Editorial
Anaesthesia 2014, 69, 801–815
Editorial Facemask ventilation before or after neuromuscular blocking drugs: where are we now? In 2008, Calder and Yentis [1] questioned the validity, safety and rationale of the practice of demonstrating that facemask ventilation is possible before giving a neuromuscular blocking drug (NBD). Their scepticism arose because the purported advantages of what has been called ‘squirt-puff-squirt’ (personal communication, Yentis SM) appeared not to be fulfilled in their practice and in large prospective series [2, 3]. Calder and Yentis argued that insistence on checking facemask ventilation, and the subsequent fear of not being able to restore spontaneous respiration should it be difficult, increased the likelihood of ‘light anaesthesia’, which itself caused difficulty with facemask ventilation. Neuromuscular blocking drugs appeared to improve facemask ventilation but evidence was lacking. In this issue of Anaesthesia, Sachdeva and colleagues [4] add to the growing body of evidence [5–7] showing that facemask ventilation is more effective following NBDs. They looked at the change in tidal volume during pressure controlled ventilation as a surrogate marker to assess the ease of mask ventilation following administration of rocuronium and confirmed that
neuromuscular blockade facilitates mask ventilation. Importantly, this increase was also seen in obese patients, in whom facemask ventilation is often more difficult [4]. There are three things we need to know before we feel safe to administer NBDs before facemask ventilation and be confident that it will either improve or stay the same, but not deteriorate.
What makes facemask ventilation difficult or impossible, how common is it, and can we reliably predict it? Difficult and (what we really fear) impossible facemask ventilation have been the subject of large prospective series [2, 3, 8] and have an incidence of 1.4% [2] and 0.15% [8], respectively. The definition of impossible facemask ventilation is obvious: an inability to exchange air using this technique. Once experienced, it is rarely forgotten. The sensation of impossible facemask ventilation is likened to attempted ventilation of a ‘brick wall’ and in my experience, has been as a result of solid physical obstruction of a compromised airway. This is a very different sensation to even the most difficult facemask ventilation. Occasionally,
© 2014 The Association of Anaesthetists of Great Britain and Ireland
in the context of difficult airways, an inexperienced trainee will declare impossible facemask ventilation– invariably before NMB – that settles to difficult ventilation. The definition of difficult facemask ventilation is not as clear and varies from subjective criteria requiring two practitioners, inadequate or unstable facemask ventilation [9], to grading based on escalating levels of intervention necessary to ventilate the lungs [10]. Factors that suggest difficult facemask ventilation include a body mass index ≥ 30 kg.m 2, a beard, Mallampati classification 3-4, age ≥ 57 years, severely limited jaw protrusion and a history of snoring [3]. Factors associated with impossible facemask ventilation include neck radiation changes, male sex, sleep apnoea, Mallampati 3-4 and presence of a beard [8]. With such a low incidence, the usefulness of predictive tests is limited, and in reality most patients predicted to be difficult are not, whereas a few who are predicted to be easy are anything but [11, 12]. We have an understanding of the incidence of difficult and impossible facemask ventilation, and some of the factors that suggest problems, but we are not good at predicting it. 811
Anaesthesia 2014, 69, 801–815
