Starling forces and hemodynamics in the digits of 5 horses were studied during early laminitis induced by oral administration of an aqueous extract of black walnut (Juglans nigra). The black walnut extract was prepared from heartwood shavings and was administered by nasogastric tube. Heart and respiratory rates, rectal temperature, central venous and arterial pressures, digital pulses, and signs of lameness were monitored. Blood samples were collected for determination of WBC count, hemoglobin concentration, and PCV and for endotoxin and tumor necrosis factor assays. Total WBC count and central venous pressure were monitored until they decreased by 30 or 20%, respectively. These decreases in WBC count and central venous pressure were observed 2 to 3 hours after dosing with black walnut extract. Respiratory and heart rates, body temperature, systolic and diastolic blood pressures, PCV, and hemoglobin concentration did not change significantly. Anesthesia was induced, heparin (500 IU/kg of body weight) was administered IV, and a pump-perfused extracorporeal digital preparation was established. Digital arterial and venous pressures were maintained at 100 and 30 mm of Hg, respectively. Blood flow, capillary pressure, lymph and plasma protein concentrations, and weight of the isolated digit during rapid increase in venous pressure were measured. Isogravimetric capillary filtration coefficient, vascular compliance, vascular and tissue oncotic pressures, tissue pressure, osmotic reflection coefficient, and precapillary and postcapillary resistances were calculated. Mean digital blood flow was 14 ml/min/100 g, capillary pressure was 52 mm of Hg, and vascular compliance was 0.06 ml/mm of Hg. The vascular and tissue oncotic pressures were 21.49 and 4.93 mm of Hg, respectively. The osmotic reflection coefficient was 0.71, and tissue pressure was 41 mm of Hg. The precapillary and postcapillary resistances were 7 and 2 mm of Hg/ml, respectively. Capillary permeability to proteins was not significantly different from that previously measured in healthy horses, suggesting that the increased capillary filtration coefficient reflected increased capillary hydrostatic pressure and perfusion of previously nonperfused capillaries. Neither endotoxin nor serum tumor necrosis factor activity was detected in any samples. The hemodynamic and Starling forces observed in this study were similar to those observed after laminitis was induced by administration of a carbohydrate gruel. Significant differences between the 2 models were detected for total vascular resistance, postcapillary resistance, and capillary filtration coefficient. It is likely that these differences were identified because the horses administered the black walnut extract were at an earlier stage in the disease process. The findings of this study suggest that the increase in capillary pressure causes transvascular fluid movement, resulting in increased tissue pressure and edema. We hypothesize that further increases in tissue pressure may collapse capillary beds and lead to tissue ischemia.

Health and ruminal variables were intensively measured during adaptation to grain-based diets in 6 beef cattle with fistulated rumens. The cows had been maintained on prairie grass hay-supplemented diets, and were converted to a grain-based finishing ration by feeding each successive diet (diets 1-4, respectively) for a period of 7 days. Each cow was evaluated and samples were obtained 3 times each day for the first 5 days that each diet was fed. Health variables monitored were rectal temperature, pulse, respiratory and rumen motility rates, fecal consistency, demeanor, blood pH, and blood glucose and L(+) lactate concentrations. Ruminal variables monitored were pH and glucose, DL-lactate, and volatile fatty acid concentrations of rumen contents. Data were analyzed by use of a multivariate ANOVA. We determined that most of the health variables were within reference rang limits throughout the adaptation period; however, analysis of pulse and respiratory rates indicated that diets 2 and 4 were stressful. Although blood pH continually decreased during feeding of the 4 diets (7.38 to 7.30), blood L(+) lactate and glucose concentrations had large increases only within diet 4. The pH of ruminal contents decreased progressively from 6.8 to 5.3. Rumen glucose concentration was low (< 1 micromole/ml), except with diet 4 in which values were 8 times higher than for other diets. By the end of the study, the ruminal contents of all animals were acidic (pH < 5.5), and, on the basis of higher than background amounts of ruminal glucose and DL-lactate, it was determined that rumen microbial equilibrium had not yet been achieved. Analysis of results of this study suggested that ruminal imbalance could be evaluated by monitoring pulse and respiratory rates, blood pH, and blood glucose concentrations. Assessment of the rumen alone could be accomplished by monitoring the variables of rumen pH, rumen glucose, and DL-lactate concentrations. Respiratory rate, blood and rumen content pH, and blood L(+) lactate concentrations were significantly (P < 0.001) affected by time after feeding.

