Electroencephalography of Detomidine-Ketamine-Halothane and Detomidine-Ketamine-lsoflurane Anesthetized Horses During Orthopedic Surgery A Comparison

This study was done to compare the electroencephalographic (EEG) response evoked by orthopedic surgery in halothane- and isoflurane-anesthetized horses. Eight horses scheduled for bilateral arthroscopic surgery of the stifle were premedicated with detomidine (20 μg/kg) intravenously and five minutes later induced to anesthesia with ketamine (2.2 mg/kg) intravenously. Anesthesia was maintained with either halothane or isoflurane. Assignment of inhalation anesthetic was done randomly. The multiple of minimal alveolar concentration (MAC) of halothane required for anesthesia was significantly higher than the multiple of MAC of isoflurane (p < .05) required. Total amplitude of the EEG with halothane was smaller than with isoflurane (p < .05), but 13.0 to 32.0 Hz high frequency/0.0 to 3.9 Hz low frequency (|3/A) ratio was greater for halothane (p < .05). Arterial partial pressure of oxygen (PaO₂) was significantly (p < .05) higher with isoflurane than with halothane. The differences in EEG frequency shift observed suggest that isoflurane provided better analgesia than halothane for this group of horses.     

Recovery Quality After Romifidine Versus Detomidine Infusion During Isoflurane Anesthesia in Horses

To examine the influence of detomidine or romifidine on recovery quality from isoflurane anesthesia, 78 anesthetic records were reviewed, from horses that had received romifidine (group R) during premedication [80–120 μg kg⁻¹ IV], anesthetic maintenance (40 μg kg⁻¹ hour⁻¹ IV), and recovery (20 μg kg⁻¹ IV) or detomidine (group D), at doses of 10–20 μg kg⁻¹ IV, 5 μg kg⁻¹ hour⁻¹ IV, and 2.5 μg kg⁻¹ IV, respectively. Duration of the different recovery phases, the number of attempts to sternal and standing, scores for transition to standing (TrSta), balance and coordination once standing (BC), and final recovery score (FS) were compared between groups using a Mann–Whitney U-test, independent t-test, or chi-squared test, as appropriate (alpha 0.05). Parametric data are represented as the mean ± standard deviation, and nonparametric data as the median (interquartile range). Compared with group D (25 horses), horses in group R (53 horses) needed significantly fewer attempts to achieve sternal recumbency [R 1 (1–1) vs. D 1 (1–2)], remained significantly longer in sternal recumbency [R 10 (3–14,5) vs. D 5 (1–9,5) minutes], needed significantly less attempts to stand [R 1 (1–1) vs. D 2 (1–4)], and a significantly shorter time to stand after making their first attempt [R 0 (0–0) vs. D 3 (0–6) minutes], with significantly better scores for TrSta, BC, and FS in group R. The results suggest that, at the doses used, romifidine provides a better recovery quality.     

Metabolic, Hormonal, and Hemodynamic Changes During Dopamine Infusions in Halothane Anesthetized Horses

Selected metabolites, hormones and cardiovascular variables were measured in halothane anesthetized horses during 1 hour of dopamine infusion at a rate of 5 μg/kg/min (low) and 10 μg/kg/min (high), and for 1 hour after infusion. Plasma Cortisol increased twofold in the low-infusion group but did not change significantly in the high-infusion group. Plasma nonesterified fatty acids, blood glucose, blood lactate, and plasma insulin increased in the high-infusion group. There was little difference in heart rate, systolic, diastolic, and mean arterial blood pressure between the two groups. The high infusion was associated with arrhythmias in several horses, and one horse showed ventricular fibrillation and died. If metabolic and hormonal changes are used as markers of a "stress response" in anesthetized horses the results must be carefully interpreted if a sympathomimetic agent such as dopamine is administered to maintain cardiovascular stability.     

