Predictive factors and the effect of phenoxybenzamine on outcome in dogs undergoing adrenalectomy for pheochromocytoma.

BACKGROUND: Some studies in dogs undergoing adrenalectomy for pheochromocytoma suggest that anesthetic complications and perioperative mortality are common. In humans, surgical outcome has improved with the use of phenoxybenzamine (PBZ) before adrenalectomy. HYPOTHESIS: Dogs treated with PBZ before adrenalectomy have increased survival compared with untreated dogs. ANIMALS: Forty-eight dogs that underwent adrenalectomy for pheochromocytoma. METHODS: A retrospective medical record review for dogs that underwent adrenalectomy for pheochromocytoma at a veterinary medical teaching hospital over the period from January 1986 through December 2005. RESULTS: Twenty-three of 48 dogs were pretreated with PBZ (median dosage: 0.6 mg/kg PO q12h) for a median duration of 20 days before adrenalectomy. Duration of anesthesia and surgery, percentage of dogs with pheochromocytoma involving the right versus left adrenal gland, size of tumor, and presence of vascular invasion were similar for PBZ-treated and untreated dogs. Thirty-three (69%) of 48 dogs survived adrenalectomy in the perioperative period. PBZ-treated dogs had a significantly (P = .014) decreased mortality rate compared with untreated dogs (13 versus 48%, respectively). Additional significant prognostic factors for improved survival included younger age (P = .028), lack of intraoperative arrhythmias (P = .0075), and decreased surgical time (P = .0089). CONCLUSIONS AND CLINICAL IMPORTANCE: Results from this retrospective study support treatment with PBZ before surgical removal of pheochromocytoma in dogs.

Evaluation of a portocaval venograft and ameroid ring for the occlusion of intrahepatic portocaval shunts in dogs.

OBJECTIVE: To evaluate the use of a portocaval venograft and ameroid constrictor in the surgical management of intrahepatic portosystemic shunts (PSS). STUDY DESIGN: Prospective, clinical study. ANIMAL POPULATION: Ten client-owned dogs with intrahepatic PSS. METHODS: Portal pressure was measured after temporary suture occlusion of the intrahepatic PSS. In dogs with an increase in portal pressure greater than 8 mm Hg, a single extrahepatic portocaval shunt was created using a jugular vein. An ameroid ring was placed around the venograft and the intrahepatic PSS was attenuated. Transcolonic pertechnetate scintigraphy was performed before surgery, 5 days after surgery, and 8 to 10 weeks after surgery. Dogs with continued portosystemic shunting were evaluated further by laparotomy or portography. Clinical outcome and complications were recorded. RESULTS: Mean (+/- SD) portal pressure increased from 6 +/- 3 to 19 +/- 6 mm Hg with PSS occlusion; in all 10 dogs, the increase in portal pressure was greater than 8 mm Hg. There were no intraoperative complications, and, after creation of the portocaval shunt, the intrahepatic PSS could be completely ligated in 8 of 10 dogs. The final portal pressure was 9 +/- 4 mm Hg. Postoperative complications included coagulopathy and death (1 dog), ascites (3 dogs), and incisional discharge (3 dogs). Five of 8 dogs had continued portosystemic shunting at 8 to 10 weeks after surgery. Multiple extrahepatic PSS were demonstrated in 4 of these dogs. Clinical outcome was excellent in all 9 surviving dogs. CONCLUSIONS AND CLINICAL SIGNIFICANCE: The surgical technique resulted in a high incidence of multiple extrahepatic PSS. Short-term clinical results were promising, but long-term outcome must be evaluated further.

Periparturient and neonatal anesthesia.

Small animal patients may need to be anesthetized in the periparturient period for emergency, nonobstetric reasons, elective ovariohysterectomy, or cesarean section. In each case, the physiologic changes in the dam must be accounted for in designing an anesthetic protocol, but the requirements of the fetuses will be different. Subsequent to birth, the neonatal animal may need to be anesthetized, and the unique physiology and pharmacology at this age is described.

Neonatal critical care.

