a single-level transthoracic paravertebral block (TPVB) at T2-3 or T3-4 plus a PECS-2 block using a combination of 0.5% levobupivacaine and 2% lignocaine with 1:200,000 adrenaline, on the background of 1-2.5mg midazolam plus 25-75mcg fentanyl. Through our experience, we have found satisfactory efficacy from a combination of a three-level TPVB (T2-3, T3-4, T4-5) plus a PECS-1 block using 0.75% ropivacaine on a background of 1-2mg midazolam IV. In addition, we have found that the discomfort experienced by our patients from prolonged shoulder abduction on the operative side can be alleviated by a superior trunk and supraclavicular nerve block using 1% lignocaine with 1:200,000 adrenaline, intended for the duration of the surgery only. Intraoperative sedation was provided to some, but not all patients, based on a combination of patient request and requiring safe intraoperative conditions. When sedation was provided, it was achieved with a target-controlled infusion of Propofol using the Marsh model with effector site concentrations of 1-2mcg/ml.

We have found great success using the aforementioned recipe, with good patient and surgical satisfaction reported. In addition, we have found great satisfaction in providing a novel, safe service to a particular demographic of patients who would otherwise be excluded from surgical management of their breast cancer. Our data corroborates with that presented by the authors, and we intend that this aids to affirm their hypothesis of providing awake breast surgery using solely regional anaesthetic techniques.

In addition, we are currently running a pilot project whereby these high risk patients are entered onto an ‘awake breast surgery pathway’ for assessment by an anaesthetist and surgeon; as well as a care of the elderly physician.  This has been set up with a view to optimise anaemia preoperatively, identify and modify risk factors for postoperative delirium and have a comprehensive geriatric assessment and advance care planning.  Postoperatively on Day 1 there is a further review from a care of the elderly physician to optimise their condition and expedite discharge.

A Byford-Brooks

P Bopanna

D Burckett-St.Laurent

Royal Gwent Hospital, Newport

Aneurin Bevan University Health Board

Email: anthony.byford-brooks@wales.nhs.uk

No external funding and no conflict no interest declared

Reference

(1)    Pawa A, Wight J, Onwochei DN, et al.  Combined thoracic paravertebral and pectoral nerve blocks for breast surgery under sedation: a prospective observational case series. Anaesthesia 2018; 73: 438-43 

The ongoing debate about manikin studies within anaesthetic airways research implies that manikin studies are of little valuE [1, 2].  Our findings do not support this belief. The Tulip^® airway development research studied identical protocols, first in manikins and then in humans and we found the comparative results to be very close, in some cases identical [3, 4]. This, to our knowledge, was the first direct reproduction of an identical protocol in both man and manikin, and therefore the first set of significant results that define the exact role of manikins in airway research. We believe it answers the ongoing manikin clinical value question.

The close correlation of these 2 sets of results does help answer the question of whether there are too many manikin studies. Both of our man and manikin studies have been published in peer reviewed journals with statistically significant results [5, 6], so the individual results are worth both noting individually and comparing together. These comparative results show a close correlation, with almost identical results in both our man and manikin studies, negating the belief that manikin simulation is of little value as there is significant correlation, which was previously unknown.

It must be remembered that manikins are ultimately safer, and allow investigations that may be unethical in humans. This includes measuring peak ventilation pressures and possibly intubation through the airway, which was of real value when developing the Tulip^® airway and understanding its unique abilities in comparison to the Guedel and Mask method it replaces.

Recently meta-analytical studies show a decline in the relative percentage of manikin studies in overall anaesthetic research [2]. This may need to be reversed in the light of the first Tulip GT^® airway man versus manikin study results. Our conclusion is that manikin simulation has real clinical value and therefore should be used as a logical step to develop a new airway, as we found simulation in high-quality manikins invaluable in our research into the Tulip^® airway.

A. Shaikh

P. N. Robinson

S. J. Harrison

Northwick Park Hospital, 

Harrow, UK.

Email: pnrfmt@msn.com

No external funding. Declaration of Interest;  Dr A Shaikh is the inventor of the Tulip^® Airway.

References

1. Popat MT, Rai MR. Evaluation of airway equipment: Man or Manikin. Anaesthesia 2011; 66: 1-3.

2. Ahmad I, El-Boghdadly K. From evidence based on practice to evidence-based practice; time for a difficult airway management strategy. Anaesthesia 2019; 74: 135-9. 

3. Kynoch M, Saini R, Robinson PN,  Shaikh A, Hasan M, Vaughan D.  Randomised crossover comparison of the Tulip® airway compared with the Guedel airway for inexperienced users in a manikin. Anaesthesia 2013; 68: 317.

4. Shaikh A, Robinson NP, Hasan M. The Tulip GT® airway versus the Guedel airway and Facemask: a randomised, controlled, cross-over clinical study comparing airway ventilation with Basic Life Support (BLS) trained airway providers in anaesthetised patients. Anaesthesia 2016; 71: 315-9.

5. Harrison S, Robinson NP, Shaikh A, Yentis SM. Manikin evaluation of the Tulip® – a new supraglottic airway. Anaesthesia 2009;64: 807.

6. Robinson PN, Shaikh A, Sabir NM, Vaughan DJA, Kynoch M, Hasan M. A pilot study to examine the effect of the Tulip® oropharyngeal airway on ventilation immediately after mask ventilation following the induction of anaesthesia. Anaesthesia 2014; 69: 707-11.

