Comparison of epidural versus intrathecal anaesthesia in dogs undergoing pelvic limb orthopaedic surgery

ObjectiveTo compare the procedural failure rate (PFR), intraoperative rescue analgesia (iRA) probability and postoperative duration of motor block after epidural and intrathecal anaesthesia in dogs undergoing pelvic limb orthopaedic surgery.Study designProspective, randomized clinical trial.AnimalsNinety-two client-owned dogs.MethodsDogs were assigned randomly to receive either lumbosacral epidural anaesthesia (EA) (bupivacaine 0.5% and morphine 1%) or intrathecal anaesthesia with the same drugs in a hyperbaric solution (HIA). Inaccurate positioning of the needle, assessed by radiographic imaging, and lack of cerebral spinal fluid outflow were considered procedural failures (PFs) of EA and HIA, respectively. Fentanyl (1 μg kg⁻¹ IV) was provided for intraoperative rescue analgesia, when either the heart rate or the mean arterial pressure increased by 30% above the pre-stimulation value. Its use was recorded as a sign of intraoperative analgesic failure. The motor block resolution was evaluated postoperatively. Variables were compared using Fisher's exact test, the Mann–Whitney U test and the Kaplan–Meier ‘survival’ analysis as relevant.ResultsThe PFRs in the EA and HIA groups were 15/47 (32%) and 3/45 (7%), respectively (p = 0.003). Differences in iRA were analysed in 26 and 30 subjects in the EA and HIA groups respectively, using Kaplan–Meier survival analysis. The iRA probability within the first 80 minutes of needle injection (NI) was higher in the EA group (p = 0.045). The incidence of dogs walking within 3 hours of NI was significantly higher in the HIA group (8/20, 40%) than in the EA group (0/17) (p = 0.004).Conclusions and clinical relevanceHIA was found to have lower PF, lower intraoperative analgesic failure and faster motor block resolution. In this study HIA was shown to provide some advantages over EA in dogs undergoing commonly performed pelvic limb orthopaedic surgery in a day-hospital regime.     

Measurement of respiratory system compliance and respiratory system resistance in healthy dogs undergoing general anaesthesia for elective orthopaedic procedures

Objective The aim of this study was to investigate normal values for the dynamic compliance of the respiratory system (Crs) and respiratory system resistance (Rrs) in mechanically ventilated anaesthetized dogs.Study design Prospective clinical study.Animals Forty healthy dogs undergoing elective orthopaedic surgery. Body weight was (mean ± SD) 26.8 ± 10.7 kg (range: 1.9–45.0 kg), age 4.7 ± 2.9 years (range: 0.1–10.6 years).Methods Dogs were premedicated with acepromazine and methadone administered intramuscularly and anaesthesia induced with propofol intravenously. After endotracheal intubation the dog's lungs were connected to an appropriate breathing system depending on body weight and isoflurane in oxygen administered for maintenance of anaesthesia. The lungs were ventilated mechanically with variables set to maintain normocapnia (end‐tidal carbon dioxide concentration 4.7–6.0 kPa). Peak inspiratory pressure, Crs, Rrs, tidal volume, respiratory rate and positive end‐expiratory pressure were recorded at 5, 30, 60, 90 and 120 minutes after start of mechanical ventilation. Cardiovascular variables were recorded at time of collection of respiratory data.Results General additive modeling revealed the following relationships: Crs = [0.895 × body weight (kg)] + 8.845 and Rrs = [?0.0966 × body weight (kg)] + 6.965. Body weight and endotracheal tube diameter were associated with Crs (p <0.001 and p =0.002 respectively) and Rrs (p = 0.017 and p =0.002 respectively), body weight being linearly related to Crs and inversely to Rrs.Conclusion and clinical relevance Body weight was linearly related to Crs while Rrs has an inverse linear relationship with body weight in mechanically ventilated dogs. The derived values of Crs and Rrs may be used for monitoring of lung function and ventilation in healthy dogs under anaesthesia.     

