RESEARCH PAPER: Romifidine as a constant rate infusion in isoflurane anaesthetized horses: a clinical study

Objective To evaluate the effects of a constant rate infusion (CRI) of romifidine on the requirement of isoflurane, cardiovascular performance and recovery in anaesthetized horses undergoing arthroscopic surgery. Study design Randomized blinded prospective clinical trial. Animals Thirty horses scheduled for routine arthroscopy. Methods After premedication (acepromazine 0.02 mg kg^?1, romifidine 80 μg kg^?1, methadone 0.1 mg kg^?1) and induction (midazolam 0.06 mg kg^?1 ketamine 2.2 mg kg^?1), anaesthesia was maintained with isoflurane in oxygen. Horses were assigned randomly to receive a CRI of saline (group S) or 40 μg kg^?1 hour^?1 romifidine (group R). The influences of time and treatment on anaesthetic and cardiovascular parameters were evaluated using an analysis of variance. Body weight (t‐test), duration of anaesthesia (t‐test) and recovery score (Wilcoxon Rank Sum Test) were compared between groups. Significance was set at p < 0.05. Results All but one horse were positioned in the dorsal recumbent position and ventilated from the start of anaesthesia. End tidal isoflurane concentrations were similar in both groups at similar time points and over the whole anaesthetic period. Cardiac output was significantly lower in horses of the R group, but there were no significant differences between groups in cardiac index, body weight or age. All other cardiovascular parameters were similar in both groups. Quality of recovery did not differ significantly between groups, but more horses in group R stood without ataxia at the first attempt. One horse from group S had a problematic recovery. Conclusions and clinical relevance No inhalation anaesthetic sparing effect or side effects were observed by using a 40 μg kg^?1 hour^?1 romifidine CRI in isoflurane anaesthetized horses under clinical conditions. Cardiovascular performance remained acceptable. Further studies are needed to identify the effective dose of romifidine that will induce an inhalation anaesthetic sparing effect in anaesthetized horses.     

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

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

Medetomidine continuous rate intravenous infusion in horses in which surgical anaesthesia is maintained with isoflurane and intravenous infusions of lidocaine and ketamine

ObjectiveTo evaluate medetomidine as a continuous rate infusion (CRI) in horses in which anaesthesia is maintained with isoflurane and CRIs of ketamine and lidocaine.Study designProspective, randomized, blinded clinical trial.AnimalsForty horses undergoing elective surgery.MethodsAfter sedation and induction, anaesthesia was maintained with isoflurane. Mechanical ventilation was employed. All horses received lidocaine (1.5 mg kg^?1 initially, then 2 mg kg^?1 hour^?1) and ketamine (2 mg kg^?1 hour^?1), both CRIs reducing to 1.5 mg kg^?1 hour^?1 after 50 minutes. Horses in group MILK received a medetomidine CRI of 3.6 μg kg^?1 hour^?1, reducing after 50 minutes to 2.75 μg kg^?1 hour^?1, and horses in group ILK an equal volume of saline. Mean arterial pressure (MAP) was maintained above 70 mmHg using dobutamine. End-tidal concentration of isoflurane (FE′ISO) was adjusted as necessary to maintain surgical anaesthesia. Group ILK received medetomidine (3 μg kg^?1) at the end of the procedure. Recovery was evaluated. Differences between groups were analysed using Mann-Whitney, Chi-Square and anova tests as relevant. Significance was taken as p < 0.05.ResultsFE′ISO required to maintain surgical anaesthesia in group MILK decreased with time, becoming significantly less than that in group ILK by 45 minutes. After 60 minutes, median (IQR) FE′ISO in MILK was 0.65 (0.4–1.0) %, and in ILK was 1 (0.62–1.2) %. Physiological parameters did not differ between groups, but group MILK required less dobutamine to support MAP. Total recovery times were similar and recovery quality good in both groups.Conclusion and clinical relevanceA CRI of medetomidine given to horses which were also receiving CRIs of lidocaine and ketamine reduced the concentration of isoflurane necessary to maintain satisfactory anaesthesia for surgery, and reduced the dobutamine required to maintain MAP. No further sedation was required to provide a calm recovery.     

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.     

Effect of detomidine or romifidine constant rate infusion on plasma lactate concentration and inhalant requirements during isoflurane anaesthesia in horses

Objective

Influence of detomidine or romifidine constant rate infusion (CRI) on plasma lactate concentration and isoflurane requirements in horses undergoing elective surgery.

