Cardiopulmonary Resuscitation (CPR) is a life-saving procedure performed when the heart and breathing stop, combining chest compressions to circulate blood and rescue breaths to supply oxygen. While oxygen is necessary for survival, the concept of “more is better” does not apply to ventilation during resuscitation. Providing excessive breaths, either too forcefully or too frequently, can severely undermine the effort to restore circulation. Guidelines, such as Pediatric Advanced Life Support (PALS), emphasize a precise, controlled approach. Understanding the physiological mechanisms that cause harm explains why restraint and precision are mandatory during a resuscitation attempt.
Impaired Blood Flow Due to Intrathoracic Pressure
The most significant danger of excessive ventilation during CPR is its negative impact on the body’s already compromised circulation. Every rescue breath creates positive pressure within the chest cavity. This pressure works against the chest compressions designed to pump blood. When breaths are delivered too quickly or with too much volume, this pressure becomes abnormally high.
This elevated pressure, known as increased intrathoracic pressure, squeezes the large veins within the chest, such as the superior and inferior vena cava. These vessels return deoxygenated blood from the body back to the heart. The pressure acts like a constriction, impeding the flow of blood back toward the heart.
If less blood returns to the heart, the heart chambers cannot properly fill between compressions, resulting in reduced venous return. Since the heart can only pump the volume of blood it receives, a reduction in venous return leads directly to a drop in cardiac output. This defeats the primary goal of CPR, which is to generate sufficient blood flow to the vital organs.
High intrathoracic pressure also reduces the coronary perfusion pressure, which drives blood flow to the heart muscle itself. The heart muscle requires its own blood supply to sustain function. Reducing this supply hinders the heart’s ability to recover and regain a spontaneous rhythm. Excessive ventilation effectively lowers the pressure gradient needed for systemic blood flow and the heart’s own perfusion, making successful resuscitation less likely. This is why continuous, high-quality chest compressions with minimal interruptions are prioritized over aggressive ventilation.
Direct Organ Damage from Over-Inflation
Beyond circulatory issues, excessive air delivery can cause mechanical damage to the lungs and digestive system. When too much volume or pressure is used, it injures the delicate lung tissue. This problem is categorized as barotrauma (injury caused by high pressure) and volutrauma (damage from excessive volume). Volutrauma specifically overstretches the tiny air sacs, or alveoli.
Overdistending the alveoli can cause them to rupture, leading to air leaking into the chest cavity, a dangerous condition called pneumothorax. A tension pneumothorax occurs when air builds up and cannot escape, collapsing the lung. This further compresses the heart and major blood vessels, compounding circulatory failure. Preventing this mechanical injury requires delivering only the minimum volume necessary to achieve a visible chest rise.
Another significant risk is gastric inflation, where air is forced into the stomach instead of the lungs. This occurs when the pressure used to deliver the breath exceeds the resistance of the esophageal sphincter. A stomach distended with air pushes upward on the diaphragm, the main muscle of breathing.
This upward pressure limits the movement of the diaphragm, making subsequent ventilation attempts more difficult and less effective. Gastric distension also increases the risk of regurgitation and aspiration, where stomach contents enter the lungs. Aspiration can cause severe pneumonia and complete airway obstruction, creating a potentially fatal complication to the original cardiac arrest.
PALS Guidelines for Effective Ventilation
To avoid the harms of excessive ventilation, professional guidelines like Pediatric Advanced Life Support (PALS) stress precision in rescue breathing. The emphasis is on controlling both the rate and the volume of each breath delivered. Rescuers should aim to deliver each breath slowly, taking approximately one second to inflate the lungs. They should use only enough volume to observe the chest begin to rise.
This controlled technique avoids the high pressures that cause gastric inflation and barotrauma. It also minimizes the interruption to chest compressions. For children and infants, the appropriate compression-to-ventilation ratio depends on the number of rescuers present. A single rescuer typically uses a ratio of 30 compressions followed by 2 breaths, prioritizing continuous circulation.
When two or more trained rescuers are present, the ratio shifts to 15 compressions for every 2 breaths. This reflects the increased importance of ventilation in pediatric arrests, which are often respiratory in origin. Once an advanced airway is secured, compressions should be continuous. Ventilations are then delivered at a fixed rate of about one breath every six seconds (10 breaths per minute). This uncoupled approach ensures that chest compressions are not interrupted, preserving blood flow to the brain and heart.
Rescuers often have a natural tendency, or “rescue reflex,” to hyperventilate the patient due to anxiety. Maintaining discipline and counting the rate of breaths is paramount to ensure the quality of resuscitation. Following the recommended rates and limiting the breath volume to just what causes a gentle chest rise protects the patient. These steps prevent the detrimental effects of excessive intrathoracic pressure and mechanical injury.