Assessment of the respiratory actions of intramuscular morphine in conscious dogs.

The actions on the respiratory system of 0.25, 0.5 and 1.0 mg kg(-1) morphine given intramuscularly were studied in conscious dogs. Dogs breathed oxygen with 0, 2 and 4 per cent CO(2), in that order, through a mask attached to a flow sensor and connected to a respiratory mechanics monitor. When a steady state period of respiration was reached breathing pure oxygen, respiratory rate, tidal volume, respiratory minute volume, peak expiratory flow rate and end tidal CO(2)(PetCO(2)) were measured. The respiratory minute volume and PetCO(2) were measured when the dogs breathed 2 and 4 per cent CO(2) in oxygen, the points plotted onto a graph and the gradient of the line, describing the PCO(2)/ventilation response, plus the intercept with the y-axis were determined. Measurements for each morphine dose were taken before injection and at 30 minutes, 1, 2, 3, 4, 6 and 8 hours post injection. The incidence of panting after morphine was dose related and it occurred in all dogs given the high dose. Morphine reduced the gradients of the PCO(2)/ventilation response lines and raised the intercept. Other changes were increased respiratory minute volume and peak expiratory flow and decreased PetCO(2) and tidal volume.

Hypomagnesemia in 188 dogs: a hospital population-based prevalence study.

Magnesium is a divalent cation involved in more than 300 metabolic processes. Magnesium acts as an intracellular regulator of most energy-demanding pathways. Clinical investigation in the human medical field has determined risk factors for hypomagnesemia and its relationship to a number of disease processes. Experimental studies have established the effects of hypomagnesemia in dogs, but little is known of its prevalence, risk factors, or clinical associations in a hospital population of dogs. To study the prevalence, risk factors, and clinical associations of hypomagnesemia in dogs, a retrospective cross-sectional study of dogs admitted to the University of Minnesota Veterinary Teaching Hospital over a 2.5-year period was undertaken. The prevalence of hypomagnesemia in the study population was 6.1% (188 of 3,102 dogs). Using both categorical and continuous variables in a univariate analysis, significant associations with hypomagnesemia were identified and used to construct a multivariate analysis of the relative risk of hypomagnesemia. Results from evaluation of 3,102 dogs indicate that the most significant predictors of hypomagnesemia were albumin (P < or = .0001; odds ratio [OR] = 0.2), potassium (P < or = .0001; OR = 0.5), total CO2 (P < or = .05; OR = 0.9), and blood urea nitrogen concentrations (P < .0001; OR = 0.9), a diagnosis of cardiovascular disease (P < .02; OR = 1.9); and being a Collie (P < .02; OR = 3.9) or German Shepherd Dog (P < .002; OR = 2.2). These results can be used to better understand and predict hypomagnesemia in dogs.

Effect of inspired air heat and humidification on anesthetic-induced hypothermia in dogs.

Dogs were evaluated for efficacy of inspired air heating and humidification in maintenance of body temperature during general anesthesia. Three separate trials were conducted: (i) a control group without thermal support (n = 5), (ii) a group supported only by a heated humidifier device placed in the inspiratory limb of an anesthesia circle delivery system (n = 7), and (iii) a group supported by combination of inspired air humidification and recirculating water blanket (n = 7). A significant difference (P greater than 0.4) was not noticed in temperature changes between control and humidifier-supported groups. A significant advantage (P less than 0.05) was noticed between the combined support and the humidifier or control groups. Seemingly, during general anesthesia, use of combined thermal support is significantly better than airway humidification for maintenance of normothermia in the dog.

Effect of diazepam pretreatment on succinylcholine-induced muscle fasciculation in the dog.

The efficacy of diazepam in attenuation of succinylcholine-induced muscle fasciculations was studied in the dog. Dosage levels of 0.11, 0.22, 0.55, or 1.1 mg of diazepam/kg of body weight were studied in 4 groups of 5 dogs each; another group of 5 dogs served as a control. There was no difference in the occurrence or severity of succinylcholine-induced muscle fasciculations between dogs given diazepam and nontreated controls. Using serum potassium as a quantitative index of physiologic effects of muscle depolarization, differences could not be detected between treated and nontreated dogs.

Pressure-induced changes in fibular motor nerve conduction velocity and fibularis (peroneus) tertius muscle-evoked potentials in a goat model of the downer cow syndrome.