Evaluation of a romifidine constant rate infusion protocol with or without butorphanol for dentistry and ophthalmologic procedures in standing horses

ObjectiveTo compare the clinical usefulness of constant rate infusion (CRI) protocols of romifidine with or without butorphanol for sedation of horses.Study designProspective ‘blinded’ controlled trial using block randomization.AnimalsForty healthy Freiberger stallions.MethodsThe horses received either intravenous (IV) romifidine (loading dose: 80 μg kg^?1; infusion: 30 μg kg^?1 hour^?1) (treatment R, n = 20) or romifidine combined with butorphanol (romifidine loading: 80 μg kg^?1; infusion: 29 μg kg^?1 hour^?1, and butorphanol loading: 18 μg kg^?1; infusion: 25 μg kg^?1 hour^?1) (treatment RB, n = 20). Twenty-one horses underwent dentistry and ophthalmic procedures, while 19 horses underwent only ophthalmologic procedure and buccal examination. During the procedure, physiologic parameters and occurrence of head/muzzle shaking or twitching and forward movement were recorded. Whenever sedation was insufficient, additional romifidine (20 μg kg^?1) was administered IV. Recovery time was evaluated by assessing head height above ground. At the end of the procedure, overall quality of sedation for the procedure was scored by the dentist and anaesthetist using a visual analogue scale. Statistical analyses used two-way anova or linear mixed models as relevant.ResultsSedation quality scores as assessed by the anaesthetist were R: median 7.55, range: 4.9–9.0 cm, RB: 8.8, 4.7–10.0 cm, and by the dentist R: 6.6, 3.0–8.2 cm, RB: 7.9, 6.6–8.8 cm. Horses receiving RB showed clinically more effective sedation as demonstrated by fewer poor scores and a tendency to reduced additional drug requirements. More horses showed forward movement and head shaking in treatment RB than treatment R. Three horses (two RB, one R) had symptoms of colic following sedation.Conclusions and clinical relevanceThe described protocols provide effective sedation under clinical conditions but for dentistry procedures, the addition of butorphanol is advantageous.     

Comparison of respiratory function during TIVA and isoflurane anaesthesia in ponies Part II: breathing patterns and transdiaphragmatic pressure

ObjectiveTo compare breathing patterns and transdiaphragmatic pressure during total intravenous (TIVA) and isoflurane anaesthesia in ponies.Study designExperimental, cross–over study.AnimalsSix healthy ponies weighing 286 (233–388) ± 61 kg, age 13 (9–16) ± 3 years.MethodsFollowing premedication with romifidine [80 μg kg^?1 intravenously (IV)], general anaesthesia was induced with midazolam (0.06 mg kg^?1 IV) and ketamine (2.5 mg kg^?1 IV) and maintained with either isoflurane (Fe’Iso = 1.1%) (T-ISO) or an IV combination of romifidine (120 μg kg^?1 per hour), midazolam (0.09 mg kg^?1 hour^?1) and ketamine (3.3 mg kg^?1 hour^?1) (T-TIVA), while breathing 60% oxygen (FIO₂). The circumference changes of the rib cage (RC) and abdominal compartment (ABD) were recorded using respiratory ultrasonic plethysmography (RUP). Balloon tipped catheters were placed in the distal oesophagus and the stomach and maximal transdiaphragmatic pressure (P_{di max)} was calculated during Mueller's manoeuvre.ResultsThe breathing pattern T-ISO was more regular and respiratory rate significantly lower compared with T-TIVA. Ponies in T-TIVA showed regularly appearing sighs, which were never observed in T-ISO. Different contribution of the RC and ABD compartments to the breathing pattern was observed with a smaller participation of the RC to the total volume change during T-ISO. Transdiaphragmatic pressures (mean 13.7 ± SD 8.61 versus 23.4 ± 7.27 cmH₂O, p < 0.0001) were higher in T-TIVA compared to T-ISO. The sum of the RC and ABD circumferential changes was lower during T-TIVA compared to T-ISO (6.32 ± 4.42 versus 11.72 ± 4.38 units, p < 0.0001).Conclusion and clinical relevanceMarked differences in breathing pattern and transdiaphragmatic pressure exist during inhalation- and TIVA and these should be taken into account for clinical estimation of anaesthetic depth.     