We thank Erodes et al. for their much needed International consensus statement on the peri-operative management of direct oral anticoagulants in cardiac surgery [1]. They state “patients who underwent cardiac surgery in a recent study did not experience increased bleeding events with rivaroxaban in comparison with vitamin K antagonist treatment” [1], referencing a paper by Patel et al. [2]. However, the referenced study is a double-blind trial of patients with atrial fibrillation examining whether rivaroxaban was noninferior to warfarin for the primary end point of stroke or systemic embolism. None of the study patients underwent cardiac surgery. We would like to ask the authors, therefore, whether they think that the conclusions they drew based on this study in their consensus statement may be misleading in the context of cardiac surgery.

We would also like to seek clarification on the meaning of the abbreviation 'Tc' in Fig. 1, which has not been included in the key.

Finally, we would like to ask the authors for clarification about their considering the administration of platelets, cryoprecipitate and prothrombin complex concentrate to be 'N/A' when the bleeding tendency is classified as severe.

L. Peltola

M. Lane

Royal Brompton Hospital,

London, UK.

Email: peltola.laura@googlemail.com

No external funding and no competing interests declared.

References

1. Erdoes G, Martinez Lopez De Arroyabe B, Bolliger D et al. International consensus statement on the peri-operative management of direct oral anticoagulants in cardiac surgery. Anaesthesia 2018;73:1535-45.

2. Patel MR, Mahaffey KW, Garg J et al. Rivaroxaban versus warfarin in nonvalvular atrial fibrillation. New England Journal of Medicine 2011; 365: 883-91.

I am concerned that Yeow at al.'s study may herald the beginning of a raft of new devices developed for emergency front of neck access (eFONA), having also recently become aware of the ScalpelCric (VBM Medizintechnik GmBH, Sulz am Neckar, Germany) [1]. The Difficult Airway Society (DAS) has only recently rationalised the terminology, technique and equipment for Plan D/'can't intubate, can't ventilate' (CICO) across the UK, enabling the elimination of the myriad of needle cricothyroidotomy devices on airway trollies and in anaesthetic rooms, in turn obviating the inherent issues of varying manufacturer, cost, size, design complexity, technique, learning and teaching strategy, availability, success rate etc. It seems rather counter-productive to be developing a range of eFONA devices that will replicate many of the same problems. 

I appreciate Ms Dill’s, on behalf of BAREMA, reply to my original letter.

With all due respect I think she has missed the point and dismissed the problem that exists every time the anaesthetic workstation is used.

The high and low agent alarms she refers to, only function once a vaporiser is switched on and anaesthesia provided. They do not detect absence of the agent in the workstation circuit at the start of an anaesthetic so are useless in alerting an anaesthetist to non-delivery of the anaesthetic agent. 

The argument about the alarm fatigue is completely out of place here if this kind of alarm can prevent accidental awareness under general anaesthesia (AAGA) while using a workstation which the main or the only purpose is to provide adequate anaesthesia.   

 For Hospital or Anaesthesia Lead to advise all anaesthesia machine users what the default alarms are set to, is unrealistic, not practised, would have no legal standing and would make no difference on the outcome of a potential AAGA. 

Since my original correspondence I have come across yet another communication relating to more cases of AAGA caused by unintentional non delivery of volatile anaesthetic (1).

The fact, as Ms Dill states, that Getinge will shortly introduce on their machines a dedicated alarm advising the user that the vaporiser has not been turned on once therapy commences speaks for itself and proves my point. I would like to see this becoming a standard alarm and implemented on all anaesthetic workstations to prevent AAGA.

J. Bernard Liban

St George’s University Hospitals NHS Foundation Trust

London, UK

Email: jbernardliban@gmail.com

No external funding or conflict of interest declared.

Reference

1. Volatile Anaesthetic Unintentionally Not Delivered, Anesthesia Patient Safety Foundation Newsletter, October 2018, p64

An argument that I often hear for not adopting colour-coded bar-coded labels for medication syringes in anaesthesia is that these are somehow expensive technologies [1]. In fact, these are cheap technologies – so cheap that your local supermarket or convenience store uses them for every item on their shelves, even though no lives are at stake. The cost of paper barcode labels and a barcode reader is very small in comparison to the costs of almost any other aspect of patient care, including personnel, equipment, drugs, and in particular the high cost of patient harm [2].

There is overwhelming evidence that drug administration error is a leading cause of iatrogenic harm in healthcare, and substantial evidence that better labelling and barcoding reduces the rate of such errors [3-5]. Even putting aside the issue of human suffering, any consideration of cost must also factor in the benefits of the money saved from injuring fewer patients. Yet this is something which is rarely, if ever done by those making the argument that new safety techniques are expensive – a topic I discussed in this journal some 14 years ago [6]. This has been the case since it was deemed prohibitively expensive to provide disposable syringes to diabetics in the United Kingdom in the 1970s, or to provide antihypoxic devices on anaesthetic machines in the 1990s [6].

In fact safety is the ultimate goal of all technological development. Name any technology, from automobiles to gene replacement therapy, and a similar safety profile can be seen as each becomes more widely used. At first accidents and harm were frequent – there were no regulations on how the new technology should be used, and no provision for building safe operation into its design. Subsequent years saw dramatic improvements in safety as the new technology became more widely used and a more systematic approach to safety was adopted.

With the high number of anaesthetics being conducted in the world every day, taking a more systematic approach to the safe administration of intravenous drugs is overdue, and we know that systematic approaches must go beyond exhortation for the clinician to be more careful [7]. We also know that systematic approaches to safety need to involve multiple safeguards, such as labels which incorporate colour-coding and bar-coding in order to ensure safe performance in particular uncommon circumstances where one safeguard, for example colour-coding, cannot be relied upon [8]. Despite this, systematic approaches to safety in anaesthesia are often given low priority compared with other costs. For example, why is it so much easier to buy a transoesophageal echocardiography machine, costing hundreds of thousands of dollars, than to convince your hospital manager that barcoded labels are money well spent? We need a better attitude to systematic safety approaches. A significant step forward would be some estimate of the savings arising from fewer injured patients. Avoiding even a single case of prolonged or unplanned stay in the intensive care unit would pay for a lot of barcoded labels.

