A prospective, randomised trial of pre-oxygenation strategies available in the pre-hospital environment

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1 Original Article doi: /anae A prospective, randomised trial of pre-oxygenation strategies available in the pre-hospital environment C. J. Groombridge, 1,2 E. Ley, 3 M. Miller 4 and T. Konig 1 1 Pre-hospital Physician, London s Air Ambulance, Bart s Health NHS Trust, London, UK 2 Pre-hospital Physician, 3 Paramedic, Essex and Herts Air Ambulance Trust, UK 4 Pre-hospital Physician, Kent Surrey and Sussex Air Ambulance Trust, Marden, UK Summary Pre-oxygenation before tracheal intubation aims to increase safe apnoea duration by denitrogenation of the functional residual capacity of the lungs, and increasing oxygen stores at the onset of apnoea. Pre-oxygenation options in the pre-hospital environment are limited due to oxygen availability and equipment portability. The aim of this study was to evaluate the effectiveness of strategies available in this setting. This was a prospective, randomised, crossover study of 30 healthy volunteers who underwent 3-min periods of pre-oxygenation by tidal volume breathing with a non-rebreather mask, a bag-valve-mask and a portable ventilator. The primary outcome measure was fractional expired oxygen concentration of the first exhaled breath after each technique. The secondary outcome measure was ease of breathing, assessed using a visual analogue scale. The mean (95%CI) fractional expired oxygen concentrations achieved with the non-rebreather mask were 64 (60 68)%, bag-valve-mask 89 (86 92)% and portable ventilator 95 (94 96)%. Pre-oxygenation efficacy with the non-rebreather mask was significantly worse than with either the bagvalve-mask (p < 0.001) or ventilator (p < 0.001). No significant difference in ease of breathing was identified between the bag-valve-mask and ventilator, but both were perceived as being significantly more difficult to breathe through than the non-rebreather mask. We conclude that, in healthy volunteers, the effectiveness of pre-oxygenation by bag-valve-mask and portable ventilator was superior to pre-oxygenation with a non-rebreather mask, although the non-rebreather mask was easier to breathe through than the other pre-oxygenation devices.... Correspondence to: C. J. Groombridge cgroombridge@doctors.org.uk Accepted: 30 January 2017 Keywords: airway management; emergency medical services; oxygen inhalational therapy; tracheal intubation Introduction Pre-oxygenation is a standard of care intervention, intended to reduce the risk of hypoxaemia associated with the drug-induced period of apnoea during rapid sequence intubation (RSI). By breathing high inspired oxygen concentrations nitrogen is displaced from the lungs, increasing both the volume of oxygen available for respiration and safe apnoea time during intubation [1]. In the hospital setting most intubations occur in the operating theatre, and pre-oxygenation is managed using an anaesthetic breathing system. Emergency intubations are also undertaken in the emergency department and intensive care unit, however, patients intubated outside the operating theatre are at higher risk of adverse events, including hypotension, aspiration and hypoxaemia [2]. In the pre-hospital setting, The Association of Anaesthetists of Great Britain and Ireland