Electroencephalographic Responses to a Noxious Surgical Stimulus in Mules,Horses, and Ponies

The aim of this study was to investigate the electroencephalographic (EEG) response of equidae to a castration stimulus. Study 1 included 11 mules (2½–8 years; 230–315 kg) and 11 horses (1½–3½ years; 315–480 kg); study 2 included four ponies (15–17 months; 176–229 kg). They were castrated under halothane anesthesia after acepromazine premedication (IV [study 1] and intramuscular [study 2]) and thiopental anesthetic induction. Animals were castrated using a semiclosed technique (study 1) and a closed technique (study 2). Raw EEG data were analyzed and the EEG variables, median frequency (F50), total power (Ptot), and spectral edge frequency (F95), were derived using standard techniques at skin incision (skin) and emasculation (emasc) time points. Baseline values of F50, Ptot, and F95 for each animal were used to calculate percentage change from baseline at skin incision and emasculation. Differences were observed in Ptot and F50 data between hemispheres in horses but not mules (study 1) and in one pony (study 2). A response to castration (>10% change relative to baseline) was observed in eight horses (73% of animals) and four mules (36% of animals) for F50 and nine horses (82%) and four mules (36%) for Ptot. No changes in F95 data were observed in any animal in study 1. Responses to castration were observed in three ponies (75% of animals) for F50, one pony (25%) for F95, and all ponies for Ptot. Alteration of acepromazine administration and castration technique produced a protocol that identified changes in EEG frequency and power in response to castration.     

Cardiopulmonary and Analgesic Effects of Epidural Lidocaine, Alfentanil, and Xylazine in Pigs Anesthetized With Isoflurane

To determine cardiopulmonary and analgesic effects of lidocaine, alfentanil, and xylazine in pigs anesthetized with isoflurane, 18 healthy Landrace-Large White pigs were studied (six for each drug). General anesthesia was induced with isoflurane in O₂ and maintained with 1% to 1.2% end-tidal ISO, ensuring presence of a pain response before epidural drug administration. Heart rate (HR), arterial blood pressures (AP), cardiac output (CO), pulmonary arterial pressure, pulmonary capillary wedge pressure (PCWP), central venous pressure, respiratory rate (RR), tidal volume (TV), minute volume (MV), arterial blood gas data, core temperature (CT), and analgesic effects (by pricking the lumbar area and the abdominal wall) were determined at various times (2, 5, 15, 30, 45, 60, and 90 minutes) after epidural administration of lidocaine (5 μg/kg), alfentanil (5 μg/kg), or xylazine (0.2 mg/kg), all diluted in NaCl 0.9% to 0.5 mL/kg. Statistical analysis included two-way analysis of variance for repeated measures and the least significant difference test for determining differences among means. A probability level of P <.05 was used. The following results were statistically significant decreases in systolic AP, HR, TV, RR, MV, CT, pH, PaO₂, and TCO₂ and increases in PCWP, PaCO₂, and HCO₃ after LID. After ALF, only CT and HCO₃ decreased. Core temperature and TV decreased after XYL. Lidocaine provided 45 to 60 minutes of analgesia. Alfentanil had no analgesic effects, and xylazine provided 90 minutes of analgesia. The authors conclude that xylazine, when injected epidurally, provides suitable analgesia in isoflurane-anesthetized pigs.     

Recovery From Sevoflurane Anesthesia in Horses: Comparison to Isoflurane and Effect of Postmedication With Xylazine

