The cardiopulmonary effects of anesthetic induction with isoflurane,ketamine‐diazepam or propofol‐diazepam in the hypovolemic dog

ObjectiveTo evaluate and compare the cardiopulmonary effects of induction of anesthesia with isoflurane (Iso), ketamine–diazepam (KD), or propofol–diazepam (PD) in hypovolemic dogs.Study designProspective randomized cross–over trial.AnimalsSix healthy intact, mixed breed, female dogs weighing 20.7 ± 4.2 kg and aged 22 ± 2 months.MethodsDogs had 30 mL kg^?1 of blood removed at a rate of 1.5 mL kg^?1 minute^?1 under isoflurane anesthesia. Following a 30–minute recovery period, anesthesia was reinduced. Dogs were assigned to one of three treatments: isoflurane via facemask using 0.5% incremental increases in the delivered concentration every 30 seconds, 1.25 mg kg^?1 ketamine and 0.0625 mg kg^?1 diazepam intravenously (IV) with doses repeated every 30 seconds as required, and 2 mg kg^?1 propofol and 0.2 mg kg^?1 diazepam IV followed by 1 mg kg^?1 propofol increments IV every 30 seconds as required. Following endotracheal intubation all dogs received 1.7% end–tidal isoflurane in oxygen. Cardiopulmonary variables were recorded at baseline (before induction) and at 5 or 10 minute intervals following endotracheal intubation.ResultsInduction time was longer in Iso (4.98 ± 0.47 minutes) compared to KD (3.10 ± 0.47 minutes) or PD (3.22 ± 0.45 minutes). To produce anesthesia, KD received 4.9 ± 2.3 mg kg^?1 ketamine and 0.24 ± 0.1 mg kg^?1 diazepam, while PD received 2.2 ± 0.4 mg kg^?1 propofol and 0.2 mg kg^?1 diazepam. End–tidal isoflurane concentration immediately following intubation was 1.7 ± 0.4% in Iso. Arterial blood pressure and heart rate were significantly higher in KD and PD compared to Iso and in KD compared to PD. Arterial carbon dioxide partial pressure was significantly higher in PD compared to KD and Iso immediately after induction.Conclusions and clinical relevanceIn hypovolemic dogs, KD or PD, as used in this study to induce anesthesia, resulted in less hemodynamic depression compared to isoflurane.     

The isoflurane sparing effect of a medetomidine constant rate infusion in horses

This clinical study analysed the anaesthetic sparing effect of a medetomidine constant rate infusion (CRI) during isoflurane anaesthesia in horses. Forty healthy horses undergoing different types of orthopaedic and soft tissue surgeries were studied in a randomized trial. Orthopaedic surgeries were primarily arthroscopies and splint bone extractions. Soft tissue surgeries were principally castrations with one ovariectomy. All horses received 0.03 mg kg^?1 acepromazine IM 1 hour prior to sedation. Group A (11 orthopaedic and nine soft tissue surgeries), was sedated with 1.1 mg kg^?1 xylazine IV, group B (13 orthopaedic and seven soft tissue surgeries) with 7 µg kg^?1 medetomidine IV. Anaesthesia was induced in both groups with 2.2 mg kg^?1 ketamine and diazepam 0.02 mg kg^?1 IV. Maintenance of anaesthesia was with isoflurane (ISO) in 100% oxygen, depth of anaesthesia was always adjusted by the first author. Group B received an additional CRI of 3.5 µg kg^?1 hour^?1 medetomidine. Respiratory rate (RR), heart rate (HR), mean arterial blood pressure (MAP), Fe ′ISO and Fe ′CO₂ were monitored with a methane insensitive monitor (Cardiocap 5, Ohmeda, Anandic, Diessenhofen) and noted every 5 minutes. Arterial blood was withdrawn for gas analysis (PaO₂, PaCO₂) 5 minutes after the induction of anaesthesia and every 30 minutes thereafter. Dobutamine (DOB) was given as a CRI to maintain mean arterial blood pressure above 70 mm Hg. Data were averaged over time (sum of measurements/number of measurements) and tested for differences between groups by unpaired t‐tests. There were no significant differences between the groups in terms of body mass (group A, 508 ± 73.7 kg; group B, 529.25 ± 78.4 kg) or duration of anaesthesia (group A, 125.5 ± 36 minutes; group B, 121.5 ± 48.4 minutes). The mean Fe ′ISO required to maintain a surgical plane of anaesthesia was significantly higher in group A (1.33 ± 0.13%) than in group B (1.07 ± 0.19%; p = 2.78 × 10^?5). Heart rate was different between the two groups (group A, 42.2 ± 8.3; group B, 32.6 ± 3.5; p = 8.8 × 10^?5). Dobutamine requirements were higher in group A (group A, 0.72 ± 0.24 μg kg^?1 minute^?1; group B, 0.53 ± 0.23 μg kg^?1 minute^?1; p = 0.023). Respiratory rate, Fe ′CO₂, PaO₂, PaCO₂ were not different between the groups. Adjustment of anaesthetic depth subjectively was easier with the medetomidine infusion and isoflurane (group B) than with isoflurane as a sole agent (group A). In group A 12 horses and in group B five horses showed purposeful movements on 27 (A) and 12 (B) occasions. They were given thiopental (group A, 0.0114 mg kg^?1 minute^?1; group B, 0.0023 mg kg^?1 minute^?1). In group A, a further 17 horses were given ketamine to deepen anaesthesia (52 occasions, 0.00426 mg kg^?1 minute^?1) whereas in group B only nine horses needed ketamine (34 occasions, 0.00179 mg kg^?1 minute^?1). An infusion of 3.5 µg kg^?1 MED during ISO anaesthesia resulted in a significantly reduced ISO requirement.     

