Which condition might affect the accuracy of pulse oximetry readings?

Cardiac arrest can significantly affect the accuracy of pulse oximetry readings due to the absence of effective circulation and blood flow. Pulse oximeters function by shining light through a part of the body, typically a fingertip or earlobe, to measure how much oxygen is bound to hemoglobin in the blood. In the event of cardiac arrest, the blood is not being effectively pumped, leading to a lack of adequate blood perfusion to the extremities. This results in unreliable readings because the pulse oximeter relies on detecting pulsatile blood flow to accurately assess oxygen saturation levels.

The influence of blood flow is crucial for pulse oximetry; insufficient circulation means that the device may not detect a signal strong enough to provide an accurate measurement, potentially leading to falsely low or undetermined oxygen saturation levels. Therefore, in the context of acute emergencies like cardiac arrest, the accuracy of pulse oximetry readings can be compromised, making it less reliable for assessing the patient's immediate oxygenation status.

While hypoxemia, anemia, and pneumothorax can influence oxygen delivery or content in the blood, they do not directly impair the fundamental function of pulse oximetry in the same immediate and dramatic way that the absence of circulation does.