The first few minutes after a neonate's birth may determine the quality of its entire life. Immediate care includes prevention of hypothermia, clearing of nasal and oral passages, stimulation of ventilation and oxygenation, and, in a few cases, advanced life support. Any additional stress during the first weeks of life can also result in neonatal morbidity and mortality. Care of the diseased newborn must focus not only on treatment of the underlying disease but on aggressive supportive care. A safe, warm, clean, proper environment and adequate nutrition are essential.

Effects of xylazine hydrochloride during isoflurane-induced anesthesia in horses.

OBJECTIVE: To quantitate dose- and time-related anesthetic-sparing effects of xylazine hydrochloride (XYL) during isoflurane-induced anesthesia in horses and to characterize selected physiologic responses of anesthetized horses to administration of XYL. ANIMALS: 6 healthy adult horses. PROCEDURE: Horses were anesthetized 2 times to determine the minimum alveolar concentration (MAC) of isoflurane in O2 and to characterize the anesthetic-sparing effect (MAC reduction) after IV administration of XYL (0.5 and 1 mg/kg of body weight, random order). Selected measures of cardiopulmonary function, blood glucose concentrations, and urinary output also were measured during the anesthetic studies. RESULTS: Isoflurane MAC (mean +/- SEM) was reduced by 24.8 +/- 0.5 and 34.2 +/- 1.9% at 42 +/- 7 and 67 +/- 10 minutes, respectively, after administration of XYL at 0.5 and 1 mg/kg. Amount of MAC reduction by XYL was dose- and time-dependent. Overall, cardiovascular and respiratory values varied little among treatments. Administration of XYL increased blood glucose concentration; the magnitude of change was dose- and time-dependent. Urine volume increased but not significantly. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of XYL reduced the anesthetic requirement for isoflurane in horses. The magnitude of the decrease is dose- and time-dependent. Administration of XYL increases blood glucose concentration in anesthetized horses in a dose-related manner.

Opioid analgesics.

Opioids are useful and potent drugs for the management of pain in small animal patients. They have a wide therapeutic index and can be given by a number of different routes. Some of these techniques (e.g., epidural and intraarticular) allow for the production of profound analgesia in a localized area of the body while limiting the dose and the side effects, and others provide a noninvasive method for the delivery of continuous analgesia (e.g., transdermal administration).

Perioperative pain management.

The management of perioperative pain starts with the use of approaches to minimize anxiety and distress before the procedure. The administration of analgesics or local anesthetics before the start of surgery reduces the nociceptive input occurring during the procedure and reduces the need for postoperative analgesics. As the animal recovers from anesthesia, it is important to administer analgesics to minimize the patient's experience of pain and to continue this therapy through at least the first 12 to 24 hours. Techniques that provide a continuous level of analgesia are more effective than those that allow the pain to return.

Perioperative risk factors for puppies delivered by cesarean section in the United States and Canada.

The purpose of this study was to evaluate perioperative risk factors affecting neonatal survival after cesarean section. Data from 807 cesarean-derived litters (3,908 puppies) was submitted by 109 practices in the United States and Canada. Survival rates immediately, two hours, and seven days after delivery were 92% (n=3,127), 87% (n=2,951), and 80% (n=2,641), respectively, for puppies delivered by cesarean section (n=3,410) and were 86% (n=409), 83% (n=366), and 75% (n=283), respectively, for puppies born naturally (n=498). Maternal mortality rate was 1% (n=9). Of 776 surgeries, 453 (58%) were done on an emergency basis. The most common breed of dog was bulldog (n=138; 17%). The most common methods of inducing and maintaining anesthesia were administration of isoflurane for induction and maintenance (n=266; 34%) and administration of propofol for induction followed by administration of isoflurane for maintenance (n=237; 30%). A model of cesarean-derived puppies surviving to birth, between birth and two hours, and between two hours and seven days was designed to relate litter survival to perioperative factors. The following factors increased the likelihood of all puppies being alive: the surgery was not an emergency; the dam was not brachycephalic; there were four puppies or less in the litter; there were no naturally delivered or deformed puppies; all puppies breathed spontaneously at birth; at least one puppy vocalized spontaneously at birth; and neither methoxyflurane nor xylazine was used in the anesthetic protocol.

