A volumetric system for monitoring minimal respiration in man.

A microvolumetric noninvasive sensor is described for the monitoring of minimal respiration in adults, children, and infants. The monitor, designated a diaphragm sensor, has been applied since 1965 in the clinical management of optimal ventilation and relaxant drug administration. As an inspiratory monitor in the curarized patient, the sensor responds quantitatively to persisting spontaneous tidal volumes of 1 ml. or more. This minimal respiration is observed between controlled lung inflations. The monitor also indicates small outboard circuit leaks and responds to cardiac pulsations when respiratory deflections disappear after succinylcholine administration or hyperventilation. Applications include easy maintenance of ventilation near or below the patient's carbon dioxide (CO2) apneic threshold despite curarization and the assessment of diaphragm paralysis when the CO2 drive is maintained slightly above threshold. In continuous routine use, the diaphragm sensor provides the anesthesiologist with a quantitative monitor of persisting spontaneous respiratory activity.