2 Groombridge et al. Comparison of pre-hospital pre-oxygenation strategies Anaesthesia 2017, 72, these risks are likely to be equivalent or even greater, and so efforts to optimise pre-oxygenation are extremely important. Various strategies for optimising pre-oxygenation have been assessed: varying the patient s position [3]; increasing the duration of tidal volume breathing or by using multiple deep breaths [4]; and even varying the mouthpiece used [5]. However, most of these studies do not inform pre-hospital practice, as pre-oxygenation is achieved by using anaesthetic breathing systems that are not available in pre-hospital settings. Identifying a strategy that achieves maximal denitrogenation and pre-oxygenation equivalent to what is able to be achieved in an operating theatre should enhance the safety of patients that require RSI outside of hospital. Options for pre-oxygenation in the pre-hospital setting currently include non-rebreather masks (NRM), bag-valve-mask devices (BVM) and adjuncts to these devices, such as nasal cannulae. A recent study by Groombridge and colleagues examined options available outside of the operating theatre. In healthy volunteers, they showed that denitrogenation with a well-fitted BVM was superior to a NRM, and comparable to what may be achieved using an anaesthetic breathing system [6]. This suggests that the BVM may represent best practice approach to pre-oxygenation. Rugged portable ventilators are carried by pre-hospital medical teams to ventilate patients following RSI, and some modern portable ventilators can deliver non-invasive ventilation (NIV). Baillard and colleagues have demonstrated the efficacy of NIV as a pre-oxygenation method [7], and this option has been recommended for patients who are already hypoxaemic before RSI in the emergency department [8]. Although this may be a readily available way to improve preoxygenation in the pre-hospital setting, the efficacy of pre-oxygenation by this method as measured by fraction of expired oxygen (FeO 2 ) has not previously been investigated or compared with standard BVM or NRM techniques. We devised a prospective, randomised study using healthy volunteers to compare the efficacy of pre-oxygenation and subjective ease of breathing with a NRM, a BVM and NIV using a pre-hospital ventilator. Methods Before data collection, approval for the study was granted by the Queen Mary University of London Ethics of Research Committee. Thirty healthy volunteers were recruited from air ambulance charity staff. Invitation to participate was by advertisement posters at the charity office, a presentation at the air ambulance clinical governance day and word of mouth. Volunteers were not studied if they had a history of respiratory disease or were pregnant, and were advised not to take part if they had claustrophobia or concerns about having a facemask held firmly to their face. Informed consent was obtained from all participants. A randomised, repeated-measures crossover design was used. Each participant completed 3 min of tidal volume breathing using a NRM, BVM and NIV from a portable ventilator, with a washout period between use of each device. For the NRM technique, the mask position was optimised by adjustment of the elasticated headband and nose clip (EcoLite TM Adult High Concentration Mask, Model , Intersurgical Ltd, Berkshire, UK). For BVM pre-oxygenation a disposable self-inflating resuscitator with a 2600-ml reservoir bag (Ambu â SPUR â II, Ambu Ltd, St. Ives, UK) was used. The ventilator used for NIV was an Oxylog â 3000 Plus ventilator in non-invasive ventilation mode with positive end expiratory pressure (PEEP) set to 5 cmh 2 0 (Draeger Medical UK Ltd, Hemel Hempstead, UK). An appropriately-sized air-cushioned facemask (Ambu â Ultraseal facemask, Ambu Ltd, St. Ives, UK) was used for both the BVM and NIV techniques. Standard ZD oxygen cylinders provided the oxygen supply to the BVM and NRM via a flowmeter set to 15 l.min 1, and to the ventilator via a Schrader valve (BOC Healthcare, Manchester, UK). The order for use of devices was determined in advance by computer number randomisation. A blinding strategy was impractical, but volunteers had limited prior knowledge of the different devices, and received standardised instructions before each pre-oxygenation session. A baseline FeO 2 measurement was taken before the start of pre-oxygenation and between interventions to ensure return to baseline. Volunteers were supine for the periods of pre-oxygenation, but were permitted 2017 The Association of Anaesthetists of Great Britain and Ireland 581

