OBJECTIVE To determine effects of fentanyl, lidocaine, and a fentanyl-lidocaine combination on the minimum alveolar concentration of sevoflurane preventing motor movement (MACNM) in dogs. ANIMALS 6 adult Beagles. PROCEDURES Dogs were anesthetized with sevoflurane in oxygen 3 times (1-week intervals). Baseline MACNM (MAC(NM-B)) was determined starting 45 minutes after induction of anesthesia. Dogs then received 1 of 3 treatments IV: fentanyl (loading dose, 15 μg/kg; constant rate infusion [CRI], 6 μg/kg/h), lidocaine (loading dose, 2 mg/kg; CRI, 6 mg/kg/h), and the fentanyl-lidocaine combination at the same doses. Determination of treatment MAC(NM) (MAC(NM-T)) was initiated 90 minutes after start of the CRI. Venous blood samples were collected at the time of each treatment MACNM measurement for determination of plasma concentrations of fentanyl and lidocaine. RESULTS Mean ± SEM overall MAC(NM-B) for the 3 treatments was 2.70 ± 0.27 vol%. The MACNM decreased from MACNM-B to MAC(NM-T) by 39%, 21%, and 55% for fentanyl, lidocaine, and the fentanyl-lidocaine combination, respectively. This decrease differed significantly among treatments. Plasma fentanyl concentration was 3.25 and 2.94 ng/mL for fentanyl and the fentanyl-lidocaine combination, respectively. Plasma lidocaine concentration was 2,570 and 2,417 ng/mL for lidocaine and the fentanyl-lidocaine combination, respectively. Plasma fentanyl and lidocaine concentrations did not differ significantly between fentanyl and the fentanyl-lidocaine combination or between lidocaine and the fentanyl-lidocaine combination. CONCLUSIONS AND CLINICAL RELEVANCE CRIs of fentanyl, lidocaine, and the fentanyl-lidocaine combination at the doses used were associated with clinically important and significant decreases in the MAC(NM) of sevoflurane in dogs.

OBJECTIVE To examine effects of continuous rate infusion of lidocaine on transmural neutrophil infiltration in equine intestine subjected to manipulation only and remote to ischemic intestine. ANIMALS 14 healthy horses. PROCEDURES Ventral midline celiotomy was performed (time 0). Mild ischemia was induced in segments of jejunum and large colon. A 1-m segment of jejunum was manipulated by massaging the jejunal wall 10 times. Horses received lidocaine (n = 7) or saline (0.9% NaCl) solution (7) throughout anesthesia. Biopsy specimens were collected and used to assess tissue injury, neutrophil influx, cyclooxygenase expression, and hypoxia-inducible factor 1α (HIF-1α) expression at 0, 1, and 4 hours after manipulation and ischemia. Transepithelial resistance (TER) and mannitol flux were measured by use of Ussing chambers. RESULTS Lidocaine did not consistently decrease neutrophil infiltration in ischemic, manipulated, or control tissues at 4 hours. Lidocaine significantly reduced circular muscle and overall scores for cyclooxygenase-2 expression in manipulated tissues. Manipulated tissues had significantly less HIF-1α expression at 4 hours than did control tissues. Mucosa from manipulated and control segments obtained at 4 hours had lower TER and greater mannitol flux than did control tissues at 0 hours. Lidocaine did not significantly decrease calprotectin expression. Severity of neutrophil infiltration was similar in control, ischemic, and manipulated tissues at 4 hours. CONCLUSIONS AND CLINICAL RELEVANCE Manipulated jejunum did not have a significantly greater increase in neutrophil infiltration, compared with 4-hour control (nonmanipulated) jejunum remote to sites of manipulation, ischemia, and reperfusion. Lidocaine did not consistently reduce neutrophil infiltration in jejunum.