Systemic effects of topical and subconjunctival ophthalmic atropine in the horse.

OBJECTIVE: To identify any systemic effects of topical and subconjunctival administration of atropine sulfate in the horse. Animals studied Six mature grade horses were treated hourly in one eye with topical ophthalmic atropine drops for 24 h. Five horses were treated subconjunctivally in one eye with 3 mg of atropine sulfate. Procedures Pupillary light reflexes, pupil size, electrocardiographic parameters, girth measurements, intestinal motility, and clinical signs of abdominal pain were monitored. RESULTS: Alteration in auscultated gut motility and clinical signs of abdominal pain were the most sensitive indicators of the systemic manifestations of the topically applied atropine. Gut motility was absent in all horses for periods of 2-18 h in all four abdominal quadrants in horses given topically administered atropine. Signs of abdominal pain were observed in four of six horses that received topical atropine. In the subconjunctival test study, gut motility was absent in three horses for periods of 3-7 h. Uniocular subconjunctival injection of 3 mg atropine sulfate produced signs of abdominal pain in one of six horses. Conclusion The ophthalmic administration of atropine can affect gut motility and induce signs of colic in selected horses.

Modification and application of a Pelorus Mark III stereotactic system for CT-guided brain biopsy in 50 dogs.

The Pelorus Mark III Stereotactic System is a commercially available device for CT-guided stereotactic brain biopsy in people. With relatively minor modifications, this device was used to safely and accurately perform CT-guided stereotactic brain biopsies in 50 dogs with intracranial lesions. Modifications were necessary to accommodate a 90 degree shift in orientation of the canine head compared to the human head during the imaging phase of the procedure, and to facilitate other phases of the biopsy procedure that are affected by the uneven and variable topography of the canine skull. Description of a typical CT-guided brain biopsy procedure in dogs using the modified Pelorus Mark III Stereotactic System is provided. Accuracy of biopsy needle placement was determined by comparing the x, y and z coordinates of the biopsy target site with the actual coordinates of the needle tip on CT images. Mean needle placement error was 3.5 +/- 1.6 mm. Needle placement error was not significantly related to operator experience, dog size (body weight), or needle path length, however, needle placement error was significantly affected by lesion location.

Haemodynamic effects of ATP in dogs during hypoxia-induced pulmonary hypertension.

Pulmonary hypertension may result from an increase in vascular resistance caused by persistent hypoxia. We have investigated the effects of adenosine triphosphate (ATP), administered into the pulmonary artery, on haemodynamic changes occurring in anaesthetized adult dogs subjected to acute hypoxic pulmonary vasoconstriction. Hypoxia alone (ventilation with 10% O2/90% N2) caused significant increases in mean pulmonary arterial blood pressure (PAP), central venous pressure (CVP), and cardiac index (CI) by 71, 102 and 38%, respectively. ATP (0.03-3.0 micromol/kg/min approximately 0.02-1.65 mg/kg/min), when infused under hypoxic conditions, significantly reduced both mean PAP and systemic arterial blood pressure (ABP) in a dose-dependent manner. The maximum decrease in mean PAP amounted to 20%; mean ABP, on the other hand, was decreased by up to 52% (P<0.01). Heart rate, CI, CVP and pulmonary occlusion pressure were not dose-dependently affected by ATP. Our data indicate that while pulmonary arterial administration of ATP in mature dogs during hypoxic pulmonary hypertension causes dilation in the pulmonary vascular bed, it is even more effective in dilating the systemic vasculature. This result suggests a need for further evaluation and warrants cautious use of ATP in the treatment of hypoxic pulmonary hypertension in adult dogs.

Effects of intravenously administered glycopyrrolate in anesthetized horses.

