Ventilation During CPR

There is good data to support some important truths about tidal volume and ventilation rates. Studies show that hyperventilation during cardiac arrest resuscitation in pig models decreased coronary perfusion pressures.² Likewise in other animal models, if ventilation rates are too low to clear CO2 then carotid blood flow and brain-tissue oxygen tension lead to poor outcomes.³  Just to throw a wrench into this conversation, in a study looking at in-hospital cardiac arrests, survival to hospital discharge after CPR in ventilated patients was 10.1% (95% CI 9.8%-10.4%), compared to 19.2% (95% CI 19.1%-19.3%) in non-ventilated patients (p<0.001). ⁴

As for tidal volume, the current recommendation is approximately 600ml or 8ml/kg or enough volume to see the chest rise. This recommendation is to minimize CPR-induced ventilation-perfusion mismatch.⁵ There is some data that shows that passive oxygenation for the first few minutes of a resuscitation may have benefit.⁶ However, some data shows that after the first few minutes of CPR, the absence of positive pressure ventilation reduces blood flow through the lung secondary to collapse of both the bronchioles and the pulmonary vasculature.⁷ Compression of the chest without positive pressure ventilation does not generate enough tidal volume to overcome the dead space of the airway to appropriately ventilate the lungs.⁸ Likewise, poorly aerated lung tissue will increase pulmonary vascular resistance leading to decreased pulmonary blood flow.⁹

So what do we know? Well, not much concerning the ideal ventilation strategy during CPR. Too much and too little of anything may be bad. This topic is extremely challenging to study due to the heterogeneity of cardiac arrest and the number of variables that need to be taken into account during this kind of research. Things not mentioned during this discussion include impedance threshold devices and continuous oxygenation strategies. The data in these topics gets a bit murky and we will be discussing them in a separate discussion. 

Currently, I follow the guidelines by either using a BVM with a close eye on the respiratory rate to ensure the delivery of no more than 10 breaths per minute, or I will use a ventilator with the assist control, RR of 10, TV of 8ml/kg, zero PEEP and FiO2 of 100%. I’ll try to set my Flow rate at 30 LPM and pressure limits set to 100 cmH₂0 if I have time. I do this with no evidence, but it feels right.