Influence of a constant rate infusion of dexmedetomidine on cardiopulmonary function and recovery quality in isoflurane anaesthetized horses

ObjectiveTo investigate the influence of a dexmedetomidine constant rate infusion (CRI) in horses anaesthetized with isoflurane.Study designProspective, randomized, blinded, clinical study.AnimalsForty adult healthy horses (weight mean 491 ± SD 102 kg) undergoing elective surgery.MethodsAfter sedation [dexmedetomidine, 3.5 μg kg^?1 intravenously (IV)] and induction IV (midazolam 0.06 mg kg^?1, ketamine 2.2 mg kg^?1), anaesthesia was maintained with isoflurane in oxygen/air (FiO₂ 55–60%). Horses were ventilated and dobutamine was administered when hypoventilation [arterial partial pressure of CO₂ > 8.00 kPa (60 mmHg)] and hypotension [arterial pressure 70 mmHg] occurred respectively. During anaesthesia, horses were randomly allocated to receive a CRI of dexmedetomidine (1.75 μg kg^?1 hour^?1) (D) or saline (S). Monitoring included end-tidal isoflurane concentration, cardiopulmonary parameters, and need for dobutamine and additional ketamine. All horses received 0.875 μg kg^?1 dexmedetomidine IV for the recovery period. Age and weight of the horses, duration of anaesthesia, additional ketamine and dobutamine, cardiopulmonary data (anova), recovery scores (Wilcoxon Rank Sum Test), duration of recovery (t-test) and attempts to stand (Mann–Whitney test) were compared between groups. Significance was set at p < 0.05.ResultsHeart rate and arterial partial pressure of oxygen were significantly lower in group D compared to group S. An interaction between treatment and time was present for cardiac index, oxygen delivery index and systemic vascular resistance. End-tidal isoflurane concentration and heart rate significantly increased over time. Packed cell volume, systolic, diastolic and mean arterial pressure, arterial oxygen content, stroke volume index and systemic vascular resistance significantly decreased over time. Recovery scores were significantly better in group D, with fewer attempts to stand and significantly longer times to sternal position and first attempt to stand.Conclusions and clinical relevance A dexmedetomidine CRI produced limited cardiopulmonary effects, but significantly improved recovery quality.     

Cardiovascular responses to transvenous electrical cardioversion of atrial fibrillation in anaesthetized horses

ObjectiveTo examine the influence of direct current shock application in anaesthetized horses with atrial fibrillation (AF) and to study the effects of cardioversion to sinus rhythm (SR).Study designProspective clinical study.AnimalsEight horses successfully treated for AF (transvenous electrical cardioversion after amiodarone pre-treatment).MethodsCardioversion catheters and a pacing catheter were placed under sedation [detomidine 10 μg kg^?1 intravenously (IV)]. After additional sedation (5–10 μg kg^?1 detomidine, 0.1 mg kg^?1 methadone IV), anaesthesia was induced with ketamine, 2.2 mg kg^?1 and midazolam, 0.06 mg kg^?1 (IV) in a sling and maintained with isoflurane in oxygen. Flunixin meglumine, 1.1 mg kg^?1, was administered IV. Shocks were delivered as biphasic truncated exponential waves, synchronized with the R-wave of the electrocardiogram. Monitoring included pulse oximetry, electrocardiography, capnography, inhalational anaesthetic agent concentration, arterial blood pressure, LiDCO and PulseCO cardiac index (CI) and arterial blood gases. Values before and after the first unsuccessful shock and before and after cardioversion to SR were compared.ResultsValues before the first shock were comparable to reported values in healthy, isoflurane anaesthetized horses. Reliable CI measurements could not be obtained using the PulseCO technique. Intermittent positive pressure ventilation was required in most horses (bradypnea and/or PaCO₂ >8 kPa, 60 mmHg), while dobutamine was administered in two horses (0.3–0.5 μg kg^?1 minute^?1). After the 1st unsuccessful shock application, systolic arterial pressure (SAP) was decreased (p = 0.025), other recorded values were not influenced (CI measurements not available for this analysis). SR was associated with increases in CI (p = 0.039) and stroke index (p = 0.002) and a decrease in SAP (p = 0.030).Conclusions and clinical relevanceDespite the presence of AF, cardiovascular function was well maintained during anaesthesia and was not affected by shock application. Cardiac index and stroke index increased and SAP decreased after cardioversion.     

