A comparison of extradural and intravenous methadone on intraoperative isoflurane and postoperative analgesia requirements in dogs

Objective To compare the effects of intravenous (IV) and extradural (ED) methadone on end‐tidal isoflurane concentration (Fe ′ISO) and postoperative analgesic requirements in dogs undergoing femoro‐tibial joint surgery. Study Design Randomized, blinded, clinical study. Animals Twenty‐four healthy client‐owned dogs undergoing surgical repair of ruptured cruciate ligaments. Methods Dogs were randomly assigned to two groups of 12 animals and received either ED or IV methadone (0.3 mg kg^?1 diluted with saline to 0.2 mL kg^?1). Pre‐anaesthetic medication was IV acepromazine (0.05 mg kg^?1). Anaesthesia was induced with propofol and maintained initially with an Fe ′ISO of 1.0% delivered in oxygen. Methadone was injected with the dogs in sternal recumbency; the observer was unaware of the administration route. At 10 minutes (stimulation 1) and 20 minutes (stimulation 2) after methadone administration pelvic limb reflexes were tested by digit‐clamping. The time at skin incision (stimulation 3), joint‐capsule incision (stimulation 4), tibial tuberosity drilling (stimulation 5), fabellar suturing (stimulation 6) and extracapsular tightening (stimulation 7) were noted. Changes in heart rate (HR) and respiratory rate and arterial blood pressure associated with surgery were recorded along with the corresponding Fe ′ISO. After 20 minutes of anaesthesia, Fe ′ISO was decreased to the minimum required to maintain stable anaesthesia. Immediately after tracheal extubation, 1, 2, 3 and 6 hours postoperatively and on the morning after surgery, the degree of pain present was assessed using a numerical rating scale. The HR, respiratory rates and blood pressure were also recorded at these times. Serum cortisol and blood glucose concentrations were measured before pre‐anaesthetic medication and at each postoperative pain scoring interval except at 1 and 2 hours. Ketoprofen (2 mg kg^?1), carprofen (4 mg kg^?1) or meloxicam (0.2 mg kg^?1) were given by subcutaneous injection whenever pain scoring indicated moderate discomfort was present. Results Controlled ventilation was required in six dogs which stopped breathing after IV methadone. The median Fe ′ISO at stimulus 5 was 1.0% in the IV and 0.83% in the ED group. At stimulus 6, Fe ′ISO was 1.0% in the IV and 0.8% in the ED group; the difference was statistically significant (p ≤ 0.05). There was no significant difference in the duration of postoperative analgesia associated with administration route. Conclusions Extradural methadone significantly reduces the isoflurane requirement compared with IV methadone during femoro‐tibial joint surgery in dogs. Clinical relevance Extradural methadone provides safe and effective pain relief in dogs undergoing cruciate ligament repair.     

Comparison of the hanging-drop technique and running-drip method for identifying the epidural space in dogs

Objective

To compare the running-drip and hanging-drop techniques for locating the epidural space in dogs.

Two cases of bradyarrhythmia and hypotension after extradural injections in dogs

OBSERVATIONS: Two healthy obese, seven-year-old, female Rottweilers weighing 40 and 57 kg were submitted for cranial cruciate repair. They were premedicated with intravenous methadone (0.1 mg kg(-1)) and acepromazine (0.01 and 0.02 mg kg(-1)). Anesthesia was induced with propofol (3.6 and 2.5 mg kg(-1)) and maintained with isoflurane in oxygen using a circle breathing system. The dogs were placed in sternal recumbency and epidural injection of lidocaine/bupivacaine or lidocaine/bupivacaine/morphine (0.2 mL/kg, 8 and 11 mL) was carried out over 1.5 and 4 minutes. Epidural pressures were 79 and 72 mmHg at the end of the injections. The first dog's heart rate decreased from 80 to 65 beats minute(-1) with a second degree atrioventricular (AV) block. The arterial pressure decreased from 100 to 50 mmHg. These responded to atropine (0.01 mg kg(-1) IV). The second dog's heart rate decreased from 120 to 60 beats minute(-1) while arterial pressure decreased from 72 to 38 mmHg. No treatment was given and heart rate and arterial blood pressure returned to acceptable ranges. CONCLUSIONS: These cases suggest that large increases in epidural pressure may cause significant cardiovascular effects. This may be avoided by using lower volumes and discontinuing injection if significant back pressure is detected.     