Crossing the Rubicon – when is the point of no return? After induction of anaesthesia, recognition of difficult or impossible facemask ventilation may theoretically allow two separate strategies: (i) no further anaesthetic agents, allowing ‘lightening’ of anaesthesia depth and the return of spontaneous respiration; or (ii) administration of short-acting NBDs such as suxamethonium or rocuronium (with suggamadex available), which may improve ventilation and facilitate tracheal intubation – or, if this fails and facemask ventilation remains difficult or impossible, allow the patient to wake up and breathe spontaneously [13–15]. This approach appears logical if spontaneous respiration is restored before severe hypoxaemia develops, but this is unlikely with suxamethonium [16] and the situation is compounded by first, any additional anaesthetic agents given in an attempt to improve facemask ventilation, and second, the inherent delayed administration of the NBD. Faced with impossible facemask ventilation, was the point of no return already crossed when spontaneous respiration was lost? Compared with the diaphragm, the upper airway muscles are more prone to a reduction in activity and obstruction as a result of anaesthetic and subanaesthetic concentrations of various agents including halothane, isoflurane, thiopental, diazepam, midazolam, opioids and propofol [17]. The
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combination of pre-existing anatomical problems that result in impossible facemask ventilation, and the effects of anaesthetic agents compounding upper airway collapse, mean that the chances of successfully restoring adequate spontaneous respiration in an apnoeic, anaesthetised patient with impossible facemask ventilation before severe hypoxaemia results is very small [18, 19]. The largest series of 53 041 attempts at facemask ventilation in all patients undergoing a general anaesthetic included 77 cases of unexpected impossible facemask ventilation and all but four of these 77 received NBDs, although it is not stated whether this was before or after facemask ventilation was found to be impossible. Sixty-five patients received suxamethonium and eight patients received a nondepolarising agent in the process of induction or management of the airway. In most (58/77), intubation was without difficulty; in 15 patients intubation was difficult or required additional equipment, three patients were woken up and one had an emergency cricothyrotomy [8]. It seems that when we are faced with impossible facemask ventilation we do not wake the patient up, and the presence of NBDs facilitates tracheal intubation [20–22]. The critical step in difficult airway management is the decision to induce anaesthesia in the first place, before securing the airway [23]. When we encounter unexpected difficult or impossible facemask ventilation, we have gone past this
juncture because we have already administered anaesthestic agents. The aim should be, as quickly as possible, optimisation of facemask ventilation, tracheal intubation, or the placement of a supraglottic airway device – all of which are improved by NBDs. It is interesting that in the 4th National Audit Project (NAP4), some local reporters commented that an aspect of ‘what went well’ was that NBDs were avoided when difficulty arose. In contrast, the review panel considered that delay or avoidance of NBDs contributed to the adverse events [24]. The recommendations of NAP4 included: “where facemask or laryngeal mask anaesthesia is complicated by failed ventilation and increasing hypoxia the anaesthetist should consider early administration of further anaesthetic agent and/or a muscle relaxant to exclude and treat laryngospasm” and: “no anaesthetist should allow airway obstruction and hypoxia to develop to the stage where an emergency surgical airway is necessary without having administered a muscle relaxant” [24]. In Kheterpal et al.’s series, when facemask ventilation was impossible the majority (73/77) of patients received NBDs and their tracheas were successfully intubated [8]. Similarly, when asked for management options in hypothetical scenarios of impossible facemask ventilation, the majority of those questioned (89%) would administer a NBD irrespective of whether they routinely checked facemask ventilation before NBDs [25].
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Editorial
Anaesthesia 2014, 69, 801–815
What makes facemask ventilation difficult or impossible after induction of anaesthesia?
laryngosapsm and chest wall rigidity [28–30], may also make facemask ventilation difficult.
