The effects of ketamine on the minimum alveolar concentration of isoflurane in cats.

OBJECTIVES: To determine the minimum alveolar concentration (MAC) of isoflurane during the infusion of ketamine. STUDY DESIGN: Prospective, experimental trial. ANIMALS: Twelve adult spayed female cats weighing 5.1 +/- 0.9 kg. METHODS: Six cats were anesthetized with isoflurane in oxygen, intubated and attached to a circle-breathing system with mechanical ventilation. Catheters were placed in a peripheral vein for the infusion of fluids and ketamine, and the jugular vein for blood sampling for the measurement of ketamine concentrations. An arterial catheter was placed to allow blood pressure measurement and sampling for the measurement of PaCO2, PaO2 and pH. PaCO2 was maintained between 29 and 41 mmHg (3.9-5.5 kPa) and body temperature was kept between 37.8 and 39.3 degrees C. Following instrumentation, the MAC of isoflurane was determined in triplicate using a tail clamp method. A loading dose (2 mg kg(-1) over 5 minutes) and an infusion (23 microg kg(-1) minute(-1)) of ketamine was started and MAC was redetermined starting 30 minutes later. Two further loading doses and infusions were used, 2 mg kg(-1) and 6 mg kg(-1) with 46 and 115 microg kg(-1) minute(-1), respectively and MAC was redetermined. Cardiopulmonary measurements were taken before application of the noxious stimulus. The second group of six cats was used for the measurement of steady state plasma ketamine concentrations at each of the three infusion rates used in the initial study and the appropriate MAC value determined from the first study. RESULTS: The MAC decreased by 45 +/- 17%, 63 +/- 18%, and 75 +/- 17% at the infusion rates of 23, 46, and 115 microg kg(-1) minute(-1). These infusion rates corresponded to ketamine plasma concentrations of 1.75 +/- 0.21, 2.69 +/- 0.40, and 5.36 +/- 1.19 microg mL(-1). Arterial blood pressure and heart rate increased significantly with ketamine. Recovery was protracted. CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of isoflurane was significantly decreased by an infusion of ketamine and this was accompanied by an increase in heart rate and blood pressure. Because of the prolonged recovery in our cats, further work needs to be performed before using this in patients.

The effect of the duration of propofol administration on recovery from anesthesia in cats.

OBJECTIVE: To determine the effect of induction, a 30-minute, and a 150-minute infusion of propofol on the rate of recovery in cats. STUDY DESIGN: Randomized, cross-over, prospective experimental study. ANIMALS: Six healthy adult spayed female cats (mean 4.3, range 2-7 years old) weighing 3.9 +/- 0.5 kg. METHODS: Cats received each of three treatments: anesthetic induction with propofol (T1), induction followed by a 30-minute infusion (T30) and induction followed by a 150-minute infusion (T150). Propofol infusions were increased or decreased to maintain a sluggish pedal withdrawal reflex. Animals were monitored throughout the anesthetic period and during the recovery. Venous blood samples were collected from a central venous catheter before anesthesia and at 30 minutes for the 30-minute infusion and at 30, 60, 90, 120 and 150 minutes for the 150-minute infusion. The ability of the cat to lift its head, crawl, stand and walk without ataxia was recorded at 5, 10, 20, 40, 60, 80, 120, 160, 180, 210 and 240 minutes after the completion of propofol administration. Data from physiological values were analyzed using either a Student's t-test (30-minute infusion) or an anova (150-minute infusion). A nonparametric Friedman test (and post-hoc Tukey's Studentized range test) was used to determine whether there were differences in the time taken to recover. Results were considered significant if p < 0.05. RESULTS: Time taken to walk without ataxia was significantly greater in T150 (148 +/- 40 minutes) compared with T1 (80 +/- 15 minutes) and T30 (74 +/- 26 minutes). (No other recovery times were significantly different). Anesthesia with propofol was accompanied by a moderate but significant respiratory depression and a decrease in PCV and total protein. CONCLUSIONS AND CLINICAL RELEVANCE: Prolonged anesthesia with propofol in healthy cats may be associated with a delayed recovery.

Evaluation of the induction and recovery characteristics of anesthesia with desflurane in cats.

OBJECTIVE: To qualitatively and quantitatively evaluate the characteristics of desflurane with regard to the induction of and recovery from anesthesia in cats. ANIMALS: 6 cats. PROCEDURE: Anesthesia was induced and maintained with desflurane in oxygen. Individual minimum alveolar concentration (MAC) values were determined; anesthesia was maintained at 1.25 x MAC for a total anesthesia time (including MAC determination) of 5 hours. Cats were allowed to recover from anesthesia. Induction and recovery periods were video recorded and later scored by use of a grading scale from 0 to 100 (100 being the best outcome). Timing of events was recorded. RESULTS: The MAC of desflurane was 10.27 +/- 1.06%, and mean dose was 5.6 +/- 0.2 MAC-hours. Times to loss of coordination, recumbency, and endotracheal intubation were 1.3 +/- 0.4, 2.3 +/- 0.3, and 6.4 +/- 1.1 minutes, respectively. Median score for quality of anesthetic induction was 93 (range, 91 to 94). Times to first movement, extubation, standing, and ability to jump and land with coordination were 2.8 +/- 1.0, 3.8 +/- 0.5, 14.3 +/- 3.9, and 26.4 +/- 5.1 minutes, respectively. Alveolar washout of desflurane was rapid. Median score for quality of anesthetic recovery was 94 (range, 86 to 96). CONCLUSIONS AND CLINICAL RELEVANCE: Desflurane was associated with rapid induction of and recovery from anesthesia in cats; assessors rated the overall quality of induction and recovery as excellent. Results appear to support the use of desflurane for induction and maintenance of anesthesia in healthy cats.

