Xylazine given IV at doses of 0.5, 1.0, and 1.5 mg/kg to mares caused a significant (P less than 0.05) dose-related increase in serum glucose concentration and urine volume. Serum glucose concentrations as much as 150 mg/dl were recorded in mares after they were given the largest xylazine dose. The greatest urine volume, similar to changes in peak glucose concentration, always occurred during the first hour after dosing with xylazine and averaged 1.82, 3.93, and 5.68 ml/kg/hour after the 0.5-, 1.0-, and 1.5-mg/kg doses, respectively, were given. Urine osmolality and specific gravity were significantly (P less than 0.05) inversely related to urine volume. Although serum glucose concentrations were significantly increased above those measured after IV injection of saline solution, significant glucosuria was not detected.

Analgesia↗

PubMed1983

Accuracy of isoflurane delivery by halothane-specific vaporizers.

The precision of isoflurane delivery from 4 vaporizers designed and calibrated for halothane was studied. Isoflurane concentration in oxygen (O2) was determined for various vaporizer dial settings (0 to maximum) and O2 flow rates (0.375 to 15 L/min). The effects on vaporizer output of time (settings constant for up to 15 minutes), ambient temperature (15, 22, 30 C), and conditions simulating intermittent positive-pressure ventilation were also studied. The performance of the 4 halothane-specific vaporizers with isoflurane was qualitatively similar and was within the range expected as normal accuracy for halothane delivery in these same vaporizers. At room temperature, isoflurane concentrations were generally greater than dialed percentages with low carrier gas flows and were less than dialed percentages at higher gas flows for most vaporizers. The relationship of halothane output relative to isoflurane measured during similar conditions fits arithmetic coordinates well. Compared with concentrations of halothane, slightly higher concentrations of isoflurane were delivered from 3 halothane vaporizers studied (av 14%, 15%, and 8%). Temporal changes in delivered isoflurane concentration at room temperature were relatively small at low dial and carrier gas-flow rate settings. However, as gas-flow rate and vaporizer dial settings increased, vaporizer output decreased with time. Alterations in accuracy of isoflurane delivery by 1 vaporizer with temperature changes were most pronounced at the higher gas-flow rates, higher vaporizer dial settings, and lowest temperature. There was little effect of simulated positive-pressure breathing on vaporizer output at peak inspired circuit pressures less than 12 mm of Hg. Use of halothane-specific vaporizers to deliver isoflurane has advantages and disadvantages which must be evaluated individually. The delivery of isoflurane by halothane-specific vaporizers is not recommended by anesthetic and vaporizer manufacturers.

Anesthesia, Inhalation↗

PubMed1982

Evaluation of an isoflurane vaporizer: the Cyprane Fortec.

The delivery performance of two Fortec vaporizers for isoflurane in oxygen (O2) was evaluated. Isoflurane concentration was measured at a constant O2 flow rate (from 0.75 to 15 L/min) as the vaporizer dial setting was changed over the range of 0% to 5%. At vaporizer dial settings of 2% or less the average delivered isoflurane concentration differed from dial settings by less than 0.25 vol% at all O2 flows. At dial settings of 3% or greater delivered concentrations were greater than dial settings at O2 flows less than 4 L/min and at O2 flow greater than 4 L/min delivered were less than dialed concentrations. Time-related reductions in delivered concentrations were most evident at dial settings of 3% or greater and O2 flow rates greater than 6 L/min. Increasing the environmental temperature to 30 degrees C or decreasing it to 15 degrees C increased or decreased, respectively, vaporized output when compared with conditions at 22 degrees C. Little or no effect on vaporizer output was noted with simulated positive pressure ventilation up to a breathing circuit pressure of 25 torr. We conclude the Fortec vaporizer is as efficient in delivering isoflurane in O2 as previous reports have shown the Fluotec Mark III to be in its delivery of halothane.

Anesthesia, Inhalation↗

PubMed1980

Comparison of circulatory and respiratory effects of isoflurane and halothane anesthesia in horses.

