[Experimental study of the safety of sustained inflation strategy in acute respiratory distress syndrome in sheep].

OBJECTIVE

To evaluate the effects of lung recruitment maneuver (RM) on hemodynamics and lung structure with sustained inflation (SI) in acute respiratory distress syndrome (ARDS) in sheep, to look for a safe range of pressure and time of SI.

METHODS

Fourteen anaesthetized sheep were subjected to lung lavage through a broncho-fibroscope to reproduce ARDS, and quasi-static pressure-volume (P-V) curves were obtained with low flow technique. The upper inflection point (UIP) and the lower inflection point (LIP) were found, and then 5 cm H(2)O (1 cm H(2)O=0.098 kPa) below UIP, UIP, 10 cm H(2)O above UIP, 20 cm H(2)O above UIP as the peak pressure of SI were selected as the test pressure. They were randomized to four groups (U-5, U+0, U+10, U+20). The duration of SI was 60 seconds. Hemodynamics and oxygenation indexes were monitored and recorded during and after SI until the study was terminated 2 hours later, then CT and lung tissue biopsy were performed.

RESULTS

Pneumothorax was found in U+20 groups, resulting in the death of sheep. Hemodynamics was affected significantly in other groups during SI. In U+10 groups, cardiac output (CO) and cardiac index (CI) were lowered at 15 seconds after RM began, and recovered slowly after RM; in U+0 group and U-5 group, the entire RM could be carried out to the end, and biopsy showed bullous emphysema in U+0 group.

CONCLUSION

The impairment of the hemodynamics and damage to the lung structure should be prevented when RM is performed in ARDS patients, and the inflation pressure should be limited within the range of UIP or 5 cm H(2)O under UIP to avoid adverse effect on hemodynamics.