Comparison of isoflurane and propofol for maintenance of anesthesia in dogs with intracranial disease undergoing magnetic resonance imaging

ObjectiveTo compare isoflurane and propofol for maintenance of anesthesia and quality of recovery in client-owned dogs with intracranial disease undergoing magnetic resonance imaging (MRI).Study designProspective, randomized, clinical trial.AnimalsTwenty-five client-owned dogs with intracranial pathology, 13 females and 12 males, ages 11 months to 13 years, weighing between 3.0 and 48.0 kg.MethodsEach dog was randomly assigned to receive propofol or isoflurane for maintenance of anesthesia. All dogs were not premedicated, were administered propofol intravenously to effect for induction, intubated and mechanically ventilated to maintain an end-tidal carbon dioxide tension 30–35 mmHg (4.0–4.7 kPa). Temperature and cardiac output were measured pre- and post-MRI. Scores for mentation, neurological status, ease of maintenance, and recovery were obtained pre- and post-anesthesia. Pulse oximetry, end-tidal gases, arterial blood pressure, heart rate (HR) and requirements for dopamine administration to maintain mean arterial pressure (MAP) >60 mmHg were recorded throughout anesthesia.ResultsEnd-tidal isoflurane concentration was 0.73 ± 0.35% and propofol infusion rate was 292 ± 119 μg kg^?1 minute^?1. Cardiac index was higher, while HR was lower, with propofol than isoflurane in dogs younger than 5 years, but not in older dogs. Dogs maintained with isoflurane were 14.7 times more likely to require dopamine than propofol dogs. Mentation and maintenance scores and temperature were not different. MAP and diastolic arterial pressure were higher in the propofol group. Recovery scores were better with propofol, although times to extubation were similar. Change in neurological score from pre- to post-anesthesia was not different between treatments.ConclusionsDogs maintained with propofol during MRI had higher arterial pressures, decreased requirements for dopamine, and better recovery scores, compared to dogs maintained with isoflurane.Clinical relevancePropofol anesthesia offered cardiovascular and recovery advantages over isoflurane during MRI in dogs with intracranial disease in this study.     

Dose and cardiopulmonary effects of propofol alone or with midazolam for induction of anesthesia in critically ill dogs

ObjectiveTo determine the dose and cardiopulmonary effects of propofol alone or with midazolam for induction of anesthesia in American Society of Anesthesiologists status ≥III dogs requiring emergency abdominal surgery.Study designProspective, randomized, blinded, clinical trial.AnimalsA total of 19 client-owned dogs.MethodsDogs were sedated with fentanyl (2 μg kg^–1) intravenously (IV) for instrumentation for measurement of heart rate, arterial blood pressure, cardiac index, systemic vascular resistance index, arterial blood gases, respiratory rate and rectal temperature. After additional IV fentanyl (3 μg kg^–1), the quality of sedation was scored and cardiopulmonary variables recorded. Induction of anesthesia was with IV propofol (1 mg kg^–1) and saline (0.06 mL kg^–1; group PS; nine dogs) or midazolam (0.3 mg kg^–1; group PM; 10 dogs), with additional propofol (0.25 mg kg^–1) IV every 6 seconds until endotracheal intubation. Induction/intubation quality was scored, and anesthesia was maintained with isoflurane. Variables were recorded for 5 minutes with the dog in lateral recumbency, breathing spontaneously, and then in dorsal recumbency with mechanical ventilation for the next 15 minutes. A general linear mixed model was used with post hoc analysis for multiple comparisons between groups (p < 0.05).ResultsThere were no differences in group demographics, temperature and cardiopulmonary variables between groups or within groups before or after induction. The propofol doses for induction of anesthesia were significantly different between groups, 1.9 ± 0.5 and 1.1 ± 0.5 mg kg^–1 for groups PS and PM, respectively, and the induction/intubation score was significantly better for group PM.Conclusions and clinical relevanceMidazolam co-induction reduced the propofol induction dose and improved the quality of induction in critically ill dogs without an improvement in cardiopulmonary variables, when compared with a higher dose of propofol alone.     