Objective—To compare recovery from sevoflurane or isoflurane anesthesia in horses. Study Design—Prospective, randomized cross-over design. Animals—Nine Arabian horses (3 mares, 3 geldings, and 3 stallions) weighing 318 to 409 kg, 4 to 20 years old. Methods—Horses were anesthetized on three occasions with xylazine (1.1 mg/kg), Diazepam (0.03 mg/kg intravenously [IV]), and ketamine (2.2 mg/kg IV). After intubation, they were maintained with isoflurane or sevoflurane for 90 minutes. On a third occasion, horses were maintained with sevoflurane and given xylazine (0.1 mg/kg IV) when the vaporizer was turned off. Horses were not assisted in recovery and all recoveries were videotaped. Time to extubation, first movement, sternal, and standing were recorded as was the number of attempts required to stand. Recoveries were scored on a 1 to 6 scoring system (1 = best, 6 = worst) by the investigators, and by three evaluators who were blinded to the treatments the horses received. These blinded evaluators assessed the degree of ataxia present at 10 minutes after each horse stood, and recorded the time at which they judged the horse to be ready to leave the recovery stall. Results—Mean times (± SD) to extubation, first movement, sternal, and standing were 4.1 (1.7), 6.7 (1.9), 12.6 (4.6), and 17.4 (7.2) minutes with isoflurane; 3.4 (0.8), 6.6 (3.1), 10.3 (3.1), and 13.9 (3.0) minutes with sevoflurane; and 4.0 (1.2), 9.1 (3.3), 13.8 (6.5), and 18.0 (7.1) with sevoflurane followed by xylazine. Horses required a mean number of 4 (2.3), 2 (0.9), and 2 (1.6) attempts to stand with isoflurane, sevoflurane, and sevoflurane followed by xylazine respectively. The mean recovery score (SD) for isoflurane was 2.9 (1.2) from investigators and 2.4 (1.1) from blinded evaluators. For sevoflurane, the mean recovery score was 1.7 (0.9) from investigators and 1.9 (1.1) from evaluators, whereas the recoveries from sevoflurane with xylazine treatment were scored as 1.7 (1.2) from investigators and 1.7 (1.0) from blinded evaluators. Conclusions—Recoveries appeared to vary widely from horse to horse, but were significantly shorter with sevoflurane than isoflurane, although sevoflurane followed by xylazine was no different from isoflurane. Under the conditions of the study, recoveries from sevoflurane and sevoflurane followed by xylazine were of better quality than those from isoflurane. Clinical Relevance—Sevoflurane anesthesia in horses may contribute to a shorter, safer recovery from anesthesia.     

Retrospective Assessment of Dobutamine Therapy for Hypotension in Anesthetized Horses

Dobutamine was infused (1.7 micrograms/kg/minute) into 200 anesthetized horses as treatment for hypotension. The horses had been premedicated with xylazine, and anesthesia was induced with guaifenesin and ketamine and maintained with halothane. One hundred fifty-seven horses (79%) responded with an average increase in systolic blood pressure of at least 10 mm Hg within 10 minutes. A cardiac arrhythmia developed in 56 horses (28%) after dobutamine administration: 34 with sinus bradycardia, 18 with atrioventricular block, 2 with premature atrial contractions, and 2 with atrioventricular dissociation. Dobutamine intravenous infusion was effective treatment for hypotension in horses anesthetized with halothane.     

Treatment of Low Arterial Oxygen Tension in Anesthetized Horses with Clenbuterol

Clenbuterol (0.8 microgram/kg intravenously) was administered to 10 anesthetized horses with an abnormally low PaO2 (less than 90 mm Hg) despite controlled ventilation with an oxygen-rich gas mixture. Results were compared with those from 10 controls to which no clenbuterol was given and in which conventional methods to increase PaO2 were ongoing. Horses treated with clenbuterol had higher PaO2 values for at least 90 minutes. Clenbuterol was associated with increased heart rate and profuse sweating. Clenbuterol can be administered intravenously to increase the PaO2 of mechanically ventilated horses that have low arterial oxygen tension while under inhalation anesthesia. Further studies are warranted to define more precisely the circumstances under which clenbuterol may be used safely.     

Gender Differences of Oxidative Stress Biomarkers and Erythrocyte Damage in Well-Trained Horses During Exercise

The aim of this study was to determine the effects of gender differences on the blood oxidative stress biomarkers, antioxidant defenses, and resistance of erythrocytes to hemolytic agents of trained horses before and after exercise. The study was carried out on nine mares and 14 stallions of Ukrainian Warmblood well-trained horses, involved in jumping, eventing, and dressage. Oxidative stress biomarkers, antioxidant defenses, and osmotic resistance of erythrocytes were assessed. Trained stallions showed a decrease in lipid peroxidation and higher glutathione reductase activity, whereas mares presented a higher superoxide dismutase activity after exercise. The resistance of erythrocytes was similar in female and male. No statistically significant differences were observed in the percentage of hemolyzed erythrocytes between after and before exercise. A correlation between the oxidative stress biomarkers and antioxidant defenses in the stallions after exercises were observed, which may indicate a protective response of superoxide dismutase and catalase against exercise-induced oxidative stress.     

