OBJECTIVE:

To characterise four different intramuscular (IM) anaesthetic protocols, two with alfaxalone and two with alfaxalone in combination with medetomidine in terrestrial tortoises.

STUDY DESIGN:

Blinded, randomized, cross-over experimental study.

ANIMALS:

Nine healthy adult male Horsfield's tortoises (Agrionemys horsfieldii).

METHODS:

Each tortoise was randomly assigned to one of four different protocols: 1) 10 mg kg(-1) alfaxalone; 2) 10 mg kg(-1) alfaxalone + 0.10 mg kg(-1) medetomidine; 3) 20 mg kg(-1) alfaxalone; and 4) 20 mg kg(-1) alfaxalone + 0.05 mg kg(-1) medetomidine. During the experiment, the following variables were recorded: heart rate; respiratory rate; peripheral nociceptive responses; muscle strength; ability to intubate; palpebral, corneal and tap reflexes; and cloacal temperature.

RESULTS:

Protocols 1 and 2 resulted in moderate sedation with no analgesia, and moderate to deep sedation with minimal analgesia, respectively. Protocols 3 and 4 resulted in deep sedation or anaesthesia with variable analgesic effect; these two protocols had the longest total anaesthetic time and allowed intubation in 6/9 and 8/9 tortoises respectively. The total anaesthesia/sedation time produced by alfaxalone was significantly increased (p < 0.05) by the addition of medetomidine. There were no significant differences regarding time to plateau phase and duration of plateau phase. Baseline heart rate of 53 ± 6 beats minute(-1) decreased significantly (p < 0.05) with all protocols, and was lower (p < 0.05) in protocols 3 and 4. Heart rate increased after atipamezole administration, but the increase was transient. In two tortoises, extreme bradycardia with no cardiac activity for 10 minutes was observed with protocols 3 and 4.

CONCLUSION

AND

CLINICAL RELEVANCE:

Alfaxalone 10 and 20 mg kg(-1)  IM can be used for sedation for non-painful procedures. Alfaxalone in combination with medetomidine can be used for deeper sedation or anaesthesia, but the observed respiratory and cardiovascular depression may limit its use.

OBJECTIVE:

To determine if the use of needle enhancing software facilitate injection technique in ultrasound-guided peripheral nerve blocks.

STUDY DESIGN:

Prospective, blinded, randomized controlled trial.

ANIMALS:

Eight hind limbs from canine cadavers.

METHODS:

The limbs were randomly allocated to two groups; software on (group I) and software off (group II). Eight anaesthetists with no previous experience of ultrasound-guided regional anaesthesia were recruited. Thirty-six procedures were carried out (18 per group). After sciatic nerve visualisation via ultrasonography, the anaesthetist introduced a needle guided by ultrasonography. When the tip of the needle was considered by the anaesthetist to be as close as possible to the nerve without touching it, 0.05 mL of methylene blue dye was injected. Parameters evaluated included: number of attempts to visualise the needle with ultrasonography, time spent to perform the technique, subjective evaluation of ease of needle visualisation, proximity of the tip of the needle to the nerve, and, at dissection of the leg, inoculation site of the dye in relation to the nerve.

RESULTS:

Significant differences between groups were identified in relation to the number of attempts (group I: median 1, IQR: 1 - 1 attempts versus group II: median 1, IQR: 1 - 4 attempts, p = 0.019), and the relationship between the dye and the nerve during hind limb dissection (72.2% of the nerves were stained in group I versus 16.6% in group II, p = 0.003). No significant difference between groups was observed with respect to the time taken to perform the procedure (group I: median 25.5, IQR: 18.4 - 44.3 seconds versus group II: median 35.7, IQR: 18.6-78.72 seconds, p = 0.31), subjective evaluation of the needle visualization (p = 0.45) or distance between the tip of the needle and the nerve as measured from the ultrasound screen (p = 0.23).

CONCLUSIONS AND CLINICAL RELEVANCE:

This study identified greater success rate in nerve staining when the needle enhancing software was used. The results suggest that the use of this technique could improve injection technique amongst inexperienced anaesthetists performing ultrasound-guided peripheral nerve blocks in dogs.

OBJECTIVE:

To assess the cardiopulmonary effects of ephedrine and phenylephrine for management of isoflurane-induced hypotension in horses.

STUDY DESIGN:

Prospective randomized clinical study.

ANIMALS:

Fourteen isoflurane-anesthetized horses undergoing digital palmar neurectomy.

METHODS:

Ephedrine (EPH group; 0.02 mg kg(-1) minute(-1); n = 7) or phenylephrine (PHE group; 0.002 mg kg(-1) minute(-1); n = 7) was administered to all horses when mean arterial pressure (MAP) was <60 mmHg. The infusions were ended when the target MAP was achieved, corresponding to a 50% increase over the pre-infusion MAP (baseline). The horses were instrumented with an arterial catheter to measure blood pressure and allow the collection of blood for pH and blood-gas analysis and a Swan-Ganz catheter for measurement of cardiac output using thermodilution. Cardiopulmonary parameters were recorded at baseline and at 5, 30, 60 and 90 minutes after achieving the target MAP.