3 Groombridge et al. Comparison of pre-hospital pre-oxygenation strategies to mobilise between interventions for comfort and to avoid potential atelectasis. The FeO 2 measurements were made with a calibrated gas analyser (Teledyne AX300 Oxygen Analyser, Viamed Ltd, West Yorkshire, UK). At the end of each pre-oxygenation period, the FeO 2 result for each technique was determined by the volunteer exhaling continuously into a separate reservoir attached to the gas analyser. This was to prevent FeO 2 readings being artificially increased by the continuous flow of oxygen from the pre-oxygenation device. For the assessment of breathing difficulty, a computer-generated visual analogue scale (VAS) was used. Immediately following a pre-oxygenation session, volunteers read a standard statement on a smartphone touch screen, instructing them to position a slider on a scale to indicate their perceived ease of breathing for that technique. All data were recorded in password-protected Microsoft â Excel â spreadsheets before data analysis. Analysis was performed using R statistical software (version 3.2.3, R Core Team, Vienna), the Post-Hoc Interaction Analysis (PHIA) package and Microsoft â Excel â for Mac 2011 (Microsoft Corporation, Redmond, WA, USA). FeO 2 comparisons were by one-way repeated-measures analysis of variance (ANOVA). Sphericity assumptions were checked using Mauchly tests for sphericity, and if violated the Greenhouse Geisser correction was used for p values. Where significant p values were found, post-hoc comparisons were performed with Bonferroni adjustment applied to p values. Effect sizes for FeO 2 comparisons were calculated using the method described by Hollands and Jarmasz [9]. Visual analogue scale scores were compared using Friedman s test with post-hoc Bonferroni adjustment applied to p values. For non-parametric tests, R provides a confidence interval for the difference in medians, and these were used to calculate effect sizes. For all comparisons, a two-sided p value < 0.05 was considered to be statistically significant. For the sample size calculation, a pooled SD of 7% was used from previous studies [6, 10]. Using the twosample independent samples t-test formula [11] for a difference in FeO 2 of 10% with a power 0.8 and alpha 0.05, nine participants in each group were required, making 27 in total. As a check, a second calculation performed using Cohen s effect size for a one-way ANOVA [12] returned 22 observations per group (or 22 participants). Allowing for a 10% dropout rate, a sample size of 30 participants was sought. Results Baseline characteristics are summarised in Table 1. Box plots are presented in Fig. 1 to illustrate spread of data. Overall, there was a significant difference in the FeO 2 achieved between the three techniques (p < 0.01). When compared with NRM, both BVM and NIV achieved a higher mean (95%CI) FeO 2 (64 [60 68]% vs. 89 [86 92]%, p < 0.001; 64 [60 68]% vs. 95 (94 96)%, p < 0.001, respectively). The NIV also achieved significantly higher FeO 2 levels than the BVM (95 [94 96]% vs. 89 [86 92]%, p < 0.01). With the ease of breathing assessment using VAS, the BVM and portable ventilator were assessed as being more difficult to breathe through, with median scores of 28.5 and 37.0, respectively, compared with NRM (2.5, p < 0.001). Box plots of the results are presented in Fig. 2. Discussion This study aimed to evaluate pre-oxygenation strategies available in the pre-hospital environment, both in terms of efficacy (as measured by denitrogenation), as well as the ease of breathing with each technique. Our results suggest that significant improvements in denitrogenation can be achieved by NIV with a portable ventilator when compared with the standard NRM or BVM pre-oxygenation strategies. Previous studies on healthy volunteers [6, 10] have demonstrated FeO 2 of 50 60% for NRM and 80 90% for a well-fitting BVM. This study supports these findings. Although inferior in terms of denitrogenation, the NRM was significantly easier to breathe through. For patients who are agitated, or those with distortion of facial anatomy due to injury, the maintenance of a Table 1 Baseline characteristics of volunteers undergoing pre-oxygenation. Values are median (IQR [range]). Volunteers Demographic n=30 Age; years 35.0 ( [ ]) Weight; kg 73 (64-87 [59-111]) Height; cm 174 ( [ ]) BMI; kg.m 2 24 (22-28 [20-36]) Sex; men The Association of Anaesthetists of Great Britain and Ireland

4 Groombridge et al. Comparison of pre-hospital pre-oxygenation strategies Anaesthesia 2017, 72, Figure 1 Box plot of FeO 2 (%) for non-rebreather mask (NRM), bag-valve-mask (BVM) and non-invasive ventilation (NIV) showing median and interquartile range. Whiskers represent minimum to maximum values excluding outliers; dots represent outliers greater than IQR outside the first and third quartiles. Figure 2 Box plots of ease of breathing visual analogue score (VAS) for non-rebreather mask (NRM), bagvalve-mask (BVM) and non-invasive ventilation (NIV) showing median and interquartile range. Whiskers represent minimum to maximum values excluding outliers; dots represent outliers greater than IQR outside the first and third quartiles. good facemask seal may not be possible, and a NRM may be better tolerated. The ventilator tested in this study attained FeO 2 measurements similar to pre-oxygenation targets in an operating theatre [13]. There are, however, logistical issues with incorporating a portable ventilator into prehospital pre-oxygenation practice. These include the number of people available to assist with the procedure, the amount of oxygen available, and the need to carry the required equipment to scene. The ventilator used in this study weighs approximately 6 kg, compared with 314 g for the BVM. Furthermore, while pre-hospital providers are familiar with the use of a NRM or BVM, using a portable ventilator for pre-oxygenation is a more complicated option, and additional training is likely to be necessary to ensure that providers can set up the device for NIV pre-oxygenation in a consistent and safe fashion. Finally, although the difference in FeO 2 between BVM and NIV was statistically significant, the mean difference was 5%, which may not be a clinically important. The ventilator used in this study is present in many emergency departments, and so the results of this study would be relevant to pre-oxygenation decisions in that setting. This may be particularly so for critically unwell patients requiring emergency intubation who are already hypoxic [8], and this is the first study to provide quantitative evidence of its efficacy. A major limitation of this study was the use of healthy volunteers whose normal respiratory physiology may not allow adequate evaluation of the true efficacy of a technique, that is, to prevent desaturation during apnoea in a critically unwell or injured patient. Furthermore, the volunteers were all able to cooperate with the 3-min period of pre-oxygenation, even when they had difficulty breathing through the device (as indicated by the VAS assessment of ease of breathing). Previous studies [10, 14] have shown the importance of achieving a good mask seal, and agitated patients may not tolerate facemask techniques as well as the NRM, which could adversely affect efficacy. This study assessed denitrogenation as a surrogate for efficacy of pre-oxygenation. Although denitrogenation is an important component of pre-oxygenation, other factors contribute to the efficacy of the technique, particularly in the critically unwell, including alveolar recruitment and improvements in ventilation perfusion matching. Future studies should address the efficacy of pre-oxygenation strategies in critically unwell patients with patient-oriented outcomes such as incidence of hypoxia or nadir oxygen saturation. In conclusion, the greatest denitrogenation was obtained with NIV using a portable ventilator. FeO The Association of Anaesthetists of Great Britain and Ireland 583