Effect of tepoxalin on renal function and hepatic enzymes in dogs exposed to hypotension with isoflurane

ObjectiveTo evaluate the possible renal and hepatic toxicity of tepoxalin in dogs exposed to hypotension during isoflurane anesthesia.Study designProspective, randomized experimental study.AnimalsTwenty adult mixed-breed dogs, weighing 18.8 ± 2.8 kg.MethodsThe animals received 10 mg kg^?1 tepoxalin orally 2 hours before the anesthetic procedure (PRE; n = 6), or 30 minutes after anesthesia (POST; n = 6), along with a control group (CON; n = 8), which were only anesthetized. The PRE and POST groups also received the same dose of tepoxalin for 5 days post-procedure. All dogs were anesthetized with propofol and maintained with isoflurane and the end-tidal isoflurane (Fe’Iso) was increased until mean arterial pressure decreased to 50–60 mmHg. These pressures were maintained for 60 minutes. Heart rate, arterial pressures and Fe’Iso were recorded at 0, 10 and every 10 minutes up to 60 minutes of hypotension. Blood gases, pH, electrolytes and bleeding time were analyzed before and at 30 and 60 minutes of hypotension. Renal and hepatic changes were quantified by serum and urinary biochemistry and creatinine clearance.ResultsSerum concentrations of alanine amino transferase (ALT), alkaline phosphatase (ALP) and σ-glutamyl transferase (GGT), blood urea nitrogen (BUN) and creatinine (Cr), and urinary output, urinary Cr, Cr clearance, and GGT:Cr ratio remained stable throughout the evaluations. During the anesthetic procedure there were no important variations in the physiological parameters. No side effects were observed in any of the groups.Conclusions and clinical relevanceTepoxalin did not cause significant effects on renal function or cause hepatic injury in healthy dogs exposed to hypotension with isoflurane, when administered pre- or postanesthetic and continued for five consecutive days.     

Do heat and moisture exchangers in the anaesthesia breathing circuit preserve body temperature in dogs undergoing anaesthesia for magnetic resonance imaging?

Objective

To investigate whether the use of a heat and moisture exchanger (HME) preserves body temperature in dogs weighing <10 kg anaesthetised for magnetic resonance imaging (MRI).

Cardiovascular effects of dose escalating of norepinephrine in healthy dogs anesthetized with isoflurane

ObjectiveTo evaluate the systemic cardiovascular effects of dose escalating administration of norepinephrine in healthy dogs anesthetized with isoflurane.Study designExperimental study.AnimalsA total of six adult laboratory Beagle dogs, 10.5 (9.2–12.0) kg [median (range)].MethodsEach dog was anesthetized with isoflurane at an end-tidal concentration of 1.7%, mechanically ventilated and administered a continuous rate infusion of rocuronium (0.5 mg kg^–1 hour^–1). Each dog was administered incremental dose rates of norepinephrine (0.05, 0.125, 0.25, 0.5, 1.0 and 2.0 μg kg^–1 minute^–1), and each dose was infused for 15 minutes. Cardiovascular variables were recorded before administration and at the end of each infusion period.ResultsNorepinephrine infusion increased mean arterial pressure (MAP), cardiac output (CO) and oxygen delivery in a dose-dependent manner. Systemic vascular resistance did not significantly change during the experiment. Stroke volume increased at the lower dose rates and heart rate increased at the higher dose rates. Oxygen consumption and lactate concentrations did not significantly change during infusions.ConclusionsIn dogs anesthetized with isoflurane, norepinephrine increased MAP by increasing the CO. CO increased with a change in stroke volume at lower dose rates of norepinephrine. At higher dosage, heart rate also contributed to an increase in CO. Norepinephrine did not cause excessive vasoconstriction that interfered with the CO during this study.Clinical relevanceNorepinephrine can be useful for treating hypotension in dogs anesthetized with isoflurane.     

The effect of volatile anaesthetics on the relative sensitivity of facial and distal thoracic limb muscles to vecuronium in dogs