Evaluation of the Nonin 8600V Veterinary Pulse Oximeter in Anesthetized Horses

S_pO₂ values from the Nonin 8600V veterinary pulse oximeter, using a lingual clip-type, transmittance sensor applied to the tongue, were compared to directly-measured S_aO₂ values from a co-oximeter, calibrated for equine blood, in 5 halothane-anesthetized horse. Normocapnia was maintained with controlled ventilartion. The inspired oxygen concentration was varied by mixing nitrogen in oxygen to obtain S_pO₂ readings of approximately 60, 65, 70, 75, 80, 85, 90, 92, and 100%. At the time of each S_pO₂ recording, an arterial blood sample was collected for immediate analysis of S_aO₂. A total of sixty paired measurements were made. The results showed excellent data correlation with a bias (precision) of 0.55 (2.57) and an R-value of 0.98 over the entire S_aO₂ range tested. Based on these findings, the Nonin 8600V veterinary pulse oximeter, with the lingual sensor, performed accurately and reliably, and appears to be suitable for clinical use in anesthetized horses. (Vet Emerg & Crit Care, 1999: 13–18)     

Blood Gas Values During Intermittent Positive Pressure Ventilation and Spontaneous Ventilation in 160 Anesthetized Horses Positioned in Lateral or Dorsal Recumbency

One hundred sixty horses were anesthetized with xylazine, guaifenesin, thiamylal, and halothane for elective soft tissue and orthopedic procedures. Horses were randomly assigned to one of four groups. Group 1 (n = 40): Horses positioned in lateral (LR_G1,; n = 20) or dorsal (DR_G1,; n = 20) recumbency breathed spontaneously throughout anesthesia. Group 2 (n = 40): Intermittent positive pressure ventilation (IPPV) was instituted throughout anesthesia in horses positioned in lateral (LR_G2; n = 20) or dorsal (DR_G2; n = 20) recumbency. Group 3 (n = 40): Horses positioned in lateral (LR_G3; n = 20) or dorsal (DR_G3; n = 20) recumbency breathed spontaneously for the first half of anesthesia and intermittent positive pressure ventilation was instituted for the second half of anesthesia. Group 4 (n = 40): Intermittent positive pressure ventilation was instituted for the first half of anesthesia in horses positioned in lateral (LR_G4; n = 20) or dorsal (DR_G4; n = 20) recumbency. Spontaneous ventilation (SV) occured for the second half of anesthesia. The mean time of anesthesia was not significantly different within or between groups. The mean time of SV and IPPV was not significantly different in groups 3 and 4. Variables analyzed included pH, PaCO₂, PaO₂, and P(A-a)O₂ (calculated). Spontaneous ventilation resulted in significantly higher PaCO₂ and P(A-a)O₂ values and significantly lower PaO₂ values in LR_G1, and DR_G1, horses compared with LR_G2 and DR_G2 horses. Intermittent positive pressure ventilation resulted in normocarbia and significantly lower P(A-a)O₂ values in LR_G2 and DR_G2 horses. In LR_G2 the Pao₂ values significantly increased from 20 minutes after induction to the end of anesthesia. The PaO₂ and P(A-a)O₂ values were not significantly different from the beginning of anesthesia after IPPV in DR_G2 or DR_G3. The PaO₂ values significantly decreased and the P(A-a)O₂ values significantly increased after return to SV in horses in LR_G4, and DR_G4. The PaO₂ values were lowest and the P(A-a)O₂ values were highest in all horses positioned in dorsal recumbency compared with lateral recumbency and in SV horses compared with IPPV horses. The pH changes paralleled the changes in PaCO₂. Blood gas values during right versus left lateral recumbency in all groups were also evaluated. The PaO₂ values were significantly lower and the P(A-a)O₂ values were significantly higher during SV in horses positioned in left lateral (LR_LG1) compared with right lateral (LR_RG1) recumbency. No other significant changes were found comparing left and right lateral recumbency. Arterial hypoxemia (PaO₂ < 60 mm Hg) developed in 35% of DR_G1 horses and 20% of DR_G2 horses at the end of anesthesia. Arterial hypercarbia (PaCO₂= 50–60 mm Hg) developed in DRoi horses. Arterial hypoxemia that developed in 20% of DR_G3 horses was not improved with IPPV. Arterial hypoxemia developed in 55% of DR_G4 horses after return to SV. Some DR_G4 horses with hypoxemia also developed hypercarbia, whereas some had PaCO₂ values within normal limits. Arterial hypoxemia developed in one LR_G1, and two LR_G4, horses. Hypercarbia developed in onlv one LR_G4 horse.     

