Effects of decreasing inspiratory flow rate during simulated basic life support ventilation of a cardiac arrest patient on lung and stomach tidal volumes
Introduction
When ventilating an unintubated patient, the distribution of gas between lungs and stomach depends on the patient's lower oesophageal sphincter pressure (LESP) [1], respiratory mechanics such as respiratory system compliance [2] and degree of airway obstruction [3]. Moreover, the technique of the rescuer performing basic life support (BLS) may influence inspiratory flow rate, peak airway pressure, and tidal volume [4]. Stomach inflation during BLS is a complex problem that may cause regurgitation [5], aspiration [6], pneumonia, and possibly, death [7]. Stomach inflation may also elevate intragastric pressure [8], push up the diaphragm, restrict lung movements, and thereby decrease the respiratory system compliance [9]. A decreased respiratory system compliance may force even more gas into the stomach, thereby inducing a respiratory vicious cycle with each tidal volume of increasing stomach inflation, and decreasing lung ventilation [10].
In order to prevent stomach inflation, managing peak airway pressure is therefore of fundamental importance during BLS ventilation of unintubated patients in respiratory and/or cardiac arrest. When experienced healthcare professionals perform bag-valve-mask ventilation, it was observed that respiratory rates were ∼40 instead of ∼15/min [11], and inspiratory times ∼0.5 instead of ∼1.5 s [12], indicating that emergency ventilation is a more complex psychomotor manoeuvre than previously thought. We have previously shown that one strategy of decreasing peak airway pressure during bag-valve-mask ventilation is simply to decrease tidal volume from 1000 to 500 ml [13]; limitation of inspiratory flow rate may be another, possibly even more effective approach. If the inspiratory flow rate is fixed, BLS ventilation may have a built-in safety margin, and ventilation quality may improve, especially when used by less experienced rescuers. Based on this concept, a flow-limited resuscitator (Oxylator EM 100, CPR Medical Devices Inc., Toronto, Canada) has been developed. (Fig. 1). Accordingly, the purpose of the present study was to assess the effects of a self inflating bag compared to this resuscitator with fixed inspiratory flow rates on respiratory variables, tidal lung and stomach volumes in a simulated unintubated cardiac arrest patient. Our hypothesis was that there would be no difference in study endpoints between groups.
Section snippets
Materials and methods
The experimental protocol of this study was approved by the institutional review board of the study institution. Twenty critical care unit registered nurses certified in BLS volunteered as participants for the study. The participants were instructed to treat an experimental model as an adult cardiac arrest patient, and ventilate the manikin via a facemask with an adult self-inflating bag (maximal volume, 1.5 l) or with the resuscitator until the chest clearly rose.
In the experimental model
Results
Twenty critical care unit registered nurses (10 women, 10 men) performed bag-mask ventilation with an adult self-inflating bag, or with a resuscitator. The self-inflating bag vs. resuscitator resulted in comparable mean±SD mask tidal volumes, significantly (P<0.05) higher peak inspiratory flow rates, and peak inspiratory pressure, but significantly shorter inspiratory times. Lung tidal volumes were comparable, but stomach tidal volumes were significantly (P<0.05) higher with the self-inflating
Discussion
In our study, we found that the self-inflatable bag vs. resuscitator resulted in comparable mean±SD mask tidal volumes, significantly (P<0.05) higher peak inspiratory flow rates and peak inspiratory pressure, but significantly shorter inspiratory times. Lung tidal volumes were comparable, but stomach tidal volumes were significantly (P<0.05) higher with the self-inflating bag.
In order to examine the effects of a resuscitator providing a decreased peak flow rate (Fig. 2) during simulated BLS
Acknowledgements
This project was supported, in part, by the Austrian Science Foundation Grant P14169-MED, Vienna, Austria; a Founders Grant of the Society of Critical Care Medicine, Anaheim, CA; and departmental funds. No author has a conflict of interest in regards of airway devices being discussed in this experiment.
References (20)
- et al.
Lower esophageal sphincter pressure during prolonged cardiac arrest and resuscitation
Ann. Emerg. Med.
(1995) - et al.
Complications of cardiac resuscitation
Chest
(1987) - et al.
Effects of smaller tidal volumes during basic life support ventilation in patients with respiratory arrest: good ventilation, less risk?
Resuscitation
(1999) - et al.
