Oxygenation effect of interventional lung assist in a lavage model of acute lung injury: a prospective experimental study

Abstract

Introduction: The aim of the study was to test the hypothesis that a pumpless arteriovenous extracorporeal membrane oxygenator (interventional lung assist (ILA)) does not significantly improve oxygenation in a lavage model of acute lung injury.

Methods: The study was designed as a prospective experimental study. The experiments were performed on seven pigs (48-60 kg body weight). The pigs were anesthetized and mechanically ventilated. Both femoral arteries and one femoral vein were cannulated and connected with ILA. Acute lung injury was induced by repeated bronchoalveolar lavage until the arterial partial pressure of O2 was lower than 100 Torr for at least 30 minutes during ventilation with 100% O2.

Results: ILA was applied with different blood flow rates through either one or both femoral arteries. Measurements were repeated at different degrees of pulmonary gas exchange impairment with the pulmonary venous admixture ranging from 35.0% to 70.6%. The mean (+/- standard deviation) blood flow through ILA was 15.5 (+/- 3.9)% and 21.7 (+/- 4.9)% of cardiac output with one and both arteries open, respectively. ILA significantly increased the arterial partial pressure of O2 from 64 (+/- 13) Torr to 71 (+/- 14) Torr and 74 (+/- 17) Torr with blood flow through one and both femoral arteries, respectively. O2 delivery through ILA increased with extracorporeal shunt flow (36 (+/- 14) ml O2/min versus 47 (+/- 17) ml O2/min) and reduced arterialization of the inlet blood. Pulmonary artery pressures were significantly reduced when ILA was in operation.

Conclusion: Oxygenation is increased by ILA in severe lung injury. This effect is significant but small. The results indicate that the ILA use may not be justified if the improvement of oxygenation is the primary therapy goal.

Figure 1

Venous admixture calculated in animals with normal and lavaged lungs. B, baseline; N-, normal lung, one arterial cannula open, no gas flow; N+, normal lung, one arterial cannula open, gas flow of 2 lO₂/minute; N++, normal lung, two arterial cannulae open, gas flow of 2 lO₂/minute; L-, lavaged lung, one arterial cannula open, no gas flow; L+, lavaged lung, one arterial cannula open, gas flow of 2 lO₂/minute; L++, lavaged lung, two arterial cannulae open, gas flow of 2 lO₂/minute.

Figure 2

Oxygenator blood flow in animals with normal and lavaged lungs. B, baseline; N-, normal lung, one arterial cannula open, no gas flow; N+, normal lung, one arterial cannula open, gas flow of 2 lO₂/minute; N++, normal lung, two arterial cannulae open, gas flow of 2 lO₂/minute; L-, lavaged lung, one arterial cannula open, no gas flow; L+, lavaged lung, one arterial cannula open, gas flow of 2 lO₂/minute; L++, lavaged lung, two arterial cannulae open, gas flow of 2 lO₂/minute. ***P < 0.001.

Figure 3

Arterial partial pressure of carbon dioxide (PaCO₂) in animals with normal and lavaged lungs. B, baseline; N-, normal lung, one arterial cannula open, no gas flow; N+, normal lung, one arterial cannula open, gas flow of 2 lO₂/minute; N++, normal lung, two arterial cannulae open, gas flow of 2 lO₂/minute; L-, lavaged lung, one arterial cannula open, no gas flow; L+, lavaged lung, one arterial cannula open, gas flow of 2 lO₂/minute; L++, lavaged lung, two arterial cannulae open, gas flow of 2 lO₂/minute. **P < 0.01, ***P < 0.001.

Figure 4

Arterial partial pressure of oxygen (PaO₂) in animals with normal and lavaged lungs. B, baseline; N-, normal lung, one arterial cannula open, no gas flow; N+, normal lung, one arterial cannula open, gas flow of 2 lO₂/minute; N++, normal lung, two arterial cannulae open, gas flow of 2 lO₂/minute; L-, lavaged lung, one arterial cannula open, no gas flow; L+, lavaged lung, one arterial cannula open, gas flow of 2 lO₂/minute; L++, lavaged lung, two arterial cannulae open, gas flow of 2 lO₂/minute. ***P < 0.001.

Figure 5

Oxygen delivery through ILA. One (circles) or two (triangles) arterial cannulae open.

Figure 6

Pulmonary artery pressures (PAP) (mean ± standard deviation) in animals with normal and lavaged lungs. sys, systolic; dias, diastolic; B, baseline; N-, normal lung, one arterial cannula open, no gas flow; N+, normal lung, one arterial cannula open, gas flow of 2 lO₂/minute; N++, normal lung, two arterial cannulae open, gas flow of 2 lO₂/minute; L-, lavaged lung, one arterial cannula open, no gas flow; L+, lavaged lung, one arterial cannula open, gas flow of 2 lO₂/minute; L++, lavaged lung, two arterial cannulae open, gas flow of 2 lO₂/minute. **P < 0.01, ***P < 0.001.