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Case-control analysis for determining possible causes of airway complications during anesthetic recovery in horses.

Anesthetic complications have multiple causes making it difficult to distinguish between inciting causes and coincidental events. Case-control analysis is used to analyze clinical cases retrospectively and identify causes of complications. This approach was used to identify causes of airway complications that occurred during recovery in 30 horses at Cornell University between 1990 and 1997. In the 30 index cases, airway complications included airway obstruction (n = 6), bronchial asthma (1), dyspnea (8), pulmonary edema (14), and respiratory arrest (1). 
 
 
 
Based on breed, age, gender and surgical procedure, each index horse was matched to six control horses, three that were operated on prior to surgery on the index case, and three that were operated on after surgery on the index case. Data were analyzed using chi-square analysis; significance was set at p ≤ 0.05. 
 
 
 
Factors not significantly associated with the index horses included: breed, gender, day of the week, physical status, surgical body region, surgeon, type of complication that may have occurred intraoperatively, fluid volume, drugs given intraoperatively, and use of nasotracheal or nasopharyngeal tubes during recovery. Factors that were associated with the index cases included: a nonsignificant tendency to be older than controls; significantly longer anesthetic episodes; fewer than expected received antibiotics, anti-inflammatory drugs, and tetanus toxoid compared with controls; and more received colloid and hypertonic saline than controls. 
 
 
 
This study did not identify a specific cause of the airway complications, but it allowed us to rule out a number of possible causes while identifying some factors that warrant further investigation such as plasma oncotic pressure effects on airway-associated complications.