Comparison of two injectable anesthetic regimes in feral cats at a large-volume spay clinic

Same‐day mass sterilization of feral cats requires rapid onset, short‐duration anesthesia. The purpose of this study was to compare our current anesthetic protocol, Telazol–ketamine–xylazine (TKX) with medetomidine–ketamine–buprenorphine (MKB). Feral female cats received either IM TKX (n = 68; 0.25 mL cat^?1; tiletamine 12.5 mg, zolazepam 12.5 mg, K 20 mg, and X 5 mg per 0.25 mL) or MKB (n = 17; M 40 µg kg^?1, K 15 mg kg^?1, and B 10 µg kg^?1). Intervals measured included time from injection to recumbency, time to surgery, duration of surgery, and time from reversal of anesthesia (TKX: yohimbine 0.50 mg cat^?1 IV; MKB: atipamezole 0.50 mg cat^?1 IM) to sternal recumbency. Following instrumentation (Vet/Ox 4403 and Vet/BP Plus 6500), physiological measurements were recorded at 5‐minute intervals, and included rectal temperature, heart rate (HR), respiratory rate (RR), SpO₂ (lingual or rectal probes), and indirect mean arterial blood pressure (MAP) (oscillometric method). Nonparametric means were compared using Mann–Whitney U‐tests. Parametric means were compared using a two‐factorial anova with Bonferroni's t‐tests. The alpha‐priori significance level was p < 0.05. Values were mean ± SD. Body weight (TKX: 2.9 ± 0.5 kg, MKB: 2.7 ± 0.7 kg), time to recumbency (TKX: 4 ± 1 minutes, MKB: 3 ± 1 minutes), time to surgery (TKX: 28 ± 7 minutes, MKB: 28 ± 5 minutes), and duration of surgery (TKX: 11 ± 7 minutes, MKB: 8 ± 5 minutes) did not differ between groups. In contrast, MKB cats required less time from reversal to sternal recumbency (TKX: 68 ± 41 minutes, MKB: 7 ± 2 minutes) and were recumbent for shorter duration (TKX: 114 ± 39 minutes, MKB: 53 ± 6 minutes). Temperature decreased during the study in both groups, but overall temperature was higher in MKB cats (38.0 ± 0.95 °C) than in TKX cats (37.5 ± 0.95 °C). RR, HR, and SpO₂ did not change during the study in either group. However, overall HR and RR were higher in TKX cats (RR: 18 ± 8 breaths minute^?1, HR: 153 ± 30 beats minute^?1) compared to MKB cats (RR: 15 ± 7 breaths minute^?1, HR: 128 ± 19 beats minute^?1). In contrast, overall SpO₂ was lower in the TKX group (90 ± 6%) compared to the MKB group (94 ± 4%). MAP was also lower in the TKX group (112 ± 29 mm Hg) compared to that in the MKB group (122 ± 20 mm Hg). However, MAP increased in the TKX group during surgery compared to pre‐surgical values, but did not change in the MKB group. The results of this study suggested that MKB might be more suitable as an anesthetic for the purpose of mass sterilization of feral female cats.     

Evaluation of cardiorespiratory and biochemical effects of ketamine‐propofol and guaifenesin‐ketamine‐xylazine anesthesia in donkeys (Equus asinus)

ObjectivesTo evaluate the cardiorespiratory and biochemical effects of ketamine-propofol (KP) or guaifenesin-ketamine-xylazine (GKX) anesthesia in donkeys.Study designProspective crossover trial.AnimalsEight healthy, standard donkeys, aged 10 ± 5 years and weighing 153 ± 23 kg.MethodsDonkeys were premedicated with 1.0 mg kg^?1 of xylazine (IV) in both treatments. Eight donkeys were administered ketamine (1.5 mg kg^?1) and propofol (0.5 mg kg^?1) for induction, and anesthesia was maintained by constant rate infusion (CRI) of ketamine (0.05 mg kg^?1 minute^?1) and propofol (0.15 mg kg^?1 minute^?1) in the KP treatment. After 10 days, diazepam (0.05 mg kg^?1) and ketamine (2.2 mg kg^?1) were administered for induction, and anesthesia was maintained by a CRI (2.0 mL kg^?1 hour^?1) of ketamine (2.0 mg mL^?1), xylazine (0.5 mg mL^?1) and guaifenesin (50 mg mL^?1) solution. Quality of anesthesia was assessed along with cardiorespiratory and biochemical measurements.ResultsAnesthetic induction took longer in GKX than in KP. The induction was considered good in 7/8 with KP and in 6/8 in GKX. Anesthetic recovery was classified as good in 7/8 animals in both treatments. Xylazine administration decreased heart rate (HR) in both treatments, but in KP the HR increased and was higher than GKX throughout the anesthetic period. Respiratory rate was higher in GKX than in KP. PaO₂ decreased significantly in both groups during the anesthetic period. Glucose concentrations [GLU] increased and rectal temperature and PCV decreased in both treatments. Arterial lactate [LAC] increased at recovery compared with all time points in KP. [GLU] and calcium were higher in GKX than in KP at recovery.Conclusion and clinical relevanceThese protocols induced significant hypoxemia but no other cardiorespiratory or metabolic changes. These protocols could be used to maintain anesthesia in donkeys, however, they were not tested in animals undergoing surgery.     