A study was conducted to determine the acceptable fibular motor nerve conduction velocity (NCV) in goats and to characterize pressure-induced changes in conduction velocity and muscle-evoked potentials (MEP). The acceptable motor NCV in the adult goat was determined to be 95.9 +/- 6.8 m/s. Limb compression in recumbent cows was modeled by application of external compression to the goat pelvic limb to increase IM pressure to a minimum of 50 mm of Hg. This pressure, when applied for a 6-hour period, caused a 30% to 100% reduction of fibular motor NCV and a 10% to 100% reduction of amplitude of MEP measured from fibularis (peroneus) tertius muscle. The reduction of motor NCV and MEP was associated with clinically evident limb dysfunction. The changes detected by the electrodiagnostic tests were proportional to the magnitude and duration of the locomotor deficits. The limb dysfunction was accompanied by muscular damage indicated by an increase of serum creatine kinase activity.

Cardiorespiratory and anesthetic effects of propofol and thiopental in dogs.

OBJECTIVE: To compare cardiorespiratory and anesthesia effects of IV administered propofol and thiopental in dogs. ANIMALS: 6 healthy mixed-breed dogs. PROCEDURE: Each dog was anesthetized with isoflurane, then a thermistor catheter was inserted in the pulmonary artery. After a minimum of 2.5 hours of recovery, a catheter was placed in a cephalic vein for administration of lactated Ringer's solution and drugs. Propofol (8 mg/kg of body weight) or thiopental (19.4 mg/kg) was administered to each dog in a randomized crossover design study. All dogs were intubated and allowed to breathe 100% oxygen spontaneously. Heart rate and rhythm; systolic, diastolic, and mean arterial blood pressures; respiratory rate; end-tidal carbon dioxide concentration; tidal volume; and reflexes (toe web pinch, palpebral response, and jaw tone) were measured before and every 2 minutes for the first 10 minutes, then at 15, 30, and 60 minutes after drug administration. Cardiac output was determined at 0, 2, 6, 10, 15, 30, and 60 minutes, and blood samples were collected at 0, 2, 10, and 30 minutes. Time to endotracheal extubation, head lift, and ability to sit sternally and walk unaided were recorded. RESULTS: 3 of 6 dogs in each group were apneic after drug administration. Reflexes were decreased similarly for both anesthetic agents, but were not completely lost. Time to sternal position and walking unaided were significantly shorter in response to propofol. CONCLUSION: Anesthesia was rapid; however, respiratory depression and apnea were major adverse effects associated with propofol and thiopental. Propofol has the advantage of inducing rapid, coordinated anesthesia recovery.

Effects of intramuscular or interpleural administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy.

OBJECTIVE: To evaluate effects of interpleural or IM administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy. DESIGN: Experimental trial. ANIMALS: 18 healthy dogs. PROCEDURE: Dogs underwent median sternotomy and were randomly assigned to groups of 6 dogs each. Group-A dogs were given morphine (1.0 mg/kg of body weight) i.m.; group-B dogs were given 0.5% bupivacaine (1.5 mg/kg) interpleurally; and group-C dogs were given morphine (1.0 mg/kg) interpleurally. Heart rate; systolic, diastolic, and mean arterial pressures; rectal temperature; pain score; and arterial blood gas partial pressures were measured and pulmonary function testing was performed immediately after extubation (time 0) and up to 48 hours later. Serum cortisol and morphine concentrations were measured at time 0 and up to 12 hours after surgery. RESULTS: There was a significant decrease in pH, PaO2, mean oxygen saturation of hemoglobin, and dynamic compliance; and a significant increase in PaCO2, alveolar-arterial difference in partial pressure of oxygen, pulmonary resistance, and work of breathing for dogs in all groups after surgery. Serum cortisol concentrations were significantly increased, compared with preoperative values, in all dogs. Serum cortisol concentrations were significantly higher in group-B dogs between 3 and 5 hours after surgery, compared with group-A dogs. CONCLUSIONS: Median sternotomy was associated with significant alterations in pulmonary function. Effects of interpleural administration of bupivacaine and morphine were similar to effects of i.m. administration of morphine.

Evaluation of the survival prediction index as a model of risk stratification for clinical research in dogs admitted to intensive care units at four locations.