Medetomidine, an investigational drug indicated for clinical use as a short-term chemical restraint in dogs, was evaluated for its cardiopulmonary effects, in 10 naturally heartworm-infected (HW+) and 10 noninfected (HW-) Beagles. The drug was randomly administered IV (30 microgram/kg of body weight) and IM (40 microgram/kg) in single injections to all dogs. Heart rate, respiratory rate, ECG, blood gas tensions, blood pH, central venous and arterial pressures were measured at 0, 15, 30, 60, 90, 120, and 180 minutes. Medetomidine induced an immediate significant (P less than or equal to 0.001) increase in mean arterial blood pressure followed by decreased blood pressure that remained below normal throughout the study in both groups, irrespective of route of administration. Medetomidine increased central venous pressure, over time, for both groups and both routes of administration. Heart and respiratory rates were significantly (P less than or equal 0.001) decreased after medetomidine administration and remained reduced for the duration of the study in all dogs. The ECG variables were not significantly different between groups or between routes of administration. The HW+ dogs tended to have higher mean PaO2 than did HW- dogs at several postinjection determination times, particularly when the drug was administered IM. The PaO2 decreased during the first 30 minutes in both groups and tended to increase gradually thereafter. The pH decreased over time for both groups and both routes. A significant (P less than or equal to 0.05) decrease in pH was seen in the HW- dogs, compared with HW+ dogs at each measuring time for both routes. The PaCO2 did not significantly change for groups or routes. In general, bradycardia was the predominant cardiovascular effect seen after medetomidine administration in all dogs, irrespective of route. Lowering of blood pressure and heart rate (after a transient blood pressure increase) was synchronized with sedation in these dogs. The overall clinical response with regard to cardiopulmonary effects in HW+ dogs was similar to that in HW- dogs.

To study behavioral and cardiopulmonary characteristics of horses recovering from inhalation anesthesia, 6 nonmedicated horses were anesthetized under laboratory conditions on 3 different days, with either halothane or isoflurane in O2. Anesthesia was maintained at constant dose (1.5 times the minimum alveolar concentration [MAC]) of halothane in O2 for 1 hour (H1), halothane in O2 for 3 hours (H3), or isoflurane in O2 for 3 hours (13). The order of exposure was set up as a pair of Latin squares to account for horse and trial effects. Circulatory (arterial blood pressure and heart rate) and respiratory (frequency, PaCO2, PaO, pHa) variables were monitored during anesthesia and for as long as possible during the recovery period. End-tidal percentage of the inhaled agent was measured every 15 seconds by automated mass spectrometry, then by hand-sampling after horses started moving. Times of recovery events, including movement of the eyelids, ears, head, and limbs, head lift, chewing, swallowing, first sternal posture and stand attempts, and the number of sternal posture and stand attempts, were recorded. The washout curve or the ET ratio (end-tidal percentage of the inhaled agent at time t to end-tidal percentage of the inhaled agent at the time the anesthesia circuit was disconnected from the tracheal tube) plotted against time was similar for HI and H3. The slower, then faster (compared with halothane groups) washout curve of isoflurane was explainable by changes in respiratory frequency as horses awakened and by lower blood/gas solubility of isoflurane. The respiratory depressant effects of isoflurane were marked and were more progressive than those for halothane at the same 1.5 MAC dose. During the first 15 minutes of recovery, respiratory frequency for group-13 horses increased significantly (P < 0.05), compared with that for the halothane groups. For all groups, arterial blood pressure increased throughout the early recovery period and heart rate remained constant. Preanesthesia temperament of horses and the inhalation agent used did not influence the time of the early recovery events (movement of eyelids, ears, head, and limbs), except for head lift. For events that occurred at anesthetic end-tidal percentage < 0.20, or when horses were awake, temperament was the only factor that significantly influenced the nature of the recovery (chewing P = 0.04, extubation P = 0.001, first stand attempt P = 0.008, and standing P = 0.005). The quality of the recoveries did not differ significantly among groups (H1, H3, I3) or horses; however 5 of 6 horses recovering from the H1 exposure had ideal recovery. During recovery, the anesthetic end-tidal percentage did not differ significantly among groups. However, when concentrations were compared on the basis of anesthetic potency (ie, MAC multiple) a significantly (P < 0.05) lower MAC multiple of isoflurane was measured for the events ear movement, limb movement, head lift, and first attempt to sternal posture, compared with that for horses given halothane, indicating that isoflurane may be a more-potent sedative than halothane in these horses.

Few safe and effective anesthesia regimens have been described for use in rabbits, partially because of the susceptibility of this species to sometimes fatal respiratory depression. Although inhalant anesthetics are generally safer than injectable anesthetics, their use may be limited by lack of equipment or facilities. This study was conducted to compare effects of several injectable anesthetics in rabbits on response to noxious stimuli, heart rate, respiratory rate, and rectal temperature. Six injectable anesthetic combinations were administered to rabbits: xylazine-ethyl-(l-methyl-propyl) malonyl-thio-urea salt (EMTU), ketamine-EMTU, xylazine-pentobarbital, xylazine-acepromazine-ketamine (XAK), ketamine-chloral hydrate, and ketamine-xylazine. All combinations induced a depression of respiratory rate. Although rectal temperature values were reduced to some degree in each group, the most profound hypothermia was induced by XAK. The combination that induced the longest duration of anesthesia was XAK. It was concluded that XAK was preferable for longer periods of anesthesia (60 to 120 minutes), although it induces severe hypothermia. For short periods of anesthesia, xylazine-pentobarbital, xylazine-EMTU, or ketamine-xylazine were deemed adequate; however, xylazine-EMTU induced the best survivability and consistency.