Four mechanisms may cause difficulty with facemask ventilation. First, mechanical problems can result in an inadequate seal between the face and mask. Second, it may be difficult to maintain a patent naso-laryngopharyngeal airway/airspace. This is probably the most important practical skill for any anaesthetist and, similar to laryngoscopy and tracheal intubation, requires practice and improves with experience. This may partly explain why the least experienced anaesthetists were almost all likely to check facemask ventilation before NBDs, whereas only a minority of the most senior group did [25]. The inexperienced may have sub-optimal skills for facemask ventilation that may be amplified by inadequate depth of anaesthesia in an attempt to keep the patient lightly anaesthetised in case there are problems requiring restoration of spontaneous respiration. Airway patency may also be affected by reduced longitudinal tension in the upper airway and retro-lingual, retro-palatal, and retro-glossal obstruction resulting from poor positioning [26]. Third, we know that anaesthetic agents and NBDs reduce upper airway muscle tone and cause airway narrowing and collapse [17, 27], which may make facemask ventilation more difficult. Fourth, an increase in upper airway reflexes in the immediate post-induction period, including
Neuromuscular blocking drugs and effects on normal, difficult and impossible facemask ventilation In patients with normal airways, Goodwin et al. [31] looked at subjective measures such as the ability to ventilate the lungs to achieve optimal chest movements using bag and mask, before and after the administration of NBDs, and showed no effect of the latter. Warters et al. [5], in patients with normal and difficult airways, found that rocuronium significantly improved facemask ventilation, with the improvement most dramatic in those few patients in whom ventilation was more difficult [5]. Ikeda et al. found that in patients with normal upper airway anatomy held in a neutral head and mandible position, suxamethonium increased tidal volume and rocuronium had no effect [7]. Amathieu et al. [6] assessed 12 221 patients for difficult airway management in a two-year prospective study and allocated patients to two groups. The higher-risk group (those with three features or more suggestive of difficult airway management) received no check of facemask ventilation, and immediately following induction of anaesthesia received suxamethonium (i.e. ‘squirt-squirt-puff’). Those with fewer than three factors suggestive of difficult airway management were assessed by facemask ventilation
© 2014 The Association of Anaesthetists of Great Britain and Ireland
following induction of anaesthesia (squirt-puff-squirt’). Those classified as easy facemask ventilation (grade 1 or 2) received a long-acting NBD; those classified as difficult (grade 3) received suxamethonium. All of the 12 221 patients received NBDs and underwent tracheal intubation. In all cases (both easy and difficult facemask ventilation), NBDs never worsened facemask ventilation, but in most cases it improved it. Of the 90 patients who received suxamethonium after difficult facemask ventilation, 56 patients improved by one grade. These studies, together with Kheterpal et al.’s study previously discussed, show that normal or difficult facemask ventilation either remains unchanged or improves – but never deteriorates – after NBDs, and when impossible facemask ventilation is encountered, NBDs facilitate tracheal intubation. They improve facemask ventilation by abolishing airway reflexes, reducing the tone and bulk of muscles and allowing more space for gas to pass through [4]. They also reduce resistance and allow easier jaw thrust, head tilt, and open mouth-type maneuvers crucial to creating an airspace in the naso-, oro- and laryngo-pharynx.
Squirt-puff-squirt or squirt-squirt-puff? Since Calder and Yentis [1] first questioned the logic of checking facemask ventilation before NBDs, three approaches have remained. First, the technique that was originally criticised; i.e. induction of anaesthesia followed by facemask
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Anaesthesia 2014, 69, 801–815
ventilation, which if difficult or impossible leads to wake-up and return of spontaneous respiration. The latter part of this approach does not appear to be used and does not appear to work [2, 3, 6, 8, 18, 19, 24, 25]. Second, a hybrid approach in which facemask ventilation is checked after induction of anaesthesia and if this is easy, a long-acting NBD is administered but if ventilation is difficult, a short-acting NBD is administered [13–15]. This appears logical, but is dependent on the return of spontaneous respiration before serious hypoxaemia occurs. It is not inconceivable that a patient with extremely difficult or impossible facemask ventilation, who has been given a short-acting NBD, becomes seriously hypoxic before spontaneous respiration has resumed. The third approach is the one favoured by Calder and Yentis: administration of NBDs before facemask ventilation. This is logical since the evidence suggests that ventilation either remains unchanged or improves, but does not deteriorate in normal and difficult facemask ventilation [4–7, 31], provides optimal conditions for facemask ventilation, and if impossible facemask ventilation develops, airway rescue is facilitated [8]. No airway technique under general anaesthesia is guaranteed to work always [32], but NBDs are much more often the answer than the problem, and should be given early – before checking facemask ventilation.