Detomidine and the combination of detomidine and MK‐467, a peripheral alpha‐2 adrenoceptor antagonist,as premedication in horses anaesthetized with isoflurane

ObjectiveTo investigate MK-467 as part of premedication in horses anaesthetized with isoflurane.Study designExperimental, crossover study with a 14 day wash-out period.AnimalsSeven healthy horses.MethodsThe horses received either detomidine (20 μg kg⁻¹ IV) and butorphanol (20 μg kg⁻¹ IV) alone (DET) or with MK-467 (200 μg kg⁻¹ IV; DET + MK) as premedication. Anaesthesia was induced with ketamine (2.2 mg kg⁻¹) and midazolam (0.06 mg kg⁻¹) IV and maintained with isoflurane. Heart rate (HR), mean arterial pressure (MAP), end-tidal isoflurane concentration, end-tidal carbon dioxide tension, central venous pressure, fraction of inspired oxygen (FiO₂) and cardiac output were recorded. Blood samples were taken for blood gas analysis and to determine plasma drug concentrations. The cardiac index (CI), systemic vascular resistance (SVR), ratio of arterial oxygen tension to inspired oxygen (P_aO₂/FiO₂) and tissue oxygen delivery (DO₂) were calculated. Repeated measures anova was applied for HR, CI, MAP, SVR, lactate and blood gas variables. The Student's t-test was used for pairwise comparisons of drug concentrations, induction times and the amount of dobutamine administered. Significance was set at p < 0.05.ResultsThe induction time was shorter, reduction in MAP was detected, more dobutamine was given and HR and CI were higher after DET+MK, while SVR was higher with DET. Arterial oxygen tension and P_aO₂/FiO₂ (40 minutes after induction), DO₂ and venous partial pressure of oxygen (40 and 60 minutes after induction) were higher with DET+MK. Plasma detomidine concentrations were reduced in the group receiving MK-467. After DET+MK, the area under the plasma concentration time curve of butorphanol was smaller.Conclusions and clinical relevanceMK-467 enhances cardiac function and tissue oxygen delivery in horses sedated with detomidine before isoflurane anaesthesia. This finding could improve patient safety in the perioperative period. The dosage of MK-467 needs to be investigated to minimise the effect of MK-467 on MAP.     

Development of a romifidine constant rate infusion with or without butorphanol for standing sedation of horses

ObjectiveTo determine constant rate infusion (CRI) protocols for romifidine (R) and romifidine combined with butorphanol (RB) resulting in constant sedation and romifidine plasma concentrations.Study designBlinded randomized crossover study.AnimalsTen adult research horses.MethodsPart I: After determining normal height of head above ground (HHAG = 100%), loading doses of romifidine (80 μg kg^?1) with butorphanol (RB: 18 μg kg^?1) or saline (R) were given intravenously (IV). Immediately afterwards, a butorphanol (RB: 25 μg kg^?1 hour^?1) or saline (R) CRI was administered for 2 hours. The HHAG was used as marker of sedation depth. Sedation was maintained for 2 hours by additional romifidine (20 μg kg^?1) whenever HHAG > 50%. The dose rate of romifidine (μg kg^?1 hour^?1) required to maintain sedation was calculated for both treatments. Part II: After loading doses, the romifidine CRIs derived from part I were administered in parallel to butorphanol (RB) or saline (R). Sedation and ataxia were evaluated periodically. Romifidine plasma concentrations were measured by HPLC-MS-MS at 0, 5, 10, 15, 30, 45, 60, 90, 105, and 120 minutes. Data were analyzed using paired t-test, Fisher's exact test, Wilcoxon signed rank test, and two-way anova for repeated measures (p < 0.05).ResultsThere was no significant difference in romifidine requirements (R: 30; RB: 29 μg kg^?1 hour^?1). CRI protocols leading to constant sedation were developed. Time to first additional romifidine bolus was significantly longer in RB (mean ± SD, R: 38.5 ± 13.6; RB: 50.5 ± 11.7 minutes). Constant plasma concentrations of romifidine were achieved during the second hour of CRI. Ataxia was greater when butorphanol was added.ConclusionRomifidine bolus, followed by CRI, provided constant sedation assessed by HHAG. Butorphanol was ineffective in reducing romifidine requirements in unstimulated horses, but prolonged the sedation caused by the initial romifidine bolus.Clinical relevanceBoth protocols need to be tested under clinical conditions.     