Effect of Intravenously Administered Crystalloid Solutions on Acid‐Base Balance in Domestic Animals

Intravenous fluid therapy can alter plasma acid‐base balance. The Stewart approach to acid‐base balance is uniquely suited to identify and quantify the effects of the cationic and anionic constituents of crystalloid solutions on plasma pH. The plasma strong ion difference (SID) and weak acid concentrations are similar to those of the administered fluid, more so at higher administration rates and with larger volumes. A crystalloid's in vivo effects on plasma pH are described by 3 general rules: SID > [] increases plasma pH (alkalosis); SID < [] decreases plasma pH (alkalosis); and SID = [] yields no change in plasma pH. The in vitro pH of commercially prepared crystalloid solutions has little to no effect on plasma pH because of their low titratable acidity. Appreciation of IV fluid composition and an understanding of basic physicochemical principles provide therapeutically valuable insights about how and why fluid therapy can produce and correct alterations of plasma acid‐base equilibrium. The ideal balanced crystalloid should (1) contain species‐specific concentrations of key electrolytes (Na⁺, Cl^?, K⁺, Ca⁺⁺, Mg⁺⁺), particularly Na⁺ and Cl^?; (2) maintain or normalize acid‐base balance (provide an appropriate SID); and (3) be isosmotic and isotonic (not induce inappropriate fluid shifts) with normal plasma.     

Suspected anaphylactoid reaction following intravenous administration of a gadolinium‐based contrast agent in three dogs undergoing magnetic resonance imaging

ObservationsAnaphylactoid reactions were suspected in three dogs following the intravenous administration of the contrast agent gadobenate dimeglumine 0.05 mmol kg^?1 (Multihance^®).Case 1: A 14 kg 6–year–old atopic female dog was anaesthetized for brain magnetic resonance imaging (MRI). All monitored parameters remained stable during the procedure. Fifteen minutes following MR completion; facial, peri–orbital and sublingual oedema were noted. Resolution of the oedema was rapid and uneventful following treatment of clinical signs over 2 hours.Case 2: A 16 kg 10–month–old male dog was anaesthetized for brain and neck MRI. Ten minutes after MR contrast intravenous (IV) injection; heart rate (HR) increased (85–120 beats minute^?1), mean arterial blood pressure (MAP) decreased (from 70 to 43 mmHg) and Pe′CO₂ decreased (from 4.66 to 3.19 kPa). Labial, periorbital and lingual oedema were noted. Clinical signs responded to fluid bolus administration. The dog vomited in recovery but oedema resolved within one hour.Case 3: A 34 kg 2–year–old atopic male dog was anaesthetized for head MRI. Within 5 minutes of MR contrast IV injection; the dog suffered severe cardiovascular collapse. MRI procedure was aborted and administration of anaesthetics discontinued. Aggressive IV fluid resuscitation and IV epinephrine administration were necessary to re–establish cardiovascular stability. Some periorbital and labial oedema were noted. The dog vomited once and had soft faeces but made a complete recovery.ConclusionsThe administration of contrast medium may result in mild to severe anaphylactoid reactions.     

Predictors of outcome in dogs undergoing thoracic surgery (2002–2011)

ObjectiveTo evaluate mortality in a canine population undergoing thoracic surgery and identify factors which may be associated with outcome.Study designRetrospective cohort study.Animals286 dogs anaesthetized for thoracic surgery at the Royal Veterinary College between June 2002 – June 2011.MethodsVariables examined included: signalment; ASA status; nature of disease; presence of co-morbidities; pre-anaesthetic oxygen requirement; surgical approach; anaesthesia management [anaesthetic agents; requirement for thoracocentesis; central venous pressure measurement; duration of surgery and anaesthesia; use of colloids, blood products, inotropes or neuromuscular blocking agents (NMBA)]. Outcome was defined as either non-survival to 24 hours after surgery or (having survived to 24 hours) to discharge. Univariate and multivariable logistic regressions were performed to identify risk factors associated with non-survival.ResultsOverall non-survival (excluding those euthanased) to discharge was 5.9%. Non-survival was 2.2% at 24 hours and 3.6% at time of discharge. Non-survival to 24 hours was associated with pre-anaesthetic oxygen requirement (odds ratio (OR) 12.2 [95% CI 1.8–84.5]) and NMBA use (OR 9.6 [95% CI 1.6–57.9]). Non-survival to discharge was associated with surgical duration, with surgeries >180 minutes having OR 16.9 [95% CI 2.0–144.0] compared to surgeries ≤90 minutes and blood product use (OR 4.6 [95% CI 1.3–14.6]). No association was found between ASA category and non-survival at 24 hours (OR 1.4 [95% CI 0.2–11.7]) or discharge (OR 4.4 [95% CI 0.6–34.3]). Significant associations were found between NMBA use and ASA category (p = 0.046), surgical duration (p = 0.002), use of colloids (p = 0.011), blood products (p = 0.001) and inotropes and/or vasopressors (p < 0.001).Conclusions and clinical relevanceVariables significantly associated with non-survival from canine thoracic surgery at 24 hours include NMBA use and pre-anaesthetic oxygen requirement. Blood product use and increasing surgical duration were associated with non-survival to hospital discharge. The associations may relate to the need for such products in the most complicated cases.     