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Competing interests No external funding and no competing interests declared. A. Patel Consultant Anaesthetist Royal National Throat, Nose and Ear Hospital & University College Hospital London, UK Email: [email protected]
References 1. Calder I, Yentis SM. Could ‘safe practice’ be compromising safe practice? Should anaesthetists have to demonstrate that face mask ventilation is possible before giving a neuromuscular blocker? Anaesthesia 2008; 63: 113–5. 2. Langeron O, Masso E, Huraux C, et al. Prediction of difficult mask ventilation. Anesthesiology 2000; 92: 1229–36. 3. Kheterpal S, Han R, Tremper KK, et al. Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006; 105: 885–91. 4. Sachdeva R, Kannan TR, Mendoca C, Patteril M. Evaluation of changes of tidal volume during mask ventilation following administration of neuromuscular blocking drugs. Anaesthesia 2014; 69: 826–32. 5. Warters RD, Szabo TA, Spinale FG, DeSantis SM, Reves JG. The effect of neuromuscular blockade on mask ventilation. Anaesthesia 2011; 66: 163–7. 6. Amathieu R, Combes X, Abdi W, et al. An algorithm for difficult airway management, modified for modern optical devices (Airtraq laryngoscope; LMA CTrachTM): a 2-year prospective validation in patients for elective abdominal, gynecologic, and thyroid surgery. Anesthesiology 2011; 114: 25–33. 7. Ikeda A, Isono S, Sato Y, et al. Effects of muscle relaxants on mask ventilation in anesthetized persons with normal upper airway anatomy. Anesthesiology 2012; 117: 487–93. 8. Kheterpal S, Martin L, Shanks AM, Tremper KK. Prediction and outcomes of impossible mask ventilation: a review of 50,000 anesthetics. Anesthesiology 2009; 110: 891–7. 9. Han R, Tremper KK, Kheterpal S, O’Reilly M. Grading scale for mask ventilation. Anesthesiology 2004; 101: 267.
10. Warters RD, Szabo TA, Spinale FG, DeSantis SM, Reves JG. The effect of neuromuscular blockade on mask ventilation. Anaesthesia 2011; 66: 163–7. 11. Yentis SM. Predicting trouble in airway management. Anesthesiology 2006; 105: 871–2. 12. Yentis SM. Predicting difficult intubation–worthwhile exercise or pointless ritual? Anaesthesia 2002; 57: 105–9. 13. Richardson MG, Litman RS. Ventilation before paralysis: crossing the Rubicon, slowly. Anesthesiology 2012; 117: 456–8. 14. Neilsen J. Could ‘safe practice’ be compromising safe practice? Should anaesthetists have to demonstrate that face mask ventilation is possible before giving a neuromuscular blocker? Correspondence 4 November 2008. http:// www.anaesthesiacorrespondence.net/ Correspond3.asp?articleid=5429&archi ve=1 (accessed 10/05/2014). 15. Pandit JJ. Checking the ability to mask ventilate before administering longacting neuromuscular blocking drugs. Anaesthesia 2011; 66: 520–2. 16. Benumof JL, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylcholine. Anesthesiology 1997; 87: 979–82. 17. Hillman DR, Platt PR, Eastwood PR. The upper airway during anaesthesia. British Journal of Anaesthesia 2003; 91: 31–9. 18. Priebe HJ. Could ‘safe practice’ be compromising safe practice? Should anaesthetists have to demonstrate that face mask ventilation is possible before giving a neuromuscular blocker? Anaesthesia 2008; 63: 671–2. 19. Priebe HJ. Ventilation before paralysis. Anesthesiology 2013; 118: 992–3. 20. Lieutaud T, Billard V, Khalaf H, Debaene B. Muscle relaxation and increasing doses of propofol improve intubating conditions. Canadian Journal of Anesthesia 2003; 50: 121–6. 21. Combes X, Andriamifidy L, Dufresne E, et al. Comparison of two induction regimens using or not using muscle relaxant: impact on postoperative upper airway discomfort. British Journal of Anaesthesia 2007; 99: 276–81. 22. Davis DP, Ochs M, Hoyt DB, Bailey D, Marshall LK, Rosen P. Paramedic-administered neuromuscular blockade improves prehospital intubation success in severely head-injured patients. Journal of Trauma 2003; 55: 713–9.
