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The purpose of this study was to evaluate selected physiological and behavioral responses to xylazine (XYL)–butorphanol (BUTOR) supplemented propofol (PROP) anesthesia in horses and the influence of BUTOR dose on outcome. Eight horses [13 ± 2 (mean ± SE) year], weighing 524 ± 9 kg were anesthetized three times with at least 3 weeks between each anesthesia. After collecting pre-drug data, horses were always medicated with 0.5 mg kg[sup -1] XYL IV. Five minutes later, BUTOR was administered IV according to a randomized order of three doses: 0.025, 0.05, and 0.075 mg kg[sup -1] ; all horses received the complete dose set. Five minutes after BUTOR, anesthesia was induced with PROP, 2 mg kg[sup -1] IV. The resultant data were grouped by treatment and parameter and analyzed by RM anova; p < 0.05 considered significant. The pre-drug values within a treatment group were not significantly different. The combined pre-drug values were heart rate (HR) = 32 ± 1 beats minute[sup -1] , respiratory frequency (f ) = 11 ± 1 breaths minute[sup -1] , PaO[sub 2] = 66.6 ± 1.5 mm Hg (Mexico City is 2240 m above sea level; yearly average P[sub BAR] = 582 mm Hg), PaCO[sub 2] = 36.2 ± 0.7 mm Hg and pH[sub a] = 7.42 ± 0.01. During 20 minutes of anesthesia HR, f and PaCO[sub 2] were not significantly different from pre-drug values. The PaO[sub 2] decreased by an average of 12 mm Hg during anesthesia but returned to the pre-drug values within 15 minutes after the horses stood. The quality of anesthetic induction varied and brief paddling limb movements occurred occasionally after recumbency regardless BUTOR dose. Recovery from anesthesia was subjectively graded good to excellent. The BUTOR dose did not significantly influence recumbency time (33 ± 2 minutes for all studies). The BUTOR dose did not markedly influence study results. However, some physiological effects likely were confounded by the notably low PaO[sub 2] that was influenced... [ABSTRACT FROM AUTHOR]

Aims to quantify changes in ventilation as a function of isoflurane (ISO) dose in the horse. Research methodology; Magnitude of respiratory depression in equidae anesthesized with ISO; Respiratory rate; Tidal volume.

The purpose of this study was to characterize urine flow and biochemical parameters in horses given xylazine (XYL) and anesthetized with ketamine and isoflurane. Nine mares [9 ± 2 (mean ± SE) years; 492 ± 17 kg] were studied. They were anesthetized for 2 hours in support of a campus-approved, laboratory-based orthopedic study. The day prior to anesthesia, a venous blood sample was obtained for biochemical analysis from each unmedicated mare. The urinary bladder was catheterized and emptied, and urine collected over the next three hours to quantitate the pre-drug values. The next day the mares were similarly catheterized. After obtaining urine and venous blood samples, XYL (1.1 mg kg[sup -1] IV) was administered. Anesthesia was induced 5 minutes later with ketamine (2.2 mg kg[sup -1] IV) and diazepam (0.04 mg kg[sup -1] IV) and maintained with isoflurane in O[sub 2] . Lactated Ringer's solution (10 mL kg[sup -1] hours[sup -1] ) was administered IV and dobutamine infused as required to maintain mean arterial blood pressure between 70 and 80 mm Hg. Mechanical ventilation maintained PaCO[sub 2] between 48 and 52 mm Hg and PaO[sub 2] > 200 mm Hg. Blood and urine were collected at 30, 60, and 120 minutes during anesthesia, and at 1 hour postanesthesia. Data were analyzed with RM anova; with p < 0.05. Control urine flow was 0.92 ± 0.17 mL kg[sup -1] hour[sup -1] . Urine flow was significantly increased at 30 and 60 minutes following XYL (2.14 ± 0.59 and 2.86 ± 0.97 mL kg[sup -1] hour[sup -1] , respectively), but returned to control levels by the end of anesthesia. The most notable biochemical change was an initial significant increase in serum glucose from 121 ± 4 to 167 ± 8 mg dL[sup -1] at 30 minutes post-XYL that was not accompanied by a significant glucosuria (control value 4 ± 1 mg dL[sup -1] ). We conclude that urine output increases in anesthetized horses following XYL, but this increase is not as a result of glucosuria. [ABSTRACT FROM AUTHOR]

