Four ways to ventilate during cardiopulmonary resuscitation in a porcine model: a randomized study

Abstract

BackgroundThe optimal method for out-of-hospital ventilation during cardiopulmonary rescue (CPR) is controversial.The aim of this study was to test different modes of ventilation during CPR for a prolonged period of 60 min.MethodsPigs were randomized to four groups after the induction of ventricular fibrillation, which was followed by one hour of mechanical cardiac compressions. The study comprised five pigs treated with free airways, five pigs treated with ventilators, six pigs treated with a constant oxygen flow into the tube, and six pigs treated with apnoeic oxygenation.ResultsThe free airway group was tested for 1 h, but in the first 15 min, the median PaO2 had already dropped to 5.1 kPa.The ventilator group was tested for 1 h and still had an acceptable median PaO2 of 10.3 kPa in the last 15 min. The group was slightly hyperventilated, with PaCO2 at 3.8 kPa, even though the ventilator volumes were unchanged from those before induction of cardiac arrest.In the group with constant oxygen flowing into the tube, one pig was excluded after 47 min due to blood pressure below 25 mmHg. For the remaining 5 pigs, the median PaO2 in the last 15 min was still 14.3 kPa, and the median PaCO2 was 6.2 kPa.The group with apnoeic oxygenation for 1 h had a resulting median PaO2 of 10.2 kPa and a median PaCO2 of 12.3 kPa in the last 15 min.DiscussionExcept for the free airway group, the other methods resulted in PaO2 above 10 kPa and PaCO2 between 3.8 and 12.3 kPa after one hour.ConclusionConstant oxgen flow and apnoeic oxygenation seemed to be useable alternatives to ventilator treatment.

Efficacy of Manual Ventilation Techniques During Cardiopulmonary Resuscitation in Dogs

“…Compression only CPR was included in this study for comparison purposes and it was associated with a very low PaO 2 . This value was similar to values reported in pigs after 5–15 min of compression only CPR ( 21 ). Compression only CPR maybe associated with poorer outcomes than conventional CPR in human clinical patients ( 22 – 24 ).…”

“…In this study, the animals ventilated via orotracheal intubation developed hypocapnia during CPR, despite a similar degree of ventilation as provided at baseline. This likely reflects the decrease in CO 2 production and reduced blood flow associated with cardiopulmonary arrest and has been reported in previous experimental animal CPR studies ( 21 , 28 – 30 ). As ventilation was performed manually in this study, we cannot guarantee what tidal volume was provided during the experiment.…”

“…In both the face mask and mouth-to-nose group, not all breaths were considered effective which would further compromise the total alveolar ventilation provided. The optimal PaCO 2 during CPR is currently unknown and generally a normal PaCO 2 is targeted ( 21 ). Hypocapnia during CPR has been associated with a higher mortality, likely due to impaired venous return with hyperventilation ( 16 , 33 ).…”

Mechanical Ventilation Management During Mechanical Chest Compressions

“…Additionally, positive pressure mechanical ventilation causes some alterations in hemodynamic physiology, the most relevant of which is the reduction in venous return and, therefore, the reduction in ventricular preload. 8,9 A recent survey reported that the most commonly used ventilation mode is volume control continuous mandatory ventilation. 10 However, no clinical studies have yet defined the "best" mode of invasive ventilation to use during mechanical CPR.…”

“…From a theoretical point of view, this distinction is essential for determining the risk of atelectasis from oxygen reabsorption; however, from a practical point of view (at least in relation to the studies conducted on animal models), no substantial difference has been identified between the 2 methods in terms of side effects, or between these methods and invasive ventilation performed at zero PEEP. 9,53,54 Although, from a theoretical point of view, the application of PEEP seems to be beneficial for achieving an adequate oxygenation target (see the section on PEEP), other clinical studies have focused on more specifically adapting ventilation to the patient, even during the inspiratory phase. Indeed, avoided an arterial blood pressure drop (P < .001).…”