The effects of preoperative extradural bupivacaine and morphine on the stress response in dogs undergoing femoro-tibial joint surgery

OBJECTIVE: To evaluate the efficacy of preoperative extradural bupivacaine and morphine in attenuating the stress response in dogs undergoing femoro-tibial joint surgery. STUDY DESIGN: Prospective clinical study. Animal population Twelve client-owned dogs undergoing surgery for either repair of cruciate ligament rupture (ten) or correction of luxating patella (two). Body masses ranged from 12 to 45 kg (mean: 28.58 +/- 18.38). Age ranged from 19 to 121 months (mean: 66.5 +/- 49.5). MATERIALS AND METHODS: Six of the dogs received extradural bupivacaine (up to 1.5 mg kg(-1)) combined with morphine (0.1 mg kg(-1); ED) while the other six received no extradural analgesia (C). The levels of cortisol, acute phase proteins (APPs), and red and white blood cell variables were measured in both groups of dogs before, and at various times after surgery. Pain was also assessed at various times after surgery. The number of postoperative morphine doses required, and their time of administration, was recorded for each animal. Method of statistical analysis Data were analysed using anova for repeated measures with p-values of <0.05 considered significant. RESULTS: Cortisol levels in the ED group were significantly (p < 0.05) lower than those of the control group at the end of surgery. No statistically significant differences were found in APPs or red and white cell variables between dogs receiving, and those not receiving extradural bupivacaine and morphine. Four dogs in the control group and one in the ED group required postoperative morphine. CONCLUSIONS AND CLINICAL RELEVANCE: Pre-emptive extradural bupivacaine and morphine was effective in lowering the neuroendocrine stress response (cortisol) in the ED group but had no effect on the inflammatory response (acute phase response).     

The effect of recumbency and hindlimb position on the lumbosacral interlaminar distance in dogs: a cadaveric computed tomography study

Objective

To examine the effect of sternal or lateral recumbency, with or without cranial extension of the hindlimbs, on the distance between the dorsal lumbosacral laminae in dogs.

Anaesthetic sparing effect of local anaesthesia of the ovarian pedicle during ovariohysterectomy in dogs

ObjectiveTo evaluate the effect of local anaesthesia of the mesovarium on end-tidal isoflurane (Fe′_iso) concentration and vital parameters during canine ovariohysterectomy.Study designProspective, randomized, blinded study.AnimalsTwenty client-owned dogs undergoing elective ovariohysterectomy. Mean age 1.7 (±0.53, SD) years and mean body weight 21 kg (±5.9, SD).MethodsPre-medication was with intravenous acepromazine (0.02 mg kg⁻¹) and methadone (0.1 mg kg⁻¹). Anaesthesia was induced with propofol and maintained with isoflurane in oxygen. One group (n = 10) received local infiltration of the mesovarium with 0.5 mL lidocaine 2% and one group (n = 10) with 0.5 mL NaCl 0.9%. Heart (HR) and respiratory rates (fr), invasive mean arterial blood pressure (MAP) and Fe′_isowere recorded. The Fe′_iso was adjusted according to changes in HR, RR and MAP. Time points used for comparison were T1 (after induction of anaesthesia before surgery), T2 (after lidocaine infiltration of the mesovarium) and T3 (surgical manipulation of the ovaries). Data were analysed using a mixed model for repeated measurement anova and the Tukey adjustment. Results are presented as mean ± SD; p < 0.05 was considered significant.ResultsIn both groups, HR and fr remained stable at the three time points. Mean values ranged from 84 to 94 beats minute⁻¹ and from 10 to 14 breaths minute⁻¹. The Fe′_iso was significantly lower at T3 compared to T1 and mean values ranged from 0.95% to 1.24%. The mean arterial blood pressure was significantly higher at T3 compared to T1 and mean values ranged from 58 to 96 mm Hg. At none of the time points were there significant differences between the two groups for HR, fr, MAP or Fe′_iso.ConclusionNeither an isoflurane sparing effect nor a difference in autonomic response to surgery was demonstrated following local anaesthesia of the mesovarium.Clinical relevanceThere appeared to be minimal benefit from local anaesthesia of the mesovarium during this study.     

