OBJECTIVE To investigate use of the plethysmographic variability index (PVI) and perfusion index (PI) for evaluating changes in arterial blood pressure in anesthetized tigers (Panthera tigris). ANIMALS 8 adult tigers. PROCEDURES Each tiger was anesthetized once with a combination of ketamine, midazolam, medetomidine, and isoflurane. Anesthetic monitoring included assessment of PI, PVI, direct blood pressure measurements, anesthetic gas concentrations, esophageal temperature, and results of capnography and ECG. Mean arterial blood pressure (MAP) was maintained for at least 20 minutes at each of the following blood pressure conditions: hypotensive (MAP = 50 ± 5 mm Hg), normotensive (MAP = 70 ± 5 mm Hg), and hypertensive (MAP = 90 ± 5 mm Hg). Arterial blood gas analysis was performed at the beginning of anesthesia and at each blood pressure condition. RESULTS Mean ± SD PI values were 1.82 ± 2.38%, 1.17 ± 0.77%, and 1.71 ± 1.51% and mean PVI values were 16.00 ± 5.07%, 10.44 ± 3.55%, and 8.17 ± 3.49% for hypotensive, normotensive, and hypertensive conditions, respectively. The PI values did not differ significantly among blood pressure conditions. The PVI value for the hypotensive condition differed significantly from values for the normotensive and hypertensive conditions. The PVI values were significantly correlated with MAP (r = −0.657). The OR of hypotension to nonhypotension for PVI values ≥ 18% was 43.6. CONCLUSIONS AND CLINICAL RELEVANCE PVI was a clinically applicable variable determined by use of noninvasive methods in anesthetized tigers. Values of PVI ≥ 18% may indicate hypotension.

OBJECTIVE To evaluate the efficacy of each of 3 incremental doses of MK-467 for alleviation of dexmedetomidine-induced hemodynamic depression in isoflurane-anesthetized cats. ANIMALS 6 healthy adult domestic shorthair cats. PROCEDURES Each cat was anesthetized with isoflurane and received a target-controlled infusion of dexmedetomidine estimated to maintain the plasma dexmedetomidine concentration at 10 ng/mL throughout the experiment. Heart rate (HR) and direct arterial pressures were measured at baseline (isoflurane administration only), during dexmedetomidine infusion, and before and after IV administration of each of 3 serially increasing doses (15, 30, and 60 μg/kg) of MK-467. Cardiac index (CI) and systemic vascular resistance (SVR) were recorded at baseline, during dexmedetomidine infusion, and at the mean arterial pressure nadir after administration of the 30- and 60-μg/kg doses of MK-467. RESULTS Compared with baseline values, the dexmedetomidine infusion significantly decreased HR and increased arterial pressures. Each dose of MK-467 caused a significant decrease in arterial pressures and a significant, albeit clinically irrelevant, increase in HR (≤ 10%). Following administration of the 30- and 60-μg/kg doses of MK-467, all cats developed clinical hypotension (mean arterial pressure, < 60 mm Hg) even though CI and SVR returned to baseline values. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated administration of small doses of MK-467 to isoflurane-anesthetized cats receiving dexmedetomidine restored CI and SVR, but caused a substantial decrease in arterial pressures and only a marginal increase in HR. Therefore, caution should be used when MK-467 is administered to alleviate dexmedetomidine-induced hemodynamic depression in isoflurane-anesthetized cats.

OBJECTIVE To determine the minimum alveolar concentration of desflurane (MACDES) and effects on cardiovascular variables in positive-pressure ventilated sheep. ANIMALS 13 adult female sheep. PROCEDURES Anesthesia was induced with desflurane. After a 30-minute equilibration at an end-tidal concentration of desflurane (etDES) of 10.5%, an electrical stimulus (5 Hz/ms and 50 mA) was applied for 1 minute or until gross purposeful movement occurred. The etDES was then changed by 0.5% (modified up-down method), depending on whether a positive motor response had been elicited, and stimulation was repeated. The MACDES was the etDES midway between a positive and negative response. After MACDES was determined, etDES was increased to 1.3 and 1.6 MACDES. Animals were allowed to equilibrate for 15 minutes, and cardiovascular, blood gas, acid-base, and hematologic variables were measured. Times to induction of anesthesia, extubation, attainment of sternal position, and standing and duration of anesthesia were recorded. RESULTS Mean ± SD MACDES was 9.81 ± 0.79%. Times to intubation, extubation, and standing were 4.81 ± 2.21 minutes, 14.09 ± 4.05 minutes, and 32.4 ± 12.5 minutes, respectively. Duration of anesthesia was 226 ± 22 minutes. Heart rate increased significantly at induction of anesthesia but otherwise remained at preanesthetic rates. Arterial blood pressures progressively decreased with increasing etDES; pressures increased slightly only in response to noxious stimulation. CONCLUSIONS AND CLINICAL RELEVANCE The MACDES determined here compared favorably with that determined for other sheep populations and indicated similar anesthetic potency as in other species. Desflurane caused dose-dependent arterial hypotension, which indicated the need for careful blood pressure monitoring.