C. S. Webster

University of Auckland,

Auckland, New Zealand.

Email: c.webster@auckland.ac.nz

 The author is a minor shareholder in SaferSleep Ltd (London, UK) a company that aims to improve safety in healthcare.

References

1. Marshall SD, Chrimes N. Medication handling: towards a practical, human-centred approach. Anaesthesia 2019; 74: 280–4.
2. Bowdle A, Jelacic S, Nair B, Jense R, Webster CS, Merry AF. Why we scan the barcodes of anaesthetic medications. British Journal of Anaesthesia 2019; 122: e24-6.
3. Poon EG, Keohane CA, Yoon CS, et al. Effect of bar-code technology on the safety of medication administration. New England Journal of Medicine 2010; 362: 1698-707.
4. Webster CS, Larsson L, Frampton CM, et al. Clinical assessment of a new anaesthetic drug administration system: a prospective, controlled, longitudinal incident monitoring study. Anaesthesia 2010; 65: 490-9.
5. Institute of Medicine. To Err Is Human - Building a Safer Health System. Washington DC, National Academy Press, 2000.
6. Webster CS. The iatrogenic-harm cost equation and new technology. Anaesthesia 2005; 60: 843-6.
7. Berwick DM. Not again! Preventing errors lies in redesign - not exhortation. British Medical Journal 2001; 322: 247-8.
8. Tapley P, Lewis R. Comment on ‘Problems with colour interpretation of syringe labels: not just colour-deficient clinicians!’. British Journal of Anaesthesia 2019; 122: e60-1.

We would like to thank the authors for their work on this novel approach to post-operative analgesia for caesarean section. We have recently introduced enhanced recovery in obstetrics in our institution, and we are considering the addition of an I-TAP block to our standard practice of spinal with diamorphine.

However, enhanced recovery patients were excluded from your study population and despite your assurances that this group is characteristically similar to the study group, we are uncertain as to whether the analgesic benefit demonstrated would be replicated in our enhanced recovery population. We would be grateful if the authors could explain this exclusion, and detail how their standard management of the enhanced recovery patients differs from the study protocol, in particular whether these patients routinely receive a block and a fentanyl PCA.

J Kerr

E Plunkett

J Pilsbury

K Cullis

A Whapples

Birmingham Women's Hospital,

Birmingham, UK.

Email: jennie.kerr@uhb.nhs.uk

No external funding and no conflicts of interest declared.

Reference

1. Staker JJ, Liu D, Church R, et al. A triple-blind, placebo-controlled randomised trial of the ilioinguinal-transversus abdominis plane (I-TAP) nerve block for elective caesarean section. Anaesthesia 2018; 73: 594-602.

We would like to raise following concerns -

1 We believe that the approach of making the packaging of all medicines look similar is akin to repealing the mandatory wearing of seatbelts by vehicle drivers in the hope that all the drivers will drive sanely without seatbelts. We need to use all safety precautions while dealing with the problem of drug misidentification and hence different pacakaging of various drugs, which we believe is an important safety precaution, must be employed.

2 Regarding use of barcodes, at least in our clinical scenarios (developing countries), they remain a distant dream. In the absence of these modern techniques, we have to rely on some simpler methods^1,2, which nevertheless have proved to be effective.

3 In fact in places where the lookalike packaging is a real concern ( there is one reported in nearly each issue of regional anesthesia journals), the only safeguard against drug misidentification is the vigilance of the handling physician.

4 We believe that prolonged physician working hours and the general OT room environment also play a part in wrong drug administration. It is also important that the local anesthetics administered by the surgeons for infiltration be kept separately from the other anesthetic drugs. 

5 A very important considertion which must also be given due recognition is administration of appropriate doses of drugs.This becomes more significant in pediatric patients. Drugs need to be serially diluted before being administered to newborns and infants predisposing patients to incorrect doses.The authors missed out on this aspect in their article.Also, we have similar packaging of different concentrations of drugs. We believe that we physicians are yet to address this concern. 

S. D. Bloria

P. Bloria

A. Luthra

K. Kataria

W. Khan

PGIMER,

Chandigarh, India.

Email: summitbloria13@gmail.com

No external funding and no conflicts of interest declared.

References

1 Pysyk CL. Differentiating muscle relaxant syringes to reduce syringe swap error. Can J Anesth 2018; 65: 850-1.

2 Bloria SD. Another easy method to reduce syringe swapping. Can J Anaesth. 2018; 65:1262-3.

We congratulate Shippam et al. on their important contribution to the current discussion about the role of high-flow nasal oxygenation (HFNO) in obstetric patients [1]. In keeping with previous published work [2], HFNO did not confer an advantage in pre-oxygenation in this patient group when compared to more standard techniques. In both studies the success of pre-oxygenation was assessed using End tidal O₂ concentration (ETO₂) as the primary outcome, and no patients received general anaesthesia. As Shippam et al. highlight, the impact of air entrainment diluting the inspired concentration is very likely to have diminished the effectiveness of HFNO, with only 25% of patients in the study group breathing with a closed mouth for the study period.

At first glance, the results of Shippam’s study may appear disappointing for obstetric anaesthetists, for whom management of the obstetric airway remains a major source of concern. However, we would suggest that discussion around the role of HFNO in obstetrics should not end here as perhaps its potential benefits lie more explicitly with a role in apnoeic oxygenation. Using facemask pre-oxygenation maternal desaturation occurs more rapidly in the pregnant patient, creating a more pressured environment in which the anaesthetist is required to achieve tracheal intubation. This may potentially increase the need to declare a failed intubation with the ensuing problems for both mother and baby.