Alpha-2 agonists cause transient dose-related increase in urine flow in normal horses. Although important clinically, effects of these drugs in dehydrated animals are not known. The purpose of this study was to describe the influence of xylazine (XYL) and detomidine (DET) on urine flow in mares deprived of food and water for 24 hours. Six clinically normal mares [12.5 ± 3.3 (mean ± SE) years] weighing 471 ± 23 kg were each studied four times; each study was separated by at least 7 days. The morning following fasting, the urinary bladder was catheterized (Foley) and emptied. Urine was then collected for 2 hours and a composite urine sample along with a sample of jugular venous blood provided baseline values. Shortly after emptying the bladder, saline, 0.5 or 1.0 mg kg[sup -1] XYL or 0.03 mg kg[sup -1] DET was injected IV (treatment randomly assigned) and urine and blood samples obtained over the next 2 hours. Data were analyzed by RM anova followed by Dunnett's test for pairwise comparisons p < 0.05; indicated by (S). Pretreatment urine flow was 0.30 ± 0.03 mL kg[sup -1] hour[sup -1] , urine specific gravity (SG) was 1.032 ± 0.001, packed cell volume (PCV) was 37.8 ± 1.0%, and total plasma solids (TP) was 6.85 ± 0.12 g dL[sup -1] ; values for four treatment periods within a grouping did not differ. At 1 hour post-treatment, urine flow (mL kg[sup -1] hour[sup -1] ) was 0.31 ± 0.04, 1.09 ± 0.48, 2.33 ± 0.89[sup (S)] , and 2.14 ± 0.58 [sup (S)] for saline, 0.5 XYL, 1.0 XYL and DET, respectively. By 2 hours, urine flow was at or returning to baseline with all treatments except DET where a further increase was noted (8.28 ± 0.92[sup (S)] ). A time related decrease in urine specific gravity (e.g. 1.010–1.021 at 1 hour post-treatment) was associated with the increase in urine flow but PCV and TP did not change significantly with time or treatment. These data indicate that XYL and DET cause an important... [ABSTRACT FROM AUTHOR]

Minimum alveolar concentration (MAC) of an inhalant is an indicator of its anesthetic potency. Individuals vary in their sensitivity to anesthetic agents as demonstrated by different individual MAC values. We hypothesized that individual animal sensitivity would be maintained with different inhalant anesthetics. As part of separate studies, six female DSH cats, aged 24 ± 2.5 (mean ± SD) months and weighing 3.5 ± 0.3 kg, were studied similarly on three separate occasions over a 12-month period to determine the MAC of isoflurane (ISO), sevoflurane (SEVO), and desflurane (DES), respectively. In each study, chamber induction was followed by orotracheal intubation, and anesthesia was maintained via a nonrebreathing circuit. ECG, pulse oximetry, Doppler systolic blood pressure, end-tidal gases, and esophageal temperature were monitored. End-tidal gases were hand-sampled from a catheter whose tip lay level with the distal end of the ET tube. Gases were analyzed by Raman spectrometry and, for each agent, the analyzer was calibrated with at least three gas standards. MAC was determined in triplicate using standard tail-clamp technique. Data were analyzed by two-way anova followed by Tukey's test and significant differences were found. Average MACs (%) for ISO, SEVO, and DES were 1.90 ± 0.18, 3.41 ± 0.65, and 10.27 ± 1.06, respectively. Body temperatures, Doppler systolic blood pressure, and SpO2 were recorded at the time of MAC determinations for ISO, SEVO, and DES were 38.3 ± 0.3, 38.6 ± 0.1, 38.3 ± 0.35 °C; 71 ± 8, 75 ± 16, 88 ± 12 mm Hg; 99 ± 1, 99 ± 1, 99 ± 1%, respectively. Both the anesthetic agent and the individual cat had significant effects on MAC (p = 0.0001 and 0.0185, respectively). MAC varied between individuals and cats were consistent in their order of sensitivity to inhalant anesthetics across the three agents. Within this group of cats, the relationship of individual MAC to the group MAC for each of the three inhalant agents was maintained. This suggests that any individual may be consistently more or less sensitive to a variety of inhalant agents. [ABSTRACT FROM AUTHOR]

