Monitoring heart function and low blood pressure in anesthetized dogs

Abstract

OBJECTIVE: To evaluate agreement between cardiac output (CO) from intermittent pulmonary artery thermodilution (iPATD-CO) and HemoSphere with Acumen IQ sensor (HSIQ-CO) in sevoflurane-anesthetized, normovolemic and hypovolemic dogs. Also, to analyze HSIQ-derived Hypotension Prediction Index (HPI) trends, and investigate its relationship with invasive mean arterial blood pressure (MAP). STUDY DESIGN: Blinded, nonrandomized, experimental observational study. ANIMALS: Eight mixed-breed female intact dogs. METHODS: Dogs were anesthetized on two occasions. In both anesthetic events, iPATD-CO and HSIQ-CO (via dorsal metatarsal artery) were measured 10 times every 10 minutes during normovolemia and 10 times every 10 minutes starting 20 minutes after a 15% blood loss (hypovolemia). Agreement between iPATD-CO and HSIQ-CO was assessed with Bland-Altman, four-quadrant and polar plot analyses. To evaluate MAP-HPI relationship, 100 standardized time points per dog per anesthetic event were uniformly sampled across the anesthetic period from instrumentation to recovery. Area under the receiver operating characteristic (AUROC) curve was used to compare HPI with short-term MAP changes (1-5 minutes) for predicting hypotension (MAP ≤ 65 mmHg > 1 minute) at 5, 10 and 15 minutes. Youden's index provided optimal HPI thresholds for predicting hypotension. RESULTS: HSIQ-CO showed significant overestimation which increased further with hypovolemia. HSIQ-CO measurements had a high percentage error (73%), and poor trending compared with iPATD-CO. HPI strongly predicted hypotension (AUROC > 0.90), outperforming short-term MAP fluctuations (AUROC ≈ 0.50). Optimal HPI thresholds of 97-98 accurately predicted hypotension 15 minutes before onset. CONCLUSIONS AND CLINICAL RELEVANCE: HSIQ proved unreliable for CO measurement; however, HPI accurately predicted hypotension up to 15 minutes, highlighting its potential clinical utility in veterinary anesthesia.