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Editorial 23. Patel A, Pearce A. Progress in management of the obstructed airway. Anaesthesia 2011; 66: 93–100. 24. Frerk C, Pearce A. Induction and maintenance of anaesthesia. In: Cook T, Woodall N, Frerk C, eds. 4th National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Major Complications of Airway Management in the United Kingdom. London: RCoA, 2011: 55–61. 25. Broomhead RH, Marks RJ, Ayton P. Confirmation of the ability to ventilate by facemask before administration of neuromuscular blocker: a non-instrumental piece of information? British Journal of Anaesthesia 2010; 104: 313–7.
Anaesthesia 2014, 69, 801–815 26. Xue FS, Cheng Y, Li RP. Facemask ventilation and neuromuscular blockade in anesthetized patients. Anesthesiology 2013; 118: 991–2. 27. Eastwood PR, Szollosi I, Platt PR, Hillman DR. Comparison of upper airway collapse during general anaesthesia and sleep. Lancet 2002; 359: 1207–9. 28. Ramachandran SK, Kheterpal S. Difficult mask ventilation: does it matter? Anaesthesia 2011; 66: 40–4. 29. Bennett JA, Abrams JT, Van Riper DF, Horrow JC. Difficult or impossible ventilation after sufentanil-induced anesthesia is caused primarily by vocal cord closure. Anesthesiology 1997; 87: 1070–4. 30. Abrams JT, Horrow JC, Bennett JA, Van Riper DF, Storella RJ. Upper airway
© 2014 The Association of Anaesthetists of Great Britain and Ireland
closure: a primary source of difficult ventilation with sufentanil induction of anesthesia. Anesthesia and Analgesia 1996; 83: 629–32. 31. Goodwin MW, Pandit JJ, Hames K, Popat M, Yentis SM. The effect of neuromuscular blockade on the efficiency of mask ventilation of the lungs. Anaesthesia 2003; 58: 60–3. 32. Calder I, Yentis S, Patel A. Muscle relaxants and airway management. Anesthesiology 2009; 111: 216–7. doi:10.1111/anae.12792
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Editorial Facemask ventilation before or after neuromuscular blocking drugs: where are we now? In 2008, Calder and Yentis [1] questioned the validity, safety and rationale of the practice of demonstrating that facemask ventilation is possible before giving a neuromuscular blocking drug (NBD). Their scepticism arose because the purported advantages of what has been called ‘squirt-puff-squirt’ (personal communication, Yentis SM) appeared not to be fulfilled in their practice and in large prospective series [2, 3]. Calder and Yentis argued that insistence on checking facemask ventilation, and the subsequent fear of not being able to restore spontaneous respiration should it be difficult, increased the likelihood of ‘light anaesthesia’, which itself caused difficulty with facemask ventilation. Neuromuscular blocking drugs appeared to improve facemask ventilation but evidence was lacking. In this issue of Anaesthesia, Sachdeva and colleagues [4] add to the growing body of evidence [5–7] showing that facemask ventilation is more effective following NBDs. They looked at the change in tidal volume during pressure controlled ventilation as a surrogate marker to assess the ease of mask ventilation following administration of rocuronium and confirmed that
neuromuscular blockade facilitates mask ventilation. Importantly, this increase was also seen in obese patients, in whom facemask ventilation is often more difficult [4]. There are three things we need to know before we feel safe to administer NBDs before facemask ventilation and be confident that it will either improve or stay the same, but not deteriorate.
