Performance of four cardiac output monitoring techniques vs. intermittent pulmonary artery thermodilution during a modified passive leg raise maneuver in isoflurane-anesthetized dogs

OBJECTIVE: This study investigated the performance among four cardiac output (CO) monitoring techniques in comparison with the reference method intermittent pulmonary artery thermodilution (iPATD) and their ability to diagnose fluid responsiveness (FR) during a modified passive leg raise (PLR(M)) maneuver in isoflurane-anesthetized dogs undergoing acute blood volume manipulations. The study also examined the simultaneous effect of performing the PLR(M) on dynamic variables such as stroke distance variation (SDV), peak velocity variation (PVV), and stroke volume variation (SVV). STUDY DESIGN: Prospective, nonrandomized, crossover design. STUDY ANIMALS: Six healthy male Beagle dogs. METHODS: The dogs were anesthetized with propofol and isoflurane and mechanically ventilated under neuromuscular blockade. After instrumentation, they underwent a series of sequential, nonrandomized steps: Step 1: baseline data collection; Step 2: removal of 33 mL kg(−1) of circulating blood volume; Step 3: blood re-transfusion; and Step 4: infusion of 20 mL kg(−1) colloid solution. Following a 10-min stabilization period after each step, CO measurements were recorded using esophageal Doppler (ED(CO)), transesophageal echocardiography (TEE(CO)), arterial pressure waveform analysis (APWA(CO)), and electrical cardiometry (EC(CO)). Additionally, SDV, PVV, and SVV were recorded. Intermittent pulmonary artery thermodilution (iPATD(CO)) measurements were also recorded before, during, and after the PLR(M) maneuver. A successful FR diagnosis made using a specific test indicated that CO increased by more than 15% during the PLR(M) maneuver. Statistical analysis was performed using one-way analysis of variance for repeated measures with post hoc Tukey test, linear regression, Lin’s concordance correlation coefficient (ρc), and Bland–Altman analysis. Statistical significance was set at p < 0.05. RESULTS: All techniques detected a reduction in CO (p < 0.001) during hemorrhage and an increase in CO after blood re-transfusion and colloid infusion (p < 0.001) compared with baseline. During hemorrhage, CO increases with the PLR(M) maneuver were as follows: 33% for iPATD (p < 0.001), 19% for EC (p = 0.03), 7% for APWA (p = 0.97), 39% for TEE (p < 0.001), and 17% for ED (p = 0.02). Concurrently, decreases in SVV, SDV, and PVV values (p < 0.001) were also observed. The percentage error for TEE, ED, and EC was less than 30% but exceeded 55% for APWA. While TEE(CO) and EC(CO) slightly underestimated iPATD(CO) values, ED(CO) and APWA(CO) significantly overestimated iPATD(CO) values. TEE and EC exhibited good and acceptable agreement with iPATD. However, CO measurements using all four techniques and iPATD did not differ before, during, and after PLR(M) at baseline, blood re-transfusion, and colloid infusion. CONCLUSION AND CLINICAL RELEVANCE: iPATD, EC, TEE, and ED effectively assessed FR in hypovolemic dogs during the PLR(M) maneuver, while the performance of APWA was unacceptable and not recommended. SVV, SDV, and PVV could be used to monitor CO changes during PLR(M) and acute blood volume manipulations, suggesting their potential clinical utility.