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

Abstract 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 (SpO 2 ) 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.