Cardiopulmonary effects of combined xylazine-guaiphenesin-ketamine infusion and extradural (inter-coccygeal lidocaine) anaesthesia in calves

Objective To investigate the cardiopulmonary effects of a xylazine–guaiphenesin–ketamine infusion combined with inter‐coccygeal extradural (lidocaine) anaesthesia in calves. Study design Prospective study. Animals Five Holstein Friesian calves (one steer, four heifers) aged 6 weeks weighing 65.2 ± 2.7 kg. Materials and methods Calves were anaesthetized with isoflurane in oxygen for instrumentation. At least 12 hours later, xylazine (0.2 mg kg^?1 IM) was given. After 15 minutes, an infusion of xylazine hydrochloride (0.1 mg mL^?1), guaiphenesin (50 mg mL^?1) and ketamine (1 mg mL^?1) (X–G–K) was infused at a rate of 1.1 mL kg^?1 hour^?1 IV. Oxygen (4 L minute^?1) was delivered by nasotracheal tube 30 minutes later. Inter‐coccygeal (Co₁–Co₂) extradural anaesthesia (lidocaine 2%, 0.18 mL kg^?1) was administered 30 minutes later. Cardiopulmonary variables were obtained in the unsedated standing calves 10 minutes after xylazine, 15 and 30 minutes after X–G–K without O₂, 15 and 30 minutes after X–G–K with O₂ and 5, 15, 30, 45 and 60 minutes after extradural anaesthesia. Data were analysed using a repeated measurement analysis of variance including an autoregressive covariance structure of order 1 (correlations at different time intervals). Results Xylazine caused significant (p < 0.05) decreases in heart rate (HR), cardiac output (Qt) and index (CI), stroke volume and stroke index, mean, systolic and diastolic arterial blood pressure (MAP, SAP, DAP), left (LVWSI) and right ventricular stroke work index (RVWSI), mean, systolic and diastolic pulmonary arterial pressure (MPAP, SPAP, DPAP), arterial pH, arterial oxygen tension (P_aO₂), arterial base excess, arterial HCO₃^? concentration, arterial saturation, packed cell volume, arterial and venous oxygen content (C_aO₂, C_vO₂), O₂ consumption and O₂ delivery (V?O₂, ?O₂). Increases in systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) were observed. During X–G–K infusion without O₂, HR, Qt and CI increased gradually while SVR, PVR and MAP decreased. Left ventricular stroke work index and P_aO₂ remained constant, while O₂ supplementation improved P_aO₂. Coccygeal extradural anaesthesia had little effect on cardiopulmonary variables. Respiratory rate (f) and P_aCO₂ significantly increased over the experiment. Conclusions and clinical relevance Xylazine caused adverse cardiopulmonary effects in calves. Improvement occurred during xylazine–guiaphenesin–ketamine infusion. Cardiac index and arterial blood pressure remained below baseline values while sustained increases in respiration rate and P_aCO₂ were observed. Inter‐coccygeal extradural anaesthesia had only minor effects. Oxygen supplementation proved advantageous during guiaphenesin, ketamine and xylazine infusion in healthy calves in combination with coccygeal extradural anaesthesia induced persistent cardiopulmonary depression.     

Cardiopulmonary effects of administration of a combination solution of xylazine, guaifenesin, and ketamine or inhaled isoflurane in mechanically ventilated calves

OBJECTIVE: To compare the cardiopulmonary effects of administration of a solution of xylazine, guaifenesin, and ketamine (XGK) or inhaled isoflurane in mechanically ventilated calves undergoing surgery. ANIMALS: 13 male calves 2 to 26 days of age. Procedures-In calves in the XGK group, anesthesia was induced (0.5 mL/kg) and maintained (2.5 mL/kg/h) with a combination solution of xylazine (0.1 mg/mL), guaifenesin (50 mg/mL), and ketamine (1.0 mg/mL). For calves in the isoflurane group, anesthesia was induced and maintained with isoflurane in oxygen. The rates of XGK infusion and isoflurane administration were adjusted to achieve suitable anesthetic depth. All calves received 100% oxygen and were mechanically ventilated to maintain end-tidal carbon dioxide concentrations from 35 to 40 mm Hg and underwent laparoscopic bladder surgery through an abdominal approach. Cardiopulmonary variables were measured before induction and at intervals up to 90 minutes after anesthetic induction. RESULTS: The quality of induction was excellent in all calves. The XGK requirements were 0.57 +/- 0.18 mL/kg and 2.70 +/- 0.40 mL/kg/h to induce and maintain anesthesia, respectively. Heart rate was significantly lower than baseline throughout the anesthetic period in the XGK group. Systolic arterial blood pressure was significantly higher in the XGK group, compared with the isoflurane group, from 5 to 90 minutes. Cardiac index was lower than baseline in both groups. Differences between groups in cardiac index and arterial blood gas values were not significant. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of XGK resulted in excellent anesthetic induction and maintenance with cardiopulmonary alterations similar to those associated with isoflurane in mechanically ventilated calves.     

