Objective—To compare the cardiopulmonary effects of continuous rate infusions (CRIs) of alfaxalone-2-hydroxypropyl-β-cyclodextrin (HPCD) and propofol in healthy dogs.
Animals—6 young adult medium-sized healthy crossbred dogs.
Procedures—A crossover design was used with a washout period of 6 days between anesthetic treatments. Each dog was sedated with acepromazine (0.02 mg/kg, IV) and hydromorphone (0.05 mg/kg, IV). Anesthesia was induced with propofol (4 mg/kg) or alfaxalone-HPCD (2 mg/kg). After endotracheal intubation, anesthesia was maintained with the same agent (propofol, 0.25 mg/kg/min; alfaxalone-HPCD, 0.07 mg/kg/min) for 120 minutes. Dogs spontaneously breathed 100% oxygen. Measurements included end-tidal partial pressure of carbon dioxide, heart and respiratory rates, mean arterial blood pressure, thermodilution-derived cardiac output, and body temperature. Paired arterial and mixed venous blood samples were collected for determination of blood pH, PaCO2, and PaO2. Data were recorded prior to induction; 5, 15, 30, 60, 90, and 120 minutes after induction of anesthesia; and 20 minutes after stopping the CRI, when feasible. Stroke volume and systemic vascular resistance were calculated. Quality of anesthetic induction and recovery and interval to recovery were recorded.
Results—Both propofol and alfaxalone-HPCD produced excellent induction of anesthesia, maintenance, and recovery. Respiratory depression was evident with both anesthetics. Clinically acceptable, mild hemodynamic changes were similar for both anesthetics.
Conclusions and Clinical Relevance—Alfaxalone-HPCD produced clinically acceptable anesthetic quality and hemodynamic values ideal for use as a CRI. Ventilation may need to be supported if hydromorphone is used at these propofol and alfaxalone-HPCD infusion rates.
Objective—To evaluate the antinociceptive effects of epidurally administered hydromorphone in conscious, healthy cats.
Animals—7 healthy adult cats.
Procedures—An epidural catheter was implanted in each cat. Thermal threshold (TT) was measured by increasing the temperature of a probe placed on the thorax and monitoring the cat's response. Mechanical threshold (MT) was measured by manually inflating a modified blood-pressure bladder affixed to a thoracic limb and monitoring the response. After the baseline TT and MT values were determined, hydromorphone (0.05 mg/kg) or an equal volume of saline (0.9% NaCl) solution was epidurally injected. The TT and MT were again measured at 15, 30, 45, 60, 120, 180, 240, 300, 360, and 480 minutes after injection.
Results—TT and MT did not change significantly from baseline values at any point after saline solution was administered. The MT and TT values were significantly higher than the baseline value at 15 minutes and at 120 and 180 minutes after hydromorphone administration, respectively. The MT and TT values after hydromorphone administration were also significantly different from those obtained at 30 minutes and at 15 minutes and 120 to 300 minutes, respectively, after administration of saline solution. No significant changes in skin temperature were detected after either treatment.
Conclusions and Clinical Relevance—Epidural administration of hydromorphone at a dosage of 0.05 mg/kg yielded thermal and some mechanical antinociceptive effects in cats, and no hyperthermia was detected. Additional studies of the antinociceptive effectiveness and duration of epidurally administered hydromorphone in clinical situations are required.
OBJECTIVE To determine effects of anesthesia on plasma concentrations and pulsatility of ACTH in samples obtained from the cavernous sinus and jugular vein of horses.
ANIMALS 6 clinically normal adult horses.
PROCEDURES Catheters were placed in a jugular vein and into the cavernous sinus via a superficial facial vein. The following morning (day 1), cavernous sinus blood samples were collected every 5 minutes for 1 hour (collection of first sample = time 0) and jugular venous blood samples were collected at 0, 30, and 60 minutes. On day 2, horses were sedated with xylazine hydrochloride and anesthesia was induced with propofol mixed with ketamine hydrochloride. Horses were positioned in dorsal recumbency. Anesthesia was maintained with isoflurane in oxygen and a continuous rate infusion of butorphanol tartrate. One hour after anesthesia was induced, the blood sample protocol was repeated. Plasma ACTH concentrations were quantified by use of a commercially available sandwich assay. Generalized estimating equations that controlled for horse and an expressly automated deconvolution algorithm were used to determine effects of anesthesia on plasma ACTH concentrations and pulsatility, respectively.
RESULTS Anesthesia significantly reduced the plasma ACTH concentration in blood samples collected from the cavernous sinus.
CONCLUSIONS AND CLINICAL RELEVANCE Mean plasma ACTH concentrations in samples collected from the cavernous sinus of anesthetized horses were reduced. Determining the success of partial ablation of the pituitary gland in situ for treatment of pituitary pars intermedia dysfunction may require that effects of anesthesia be included in interpretation of plasma ACTH concentrations in cavernous sinus blood.
Objective—To evaluate the pharmacokinetics and thermal and mechanical antinociceptive effects of a fentanyl constant rate infusion (CRI) in conscious cats.
Animals—8 healthy adult cats.
Procedures—At a ≥ 14-day interval, 7 cats received a loading dose (LD) of fentanyl (5 μg/kg, IV [administered at 0 hours]) followed by fentanyl infusion (5 μg/kg/h, IV) for 2 hours or similar administrations of equivalent volumes of 0.9% saline (NaCl) solution. One cat received only the fentanyl treatment. For both treatments, sedation and adverse events were evaluated and mechanical threshold (MT) and thermal threshold (TT) testing was performed prior to (baseline) and at predetermined times up to 26 hours after LD administration; plasma fentanyl concentrations were determined at similar times when the cats received fentanyl.
Results—Fentanyl induced mild sedation during the infusion. The only adverse effect associated with fentanyl LD administration was profuse salivation (1 cat). Saline solution administration did not significantly change MT or TT over time. For the duration of the CRI, MT and TT differed significantly between treatments, except for TT 1 hour after LD administration. For the fentanyl treatment, MT and TT were significantly higher than baseline at 0.25 to 0.75 hours and at 0.25 to 1 hour, respectively. During the fentanyl CRI, mean ± SD plasma fentanyl concentration decreased from 4.41 ± 1.86 ng/mL to 2.99 ± 1.28 ng/mL and was correlated with antinociception; plasma concentrations < 1.33 ± 0.30 ng/mL were not associated with antinociception.
Conclusions and Clinical Relevance—Fentanyl CRI (5 μg/kg/h) induced mechanical and thermal antinociception in cats.