OBJECTIVE To evaluate agreement among diplomates of the American College of Veterinary Anesthesia and Analgesia for scores determined by use of a simple descriptive scale (SDS) or a composite grading scale (CGS) for quality of recovery of horses from anesthesia and to investigate use of 3-axis accelerometry (3AA) for objective evaluation of recovery. ANIMALS 12 healthy adult horses. PROCEDURES Horses were fitted with a 3AA device and then were anesthetized. Eight diplomates evaluated recovery by use of an SDS, and 7 other diplomates evaluated recovery by use of a CGS. Agreement was tested with κ and AC1 statistics for the SDS and an ANOVA for the CGS. A library of mathematical models was used to map 3AA data against CGS scores. RESULTS Agreement among diplomates using the SDS was slight (κ = 0.19; AC1 = 0.22). The CGS scores differed significantly among diplomates. Best fit of 3AA data against CGS scores yielded the following equation: RS = 9.998 × SG(0.633) × ∑UG(0.174), where RS is a horse's recovery score determined with 3AA, SG is acceleration of the successful attempt to stand, and ∑UG is the sum of accelerations of unsuccessful attempts to stand. CONCLUSIONS AND CLINICAL RELEVANCE Subjective scoring of recovery of horses from anesthesia resulted in poor agreement among diplomates. Subjective scoring may lead to differences in conclusions about recovery quality; thus, there is a need for an objective scoring method. The 3AA system removed subjective bias in evaluations of recovery of horses and warrants further study.

OBJECTIVE To determine whether a maxillary nerve block via a modified infraorbital approach, applied before rhinoscopy and nasal biopsy of dogs, would decrease procedural nociception, minimize cardiorespiratory anesthetic effects, and improve recovery quality. ANIMALS 8 healthy adult hound-type dogs PROCEDURES In a crossover study, dogs received 0.5% bupivacaine (0.1 mL/kg) or an equivalent volume of saline (0.9% NaCl) solution as a maxillary nerve block via a modified infraorbital approach. A 5-cm, 20-gauge over-the-needle catheter was placed retrograde within each infraorbital canal, and bupivacaine or saline solution was administered into each pterygopalatine region. Rhinoscopy and nasal biopsy were performed. Variables monitored included heart rate, systolic arterial blood pressure (SAP), mean arterial blood pressure (MAP), diastolic arterial blood pressure (DAP), plasma cortisol and norepinephrine concentrations, purposeful movement, and pain scores. After a 14-day washout period, the other treatment was administered on the contralateral side, and rhinoscopy and nasal biopsy were repeated. RESULTS SAP, MAP, and DAP were significantly higher for the saline solution treatment than for the bupivacaine treatment, irrespective of the time point. Plasma cortisol concentrations after saline solution treatment were significantly higher 5 minutes after nasal biopsy than at biopsy. Heart rate, norepinephrine concentration, purposeful movement, and pain score were not significantly different between treatments. CONCLUSIONS AND CLINICAL RELEVANCE Maxillary nerve block via a modified infraorbital approach prior to rhinoscopy and nasal biopsy reduced procedural nociception as determined on the basis of blood pressures and plasma cortisol concentrations during anesthesia. These findings warrant further evaluation in dogs with nasal disease.

OBJECTIVE To characterize the maternal and fetal cardiopulmonary effects of a low-dose infusion of dexmedetomidine without a loading dose in pregnant ewes anesthetized with sevoflurane. ANIMALS 11 pregnant ewes. PROCEDURES Anesthesia was induced with propofol and maintained with sevoflurane. Ewes and fetuses were instrumented with arterial and venous catheters, and thermodilution–pulmonary arterial catheters were placed in the ewes. Baseline measurements were obtained at an end-tidal sevoflurane concentration of 3.4%, then dexmedetomidine (2 μg/kg/h, IV) was infused for 90 minutes without a loading dose. Cardiovascular and blood gas variables were measured at predetermined time points. RESULTS Dexmedetomidine infusion resulted in approximately 30% decreases in maternal systemic vascular resistance, blood pressure, and heart rate. Maternal cardiac index, oxygenation variables, and acid-base status remained unchanged, whereas pulmonary arterial pressure, pulmonary vascular resistance, and stroke volume increased, compared with baseline values. Uterine blood flow decreased by approximately 30% to 36%. Fetal heart rate and blood pressure remained unchanged, but significant increases in fetal plasma glucose and lactate concentrations were detected. CONCLUSIONS AND CLINICAL RELEVANCE Pregnant ewes receiving a combination of sevoflurane and an infusion of dexmedetomidine without a loading dose had cardiac index in acceptable ranges and maintained normoxia. This balanced anesthesia did not produce significant changes in fetal blood pressure or heart rate. However, the increase in fetal plasma lactate concentration and changes in maternal pulmonary vascular resistance and uterine blood flow require further investigation to better elucidate these effects.

