Burn edema is accentuated by a moderate smoke inhalation injury in sheep

We determined the lung and systemic response of a moderate smoke inhalation injury combined with a 15% total body surface third-degree burn compared with a burn alone and inhalation alone. Adult sheep were prepared with chronic lung and bilateral prefemoral soft tissue lymph fistula. The burn was confined to one side. Physiologic parameters, lymph flow (QL), and lymph/plasma protein ratio were monitored. Oxidant changes were measured as lipid peroxidation by circulating and lymph-conjugated dienes and lung tissue malondialdehyde. Animals were resuscitated with lactated Ringer's solution during the 24-hour study period to restore and maintain vascular filling pressures and cardiac index. We found net 24-hour fluid balance for burn-inhalation injuries to be 4.1 +/- 1.2 L compared with burn alone of 2.9 +/- 0.9 L and inhalation alone of 2.4 +/- 0.5 L, a significant difference. Protein-rich burn tissue QL increased by fivefold to sixfold with burn alone compared with more than tenfold with burn-inhalation injury. A twofold increase in both lung and nonburn soft tissue QL was also seen in the combined injury not seen with burn alone. Arterial blood gases decreased only at 12 hours. Plasma conjugated dienes were increased in all groups, whereas burn lymph values were increased only in combined insult. In addition, lung malondialdehyde content at 24 hours was 155 +/- 11 nmol/gm with burn-inhalation injury compared with 62 +/- 8 nmol/L for burn alone, 55 +/- 9 nmol/L in inhalation alone, and 45 +/- 4 nmol/L for controls. However, no alveolar flooding was noted in any group. We conclude that a modest smoke inhalation (carboxyhemoglobin of 25%) added to a 15% total body surface burn markedly increases the degree of burn edema, as well as nonburn soft tissue and lung QL, compared with burn alone, indicating increased plasma to interstitial fluid transport in these tissues as well. Increased burn tissue lipid peroxidation products corresponded with the increased burn fluid losses. The increased lung lipid peroxidation also indicates further lung oxidant activity as well.