An investigation into the detection of the pulse in conscious and anaesthetized dogs

ObjectivesTo record the success rate of veterinary professionals and students at identifying the pulse in conscious and anaesthetized dogs. To explore the influence of clinical experience, pulse location, anaesthesia and likely confounding variables on the success of pulse palpation.Study designProspective, observational, randomized study.AnimalsA total of 54 client-owned dogs scheduled for general anaesthesia.MethodsFor each dog, three participants (senior anaesthetist, anaesthesia resident/nurse, veterinary student/animal care assistant) attempted pulse palpation at three locations (femoral, radial and dorsal pedal pulse) in conscious and anaesthetized dogs. The time to pulse palpation was measured with a stopwatch for each attempt and data were modelled using a multivariate Cox regression survival analysis (significance p < 0.05).ResultsThe overall success rate of pulse palpation was 77%, with a median time of 10.91 seconds (interquartile range 9.09 seconds). Success rate was lower in conscious dogs (67%) than in anaesthetized dogs (87%). There was a 77% lower likelihood of success at the radial than at the femoral pulse [hazard ratio (HR) 0.23, 95% confidence interval (CI) 0.38–0.69, p < 0.001]. Veterinary students/animal care assistants had a 71% lower likelihood of success than senior anaesthetists (HR 0.29, 95% CI 0.22–0.39, p < 0.001). Age, weight and American Society of Anesthesiologists physical status had no significant influence. Premedication/anaesthetic drugs, heart rate or mean arterial pressure had no significant influence on the time to pulse palpation in anaesthetized dogs. The median time to palpation was less than 10 seconds for all experience groups at the femoral location.ConclusionsPalpation of the femoral location had the greatest likelihood of success with the least amount of time. Monitoring the femoral pulse during induction of anaesthesia is suggested as a method for confirming spontaneous circulation. Pulse palpation improves with clinical experience.     

Development and optimization of a fentanyl pharmacokinetic model for target-controlled infusion in anaesthetized dogs

ObjectiveTo investigate pharmacokinetics (PK) of fentanyl administered by target-controlled infusion (TCI), and to develop a PK model optimized by covariates for TCI in anaesthetized dogs.Study designProspective clinical study.AnimalsA group of 20 client-owned dogs with spinal pain undergoing anaesthesia for magnetic resonance imaging.MethodsFentanyl was administered as an infusion to 20 anaesthetized dogs using a TCI system incorporating a previously described fentanyl two-compartment PK. Arterial blood samples were collected at specific time points during the infusion and over 60 minutes post-infusion for measurement of fentanyl plasma concentrations. The predictive performance of the Sano PK model was assessed by comparing predicted and measured plasma concentrations. A population PK analysis was then performed using a nonlinear mixed-effect modelling approach, allowing inter- and intra-individual variability estimation. Finally, a quantitative stepwise evaluation of the influence of various covariates such as weight, body condition score, size, size-related age, sex and type of premedication on the PK model was considered.ResultsOverall predictive performance of the Sano PK set of variables was not clinically acceptable in anaesthetized dogs. Fentanyl PK was best described by a three-compartment model. Weight and sex were found to affect the volume of distribution of the central compartment. Addition of these two covariate/variable associations resulted in a reduction of the objective function value (OFV) from –340.18 to –448.34, and of the median population weighted residual and the median population absolute weighted residual from 16.1% and 38.6% to 3.9% and 20.3%, respectively. Fentanyl infusions at measured concentrations up to 5.4 ng mL^–1 in sevoflurane-anaesthetized dogs resulted in stable anaesthesia and smooth recoveries without complications.Conclusions and clinical relevanceA population three-compartment PK model for fentanyl TCI in anaesthetized dogs was developed. Weight and sex have been detected and incorporated as significant covariates.     