ObjectiveTo compare n. facialis-m. nasolabialis (nF-mNL) and n. ulnar-mm. carpi flexorii (nU-mCF) sensitivity to vecuronium during halothane or isoflurane anaesthesia.Study designRandomized, prospective, experimental study.AnimalsForty-four client-owned dogs (19 male, 25 female) undergoing surgery; mean age: 5.0 years; mean body mass: 24.7 kg.MethodsThirty minutes after acepromazine (0.05 mg kg^?1) and morphine (0.5 mg kg^?1), anaesthesia was induced with intravenous (IV) thiopental and maintained with either halothane (n = 22) or isoflurane (randomly allocated) in oxygen. The lungs were mechanically ventilated and end-tidal inhaled anaesthetic (Fe’_IAA) maintained at 1.2 × MAC values. Neuromuscular transmission at nF-uNL and nU-mCF was monitored using the train of four count. Vecuronium (50 μg kg^?1 IV) was injected (t = 0) after 15 trains, 50-60 minutes after inhalational anaesthesia began, when Fe’_IAA had been constant for >15 minutes. Times of the disappearance (-) and reappearance (+) of the fourth (T4) and first twitch (T1) were recorded allowing the calculation of: latent (t = 0 to T4-) and manifest onset times (t = 0 to T1-) duration of blockade (T1- to T1+) and drug effect (T4- to T4+) and recovery time (T1+-T4+). Student’s paired t-test was used to compare simultaneous responses at nF-uNL and nU-mCF. An unpaired t-test was used to compare anaesthetic effects.ResultsLatent and manifest onset times were significantly (p < 0.05) briefer, blockade and drug effects were significantly longer and recovery from blockade were significantly slower in the nF-mNL unit in both halothane and isoflurane recipients. Profound block duration and drug action were significantly longer and recovery from blockade were significantly slower in halothane recipients at both nerve-muscle units.Conclusion and clinical relevanceThe nF-mNL was more sensitive than nU-mCF to vecuronium, particularly in halothane-anaesthetized dogs.     

Effect of the reverse Trendelenburg position on the incidence of gastroesophageal reflux in dogs anesthetized for elective stifle surgery

ObjectiveTo determine if a 15° reverse Trendelenburg position decreases the incidence of gastroesophageal reflux (GER) compared with a horizontal position in dogs anesthetized for stifle surgery.Study designProspective, randomized parallel-arm study.AnimalsA total of 44 healthy client-owned dogs were enrolled and data from 36 dogs were analyzed.MethodsDogs requiring preoperative radiographs under anesthesia, or with a history of gastrointestinal signs or administered gastroprotectant therapy within 1 month of surgery were excluded. Anesthesia protocol was standardized to include hydromorphone, dexmedetomidine, ketamine, propofol and isoflurane. Dogs were randomly assigned at enrollment to be positioned in a 15° reverse Trendelenburg or a horizontal position for surgery. Continuous pH monitoring was documented throughout the procedure with a 6.4 Fr (2.13 mm) esophageal pH probe positioned in the distal esophagus via the oral cavity. GER was defined as pH < 4.0 (acidic) or > 7.5 (alkaline) for more than 30 seconds. The proportions of dogs developing GER were compared between groups using Fisher’s exact test. Time to reflux was compared using survival curves and the Gehan–Breslow–Wilcoxon test. Statistical significance was set as p < 0.05.ResultsAn episode of GER occurred in 11/36 (30%) dogs. Reflux was alkaline in two dogs and acidic in nine dogs. The proportion of dogs with GER was 5/18 (28%) and 6/18 (33%) for dogs in the reverse Trendelenburg position and horizontal position, respectively, and was not statistically significant (p > 0.99). Median (range) time until reflux was 44 (23–135) and 44.5 (9–56) minutes when dogs were positioned in reverse Trendelenburg position and horizontal position, respectively (p = 0.66; two-tailed Mann–Whitney U test).Conclusions and clinical relevancePositioning the surgery table in a 15° rostral elevation for dogs anesthetized for elective stifle surgical procedures did not decrease the incidence of GER.     

Comparison between intravenous lidocaine and fentanyl on cough reflex and sympathetic response during endotracheal intubation in dogs