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.     

Behavioural and cardiovascular effects of medetomidine constant rate infusion compared with detomidine for standing sedation in horses

ObjectiveTo compare the efficacy of a medetomidine constant rate infusion (CRI) with a detomidine CRI for standing sedation in horses undergoing high dose rate brachytherapy.Study designRandomized, controlled, crossover, blinded clinical trial.AnimalsA total of 50 horses with owner consent, excluding stallions.MethodsEach horse was sedated with intravenous acepromazine (0.02 mg kg^–1), followed by an α₂-adrenoceptor agonist 30 minutes later and then by butorphanol (0.1 mg kg^–1) 5 minutes later. A CRI of the same α₂-adrenoceptor agonist was started 10 minutes after butorphanol administration and maintained for the treatment duration. Treatments were given 1 week apart. Each horse was sedated with detomidine (bolus dose, 10 μg kg^–1; CRI, 6 μg kg^–1 hour^–1) or medetomidine (bolus dose, 5 μg kg^–1; CRI, 3.5 μg kg^–1 hour^–1). If sedation was inadequate, a quarter of the initial bolus of the α₂-adrenoceptor agonist was administered. Heart rate (HR) was measured via electrocardiography, and sedation and behaviour evaluated using a previously published scale. Between treatments, behaviour scores were compared using a Wilcoxon signed-rank test, frequencies of arrhythmias with chi-square tests, and HR with two-tailed paired t tests. A p value <0.05 indicated statistical significance.ResultsTotal treatment time for medetomidine was longer than that for detomidine (p = 0.04), and ear movements during medetomidine sedation were more numerous than those during detomidine sedation (p = 0.03), suggesting there may be a subtle difference in the depth of sedation. No significant differences in HR were found between treatments (p ≥ 0.09). Several horses had arrhythmias, with no difference in their frequency between the two infusions.Conclusions and clinical relevanceMedetomidine at this dose rate may produce less sedation than detomidine. Further studies are required to evaluate any clinical advantages to either drug, or whether a different CRI may be more appropriate.     

Effects of fentanyl–lidocaine–ketamine versus sufentanil–lidocaine–ketamine on the isoflurane requirements in dogs undergoing total ear canal ablation and lateral bulla osteotomy

ObjectiveTo compare the isoflurane-sparing effects of sufentanil–lidocaine–ketamine (SLK) and fentanyl–lidocaine–ketamine (FLK) infusions in dogs undergoing total ear canal ablation and lateral bulla osteotomy (TECA–LBO).Study designRandomized blinded clinical study.AnimalsA group of 20 client-owned dogs undergoing TECA–LBO.MethodsIntravenous (IV) administration of lidocaine (3 mg kg^–1) and ketamine (0.6 mg kg^–1) with fentanyl (5.4 μg kg^–1; n = 10; FLK group) or sufentanil (0.72 μg kg^–1; n = 10; SLK group) was immediately followed by the corresponding constant rate infusion (CRI) (lidocaine 3 mg kg^–1 hour^–1; ketamine 0.6 mg kg^–1 hour^–1; either fentanyl 5.4 μg kg^–1 hour^–1 or sufentanil 0.72 μg kg^–1 hour^–1). Anaesthesia was induced with propofol 3–5 mg kg^–1 IV and was maintained with isoflurane. End-tidal isoflurane concentration (Fe′Iso) was decreased in 0.2% steps every 15 minutes until spontaneous movements were observed (treated with propofol 1 mg kg^–1 IV) or an increase of > 30% in heart rate or mean arterial pressure from baseline occurred (treated with rescue fentanyl or sufentanil). Quality of recovery and pain were assessed at extubation using the short-form Glasgow Composite Pain Scale (SF-GCPS), Colorado State University Canine Acute Pain scale (CSU-CAP), and visual analogue scale (VAS). Data were analysed with analysis of variance, t tests, Fisher test and Spearman coefficient (p < 0.05).ResultsFe′Iso decreased significantly in SLK group (45%; p = 0.0006) but not in FLK (15%; p = 0.1135) (p = 0.0136). SLK group had lower scores for recovery quality (p = 0.0204), SF-GCPS (p = 0.0071) and CSU-CAP (p = 0.0273) than FLK at extubation. Intraoperative rescue analgesia and VAS were not significantly different between groups.Conclusions and clinical relevanceCompared with FLK infusion, CRI of SLK at these doses decreased isoflurane requirements, decreased pain scores and improved recovery quality at extubation in dogs undergoing TECA–LBO.     