The cardiopulmonary effects of 4 positions (standing, right lateral, left lateral, and dorsal recumbency) were evaluated in conscious cattle in which no sedatives or anesthetic drugs were given. Each position was maintained for 30 minutes, during which time there were no significant changes in heart rate, respiratory rate, mean arterial blood pressure, arterial pH, PaCO2, arterial base excess, or venous blood gas values. Significant decreases in PaO2 developed when cattle were in lateral positions and dorsal recumbency. Cardiac index was unchanged in all positions, except in dorsal recumbency at 30 minutes, when it was significantly decreased.

A technique for measuring upper airway resistance was developed in awake untrained dolichocephalic and mesaticephalic dogs. Twenty healthy dogs, 10 Collies (group dolichocehalic) and 10 mixed-breed dogs (group B-mesaticephalic), were studied. All dogs tolerated the procedure well and adverse effects were not observed. Mean (+/- SEM) value for upper airway resistance was 7.1 +/- 0.50 cm of H2O/L/s. There was a trend toward lower upper airway resistance (Ruaw) values in group-A dogs, compared with those in group-B dogs. Values of Ruaw were reproducible for an individual dog. The mean individual dog coefficient of variation for Ruaw was 7.5%. The overall Ruaw coefficient of variation for all 20 dogs was 31.4%. This technique for measuring upper airway resistance in dogs is clinically applicable for objectively assessing response to treatment of obstructive upper airway disorders.

The minimum anesthetic dose (MAD) and the cardiopulmonary dose-response for halothane were determined in male chickens. The MAD for halothane was 0.85 +/- 0.09% (mean +/- SD), with a range of 0.75% to 0.98%. There was a significant (P less than 0.002) positive correlation between increasing concentrations of halothane and PaCO2, and significant negative correlations of halothane concentration with respiratory rate (P less than 0.04), arterial blood pH (P less than 0.008), and mean arterial blood pressure P less than 0.008). A significant correlation was not found between halothane concentration and heart rate or arterial blood bicarbonate concentration. It was concluded that the MAD for halothane in chickens is similar to values for minimum alveolar concentrations of halothane in mammalian species, and that there is substanial dose-dependent depression of cardiopulmonary function in chickens.

The effects of 3 commonly used dosages (0.3, 0.5, and 1.1 mg/kg of body weight, IV) of xylazine on ventilatory function were evaluated in 6 Thoroughbred geldings. Altered respiratory patterns developed with all doses of xylazine, and horses had apneic periods lasting 7 to 70 seconds at the 1.1 mg/kg dosage. Respiratory rate, minute volume, and partial pressure of oxygen in arterial blood (PaO2) decreased significantly (P < 0.001) with time after administration of xylazine, but significant differences were not detected among dosages. After an initial insignificant decrease at 1 minute after injection, tidal volume progressively increased and at 5 minutes after injection, tidal volume was significantly (P < 0.01) greater than values obtained before injection. Partial pressure of carbon dioxide in arterial blood (PaCO2) was insignificantly increased. After administration of xylazine at a dosage of 1.1 mg/kg, the mean maximal decrease in PaO2 was 28.2 +/- 8.7 mm of Hg and 22.2 +/- 4.9 mm of Hg, measured with and without a respiratory mask, respectively. Similarly, the mean maximal increase in PaCO2 was 4.5 +/- 2.3 mm of Hg and 4.2 +/- 2.4 mm of Hg, measured with and without the respiratory mask, respectively. Significant interaction between use of mask and time was not detected, although the changes in PaO2 were slightly attenuated when horses were not masked. The temporal effects of xylazine on ventilatory function in horses should be considered in selecting a sedative when ventilation is inadequate or when pulmonary function testing is to be performed.

The cardiopulmonary effects of 2 planes of halothane anesthesia (halothane end-tidal concentrations of 1.78% [light anesthesia] and 2.75% [deep anesthesia]) and 2 ventilatory modes (spontaneous ventilation [SV] or mechanically controlled ventilation [CV]) were studied in 8 cats. Anesthesia was induced and maintained with halothane in O2 only, and each cat was administered each treatment according to a Latin square design. Cardiac output, arterial blood pressure, pulmonary arterial pressure, heart rate, respiratory frequency, and PaO2, PaCO2, and pH were measured during each treatment. Stroke volume, cardiac index, and total peripheral resistance were calculated. A probability value of less than 5% was accepted as significant. In the cats, cardiac output, cardiac index, and stroke volume were reduced by deep anesthesia and CV, although only the reduction attributable to CV was significant. Systemic arterial pressure was significantly reduced by use of deep anesthesia and CV. Respiratory frequency was significantly lower during CV than during SV. Arterial P(O2) was significantly decreased at the deeper plane of anesthesia, compared with the lighter plane. At the deeper plane of anesthesia, arterial P(CO2) and pulmonary arterial pressure were significantly lower during CV than during SV. The deeper plane of halothane anesthesia depressed cardiopulmonary function in these cats, resulting in hypotension and considerable hypercapnia. Compared with SV, CV significantly reduced circulatory variables and should be used with care in cats. Arterial blood pressure was judged to be more useful for assessing anesthetic depth than was heart rate or respiratory frequency.