Retrospective comparison of three locoregional techniques for pelvic limb surgery in dogs

ObjectiveTo retrospectively compare the efficacy and duration of effect of three commonly used locoregional blocks in dogs undergoing pelvic limb orthopaedic surgery.Study designRetrospective clinical study.AnimalsA total of 236 dogs that underwent pelvic limb surgery and were administered a locoregional technique.MethodsA total of 236 hospital records were reviewed and 230 included in statistical analysis. Dogs were grouped as following: electrostimulation-guided pre-iliac femoral and sciatic nerve block (group PFS, n = 70); ultrasound-guided saphenous and sciatic nerve block (group SS, n = 76); or lumbosacral epidural (group EPI, n = 84). In group EPI, bupivacaine 0.5% or ropivacaine 0.75% was used with morphine. Dogs were pain scored (short form of the Glasgow Composite Measure Pain Scale) hourly following recovery from anaesthesia. Analysed data included: time to first postoperative dose of methadone, pain score at that time, intraoperative rescue analgesia, intraoperative hypotension and ability to walk and urinate overnight. Separate analyses were performed including all pelvic limb surgeries and including only elective stifle surgeries. Kruskal–Wallis and Mann–Whitney tests were performed. A p value < 0.05 was considered significant. The median (range) is reported.ResultsFor all pelvic limb surgeries, the time to first postoperative methadone was 530 (110–1337), 440 (140–1030) and 466 (135–1094) minutes in groups EPI, PFS and SS, respectively, and was not significantly different. Postoperatively, 10/84, 15/70 and 12/76 dogs in groups EPI, PFS and SS, respectively, did not require methadone (nonsignificant). Significantly fewer dogs in group EPI (18%) required intraoperative rescue analgesia compared with group SS (38%), but not compared with PFS (30%). Significantly more dogs in group EPI had hypotension intraoperatively (30%) and urinary retention postoperatively (62%).Conclusions and clinical relevanceIntraoperative analgesia may be superior with EPI than SS for some surgeries of the pelvic limb, but not for stifle surgeries. All three techniques provided similar requirement for postoperative analgesia, but EPI caused higher incidence of intraoperative hypotension and postopertive urinary retention.     

Analgesia for pelvic limb surgery. A review of peripheral nerve blocks and the extradural technique

ObjectivesTo describe the anatomy and approaches reported for peripheral nerve blockade (PNB) of the pelvic limb in dogs and cats and to consider the role of PNB in relation to the extradural technique.Databases usedThis review was conducted using the terms ‘nerve block’, ‘extradural’ ‘dog’ and ‘cat’ entered into Pubmed and Google. Results were filtered manually to narrow the field to pelvic limb nerve blocks. The reference lists of retrieved papers were scrutinized to identify further studies for inclusion.ConclusionsSuccessful PNB techniques require thorough anatomical knowledge for the establishment of reliable landmarks, puncture sites, the direction and depth of needle insertion, and relevant structures to be avoided. To date, clinical evaluations have been made in subjects undergoing stifle surgery where the sciatic nerve has been blocked in combination with various approaches to the femoral nerve. Currently the bulk of literature examines new approaches to these nerves and each of these is described. To date there are no veterinary studies directly comparing one approach versus another, and therefore one is unable to draw conclusions of superiority. The role of PNB’s versus the extradural technique is discussed.     

Comparison of high definition oscillometric and Doppler ultrasound devices with invasive blood pressure in anaesthetized dogs

Objective To use the American College of Veterinary Internal Medicine (ACVIM) validation criteria to evaluate the performance of high definition oscillometric (HDO) and Doppler blood pressure measurement techniques against invasive blood pressure measurements in anaesthetized dogs. Study design Prospective clinical study. Animals Twenty client‐owned dogs. Materials and Methods Invasive blood pressure was measured using a catheter inserted into a pedal artery and an electronic transducer. The sites of cuff placement for the HDO measurements were the mid antebrachium or the proximal tail and, for the Doppler technique, the distal tibia. Agreement between invasive and non‐invasive blood pressure measurements was estimated by the Bland–Altman method. Results Only 10% and 34% of Doppler measurements were within 10 and 20 mmHg of invasive blood pressure values, respectively. The Doppler device failed to meet the ACVIM validation criteria for blood pressure measurement devices. The best agreement between HDO and invasive blood pressure measurement technique was observed for mean arterial blood pressure (MAP); 67% and 95% of readings were within 10 and 20 mmHg of invasive blood pressure values respectively. In addition, 52% and 87% of diastolic arterial blood pressure (DAP) measurements were within 10 and 20 mmHg of invasive readings. High definition oscillometric readings did not meet ACVIM recommended limits for SAP. Conclusion and clinical relevance The Doppler technique overestimated and the HDO device showed limited agreement with invasive blood pressure measurement in anaesthetized dogs. High definition oscillometry met most of the ACVIM requirements for MAP and DAP while the Doppler technique did not.     