Blood pressure and electrocardiographic effects of acepromazine in anaesthetized horses

Acepromazine, a phenothiazine tranquilizer, causes hypotension in standing horses ( Parry et al. 1982 ). However, a retrospective study ( Taylor & Young 1993 ) showed that acepromazine pre‐anesthetic medication did not affect arterial blood pressure (MAP) in anaesthetized horses. This study examined the effects of acepromazine on MAP during romifidine–ketamine–halothane anaesthesia in horses anaesthetized for various surgical procedures. Forty‐four horses were allocated by block randomization to groups A and B. Group A received acepromazine 0.05 mg kg^?1 IM 30 minutes before induction of anaesthesia, group B did not. All horses received romifidine 0.1 mg kg^?1 IV 5 minutes before anaesthesia was induced with diazepam 0.05 mg kg^?1 and 2.2 mg kg^?1 ketamine IV. The horses' trachea were intubated and horses breathed 50% oxygen and 50% nitrous oxide plus halothane (concentration adjusted as required clinically) from a circle breathing system. Nitrous oxide was discontinued after 10 minutes and analgesics, flunixin 1.1 mg kg^?1 and either morphine 0.1 mg kg^?1 or butorphanol 0.05 mg kg^?1 (matched for horses undergoing the same procedure) administered IV. The facial or dorsal metatarsal artery was catheterized for direct measurement of MAP (every 10 min) and withdrawal of blood for gas analysis (every 30 min). The electrocardiogram (ECG) was monitored continuously with a 10 seconds printout obtained every 10 minutes. Intermittent positive pressure ventilation (IPPV) was instigated if PaCO₂ exceeded 9.3 kPa (70 mm Hg). Dobutamine was infused (1.0–5.0 kg^?1minute^?1) if MAP < 58 mm Hg and was continued until MAP > 70 mm Hg. Mean age, weight and duration of anaesthesia were compared between the groups using a t‐test for independent samples. Gender distribution and numbers of horses requiring IPPV or dobutamine were compared between groups using a chi‐squared test (with Yates correction). To compare MAP over time, the area under the curve (MAPAUC) was calculated and compared between groups using a t‐test. Horses receiving dobutamine were excluded from MAPAUC and MAP comparisons. The ECG printouts were examined for arrhythmias. There were no significant differences between groups (p > 0.05). Group A contained three stallions, 10 geldings and nine mares, aged 6.3 years (range 0.75–18). Group B comprised eight stallions, 11 geldings and three mares aged 7.3(1–16) years. Duration of anaesthesia was group A 97 (50–140) minutes, group B 99 (50–160) minutes. Eight horses in group A and three in group B required IPPV. Nine horses in group A and four in group B received dobutamine. Mean arterial pressure ranged from 60 to 128 mm Hg in group A and 58–96 mm Hg in group B. Mean MAPAUC was 5941 mm Hg minute^?1 in group A, in B 6000 mm Hg minute^?1. Atrial pre‐mature complexes were recorded from one horse in group B. No other arrhythmias were detected. Although MAP was lower in the acepromazine group, this appeared unlikely to cause a clinical problem. The incidence of arrhythmias was too low to determine the influence of acepromazine in this study.     

The effects of maternal plasma dobutamine levels on fetal oxygenation in anaesthetized sheep

Objective To measure the effects of dobutamine infusion on fetal oxygenation during isoflurane anaesthesia in pregnant ewes. Study design Prospective randomized experimental study. Animals Seven clinically normal adult pregnant Rambouillet‐Dorset cross ewes with fetuses of 117–122 days gestational age. Methods The ewes were anaesthetized with ketamine (2 mg kg^?1) IM, and isoflurane (F_E′ISO 2.0%) in oxygen. After instrumentation and stabilization, dobutamine was infused at 4 µg kg^?1minute^?1 for 60 minutes and 10 µg kg^?1minute^?1 for 60 minutes in random order, separated by a 20‐minute washout period. Catheters were placed in the maternal and fetal carotid arteries; these were used for continuous blood pressure measurement and intermittent blood sampling. Results Maternal mean systemic carotid arterial pressure was 60 mm Hg prior to dobutamine infusion. After 5 minutes of dobutamine infusion, fetal oxygen saturation increased (p < 0.05) from 0.62 (0.17–0.71, minimum–maximum) to 0.72 (0.28–0.78) at a dose of 4 µg kg^?1minute^?1 and to 0.70 (0.20–0.73) at a dose of 10 µg kg^?1minute^?1. These increases were maintained during the infusion and were not significantly different between doses. Maternal oxygen saturation remained constant at 1.0 before and during all infusions. Although maternal heart rate and blood pressure increased (p < 0.05) by 90% and 25%, respectively, with dobutamine, this stimulant effect was not evident in the corresponding fetal variables. Maternal haemoglobin concentration increased 30% (p < 0.05) with each infusion. Conclusions Dobutamine at 4 µg kg^?1minute^?1 increases fetal oxygenation that is not improved by a dose of 10 µg kg^?1minute^?1. This increase is largely due to an increase in maternal haemoglobin concentration that, in turn, increases oxygen delivery to the placenta. Clinical relevance The use of dobutamine to treat hypotension in pregnant sheep during isoflurane anaesthesia improves fetal oxygenation. This may be true in other species.     

A clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery characteristics

ObjectiveTo test if the addition of butorphanol by constant rate infusion (CRI) to medetomidine–isoflurane anaesthesia reduced isoflurane requirements, and influenced cardiopulmonary function and/or recovery characteristics.Study designProspective blinded randomised clinical trial.Animals61 horses undergoing elective surgery.MethodsHorses were sedated with intravenous (IV) medetomidine (7 μg kg^?1); anaesthesia was induced with IV ketamine (2.2 mg kg^?1) and diazepam (0.02 mg kg^?1) and maintained with isoflurane and a CRI of medetomidine (3.5 μg kg^?1 hour^?1). Group MB (n = 31) received butorphanol CRI (25 μg kg^?1 IV bolus then 25 μg kg^?1 hour^?1); Group M (n = 30) an equal volume of saline. Artificial ventilation maintained end-tidal CO₂ in the normal range. Horses received lactated Ringer’s solution 5 mL kg^?1 hour^?1, dobutamine <1.25 μg kg^?1 minute^?1 and colloids if required. Inspired and exhaled gases, heart rate and mean arterial blood pressure (MAP) were monitored continuously; pH and arterial blood gases were measured every 30 minutes. Recovery was timed and scored. Data were analyzed using two way repeated measures anova, independent t-tests or Mann–Whitney Rank Sum test (p < 0.05).ResultsThere was no difference between groups with respect to anaesthesia duration, end-tidal isoflurane (MB: mean 1.06 ± SD 0.11, M: 1.05 ± 0.1%), MAP (MB: 88 ± 9, M: 87 ± 7 mmHg), heart rate (MB: 33 ± 6, M: 35 ± 8 beats minute^?1), pH, PaO₂ (MB: 19.2 ± 6.6, M: 18.2 ± 6.6 kPa) or PaCO_2. Recovery times and quality did not differ between groups, but the time to extubation was significantly longer in group MB (26.9 ± 10.9 minutes) than in group M (20.4 ± 9.4 minutes).Conclusion and clinical relevanceButorphanol CRI at the dose used does not decrease isoflurane requirements in horses anaesthetised with medetomidine–isoflurane and has no influence on cardiopulmonary function or recovery.     

Cardiopulmonary effects and recovery characteristics of horses anesthetized with xylazine–ketamine with midazolam or propofol

Objective

To evaluate cardiopulmonary and recovery characteristics of horses administered total intravenous anesthesia (TIVA) with xylazine and ketamine combined with midazolam or propofol.

A comparison of anesthetic risk factors and outcomes in light and draft horses

As a result of anatomic and physiologic differences, draft breeds may be at greater risk of developing anesthetic complications. The aim of the study was to evaluate and compare anesthetic management of draft (DR) and light (LT) horses. A case‐matched retrospective study of 371 clinical case records of DR (124 cases) and LT (247 cases) horses presented for general anesthesia between 1991 and 1998 was performed. Data were tabulated and comparisons were made using Student's t‐test (significance p < 0.05). Prior to induction, there were significant differences in mean body weight, rectal temperature, PCV, RBC, and serum TP concentration between DR and LT breeds. There were differences in mean doses of pre‐operative butorphanol (LT 21 µg kg^?1; DR 17 µg kg^?1), induction guaifenesin (LT 99 mg kg^?1; DR 88 mg kg^?1), and intraoperative ketamine (LT 0.35 mg kg^?1; DR 0.56 mg kg^?1) required. There were no significant differences in the mean doses of pre‐operative xylazine, detomidine, or induction barbiturate administered. The mean, average, and maximum concentrations of inspired halothane were significantly higher for DR than for LT horses. Draft horses received 33% less intraoperative IV fluids (8.2 mL kg^?1 hour^?1) than LT horses. Mean anesthetic duration, time to extubation, and standing recovery were not significantly different. Induction complications were not reported for either group. Rates of occurrence of intraoperative bradycardia, hypercarbia, hypoxemia, and metabolic acidosis (SBE, TCO₂, and bicarbonate concentration) did not differ significantly. Average MAP was greater in DR horses, but neither the degree nor the mean duration of hypotension differed between DR and LT horses. Mean PaO₂ was significantly lower in DR (246 mm Hg, 32.8 kPa) than in LT (305 mm Hg, 40.7 kPa) breeds. Draft horses were at greater relative risk of hypoventilation than LT horses. The greater MAP and requirement for halothane and intraoperative ketamine may indicate problems in achieving and maintaining a surgical plane of anesthesia. Draft horses may be at a greater risk of ventilation–perfusion mismatching.     

Effect of adenosine infusion on isoflurane MAC in dogs.

Adenosine is a potent analgesic in people and reduces the MAC of halothane in dogs. The purpose of this study was to determine whether adenosine reduces the MAC of isoflurane in dogs. Seven beagles (four males and three females) were anesthetized and randomly assigned to receive adenosine (0.3 mg kg^–1 minute^–1; 6 mL kg^–1 hour^–1, IV) or saline (0.9%, 6 mL kg^–1 hour^–1IV). After an interval of ≥7 days, each dog was reanesthetized and treated with the alternate infusion. Anesthesia was induced and maintained with isoflurane in oxygen. Dogs were intubated and instrumented for measurement of mean systemic arterial blood pressure and airway concentration of isoflurane and end‐tidal partial pressure of carbon dioxide. The MAC for isoflurane was determined using the tail‐clamp technique. Baseline MAC values were 1.25 (1.15, 1.35)% [median (minimum, maximum)] and 1.25 (1.05, 1.45)% before the saline and adenosine treatments, respectively. After 2 hours of infusion with saline or adenosine, MAC values were not different (p = 0.156) and were 1.25 (0.95, 1.35)% and 1.05 (1.00, 1.25)%, respectively. Two hours following the end of each infusion, the MAC values for saline and adenosine treatment groups differed significantly (p = 0.015), but by no more than the normal variation inherent in this study, and were 1.15 (1.15, 1.35)% and 1.05 (1.05, 1.25)%, respectively. Mean arterial blood pressure was 93 (74, 123) mm Hg for saline treated dogs and 67 (52, 72) mm Hg (p = 0.008) during adenosine infusion. End‐tidal carbon dioxide was not different between the two treatment groups. We conclude that adenosine administered at 0.3 mg kg^–1 minute^–1had no effect on isoflurane MAC in dogs, but decreased mean arterial blood pressure.     