Electroencephalographic Power Spectrum Analysis as a Monitor of Anesthetic Depth in Horses

Electroencephalographic (EEG) power spectrum analysis was performed in 18 conscious, adult horses for evaluation as control values for EEG data obtained during anesthesia. Computer-processed total amplitudes for the frequency range 0 to 32 Hz were mainly between 400 and 600 microV, with 80% spectral edge frequency between 16.6 and 32.5 Hz. The highest electrical activity was in the delta band (41.3 +/- 4.4% of total amplitude); there was a less pronounced activity in the beta (34.2 +/- 5.2%), theta (13.6 +/- 1.5%), and alpha (10.0 +/- 1.0%) bands. The applicability of EEG power spectrum analysis as a guide to depth of anesthesia was evaluated in four horses by comparing simultaneously recorded EEG data and clinical signs of anesthesia. Global changes in cerebrocortical electrical activity were detected with a single, monopolar (left frontoatlanto-occipital) EEG lead. Increasing depth of halothane anesthesia was accompanied by a pronounced shift in EEG activity from beta to theta and delta frequency bands, a decrease in 80% spectral edge frequency from 21.5 +/- 2.4 Hz to 12.6 +/- 2.2 Hz, a reduction in the beta/delta ratio of fractional amplitudes from 2.37 +/- 0.84 to 0.49 +/- 0.04, and a slight inconsistent increase in total amplitude from 96.1 +/- 37.3 microV to 185.5 +/- 53 microV. These results show that changes in the clinical signs of anesthetic depth in horses can be described numerically by use of EEG power spectrum analysis.     

Radiographic Differences Between Uneven Feet in Horses With Foot Lameness and Admitted for MRI Examination

Unevenness is an important feature of foot conformation and coincides with both kinetic and kinematic asymmetrical locomotor differences. It reportedly may lead to early retirement of elite horses from a warmblood population. The aim of this study was to evaluate the radiological consequences of an uneven feet conformation and on distal limb tissue development. In a retrospective study, the complete sets of good quality radiographs of both distal forelimbs were compared objectively for 121 “foot lame” horses that had been admitted for magnetic resonance imaging of one or both front feet (2003–2010). A chi-square test was used to test for significant radiometric differences between the upright and the lower angle foot (P < .05); 60% of the horses were unilaterally lame in the upright foot, whereas 40% were lame in the lower angle foot, which appeared to be a nonsignificant difference. In 84% of the horses, the navicular bone (NB) had a substantially more radiolucent, osteoporotic structure (P < .05). In 88% of the horses, the deep digital flexor tendon (DDFT) in the upright foot was significantly more radiodense and pronounced than in the lower angle foot (P < .05). The NB showed a significantly more osteoporotic structure as scored in the upright foot than in the lower angle foot, whereas the DDFT appeared was scored more compact in the upright foot than in the lower angle foot, suggesting less tension on the DDFT. In conclusion, radiological differences between uneven feet in foot lame horses seem to be related to differences in distal limb locomotor tissue development.     

