Retrospective review of clinical and anesthetic findings in 164 heartworm-positive dogs undergoing spay-neuter surgery.

BACKGROUND: Timing of spay-neuter surgery in heartworm-positive dogs has been a concern, primarily due to perceived risk of anesthetic complications secondary to cardiovascular compromise. In shelter settings, timing of spay-neuter surgery impacts length of stay and ultimate chance of adoption for heartworm-positive dogs, yet up to 13% of animal shelters may delay spay-neuter procedures until after adulticidal therapy. METHODS: This retrospective review of medical records describes clinical and anesthetic monitoring parameters of heartworm-positive dogs presented for elective spay-neuter surgery in a veterinary student clinical training program. Dogs were assessed for anesthetic/surgical candidacy based on physical examination findings alone and experienced standardized anesthetic protocols. RESULTS: Patients included 94 females, 69 males, and one intersex patient with ages ranging from 6 months to 15 years. The heartworm status of 73 dogs (44.5%) was unknown at the time of anesthesia and surgery. Noteworthy cardiopulmonary findings on preoperative physical examination included two dogs with a cough and normal heart and lung sounds on auscultation, and five dogs with heart murmurs (grade 2, n = 2; grade 3, n = 3) with normal lung sounds on auscultation. Two of the dogs with a grade 3 heart murmur were evaluated by a veterinary cardiologist; one was determined to have no pulmonary artery disease, and one was identified as previously diagnosed with mitral valve insufficiency. Average anesthetic time was 98.6 min (range 13-285 min.), 50.3 min for males and 133.7 min for females. Average oxygen saturation (SpO2) reading was 96% (range 89-99%); hypoxemia (< 90%) was identified at five specific time points in four patients. Bradycardia (< 60 beats per minutes [bpm]) was identified in four patients (2.4%). There were no perioperative anesthetic emergencies or deaths. A total of nine perioperative surgical complications were identified, six of which were unrelated to heartworm status. The remaining three reports consisted of blood-tinged mucus identified on the endotracheal tube after extubation. CONCLUSIONS: There was no evidence of increased risk of anesthetic or surgical complications in heartworm-positive dogs when screening was limited to a preoperative physical examination and standardized anesthetic protocols were used for elective sterilization procedures.