What makes facemask ventilation difficult or impossible, how common is it, and can we reliably predict it? Difficult and (what we really fear) impossible facemask ventilation have been the subject of large prospective series [2, 3, 8] and have an incidence of 1.4% [2] and 0.15% [8], respectively. The definition of impossible facemask ventilation is obvious: an inability to exchange air using this technique. Once experienced, it is rarely forgotten. The sensation of impossible facemask ventilation is likened to attempted ventilation of a ‘brick wall’ and in my experience, has been as a result of solid physical obstruction of a compromised airway. This is a very different sensation to even the most difficult facemask ventilation. Occasionally,
© 2014 The Association of Anaesthetists of Great Britain and Ireland
in the context of difficult airways, an inexperienced trainee will declare impossible facemask ventilation– invariably before NMB – that settles to difficult ventilation. The definition of difficult facemask ventilation is not as clear and varies from subjective criteria requiring two practitioners, inadequate or unstable facemask ventilation [9], to grading based on escalating levels of intervention necessary to ventilate the lungs [10]. Factors that suggest difficult facemask ventilation include a body mass index ≥ 30 kg.m 2, a beard, Mallampati classification 3-4, age ≥ 57 years, severely limited jaw protrusion and a history of snoring [3]. Factors associated with impossible facemask ventilation include neck radiation changes, male sex, sleep apnoea, Mallampati 3-4 and presence of a beard [8]. With such a low incidence, the usefulness of predictive tests is limited, and in reality most patients predicted to be difficult are not, whereas a few who are predicted to be easy are anything but [11, 12]. We have an understanding of the incidence of difficult and impossible facemask ventilation, and some of the factors that suggest problems, but we are not good at predicting it. 811
Anaesthesia 2014, 69, 801–815
Crossing the Rubicon – when is the point of no return? After induction of anaesthesia, recognition of difficult or impossible facemask ventilation may theoretically allow two separate strategies: (i) no further anaesthetic agents, allowing ‘lightening’ of anaesthesia depth and the return of spontaneous respiration; or (ii) administration of short-acting NBDs such as suxamethonium or rocuronium (with suggamadex available), which may improve ventilation and facilitate tracheal intubation – or, if this fails and facemask ventilation remains difficult or impossible, allow the patient to wake up and breathe spontaneously [13–15]. This approach appears logical if spontaneous respiration is restored before severe hypoxaemia develops, but this is unlikely with suxamethonium [16] and the situation is compounded by first, any additional anaesthetic agents given in an attempt to improve facemask ventilation, and second, the inherent delayed administration of the NBD. Faced with impossible facemask ventilation, was the point of no return already crossed when spontaneous respiration was lost? Compared with the diaphragm, the upper airway muscles are more prone to a reduction in activity and obstruction as a result of anaesthetic and subanaesthetic concentrations of various agents including halothane, isoflurane, thiopental, diazepam, midazolam, opioids and propofol [17]. The
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combination of pre-existing anatomical problems that result in impossible facemask ventilation, and the effects of anaesthetic agents compounding upper airway collapse, mean that the chances of successfully restoring adequate spontaneous respiration in an apnoeic, anaesthetised patient with impossible facemask ventilation before severe hypoxaemia results is very small [18, 19]. The largest series of 53 041 attempts at facemask ventilation in all patients undergoing a general anaesthetic included 77 cases of unexpected impossible facemask ventilation and all but four of these 77 received NBDs, although it is not stated whether this was before or after facemask ventilation was found to be impossible. Sixty-five patients received suxamethonium and eight patients received a nondepolarising agent in the process of induction or management of the airway. In most (58/77), intubation was without difficulty; in 15 patients intubation was difficult or required additional equipment, three patients were woken up and one had an emergency cricothyrotomy [8]. It seems that when we are faced with impossible facemask ventilation we do not wake the patient up, and the presence of NBDs facilitates tracheal intubation [20–22]. The critical step in difficult airway management is the decision to induce anaesthesia in the first place, before securing the airway [23]. When we encounter unexpected difficult or impossible facemask ventilation, we have gone past this
juncture because we have already administered anaesthestic agents. The aim should be, as quickly as possible, optimisation of facemask ventilation, tracheal intubation, or the placement of a supraglottic airway device – all of which are improved by NBDs. It is interesting that in the 4th National Audit Project (NAP4), some local reporters commented that an aspect of ‘what went well’ was that NBDs were avoided when difficulty arose. In contrast, the review panel considered that delay or avoidance of NBDs contributed to the adverse events [24]. The recommendations of NAP4 included: “where facemask or laryngeal mask anaesthesia is complicated by failed ventilation and increasing hypoxia the anaesthetist should consider early administration of further anaesthetic agent and/or a muscle relaxant to exclude and treat laryngospasm” and: “no anaesthetist should allow airway obstruction and hypoxia to develop to the stage where an emergency surgical airway is necessary without having administered a muscle relaxant” [24]. In Kheterpal et al.’s series, when facemask ventilation was impossible the majority (73/77) of patients received NBDs and their tracheas were successfully intubated [8]. Similarly, when asked for management options in hypothetical scenarios of impossible facemask ventilation, the majority of those questioned (89%) would administer a NBD irrespective of whether they routinely checked facemask ventilation before NBDs [25].
