Reply to the comment by Dr. Maliaga et al.

Excerpt

Sir: In their comment on my contribution to Intensive Care Medicine [1] Dr. Maliaga et al. propose that variation in the plethysmographic waveform of the pulse oximeter during mechanical ventilation can be used clinically to detect hypovolemia under normotensive conditions. Unfortunately, ventilatory-induced cyclic changes in the pulse oximeter waveform are inaccurate in estimating blood volume in the presence of hypotension, which is often associated with hypovolemia [2]. Moreover, the use of pulse oximetry for monitoring intravascular volume status has been tested only in anesthetized patients receiving control ventilation, a mode of ventilation rarely used in the critical care setting. Until more data are available, pulse oximetry cannot be recommended for assessing volume status in ventilated patients. I agree with Dr. Maliaga et al. that hyperbilirubinemia does not affect the accuracy of pulse oximeters. Accordingly, I did not list jaundice as a limitation of pulse oximetry. In fact, bilirubin levels as high as 30 mg/dl have been shown to have no effect on the accuracy of pulse oximetry in estimating oxygen saturation [3]. …