Exaggerated cardiopulmonary response after bacteremia in sheep with week-old thermal injury

To determine if thermal injury impairs pulmonary intravascular clearance of bacteria and therefore leads to exaggerated cardiopulmonary dysfunction in sheep, since endotoxin infusion has been previously shown to induce more severe pulmonary injury after thermal injury.

Prospective, unblinded, randomized, controlled trial.

Laboratory at a large university medical center.

Chronically instrumented, anesthetized sheep received a 40% total body surface area, third-degree thermal injury. Live Pseudomonas aeruginosa (10(7) P. aeruginosa/min for 1 hr; n = 6) were infused 7 to 10 days after thermal injury. Similarly prepared noninjured sheep received the same pseudomonas infusion (n = 7) or saline (n = 7).

Bacterial clearance, which measures phagocytosis by the pulmonary intravascular macrophages, was equally efficient in intact sheep 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 thermal injury group. Both bacteremic groups developed a hyperdynamic circulation from 6 to 8 hrs, but cardiac index was 1 to 1.5 L/min/m2 higher in thermally injured sheep. Total peripheral resistance index decreased significantly from 6 to 24 hrs in thermally injured sheep and from 6 to 12 hrs in intact bacteremic sheep. Mean arterial pressure of thermally injured sheep was increased at baseline and for the first 6 hrs compared with noninjured animals. Mean arterial pressure decreased from 6 to 24 hrs in sheep with thermal injury but did not change in intact bacteremic sheep.

Bacterial clearance was not impaired by preceding thermal injury in sheep. Bacteremia in the presence of a preexisting thermal injury led to more persistent pulmonary hypertension and an exaggerated hyperdynamic circulation.