ObjectiveTo compare the effects of intravenous (IV) lidocaine and fentanyl on the cough reflex and autonomic response during endotracheal intubation in dogs.Study designRandomized, blinded, superiority clinical trial.AnimalsA total of 46 client-owned dogs undergoing magnetic resonance imaging.MethodsAfter intramuscular methadone (0.2 mg kg^–1), dogs were randomized to be administered either IV lidocaine (2 mg kg^–1; group L) or fentanyl (7 μg kg^–1; group F). After 5 minutes, alfaxalone was administered until endotracheal intubation was possible (1 mg kg^–1 IV over 40 seconds followed by 0.4 mg kg^–1 increments to effect). Total dose of alfaxalone was recorded and cough reflex at endotracheal intubation was scored. Heart rate (HR) was continuously recorded, Doppler systolic arterial blood pressure (SAP) was measured every 20 seconds. Vasovagal tonus index (VVTI) and changes (Δ) in HR, SAP and VVTI between pre-intubation and intubation were calculated. Groups were compared using univariate and multivariate analysis. Statistical significance was set as p < 0.05.ResultsGroup F included 22 dogs and group L 24 dogs. The mean (± standard deviation) alfaxalone dose was 1.1 (± 0.2) and 1.35 (± 0.3) mg kg^–1 in groups F and L, respectively (p = 0.0008). At intubation, cough was more likely in group L (odds ratio = 11.3; 95% confidence intervals, 2.1 – 94.2; p = 0.01) and HR increased in 87.5% and 54.5% of groups L and F, respectively (p = 0.02). The median (range) ΔHR between pre-intubation and intubation was higher (13.1%; – 4.3 to + 55.1) in group L (p = 0.0021). Between groups, SAP and VVTI were similar.Conclusion and clinical relevanceAt the stated doses, whilst reducing the alfaxalone dose, fentanyl is superior to lidocaine in suppressing the cough reflex and blunting the increase in HR at endotracheal intubation in dogs premedicated with methadone.     

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.     

Clinical comparison of recovery from total intravenous anesthesia with propofol and inhalation anesthesia with isoflurane in dogs

The characteristics of recovery from total intravenous anesthesia (TIVA) with propofol and inhalation anesthesia with isoflurane was clinically compared in 149 client-owned dogs that anesthetized for surgical or diagnostic procedures. In all dogs, anesthesia was induced with an intravenous injection of propofol following premedication with acepromazine or diazepam. As a result, 58 dogs anesthetized with propofol-TIVA showed slower but smoother recovery than 91 dogs anesthetized with isoflurane anesthesia. The dogs stood at 34.5 +/- 19.3 and 27.7 +/- 17.2 min after propofol-TIVA and isoflurane anesthesia, respectively. Adverse effects, including hypersalivation, neurologic excitement (paddling, muscle tremor/twitching, opisthotonos) and vomiting/retching, were observed in similar infrequent incidences during the recovery from both anesthetic protocols. Propofol-TIVA is suggested to be an alternative anesthetic protocol for canine practice.     

Laryngeal function in normal dogs administered isoflurane following partial clearance of alfaxalone or propofol

ObjectiveTo assess laryngeal function in normal dogs administered isoflurane following partial clearance of alfaxalone or propofol.Study designRandomized experimental crossover study.AnimalsA group of 12 purpose-bred, male Beagle dogs.MethodsDogs were randomly assigned to one of two treatments: alfaxalone–isoflurane (ALF-ISO) or propofol–isoflurane (PRO-ISO) and anesthetized for three video laryngoscopy examinations. The alternate treatment occurred after ≥ 14 days interval. Examinations were performed after induction of anesthesia (LS-A), after 20 minutes of breathing isoflurane via a facemask (LS-B) and after a further 20 minutes of isoflurane (LS-C). Parameters of objective laryngeal function included inspiratory rima glottidis surface area (RGSA-I), expiratory rima glottidis surface area (RGSA-E) and % RGSA increase, calculated from three consecutive respiratory cycles in the final 15 seconds of each video laryngoscopy examination. The % RGSA increase was calculated using [(RGSA-I – RGSA-E)/RGSA-E] × 100. Subjective laryngeal function was evaluated independently by two experienced surgeons blinded to treatment.ResultsThe % RGSA increase within each treatment was greater for LS-B and LS-C than for LS-A (ALF-ISO: p = 0.03, PRO-ISO: p = < 0.001). There was no difference within each treatment from LS-B compared with LS-C. RGSA-I increased within each treatment from LS-A to both LS-B and LS-C (ALF-ISO: p = 0.002) and to LS-C (PRO-ISO: p = 0.006). Subjective laryngeal function scores improved from LS-A to LS-C.Conclusions and clinical relevanceLaryngeal function improved from postinduction examination following either 20 or 40 minutes of anesthesia with isoflurane via facemask. This study demonstrates that isoflurane may have a lesser effect on arytenoid abduction activity compared with more commonly used intravenous induction anesthetics (alfaxalone and propofol).     