In contrast to Shippam’s findings, Mir et al. randomised 40 non-pregnant patients comparing HFNO with facemask pre-oxygenation in rapid-sequence induction [3], finding that despite significant prolongation of apnoea time in the HFNO group there was no difference in arterial PaO₂, PCO₂ or pH. Furthermore, in a similar study of 80 non-pregnant patients undergoing rapid sequence induction randomised to either HFNO or facemask preoxygenation, Lodenius et al. found that significantly more patients desaturated to below 93% in the facemask group despite similar times to achieve tracheal intubation [4].

Currently, there are no clinical studies looking at time to desaturation in the obstetric patient. However, in computational model, Pillai et al. demonstrated the positive effect of increasing oxygen concentration at the open glottis on oxygen saturation during apnoea in the average term parturient; a FiO₂ of greater than 0.6 delayed desaturation by almost 15 minutes, with an FiO₂ of 1.0 increasing this time to more than 70 minutes [5]. Although this was a computational study, there are an increasing number of case reports highlighting the benefits of HFNO in the management of the difficult obstetric airway [6-8].

The Obstetric Anaesthetist's Association/Difficult Airway Socety guidelines for the management of failed intubation in obstetrics state that in obstetric general anaesthesia, the anaesthetist should consider attaching nasal cannulae with 5 L.min^-1 oxygen flow before starting pre-oxygenation to maintain bulk flow of oxygen during intubation attempts [9]. Whilst this may provide some benefit in delaying maternal desaturation, the use of HFNO offers a far more effective way of delivering a high FiO₂ at the glottis during the apnoeic period [5] and future work should perhaps focus on this area.

D. N. Lucas

Northwick Park Hospital,

Harrow, UK.

R. Russell

John Radcliffe Hospital,

Oxford, UK.

Email: nuala.lucas@nhs.net

No external funding and no conflicts of interest declared.

References 

1. Shippam W, Preston R, Douglas J, Taylor J, Albert A, Chau A. High-flow oxygen vs. standard flow-rate facemask pre-oxygenation in pregnant patients: a randomised physiological study. Anaesthesia 2019; 74:450-6.
2. Tan PCF, O’Millay OJ, Leeton L, Dennis AT. High-flow humidified nasal preoxygenation in pregnant women: a prospective observational study. British Journal of Anaesthesia 2019; 122: 86-91.
3. Mir F, Patel A, Iqbal R, Cecconi M, Nouraei SA. A randomised controlled trial comparing transnasal humidified rapid insufflation ventilator exchange (THRIVE) pre-oxygenation with facemask pre-oxygenation in patients undergoing rapid sequence induction of anaesthesia. Anaesthesia 2017; 72: 439-43.
4. Lodenius A, Piehl J, Ostlund A, Ullman J, Josson Fagerlund M. Transnasal humidified rapid-insufflation ventilator exchange (THRIVE) vs. facemask breathing pre-oxygenation for rapid sequence induction in adults: a prospective randomised non-blinded clinical trial. Anaesthesia 2018; 73: 564-71.
5. Pillai A, Dada V, Lewis J, Mahmoud M, Mushambi M, Bogod D. High-flow humidified nasal oxygen vs. standard face mask oxygenation. Anaesthesia 2016; 71: 1280-3.
6. Phillips S, Subair S, Husain T, Sultan P. Apnoeic oxygenation during maternal cardiac arrest in a parturient with extreme obesity. International Journal of Obstetric Anesthesia 2017: 29: 88-90.
7. Hengen M, Willemain R, Meyer A, Langer B, Joshi GP, Diemunsch P. Transnasal humidified rapid-insufflation ventilator exchange for preoxygenation before caesarean delivery under general anesthesia: a case report. Anaesthesia and Analgesia Case Reports 2017; 9: 216-8.
8. Creaney M, Moriarty RM, Milner M, Murphy C. Dexmedetomidine high-flow nasal oxygen and sugammadex-reversal of rocuronium: overcoming anaesthetic challenges in a parturient with congenital muscular dystrophy presenting for caesarean section. International Journal of Obstetric Anesthesia 2018; 34: 108-12.
9. Obstetric Anaesthetists’ Association/Difficult Airway Society. Obstetric Airway Guidelines 2015. https://www.oaa-anaes.ac.uk/ui/content/content.aspx?ID=70 [accessed 24/02/ 2019].

In a cross-sectional observational study of 49 healthy doctors, Cheung et al. demonstrated that, compared with normal sleep patterns, acute sleep deprivation through overnight on-site call activity was associated with significantly more DNA breaks and lower baseline DNA repair gene expression [1]. An accompanying editorial by Fuller and Eikermann eloquently cautioned against misinterpreting the clinical consequences of these preliminary results, but went on to summarise other accepted health implications of occupational sleep disruption [2].

If these findings can be repeated (longitudinally) in other geographical populations, individual clinicians and the medical profession as a whole would be right to be concerned, particularly as Cheung et al’s work demonstrates genotoxicity after only a single night’s sleep disruption. Further work is needed to ascertain whether such damage is cumulative, and therefore whether clinicians incur greater amounts of both DNA damage (risking malignancy, cardio-metabolic and neurodegenerative diseases) and telomere shortening (accelerating aging) [3] throughout a career involving on call/shift work activity. 

In the interim, what can the clinician do practically to offset such damage? It is unrealistic to expect anaesthetists not to undertake on-call activities in a 24/7 society. Nor, currently, is it possible pharmacologically to either mitigate DNA damage using anti-oxidants or manipulate telomerase activity to any great effect [4], although CRISPR-Cas9 editing/non-homologous and homologous repair technology offers future promise [5].

