CARDIOPULMONARY FUNCTION AFTER PULMONARY CONTUSION AND PARTIAL LIQUIDVENTILATION

Purpose: To compare the effects of mechanical ventilation with either positive end-expiratory pressure (PEEP) or partial liquid ventilation (PLV) on cardiopulmonary function after severe pulmonary contusion. Me thods: Mongrel pigs (32 +/- 1 kg) were anesthetized, paralyzed, and me chanically ventilated (8-10 mL/kg tidal volume; 12 breaths/min; FiO(2) = 0.5). Systemic hemodynamics and pulmonary function were measured fo r 7 hours after a captive bolt gun delivered a blunt injury to the rig ht chest. After 5 hours, FiO(2) was increased to 1.0 and either PEEP ( n = 7) in titrated increments to 25 cm H2O or PLV with perflubron (Liq uiVent, 30 mL/kg, endotracheal) and no PEEP (n = 7) was administered f or 2 hours, Two control groups received injury without treatment (n = 6) or no injury with PLV (n = 3), Fluids were liberalized with PEEP ve rsus PLV (27 +/- 3 vs. 18 +/- 2 ml kg(-1).h(-1)) to maintain cardiac f illing pressures. Results: Before treatment at 5 hours after injury, p hysiologic dead space fraction (30 +/- 4%), pulmonary vascular resista nce (224 +/- 20% of baseline), and airway resistance (437 +/- 110% of baseline) were all increased (p < 0.05). In addition, PaO2/FiO(2) had decreased to 112 +/- 18 mm Hg, compliance was depressed to 11 +/- 1 mL /cm H2O (36 +/- 3% of baseline), and shunt fraction was increased to 2 2 +/- 4% (all p < 0.05). Blood pressure and cardiac index remained sta ble relative to baseline, but stroke index and systemic oxygen deliver y were depressed by 15 to 30% (both p < 0.05). After 2 hours of treatm ent with PEEP versus PLV, PO2/FiO(2) was higher (427 +/- 20 vs, 263 +/ - 37) and dead space ventilation was lower (4 +/- 3 vs. 28 +/- 7%) (bo th p < 0.05), whereas compliance tended to be higher (26 +/- 2 vs. 20 +/- 2) and shunt fraction tended to be lower (0 +/- 0 vs. 7 +/- 4), Wi th PEEP versus PLV, however, cardiac index, stroke index, and systemic oxygen delivery were 30 to 60% lower (all p < 0.05). Furthermore, alt hough contused lungs showed similar damage with either treatment, the secondary injury in the contralateral lung (as manifested by intra-alv eolar hemorrhage) was more severe with PEEP than with PLV. Conclusions : Both PEEP and PLV improved pulmonary function after severe unilatera l pulmonary contusion, but negative hemodynamic and histologic changes were associated with PEEP and not with PLV, These data suggest that P LV is a promising novel ventilatory strategy for unilateral pulmonary contusion that might ameliorate secondary injury in the contralateral uninjured lung.