Traditional teaching dictates that bag-mask ventilation (BMV) is not recommended during rapid sequence induction (RSI) due to the concern of insufflating the stomach, precipitating reflux of gastric contents and potentially pulmonary aspiration. However, there are patient groups at risk of pulmonary aspiration who are challenging to preoxygenate. These include those with decreased functional residual capacity, for example the morbidly obese, or the term parturient; those with preexisting respiratory disease, for example pneumonia; and those intolerant of a close-fitting mask, for example the distressed child. We hypothesised that expert operators modify their RSI technique, balancing risks of pulmonary aspiration with other considerations, frequently using BMV in patients at risk of hypoxaemia.
We would like to report the results from a SurveyMonkey questionnaire of members of the UK Difficult Airways Society (DAS).
Clinicians were given five scenarios:
- Appendicectomy, BMI 50
- Healthy 50-year-old, with pneumonia and hypoxic respiratory failure
- Stat caesarean section, parturient BMI 35
- Severe head injury
- Six-year-old, emergency laparotomy
Respondents were asked if they would undergo BMV after anaesthetic induction and prior to endotracheal intubation. Responses were analysed according to respondent level of training, and which regular clinical sessions they performed (critical care sessions, emergency operating, obstetric or paediatric lists).
Eight hundred and twenty-four responses were received (24% registrars, 69% consultants, response rate 36%). Nine percent would always or frequently undergo BMV during RSI, and a further 67% would undergo BMV depending on the scenario (Fig. 1). Some clinicians who stated that they would never undertake BMV during RSI then considered BMV when presented with specific scenarios: 7% for scenario A, 46% for B, 5% for C, 3% for D and 33% for E. Clinicians were most likely to undergo BMV in the pneumonia (83%) and paediatric (60%) scenarios. Consultants were more likely to undertake BMV than junior trainees (Table 1), odds ratio (OR) 2.2 [95% confidence interval (95% CI) 1.5 to 3.4: P = 0.00006]. Clinicians undertaking regular paediatric sessions were more likely to undertake BMV in all scenarios, not just the paediatric scenario [Table 2; OR 1.4 (95% CI 1.2 to 1.6: P = 0.00003)]. No significant difference was demonstrated when responses were analysed by whether or not clinicians regularly performed clinical sessions other than paediatric lists.
Hunter (1776) was the first to observe the benefit of cricoid pressure in preventing gastric insufflation in recovery of ‘people apparently drowned’. The ‘larynx gently pressed against the oesophagus and spine’ prevents ‘stomach and intestines being too much distended by air’. Opposing views of whether to undertake BMV as part of RSI were first presented in the 1960s: Sellick (1961) stated that, with cricoid pressure, ‘lungs may be ventilated without the risk of gastric distension’, whereas Wylie (1963) put forward the alternate position: ‘inflation of the patient's lungs … must not be carried out until endotracheal intubation’. Neither presented evidence to support their statements.
Available evidence suggests that BMV, especially with cricoid pressure, is unlikely to cause significant gastric insufflation. In elective surgery, Lawes et al.1 demonstrated that, with cricoid pressure applied, gastric insufflation did not occur, even with airway pressures of up to 60 cmH20. Ruben et al.2 found that with cricoid pressure, airway pressures of more than 50 cmH2O were required to cause insufflation. Petito investigated the volume of gas in the stomach of patients ventilated with cricoid pressure (15 ml kg−1): 92% were found to have less than 15 ml, and two patients who suffered stomach insufflation (355 and 500 ml) were noted to require ‘higher than usual inspiratory pressure … to deliver … 15 ml kg−1. A cadaveric study demonstrated that 30 N cricoid pressure prevented regurgitation with oesophageal pressures up to 55 cmH2O.3
Pulmonary aspiration was the commonest cause of death associated with anaesthesia in cases reported to the fourth UK National Audit Project (NAP 4).4 The majority of these were in cases in which risk factors for regurgitation were not identified, and RSI not undertaken, or they occurred intraoperatively in cases managed with a nondefinitive airway. Aspiration when RSI was undertaken was relatively rare; only two cases were reported in NAP 4, one in a patient with small bowel obstruction and another in an obstetric case following difficult intubation.
A meta-analysis of the available literature on RSI concluded that ‘there is no evidence to support the avoidance of BMV… to decrease the incidence of aspiration (Grade B recommendation)’ and ‘keeping peak airway pressures below 15–20 cmH2O will allow for ventilation without increasing the risk of air entry into the stomach (Grade C recommendation)’.5
Some respondents suggested BMV in response to desaturation, as an alternative to routine BMV during RSI. A randomised simulation study comparing the two strategies demonstrated that those responding to desaturation were more likely to use higher pressures to BMV (>20 cmH2O), and more likely to attempt intubation before allowing adequate time for paralysis; in addition, operators had significantly elevated stress hormones compared with the group who electively used BMV.6 BMV after desaturation places patients at a greater risk of gastric insufflation, coughing and bucking (predictors of regurgitation) and raises operator stress (shown to reduce situational awareness).
In light of the increased awareness of human factors in managing critical incidents, in our opinion, there is a potential advantage of performing at least one ‘gentle puff’ in all patients undergoing RSI. This will reassure the anaesthetist that they are able to undergo BMV in the event of a difficult or failed intubation; the incidence of both of these is increased with RSI. Once the ability to BMV is confirmed, the operator can feel reassured and concentrate on securing the airway, improving performance. Similarly, if the practitioner was unable to perform BMV at this stage, it would prompt them to call for help earlier when faced with a ‘Can’t Intubate, Can’t Ventilate’ scenario.
Many patient groups are at risk of hypoxaemia during RSI and would benefit from BMV. Where there is no higher level of evidence available, consensus opinion of experts is used as a basis for practice guidelines. Trainees are more likely to use ‘classical RSI’, as prescriptively taught. Is it time to review specific teaching of RSI technique in selected groups, reflecting current expert practice?
Acknowledgements relating to this article
Assistance with the survey: we would like to thank all the DAS members who took the time to complete the survey. Thanks also to Andrew Bailey, Peninsula Medical School, for his assistance with the statistical analysis.
Financial support and sponsorship: no external funding received.
Conflicts of interest: none.
1. Lawes EG, Campbell I, Mercer D. Inflation pressure, gastric insufflation and rapid sequence induction. Br J Anaesth
2. Ruben H, Krudsen E, Carugati G. Gastric insufflation in relation to airway pressure. Acta Anaesthesiol Scand
3. Vanner RG, Pryle BJ. Regurgitation and oesophageal rupture with cricoid pressure: a cadaver study. Anaesthesia
4. Cook T, Woodall N, Frerk C. The Fourth National Audit Project. Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1: anaesthesia. Br J Anaesth
5. Neilipovitz DT, Crosby ET. No evidence for decreased incidence of aspiration after rapid sequence induction. Can J Anaesth
6. Eich C, Timmermann A, Russo SG, et al. A controlled rapid-sequence induction technique for infants may reduce unsafe actions and stress. Acta Anaesthesiol Scand