Instead, a relatively low-tech, integrative approach to self-care appears to best offset the occupational epigenesis of cancer, with the added benefit of ameliorating other ‘diseases of affluence’ including cardiovascular disease, obesity, diabetes, dementia and auto-immune disease. Thematically, such limited evidence as there is currently supports the lifestyle adoption of a supplemented, plant-based, whole food diet [6] plus physical exercise [7], sleep hygiene [8] and stress reduction [9]: medice, cura te ipsum (‘Physician, heal thyself’). I would encourage the Association of Anaesthetists to consider promoting elements of this advice in its forthcoming Wellbeing and Support guidance on ‘Looking after your own health and work life balance’, and when updating its 2014 guidance (due 2019) ‘Occupational Health and the Anaesthetist’ [10].

S. M. White

Royal Sussex County Hospital,

Brighton, UK.

Email: stuart.white6@nhs.net

No external funding declared. SW is an Editor of Anaesthesia. 

References

1.Cheung V, Yuen VM, Wong GTC, Choi SW. The effect of sleep deprivation and disruption on DNA damage and health of doctors. Anaesthesia 2019; 74: 434-40. 

2.Fuller PM, Eikermann M. Genomic consequences of sleep restriction: the devil is in the details. Anaesthesia 2019; 74: 417-9. 

3.Jackowska M, Hamer M, Carvalho LA, Erusalimsky JD, Butcher L, Steptoe A. Short sleep duration is associated with shorter telomere length in healthy men: findings from the Whitehall II cohort study. PLoS One 2012; 7: e47292. 

4.Jäger K, Walter M. Therapeutic targeting of telomerase. Genes (Basel) 2016; 7: 39. 

5.Richardson CD, Kazane KR, Feng SJ, et al. CRISPR-Cas9 genome editing in human cells occurs via the Fanconi anemia pathway. Nature Genetics 2018; 50: 1132-9. 

6.Freitas-Simoes TM, Ros E, Sala-Vila A. Nutrients, foods, dietary patterns and telomere length: Update of epidemiological studies and randomized trials. Metabolism 2016; 65: 406-15. 

7.Ji N, Zhao W, Qian H, Yan X, Zong R, Zhang Y, Lao K. Aerobic exercise promotes the expression of ERCC1 to prolong lifespan: A new possible mechanism.  Medical Hypotheses 2019; 122: 22-5. 

8.Walker M. Why we sleep. Penguin books, St. Ives, 2018.

9.Buric I, Farias M, Jong J, Mee C, Brazil IA. What is the molecular signature of mind-body interventions? A systematic review of gene expression changes induced by meditation and related practices. Frontiers in Immunology 2017; 8: 670.

10.Association of Anaesthetists. Occupational Health and the Anaesthetist 2014. https://www.aagbi.org/sites/default/files/Occupational%20Health%202014%20web_0.pdf (accessed 12th March, 2019).

I would like to congratulate  Hermez et al. on their extensive efforts ofin determining the mechanism of carbon dioxide clearance during apnoeic oxygenation with high-flow nasal oxygenation (HFNO) cannulae   [1], and would like to invite the authors to respond to a number of observations I have about their work.

All patients undergoing successful apnoeic oxygenation with high-flow nasal cannulae have beating hearts and a patent airway. Therefore, turbulent airflow and cardiogenic oscillations are present universally. Yet, in one series, CO₂ clearance rates varied as much as three-fold despite comparable oxygenation success [2]. A better ‘oxygenator’ did not appear synonymous with a better ‘ventilator’ during apnoeic oxygenation, and vice versa. Therefore, other factors must be at play in the mechanism of CO₂ clearance. Perhaps differences in airway pathologies and interventions may influence ingress of oxygen and egress of carbon dioxide, and do so separately. Flow vortices arise in the context of their environment. For example, patterns of gas flow would not be identical in a normal trachea compared to a long segment of subglottic stenosis. A normal airway that is not being subjected to any intervention, such as laryngoscopy or surgical procedure, is modelled in this instance. This is not representative of the clinical scenarios in which HFNO is used. 

The hypothesis explored by this article is called into question by the disparity between successful oxygenation and ventilation that is observed in apnoeic infants and children, who undergo prolonged oxygenation with high-flow nasal cannulae but who have not demonstrated CO₂ clearance [3, 4]. In these studies, the ingredients of high-flow nasal cannulae and cardiogenic oscillations were clearly not sufficient in themselves as a recipe for ventilation success.  In light of the above, the statement of the authors that ‘we would expect an improvement in oxygen transport to go hand-in-hand with the enhancement of carbon dioxide clearance’, does not seem to hold true in clinical practice, and has not been demonstrated scientifically by them. 

Clinically, there are two important influences on the ability of HFNO to generate a positive airway pressure: the sizing of the nasal cannulae relative to the nares and the degree of mouth opening. These are essential routes for gas escape and prevention of barotrauma, but also reduce the magnitude of positive airway pressure generated, and so likely impact upon gas exchange. The extent to which nasal and oral escape of oxygen was enabled by this rigid model is not outlined. Based on prior use of the model, it would appear that the mouth is closed [5], and unrepresentative of the most clinically relevant scenarios of laryngoscopy and tubeless laryngeal surgery.

