Respiratory monitoring in the intensive care unit

Continuous monitoring of important respiratory indices has the potential for predicting catastrophes and providing an opportunity for the timely institution of lifesaving measures. Arterial oxygenation can be monitored noninvasively using oximetry or transcutaneous oxygen electrodes, while mixed venous oxygenation can be recorded continuously with modified pulmonary artery catheters. A satisfactory method of monitoring carbon dioxide tension does not exist. Measurements of respiratory drive can be obtained at the bedside, but their clinical usefulness remains unknown. Assessment of respiratory muscle strength is helpful in determining the need for mechanical ventilation, but a practical method of diagnosing respiratory muscle fatigue remains elusive. Measurement of thoracic compliance and detailed examination of the breathing pattern, i.e., tidal volume, respiratory frequency, and the pattern of rib cage-abdominal motion, are helpful in assessing abnormal pulmonary mechanics. The detailed information provided by respiratory monitoring can complement but not replace careful bedside examination.