Cardiovascular,respiratory, electrolyte and acid–base balance during continuous dexmedetomidine infusion in anesthetized dogs

ObjectiveTo evaluate the cardiovascular, respiratory, electrolyte and acid–base effects of a continuous infusion of dexmedetomidine during propofol–isoflurane anesthesia following premedication with dexmedetomidine.Study designProspective experimental study.AnimalsFive adult male Walker Hound dogs 1–2 years of age averaging 25.4 ± 3.6 kg.MethodsDogs were sedated with dexmedetomidine 10 μg kg^?1 IM, 78 ± 2.3 minutes (mean ± SD) before general anesthesia. Anesthesia was induced with propofol (2.5 ± 0.5 mg kg^?1) IV and maintained with 1.5% isoflurane. Thirty minutes later dexmedetomidine 0.5 μg kg^?1 IV was administered over 5 minutes followed by an infusion of 0.5 μg kg^?1 hour^?1. Cardiac output (CO), heart rate (HR), ECG, direct blood pressure, body temperature, respiratory parameters, acid–base and arterial blood gases and electrolytes were measured 30 and 60 minutes after the infusion started. Data were analyzed via multiple linear regression modeling of individual variables over time, compared to anesthetized baseline values. Data are presented as mean ± SD.ResultsNo statistical difference from baseline for any parameter was measured at any time point. Baseline CO, HR and mean arterial blood pressure (MAP) before infusion were 3.11 ± 0.9 L minute^?1, 78 ± 18 beats minute^?1 and 96 ± 10 mmHg, respectively. During infusion CO, HR and MAP were 3.20 ± 0.83 L minute^?1, 78 ± 14 beats minute^?1 and 89 ± 16 mmHg, respectively. No differences were found in respiratory rates, PaO₂, PaCO₂, pH, base excess, bicarbonate, sodium, potassium, chloride, calcium or lactate measurements before or during infusion.Conclusions and clinical relevanceDexmedetomidine infusion using a loading dose of 0.5 μg kg^?1 IV followed by a constant rate infusion of 0.5 μg kg^?1 hour^?1 does not cause any significant changes beyond those associated with an IM premedication dose of 10 μg kg^?1, in propofol–isoflurane anesthetized dogs. IM dexmedetomidine given 108 ± 2 minutes before onset of infusion showed typical significant effects on cardiovascular parameters.     

Nerve stimulator‐guided sciatic‐femoral nerve block in raptors undergoing surgical treatment of pododermatitis

ObjectiveTo describe the nerve stimulator-guided sciatic-femoral nerve block in raptors undergoing surgical treatment of pododermatitis.Study designProspective clinical trial.AnimalsFive captive raptors (Falco peregrinus) aged 6.7 ± 1.3 years.MethodsAnaesthesia was induced and maintained with isoflurane in oxygen. The sciatic-femoral nerve block was performed with 2% lidocaine (0.05 mL kg⁻¹ per nerve) as the sole intra-operative analgesic treatment. Intraoperative physiological variables were recorded every 10 minutes from endotracheal intubation until the end of anaesthesia. Assessment of intraoperative nociception was based on changes in physiological variables above baseline values, while evaluation of postoperative pain relied on species-specific behavioural indicators.ResultsThe sciatic-femoral nerve block was feasible in raptors and the motor responses following electrical stimulation of both nerves were consistent with those reported in mammalian species. During surgery no rescue analgesia was required. The anaesthesia plane was stable and cardiorespiratory variables did not increase significantly in response to surgical stimulation. Iatrogenic complications, namely nerve damage and local anaesthetic toxicity, did not occur. Recovery was smooth and uneventful. The duration (mean ± SD) of the analgesic effect provided by the nerve block was 130 ± 20 minutes.Conclusion and clinical relevanceThe sciatic-femoral nerve block as described in dogs and rabbits can be performed in raptors as well. Further clinical trials with a control groups are required to better investigate the analgesic efficacy and the safety of this technique in raptors.     