A comparison of the duration and quality of recovery from isoflurane, sevoflurane and desflurane anaesthesia in dogs undergoing magnetic resonance imaging

ObjectiveTo compare the recovery after anaesthesia with isoflurane, sevoflurane and desflurane in dogs undergoing magnetic resonance imaging (MRI) of the brain.Study designProspective, randomized clinical trial.AnimalsThirty‐eight dogs weighing 23.7 ± 12.6 kg.MethodsFollowing pre‐medication with meperidine, 3 mg kg^?1 administered intramuscularly, anaesthesia was induced intravenously with propofol (mean dose 4.26 ± 1.3 mg kg^?1), the trachea was intubated, and an inhalational anaesthetic agent was administered in oxygen. The dogs were randomly allocated to one of three groups: group I (n = 13) received isoflurane, group S (n = 12) received sevoflurane and group D (n = 13) received desflurane. Parameters recorded included cardiopulmonary data, body temperature, end‐tidal anaesthetic concentration, duration of anaesthesia, and recovery times and quality. Qualitative data were compared using chi‐squared and Fisher's exact tests and quantitative data with anova and Kruskal–Wallis test. Post‐hoc comparisons for quantitative data were undertaken with the Mann–Whitney U‐test.ResultsThe duration of anaesthesia [mean and standard deviation (SD)] in group I was: 105.3 (27.48) minutes, group S: 120.67 (19.4) minutes, and group D: 113.69 (26.68) minutes (p = 0.32). Times to extubation [group I: 8 minutes, (interquartile range 6–9.5), group S: 7 minutes (IQR 5–7), group D: 5 minutes (IQR 3.5–7), p = 0.017] and to sternal recumbency [group I: 11 minutes (IQR 9.5–13.5), group S: 9.5 minutes (IQR 7.25–11.75), group D: 7 minutes (range 3.5–11.5), p = 0.048] were significantly different, as were times to standing. One dog, following sevoflurane, had an unacceptable quality of recovery, but most other recoveries were calm, with no significant difference between groups.Conclusions and clinical relevanceAll three agents appeared suitable for use. Dogs’ tracheas were extubated and the dogs recovered to sternal recumbency most rapidly after desflurane. This may be advantageous for animals with some neurological diseases and for day case procedures.     

Efficacy of preanesthetic intramuscular administration of ephedrine for prevention of anesthesia-induced hypotension in cats and dogs

To determine if the preanesthetic administration of ephedrine would prevent anesthesia-induced hypotension in dogs and cats, 10 cats were anesthetized with acepromazine, butorphanol, ketamine, and isoflurane, and 8 dogs were anesthetized with acepromazine, morphine, propofol, and halothane. Cats received ephedrine or saline 10 minutes after premedication. Dogs received ephedrine or saline at the time of premedication. Systolic arterial blood pressure, respiratory rate, heart rate, end-tidal CO₂, O₂ saturation, cardiac rhythm, and rectal temperature were recorded.     

Comparison of the neuromuscular blocking effects of cisatracurium during isoflurane or propofol anesthesia in dogs

ObjectiveTo compare the neuromuscular blocking effects of cisatracurium during isoflurane versus propofol anesthesia in dogs.Study designProspective, randomized study.AnimalsA total of 20 healthy, client-owned dogs (16 females, four males) weighing 12.5–22 kg and aged 1–8 years.MethodsDogs undergoing elective surgery were randomized in equal numbers to an isoflurane (ISO) or propofol (PPF) group. Other drugs used during anesthesia were equal between groups. Single-twitch (ST) stimulation was used to monitor neuromuscular response. After recording the baseline ST (T0), cumulative doses of cisatracurium (0.05 mg kg^–1) were administered intravenously until ST/T0 ≤5%. Effective doses 50 (ED₅₀) and 95 (ED₉₅) of cisatracurium in each group were calculated from group dose-response curves. Recovery of ST (TR) was defined as spontaneous recovery of ST to 80–120% of T0 remaining stable for 2 minutes. The ST after each dose of cisatracurium, duration 25% (time after the last dose until 25% recovery of TR), recovery index (time to recovery from 25% to 75% of TR) and duration to TR (time after the last dose until recovery of TR) were recorded.ResultsIncremental doses of cisatracurium, median (range), were 2 (1–3) in ISO and 4 (2–5) in PPF to achieve ≥95% depression of ST/T0 (p < 0.01). ED₅₀ and ED₉₅ were 20 μg kg^–1 and 117 μg kg^–1 in ISO and 128 μg kg^–1 and 167 μg kg^–1 in PPF, respectively. The duration 25%, recovery index and duration to TR, median (range), were longer in ISO [22.6 (10.3–24.3), 5.3 (3.0–7.8) and 36.1 (20.1–49.7) minutes, respectively] than in PPF [10.2 (6.8–16.5), 3.0 (2.0–3.8) and 17.7 (14.2–28.7) minutes, respectively] (p < 0.01).Conclusions and clinical relevanceCisatracurium-induced neuromuscular blockade was significantly enhanced and prolonged by isoflurane compared with propofol.     