Smaller tidal volumes with room-air are not sufficient to ensure adequate oxygenation during basic life support
Resuscitation
(2000) - et al.
Measurement of ventilation during cardiopulmonary resuscitation
Crit. Care Med.
(1983) Ventilatory efficacy of mouth-to-mouth artificial respiration
JAMA
(1958)- et al.
The current status of ventilation strategies during cardiopulmonary resuscitation
Curr. Opin. Crit. Care
(1997) - et al.
Anaesthetic deaths due to regurgitation or vomiting
Anaesthesia
(1951) - et al.
Pulmonary aspiration during unsuccessful cardiopulmonary resuscitation
Intens. Care. Med.
(1987) - et al.
Observations on intragastric pressure
Anaesthesia
(1967)
Cited by (26)
The effects of an automatic, low pressure and constant flow ventilation device versus manual ventilation during cardiovascular resuscitation in a porcine model of cardiac arrest
2013, ResuscitationCitation Excerpt :Thus there is a need for a method of ventilation which can be applied with minimal delay, does not lead to hyperventilation, and which does not require cessation of chest compressions. In this study, we tested the Oxylator®, an automatic ventilation device, in experimental CPR (see Fig. 1) [9–12]. This simple-to-use, non-electronic device can be applied with minimal delay using a mask or an endotracheal tube.
Comparison of manually triggered ventilation and bag-valve-mask ventilation during cardiopulmonary resuscitation in a manikin model
2012, ResuscitationCitation Excerpt :In addition, chest compressions had to be stopped to apply these ineffective ventilations, a process that could cause definitive harm to the patient.8–10 Although significantly higher Pmax values are associated with the use of the BVM, we found no significant differences between the two groups.11 Nevertheless, a few higher maximum Pmax values were observed in the BVM group, and each pressure peak that occurs statistically increases the risk for aspiration.
Automated emergency ventilation devices in a simulated unprotected airway
2011, Journal of Emergency MedicineCitation Excerpt :Further, high airway pressures during face-mask ventilation can result in substantial stomach inflation with consecutive regurgitation (2,3). In these stressful emergency situations, an automated ventilation device might help the rescuer to avoid substantial ventilation-related complications and to provide adequate ventilation (4–6). Further, it may allow the rescuer to hold a face mask with both hands, which may reduce mask leakage without tying up a second rescuer squeezing a bag-valve device (7).
Performance of supraglottic airway devices and 12 month skill retention: A randomized controlled study with manikins
2011, ResuscitationCitation Excerpt :The great gap between the high number of successful first attempts (which was determined by visible chest rise) and the low number of objectively measured ideal tidal volumes indicates that visible chest rise might not be a valid indicator for sufficient tidal volume at all. The known problem with BVM – gastric inflation when used by inexperienced rescuers – was also seen in our study.28–30,32 All SADs performed far better compared to BVM; LMA Supreme™ was the best overall.
European Resuscitation Council Guidelines for Resuscitation 2010 Section 4. Adult advanced life support
2010, ResuscitationCitation Excerpt :Are associated with lower peak airway pressures than manual ventilation, which reduces intrathoracic pressure and facilitates improved venous return and subsequent cardiac output. A manikin study of simulated cardiac arrest and a study involving fire-fighters ventilating the lungs of anaesthetised patients both showed a significant decrease in gastric inflation with manually-triggered flow-limited oxygen-powered resuscitators and mask compared with a bag-mask.345,346 However, the effect of automatic resuscitators on gastric inflation in humans in cardiac arrest has not been studied, and there are no data demonstrating clear benefit over bag-valve-mask devices.
Effects of stomach inflation on haemodynamic and pulmonary function during cardiopulmonary resuscitation in pigs
2009, ResuscitationCitation Excerpt :In cardiac arrest patients, ventilation of an unprotected airway is a common manoeuvre during cardiopulmonary resuscitation (CPR) before intubation. When the airway is unprotected, the combination of peak inspiratory flow rate, respiratory system compliance, airway resistance, and especially lower oesophageal sphincter pressure determines whether assisted ventilation produces lung ventilation, or causes stomach inflation.1,2 In a patient undergoing routine induction of anaesthesia, normal lower oesophageal sphincter pressure is ∼20 cmH2O, thus minimising stomach inflation in the unprotected airway.3