Validity and reliability of Doppler ultrasonography and direct arterial blood pressure measurements in anaesthetized dogs weighing less than 5 kg

Objective

To assess the validity and reliability of Doppler ultrasonography (DOP) as compared with invasive arterial blood pressure measurements in anaesthetized dogs weighing less than 5 kg.

The effects of propofol, isoflurane and sevoflurane on vecuronium infusion rates for surgical muscle relaxation in dogs

OBJECTIVE: To compare the constant rate infusion (CRI) of vecuronium required to maintain a level of neuromuscular blockade adequate for major surgeries, e.g. thoracotomy or laparotomy, in dogs anaesthetized with a CRI of fentanyl and either propofol, isoflurane or sevoflurane. STUDY DESIGN: Prospective, randomized, cross-over study. ANIMALS: Thirteen male beagles (age, 9-22 months; body mass 6.3-11.3 kg). MATERIALS AND METHODS: Dogs were anaesthetized with propofol (24 mg kg(-1) hour(-1) IV CRI; group P), isoflurane (1.3% end-tidal concentration; group I) or sevoflurane (2.3% end-tidal concentration; group S) with fentanyl (5 microg kg(-1) hour(-1) IV, CRI). Sixty to seventy minutes after induction of anaesthesia, vecuronium was administered at a rate of 0.4, 0.3 and 0.2 mg kg(-1) hour(-1) in groups P, I and S respectively. To determine the degree of neuromuscular block, a peripheral nerve was stimulated electrically using the train-of-four (TO4) stimulus pattern. Evoked muscle contractions were evaluated using a neuromuscular monitoring device. Once the TO4 ratio reached 0, the continuous infusion rate was decreased and adjusted to maintain a TO4 count of 1. Continuous infusion was continued for 2 hours. The infusion rate of vecuronium was recorded 20, 40, 60, 80, 100 and 120 minutes after the start of infusion. RESULTS: The mean continuous infusion rates of vecuronium during stable infusion were 0.22 +/- 0.04 (mean +/- SD), 0.10 +/- 0.02 and 0.09 +/- 0.02 mg kg(-1) hour(-1) in groups P, I and S respectively. There were statistically significant differences between the rates in groups P and I and between the rates in groups P and S. Conclusions and clinical relevance In healthy dogs, the recommended maintenance infusion rate of vecuronium is 0.2 mg kg(-1) hour(-1) under CRI propofol-fentanyl anaesthesia and 0.1 mg kg(-1) hour(-1) during CRI fentanyl-isoflurane or sevoflurane anaesthesia.     

An evaluation of anaesthetic induction in healthy dogs using rapid intravenous injection of propofol or alfaxalone

ObjectiveTo evaluate quality of anaesthetic induction and cardiorespiratory effects following rapid intravenous (IV) injection of propofol or alfaxalone.Study designProspective, randomised, blinded clinical study.AnimalsSixty healthy dogs (ASA I/II) anaesthetized for elective surgery or diagnostic procedures.MethodsPremedication was intramuscular acepromazine (0.03 mg kg^?1) and meperidine (pethidine) (3 mg kg^?1). For anaesthetic induction dogs received either 3 mg kg^?1 propofol (Group P) or 1.5 mg kg^?1 alfaxalone (Group A) by rapid IV injection. Heart rate (HR), respiratory rate (f_R) and oscillometric arterial pressures were recorded prior to induction, at endotracheal intubation and at 3 and 5 minutes post-intubation. The occurrence of post-induction apnoea or hypotension was recorded. Pre-induction sedation and aspects of induction quality were scored using 4 point scales. Data were analysed using Chi-squared tests, two sample t-tests and general linear model mixed effect anova (p < 0.05).ResultsThere were no significant differences between groups with respect to sex, age, body weight, f_R, post-induction apnoea, arterial pressures, hypotension, SpO₂, sedation score or quality of induction scores. Groups behaved differently over time with respect to HR. On induction HR decreased in Group P (?2 ± 28 beats minute^?1) but increased in Group A (14 ± 33 beats minute^?1) the difference being significant (p = 0.047). However HR change following premedication also differed between groups (p = 0.006). Arterial pressures decreased significantly over time in both groups and transient hypotension occurred in eight dogs (five in Group P, three in Group A). Post-induction apnoea occurred in 31 dogs (17 in Group P, 14 in Group A). Additional drug was required to achieve endotracheal intubation in two dogs.Conclusions and Clinical relevanceRapid IV injection of propofol or alfaxalone provided suitable conditions for endotracheal intubation in healthy dogs but post-induction apnoea was observed commonly.     