Circulatory and respiratory effects of alveolar concentrations of 1.31, 1.97, and 2.62 vol% of isoflurane in oxygen were studied in eight young, healthy horses during spontaneous and controlled ventilation. These isoflurane concentrations were equivalent, respectively, to 1.0, 1.5, and 2.0 times the minimal alveolar concentration of isoflurane, which prevents movement in horses in response to a standard pain stimulus. Results of the isoflurane studies were compared with similarly derived findings in these same horses during equipotent halothane in oxygen anesthesia. Isoflurane, similar to halothane, produced a dose-related depression of cardiovascular function which was less severe during spontaneous ventilation and associated hypercapnia. The two anesthetic agents produced similar circulatory effects during controlled ventilation and constant arterial carbon dioxide tension except for a significantly (P less than 0.05) less depressed cardiac output/kg of body weight and stroke volume that occurred with minimal alveolar concentration 1.5 and 2.0 isoflurane. Total peripheral resistance was greatest when these horses were anesthetized with halothane regardless of the alveolar dose. In horses, isoflurane was, in general, no more depressing than was halothane to circulatory and respiratory function.

Anesthesia↗

PubMed1979

Halothane anesthesia in calves.

Because of the calf's popularity as an experimental animal and its often noted sensitivity to anesthetics and anesthesia, the potency of halothane was studied in eight, young (x = 5.85 weeks), healthy, male Holstein-Friesian calves. The minimal alveolar halothane-O2 concentration (MAC) which just prevented calf movement in response to a tail clamp was 0.76 +/- SEM 0.03 vol% and is less than predictions based on studies in man. The addition of 50% N2O to inspired gases decreased the halothane MAC to 0.59 +/- 0.03%. In the absence of common modifying factors of anesthesia, halothane-O2 caused cardiopulmonary depression in these calves in proportion to anesthetic dose. Only two (total protein and albumin) of 17 selected blood clinical biochemical values were significantly (P less than 0.05) altered from base line within seven days of anesthesia, indicating insults to major organ systems did not occur.

Anesthesia, Inhalation↗

PubMed1979

Minimal changes in blood cell counts and biochemical values associated with prolonged isoflurane anesthesia of horses.

The potential toxicity to horses of 7.33 +/- 0.87 SD minimal alveolar concentration hours of isoflurane anesthesia was evaluated by sequential determination of blood cell counts, electrolyte concentrations, and certain blood chemical values. Minimal or no serious toxicosis was observed for up to 7 days after anesthesia was terminated.

Anesthesia, Inhalation↗

PubMed1978

Potency of enflurane in dogs: comparison with halothane and isoflurane.

Circulatory and respiratory responses to graded increases in alveolar concentrations of enflurane were investigated in unpremedicated healthy dogs during conditions of spontaneous and controlled ventilation. The minimal alveolar concentration (MAC) of enflurane that prevented movement in response to a standard painful stimulus was determined for each dog and averaged 2.06 vol%. In these studies, enflurane produced cardiopulmonary depression in proportion to the alveolar dose. The average end-tidal enflurane concentration that produced at least 60 s of apnea was 5.29 vol% (ie, MAC 2.57). A comparison of these data with previous studies in dogs indicates that equipotent concentrations of enflurane are at least as depressant to the cardiopulmonary system as halothane and isoflurane.

Anesthesia, Inhalation↗

PubMed1978

Cardiovascular effects of halothane in the horse.