Isoflurane (ISO) is the most commonly administered feline inhalant anesthetic in North America. A newer agent, sevoflurane (SEVO), may provide faster induction and recovery from anesthesia based on its physical characteristics. Accordingly, we compared some induction and recovery characteristics of ISO and SEVO in healthy cats. Six female DSH cats (17.9 ± 9.0 (mean ± SD) months, 3.7 ± 0.3 kg) received four randomly assigned treatments: ISO for 1 hour (IS), SEVO for 1 hour (SS), ISO for 5 hours (IL), and SEVO for 5 hours (SL). Anesthesia was induced in a chamber into which ISO or SEVO was delivered at 2.7 times the individual's MAC (determined previously) in 6 L minute-1 O2 . Measured (Rascal II, Ohmeda) anesthetic concentration was reported after correction using a multiple gas, standard-defined calibration curve. For induction, time (seconds) from introduction of inhalant to onset of incoordinated movement (IM), recumbency with movement (RM), recumbency without movement, loss of pedal reflex (PD), and intubation (ET) were recorded. Following intubation, anesthesia was maintained for the required time at 1.25 times the individual's MAC. For recovery, time (seconds) from discontinuation of the inhalant (with continuation of O2 ) to first movement, extubation (EXT), start of incoordinated movement, head-lift, sternal recumbency (SR), crawl, stand/walk with incoordination, and jump without incoordination were recorded. Esophageal normothermia was maintained. Data were analyzed by paired t -test (induction) or One-way Repeated Measures anova followed, when appropriate, by Tukey's test (recovery). p < 0.05 was regarded as significant. For induction, IM was not significantly different between ISO and SEVO (118 ± 28 seconds vs. 104 ± 28 seconds). All other induction times were significantly shorter with SEVO vs. ISO, e.g. RM (181 ± 31 seconds vs. 213 ± 31 seconds), PD (426 ± 68 seconds vs. 504 ± 70 seconds), and ET (434 ± 66 seconds vs. 515 ± 69 seconds). For recovery, there were no differences between ISO and SEVO for any stage of recovery, e.g. EXT (IS 588 ± 163 seconds vs. SS 425 ± 109 seconds), SR (IS 735 ± 215 seconds vs. SS 655 ± 337 seconds), and IL (710 ± 658 seconds vs. SL 807 ± 465 seconds). We concluded that quantitative recovery characteristics did not depend on whether cats are anesthetized with equipotent amounts of SEVO or ISO, but some induction end-points were reached more quickly with SEVO. [ABSTRACT FROM AUTHOR]

Examines the behavioral and alveolar anesthetic wash-out characteristics of horses recovering from anesthesia maintained with desflurane (D) and isoflurane (I) in O[sub 2]. Research methodology; More rapid elimination of D than I; Results supporting earlier studies of smaller pieces that report rapid elimination following D compared to agents of greater blood solubility.

Determines the degree to which intracranial pressure (ICP) and cerebral perfusion pressure (CPP) are affected by ventilation in horses anesthesized with isoflurane (ISO). Research methodology; Indication that CPP remains unchanged in the face of increasing ICP caused by hypoventilation; Conclusion that cerebrovascular autoregulation is preserved in ISO anesthetized horses.

Eight horses [5.6 ± 3.6 years, 489 ± 48.6 kg (mean ± SD)] were anesthetized four times under laboratory conditions to characterize physiologic and behavioral (reported elsewhere) responses associated with a 1-hours period of total intravenous anesthesia (TIA). Each horse was premedicated with xylazine (X, 0.75 mg kg[sup -1]) and anesthesia induced 5 minutes later with 5% guaifenesin (75 mg kg[sup -1]) and ketamine (K, 2 mg kg[sup -1]), all given IV. After anesthetic induction, horses were intubated and received one of six treatments [X 35, K 90, O[sub 2]; X 35, K 120, O[sub 2]; X 35, K 120, air; X 35, K150, O[sub 2]; X 70, K 90, O[sub 2]; no X, K150, O[sub 2]; all infusions in µg kg[sup -1]min[sup -1], O[sub 2] = FIO[sub 2] > 0.95 (inhalation agent free LA breathing circuit], air = FIO[sub 2] = 0.21, mean P[sub atm] = 640 mmHg)]. Treatments were assigned using a computer generated incomplete block design (each treatment repeated a minimum of five times, no treatment repeated in any animal). Cardiopulmonary variables (HR, MAP, CO, MPAP, RR, pHa, PaCO[sub 2] and PaO[sub 2]) were measured at 20, 40 and 60 minutes following the start of the infusion. After the final set of measurements, the infusions were discontinued and horses allowed to recover unassisted. An incomplete block design with repeated measures was used to analyze data. [ABSTRACT FROM AUTHOR]