Fig. 6 of the article, which compares the rates of rise of carbon dioxide under different oxygenation conditions, exaggerates the capacity of THRIVE. The aventilatory state is mapped as a CO₂ accumulation of 0.48 kPa.min^-1, whilst that of THRIVE is mapped as 0.15 kPa.min^-1 - implying CO₂ clearance of 69%. However, the 0.48 kPa value is derived from four studies using blood gas analysis whilst the THRIVE value of 0.15 kPa is an end-tidal value from the original case series [6]. End-tidal measurement can significantly overestimate CO₂ clearance, as demonstrated by two studies using both end-tidal and blood gas measurements [2, 7]. The appropriate value for comparison based on those studies is 0.23kPa.min^-1, representing a CO₂ clearance of 52% rather than 69% with THRIVE. It is also stated that the positive airway pressure generated by HFNO ‘reduces atelectasis’ and partly explains the dramatic increases in safe apnoea time. However, the supporting references relate to spontaneously breathing patients, and to my knowledge, such a reduction in atelectasis has not been demonstrated in apnoeic individuals.

The authors state that cardiogenic oscillations are believed to relate to ‘compression and expansion of small airways’. However, these small airways are absent in this model, and is another reason why the modelling may not translate well to clinical practice. Cardiogenic oscillations were created at a rate of 60-70 beats per minute. No information is offered as to the duration of cardiac ‘inspiration’ and ‘expiration’. Clinically, greater time is spent in diastole at this heart rate, which would impact upon gas flow in the airway. Furthermore, selection of maximum stroke volumes of 40mls would appear unphysiological. Carbon dioxide clearance is a limiting factor for safe duration of tubeless laryngeal surgery. This study, and others prior, would prompt the question as to whether pharmacologically augmenting heart rate under apnoea would promote greater CO₂ clearance. Patient heart rates are typically low-normal given use of remifentanil-based TIVA regimens for the technique, which can be postulated as a barrier to ventilation if cardiogenic oscillations are a major contributor to gas exchange.

Our knowledge of the mechanisms and uses of apnoeic oxygenation remains somewhat primitive. I believe this study is a step forward in our understanding of carbon dioxide clearance in apnoeic patients, but for the reasons outlined above, is by no means sufficient to conclude that ‘our work … explains apnoeic gas exchange’.

C. Lyons

Our Lady’s Children’s Hospital, Crumlin,

Dublin, Ireland.

Email:craigmacliathain@gmail.com

No external funding and no conflicts of interest declared.

References

1. Hermez LA, Spence CJ, Payton MJ, Nouraei SAR, Patel A, Barnes TH. A physiological study to determine the mechanism of carbon dioxide clearance during apnoea when using transnasal humidified rapid insufflation ventilatory exchange (THRIVE). Anaesthesia 2019; 74: 441-9.
2. Lyons C, Callaghan M. Apnoeic oxygenation with high-flow nasal oxygen for laryngeal surgery: a case series. Anaesthesia 2017; 72: 1379-87.
3. Humphreys S, Lee-Archer P, Reyne G, Long D, Williams T, Schibler A. Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) in children: a randomized controlled trial. British Journal of Anaesthesia 2017; 118: 232-8.
4. Riva T, Pedersen TH, Seiler S, et al. Transnasal humidified rapid insufflation ventilatory exchange for oxygenation of children during apnoea: a prospective randomised controlled trial. British Journal of Anaesthesia 2018; 120: 592-9.
5. Van Hove SC, Storey J, Adams C, et al. An Experimental and Numerical Investigation of CO₂ Distribution in the Upper Airways During Nasal High Flow Therapy. Annals of Biomedical Engineering 2016; 44: 3007-19.
6. Patel A, Nouraei SA. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia 2015; 70: 323-9.
7. Gustafsson IM, Lodenius A, Tunelli J, Ullman J, Jonsson Fagerlund M. Apnoeic oxygenation in adults under general anaesthesia using Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) - a physiological study. British Journal of Anaesthesia 2017; 118: 610-7.

Morrison et al. assessed the role of fibrinogen concentrate in enhancing haemostasis during open thoraco-abdominal aortic aneurysm (TAAA) repair [1]. We commend the authors for conducting a randomized controlled trial in such a difficult setting. Studying coagulation patterns during this procedure is essential, given the large volume blood losses and transfusion requirement, which render open TAAA repair  a perfect model for haemorrhagic shock.

Understanding fibrinolysis is the cornerstone of treatment in this kind of coagulopathy [2], with tranexamic acid and fibrinogen concentrate currently the most reliable treatments. In the study, rotational thromboelastometry (ROTEM) results were crucial in triggering fibrinogen administration. However, fibrinogen administration was started early and solely on the basis of the FIBTEM assay, regardless of actual bleeding. However, ROTEM has a high negative predictive power and low positive predictive power, and so theoretically, administering fibrinogen may have corrected the ROTEM result than the microvascular bleeding/thrombosis which can complicate open TAAA repair [3].

Secondly, tranexamic acid was administrated according to maximum lysis and APTEM assay. However, these viscoelastic tests might only detect massive hyperfibrinolysis, but miss milder fibrinolytic states that could benefit from tranexamic acid administration [4].

Thirdly, as fibrinogen acts on microvascular bleeding, data about postoperative bleeding might have been interesting to collect, to assess the real magnitude of the proposed intervention. Are the authors considering collecting such data when they go on to expand their pilot study into a full RCT?

F. Monaco

P. Nardelli

IRCCS San Raffaele Scientific Institute,

Milan, Italy

Email: monaco.fabrizio@hsr.it

No external funding and no conflicts of interest declared.

References

1. Morrison GA, Koch J, Royds M, et al. Fibrinogen concentrate vs. fresh frozen plasma for the management of coagulopathy during thoraco-abdominal aortic aneurysm surgery: a pilot randomised controlled trial. Anaesthesia 2019; 74: 180-9.

2. Gertler JP, Cambria RP, Brewster DC, et al. Coagulation changes during thoracoabdominal aneurysm repair. Journal of Vascular Surgery 1996; 24: 936-43.

3. Schmitz A, Hartmann M. Acute intracardiac thrombus formation during thoracoabdominal aortic surgery. Anesthesia and Analgesia 2006; 102: 1658-9.

