Cardiopulmonary resuscitation (CPR) is a time-sensitive intervention designed to circulate oxygenated blood to the brain and other vital organs when the heart has stopped. CPR involves two primary actions: chest compressions, which mechanically pump blood, and rescue breathing, which supplies oxygen to the lungs. When an advanced airway device is placed, the ventilation protocol changes significantly, moving from an interrupted cycle to continuous, asynchronous delivery. This modified technique is guided by specific recommendations to maximize blood flow and optimize the chances of a successful outcome during a cardiac arrest event.
Understanding the Advanced Airway Context
An advanced airway is a device placed directly into the trachea or larynx to secure the patient’s breathing tube and effectively seal the airway. Common examples include the endotracheal tube and various supraglottic devices, such as the laryngeal mask airway. The presence of this sealed airway fundamentally alters how ventilation is performed during resuscitation.
In standard CPR without an advanced airway, rescuers must briefly pause chest compressions every 30 compressions to deliver two breaths (the 30:2 ratio). This interruption is necessary to inflate the lungs and minimize air entering the stomach. However, each pause causes a temporary drop in blood pressure, reducing the perfusion of the heart and brain.
Once an advanced airway is properly secured, the need to pause compressions for ventilation is eliminated. The sealed tube ensures that the delivered air goes directly to the lungs, allowing continuous chest compressions. This shift to asynchronous ventilation prioritizes uninterrupted blood flow, which is the most important factor in effective CPR. The ventilation provider then delivers breaths independent of the compression timing.
Recommended Ventilation Rate and Delivery
The current recommendation for adult patients in cardiac arrest with an advanced airway is to deliver one breath every six seconds. This equates to a rate of 10 breaths per minute, which is significantly lower than a person’s normal resting respiratory rate. The guidelines emphasize maintaining this specific, measured rate to strike a balance between providing adequate oxygenation and avoiding detrimental physiological effects.
Proper technique focuses on a measured and gentle approach. Each rescue breath should be delivered over a period of approximately one second. This slow delivery ensures the lungs have time to inflate without excessive force or pressure.
The goal for the volume of air delivered, known as the tidal volume, is to use only enough to cause a visible rise of the patient’s chest. While this volume is often estimated to be around 500 to 600 milliliters for an adult, visual confirmation of chest rise is the preferred clinical target. Using this minimal volume helps to prevent over-inflation of the lungs and minimizes the chance of excessive pressure building up inside the chest cavity.
Why Hyperventilation Is Detrimental During CPR
The specific, slow rate of 10 breaths per minute is intentionally chosen because ventilation rates exceeding this, or hyperventilation, have severe negative consequences for circulation. Delivering breaths too frequently or too forcefully increases the mean intrathoracic pressure, which is the pressure within the chest cavity. This elevated pressure acts as a physical barrier to the blood returning to the heart.
During the chest relaxation phase of CPR, the heart relies on negative pressure within the chest to draw deoxygenated blood back from the body, known as venous return. When the intrathoracic pressure is artificially kept high by excessive ventilation, this crucial vacuum effect is impaired. The resulting decrease in venous return directly reduces the amount of blood the heart has available to pump with each compression.
The downstream effect is a reduction in cardiac output, meaning less blood is circulated to the vital organs. This leads to a significant decrease in coronary perfusion pressure (CPP), which is the pressure that drives blood flow to the heart muscle itself. Studies have shown that a high ventilation rate is inversely proportional to this pressure. Ultimately, hyperventilation lowers the probability of achieving Return of Spontaneous Circulation (ROSC).
Furthermore, excessive ventilation can cause hypocapnia, or abnormally low levels of carbon dioxide in the blood. This hypocapnia can constrict the blood vessels supplying the brain. This cerebral vasoconstriction further compromises the already reduced blood flow to the brain, exacerbating the risk of neurological damage. Therefore, maintaining the slow, controlled rate of 10 breaths per minute is a deliberate strategy to protect the heart and brain.