Hemodynamic Effects of External Continuous Negative Pressure Ventilation Compared with Those of Continuous Positive Pressure Ventilation in Dogs with Acute Lung Injury

Abstract

Patients with noncardiogenic pulmonary edema requiring ventilatory assistance are usually supported with CPPV using positive end-expiratory pressure (PEEP), but CPPV requires endotracheal intubation and may decrease cardiac output (QT). The purpose of this study was to examine thoracoabdominal continuous negative pressure ventilation (CNPV) using external negative end-expiratory pressure (NEEP). The effects on gas exchange and hemodynamics were compared with those of CPPV with PEEP, with the premise that CNPV might sustain venous return and improve QT. In 6 supine, anesthetized and paralyzed dogs with oleic-acid-induced pulmonary edema, 30 min of CNPV was alternated twice with 30 min of CPPV. Positive and negative pressure ventilation were carefully matched for fractional inspired oxygen concentration (FIO2 = 0.56), breathing frequency, and tidal volume. In addition, we matched the increase in delta FRC obtained with the constant distending pressures produced by both modes of ventilation. An average of -9 cm H2O of NEEP produced the same delta FRC as 10.8 cm H2O of PEEP. Gas exchange did not differ significantly between the 2 modes. However, QT was 15.8% higher during CNPV than during CPPV (p less than 0.02). Mixed venous oxygen saturation also improved during CNPV compared with that during CPPV (58.3 versus 54.5%, p less than 0.01). Negative pressure ventilation using NEEP may be a viable alternative to positive pressure ventilation with PEEP in the management of critically ill patients with noncardiogenic pulmonary edema. It offers comparable improvement in gas exchange with the advantages of less cardiac depression and the possible avoidance of endotracheal intubation.

Negative-pressure ventilation: is there still a role?

“…This is because intrathoracic pressure is actually raised relative to body surface pressure, thereby reducing the gradient for venous return. It has been shown that this is not the case when the application of NPV is confined to the chest wall by using cuirass or jacket [39,40]. Unlike tank ventilators, these machines selectively decrease intrathoracic pressure so that right atrial pressure becomes more negative relative to the rest of the body, enhancing the gradient for venous return [40].…”

Mechanical Ventilation

“…Ventilation using a chest device (i.e., a cuirass or a jacket) causes hemodynamic effects that closely reflect spontaneous ventilation. However, ventilation with a total body device (e.g., a tank ventilator) results in hemodynamic effects that are comparable to those produced by the PPV; this is because of the loss of the driving pressure between the abdomen and the right atrium caused by the negative pressure applied to the abdominal surface (Lockhat et al 1992;Skaburskis et al 1987).…”

Negative pressure ventilation in the treatment of acute respiratory failure: an old noninvasive technique reconsidered

“…This is because intrathoracic pressure is actually raised relative to body surface pressure, thereby reducing the gradient for venous return. SKABURSIS et al [49] and LOCKHAT et al [50] have shown that this is not the case when the application of NPV is confined to the thorax and upper abdomen by using cuirass or ponchowrap. Unlike tank ventilator, these machines selectively decrease intrathoracic pressure, so that right atrial pressure becomes more negative (relative to the rest of body), potentially enhancing the gradient for the venous return.…”

“…Unlike tank ventilator, these machines selectively decrease intrathoracic pressure, so that right atrial pressure becomes more negative (relative to the rest of body), potentially enhancing the gradient for the venous return. SKABURSIS et al [49] compared the effects of NPV plus negative end-expiratory pressure (NEEP) with PPV plus PEEP in six anaesthetized dogs with oleic acid induced pulmonary oedema. The two ventilatory modes were carefully matched for inspired oxygen fraction (FI,O 2 ), breathing frequency, tidal volume, and the increase in FRC.…”

“…The two ventilatory modes were carefully matched for inspired oxygen fraction (FI,O 2 ), breathing frequency, tidal volume, and the increase in FRC. Whereas gas exchange did not differ significantly between the two modes, cardiac output was higher during NPV plus NEEP than during PPV plus PEEP [49]. LOCKHAT et al [50] compared the effects of PPV plus PEEP, NPV plus NEEP applied by iron lung, and NPV plus NEEP applied only to the thorax and upper abdomen by a grid and wrap device in seven anaesthetized dogs.…”