4. Longstaff C. Measuring fibrinolysis: from research to routine diagnostic assays. Journal of Thrombosis and Haemostasis 2018; 16: 652-62.

We read with interest the review article titled 'A review of ASA physical status–historical perspectives and modern developments' by Mayhew et al.[1]. The article lucidly covered the birth and emergence of ASA-PS classification to classify a patient's general condition before surgery.

Recently ASA-PS has given special recognition to obstetric and pediatric patients depending on various scenarios. However till date, no such consideration or recognition has been given to patients undergoing major onological surgeries. Till date, patients are classified based on co-morbidities rather than the stage of cancer or the magnitude of planned surgery. We agree to the authors statement that misclassification of a patient's ASA-PS can have significant implications on peri-operative care.

Major oncological surgeries involves extensive cytoreductive surgeries, heated intraperitoneal chemotherapy(HIPEC), multiple organ resections. All this leads to a stormy postoperative course which can lead to significant morbidity and prolonged hospital stay [2, 3]. The insult is variable and cannot be predicted by co-morbidities. Therefore ASA-PS can misclassify physical status in such patients.

The paper also addressed fraility and its importance in perioperative outcomes, morbidity and mortality. Ethun et al has discussed the fraility in cancer patients and its implications for oncosurgeries, medical and radiation oncological treatment modalities [4]. Baseline nutritional status has important prognostic implications especially in colorectal and gastrointestinal cancer patients who undergo major resection and anastomosis. This should also be considered along with physical status. Preoperative prognostic nutritional index is an important tool which can help clinicians in predicting survival outcomes after major oncological surgeries [5].

We suggest that by using fraility status, baseline nutritional status and nature of surgical intervention planned, the ASA-PS of the patient needs to be modified as it is difficult to classify a PS of a cancer patient based only on co-morbidities.

A. Nair

Basavatarakam Indo-American Cancer Hospital and Research Institute,

Hyderabad,

India

Email: abhijitnair95@gmail.com

No external funding and no conflicts of interest declared.

References

 1. Mayhew D, Mendonca V, Murthy BVS.A review of ASA physical status - historical perspectives and modern developments. Anaesthesia. 2019;74:373-9.

2. Simões CM, Carmona MJC, Hajjar LA, et al. Predictors of major complications after elective abdominal surgery in cancer patients. BMC Anesthesiol. 2018;18:49.

3. Simkens GA, Rovers KP, Nienhuijs SW, de Hingh IH. Patient selection for cytoreductive surgery and HIPEC for the treatment of peritoneal metastases from colorectal cancer. Cancer Manag Res. 2017;9:259-66.

4. Ethun CG, Bilen MA, Jani AB, Maithel SK4, Ogan K, Master VA. Frailty and cancer: Implications for oncology surgery, medical oncology, and radiation oncology. CA Cancer J Clin. 2017;67:362-77.

5. Tokunaga R, Sakamoto Y, Nakagawa S, Miyamoto Y, Yoshida N, Oki E, et al. Prognostic nutritional index predicts severe complications, recurrence, and poor prognosis in patients with colorectal cancer undergoing primary tumor resection. Dis Colon Rectum. 2015;58:1048–57.

The subject of capnography continues to be widely discussed in ‘Anaesthesia’. In their recent correspondence, Nielsen and Lim [1]concur with the importance of capnography in defining a successful airway intervention as described by Chimes and Marshall[2] when discussing the ‘million dollar question’ concept in their ‘Attempt XYZ’ article. They also suggest the additional use of capnography as an objective indicator of the effectiveness of bag mask ventilation. This type of objective indicator can be used to grade the difficulty of bag mask ventilation in any given patient. 

UK guidelines currently emphasise the importance of capnography as part of the minimum monitoring requirements of an anaesthetised patient and to confirm correct endotracheal tube placement [3,4]. However, consideration should also be given in such guidelines to the use of capnography both to assess the efficacy of bag mask ventilation and as a means of objectively grading patients in terms of difficulty of bag mask ventilation.

Interestingly this regard for capnography does not appear to be universal. 

In a multi-centre, randomised, controlled trial conducted within the United States, Casey et al. [5], presented convincing data on the bag mask ventilation on hypoxaemia in the period between induction and laryngoscopy in an intensive care setting. The authors do not indicate whether capnography was used in their study. They do, however, describe using the ‘smallest volume to generate a visible chest rise’ during bag mask ventilation. Capnography is generally considered a better indicator of effective bag mask ventilation than chest rise and it should be routinely employed in any future studies on effective airway management [6]. The use of Nielsen and Lim’s grading system [1] should also be considered in any future trial of this type.

E. L. Scahill

V. Perkins

Dumfries and Galloway Royal Infirmary,

Dumfries, Scotland.

Email: emma.scahill@nhs.net

No external funding and no conflicts of interest declared.

References

1. Nielsen JR, Lim KS. Airway plans and capnography. Anaesthesia 2019; 74: 394-408
2. Chrimes N, Marshall SD. Attempt XYZ: airway management at the opposite end of the alphabet. Anaesthesia 2018; 73: 1464–8.
3. Association of Anaesthetists of Great Britain and Ireland. Recommendations for standards of monitoring during anaesthesia and recovery 2015. Anaesthesia 2016; 71: 85-93.
4. Frerk C, Mitchell VS, McNarry AF et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults.British Journal of Anaesthesia 2015; 115: 827-48.
5. Casey JD, Janz DR, Russell DW et al. Bag-Mask Ventilation during Intubation of Critically Ill Adults. New England Journal of Medicine 2019; 380: 811-21
6. Matten EC, Shear T, Vender S. Non-intubation Management of the Airway: Airway Maneuvers and Mask Ventilation. In: Hagberg CA (ed.) Benumof and Hagberg’s Airway Management. Third edition. Philadelphia: Saunders; 2013 p 324-39.