As a cerebral vasodilator, isoflurane (ISO) can interfere with normal cerebrovascular autoregulation and may exacerbate cerebral perfusion pressure (CPP) changes in horses brought about by drugs that decrease mean arterial pressure (MAP) and by body positions that alter the hydrostatic gradient between brain and heart. It was, therefore, hypothesized that ISO-anesthetized horses in lateral recumbency would have increased intracranial pressure (ICP) and decreased CPP compared to standing, unmedicated horses. Anesthesia was induced and maintained in six healthy horses in left lateral recumbency using only ISO in oxygen. Central venous pressure (CVP) from the right atrium and MAP from the right carotid artery were recorded on a calibrated physiograph. A Codman Microsensor ICP transducer was placed in the subarachnoid space through a right parietal craniotomy. The PaO[sub 2] , PaCO[sub 2] , and pH[sub a] were obtained using an automated blood gas analyzer with values corrected to tonometrically derived standard curves. Horses were ventilated to 18–22 cm H[sub 2] O inspiratory pressure and 0–2 cm H[sub 2] O end-expiratory pressure. End-tidal isoflurane was measured by calibrated gas analyzers and maintained at 1.57%, or 1.2 times minimum alveolar concentration. Measurements in laterally recumbent horses were made at least 20 minutes following constant end-tidal isoflurane conditions. Measurements in awake horses were made 1 hour following standing recovery from anesthesia. The following data were obtained from anesthetized and awake horses, respectively (mm Hg; mean ± SD): MAP = 71 ± 6 and 133 ± 17, CVP = 9 ± 3 and 4 ± 14, ICP = 24 ± 5 and 2 ± 4, CPP = 48 ± 4 and 102 ± 26. Paired t -tests showed significant differences between anesthetized and awake horses for MAP (p < 0.0005), ICP (p < 0.00005), and CPP (p < 0.005), but not for CVP. In both groups, PaCO[sub 2] ranged between 34 and 43 mm Hg, and PaO[sub 2]... [ABSTRACT FROM AUTHOR]

This study was conducted to determine the isoflurane (ISO) minimum alveolar concentration (MAC) reduction induced by nitrous oxide in cats. Twelve cats (four females, eight males; 3.8–8.8 kg; 2–3 years) were anesthetized with only ISO in O[sub 2] . Ventilation was spontaneous. The MAC of ISO was determined at four concentrations of N[sub 2] O (0, 30, 50, and 70%) using the tail-clamp technique. The dose order of N[sub 2] O was randomly assigned. The average of three measurements was considered MAC at each N[sub 2] O concentration. Prior to each MAC measurement, heart rate (HR), direct arterial blood pressure (ABP), respiratory frequency (f ), PaO[sub 2] , PaCO[sub 2] , pH[sub a] , PCV, total protein concentration, and the bispectral index (BIS) were determined. The esophageal temperature was kept constant [38.5 ± 0.35 °C (mean ± SD)]. A negative linear relationship between N[sub 2] O and ISO[sub MAC] was demonstrated by four cats (Group 1), but not by the other eight cats (Group 2). Gender did not appear to influence these results. The ISO[sub MAC] (%) for Group 1 was 2.06 ± 0.08, 1.90 ± 0.17, 1.83 ± 0.07, and 1.58 ± 0.22 at 0, 30, 50, and 70% N[sub 2] O, respectively, and similarly, ISO[sub MAC] for Group 2 was 1.86 ± 0.22, 1.80 ± 0.23, 1.84 ± 0.19, and 1.85 ± 0.22 at 0, 30, 50, and 70% N[sub 2] O, respectively. The relationships between N[sub 2] O concentration and ISO[sub MAC] were significantly different for the two groups of cats (p < 0.0001). The MAC at 70% N[sub 2] O in Group 1 was significantly less than that at 0, 30, and 50% N[sub 2] O. The relationships between N[sub 2] O concentration and other physiological variables were not statistically different for the two groups of cats, so the values for the two groups were combined. In this case, an increase in HR, ABP, PCV, f , and BIS values was associated with an increase in N[sub 2] O concentration and values at 70% were significantly... [ABSTRACT FROM AUTHOR]

Discusses observations and laboratory results which suggested a diagnosis of malignant hyperthermia in a Quarter horse anesthetized with halothane. Research methodology; Serum biochemistry profile; Hypothesis on the association between nerve stimulation and the onset of clinical signs.