Cardiopulmonary resuscitation (CPR) is a technique used in emergencies to maintain brain function until further measures can be taken to restore spontaneous blood circulation and breathing. While chest compressions are often emphasized as a primary action during CPR, providing rescue breaths, also known as ventilation, is also a component of the resuscitation process. Proper execution of both compressions and ventilations is important, as even actions intended to be helpful, such as ventilation, can become counterproductive if not performed appropriately.
What is Ventilation in CPR?
Ventilation in CPR refers to delivering air into a person’s lungs to provide oxygen and remove carbon dioxide. This action aims to maintain oxygen levels in the blood and tissues, especially in the brain and heart, which are sensitive to oxygen deprivation.
“Excessive ventilation” during CPR means delivering either too much air per breath (high tidal volume) or providing breaths too frequently (high respiratory rate). Appropriate ventilation aims for a specific volume and rate to support oxygenation without causing harm.
How Excessive Ventilation Affects the Body
Over-inflating the lungs during CPR increases the pressure within the chest cavity, known as intrathoracic pressure. This pressure buildup occurs because the delivered air has nowhere else to go once the lungs are filled, causing the pressure inside the chest to rise. This elevated pressure can have several physiological consequences that hinder effective CPR.
Increased intrathoracic pressure can compress the major veins, such as the superior and inferior vena cava, which carry deoxygenated blood back to the heart. This compression reduces the volume of blood that can return to the heart, a process known as venous return.
Reduced venous return significantly decreases the amount of blood the heart can pump out with each compression, or cardiac output. A lower cardiac output means less blood is reaching vital organs, directly counteracting the mechanical benefit of chest compressions.
Decreased cardiac output leads to insufficient blood flow to the heart muscle itself (coronary perfusion) and to the brain (cerebral perfusion). The heart requires a steady supply of oxygenated blood to regain its normal rhythm, and the brain needs continuous oxygen and nutrients to prevent irreversible damage. Compromised perfusion to these organs can reduce the chances of a successful resuscitation.
Additionally, excessive force or volume during ventilation can inadvertently push air into the stomach, causing gastric inflation. An inflated stomach can elevate the diaphragm, which is the primary muscle involved in breathing, thereby making effective chest compressions more difficult to perform. Gastric inflation also increases the risk of vomiting and subsequent aspiration of stomach contents into the lungs, which can lead to severe lung complications.
Why This Harms Resuscitation Success
The physiological effects of excessive ventilation directly impede CPR success. By increasing intrathoracic pressure and reducing venous return, excessive ventilation significantly diminishes the amount of blood that can be circulated with each chest compression, lowering the effective cardiac output generated by compressions.
Reduced blood flow to the heart and brain means these organs receive less oxygen and nutrients. The primary goal of CPR is to maintain sufficient blood flow to the brain and heart to prevent damage and facilitate the return of spontaneous circulation (ROSC). Excessive ventilation actively works against this objective.
When blood flow to the heart muscle is inadequate, the heart’s ability to respond to defibrillation or medications is compromised. Similarly, insufficient cerebral perfusion increases the likelihood of neurological damage, even if ROSC is achieved. Thus, over-ventilating can lead to poorer neurological outcomes and decrease the overall chances of survival.
How to Ventilate Safely During CPR
To avoid the harmful effects of excessive ventilation, specific recommendations for rate and volume are followed during CPR. For adults, guidelines suggest delivering breaths at a rate of 10 to 12 per minute, or one breath every 5 to 6 seconds. A common ratio for a single rescuer is 30 compressions followed by 2 breaths.
Each breath should be delivered over about one second, with just enough volume to cause a visible rise of the chest. Observing the chest rise provides a visual cue that enough air has been delivered without over-ventilating.
Proper CPR training from certified organizations provides individuals with the practical skills needed to perform ventilations safely and effectively. These courses teach the correct techniques for delivering breaths, including how to gauge appropriate volume and rate, and emphasize the importance of minimizing interruptions to chest compressions. Regular practice helps rescuers develop the muscle memory and judgment necessary to provide high-quality CPR.