OBJECTIVE: To prospectively evaluate a survival prediction index (SPI) in dogs admitted to intensive care units (ICU) and to generate and test an improved SPI (ie, SPI2). SAMPLE POPULATION: Medical records of 624 critically ill dogs admitted to an ICU. PROCEDURE: Data were collected from dogs within 24 hours after admission to an ICU. Variables recorded reflected function of vital organ systems, severity of underlying physiologic derangement, and extent of physiologic reserve; outcome was defined as dogs that survived or did not survive until 30 days after admission to the ICU. Probabilities of survival were calculated, using an established model (SPI). We then performed another logistic regression analysis, thereby reestimating the variables to create the new SPI2. Cross-validation of the models obtained was performed by randomly assigning the total sample of 624 dogs into an estimation group of 499 dogs and validation group of 125 dogs. RESULTS: Testing of SPI resulted in an area under the curve (AUC) of 0.723. Testing of SPI2 revealed an AUC of 0.773. A backwards-elimination procedure was used to create a model containing fewer variables, and variables were sequentially eliminated. The AUC for the reduced model of SPI2 was 0.76, indicating little loss in predictive accuracy. CONCLUSIONS AND CLINICAL RELEVANCE: The new SPI2 objectively stratified clinical patients into groups according to severity of disease. This index could provide an important tool for clinical research.

Evaluation of pulmonary function and analgesia in dogs after intercostal thoracotomy and use of morphine administered intramuscularly or intrapleurally and bupivacaine administered intrapleurally.

Eighteen dogs undergoing lateral thoracotomy at the left fifth intercostal space were randomly assigned to 1 of 3 postoperative analgesic treatment groups of 6 dogs each as follows: group A, morphine, 1.0 mg/kg of body weight, IM; group B, 0.5% bupivacaine, 1.5 mg/kg given interpleurally; and group C, morphine, 1.0 mg/kg given interpleurally. Heart rate, respiratory rate, arterial blood pressure, arterial blood gas tensions, alveolar-arterial oxygen differences, rectal temperature, pain score, and pulmonary mechanics were recorded hourly for the first 8 hours after surgery, and at postoperative hours 12, 24, and 48. These values were compared with preoperative (control) values for each dog. Serum morphine and cortisol concentrations were measured at 10, 20, and 30 minutes, hours 1 to 8, and 12 hours after treatment administration. All dogs had significant decreases in pHa, PaO2, and oxygen saturation of hemoglobin, and significant increases in PaCO2 and alveolar-arterial oxygen differences in the postoperative period, but these changes were less severe in group-B dogs. Decreases of 50% in lung compliance, and increases of 100 to 200% in work of breathing and of 185 to 383% in pulmonary resistance were observed in all dogs after surgery. Increases in work of breathing were lower, and returned to preoperative values earlier in group-B dogs. The inspiratory time-to-total respiratory time ratio was significantly higher in group-B dogs during postoperative hours 5 to 8, suggesting improved analgesia. Blood pressure was significantly lower in group-A dogs for the postoperative hour. Significant decreases in rectal temperature were observed in all dogs after surgery, and hypothermia was prolonged in dogs of groups A and C. Significant differences in pain score were not observed between treatment groups. Cortisol concentration was high in all dogs after anesthesia and surgery, and was significantly increased in group-B dogs at hours 4 and 8. Significant differences in serum morphine concentration between groups A and C were only observed 10 minutes after treatment administration. In general, significant differences in physiologic variables between groups A and C were not observed. Results of the study indicate that the anesthesia and thoracotomy are associated with significant alterations in pulmonary function and lung mechanics. Interpleurally administered bupivacaine appears to be associated with fewer blood gas alterations and earlier return to normal of certain pulmonary function values. Interpleural administration of morphine does not appear to provide any advantages, in terms of analgesia or pulmonary function, compared with its IM administration.

Neuropathy associated with diabetes mellitus in the cat.

Distal polyneuropathy was associated with diabetes mellitus in 7 cats. Clinical signs relative to the neuropathy included a plantigrade stance, depressed patellar reflexes, hindlimb weakness, and poor postural reactions. Electromyography demonstrated reduced conduction velocity in the sciatic and ulnar nerves in 3 cats. A total of 5 cats had abatement of clinical signs following insulin therapy and blood glucose regulation or after resolution of the diabetes mellitus.

