Respiratory monitoring during mechanical ventilation

Continuous monitoring of important respiratory indices has the potential for predicting catastrophes and for providing an opportunity for the timely institution of lifesaving measures. Pulmonary gas exchange can be assessed by indices derived from arterial blood gas measurements, but these are limited by their invasive and intermittent nature. Intra-arterial electrodes that provide a continuous recording of blood gases are under development and appear very promising. Specially designed pulmonary artery catheters permit continuous recording of mixed venous O2 saturation, whereas continuous, non-invasive recordings of arterial oxygenation can be obtained with pulse oximetry and transcutaneous electrodes. A satisfactory method of monitoring CO2 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. Recordings of the airway pressure waveform, calculation of thoracic compliance, and detailed examination of the pattern of breathing are helpful in assessing pulmonary mechanics. Although respiratory monitoring provides much useful information, it does not substitute for careful bedside examination.