Electrical velocimetry for noninvasive cardiac output and stroke volume variation measurements in dogs undergoing cardiovascular surgery

Objective

To compare electrical velocimetry (EV) noninvasive measures of cardiac output (CO) and stroke volume variation (SVV) in dogs undergoing cardiovascular surgery with those obtained with the conventional thermodilution technique using a pulmonary artery catheter.

Romifidine and low doses of tiletamine‐zolazepam in dogs

ObjectiveTo evaluate clinical effects of romifidine and low doses of tiletamine‐zolazepam (TZ) in dogs.Study designRandomized “blinded” cross‐over study.AnimalsSix healthy beagle dogs (two males, four females).MethodsIn separate preliminary experiments dogs received intravenous (IV) tiletamine‐zolazepam (TZ) at 1 and 2 mg kg^?1. For the main trial, dogs received romifidine (R) followed 5 minutes later by IV at six dose regimens: R40TZ1, R60TZ1, R80TZ1 (Romifidine at 40, 60, 80 μg kg^?1 and TZ at 1 mg kg^?1), R40TZ2, R60TZ2 and R80TZ2 (Romifidine at 40, 60, 80 μg kg^?1 and TZ at 2 mg kg^?1). Dogs underwent endotracheal intubation, but breathed room air. Cardiorespiratory variables were measured and arterial blood analyzed. Quality of sedation, duration of anaesthesia and time to recovery (TR) were recorded. Data were analysed by anova or Friedman test as relevant.ResultsEndotracheal intubation was possible with all romifidine/TZ combinations but not with TZ alone. Mean times (minutes) from TZ injection to return of pedal reflex were 1–3 minutes for TZ alone, and 9–17 minutes for romifidine combinations. In the main trial (romifidine combinations) mean time (minutes) to standing increased with increasing dosage (R40TZ1 13; R80TZ2 32). Five minutes after TZ administration, when compared with baseline arterial blood pressures and arterial carbon dioxide had increased, and respiratory rate, pH and arterial oxygen tensions decreased, these changes becoming statistically significant with the higher dose rates. One dog in R60TZ2 and three dogs in R80TZ2 became hypoxaemic.Conclusions and clinical relevanceRomifidine improves the quality and lengthens the duration of anaesthesia induced by TZ. The combination provides a suitable protocol for induction of or short‐term anaesthesia in healthy dogs. However, the higher doses cause cardiovascular stimulation and respiratory depression, and precautions should be taken accordingly.     

The effect of the stage of the ovarian cycle (anoestrus or dioestrus) and of pregnancy on the incidence of gastro‐oesophageal reflux in dogs undergoing ovariohysterectomy

ObjectiveTo investigate the potential association of increased blood progesterone (P₄) concentrations and/or late pregnancy with the incidence of gastro-oesophageal reflux (GOR), in healthy bitches undergoing ovariohysterectomy under general anaesthesia during anoestrus or dioestrus or during the second half of pregnancy.Study designProspective observational study.AnimalsNinety-four healthy, female, dogs, aged 1–8 years presented for elective ovariohysterectomy.MethodsNon-pregnant animals were classified into group A (anoestrus) (n = 35) if blood P₄ concentration was sufficiently low or group D (dioestrus) (n = 26) if blood P₄ concentration was sufficiently high. All animals in the second half of pregnancy were classified into group P (n = 33). Acepromazine (0.05 mg kg⁻¹) was administered intramuscularly as preanaesthetic medication, and sodium thiopental (10 mg kg⁻¹, with additional doses if needed) was administered intravenously (IV) for induction of anaesthesia. After endotracheal intubation, halothane (1.1–1.3% end-tidal concentration) in oxygen was used for maintenance of anaesthesia. Lower oesophageal pH was monitored continuously throughout surgery using a pH-measuring probe. Reflux was considered to have occurred whenever pH values of >7.5 (alkaline reflux) or <4 (acid reflux) were recorded. On completion of surgery, carprofen (4 mg kg⁻¹) was administered IV. Further administration of analgesics post-operatively was dictated by visual analogue scale pain scoring.ResultAcid GOR was observed in five of 26 dogs in group D, six of 35 group A, and 12 of 33 group P (p = 0.152). The incidence of GOR in group P approached statistical significance and was higher than the incidence in the combined group A + D (one sided p = 0.044, two sided p = 0.077).ConclusionsIn dogs undergoing ovariohysterectomy, GOR during anaesthesia occurs with a high incidence in dogs in the second half of pregnancy compared to non-pregnant animals during anoestrus or dioestrus.Clinical relevanceMeasures could be taken in such cases to avoid the consequences of potential reflux.     