Epidural administration of bupivacaine, morphine, or their combination for postoperative analgesia in dogs.

OBJECTIVE: To compare the analgesic effects of epidural administration of morphine (MOR), bupivacaine hydrochloride (BUP), their combination (COM), and 0.9% sterile NaCl solution (SAL) in dogs undergoing hind limb orthopedic surgeries. DESIGN: Blinded, randomized clinical trial. ANIMALS: 41 healthy dogs admitted for elective orthopedic surgeries involving the pelvis or hind limbs. PROCEDURE: Analgesic and control agents were administered postoperatively prior to recovery from isoflurane anesthesia. Ten dogs received MOR, 0.1 mg/kg of body weight; 10 received BUP, 0.5%, 1 ml/10-cm distance from the occipital protuberance to the lumbosacral space; 11 received COM; and 10 received SAL epidurally. Dogs were monitored for 24 hours after epidural injection for pain score, heart and respiratory rates, blood pressure, time to required administration of supplemental analgesic agent, total number of supplemental doses of analgesic agent required, and plasma concentrations of cortisol, MOR, and BUP. RESULTS: Pain scores were significantly lower in dogs in the COM and BUP groups than in dogs in the SAL group. Pain scores also were significantly lower in dogs in the COM group than in dogs in the MOR group. Time to required administration of supplemental analgesic agent was longer for dogs in the COM group than for dogs in the MOR and SAL groups. Total number of supplemental doses of analgesic agent required was lower for dogs in the BUP and COM groups than for dogs in the SAL group. CLINICAL IMPLICATIONS: Postoperative epidural administration of COM or BUP alone provides longer-lasting analgesia, compared with MOR or SAL.

Hepatic necrosis following halothane anesthesia in goats.

One goat anesthetized with thiamylal sodium, xylazine, and halothane for repair of an abominal hernia, and 7 of 29 goats similarly anesthetized for an experiment unrelated to considerations of anesthesia, developed signs of hepatic failure within 24 hours of anesthesia. Affected goats had high values for serum aspartate transaminase and serum total bilirubin by 12 to 24 hours after induction of anesthesia. Necropsy of the 8 affected goats revealed centrilobular to massive hepatic necrosis (8 of 8), brain lesions consistent with hepatic encephalopathy (3 of 4), and acute renal tubular necrosis (6 of 6). Two unaffected goats had no hepatic necrosis. Causes of hepatic necrosis other than those related to anesthesia (eg, infectious agents, toxins) were ruled out by lack of supporting necropsy findings or were considered unlikely because of lack of opportunity for exposure. Hepatic lesions in these goats closely resembled those described in human beings with halothane-associated hepatic injury, although in both species these lesions are nonspecific at the gross and light microscopic levels. The pathogenesis of halothane-associated hepatic injury in goats, as in human beings, remains to be determined.

Precautions when using opioid agonist-antagonist analgesics.

Agonist-antagonists are attractive because of their availability and absence of strict regulation. They do provide effective analgesia in many cases, and they are cost-effective. Incomplete analgesia can be noted in moderate to severe pain. Cardiopulmonary depression may be noted following agonist-antagonist administration. Interference with coadministered opiate agents may occur.

The case for qualitative anesthesia.

Qualitative anesthesia is an effective, time-honored, familiar, and simple technique for maintaining general anesthesia. There is no reason to change.

The case for routine fluid administration.

Because the risks associated with fluid administration are small, but the effects of fluid withdrawal during anesthesia can be significant, routine fluids should be considered in all cases in which general anesthesia exceeds 45 minutes.

Anesthesia for severe liver dysfunction.

By using these guidelines, we have safely anesthetized high-risk liver patients with minimal complications. By understanding the consequences of the underlying disease, prudent selection of agents that use alternate methods of excretion, careful perioperative support and management, and close observation during the postoperative period, the liver disease patient may be safely anesthetized with minimal complications.

Anesthetic management of thoracotomy.

Successful anesthesia for thoracic surgery requires an understanding of the clinical disease and the physiologic changes accompanying the disease, as well as anesthetic agents available for use. The authors discuss selection of appropriate anesthetic drugs, perioperative management considerations, pharmacologic support, intraoperative monitoring and postoperative pain management.