Blood Viscosity in Horses With Colic

Whole blood viscosity (WBV) was measured on six healthy horses and ten horses presented for colic surgery. A Wells-Brookfield cone-and-plate microviscometer at 6 rpm was used to determine WBV and WBV was adjusted for packed cell volume (PCV). The ten colic horses were divided into two groups: five horses that died or were euthanatized (group 1) and five horses that were discharged after surgery and medical therapy (group 2). The mean WBV for each group was compared using analysis of variance followed by Duncan multiple-range tests. Mean WBV of group 2 (5.81 +/- 1.48 centipoise [cp]) and normal horses (7.1 +/- 2.3 cp) was significantly (P less than 0.01) lower than group 1 (17.15 +/- 5.71 cp). This preliminary trial shows that horses that died or were euthanatized had a significantly higher WBV than horses surviving. Since viscosity was adjusted for PCV, the differences may represent changes in other factors such as fibrinogen, rouleaux formation, red blood cell deformability, PaO2, or intracellular calcium ion concentration. Thus, increases in WBV in horses with colic may indicate severely compromised regional perfusion that may lead to significant tissue damage. In this preliminary study, it appears that WBV may be a prognostic aid in horses with colic.     

Evaluation of Urinary Variables as Diagnostic Indicators of Acute Kidney Injury in Egyptian Draft Horses Treated With Phenylbutazone Therapy

The present study was undertaken to evaluate the diagnostic significance of various urinary variables to detect acute kidney injury (AKI) in Egyptian draft horses treated with phenylbutazone (PBZ) therapy. Medical records of 52 draft horses, with a history of musculoskeletal painful conditions and treated frequently with various daily doses of injectable PBZ, were reviewed. Of those 52 horses, 38 were enrolled in this study. AKI was tentatively diagnosed based on thorough history and clinical findings and in conjunction with multiple biochemical screening tests. Accordingly, diseased horses were categorized into two main groups; the first group included 14 horses with prerenal azotemia, whereas the second group included 24 horses with renal azotemia. Biochemically, urinary malondialdehyde, urinary gamma-glutamyl transferase/creatinine (Cr) ratio, urinary protein/Cr ratio, urinary glucose, urinary sodium, fractional excretion of sodium, and renal failure index were significantly higher (P < .05) in horses of group 2 than those of group 1. However, values of urinary Cr, urine/plasma Cr ratio, urinary urea, and urine/plasma urea ratio were significantly decreased (P < .05) in horses of group 2. Analysis of receiver operating characteristic curve showed high sensitivity and specificity of most tested urinary variables as well as their derived indices for detection of AKI in diseased horses. Our findings suggest that the examined urinary variables as well as their ratios are helpful in documenting AKI associated with PBZ nephrotoxicity in Egyptian draft horses; however, their interpretation should be done in the light of the specific clinical setting and in conjunction with a thorough clinical and physical examination.     

Interstitial pH and Pressure in the Dependent Biceps Femoris Muscle of Laterally Recumbent Anesthetized Horses

Interstitial pressure and pH in the dependent biceps femoris muscle were measured in anesthetized, laterally recumbent horses. The mean (+/- standard deviation) interstitial pressure in 10 horses was 19.70 +/- 0.15 mmHg in the 30 to 180 minute interval after induction of anesthesia. Pressures of this order have been associated with reduction in muscle perfusion. Mean (+/- standard deviation) interstitial pH in six horses decreased from 7.07 +/- 0.30 to 6.73 +/- 0.21 between 45 and 150 minutes of anesthesia. These results indicated the presence of circulatory compromise to intracompartmental structures.     

Surgical Treatment of Colic Results in 181 Horses

A retrospective study was performed of 181 horses that underwent an exploratory celiotomy because of acute abdominal disease. Forty-four horses died or were euthanized during surgery. Of the 137 horses that recovered from anesthesia, 72 died of associated diseases or complications, 86 were discharged from the hospital of which 60 survived at least 7 months. Horses with disorders affecting the small intestine had a significantly lower survival rate. Causes of death early in the postoperative period included long bone fracture, shock, ileus, gastric rupture, and peritonitis. After discharge from the hospital, deaths were attributed to colic of unknown cause, malabsorption syndrome, adhesive small bowel obstruction, small and large intestinal volvulus, perforated bowel, and laminitis. Of the 60 horses that were alive at the time of survey, 93.3% had returned to their previous use. A second occurrence of the initial acute abdominal disease was not documented in any horse.