The purpose of this study was to determine the heart rate (HR) and blood pressure (BP) effect of glycopyrrolate in anesthetized horses with low HR (< or = 30 beats/min). The horses were randomly treated with glycopyrrolate (2.5 micrograms/kg body weight (BW)) or saline, intravenously (i.v.) (n = 17). If HR failed to increase (by > 5 beats/min within 10 min), glycopyrrolate (same dose) was administered. Heart rate increased by > 5 beats/min in 3 out of 9 horses following the initial glycopyrrolate treatment. Overall changes in HR and mean BP were not significantly different, while systolic and diastolic BP increased significantly (P < 0.025 using a Bonferroni corrected paired t-test). On the 2nd treatment, 3 out of 7 horses given 2.5 micrograms/kg BW glycopyrrolate, and 4 out of 5 horses given 5.0 micrograms/kg BW (total dose) showed an increase in heart rate of > 5 beats/min, which was significant. A significant increase in BP was produced following treatment with 2.5 micrograms/kg BW, but not following 5.0 micrograms/kg BW. A final increase in HR, of > 5 beats/min, was associated with a significant rise in BP (P < 0.05 using an unpaired t-test). In conclusion, an increase in HR can occur with 2.5 to 5.0 micrograms of glycopyrrolate/kg BW, i.v., and results in improvement in BP in anesthetized horses.

Comparison of two techniques for total intravenous anesthesia in horses.

OBJECTIVE: To characterize responses associated with two 1-hour total intravenous anesthesia techniques in horses. ANIMALS: 6 mature, healthy mares. PROCEDURE: Each horse was anesthetized 3 times. Treatment order was determined by a series of Latin squares. After baseline measurements and instrumentation, horses were given xylazine (XYL) i.v.; anesthesia was induced 5 minutes later with 10% guaifenesin given i.v., then either ketamine (KET) or propofol (PRO) was given i.v. After anesthesia induction, each horse received an infusion of XYL and either KET or a low or high dose of PRO. Cardiopulmonary variables were measured at 20, 40, and 60 minutes after the start of the infusion; arterial blood samples were collected prior to each set of measurements, and blood gas tensions and plasma drug concentration were determined. A noxious stimulus was applied after each of the 3 sets of measurements. RESULTS: Differences in measured cardiopulmonary variables were significant among all treatments at different times. Most notable differences were between KET and high PRO. Times to regaining sternal and standing posture were shortest for KET, and differed significantly from values for low and high PRO. Purposeful responses were not observed for high PRO in horses after noxious stimulation. In contrast, 4 horses given KET responded at all time points and 1 horse given low PRO responded. CONCLUSION: None of the infusion techniques were flawless, but results support continued efforts at technique refinement and selected clinical use.

Perioperative management and mortality rates of dogs undergoing cesarean section in the United States and Canada.

OBJECTIVE: To describe dogs undergoing cesarean section in the United States and Canada, to determine perioperative management, and to calculate survival proportions. DESIGN: Multicenter prospective case series. ANIMALS: 3,908 puppies from 808 dams. RESULTS: Survival rates immediately, 2 hours, and 7 days after delivery were 92, 87, and 80%, respectively, for puppies delivered by cesarean section (n = 3,410) and 86, 83, and 75%, respectively, for puppies born naturally (498). For 614 of 807 (76%) litters, all puppies delivered by cesarean section were born alive. Maternal mortality rate was 1% (n = 9). Of 776 surgeries, 453 (58%) were done on an emergency basis. The most common breeds of dogs that underwent emergency surgery were Bulldog, Labrador Retriever, Boxer, Corgis, and Chihuahua. The most common breeds of dogs that underwent elective surgery were Bulldog, Labrador Retriever, Mastiff, Golden Retriever, and Yorkshire Terrier. The most common methods of inducing and maintaining anesthesia were administration of isoflurane for induction and maintenance (n = 266; 34%) and administration of propofol for induction followed by administration of isoflurane for maintenance (237; 30%). CLINICAL IMPLICATIONS: Mortality rates of dams and puppies undergoing cesarean section in the United States and Canada are low. Knowledge of mortality rates should be useful to veterinarians when advising clients on the likelihood of puppy and dam survival associated with cesarean section.

Cardiovascular effects of equipotent isoflurane and alfentanil/isoflurane minimum alveolar concentration multiple in cats.