The adoption of viscoelastic haemostatic assays (VHA) technology for point of care testing in routine clinical practice and research into its role for improving patient care, has been hampered by concerns about errors due to user technique and the paucity of relevant population reference range data [1]. The introduction of automated cartridge technology into VHA with the TEG®6s and ROTEM®sigma systems may address many of the concerns about user errors. The study by Schenk and colleagues is intended to provide useful reference range data for the ROTEM®sigma technology [2]. Unfortunately, the normal population sample size in their study included only 15 male subjects and 15 female subjects. It is recommended that reference values should be established with a minimum population sample size of at least 120 subjects [3]. The small samples sizes used by Schenk et al are suitable only for local verification of established reference ranges.  Previous studies have shown that the reference range for VHA is different between men and women [4]. To establish useful reference ranges for the ROTEM®sigma it would be necessary to have 120 male subjects and 120 nonpregnant female subjects. The parameters measured by VHA are also affected by pregnancy therefore separate reference ranges would also need to be established for pregnant women so that the ROTEM®sigma results could be usefully interpreted in obstetric practice.

In their study, Schenk et al also compared the results derived from using the ROTEM®sigma with results from using the ROTEM®delta which requires the users to pipette blood and reagents in a sequence of stages. The authors found a good correlation between the two technologies although the correlation coefficient for the ‘clot formation time’ (CFT) was only 0.8 (confidence intervals for the correlation coefficients were not provided in the paper). It would have been unexpected if the correlation coefficients were not good as the technologies are similar, but the correlation does not provide information as to whether the results from the ROTEM®sigma are equivalent to those provided by the ROTEM®delta. A better measure of comparability between the two technologies would be to study the differences between the two measurements using a Bland Altman plot analysis [5]. The authors have provided Bland Altman plot analysis but only as supplementary data to their paper without explanatory text or analysis and without defining a priori the limits of maximum acceptable differences (limits of agreement expected). As a result, it cannot be assumed with confidence from this study that published population reference ranges for the ROTEM®delta can be used interchangeably for ROTEM®sigma test results.  Despite the work by Schenk and colleagues, the population reference ranges for the ROTEM®sigma remain undefined.

A. Field

T. Poole

J. H. Bamber 

Addenbrooke’s Hospital,

Cambridge, UK.

Email: field.360@gmail.com

No external funding and no conflicts of interest declared.

References

1. Curry NS, Davenport R, Pavord, et al. The use of viscoelastic haemostatic assays in the management of major bleeding. British Journal of Haematology. 2018; 182: 789-806.

2. Schenk B, Gorlinger K, Treml B, et al. A comparison of the new ROTEM ®sigma with its predecessor, the ROTEM delta. Anaesthesia 2018; 74: 348-56.

3. CLSI. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline—Third Edition. CLSI document EP28-A3c. Wayne, PA: Clinical and Laboratory Standards Institute; 2008.

4. Gorton HJ, Warren ER, Simpson NA, Lyons GR, Columb MO. Thromboelastography identifies sex-related differences in coagulation. Anesthesia & Analgesia. 2000; 91: 1279–81.

5. Giavarina D. Understanding Bland Altman analysis. Biochemia Medica 2015; 25: 141-51.

I've followed the topic of " force applied to the left paratracheal oesophagus on air entry into the gastric antrum during positive-pressure ventilation" in recent issues of your valuable journal. First of all, let me congratulate to Gautier et al. for a novel method in purpose to avoid gastric insufflation during positive pressure ventilation through face mask.(1) usefulness of traditional cricoid pressure in preventing aspiration of gastric contents is highly challenging.(2-4) For this reason thinking about an alternative technique is highly appreciated, as Lucas et al. commended it.(3) But two concerns shouldn’t be ignored. First, focusing on finding the proper location for applying force in order to occlude proximal portion of oesophagus shouldn’t distract us from established and more effective modalities for preventing aspiration of gastric contents (such as sufficient pre-oxygenation, minimizing the time of positive pressure ventilation and etc.) and second, risks of occluding the upper oesophageal sphincter (specially in cases of gastrointestinal obstruction) should keep in mind always.(4) In cases such as cesarean section, considering neuraxial anesthesia may be the more prudent choice instead of falling in the well of general anesthesia. However, head-up positioning, premedication by antacids plus H2 antagonists, proper pre-oxygenation and injecting short acting muscle relaxants can help us minimizing the time of positive pressure ventilation.(5)

R. Aminnejad

Shahid Beheshti Hospital,

Qom, Iran.

Email: r.aminnejad@yahoo.com

No external funding and no conflicts of interest declared.

References

1.           Gautier N, Danklou J, Brichant JF, Lopez AM, Vandepitte C, Kuroda MM, et al. The effect of force applied to the left paratracheal oesophagus on air entry into the gastric antrum during positive-pressure ventilation using a facemask. Anaesthesia 2019; 74: 22-8.

2.           Naik K, Frerk C. Cricoid force: time to put it to one side. Anaesthesia 2019; 74: 6-8.

3.           Lucas DN, Vaughan DJA, Pearson NK. Paratracheal force, cricoid pressure and obstetric anaesthesia. Anaesthesia 2019; 74: 547-.

4.           Ewart L. The efficacy of cricoid pressure in preventing gastro-oesophageal reflux in rapid sequence induction of anaesthesia. Journal of perioperative practice 2007; 17: 432-6.

5.           STUART JC, KAN AF, ROWBOTTOM SJ, YAU G, GIN T. Acid aspiration prophylaxis for emergency Caesarean section. Anaesthesia 1996; 51: 415-21.