Prompted by our experience with complications occurring with
apnea testing (AT), we discuss complications reported in the literature. AT is an integral part of
brain death assessment. Many complications of AT have been described, including
hypoxemia, arterial
hypotension,
tension pneumothorax and
cardiac arrest. We conclude that a commonly used technique in conducting AT can create auto-
positive end expiratory pressure (PEEP) and contributes to many complications. The mechanism of occult
auto-PEEP in AT is discussed. Intensive care unit patients may have a compensated and asymptomatic relative
hypovolemia that can be decompensated by a small amount of
auto-PEEP produced by air trapping during insufflating
oxygen (O2) through a 7.0 endotracheal tube (ETT). It could then lead to decreased preload, decreased stroke volume, decreased cardiac output and thus, to
hypotension and a compensatory
tachycardia. The placement of the standard O2 tubing (6mm outside diameter [OD]) inside the 7.0 ETT (7mm inside diameter [ID]) greatly decreased the ETT lumen (73%). We changed our practice to instead use readily available small pressure tubing to insufflate O2 for AT to avoid excessive reduction in the ETT lumen. The change from standard O2 tubing (6mm OD) to pressure tubing (3mm OD) will greatly decrease the reduction in cross-sectional area of 7.0 ETT lumen from 73 to 18% and avoid potential complications of air trapping,
auto-PEEP and
barotrauma. We have successfully used this new simple technique with readily available equipment to eliminate
auto-PEEP in AT while preserving oxygenation.