To investigate the effects of a xylazine infusion during isoflurane anesthesia on global perfusion parameters and gastrointestinal oxygenation and microperfusion, 8 adult warmblood horses were sedated with xylazine and anesthesia induced with midazolam and ketamine. Horses were mechanically ventilated during anesthesia. After 3 h of stable isoflurane anesthesia (FEIso 1.3 Vol %), a xylazine infusion with 1 mg/kg body weight (BW) per hour was started for 1 h and then stopped. Before, during, and after xylazine infusion, heart rate (HR), arterial blood pressure (MAP), cardiac output (CO), central venous pressure (CVP), and pulmonary artery pressure (PAP) were measured and systemic vascular resistance (SVR) was calculated. Arterial blood gases were taken and oxygen delivery (DO2) and alveolar dead space (VDalv) were calculated. Further intestinal oxygen and microperfusion were measured using white light spectroscopy and laser Doppler flowmetry. Surface probes were placed via median laparotomy on the stomach, the jejunum, and the colon. Wilcoxon rank-sum test was used to compare values over time (P < 0.05). During xylazine infusion, MAP, CVP, PAP, SVR, and VDalv increased significantly, whereas CO, DO2, and intestinal microperfusion decreased. Intestinal oxygenation remained unchanged. All parameters returned to pre-xylazine values within 1 h after stopping xylazine infusion. A xylazine infusion during constant isoflurane anesthesia in horses impairs global and intestinal perfusion without changing tissue oxygenation in normoxic healthy horses. Further studies are necessary, however, to evaluate whether a possible reduction of isoflurane concentration by xylazine infusion will ameliorate these negative effects.

OBJECTIVE To assess the possible impact of medetomidine on concentrations of alfaxalone in plasma, when coadministered as a constant rate infusion (CRI) to dogs, and to determine the possible impact of medetomidine on the cardiopulmonary effects of alfaxalone during CRI. ANIMALS 8 healthy adult Beagles. PROCEDURES 3 treatments were administered in a randomized crossover design as follows: 1 = saline (0.9% NaCl) solution injection, followed in 10 minutes by induction of anesthesia with alfaxalone (loading dose, 2.4 mg/kg; CRI, 3.6 mg/kg/h, for 60 minutes); 2 = medetomidine premedication (loading dose, 4.0 μg/kg; CRI, 4.0 μg/kg/h), followed by alfaxalone (as in treatment 1); and, 3 = medetomidine (as in treatment 2) and MK-467 (loading dose, 150 μg/kg; CRI, 120 μg/kg/h), followed by alfaxalone (as in treatment 1). The peripherally acting α2-adrenoceptor antagonist MK-467 was used to distinguish between the peripheral and central effects of medetomidine. Drugs were administered IV via cephalic catheters, and there was a minimum of 14 days between treatments. Cardiopulmonary parameters were measured for 70 minutes, and jugular venous blood samples were collected until 130 minutes after premedication. Drug concentrations in plasma were analyzed with liquid chromatography–tandem mass spectrometry. RESULTS The characteristic cardiovascular effects of medetomidine, such as bradycardia, hypertension, and reduction in cardiac index, were obtunded by MK-467. The concentrations of alfaxalone in plasma were significantly increased in the presence of medetomidine, indicative of impaired drug distribution and clearance. This was counteracted by MK-467. CONCLUSIONS AND CLINICAL RELEVANCE The alteration in alfaxalone clearance when coadministered with medetomidine may be attributed to the systemic vasoconstrictive and bradycardic effects of the α2-adrenoceptor agonist. This could be clinically important because the use of α2-adrenoceptor agonists may increase the risk of adverse effects if standard doses of alfaxalone are used.

The aim of this study was to compare nasopharyngeal and esophageal temperature measurements in anesthetized sheep with a range of fresh gas flows (1 to 6 L/min) through the breathing system. Data were compared using a Bland-Altman plot and correlation coefficients, and error measures were calculated. One hundred and ninety-five sets of data were collected from 20 sheep weighing 41 kg (31 to 51.5 kg). The bias (95% limit of agreement), correlation coefficient, and absolute error for nasopharyngeal compared to esophageal temperature were 0.04°C (-0.77°C to 0.85°C), 0.92, and 0.29°C ± 0.29°C, respectively. The percentage of nasopharyngeal readings within 0.5°C of the esophageal temperature was 77.44%. The error did not significantly increase with increasing fresh gas flow. Nasopharyngeal temperature measurement is suitable for estimation of esophageal temperature during general anesthesia of sheep when the fresh gas flow through the breathing system is between 1 and 6 L/min.