Comparison of isoflurane and halothane as inhalation anaesthetics in the dog

Summary

A number of clinically important features of isoflurane anaesthesia were studied in comparison to those of halothane. Two groups of dogs were used. After light premedication, anaesthesia was induced by mask, and both groups of dogs were maintained for 30 minutes at 1.5 × MAC value of either halothane or isoflurane in a combination of oxygen and nitrous oxide (50:50). All animals were ventilating spontaneously.

There was no difference in the speed of induction of the halothane and isoflurane groups. Blood pressure in both groups dropped to approximately 7.5 kPa (56 mm Hg) during maintenance anesthesia (1.5 MAC), while the heart rate was significantly higher in the isoflurane group. Individual respiratory variables were not significantly different between the two groups, however the differences between the trends of the mean values were significant (Sign‐test). In general, with isoflurane, respiration rates were lower, with the tidal volume and end tidal CO₂ being greater.

The trends in pH and arterial pCO₂ showed a slightly more severe respiratory acidosis in the isoflurane group. However, neither group showed values corresponding to any expected clinical problems. Speed of recovery (determined by times to head‐lift and righting‐reflex) was greater in the isoflurane group. Previously known important features of isoflurane are low biodegradability, low blood: gas partition coefficient, and decreased myocardial sensitivity to catecholamines. It is concluded from this study that isoflurane deserves a place in canine anesthesia whenever these specific pharmacologic properties are desired.     

Comparison of racemic ketamine and S-ketamine as agents for the induction of anaesthesia in goats

ObjectiveTo compare racemic ketamine and S-ketamine as induction agents prior to isoflurane anaesthesia.Study designProspective, blinded, randomized experimental study.AnimalsThirty-one healthy adult goats weighing 39-86 kg.MethodsGoats were premedicated with xylazine (0.1 mg kg^?1) intravenously (IV) given over 5 minutes. Each goat was assigned randomly to one of two treatments for IV anaesthetic induction: group RK (15 goats) racemic ketamine (3 mg kg^?1) and group SK (16 goats) S-ketamine (1.5 mg kg^?1). Time from end-injection to recumbency was measured and quality of anaesthetic induction and condition for endotracheal intubation were scored. Anaesthesia was maintained with isoflurane in oxygen for 90 minutes. Heart rate, invasive arterial blood pressure, oxygen saturation, temperature, end-tidal carbon dioxide and isoflurane were recorded every 5 minutes. Arterial blood samples were taken for analysis every 30 minutes. Recovery time to recurrence of swallowing reflex, to first head movement and to standing were recorded and recovery quality was scored. Two-way repeated measures anova, Mann-Whitney and a Mantel-Cox tests were used for statistical analysis as relevant with a significance level set at p < 0.05.ResultsInduction of anaesthesia was smooth and uneventful in all goats. There was no statistical difference between groups in any measured parameter. Side effects following anaesthetic induction included slight head or limb twitching, moving forward and backward, salivation and nystagmus but were minimal. Endotracheal intubation was achieved in all goats at first or second attempt. Recovery was uneventful on all occasions. All goats were quiet and needed only one or two attempts to stand.Conclusions and clinical relevanceS-ketamine at half the dose rate of racemic ketamine in goats sedated with xylazine and thereafter anaesthetised with isoflurane induces the same clinically measurable effects.     