Cardiovascular effects of venous alveolar concentrations of halothane in oxygen were studied in 8 young, healthy horses under conditions of constant arterial carbon dioxide tension. The alveolar concentration of halothane was expressed as a multiple of the minimal alveolar concentration (MAC) which was known for each animal. Increasing alveolar halothane concentrations to MAC 2.0 resulted in a progressive and significant (P less than 0.05) decline in systemic arterial pressure and left ventricular work. Cardiac output decreased between MAC 1.0 and MAC 2.0 as a result of a significant (P less than 0.05) decrease in stroke volume. Heart rate, total peripheral resistance, pulmonary artery pressure, hematocrit, plasma protein concentration, arterial oxygen tension, and arterial pH remained constant over the same range of anesthetic dosages. Continuation of anesthesia, spontaneous ventilation, and the accompanying rise in arterial carbon dioxide tension and electrical stimulation of the horse's oral mucous membranes produced varying degrees of stimulation of cardiovascular function at MAC 1.5.

Anesthesia, Inhalation↗

PubMed1978

Potency of halothane-N20 in the horse.

The minimal alveolar concentration (MAC) of halothane which just prevented purposeful movement in response to electrical stimulation was determined in 11 young, healthy, unpremedicated horses breathing oxygen (O2) or nitrous oxide (N2O) and O2. Ventilation was controlled during these MAC studies. The arterial PO2 was always greater than 90 mm of Hg and the average PaCO2. range was 36 to 40 mm of Hg. The MAC for halothane in O2 was 0.93 vol %. Alveolar N2O concentrations of 25% and 50% reduced the halothane MAC about 12% and 25%, respectively. In 8 of these horses, the cardiovascular effects of halothane-50% N2O-balance O2 (H50N2O) were determined during spontaneous and controlled ventilation and were compared with previously reported results of halothane-O2 studies. Similar to halothane-O2 anesthesia, increasing dosages of H50N2O caused a decrease in cardiovascular function. With the exception of N2O-associated increase in cardiac output and left ventricular work at MAC 1.0 and 1.5, little difference was seen between the 2 forms of general anesthesia during controlled ventilation. However, when H50N20 was administered to spontaneously breathing horses, most indices of cardiovascular function were depressed less than with a similarly administered equipotent level (MAC 1.5) of halothane-O2 anesthesia.

Anesthesia, Inhalation↗

PubMed1977

Meperidine-halothane interaction in dogs.

We studied the interaction of meperidine and halothane in 24 unmedicated, spontaneously breathing dogs. Intramuscular (i.m.) injections of meperidine, 2.75 mg/kg, 5.5 mg/kg and 11.0 mg/kg reduced the minimal alveolar concentration (MAC) of halothane required for anaesthesia. The magnitude and duration of MAC depression were dose related. Plasma meperidine concentrations following an i.m. injection of 2.75 mg/kg were lower in the awake, unsedated dogs than in the dogs anaesthetized with halothane.

Anesthesia↗

PubMed1977

Rate of change of halothane concentration in a large animal circle anesthetic system.

The slow rate of change of inspired halothane concentration which results in a conventional large animal circle anesthetic delivery system when low carrier gas flow rates are used was confirmed, using a model system. To obtain a 63% change in inspired halothane concentration in the 32-L large animal circle anesthetic machine at fresh gas inflow rates of 3, 6, and 12 L/minute required 10.7, 5.3, and 2.7 minutes, respectively. At a given inflow rate, increasing the rebreathing bag size from 20 to 40 L prolonged the time for equilibration between the gas flowing into the anesthetic circuit and the inspired gas. The extent to which an adult horse further slowed the rate of rise of inspired anesthetic concentration was also demonstrated.

Anesthesia, Inhalation↗

PubMed1977

Enflurane, halothane, and isoflurane potency in horses.

The minimal alveolar concentration of anesthetic required to prevent gross purposeful movement in response to electrical stimulation of oral mucous membranes was determined in horses for 3 agents. Equipotent concentrations of enflurane were 2.12 volumes %; of halothane, 0.88 volumes %; and of isoflurane, 1.31 volumes +. The alveolar concentration required to produce at least 60 seconds of apnea was also determined for these agents. From these data and the minimal alveolar concentration information, anesthetic indices were determined for each agent. The indices for enflurane, halothane, and isoflurane were 2.26, 2.60, and 2.33, respectively.

Anesthesia, Inhalation↗