Regional intrapulmonary gas distribution in awake and anesthetized-paralyzed man

Abstract

Intrapulmonary distribution of ventilation/unit lung volume was studied in 28 volunteers in the sitting, supine, or right lateral decubitus position, either awake or anesthetized-paralyzed and mechanically ventilated. We found significant differences between the awake state and anesthesia-paralysis with mechanical ventilation in 1) intrapulmonary gas distribution, and 2) the vertical gradient of regional functional residual capacities for the subjects in the lateral decubitus position, but not for those in the sitting and supine positions. The effect of increasing the tidal volume on distribution of ventilation was significantly different 1) between the three body positions for a given state, and 2) between the two states for a given body position. The data suggest thoracoabdominal mechanics are different in the three body positions and that anesthesia-paralysis and mechanical ventilation may cause a different pattern of expansion of the respiratory system than spontaneous breathing in the awake state.

Regional Lung Function in Bilateral Diaphragmatic Paralysis

“…The distribution of regional volume in patients with bilateral diaphragmatic paralysis has not been reported. The work of ROUSSOS, Martin & Engel (1977a) on diaphragmatic relaxation and Rehder, Sessler & Rodarte (1977) on the effects of anaesthesia and muscle paralysis in normal subjects in decubitus postures suggest that patients with diaphragmatic paralysis may have a low end-expiratory lung volume and the vertical gradient of regional lung volume may increase, particularly in horizontal postures. Under these circumstances, the expansion of dependent lung regions may be so reduced that airway closure and gas trapping occurs.…”

Other approaches to open-lung ventilation: Airway pressure release ventilation

“…Mechanical breaths shift ventilation to nondependent lung regions as the passive respiratory system accommodates the displacement of gas in to the lungs. However, spontaneous breathing during APRV results in a more dependent gas distribution when the active respiratory system draws gas into the lung as pressure changes and flow follow a similar time course (7)(8)(9). As a result, by allowing patients to spontaneously breathe during APRV, dependent lung regions may be preferentially recruited without the need to raise applied airway pressure.…”

Effect of neuromuscular blocking agents on gas exchange in patients presenting with acute respiratory distress syndrome*

“…It has been suggested that anesthesia and paralysis may increase the mismatch between ventilation and perfusion and could result in impaired pulmonary gas exchange (9). Moreover, sedation and paralysis might increase the risk of infection, hypothermia, and death associated with disconnection from the ventilator.…”