Peri-operative body temperatures in isoflurane-anaesthetized rabbits following ketamine-midazolam or ketamine-medetomidine

OBJECTIVE: To investigate alterations in peri-operative body temperatures and oesophageal-skin temperatures in isoflurane-anaesthetized rabbits following either ketamine-midazolam or ketamine-medetomidine induction of anaesthesia. ANIMAL POPULATION: Fifty client-owned rabbits, (25 male, 25 female) of different breeds anaesthetized for elective neutering (age range: 3-42 months; mass range: 1.15-4.3 kg). STUDY DESIGN: Randomized, blinded clinical study. METHODS: Pre-anaesthetic rectal temperature was measured. A 24 SWG catheter was placed in a marginal ear vein after local anaesthesia. Ketamine (15 mg kg(-1)) with medetomidine (0.25 mg kg(-1)) (group KMT) or with midazolam (3 mg kg(-1)) (group KMZ) was injected intramuscularly (IM). Following endotracheal intubation anaesthesia was maintained with isoflurane in oxygen. Carprofen (3 mg kg(-1)) and glucose saline (5 mL kg(-1) hour(-1)) were administered through the intravenous catheter. Room temperature and humidity, skin temperature (from tip of pinna) and oesophageal temperature were measured during anaesthesia. Ovariohysterectomy or castration was performed. Rectal temperature was taken when isoflurane was discontinued (time zero) and 30, 60 and 120 minutes thereafter. Atipamezole (0.5 mg kg(-1)) was administered IM to rabbits in group KMT at zero plus 30 minutes. Mass, averaged room temperature and duration of anaesthesia data were compared using a two-tailed t-test. Age, averaged room humidity, rectal temperature decrease, oesophageal temperature decrease and oesophageal-skin difference data were compared using a Kruskal-Wallis test. p < 0.05 was considered significant. RESULTS: The averaged oesophageal-skin temperature difference was significantly greater in group KMT [median 9.85 degrees C (range 6.42-13.85 degrees C)] than in group KMZ [4.38 degrees C (2.83-10.43 degrees C)]. Rectal temperature decreased over the anaesthetic period was not significantly different between the two groups; however, oesophageal temperature decrease was significantly less in group KMT [1.1 degrees C (-0.1-+2.7 degrees C)] than in group KMZ [1.4 degrees C (0.6-3.1 degrees C)]. CONCLUSIONS: Oesophageal-skin temperature difference is larger in rabbits anaesthetized with ketamine-medetomidine combination than ketamine-midazolam. CLINICAL RELEVANCE: The oesophageal temperature in rabbits anaesthetized with ketamine-medetomidine and isoflurane decreases significantly less than in animals anaesthetized with ketamine-midazolam and isoflurane, during anaesthesia.     

Effect of intravenous lidocaine on isoflurane MAC in dogs

Lidocaine decreases minimum alveolar concentration (MAC) of inhalational anesthetics. This study determined the influence of a low dose, 50 µg kg^?1 minute^?1 (LDI) and high dose, 200 µg kg^?1 minute^?1 (HDI) constant rate infusion of lidocaine on the MAC of isoflurane (I) in dogs. Ten mongrel dogs were anesthetized with I in oxygen and mechanically ventilated. End‐tidal anesthetic (Fe ′A) and CO₂ (Pe ′CO₂) concentrations were monitored at the endotracheal tube adaptor with an infrared gas analyzer calibrated before each experiment with a standardized calibration gas mixture designed for the analyzer. Pe ′CO₂ and body temperature were maintained within normal limits. Noxious stimuli included clamping the hindlimb paw (HC) and electrical current (50 V at 50 cycles second^?1 for 10 milliseconds pulse^?1) applied subcutaneously to the forelimb (FE) at the level of the ulna. After an initial equilibration period of at least 40 minutes at an Fe ′A of 1.7%, the Fe ′A was decreased to a value close to the estimated MAC for dogs. MAC was defined as the Fe ′A mid‐way between the value permitting and preventing purposeful movement. Following baseline MAC, a loading dose of 2 mg kg^?1 of lidocaine IV was administered over 3 minutes followed by the LDI, and MAC determinations for the combination started after 30 minutes of infusion. Once determined, the lidocaine infusion was stopped for 30 minutes and the dog maintained at the ETC that prevented movement without the lidocaine. Following this period, a second loading dose of lidocaine was given (2 mg kg^?1) over 3 minutes followed by the HDI, and the MAC determination procedure repeated after 30 minutes of infusion. Data were analyzed using an anova for repeated measures. MAC of I was 1.34 ± 0.035% (mean ± SEM) for both the FE and HC stimuli. The LDI significantly decreased MAC to 1.09 ± 0.043% (18.7% reduction) and HDI to 0.76 ± 0.030% (43.3% reduction). In conclusion, lidocaine infusions decreased the MAC of isoflurane in a dose‐dependent manner.     

