The assessment of cardiopulmonary resuscitation (CPR) quality is a multi-faceted process when a patient has an advanced airway, such as an endotracheal tube. Intubation allows for continuous, asynchronous chest compressions because the need to pause for breaths is removed. This continuous delivery makes real-time quality assessment important to ensure maximum blood flow to the brain and heart. Maximizing perfusion is the primary goal of high-quality CPR, requiring continuous monitoring of the physical performance of compressions and the patient’s physiological response.
Mechanical Standards for High-Quality Compressions
Effective CPR requires the physical actions of the rescuer to meet metrics that ensure blood circulation. The compression rate must be maintained within a narrow range of 100 to 120 compressions per minute to maximize blood flow and minimize rescuer fatigue. Compressing too fast can result in shallow compressions, while compressing too slowly may not circulate enough blood to vital organs. The compression depth for an adult must be at least two inches (five centimeters) but should not exceed 2.4 inches (six centimeters).
Full chest wall recoil, the complete release of pressure on the chest, is necessary for adequate circulation. Allowing the chest to fully recoil permits the heart to refill with blood between compressions. Defibrillators and monitor pads incorporate real-time feedback devices that provide immediate audio and visual prompts regarding compression rate and depth. These devices help rescuers stay within the recommended ranges and avoid leaning on the chest, ensuring the mechanical standards of high-quality CPR are met.
Physiological Assessment Using Capnography
End-Tidal Carbon Dioxide (ETCO2) monitoring, or capnography, is a non-invasive, continuous method for assessing the physiological effectiveness of CPR in an intubated patient. The ETCO2 value reflects the amount of carbon dioxide being delivered to the lungs. During cardiac arrest, this value serves as an indirect but reliable indicator of cardiac output and pulmonary blood flow generated by chest compressions.
Carbon dioxide is a product of cellular metabolism and is transported by the blood to the lungs for removal. When compressions are effective, blood is circulated, carrying CO2 to the lungs, which results in a higher ETCO2 reading. An ETCO2 value of at least 10 millimeters of mercury (mmHg) is required for adequate perfusion during CPR, with values ideally greater than 20 mmHg being associated with a higher likelihood of successful resuscitation.
If the ETCO2 reading drops below 10 mmHg, it signals that the quality of chest compressions is likely insufficient to maintain adequate blood flow. This immediate feedback prompts rescuers to evaluate and correct their compression technique, check for rescuer fatigue, or consider other interventions. Conversely, a sudden and sustained rise in ETCO2, often increasing to a range near the normal 35-45 mmHg, is one of the earliest and most reliable indicators of Return of Spontaneous Circulation (ROSC). Capnography provides a continuous window into the patient’s physiological response, guiding real-time adjustments.
Advanced Hemodynamic Monitoring
Beyond non-invasive capnography, advanced hemodynamic monitoring provides a more direct measure of blood flow to the heart muscle. This method requires the placement of an arterial line to continuously measure arterial blood pressure (ABP). The most accurate physiological indicator of CPR effectiveness is the Coronary Perfusion Pressure (CPP).
CPP is calculated as the difference between the diastolic arterial blood pressure (DBP) and the right atrial pressure (RAP) during the relaxation phase of chest compressions. This pressure gradient drives blood flow through the coronary arteries, nourishing the heart muscle. For successful resuscitation, a minimum target CPP of at least 15 mmHg is required, though some studies suggest a threshold of 20 mmHg or higher.
To achieve this minimum CPP, the diastolic arterial blood pressure needs to be maintained at a level of around 40 mmHg, assuming a right atrial pressure of 10 mmHg. Monitoring ABP allows the resuscitation team to use vasoactive medications and adjust compression quality to ensure this target DBP is met. Although invasive and less universally available than capnography, this direct pressure monitoring confirms the heart muscle is receiving the necessary blood flow to regain function.