Comparison between S(+) ketamine–diazepam and S(+) ketamine–midazolam on anesthetic induction and recovery in dogs

S(+) ketamine, one of the two enantiomers of racemic ketamine, is a phencyclidine derivative that induces amnesia and analgesia. Its activity is related to blockade of NMDA receptors and some opioid action. We compared anesthetic induction and recovery quality with S(+) ketamine in combination with diazepam or midazolam in 10 dogs (ASA 1) admitted for elective surgery. After all clinical examinations, the dogs were separated into two groups (G I and G II). All animals received acepromazine (0.1 mg kg^?1) and fentanyl (5 µg kg^?1) IM, 20 minutes before induction with S(+) ketamine (6 mg kg^?1) and diazepam (0.5 mg kg^?1) IV (G I) or midazolam 0.2 mg kg^?1 (G II) IV. The doses of diazepam and midazolam were chosen according to the literature. All dogs were intubated and then maintained with halothane in oxygen at a vaporizer setting sufficient to maintain surgical anesthesia. Quality of induction, time needed for intubation, heart rate, respiratory rate, SpO₂, time to extubation, and quality of recovery were evaluated. The results were analyzed by Student's t‐test. Smooth induction and recovery were observed in all animals. The time to intubation was 45 ± 20 (GI) and 25 ± 6 seconds (GII), HR was 122 ± 12 (GI) and 125 ± 7 beats minute^?1 (GII), RR was 17 ± 2 (GI) and 21 ± 3 breaths minute^?1 (GII), SpO₂ was 96 ± 2 (GI) and 94 ± 1% (GII), time to extubation was 7 ± 3 (GI) and 4 ± 1 minutes (GII). No statistical differences were found in analyses, although time to intubation was less in GII. The results suggested that both combinations could be used safely for anesthetic induction in healthy dogs.     

Pharmacokinetics of ketamine following a short intravenous infusion to isoflurane-anesthetized New Zealand White rabbits (Oryctolagus cuniculus)

ObjectiveTo describe the pharmacokinetics of ketamine following a short intravenous (IV) infusion to isoflurane-anesthetized rabbits.Study designProspective experimental study.AnimalsA total of six adult healthy female New Zealand White rabbits.MethodsAnesthesia was induced with isoflurane in oxygen. Following determination of isoflurane minimum alveolar concentration (MAC), the isoflurane concentration was reduced to 0.75 MAC and ketamine hydrochloride (5 mg kg^–1) was administered IV over 5 minutes. Blood samples were collected before and at 2, 5, 6, 7, 8, 9, 13, 17, 21, 35, 65, 125, 215 and 305 minutes after initiating the ketamine infusion. Samples were processed immediately and the plasma separated and stored at –80 °C until analyzed for ketamine and norketamine concentrations using liquid chromatography–mass spectrometry. Compartment models were fitted to the concentration–time data for ketamine and for ketamine plus norketamine using nonlinear mixed-effects (population) modeling.ResultsA three- and five-compartment model best fitted the plasma concentration–time data for ketamine and for ketamine plus norketamine, respectively. For the ketamine only model, the volume of distribution at steady state (Vss) was 3217 mL kg^–1, metabolic clearance was 88 mL minute^–1 kg^–1 and the terminal half-life was 59 minutes. For the model including both ketamine and norketamine, Vss were 3224 and 2073 mL kg^–1, total metabolic clearance was 107 and 52 mL minute^–1 kg^–1 and terminal half-lives were 52 and 55 minutes for the parent drug and its metabolite, respectively.Conclusions and clinical relevanceThis study characterized the pharmacokinetics of ketamine and norketamine in isoflurane-anesthetized New Zealand White rabbits following short IV infusion. The results obtained herein will be useful to determine ketamine infusion regimens in isoflurane-anesthetized rabbits.     

Clinical evaluation of ketamine and lidocaine intravenous infusions to reduce isoflurane requirements in horses under general anaesthesia

ObjectiveTo compare isoflurane alone or in combination with systemic ketamine and lidocaine for general anaesthesia in horses.Study designProspective, randomized, blinded clinical trial.AnimalsForty horses (ASA I-III) undergoing elective surgery.MethodsHorses were assigned to receive isoflurane anaesthesia alone (ISO) or with ketamine and lidocaine (LKI). After receiving romifidine, diazepam, and ketamine, the isoflurane end-tidal concentration was set at 1.3% and subsequently adjusted by the anaesthetist (unaware of treatments) to maintain a light plane of surgical anaesthesia. Animals in the LKI group received lidocaine (1.5 mg kg⁻¹ over 10 minutes, followed by 40 μg kg⁻¹ minute⁻¹) and ketamine (60 μg kg⁻¹ minute⁻¹), both reduced to 65% of the initial dose after 50 minutes, and stopped 15 minutes before the end of anaesthesia. Standard clinical cardiovascular and respiratory parameters were monitored. Recovery quality was scored from one (very good) to five (very poor). Differences between ISO and LKI groups were analysed with a two-sample t-test for parametric data or a Fischer's exact test for proportions (p < 0.05 for significance). Results are mean ± SD.ResultsHeart rate was lower (p = 0.001) for LKI (29 ± 4) than for ISO (34 ± 6). End-tidal concentrations of isoflurane (ISO: 1.57% ± 0.22; LKI: 0.97% ± 0.33), the number of horses requiring thiopental (ISO: 10; LKI: 2) or dobutamine (ISO:8; LKI:3), and dobutamine infusion rates (ISO:0.26 ± 0.09; LKI:0.18 ± 0.06 μg kg⁻¹ minute⁻¹) were significantly lower in LKI compared to the ISO group (p < 0.001). No other significant differences were found, including recovery scores.Conclusions and clinical relevanceThese results support the use of lidocaine and ketamine to improve anaesthetic and cardiovascular stability during isoflurane anaesthesia lasting up to 2 hours in mechanically ventilated horses, with comparable quality of recovery.     