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Editorial
Anaesthesia 2014, 69, 801–815
What makes facemask ventilation difficult or impossible after induction of anaesthesia?
laryngosapsm and chest wall rigidity [28–30], may also make facemask ventilation difficult.
Four mechanisms may cause difficulty with facemask ventilation. First, mechanical problems can result in an inadequate seal between the face and mask. Second, it may be difficult to maintain a patent naso-laryngopharyngeal airway/airspace. This is probably the most important practical skill for any anaesthetist and, similar to laryngoscopy and tracheal intubation, requires practice and improves with experience. This may partly explain why the least experienced anaesthetists were almost all likely to check facemask ventilation before NBDs, whereas only a minority of the most senior group did [25]. The inexperienced may have sub-optimal skills for facemask ventilation that may be amplified by inadequate depth of anaesthesia in an attempt to keep the patient lightly anaesthetised in case there are problems requiring restoration of spontaneous respiration. Airway patency may also be affected by reduced longitudinal tension in the upper airway and retro-lingual, retro-palatal, and retro-glossal obstruction resulting from poor positioning [26]. Third, we know that anaesthetic agents and NBDs reduce upper airway muscle tone and cause airway narrowing and collapse [17, 27], which may make facemask ventilation more difficult. Fourth, an increase in upper airway reflexes in the immediate post-induction period, including
Neuromuscular blocking drugs and effects on normal, difficult and impossible facemask ventilation In patients with normal airways, Goodwin et al. [31] looked at subjective measures such as the ability to ventilate the lungs to achieve optimal chest movements using bag and mask, before and after the administration of NBDs, and showed no effect of the latter. Warters et al. [5], in patients with normal and difficult airways, found that rocuronium significantly improved facemask ventilation, with the improvement most dramatic in those few patients in whom ventilation was more difficult [5]. Ikeda et al. found that in patients with normal upper airway anatomy held in a neutral head and mandible position, suxamethonium increased tidal volume and rocuronium had no effect [7]. Amathieu et al. [6] assessed 12 221 patients for difficult airway management in a two-year prospective study and allocated patients to two groups. The higher-risk group (those with three features or more suggestive of difficult airway management) received no check of facemask ventilation, and immediately following induction of anaesthesia received suxamethonium (i.e. ‘squirt-squirt-puff’). Those with fewer than three factors suggestive of difficult airway management were assessed by facemask ventilation
© 2014 The Association of Anaesthetists of Great Britain and Ireland
following induction of anaesthesia (squirt-puff-squirt’). Those classified as easy facemask ventilation (grade 1 or 2) received a long-acting NBD; those classified as difficult (grade 3) received suxamethonium. All of the 12 221 patients received NBDs and underwent tracheal intubation. In all cases (both easy and difficult facemask ventilation), NBDs never worsened facemask ventilation, but in most cases it improved it. Of the 90 patients who received suxamethonium after difficult facemask ventilation, 56 patients improved by one grade. These studies, together with Kheterpal et al.’s study previously discussed, show that normal or difficult facemask ventilation either remains unchanged or improves – but never deteriorates – after NBDs, and when impossible facemask ventilation is encountered, NBDs facilitate tracheal intubation. They improve facemask ventilation by abolishing airway reflexes, reducing the tone and bulk of muscles and allowing more space for gas to pass through [4]. They also reduce resistance and allow easier jaw thrust, head tilt, and open mouth-type maneuvers crucial to creating an airspace in the naso-, oro- and laryngo-pharynx.
