Evaluation of the Self-Inflating Bag-Valve-Mask and Non-Rebreather
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Open Access Research BMJ Open: first published as 10.1136/bmjopen-2012-001785 on 26 October 2012. Downloaded from Evaluation of the self-inflating bag-valve-mask and non-rebreather mask as preoxygenation devices in volunteers Amelia Robinson,1 Ari Ercole2 To cite: Robinson A, ABSTRACT ARTICLE SUMMARY Ercole A. Evaluation of the Objective: To evaluate and compare the effectiveness self-inflating bag-valve-mask and tolerability of preoxygenation with the self-inflating and non-rebreather Article focus bag-valve-mask (BVM) and non-rebreather mask mask as preoxygenation ▪ Preoxygenation is an important safety procedure devices in volunteers. BMJ (NRM) as are used before emergency anaesthesia. before emergency anaesthesia and aims to prevent Open 2012;2:e001785. Design: Device performance evaluation. hypoxia in the event of prolonged apnoea. doi:10.1136/bmjopen-2012- Setting: Experimental study. ▪ The self-inflating bag-valve-mask (BVM) is com- 001785 Participants: 12 male and 12 female healthy monly used for preoxygenation when an anaes- volunteers (age range 24–47) with no history of thetic circuit is not available, such as in the ▸ Prepublication history for clinically significant respiratory disease. prehospital environment. this paper is available online. Interventions: End-expiration oxygen measurements ▪ Recently the use of non-rebreather masks (NRM) To view these files please (FEO2) after 3 min of preoxygenation with BVM as an alternative has become common to avoid visit the journal online (without mechanical assistance) and NRM devices. increased work of breathing but the effectiveness (http://dx.doi.org/10.1136/ Mask pressures were measured and subjective of this approach has not been formally evaluated. bmjopen-2012-001785). difficulty of breathing was also assessed with a visual Key messages analogue score (VAS). Received 12 July 2012 ▪ The BVM and NRM are comparable techniques in Accepted 26 September 2012 Primary and secondary outcome measures: The terms of the degree of denitrogenation achieved. final FEO2 achieved was 58.0% (SD 7.3%) for the NRM ▪ The BVM is well tolerated but subjectively more dif- http://bmjopen.bmj.com/ This final article is available compared to 53.1% (SD 13.4%) for the BVM ficult to breath through than the NRM, which may for use under the terms of (p=0.072). Preoxygenation was associated with small the Creative Commons lead to reduced patient compliance. Therefore, the increases in FECO2 that were greater for the BVM NRM may be a reasonable alternative. Attribution Non-Commercial (0.50%; 95% CI 0.48 to 0.52) than the NRM (0.29%; 2.0 Licence; see ▪ By comparison with the existing literature, 95% CI 0.31 to 0.28); this difference was statistically http://bmjopen.bmj.com however, neither technique is as effective as the significant (p=0.028). Both devices were well tolerated use of a traditional anaesthetic circuit. on VAS assessment of difficulty of breathing although this was higher for the BVM than the NRM (median Strengths and limitations of this study ▪ VAS 1.85/10 compared to 1.1/10; p=0.041). Inspiratory Generalisation of the results from healthy volun- on September 25, 2021 by guest. Protected copyright. and expiratory mask pressures were higher for the teers in an optimal environment to critically ill BVM. patients in a suboptimal environment is difficult. Conclusions: In healthy volunteers, the NRM ▪ Our results are likely to represent a ‘best case’ performs comparably to the BVM in terms of the upper bound to device performance in combat- degree of denitrogenation achieved although neither ive, critically ill or obtunded patients where performed well. Although it was well tolerated, the effective preoxygenation would be expected to be BVM was subjectively more difficult to breathe through further compromised. and was associated with greater mask pressures and a small increase in FECO2 consistent with hypoventilation or rebreathing. Our results suggest that preoxygenation emergency department such as the prehospi- with the NRM may be a preferable approach in tal environment where available resources may spontaneously breathing patients. 1Clinical School, University of be suboptimal. Preoxygenation before induc- Cambridge, Cambridge, UK tion of anaesthesia is an important safety pro- 2Division of Anaesthesia, cedure and aims to replace residual nitrogen University of Cambridge, in the lungs with oxygen. The denitrogenation Cambridge, UK of the functional residual capacity provides a Correspondence to Emergency anaesthesia is a high-risk interven- reserve oxygen store which may transiently Dr Ari Ercole; tion, particularly when undertaken in an envir- prevent arterial oxygen desaturation even [email protected] onment outside of the operating theatre or during prolonged apnoea1 as might result Robinson A, Ercole A. BMJ Open 2012;2:e001785. doi:10.1136/bmjopen-2012-001785 1 Comparison of the bag valve mask and non-rebreather mask for pre-oxygenation BMJ Open: first published as 10.1136/bmjopen-2012-001785 on 26 October 2012. Downloaded