Letters Section Editor: Robert M. Golub, MD, Senior Editor.
In Reply: The intubated patients in our study were randomly assigned to receive either 30% or 80% oxygen. These concentrations were accurately provided intraoperatively by the anesthesia machine. Dr Agarwal is concerned that our patients may not have received the designated concentration postoperatively. We ensured proper delivery by using adult Intersurgical High Concentration Oxygen Masks with a 1-L fresh gas reservoir, with the assigned oxygen concentration provided at 16 L /min. Even at a respiratory rate of 20/min and minute ventilation of 10 L /min, patients take 500 mL during inspiration from the reservoir, which must be refilled during expiration. A constant flow of 16 L /min provides 520 mL to the reservoir during 2 seconds of expiration, which is more than needed to refill the reservoir, thus assuring delivery of the assigned concentration. During the initial phase of the study, we measured oxygen concentration inside the masks and found the designated oxygen concentration was well maintained throughout the respiratory cycle.
Belda FJ, Sessler DI. Supplemental Oxygen and Risk of Surgical Wound Infection—Reply. JAMA. 2006;295(14):1641-1643. doi:10.1001/jama.295.14.1642-b