Effects of phenylbutazone and indomethacin on the post-operative course following experimental orthopaedic surgery in dogs

Randomized placebo-controlled crossover studies were carried out in dogs to evaluate how two non-steroidal anti-inflammatory drugs (NSAID) might modulate an acute post-traumatic inflammatory reaction. Two "identical" surgical interventions were performed on the forelimbs of each animal with an interval of 28 days, to enable a paired comparison of the inflammatory signs and the wound/bone healing processes. At one operation 8 dogs received 300 mg phenylbutazone twice daily for 8 days starting on the day before surgery, and at the other operation matching placebo tablets were given. In a similar placebo-controlled trial another group of 8 dogs received 5 mg indomethacin twice daily. With phenylbutazone the post-operative swelling was not significantly reduced compared to placebo, but there was less pain and limping. With indomethacin the swelling was somewhat reduced, but there was no consistent difference to placebo in the pain and limping assessments. None of the drugs appeared to distinctly effect the wound or fracture healing, as evaluated by clinical inspection, comparison of radiographs and comparison of bone sections from the sites of surgery. It proved difficult to select an appropriate dosage of indomethacin due to its high potential to induce GI ulceration and bleeding in dogs. In this experimental surgical model with an acute inflammation, neither phenylbutazone nor indomethacin showed impressive anti-inflammatory or analgesic properties. In the same model paracetamol has proved to significantly and more efficiently, reduce both swelling and pain without any noticeable adverse effects, and appears to be a better alternative than the two presently tested NSAID.     

A retrospective study of efficacy and side effects of intrathecal administration of hyperbaric bupivacaine and morphine solution in 39 dogs undergoing hind limb orthopaedic surgery

ObjectiveTo evaluate the intraoperative efficacy of intrathecal anaesthesia with hyperbaric bupivacaine 0.5% and morphine 1% solution (HIA) in dogs undergoing hind limb orthopaedic surgery, using the cardiovascular response to surgical stimulation and to report the perioperative side effects.Study designRetrospective clinical study.AnimalsForty-three dogs that underwent general anaesthesia for hind limb orthopaedic surgery between 2010 and 2011.MethodsThe anaesthesia records of dogs that received HIA were reviewed. The bupivacaine and morphine doses were calculated based on body mass (BM) and spinal cord length (SCL). Cardiovascular response (CR) to surgical stimulation, the incidence of hypotension, bradycardia, urinary retention, pruritus and offset of motor block were all reported. The intraoperative time-to-event probability of CR was analyzed using Kaplan–Meier survival analysis.ResultsThe median (range) bupivacaine dose related to BM was 0.57 (0.40–0.78) mg kg^?1, while that related to SCL was 0.13 (0.08–0.19) mg cm^?1. A CR was observed in 3/39 (8%) dogs within the first hour after intrathecal injection (Ii) and in 9/39 (23%) dogs over the entire duration of surgery. At 70 minutes from Ii the event-free probability of CR fell below 80%. Hypotension was observed in 12/39 (31%), bradycardia in 6/39 (15%), pruritus in 3/39 (8%), and urinary retention in 3/39 (8%) dogs respectively. Five hours after Ii, 35/39 (89%) dogs were able to walk with only residual ataxia.Conclusions and clinical relevanceIntrathecal anaesthesia with hyperbaric bupivacaine 0.5% and morphine 1% solution provided effective intraoperative antinociception up to 70 minutes in dogs undergoing hind limb surgery. The technique of HIA can provide effective analgesia during short hind limb surgeries in dogs.