OBJECTIVE: To determine whether administration of opioids to anesthetized cats induced less cardiovascular depression than that induced by an equivalent amount of anesthetic alone, and to measure endocrine responses to a noxious stimulus. ANIMALS: 6 healthy female cats. PROCEDURE: Anesthesia was induced with isoflurane and was maintained for 60 minutes at 1.3 isoflurane MAC. Blood gas tensions, pH, and plasma alfentanil and hormone concentrations, blood pressures, and cardiac output were measured. A noxious stimulus was applied for 5 minutes, while blood acquisition and measurements were repeated. Alfentanil was administered i.v. to achieve estimated plasma concentration of 500 ng/ml, and end-tidal isoflurane concentration was reduced by 35%. After another 60 minutes, blood was obtained and measurements were taken, then a second 5-minute noxious stimulus was applied while blood acquisition and measurements were retaken. RESULTS: Alfentanil administration and reduction of isoflurane concentration significantly increased body temperature, heart rate, mean arterial pressure, mean pulmonary arterial pressure, stroke index, cardiac index, hemoglobin, oxygen delivery index, PvO2 and PvCO2, dopamine, epinephrine (EPI), norepinephrine (NOREPI), and cortisol values, and significantly decreased arterial and venous pH. Application of a noxious stimulus significantly increased heart rate, stroke index, cardiac index, PaO2, oxygen delivery index, arterial and venous pH, and NOREPI values, and decreased bicarbonate, PaCO2, PvCO2, and EPI values. Alfentanil administration blunted cardiac index, PaCO2, oxygen delivery index, arterial pH, PaO2, and EPI, and NOREPI responses to a noxious stimulus. CONCLUSIONS: Compared with isoflurane alone, alfentanil administration and reduction of isoflurane MAC improved cardiovascular variables, and blunted respiratory, hormonal, and most hemodynamic responses to a noxious stimulus in cats. CLINICAL RELEVANCE: Use of the balanced opioid anesthesia regimen induced some beneficial effects in healthy cats; effects were similar to, although greater in nature, than effects induced by a noxious stimulus.

Effect of alfentanil on the minimum alveolar concentration of isoflurane in cats.

OBJECTIVE: To evaluate effect of incremental doses of alfentanil on isoflurane minimum alveolar concentration (MAC) in cats to determine whether alfentanil reduces isoflurane MAC and, if so, maximal isoflurane MAC reduction. ANIMALS: 6 healthy spayed female cats. PROCEDURE: Cats were anesthetized with isoflurane and instrumented to allow collection of arterial blood for measurement of gas tensions, pH, and plasma alfentanil concentration and to measure arterial blood pressure. Isoflurane MAC was determined in triplicate, and alfentanil was administered i.v., using a computer-driven syringe pump to achieve estimated plasma alfentanil concentrations of 50, 100, 250, 500, 750, and 1,000 ng/ml; isoflurane MAC was determined at each alfentanil concentration. Cats were allowed to recover, and the process was graded as poor, good, or excellent. RESULTS: Alfentanil had a significant dose effect on isoflurane MAC reduction. Significant regression was found for normalized isoflurane MAC versus estimated plasma alfentanil concentration. A quadratic term was necessary to fit the model and, using this curve, MAC reduction (35.0 +/- 6.6%) was estimated to be maximal at a plasma alfentanil concentration of 500 ng/ml. Significant differences were evident in rectal temperature, bicarbonate concentration, base deficit, arterial carbon dioxide and oxygen tensions, and arterial pH between isoflurane alone and some plasma alfentanil concentration and the corresponding reduction in isoflurane concentration. CONCLUSIONS: Infusion of alfentanil resulted in maximal MAC reduction midway between that reported for horses and dogs. At such plasma alfentanil concentration, adverse effects were minimal, but included increase in rectal temperature, metabolic acidosis, and decrease in PaO2. Provided cats were not handled during the recovery period, recovery was smooth and quiet. CLINICAL RELEVANCE: Infusion of alfentanil decreases the need for potent inhalant anesthetics in cats and could potentially be a clinically useful anesthetic regimen in sick cats.