Surgical management of adrenal gland tumors with and without associated tumor thrombi in dogs: 40 cases (1994-2001).

OBJECTIVE: To compare pathologic findings and results of adrenalectomy for adrenal gland tumors in dogs with and without vena caval tumor thrombi. DESIGN: Retrospective study. ANIMALS: 40 dogs with adrenal gland tumors. PROCEDURE: Medical records were examined. An exact logistic regression analysis was used to evaluate associations between tumor type or right-sided versus left-sided tumor involvement and development of caval tumor thrombi and associations between tumor thrombi, tumor type, or right- versus left-sided location and perioperative complications and mortality rate. Survival was compared between dogs with and without tumor thrombi. RESULTS: Caval thrombi were detected in 25% of dogs, including 3 of 28 (11%) dogs with an adrenocortical tumor and 6 of 11 dogs with a pheochromocytoma. A caval tumor thrombus was detected in 6 of 17 right-sided and 4 of 20 left-sided tumors. Sensitivity and specificity of abdominal ultrasonography for detection of caval thrombi were 80 and 90%, respectively. Intraoperative and postoperative complications developed in 15 and 51% of dogs, respectively. The mortality rate was 22%. There were no significant differences in perioperative morbidity and mortality rates between dogs with and without tumor thrombi. CONCLUSIONS AND CLINICAL RELEVANCE: Caval thrombi associated with adrenal gland tumors are amenable to adrenalectomy and thrombectomy without significantly increased perioperative morbidity and mortality rates, assuming the surgeon is experienced in appropriate techniques.

Anesthetic management in feline renal transplantation.

OBJECTIVE: To document perioperative and anesthetic management of 30 feline renal transplant recipients (1996-1998). STUDY DESIGN: Retrospective clinical study. ANIMALS: Thirty adult cats in end-stage renal failure that underwent heterotopic renal transplantation. MATERIALS AND METHODS: The medical records were reviewed from 30 feline heterotopic renal transplant recipients. Cases were included only if they had been treated for hypertension using a beta-adrenergic antagonist, a calcium channel blocker or hemodialysis. Data regarding signalment, preoperative management, surgical technique, type and doses of anesthetics administered, perioperative hemodynamics and intra- and postoperative complications, postoperative analgesia, morbidity and early mortality were recorded. Data were expressed as mean ± SD. RESULTS: Preanesthetic medication included a combination of an anticholinergic and an opioid (oxymorphone). Anesthesia induction was performed mostly with isoflurane and oxygen delivered by mask. Anesthesia maintenance was primarily achieved with isoflurane in 100% oxygen. Nitrous oxide was often used as part of the anesthetic technique. The mean duration of anesthesia was 4.6 hours ± 27 minutes. The mean renal allograft ischemic time was 60 minutes. During the anesthetic period, the majority of the recipient cats received either fresh whole blood (FWB) (N = 25, 83%), cross-matched packed red blood cells (PRBC) (N = 3, 10%) or fresh frozen plasma (FFP) (N = 2, 7%) combined with a balanced electrolyte solution. Blood products administered averaged 63 ± 34 mL and crystalloid 94 ± 62 mL. The most common treated intraoperative complications were hypotension (N = 14, 47%), hypothermia (N = 13, 43%), metabolic acidosis (N = 11, 37%), hypocalcemia (N = 5, 17%), hypoglycemia (N = 4, 13%), hypertension (N = 2, 7%), bradycardia (N = 1, 3%), and ventricular premature contractions (N = 1, 3%). All cats received opioid analgesics postoperatively. Complications observed in the first 24 hours postoperatively were hypertension (N = 20, 67%), hematuria (N = 14, 47%), electrolyte disturbances (N = 9, 30%), temperature imbalances (N = 5, 17%), decreased PCV requiring blood transfusion (N = 5, 17%), decreased perfusion of a foot associated with external iliac anastomosis technique (N = 5, 17%), seizures associated with hypertension (N = 3, 10%), uroabdomen (N = 2, 7%), acute graft rejection (N = 1, 3%) and, corneal ulceration (N = 1, 3%). Survival rates in the perioperative period were 100, 96.7, and 93.4% intraoperatively, at 24 hours, and 7 days following surgery. CONCLUSION: Successful anesthesia can be performed in critically ill renal transplant recipients. However, for optimal graft function and patient survival, normothermia, normovolemia, normotension, and normal acid-base and electrolyte balance should be carefully maintained. Successful anesthetic management requires understanding of the pathophysiology of end-stage renal disease and the maintenance of homeostasis during the different stages of the perioperative period.