BLOOD-GAS ANALYSIS IN DOGS WITH HEARTWORM CAVAL SYNDROME

Blood gases and cardiopulmonary function were analyzed in 67 dogs with heartworm (HW) caval syndrome (CS) and 19 HW-free dogs. Arterial oxygen tension (PaO2) was 91.5+/-7.3 mmHg in the HW-free dogs, 74.9+/-14.3 mmHg in 46 dogs that subsequently survived surgical HW removal (surviving dogs) and 64.6+/-14.7 mmHg in 21 dogs which later died or were euthanatized following surgical treatment (nonsurviving dogs). PaO2 levels less than 60 mmHg were detected in 30.4% and 38.1% dogs in the surviving and nonsurviving groups, respectively. Arterial carbon dioxide tension (PaCO2) was 35.8+/-4.9 mmHg in the HW-free dogs, 30.7+/-5.6 mmHg in the surviving dogs, and 28.8+/-6.2 mmHg in nonsurviving dogs. PaO2 (p<0.01) and PaCO2 were lower (p<0.01) and the alveolar-arterial oxygen difference (AaDO2) was higher (p<0.01) in CS dogs than in HW-free dogs. PaO2 was lower (p<0.01) and AaDO2 was larger (p<0.01) in the nonsurviving dogs than in the surviving dogs. Arterial blood pH and bicarbonate concentration were lower (p<0.01) and the anion gap was larger (p<0.01) in CS dogs than in the HW-free dogs. Serum lactic acid level in nonsurviving dogs (13.2+/-3.9 mmol/l) was higher (p<0.01) than in the HW-free (1.7+/-0.8 mmol/l) and surviving dogs (2.7+/-1.8 mmol/l). The PaO2 correlated significantly with mean pulmonary arterial pressure (r = 0.65, p<0.01), cardiac index (r = 0.44, p<0.05) and total pulmonary resistance (r = -0.70, p<0.01). Blood gas analysis was repeated 1 week after HW removal in 21 dogs that survived and 10 dogs that did not survive. PaO2 (p<0.05) and PaCO2 (p<0.01) increased, and AaDO2 (p<0.01) decreased in the surviving dogs, but not in the nonsurviving dogs. Blood gas values reflecting circulatory disturbance and ventilation insufficiency are predictors of survival following surgical HW removal in dogs with CS.