Cardiopulmonary resuscitation (CPR) is a life-saving procedure used during cardiac arrest, a condition where the heart suddenly stops beating effectively. This emergency intervention combines chest compressions and, in many cases, rescue breaths to maintain blood flow and oxygen delivery to the body’s vital organs. A common question arises regarding how CPR can be effective when rescue breaths involve exhaling air, which contains carbon dioxide. CPR provides temporary support until professional medical help can intervene.
The Immediate Challenge of Cardiac Arrest
During cardiac arrest, the heart ceases its pumping function, leading to an interruption of blood flow throughout the body. This cessation of circulation means that oxygen, which is essential for cell survival, no longer reaches the brain and other vital organs. Without oxygen, brain cells begin to sustain damage within approximately four to six minutes, with irreversible damage likely within seven to ten minutes.
Beyond the lack of oxygen, metabolic waste products, like carbon dioxide, accumulate because circulation has stopped. While carbon dioxide buildup can have adverse effects, the primary threat during cardiac arrest is the absence of oxygen delivery to the brain and heart. This inability to circulate blood and transport oxygen is the primary challenge CPR aims to overcome.
How CPR Addresses Oxygen and Carbon Dioxide
Rescue breaths involve exhaling air into the person’s lungs. This exhaled air contains sufficient oxygen. While room air contains about 21% oxygen, exhaled air typically contains around 16% to 17% oxygen, along with approximately 4% carbon dioxide. This concentration is enough to provide temporary oxygenation to the blood during CPR.
Chest compressions play a dual role. They manually pump the heart, creating a pressure gradient that circulates the limited oxygenated blood to the brain and other organs. The mechanical action of chest compressions can facilitate the passive exhalation of some carbon dioxide from the lungs.
During cardiac arrest, the body’s metabolic activity significantly decreases, reducing carbon dioxide production. Therefore, the limited removal of carbon dioxide achieved through passive exhalation during compressions and the small amount exhaled during rescue breaths are generally sufficient for short-term survival. The body can tolerate a temporary increase in carbon dioxide levels better than a complete lack of oxygen to the brain.
Why CPR Prioritizes Circulation
CPR aims to maintain blood flow to the brain and other vital organs. This is because irreversible brain damage can occur rapidly without oxygenated blood. CPR, the chest compressions, acts as an artificial pump, ensuring that oxygen that remains in the blood and is introduced through rescue breaths reaches these vital areas.
Even if oxygen delivery and carbon dioxide removal are not perfectly efficient, circulating any oxygenated blood is essential. The body possesses a reserve of oxygen within the blood and tissues, which CPR helps to distribute. This temporary circulation buys crucial time until advanced medical care, such as defibrillation or medication, can be administered to restart the heart.
Maintaining blood flow outweighs concerns about exhaled carbon dioxide in the short term. While carbon dioxide is a waste product, the immediate threat of oxygen deprivation to the brain is more severe. Therefore, CPR’s focus on preserving circulation, even with imperfect ventilation, prevents devastating neurological damage and increases the chances of survival.