Increased Early Postburn Fluid Requirements and Oxygen Demands Are Predictive of the Degree of Airways Injury by Smoke Inhalation

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Abstract
The combination of burn and smoke inhalation was studied to determine if early hemodynamic and metabolic abnormalities would correspond with the degree of subsequent smoke-induced airways injury. Adult sheep (n = 45) given an 18% total body surface third-degree burn alone or with smoke exposures of 12 breaths of 5, 10, or 20 mL/kg tidal volume were continuously monitored with airways assessed at 4 or 24 hours. With increased smoke exposure (20 mL/kg tidal volume), oxygen consumption (VO2) in the first several hours and net positive fluid balance, especially in the first 6 hours, increased by 100% and 300%, respectively, over that seen with burn alone. The degree of increase in fluid requirement, net fluid retention, and VO2 with smoke, compared with burn alone, correlated best with the degree of airways damage quantitated at 24 hours, r = 0.83, 0.85, and 0.89, respectively. Airways damage at 4 hours did not predict the damage seen at 24 hours. Systemic changes were not caused by gas-phase toxins, such as carbon monoxide, because smoke filtered of particles had the same blood carbon monoxide control as whole smoke, but the systemic response was equal to burn alone, and there was no airways injury. The cause of the systemic changes is likely the result of the intense airways inflammation.