A comparison of two intramuscular doses of xylazine–ketamine combination and tolazoline reversal in llamas

The anesthetic and cardiorespiratory effects of a low dose (LD, 0.4 mg kg^?1 xylazine and 4 mg kg^?1 ketamine) and a high dose (HD, 0.8 mg kg^?1 xylazine and 8 mg kg^?1 ketamine) of IM xylazine–ketamine combination were compared in a randomized cross‐over study using six castrated male llamas. Three llamas in each dosage group (LDT, HDT) were assigned to receive IM tolazoline (2 mg kg^?1) after 30 minutes of recumbency. All IM injections were given in the semitendinosus or semimembranosus muscles. Pulse, respiratory rate, and indirect arterial blood pressure were recorded every 10 minutes, and hemoglobin oxygen saturation was recorded every 5 minutes during lateral recumbency. Samples for arterial blood gas analysis were collected 5 minutes following recumbency and every 30 minutes thereafter. Base‐to‐apex ECG was monitored continuously. Analgesia was evaluated every 5 minutes by both a 30 minutes skin pinch and a needle prick of the toe. Most llamas breathed room air throughout anesthesia. Two llamas that developed severe hypoxemia (SpO₂ < 75%) received 5 minutes of nasal oxygen insufflation, but were maintained on room air for the rest of the anesthetic period. anova for repeated measures and Tukey's test were used to analyze cardiorespiratory data. Fischer's exact test was used to compare the ability of each to provide >30 minutes of lateral recumbency and analgesia. A p‐value < 0.05 was considered significant. Both dosages provided reasonably rapid induction following injection (LD: 10.8 ± 6.3 minutes; HD: 5.0 ± 1.1 minutes; p = 0.07). Duration of lateral recumbency and analgesia were 34.7 ± 6.7 and 27.3 ± 4.6 minutes, respectively, in the LDT llamas. None of the three remaining LD llamas remained in lateral recumbency for longer than 12 minutes. Duration of lateral recumbency and analgesia were 87.3 ± 18.5 and 67.7 ± 16.0 minutes, respectively, for the HD llamas that did not receive tolazoline. The HDT llamas were recumbent for a significantly shorter time (43.3 ± 0.6 minutes; p = 0.05). The ability to provide >30 minutes of recumbency and analgesia was better in the HD group (6/6) than in the LD group (2/6) (p = 0.03). No differences between dosages were seen in pulse rate, respiratory rate, or arterial pressures. No ECG abnormalities were seen. Transient hypoxemia was seen in the first 10 minutes of lateral recumbency in the HD group by both hemoglobin oxygen saturation (84 ± 9.5%) and by blood gas PaO₂ (44.5 ± 5.8 mm Hg). It was concluded that the HD provided more consistent results than the LD, but induced transient hypoxemia. Tolazoline shortened the recovery time in llamas receiving the HD.     

Intravenous anaesthesia using detomidine, ketamine and guaiphenesin for laparotomy in pregnant pony mares

Objective To characterize intravenous anaesthesia with detomidine, ketamine and guaiphenesin in pregnant ponies. Animals Twelve pony mares, at 260–320 days gestation undergoing abdominal surgery to implant fetal and maternal vascular catheters. Materials and methods Pre‐anaesthetic medication with intravenous (IV) acepromazine (30 µg kg^?1), butorphanol (20 µg kg^?1) and detomidine (10 µg kg^?1) preceded induction of anaesthesia with detomidine (10 µg kg^?1) and ketamine (2 mg kg^?1) IV Maternal arterial blood pressure was measured directly throughout anaesthesia and arterial blood samples were taken at 20‐minute intervals for measurement of blood gases and plasma concentrations of cortisol, glucose and lactate. Anaesthesia was maintained with an IV infusion of detomidine (0.04 mg mL^?1), ketamine (4 mg mL^?1) and guaiphenesin (100 mg mL^?1) (DKG) for 140 minutes. Oxygen was supplied by intermittent positive pressure ventilation (IPPV) adjusted to maintain PaCO₂ between 5.0 and 6.0 kPa (38 and 45 mm Hg), while PaO₂ was kept close to 20.0 kPa (150 mm Hg) by adding nitrous oxide. Simultaneous fetal and maternal blood samples were withdrawn at 90 minutes. Recovery quality was assessed. Results DKG was infused at 0.67 ± 0.17 mL kg^?1 hour^?1 for 1 hour then reduced, reaching 0.28 ± 0.14 mL kg^?1 hour^?1 at 140 minutes. Arterial blood gas values and pH remained within intended limits. During anaesthesia there was no change in heart rate, but arterial blood pressure decreased by 10%. Plasma glucose and lactate increased (10‐fold and 2‐fold, respectively) and cortisol decreased by 50% during anaesthesia. Fetal umbilical venous pH, PO₂ and PCO₂ were 7.34 ± 0.06, 5.8 ± 0.9 kPa (44 ± 7 mm Hg) and 6.7 ± 0.8 kPa (50 ± 6 mm Hg); and fetal arterial pH, PO₂ and PCO₂ were 7.29 ± 0.06, 4.0 ± 0.7 kPa (30 ± 5 mm Hg) and 7.8 ± 1.7 kPa (59 ± 13 mm Hg), respectively. Surgical conditions were good but four ponies required a single additional dose of ketamine. Ponies took 60 ± 28 minutes to stand and recovery was good. Conclusions and clinical relevance Anaesthesia produced with DKG was smooth while cardiovascular function in mare and fetus was well preserved. This indicates that DKG infusion is suitable for maintenance of anaesthesia in pregnant equidae.     

