Respiratory and haemodynamic effects of the prone position at two different levels of PEEP in a canine acute lung injury model

This study was designed to examine whether the oxygenation response in the prone position differs in magnitude depending on the level of positive end- expiratory pressure (PEEP) applied in the supine position, and whether card iac output (CO) increases in the prone position. Medicine In seven supine dogs, acute lung injury was established by saline lavage (a rterial oxygen tension (Pa,O-2)/inspiratory oxygen fraction (FI,O-2) 17.8+/ -9.6 kPa (134+/-72 mmHg)), and inflection point (Pflex) of the respiratory system was measured (6.6+/-1.4 cmH(2)O), Pa,O-2/FI,O-2 and CO of the supine and prone positions were obtained under the application of low PEEP and th en under optimal PEEP (2 cmH(2)O below and above Pflex, respectively). The net increase in Pa,O-2/FI,O-2 by prone positioning was greater at low P EEP (27.3+/-12.0 kPa (205+/-90 mmHg)) than at optimal PEEP (4.4+/-13.0 kPa (33+/-98 mmHg)) (p=0.006), CO decreased significantly with optimal PEEP in the supine position (2.4+/-0.5 versus 3.1+/-0.4 L . min.(1) at baseline, p< 0.001), and increased to 3.4+/-0.6 and 3.6+/-0.7 L min I in the prone posit ion at 5 min and 30 min, respectively (both p=0.018), When the dogs were tu rned supine at optimal PEEP, CO again decreased (2.4+/-0.5 L.min.(1), p<0.0 01), In conclusion, the prone position augmented the effect of relatively low po sitive end-expiratory pressure on oxygenation, and attenuated the haemodyna mic impairment of relatively high positive end-expiratory pressure in a can ine acute lung injury model.