Cardiopulmonary effects of dexmedetomidine and ketamine infusions with either propofol infusion or isoflurane for anesthesia in horses

ObjectiveTo examine the cardiopulmonary effects of two anesthetic protocols for dorsally recumbent horses undergoing carpal arthroscopy.Study designProspective, randomized, crossover study.AnimalsSix horses weighing 488.3 ± 29.1 kg.MethodsHorses were sedated with intravenous (IV) xylazine and pulmonary artery balloon and right atrial catheters inserted. More xylazine was administered prior to anesthetic induction with ketamine and propofol IV. Anesthesia was maintained for 60 minutes (or until surgery was complete) using either propofol IV infusion or isoflurane to effect. All horses were administered dexmedetomidine and ketamine infusions IV, and IV butorphanol. The endotracheal tube was attached to a large animal circle system and the lungs were ventilated with oxygen to maintain end-tidal CO₂ 40 ± 5 mmHg. Measurements of cardiac output, heart rate, pulmonary arterial and right atrial pressures, and body temperature were made under xylazine sedation. These, arterial and venous blood gas analyses were repeated 10, 30 and 60 minutes after induction. Systemic arterial blood pressures, expired and inspired gas concentrations were measured at 10, 20, 30, 40, 50 and 60 minutes after induction. Horses were recovered from anesthesia with IV romifidine. Times to extubation, sternal recumbency and standing were recorded. Data were analyzed using one and two-way anovas for repeated measures and paired t-tests. Significance was taken at p=0.05.ResultsPulmonary arterial and right atrial pressures, and body temperature decreased from pre-induction values in both groups. PaO₂ and arterial pH were lower in propofol-anesthetized horses compared to isoflurane-anesthetized horses. The lowest PaO₂ values (70–80 mmHg) occurred 10 minutes after induction in two propofol-anesthetized horses. Cardiac output decreased in isoflurane-anesthetized horses 10 minutes after induction. End-tidal isoflurane concentration ranged 0.5%–1.3%.Conclusion and clinical relevanceBoth anesthetic protocols were suitable for arthroscopy. Administration of oxygen and ability to ventilate lungs is necessary for propofol-based anesthesia.     

Diabetes mellitus affects the duration of action of vecuronium in dogs

ObjectiveTo compare the duration of action of vecuronium in diabetic dogs with a control group.Study designProspective clinical study.AnimalsForty client-owned diabetic (n = 20) and non-diabetic dogs.MethodsDogs were considered free from other concurrent disease based on clinical examination and laboratory data. After pre-anaesthetic medication with acepromazine and methadone, anaesthesia was induced with intravenous (IV) propofol and maintained with isoflurane-nitrous oxide in oxygen. Neuromuscular blockade (NMB) was achieved with vecuronium, 0.1 mg kg^?1 IV and its effects recorded by palpation (pelvic limb digital extension) and electromyography (m. tibialis cranialis) of responses (twitches; T) to repeated train-of-four (TOF) nerve stimulation. Time to onset of NMB was the period between vecuronium injection and loss of fourth twitch (T4) in the TOF pattern recorded by EMG and palpation. Duration of NMB was defined as the time from drug administration to return of T1 by palpation (T1_tactile) and EMG (T1_EMG). Times to return of T2-4 were also recorded. Time from induction of anaesthesia to vecuronium injection was recorded. Heart rate, non-invasive mean arterial pressure, body temperature, end-tidal isoflurane and end-tidal CO₂ concentrations were recorded at onset of NMB and when T1_EMG returned. Loss and return of palpable and EMG responses for diabetic and non-diabetic dogs were compared using t-tests and Mann Whitney U-tests.ResultsThere were significant (p < 0.05) differences between diabetic and non-diabetic dogs for the return of all four palpable and EMG responses. Times (mean ± SD) for return of T1_tactile were 13.2 ± 3.5 and 16.9 ± 4.2 minutes in diabetic and non-diabetic dogs respectively. There were no differences between diabetic and non-diabetic dogs in the time to onset of vecuronium with EMG or tactile monitoring.Conclusions and clinical relevanceThe duration of action of vecuronium was shorter in diabetic dogs as indicated by both tactile and EMG monitoring.