Case-control study of the association between intraoperative administration of nafcillin and acute postoperative development of azotemia.

OBJECTIVE: To describe 7 cases of acute postoperative azotemia in dogs and to examine by use of a case-control study the possible association between this complication and administration of nafcillin. DESIGN: Retrospective and case-control study. ANIMALS: 7 case dogs and 28 matched control dogs. PROCEDURE: Cases of acute renal failure or acute renal insufficiency were identified by retrospective study of records of dogs treated between July 1, 1992, and Feb 28, 1995, and from information received from a practitioner. A random sample of records of dogs undergoing invasive procedures between Dec 1, 1992, and Nov 30, 1993, was examined to determine the prevalence of nafcillin use. Each case dog was matched with 4 control dogs, and data were subjected to logistic regression analysis, employing exact conditional inference on the parameter estimates. RESULTS: Case dogs were between 1 and 9 years old and weighed between 21 and 60 kg. Preoperatively, none of the dogs had a history of renal disease, and BUN concentrations, hematocrit, and plasma protein concentrations were within reference ranges. Postoperatively, each dog became azotemic and had clinical signs consistent with uremia. Hyponatremia was recorded in 6 case dogs. One dog did not respond to treatment and was euthanatized. Two dogs had persistent isosthenuria, and 4 dogs recovered. Nafcillin was used in approximately 502 of 2,184 (23%) dogs that underwent invasive procedures between Dec 1, 1992, and Nov 30, 1993. The use of nafcillin ceased on Nov 30, 1993, and no further cases were recorded in the following 15 months. In the case-control study, the only factor that was significantly associated with the occurrence of acute postoperative azotemia was administration of nafcillin. CLINICAL IMPLICATIONS: Intraoperative use of nafcillin maybe associated with development of acute postoperative azotemia in dogs.

Evaluation of propofol for general anesthesia in premedicated horses.

OBJECTIVE: To evaluate selected hemodynamic, respiratory, and behavioral responses to propofol in horses premedicated with xylazine or detomidine. DESIGN: Xylazine (0.5 and 1.0 mg/kg of body weight) was administered IV on different days to each of 6 horses prior to IV administration of propofol (2 mg/kg). In a second group of 6 horses, detomidine (15 and 30 micrograms/kg) was similarly studied. ANIMALS: 2 groups of 6 mature healthy horses. PROCEDURE: Rectal temperature, heart and respiratory rates, arterial blood gas tensions, and direct arterial blood pressures were recorded before and at fixed intervals after drug administration. Induction and recovery events were quantitatively and qualitatively assessed. Cardiopulmonary and behavioral data to follow were statistically analyzed (P < or = 0.05). RESULTS: Heart rate decreased in dose-dependent manner from a mean (+/- SD) of 39.5 +/- 5.1 beats/min after xylazine and detomidine. Second-degree atrioventricular dissociation was commonly seen at the higher drug doses. After propofol administration, heart rate either transiently increased or was less depressed early in recumbency, compared with predrug values. Direct arterial blood pressures varied inconsistently from predrug values. Mean arterial carbon dioxide tension tended to increase after drug administration (significance variable) from predrug values of 42 to 46 mm of Hg in both drug groups. After xylazine or detomidine administration, arterial oxygen tension decreased significantly from predrug values of 97 to 103 mm of Hg. The magnitude and duration of decrease was dose-dependent and greatest during recumbency. Behavioral responses to anesthetic induction were variable, but horses were uniformly calm and coordinated during recovery. Recumbency time increased in response to the higher dose of either premedicant drug. Mean (+/- SD) times to standing were 25.02 +/- 4.42 and 35.57 +/- 6.83 minutes for the low and high doses of xylazine, respectively and 41.04 +/- 11.21 and 52.64 +/- 14.67 minutes for the low and high doses of detomidine, respectively. CONCLUSION: Neither xylazine nor detomidine prevented excitation associated with propofol injection in horses. CLINICAL RELEVANCE: Xylazine or detomidine-propofol combinations likely will not replace common anesthetic induction techniques for horses. However, recovery characteristics associated with propofol encourage further study in horses.