from in the event of a difficult tracheal intubation. better-tolerated alternative to the BVM. On this basis, Preoxygenation is particularly important in circumstances the practise of using an NRM for emergency preoxy- where securing the airway is predicted to be difficult or genation is becoming increasingly widespread. However, where artificially ventilating a patient without a properly to date, there has not been a study comparing these two secured airway may be dangerous, such as in emergency methods and air entrainment may still be significant anaesthesia and/or in patients at risk of aspiration. The compared to a cushioned mask.8 In this study, we critically ill may be both particularly prone and sensitive compare the efficacy of the BVM and the NRM for pre- to rapid arterial oxygen desaturation making optimal pre- oxygenation and the ease of breathing with each mask oxygenation before emergency anaesthesia even more in volunteers. important. A common procedure utilised clinically involves 3 min METHODS of tidal breathing from a high oxygen concentration Volunteer group source, that is, through a tightly fitting mask connected The study was reviewed and approved by the local to an anaesthetic circuit that prevents rebreathing of ethical review board (NRES Committee East of CO . The performance of such anaesthetic circuits has 2 England—Cambridge Central, study 12/EE/0057). A been extensively evaluated. Measurement of end expira- total of 24 healthy volunteers were recruited from hos- tory oxygen fraction (F O ) gives an estimate of the E 2 pital staff by advertisement. The volunteers had a degree of denitrogenation and therefore the adequacy working association with the investigators but no of preoxygenation. Optimal preoxygenation increases organisational involvement in the study. Volunteers the F O to approaching 90%.2 Other studies have E 2 with acute respiratory disease or receiving treatment demonstrated that extending the period of preoxygena- for chronic respiratory disease, including asthma, were tion beyond 3 min does not lead to a clinically signifi- excluded. Pregnancy, body mass index of greater than cant improvement in denitrogenation.34 35, known or suspected coronary or cerebrovascular In some situations, most notably in the prehospital disease and previous exposure to bleomycin were also environment, anaesthetic breathing circuits are less avail- exclusion criteria. Informed consent was obtained able. In the absence of an anaesthetic circuit, the self- from all participants. inflating bag-valve-mask (BVM) device is often used5 as it is readily available, can still provide ventilation with air in the event of oxygen supply failure and can be used STUDY DESIGN for both preoxygenation or to assist breathing. However, The study was conducted with the subjects in the fully the BVM may increase resistance to passive breathing supine position. Each subject was preoxygenated for and feel claustrophobic. Gentle assistance with breathing 3 min by normal tidal breathing with each mask in turn http://bmjopen.bmj.com/ using light pressure on the BVM can overcome this but, and the procedure repeated (ie two attempts with each if not carefully performed, could also cause stomach dis- mask with the results averaged). An oxygen flow rate of tension in semiconscious patients, increasing the risk of 10 l/min was chosen for both the BVM and NRM and aspiration. this was sufficient that the reservoir bag remained well As a possible alternative, a number of investigators filled at end inspiration in all cases. Thus, at this flow have examined whether effective preoxygenation can be rate, free supply of oxygen to meet peak inspiratory flow delivered with a standard oxygen face-mask (‘Hudson’ without avoidable entrainment should have been avail- fi mask), which is less tightly tting and therefore well tol- able. FEO2 and FECO2 measurements were made before on September 25, 2021 by guest. Protected copyright. erated.467Results from these studies have shown that and after each mask was tested by slow end expiratory the degree of denitrogenation achieved is inferior with reserve exhalation into a mouthpiece connected to a the Hudson mask. This is due to air entrainment calibrated gas analyser (Datex-Ohmeda S/5, GE around the mask during inspiration, which occurs Healthcare, Chalfont St. Giles, Buckinghamshire, UK). because peak inspiratory flow may be far greater than The subjects breathed room air between each set of the rate at which oxygen can be practically supplied observations until the end expired samples had returned from cylinders. to baseline composition. High-flow non-rebreather masks (NRM) are similar to The starting mask was predetermined by block ran- traditional Hudson masks but additionally incorporate a domisation so as to eliminate a systematic error from simple valve system so that peak inspiratory flow demand ‘training’ effects. There are two sizes of BVM commonly may be met with oxygen from an attached reservoir bag used in our unit. Half the subjects were randomly allo- rather than air entrained through leaks around the cated to a 1.5 litre BVM the other half tested with a mask.