Editor’s note: This post marks the final in a series of posts outlining the evidence surrounding various aspects of CPR by Dr. Stu Netherton. Previously this series covered Rate of Compression, Depth of Compression, Chest Wall Recoil, and Minimizing Interruptions.
Part 5 – Avoiding excessive ventilation
There are many recommendations, for a wide variety of situations, on how to provide ventilation during a resuscitation; mouth to mouth, mouth to nose, bag mask use, suggestions after securing the airway, etc. We will be unable to discuss them all, but there is one underlying theme present when giving rescue breaths, no matter how you do it, and that is to “Avoid excessive ventilation”
To lessen any confusion, we are discussing ventilation in patients whom have an arrest of a presumed cardiac origin. These guidelines may not be applicable to all arrests, especially those of an asphyxial nature – drowning, hanging, toxicological – in which the focus of ventilation is different than that presented here.
The guidelines for providing rescue breaths are that “It is reasonable for rescuers trained in CPR using chest compressions and ventilation (rescue breaths) to provide a compression-to-ventilation ratio of 30:2 for adults in cardiac arrest.”
In the past decade, traditional CPR instruction included a compression to ventilation ratio of 30:2 1, and breaths were given during a pause in chest compressions. The degree of, and even the necessity of ventilation during CPR has recently been questioned.
It is important to understand why over ventilation is bad, as in high pressure situations like cardiac arrest resuscitations, even highly trained providers excessively ventilate their patients.2
Early during cardiac arrests, the importance of rescue breaths are less that the importance of chest compressions. 3,4 Since the oxygen content in the non-circulating arterial blood remains unchanged until CPR is started and that the blood oxygen content then continues to be adequate during the first several minutes of CPR, early ventilation is less valuable than chest compressions.
Time to ventilate has traditionally lead to decreases in chest compression fraction 5, and providing positive ventilation may impede venous return to the heart, partially through inhibition of negative intrathoracic pressure which is achieved during chest compressions.6 Hyperventilation in animal models has shown that 30 breaths per minute vs. 12 breaths per minute yields a survival rate of 17% vs 86% respectively 6, and that excessive ventilation significantly decreased coronary perfusion pressure, increased intra-thoracic pressures and decreased survival rates in a porcine model of OHCA. 7,8
As the absolute need for ventilations during CPR are becoming into question, and in an attempt to encourage bystander CPR, public education programs highlighting hands only CPR are becoming increasingly popular and effective.2
As there are a wide variety of situations and ways to deliver rescue breaths, there may be health region or institution specific guidelines for ventilation during CPR. Be sure to be aware of your local pattern of practice.
Uploaded by Amy Chung
Reviewing with the staff
Excessive ventilations kill people through the impact on intrathoracic pressure and cerebral perfusion pressure. But some ventilation, as shown in recent meta-analysis is required to improve outcomes. Whether this is 30:2 or continuous compressions with interspersed ventilations in not as important as the avoidance of hyperventilation. So compress hard, compress fast and don’t hyperventilate.