Effect of hind limb position on the craniocaudal length of the lumbosacral space in anesthetized dogs

Objective To investigate whether rostral extension of the hind limbs increases the cranio‐caudal dorsal interlaminar distance between the seventh lumbar vertebra and the sacral bone (LS distance) in sternally recumbent anesthetized dogs. Study design Prospective clinical study. Animals Eighteen dogs (eight neutered males, three intact males, six spayed females, one intact female) of various breeds, weighing 4–34 kg and ranging in age from 1 to 13 years. Methods Each dog was grouped by size: small (≤10 kg), medium (15–20 kg) or large (≥25 kg). Each dog was anesthetized and positioned in sternal recumbency. Computed tomography (CT) of the lumbosacral area was performed with the hind limbs resting on the stifle and the feet extended posteriorly, and then with the hind limbs extended rostrally. LS distance, craniocaudal dorsal interlaminar distance between sixth and seventh lumbar vertebra (L6–L7 distance), length of L7 vertebral body and lumbosacral angle (LS angle) were measured on a reconstructed mid‐sagittal CT image from the two hind limb positions. The measurements from the two hind limb positions for the whole dog population and by size were compared using Student’s T tests. Diagnostic interpretation of the CT images was performed. Results The length of L7 was taken as the reference value as it was not affected by hind limb position. LS distance, L6–L7 distance and LS angle were significantly higher when the hind limbs were extended rostrally in all three size groups. The CT images of ten dogs showed clinically undetected osteoarthrosis of the ileo‐ and lumbosacral area. Conclusions and clinical relevance Rostral extension of the hind limbs significantly increases LS and L6–L7 distance and LS angle even in dogs with clinically undetected osteoarthrosis of the ileo‐ and lumbosacral area, and may enhance the ease of lumbosacral epidural injection in sternally recumbent anesthetized dogs.     

Cardiopulmonary effects of sufentanil long acting on sevoflurane anaesthesia in dogs

OBJECTIVE: To evaluate the cardiopulmonary effects of sufentanil long acting (SLA) in sevoflurane-anaesthetized dogs. STUDY DESIGN: Randomized prospective study. Animals Forty female dogs (beagles) aged 1-2 years, weighing 11.97 +/- 1.40 kg. MATERIALS AND METHODS: The dogs were divided into five groups of eight. Two control groups were used: group A received intramuscular (IM), SLA (50 microg kg(-1)) alone, while group B received the SLA vehicle followed by sevoflurane anaesthesia for 90 minutes. In the other groups, SLA (50 microg kg(-1) IM) was given immediately before (group C(0)), 15 minutes before (group D(15)) or 30 minutes (group E(30)) before induction [with intravenous (IV) thiopental] of sevoflurane anaesthesia lasting for 90 minutes. Heart rate, arterial blood pressure, respiratory rate (f(r)), arterial oxygen haemoglobin saturation and end-tidal sevoflurane concentration (Fe'SEVO) were measured every 10 minutes during anaesthesia and at 2, 4 and 24 hours after induction (not Fe'SEVO). Acid-base and blood gas analyses were performed. RESULTS: Sufentanil LA reduced heart rate and increased arterial CO(2) tensions during anaesthesia. Respiratory depression was least in group E(30) compared with groups C(0) and D(15). Bradycardia was present for at least 24 hours. Respiratory rate was least in group B although arterial O(2) and CO(2) tension values were acceptable up to 24 hours after anaesthesia. CONCLUSIONS: Pre-anaesthetic medication with SLA moderately aggravated the cardiopulmonary effects of sevoflurane. CLINICAL RELEVANCE: In spite of a moderate depressant effect on cardiorespiratory parameters, SLA may be of use as pre-anaesthetic medication before sevoflurane anaesthesia in dogs. Intermittent positive pressure ventilation may occasionally be necessary.     