RESULTS:

In both groups, the MAP and systemic vascular resistance (SVR) increased significantly at 5, 30, 60 and 90 minutes post infusion compared to baseline (p < 0.05). The EPH group had a significant increase in cardiac index (CI) and systemic oxygen delivery index at 5, 30, 60 and 90 minutes post infusion compared to baseline (p < 0.05) and compared to the PHE group (p < 0.05). The PHE group had significantly higher SVR and no decrease in oxygen extraction compared with the EPH group at 30, 60 and 90 minutes post infusion (p < 0.05). No significant differences in ventilatory parameters were observed between groups after the infusion.

CONCLUSIONS:

Ephedrine increased the MAP by increasing CI and SVR. Phenylephrine increased MAP by increasing SVR but cardiac index decreased. Ephedrine resulted in better tissue oxygenation than phenylephrine.

CLINICAL RELEVANCE:

Ephedrine would be preferable to phenylephrine to treat isoflurane-induced hypotension in horses since it increases blood flow and pressure.

OBJECTIVE:

To evaluate the pharmacokinetics, in dogs, of liposome-encapsulated oxymorphone and hydromorphone made by the ammonium sulfate gradient loading technique (ASG).

ANIMALS:

Four healthy purpose-bred Beagles aged 9.5 ± 3.2 months and weighing 13.4 ± 2.3 kg.

STUDY DESIGN:

Randomized cross-over design.

METHODS:

Each dog was given either 4.0 mg kg(-1) of ASG-oxymorphone or 8.0 mg kg(-1) of ASG-hydromorphone SC on separate occasions with a 3-month washout period. Blood was collected at baseline and at serial time points up to 1032 hours (43 days) after injection for determination of serum opioid concentrations. Serum opioid concentrations were measured with HPLC-MS and pharmacokinetic parameters were calculated using commercial software and non-compartmental methods.

RESULTS:

Serum concentrations of oxymorphone remained above the limit of quantification for 21 days, while those for hydromorphone remained above the limit of quantification for 29 days. Cmax for ASG-oxymorphone was 7.5 ng mL(-1) ; Cmax for ASG-hydromorphone was 5.7 ng mL(-1) .

CONCLUSIONS AND CLINICAL RELEVANCE:

Oxymorphone and hydromorphone, when encapsulated into liposomes using the ammonium sulfate gradient loading technique, result in measureable serum concentrations for between 3 to 4 weeks. This formulation may have promise in the convenient use of opioids for clinical treatment of chronically painful conditions in dogs.

OBJECTIVE:

To determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses.

STUDY DESIGN:

Prospective randomized clinical study.

ANIMALS:

Twenty client-owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg.

METHODS:

In the control group (CG; n = 10) weaning was performed by a gradual decrease in respiratory rate (fR ) and in the PSV group (PSVG; n = 10) by a gradual decrease in fR with PSV. The effect of weaning was considered suboptimal if PaCO2  > 50 mmHg, arterial pH < 7.35 plus PaCO2  > 50 mmHg or PaO2  < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested.

RESULTS:

Pressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO2 41 ± 3 mmHg at weaning and the average lowest PaO2 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO2 57 ± 6 mmHg at weaning and the average lowest PaO2 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for fR (p = 0.3474), minute volume (p = 0.1153), SaO2 (p = 0.1737) and PaO2 /PAO2 (p = 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for VT  > 10 L (p = 0.0001), fR /VT ratio ≤ 0.60 breaths minute(-1)  L(-1) (p = 0.0001), VT /bodyweight > 18.5 mL kg(-1) (p = 0.0001) and PaO2 /FiO2  > 298 (p = 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for VT  < 10 L (p = 0.0001), fR /VT ratio ≥ 0.60 breaths minute(-1)  L(-1) (p = 0.0001) and Pe'CO2  ≥ 38 mmHg (p = 0.0001) at weaning.

CONCLUSIONS AND CLINICAL RELEVANCE:

Pressure support ventilation (PSV) weaning had a better respiratory outcome. A higher VT , VT /body weight, PaO2 /FiO2 ratio and a lower fR /VT ratio and Pe'CO2 were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.

OBJECTIVES:

Anaesthetized horses commonly become hypoxaemic due to ventilation/perfusion (V·A/Q·) mismatch and increased pulmonary shunt fraction (Qs·/Qt·). Pulse-delivered inhaled nitric oxide may improve oxygenation but may increase plasma concentration of the potent vasoconstrictor, endothelin-1 (ET-1).

Objectives:

Study 1) compare arterial oxygen concentration (PaO2 ) and saturation (SaO2 ), calculated Qs·/Qt· and ET-1 concentration; and Study 2) assess V·A/Q· matching and measured Qs·/Qt· in isoflurane-anaesthetized horses in left lateral recumbency receiving pulse-delivered inhaled nitric oxide (PiNO group) or inhalant gas only (C group).

STUDY DESIGN:

Prospective research trial.

ANIMALS:

Ten Healthy adult Standardbred horses. Two horses were anaesthestized in both groups in a random cross-over design with >4 weeks between studies.