The effect of ketamine on the MACBAR of sevoflurane in dogs

ObjectiveTo determine the effect of intravenous ketamine on the minimum alveolar concentration of sevoflurane needed to block autonomic response (MAC_BAR) to a noxious stimulus in dogs.Study designRandomized, crossover, prospective design.AnimalsEight, healthy, adult male, mixed-breed dogs, weighing 11.2–16.1 kg.MethodsDogs were anesthetized with sevoflurane on two occasions, 1 week apart, and baseline MAC_BAR (B-MAC_BAR) was determined on each occasion. MAC_BAR was defined as the mean of the end-tidal sevoflurane concentrations that prevented and allowed an increase (≥15%) in heart rate or invasive mean arterial pressure in response to a noxious electrical stimulus (50 V, 50 Hz, 10 ms). Dogs then randomly received either a low-dose (LDS) or high-dose series (HDS) of ketamine, and treatment MAC_BAR (T-MAC_BAR) was determined. The LDS had an initial loading dose (LD) of 0.5 mg kg^?1 and constant rate infusion (CRI) at 6.25 μg kg^?1 minute^?1, followed, after T-MAC_BAR determination, by a second LD (1 mg kg^?1) and CRI (12.5 μg kg^?1 minute^?1). The HDS had an initial LD (2 mg kg^?1) and CRI (25 μg kg^?1 minute^?1) followed by a second LD (3 mg kg^?1) and CRI (50 μg kg^?1 minute^?1). Data were analyzed with a mixed-model anova and are presented as LSM ± SEM.ResultsThe B-MAC_BAR was not significantly different between treatments. Ketamine at 12.5, 25, and 50 μg kg^?1 minute^?1 decreased sevoflurane MAC_BAR, and the maximal decrease (22%) occurred at 12.5 μg kg^?1 minute^?1. The percentage change in MAC_BAR was not correlated with either the log plasma ketamine or norketamine concentration.Conclusions and clinical relevanceKetamine at clinically relevant doses of 12.5, 25, and 50 μg kg^?1 minute^?1 decreased sevoflurane MAC_BAR, although the reduction was neither dose-dependent nor linear.     

Comparison of noninvasive cardiac output measurements by transthoracic bioimpedance, partial carbon dioxide rebreathing, and transesophageal echocardiography with the thermodilution technique in beagle dogs

Most methods for determining cardiac output (CO) have limited application in clinical practice due to the invasive techniques required. This study compared the thermodilution technique (TDCO) with three noninvasive methods for determining CO in anesthetized dogs: transthoracic bioimpedance (BICO), partial CO₂ rebreathing (NICO), and transesophageal echocardiography (TEECO). TDCO was compared to BICO, NICO, and TEECO in six adult sevoflurane anesthetized beagle dogs (9.1–13.0 kg). All dogs were administered midazolam [0.3 mg kg^?1, intravenously (IV)] and butorphanol (0.1 mg kg^?1 IV), followed by ketamine (5.0 mg kg^–1 IV) and sevoflurane in nitrous oxide (1 L minute^–1) and oxygen (1 L minute^–1) and mechanically ventilated. Dogs were maintained at 2.2% end‐tidal sevoflurane (ETsev) concentration for instrumentation and baseline measurements. Low (5.0% ETsev), intermediate (3.3% ETsev), and high cardiac output values were achieved by varying the end‐tidal sevoflurane concentration and the administration of dobutamine (3–10 g kg^–1 minute^–1 and 2.2% ETsev). A minimum of thirty data sets was obtained for each comparison. The correlation coefficients when compared to TDCO were 0.684 for BICO (p < 0.0001), 0.883 for NICO (p < 0.0001), and 0.991 for TEECO (p < 0.0001). Cardiac output values ranged 50–444 mL kg^–1 minute^–1 for TDCO, 100–253 mL kg^–1 minute^–1 for BICO, 64–214 mL kg^–1 minute^–1 for NICO, and 52–401 mL kg^–1 minute^–1 for TEECO. The differences when compared to TDCO ranged – 62–235 mL kg^?1minute^?1 for BICO, 18–220 mL kg^?1 minute^?1 for NICO, and – 35–32 mL kg^–1 minute^–1 for TEECO. Differences were maximum at the highest CO in BICO and NICO. In conclusion, this study demonstrated that BICO and NICO underestimate CO in sevoflurane anesthetized dogs. TEECO is a viable noninvasive method for determining CO in sevoflurane anesthetized dogs.