The isoflurane-sparing and clinical effects of a constant rate infusion of remifentanil in dogs

OBJECTIVE: To evaluate the isoflurane-sparing and clinical effects of two constant rate infusions of remifentanil in healthy dogs undergoing orthopaedic surgery. STUDY DESIGN: Prospective, randomized clinical study. ANIMALS: Forty-one American Society of Anesthesiologists I-II client-owned dogs (age, 7 months-9 years; body mass 11-59 kg). METHODS: Dogs were randomly assigned to one of three groups and received either: intramuscular (IM) meperidine 2 mg kg(-1) every 2 hours throughout surgery (control group (C); n = 13); remifentanil infused intravenously (IV) at 0.1 microg kg(-1) minute(-1) (low remifentanil group (L); n = 14) or remifentanil infused at 0.25 microg kg(-1) minute(-1) IV (high remifentanil group (H); n = 14). Anaesthesia was induced with thiopental administered to effect and maintained using isoflurane in 100% oxygen. During controlled ventilation when the end-tidal CO(2) was maintained between 4.65 and 5.98 kPa [35-45 mmHg], the end-tidal isoflurane concentration (e'iso%), mean arterial blood pressure (MAP) and heart rate (HR) were measured every 5 minutes. Bradycardia (HR < 40 minute(-1) lasting >5 minutes) was corrected with 0.01 mg kg(-1) IV glycopyrrolate. Data were analysed using the Kruskal-Wallis test with a post-hoc Mann-Whitney U-test and Bonferroni correction. Statistical significance was accepted at < or = 0.05. Data are expressed as mean +/- standard deviation. RESULTS: The e'iso% was reduced in a dose-dependent manner by remifentanil. In C, e'iso% was 1.28 +/-0.13 and was significantly different from L (0.78 +/- 0.17, p < 0.001) and H (0.65 +/- 0.16, p < 0.001). HR was significantly different between groups (p < 0.001). There were no significant differences in MAP between groups. Glycopyrrolate was required in two, three and six dogs in the C, L and H groups respectively. CONCLUSIONS: Remifentanil infusion reduced the isoflurane concentration required for surgical anaesthesia during orthopaedic surgery. CLINICAL RELEVANCE: Remifentanil infusions may be a useful additive to isoflurane anaesthesia in healthy dogs.     

Effect of alfaxalone infusion on the electroencephalogram of dogs anaesthetized with halothane

ObjectiveTo describe the effects of alfaxalone on the canine electroencephalogram (EEG).Study designExperimental study.AnimalsEight healthy adult Huntaway dogs.MethodsAnaesthesia was induced with propofol and maintained with halothane (0.85-0.95 end-tidal volume %) in oxygen. Animals were ventilated to maintain stable end-tidal CO₂ and halothane concentrations. Following a 30 minute stabilisation period, alfaxalone (0.5 mg kg^?1) was infused intravenously over a 5 minute period. The electroencephalogram was recorded from the beginning of the stabilisation period until 60 minutes following the start of alfaxalone treatment. Data were subjected to fast Fourier transformation, and median frequency, 95% spectral edge frequency and total EEG power were calculated. Two-factorial repeated measures anova (time and EEG channels were factors) was used for statistical analysis (p<0.05).ResultsA shift in the dominant frequency band from beta to delta after alfaxalone treatment and occasional burst suppression were observed. Median frequency decreased significantly below baseline (9.2 ± 1.4 Hz) (mean ± SD) during alfaxalone infusion. The lowest value (4.8 ± 1.2 Hz) was recorded 5 minutes after the start of infusion. Spectral edge frequency also decreased below baseline (26.2 ± 1.5 Hz) and the lowest value (22.6 ± 1.5 Hz) also was detected at 5 minutes after the start of infusion. Total EEG power did not change significantly. In some frequencies EEG power increased soon after the start of alfaxalone infusion, then decreased below baseline later (biphasic pattern).Conclusions and clinical relevanceAlfaxalone induced biphasic changes on EEG and decreased F₅₀ and F₉₅ in halothane anaesthetized dogs.