EXAGGERATED CARDIOPULMONARY RESPONSE AFTER BACTEREMIA IN SHEEP WITH WEEK-OLD THERMAL-INJURY

Objective: To determine if thermal injury impairs pulmonary intravascu lar clearance of bacteria and therefore leads to exaggerated cardiopul monary dysfunction in sheep, since endotoxin infusion has been previou sly shown to induce more severe pulmonary injury after thermal injury. Design: Prospective, unblinded, randomized, controlled trial. Setting . Laboratory at a large university medical center. Interventions: Chro nically instrumented, anesthetized sheep received a 40% total body sur face area, third-degree thermal injury. Live Pseudomonas aeruginosa (1 0(7) P. aeruginosa/min for 1 hr, n = 6) were infused 7 to 10 days afte r thermal injury. Similarly prepared noninjured sheep received the sam e pseudomonas infusion (n = 7) or saline (n = 7). Measurements and Mai n Results. Bacterial clearance, which measures phagocytosis by the pul monary intravascular macrophages, was equally efficient in intact shee p and sheep with thermal injury. Pulmonary hypertension persisted for 18 hrs after thermal injury, compared with 8 hrs in noninjured sheep. Lung lymph flow significantly increased from 6 to 8 hrs in only the th ermal injury group. Both bacteremic groups developed a hyperdynamic ci rculation from 6 to 8 hrs, but cardiac index was 1 to 1.5 L/min/m2 hig her in thermally injured sheep. Total peripheral resistance index decr eased significantly from 6 to 24 hrs in thermally injured sheep and fr om 6 to 12 hrs in intact bacteremic sheep. Mean arterial pressure of t hermally injured sheep was increased at baseline and for the first 6 h rs compared with noninjured animals. Mean arterial pressure decreased from 6 to 24 hrs in sheep with thermal injury but did not change in in tact bacteremic sheep. Conclusions: Bacterial clearance was not impair ed by preceding thermal injury in sheep. Bacteremia in the presence of a preexisting thermal injury led to more persistent pulmonary hyperte nsion and an exaggerated hyperdynamic circulation.