METHODS:

Study 1) Cardiopulmonary data including PaO2 , SaO2 , Qs·/Qt· and ET-1 concentration were measured or calculated prior to and at various points during PiNO administration in 6PiNO and 6C horses. Two-way repeated measures anova with Bonferroni significant difference test was used for data analysis with p < 0.05 considered significant. Study 2) V·A/Q· matching and Qs·/Qt· were determined using the multiple inert gas elimination technique in 3 horses. Data were collected after 60 minutes of anaesthesia without PiNO (baseline) and 15 minutes after PiNO was pulsed during the first 30%, and then the first 60%, of inspiration. Data were descriptive only.

RESULTS:

Study 1) PaO2 and SaO2 were higher and calculated Qs·/Qt· was lower in the PiNO group than the C group at most time points. ET-1 was not different over time or between groups. Study 2) V·A/Q· matching and measured Qs·/Qt· were improved from baseline in all horses but PiNO60% provided no improvement when compared to PiNO30%.

CONCLUSIONS AND CLINICAL RELEVANCE:

PiNO delivered in the initial portion of the inspiration effectively relieves hypoxaemia in anaesthetized horses by improving V·A/Q· matching and decreasing Qs·/Qt· without affecting ET-1.

OBJECTIVE:

To evaluate the cardiovascular, respiratory, electrolyte and acid-base effects of a continuous infusion of dexmedetomidine during propofol-isoflurane anesthesia following premedication with dexmedetomidine.

STUDY DESIGN:

Prospective experimental study.

ANIMALS:

Five adult male Walker Hound dogs 1-2 years of age averaging 25.4 ± 3.6 kg.

METHODS:

Dogs 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.

RESULTS:

No 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 RELEVANCE:

Dexmedetomidine 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.

HISTORY: Two cats were presented for orthopaedic surgery. PHYSICAL EXAMINATION: With the exception of the orthopaedic injuries found, clinical examination showed no abnormality.

MANAGEMENT:

As part of anaesthetic management, one cat received intrathecal morphine, the other epidural morphine. Following recovery, intense grooming was observed. After ensuring adequate analgesia this behaviour was interpreted as pruritus.In the first cat, pruritus was initially managed with medetomidine constant rate infusion (CRI) at 1 and 1.5 μg kg(-1)  hour(-1) . The lower dose produced sedation and no relief from pruritus, the higher dose ablated pruritus but induced sedation. Two propofol (lipid emulsion formulation) boli of 0.1 mg kg(-1) ablated pruritus without causing sedation. The second cat was successfully treated with four boli of 0.1 mg kg(-1) propofol over 20 minutes. FOLLOW-UP: Following treatment with propofol, pruritus did not recur in either cat and both were discharged from the hospital.

CONCLUSIONS:

This is the first clinical report of morphine-induced pruritus in cats and management with low-dose propofol. These cases suggest an antipruritic mechanism for lipid-formulation propofol.

OBJECTIVE:

To assess the effects of varying the sequence of midazolam and propofol administration on the quality of induction, cardiorespiratory parameters and propofol requirements in dogs.

STUDY DESIGN:

Randomized, controlled, clinical study.

ANIMALS:

Thirty-three client owned dogs (ASA I-III, 0.5-10 years, 5-30 kg).

METHODS:

Dogs were premedicated with acepromazine (0.02 mg kg(-1) ) and morphine (0.4 mg kg(-1) ) intramuscularly. After 30 minutes, group midazolam-propofol (MP) received midazolam (0.25 mg kg(-1) ) intravenously (IV) before propofol (1 mg kg(-1) ) IV, group propofol-midazolam (PM) received propofol before midazolam IV at the same doses, and control group (CP) received saline IV, instead of midazolam, before propofol. Supplementary boluses of propofol (0.5 mg kg(-1) ) were administered to effect to all groups until orotracheal intubation was completed. Behaviour after midazolam administration, quality of sedation and induction, and ease of intubation were scored. Heart rate (HR), respiratory rate, and systolic arterial blood pressure were recorded before premedication, post-premedication, after midazolam or saline administration, and at 0, 2, 5, and 10 minutes post-intubation. End-tidal CO2 and arterial oxygen haemoglobin saturation were recorded at 2, 5 and 10 minutes post-intubation.

RESULTS:

Quality of sedation and induction, and ease of intubation were similar in all groups. Incidence of excitement was higher in the MP compared to CP (p = 0.014) and PM (p = 0.026) groups. Propofol requirements were decreased in MP and PM groups with respect to CP (p < 0.001), and in PM compared to MP (p = 0.022). The HR decreased after premedication in all groups, and increased after midazolam and subsequent times in MP (p = 0.019) and PM (p = 0.001) groups. Incidence of apnoea and paddling was higher in CP (p = 0.005) and MP (p = 0.031) groups than in PM.

CONCLUSIONS AND CLINICAL RELEVANCE:

Administration of midazolam before propofol reduced propofol requirements although caused mild excitement in some dogs. Administration of propofol before midazolam resulted in less excitatory phenomena and greater reduction of propofol requirements.