Which of the following factors can lead to falsely low pulse oximetry measurements?

Falsely low pulse oximetry measurements can occur due to a range of factors, and the correct choice reflects that all mentioned factors can indeed contribute to this issue.

Vascular injection of indigo carmine can cause interference by absorbing light in the wavelengths used by pulse oximeters, leading to inaccurate readings. Methemoglobin is a form of hemoglobin that cannot bind oxygen efficiently, and when present in significant amounts, it can also distort the measurements provided by pulse oximetry, yielding lower saturation levels. Poor perfusion, characterized by inadequate blood flow to the extremities, can reduce the ability of the pulse oximeter to detect adequate signals, often resulting in readings that do not accurately reflect the true oxygen saturation levels in the blood.

The collective nature of these factors means that reliance on pulse oximeter readings in certain conditions must be tempered with additional clinical evaluation, as these factors can separately or together obscure the true physiological parameters they aim to measure. Thus, the answer encapsulates the complexity of monitoring oxygen saturation in diverse medical scenarios.