Ventilation, the process of moving air into and out of the lungs, is a fundamental aspect of life-sustaining support, particularly in emergency situations like cardiopulmonary resuscitation (CPR). While delivering breaths is necessary to supply oxygen, providing too much air, or ventilating excessively, can hinder resuscitation efforts and negatively impact patient outcomes.
Understanding Excessive Ventilation
Excessive ventilation in the context of resuscitation refers to providing breaths too frequently or with too much volume. The ideal ventilation rate for adults during CPR, when an advanced airway is not in place, is typically two breaths after every 30 chest compressions. When an advanced airway is in place, the recommended rate is generally one breath every 6 to 8 seconds, or about 8 to 10 breaths per minute, without interrupting chest compressions.
For each breath, rescuers should aim to deliver a volume of air just sufficient to cause visible chest rise, typically around 500 to 600 mL, or 6 to 7 mL per kilogram of body weight for an average adult. This volume is significantly less than a full breath taken by a healthy person. The problem arises not from ventilation itself, but from exceeding these recommended rates and volumes, which can lead to various complications.
The Body’s Response to Over-Ventilation
Over-ventilation can trigger several adverse physiological responses that undermine the effectiveness of CPR. One of the most significant consequences is a reduction in cardiac output. When too much air is forced into the lungs, it increases pressure inside the chest cavity, known as intrathoracic pressure. This elevated pressure compresses major blood vessels within the chest, making it more difficult for blood to return to the heart from the body’s veins.
The reduced blood return to the heart means there is less blood for the heart to pump out with each beat, leading to a decrease in cardiac output. This diminished blood flow directly impacts the delivery of oxygen and nutrients to vital organs, including the brain and the heart itself. Studies in animal models have shown that excessive ventilation rates, such as 30 breaths per minute compared to 12 breaths per minute, can lead to significantly increased intrathoracic pressure and decreased coronary perfusion pressure, which is the blood flow to the heart muscle.
Another complication of excessive ventilation is gastric inflation, where air is inadvertently forced into the stomach instead of the lungs. This occurs when the pressure from the rescue breath is too high, causing the air to bypass the trachea and enter the esophagus. Gastric inflation can lead to abdominal distension, which can further impede diaphragm movement and lung expansion. It also increases the risk of vomiting and aspiration, where stomach contents are inhaled into the lungs, potentially causing severe lung injury or pneumonia.
Ultimately, these physiological impacts can delay the return of spontaneous circulation (ROSC), which is the primary goal of CPR. The combined effects of reduced cardiac output, impaired blood flow to the heart and brain, and potential complications like aspiration make it harder for the patient’s heart to restart on its own.
Strategies for Proper Ventilation
Preventing excessive ventilation during CPR involves adhering to specific techniques and undergoing appropriate training. Proper CPR training, often through certified courses, emphasizes the correct rate and volume for rescue breaths. Rescuers are taught to deliver breaths at a controlled pace, typically one breath every 5 to 6 seconds for adults, which translates to about 10 to 12 breaths per minute when not combined with compressions. When combined with compressions, the ratio is commonly 30 compressions to 2 breaths.
Controlling the volume of air delivered is also important. Instead of forceful breaths, rescuers should provide just enough air to observe a visible rise of the chest over approximately one second. This visual cue helps ensure that adequate, but not excessive, air is entering the lungs without over-inflating them or causing gastric distension. Avoiding rapid or forceful breaths minimizes the risk of increasing intrathoracic pressure and its associated complications.
Bag-valve-mask (BVM) devices are commonly used for ventilation during CPR, and proper technique with these devices is also important. Some modern CPR training kits and devices offer real-time feedback on ventilation rate and pressure, which can help rescuers refine their technique and maintain recommended parameters during an emergency.