Squirt-puff-squirt or squirt-squirt-puff? Since Calder and Yentis [1] first questioned the logic of checking facemask ventilation before NBDs, three approaches have remained. First, the technique that was originally criticised; i.e. induction of anaesthesia followed by facemask
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Anaesthesia 2014, 69, 801–815
ventilation, which if difficult or impossible leads to wake-up and return of spontaneous respiration. The latter part of this approach does not appear to be used and does not appear to work [2, 3, 6, 8, 18, 19, 24, 25]. Second, a hybrid approach in which facemask ventilation is checked after induction of anaesthesia and if this is easy, a long-acting NBD is administered but if ventilation is difficult, a short-acting NBD is administered [13–15]. This appears logical, but is dependent on the return of spontaneous respiration before serious hypoxaemia occurs. It is not inconceivable that a patient with extremely difficult or impossible facemask ventilation, who has been given a short-acting NBD, becomes seriously hypoxic before spontaneous respiration has resumed. The third approach is the one favoured by Calder and Yentis: administration of NBDs before facemask ventilation. This is logical since the evidence suggests that ventilation either remains unchanged or improves, but does not deteriorate in normal and difficult facemask ventilation [4–7, 31], provides optimal conditions for facemask ventilation, and if impossible facemask ventilation develops, airway rescue is facilitated [8]. No airway technique under general anaesthesia is guaranteed to work always [32], but NBDs are much more often the answer than the problem, and should be given early – before checking facemask ventilation.
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Editorial
Competing interests No external funding and no competing interests declared. A. Patel Consultant Anaesthetist Royal National Throat, Nose and Ear Hospital & University College Hospital London, UK Email: [email protected]
References 1. Calder I, Yentis SM. Could ‘safe practice’ be compromising safe practice? Should anaesthetists have to demonstrate that face mask ventilation is possible before giving a neuromuscular blocker? Anaesthesia 2008; 63: 113–5. 2. Langeron O, Masso E, Huraux C, et al. Prediction of difficult mask ventilation. Anesthesiology 2000; 92: 1229–36. 3. Kheterpal S, Han R, Tremper KK, et al. Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006; 105: 885–91. 4. Sachdeva R, Kannan TR, Mendoca C, Patteril M. Evaluation of changes of tidal volume during mask ventilation following administration of neuromuscular blocking drugs. Anaesthesia 2014; 69: 826–32. 5. Warters RD, Szabo TA, Spinale FG, DeSantis SM, Reves JG. The effect of neuromuscular blockade on mask ventilation. Anaesthesia 2011; 66: 163–7. 6. Amathieu R, Combes X, Abdi W, et al. An algorithm for difficult airway management, modified for modern optical devices (Airtraq laryngoscope; LMA CTrachTM): a 2-year prospective validation in patients for elective abdominal, gynecologic, and thyroid surgery. Anesthesiology 2011; 114: 25–33. 7. Ikeda A, Isono S, Sato Y, et al. Effects of muscle relaxants on mask ventilation in anesthetized persons with normal upper airway anatomy. Anesthesiology 2012; 117: 487–93. 8. Kheterpal S, Martin L, Shanks AM, Tremper KK. Prediction and outcomes of impossible mask ventilation: a review of 50,000 anesthetics. Anesthesiology 2009; 110: 891–7. 9. Han R, Tremper KK, Kheterpal S, O’Reilly M. Grading scale for mask ventilation. Anesthesiology 2004; 101: 267.
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