Evaluation of the perioperative stress response from dexmedetomidine infusion alone,with butorphanol bolus or remifentanil infusion compared with ketamine and morphine infusions in isoflurane-anesthetized horses

ObjectiveTo evaluate perioperative stress-related hormones in isoflurane-anesthetized horses administered infusions of dexmedetomidine alone or with butorphanol or remifentanil, compared with ketamine–morphine.Study designRandomized, prospective, nonblinded clinical study.AnimalsA total of 51 horses undergoing elective surgical procedures.MethodsHorses were premedicated with xylazine, anesthesia induced with ketamine–diazepam and maintained with isoflurane and one of four intravenous infusions. Partial intravenous anesthesia (PIVA) was achieved with dexmedetomidine (1.0 μg kg^–1 hour^–1; group D; 12 horses); dexmedetomidine (1.0 μg kg^–1 hour^–1) and butorphanol bolus (0.05 mg kg^–1; group DB; 13 horses); dexmedetomidine (1.0 μg kg^–1 hour^–1) and remifentanil (3.0 μg kg^–1 hour^–1; group DR; 13 horses); or ketamine (0.6 mg kg^–1 hour^–1) and morphine (0.15 mg kg^–1, 0.1 mg kg^–1 hour^–1; group KM; 13 horses). Infusions were started postinduction; butorphanol bolus was administered 10 minutes before starting surgery. Blood was collected before drugs were administered (baseline), 10 minutes after ketamine–diazepam, every 30 minutes during surgery and 1 hour after standing. Mean arterial pressure (MAP), pulse rate, end-tidal isoflurane concentration, cortisol, nonesterified fatty acids (NEFA), glucose and insulin concentrations were compared using linear mixed models. Significance was assumed when p < 0.05.ResultsWithin D, cortisol was lower at 120–180 minutes from starting surgery compared with baseline. Cortisol was higher in KM than in D at 60 minutes from starting surgery. Within all groups, glucose was higher postinduction (except DR) and 60 minutes from starting surgery, and insulin was lower during anesthesia and higher after standing compared with baseline. After standing, NEFA were higher in KM than in DB. In KM, MAP increased at 40–60 minutes from starting surgery compared with 30 minutes postinduction.Conclusions and clinical relevanceDexmedetomidine suppressed cortisol release more than dexmedetomidine–opioid and ketamine–morphine infusions. Ketamine–morphine PIVA might increase catecholamine activity.     

Comparison of respiratory function during TIVA (romifidine,ketamine, midazolam) and isoflurane anaesthesia in spontaneously breathing ponies Part I: blood gas analysis and cardiorespiratory variables

ObjectiveTo compare pulmonary function and gas exchange in ponies during maintenance of anaesthesia with isoflurane or by a total intravenous anaesthesia (TIVA) technique.Study designExperimental, cross–over study.AnimalsSix healthy ponies weighing mean 286 (range 233–388) ± SD 61 kg, age 13 (9-16) ± 3 years.MethodsThe ponies were anaesthetized twice, a minimum of two weeks apart. Following sedation with romifidine [80 μg kg^?1 intravenously (IV)], anaesthesia was induced IV with midazolam (0.06 mg kg^?1) and ketamine (2.5 mg kg^?1), then maintained either with inhaled isoflurane (Fe’Iso = 1.1 vol%) (T-ISO) or an IV infusion of romifidine (120 μg kg^?1 hour^?1), midazolam (0.09 mg kg^?1 hour^?1 IV) and ketamine (3.3 mg kg^?1 hour^?1) (T-TIVA). Ponies were placed in lateral recumbency. Breathing was spontaneous and Fi’O₂ 60%. After an instrumentation/stabilisation period of 30 minutes, arterial and mixed venous blood samples were taken simultaneously every 10 minutes for 60 minutes and analysed immediately. Oxygen extraction ratio (O₂ER) and venous admixture were calculated. Tidal volume (TV), minute volume (MV), respiratory rate (f_R), packed cell volume (PCV), arterial blood pressure and heart rate (HR) were measured and recorded. Data were analysed with mixed model anova (a = 0.05). Treatments were compared overall and at two selected time points (T30 and T60) using Bonferroni correction.ResultsArterial and mixed venous partial pressures of O₂ and CO₂, and TV were significantly lower and MV and f_R were higher in T-TIVA compared to T-ISO. Venous admixture did not differ between treatments. O₂ER was significantly higher in T-TIVA. Mean arterial pressure was higher and HR was lower in T-TIVA compared to T-ISO.Conclusions and clinical relevanceWhilst arterial CO₂ was within an acceptable range during both protocols, the impairment of oxygenation was more pronounced with the T-TIVA evidenced by lower arterial and venous oxygen partial pressures.     

Anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in isoflurane‐anaesthetized sheep

ObjectiveTo determine the anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in sheep anaesthetized with isoflurane and undergoing orthopaedic surgery.Study designProspective, randomised, ‘blinded’ controlled study.AnimalsTwenty healthy sheep (weight mean 41.1 ± SD 4.5 kg).MethodsSheep were sedated with intravenous (IV) dexmedetomidine (4 μg kg⁻¹) and morphine (0.2 mg kg⁻¹). Anaesthesia was induced with propofol (1 mg kg⁻¹ minute⁻¹ to effect IV) and maintained with isoflurane in oxygen and a continuous rate infusion (CRI) of fentanyl 10 μg kg⁻¹ hour⁻¹ (group F) or saline (group P) for 100 minutes. The anaesthetic induction dose of propofol, isoflurane expiratory fraction (Fe’iso) required for maintenance and cardiorespiratory measurements were recorded and blood gases analyzed at predetermined intervals. The quality of recovery was assessed. Results were compared between groups using t-tests or Mann–Whitney as relevant.ResultsThe propofol induction dose was 4.7 ± 2.4 mg kg⁻¹. Fe’iso was significantly lower (by 22.6%) in group F sheep than group P (p = 0). Cardiac index (mean ± SD mL kg⁻¹ minute⁻¹) was significantly (p = 0.012) lower in group F (90 ± 15) than group P (102 ± 35). Other measured cardiorespiratory parameters did not differ statistically significantly between groups. Recovery times and recovery quality were statistically similar in both groups.Conclusions and clinical relevanceFentanyl reduced isoflurane requirements without clinically affecting the cardiorespiratory stability or post-operative recovery in anaesthetized sheep undergoing orthopaedic surgery.     

Cardiopulmonary effects of an infusion of remifentanil or morphine in horses anesthetized with isoflurane and dexmedetomidine

ObjectiveTo examine the cardiopulmonary effects of infusions of remifentanil or morphine, and their influence on recovery of horses anesthetized with isoflurane and dexmedetomidine.Study designRandomized crossover study with 7-day rest periods.AnimalsSix adult horses (507 ± 61 kg).MethodsAfter the horses were sedated with xylazine, anaesthesia was induced with ketamine and diazepam, and maintained with isoflurane. After approximately 60 minutes, a dexmedetomidine infusion was started (0.25 μg kg^?1 then 1.0 μg^?1 kg^?1 hour^?1) in combination with either saline (group S), morphine (0.15 mg kg^?1 then 0.1 mg kg^?1 hour^?1; group M), or remifentanil (6.0 μg kg^?1 hour^?1; group R) for 60 minutes. Mean arterial pressure, heart rate, end-tidal carbon dioxide tension, and end-tidal isoflurane concentration were recorded every 5 minutes. Core body temperature, cardiac output, right ventricular and arterial blood-gas values were measured every 15 minutes. Cardiac index, systemic vascular resistance (SVR), intrapulmonary shunt fraction, alveolar dead space, oxygen delivery and extraction ratio were calculated. Recoveries were videotaped and scored by two observers blinded to the treatment. Data were analyzed using repeated measures anova followed by Dunnett’s or Bonferroni’s significant difference test. Recovery scores were analyzed using a Kruskal–Wallis test.ResultsNo significant differences were found among groups. Compared to baseline, heart rate decreased and SVR increased significantly in all groups, and cardiac index significantly decreased in groups S and M. Hemoglobin concentration, oxygen content and oxygen delivery significantly decreased in all groups. The oxygen extraction ratio significantly increased in groups M and R. Lactate concentration significantly increased in group S. Recovery scores were similar among groups.Conclusions and clinical relevanceDexmedetomidine alone or in combination with remifentanil or morphine infusions was infused for 60 minutes without adverse effects in the 6 healthy isoflurane-anesthetized horses in this study.