5 Groombridge et al. Comparison of pre-hospital pre-oxygenation strategies measurements similar to pre-oxygenation targets in an operating theatre were achieved. However, this technique was reported as difficult to breathe through, and may not be tolerated by agitated patients. The BVM represents a lightweight and familiar alternative, and with a good seal may represent an optimal pre-oxygenation strategy before RSI in the pre-hospital environment. The NRM is likely to still have a role for patients in whom a good facemask seal cannot be achieved, but pre-hospital teams should be aware of its limitations in terms of efficacy. Acknowledgements The authors thank the staff of Essex and Herts Air Ambulance Trust for volunteering their time; Viamed Ltd, UK for the loan of the oxygen analyser device; and Draeger Medical UK Ltd for the loan of the portable ventilator. The study was registered at ClinicalTrials.gov (NCT ). No external funding or competing interests declared. References 1. Heller ML, Watson TR Jr. Polarographic study of arterial oxygenation during apnea in man. New England Journal Medicine 1961; 264: Bowles TM, Freshwater-Turner DA, Janssen DJ, Peden CJ. Outof theatre tracheal intubation: prospective multicentre study of clinical practice and adverse events. British Journal of Anaesthesia 2011; 107: Smith SJ, Harten JM, Jack E, Carter R, Kinsella J. Pre-oxygenation in healthy volunteers: a comparison of the supine and 45 seated positions. Anaesthesia 2010; 65: Baraka AS, Taha SK, Aouad MT, El-Khatib MF, Kawkabani NI. Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques. Anesthesiology 1999; 91: Hirsch J, F uhrer I, Kuhly P, Schaffartzik W. Preoxygenation: a comparison of three different breathing systems. British Journal of Anaesthesia 2001; 87: Groombridge C, Chin CW, Hanrahan B, Holdgate A. Assessment of common preoxygenation strategies outside of the operating room environment. Academic Emergency Medicine 2016; 23: Baillard C, Fosse JP, Sebbane M, et al. Noninvasive ventilation improves preoxygenation before intubation of hypoxic patients. American Journal of Respiratory and Critical Care Medicine 2006; 174: Weingart SD, Levitan RM. Preoxygenation and prevention of desaturation during emergency airway management. Annals of Emergency Medicine 2012; 59: Hollands JG, Jarmasz J. Revisiting confidence intervals for repeated measures designs. Psychonomic Bulletin and Review 2010; 17: Hayes-Bradley C, Lewis A, Burns B, Miller M. Efficacy of nasal cannula oxygen as a preoxygenation adjunct in emergency airway management. Annals of Emergency Medicine 2016; 68: Wellek S, Blettner M. On the proper use of the crossover design in clinical trials: part 18 of a series on evaluation of scientific publications. Deutsches Arzteblatt International 2012; 109: Cohen J. Statistical Power Analysis for the Behavioral Sciences. Abingdon-on-Thames: Routledge, Tanoubi I, Drolet P, Donati F. Optimizing preoxygenation in adults. Canadian Journal of Anesthesia 2009; 56: Gagnon C, Fortier LP, Donati F. When a leak is unavoidable, preoxygenation is equally ineffective with vital capacity or tidal volume breathing. Canadian Journal of Anesthesia 2006; 53: The Association of Anaesthetists of Great Britain and Ireland

Assessment of Common Preoxygenation Strategies Outside of the Operating Room Environment

Received Date : 04-Jun-2015 Revised Date : 13-Sep-2015 Accepted Date : 02-Nov-2015 Article type 15-447-1 March 2016 #7 : Original Contribution Assessment of Common Preoxygenation Strategies Outside of