Assessment of microcirculation variables and endothelial glycocalyx using sidestream dark field videomicroscopy in anesthetized dogs undergoing cardiopulmonary bypass.

Introduction: To evaluate microcirculation and endothelial glycocalyx (eGC) variables using sidestream darkfield (SDF) videomicroscopy in canine cardiopulmonary bypass (CPB). Methods: Dogs undergoing CPB for surgical correction of naturally-occurring cardiac disease were prospectively included. Variables collected included patient demographics, underlying cardiac disease, red blood cell flow (Flow), 4-25 µm vessel density (Density), absolute capillary blood volume (CBVabs), relative capillary blood volume (CBVrel) and eGC width assessed by perfused boundary region (PBR). Anesthetized healthy dogs were used as control. Microcirculation and eGC variables were compared at baseline under anesthesia (T0), on CPB prior to cross clamping (T1), after cross clamp removal following surgical correction (T2) and at surgical closure (T3). Results: Twelve dogs were enrolled, including 10 with a complete dataset. Median Flow was 233.9, 79.9, 164.3, and 136.1 µm/s at T0, T1, T2, and T3, respectively, (p = 1.00). Median Density was 173.3, 118.4, 121.0 and 155.4 mm/mm2 at T0, T1, T2, and T3, respectively, (p = 1.00). Median CBVabs decreased over time: 7.4, 6.6, 4.8 and 4.7 103µm3 at T0, T1, T2, and T3, respectively, (p < 0.01). Median CBVrel increased over time: 1.1, 1.5,1.1, and 1.3 103µm3 at T0, T1, T2, and T3, respectively, (p < 0.001). Median PBR increased over time: 1.8, 2.1, 2.4, 2.1 µm at T0, T1, T2, and T3, respectively, (p < 0.001). Compared to control dogs (n = 8), CPB dogs had lower CBVabs at T0. Conclusion: Alterations in eGC thickness and microvascular occur in dogs undergoing CPB for naturally-occurring cardiac disease.

Sedative and cardiopulmonary effects of intramuscular combinations of hydromorphone, acepromazine, dexmedetomidine, and glycopyrrolate followed by intravenous propofol and inhalant isoflurane anesthesia in healthy dogs.

OBJECTIVE: To evaluate the sedative and cardiopulmonary effects of various combinations of acepromazine, dexmedetomidine, hydromorphone, and glycopyrrolate, followed by anesthetic induction with propofol and maintenance with isoflurane in healthy dogs. ANIMALS: 6 healthy adult female Beagles. PROCEDURES: Dogs were instrumented for hemodynamic measurements while anesthetized with isoflurane. Two hours after recovery, dogs received 1 of 4 IM combinations in a crossover design with 1 week between treatments: hydromorphone (0.1 mg/kg) and acepromazine (0.005 mg/kg; HA); hydromorphone and dexmedetomidine (0.0025 mg/kg; HD); hydromorphone, acepromazine, and dexmedetomidine (HAD); and hydromorphone, acepromazine, dexmedetomidine, and glycopyrrolate (0.02 mg/kg; HADG). Sedation was scored after 30 minutes. Physiologic variables and cardiac index were measured after sedation, after anesthetic induction with propofol, and every 15 minutes during maintenance of anesthesia with isoflurane for 60 minutes (target expired concentration at 760 mm Hg, 1.3%). RESULTS: Sedation scores were not significantly different among treatments. Mean ± SD cardiac index was significantly higher for the HA (202 ± 45 mL/min/kg) and HADG (185 ± 59 mL/min/kg) treatments than for the HD (88 ± 31 mL/min/kg) and HAD (103 ± 25 mL/min/kg) treatments after sedation and through the first 15 minutes of isoflurane anesthesia. No ventricular arrhythmias were noted with any treatment. CLINICAL RELEVANCE: In healthy dogs, IM administration of HADG before propofol and isoflurane anesthesia provided acceptable cardiopulmonary function with no adverse effects. This combination should be considered for routine anesthetic premedication in healthy dogs.

Cardiopulmonary function and intestinal blood flow in anaesthetised, experimentally endotoxaemic horses given a constant rate infusion of dexmedetomidine.

BACKGROUND: Endotoxaemia causes untoward inflammatory-mediated effects that might be attenuated by dexmedetomidine. OBJECTIVES: To evaluate the effects of a dexmedetomidine intravenous (IV) infusion on systemic and intestinal haemodynamics and arterial blood gas values in sevoflurane-anaesthetised horses administered Escherichia coli O55:B5 lipopolysaccharides (LPS). STUDY DESIGN: Randomised controlled in vivo experiment. METHODS: A total of 13 horses weighing 456 ± 86 kg (mean ± standard deviation) and aged 13.9 ± 9.0 years donated for euthanasia underwent ventral midline celiotomy using sevoflurane anaesthesia. Baseline physiological variables were recorded after a 90-minute equilibration period. All horses were given 0.1 mcg/kg bwt LPS IV. Horses were randomly assigned to no further treatment (group LPS; seven horses) or IV administration of dexmedetomidine (loading dose 1.75 mcg/kg bwt followed by 1.75 mcg/kg bwt/h; group LPS-Dex; six horses) with concurrent target sevoflurane dose reduction of 50%. Cardiac index (CI; thermodilution), intestinal blood flow, arterial blood parameters and plasma dexmedetomidine concentration measurements were recorded every 30 minutes until euthanasia at 390 minutes. Data were compared between and within groups to baseline using a mixed model analysis (significance P < .05). RESULTS: In LPS-Dex horses, intestinal blood flow and CI were transiently decreased after the dexmedetomidine loading dose, but no significant differences were found compared with baseline during the infusion. Sevoflurane dose was reliably reduced by approximately 40%. Significant differences were identified in creatinine (115  umol/L LPS-Dex; 195 umol/L LPS), bicarbonate (29.7 mmol/L LPS-Dex; 23 mmol/L LPS) and base excess (2.0 mmol/L LPS-Dex; -5.3 mmol/L LPS). Dexmedetomidine plasma concentrations were highest after the loading dose and stable during infusion dosing. MAIN LIMITATIONS: Experimental conditions are not reflective of clinical colic management. CONCLUSIONS: A dexmedetomidine infusion with sevoflurane dose reduction attenuated some deleterious changes in anaesthetised horses administered LPS without sustained negative cardiovascular effects and may be beneficial during colic surgery.

Combined effects of dexmedetomidine and vatinoxan infusions on minimum alveolar concentration and cardiopulmonary function in sevoflurane-anesthetized dogs.

OBJECTIVE: To evaluate the effects of combined infusions of vatinoxan and dexmedetomidine on inhalant anesthetic requirement and cardiopulmonary function in dogs. STUDY DESIGN: Prospective experimental study. METHODS: A total of six Beagle dogs were anesthetized to determine sevoflurane minimum alveolar concentration (MAC) prior to and after an intravenous (IV) dose (loading, then continuous infusion) of dexmedetomidine (4.5 µg kg-1 hour-1) and after two IV doses of vatinoxan in sequence (90 and 180 µg kg-1 hour-1). Blood was collected for plasma dexmedetomidine and vatinoxan concentrations. During a separate anesthesia, cardiac output (CO) was measured under equivalent MAC conditions of sevoflurane and dexmedetomidine, and then with each added dose of vatinoxan. For each treatment, cardiovascular variables were measured with spontaneous and controlled ventilation. Repeated measures analyses were performed for each response variable; for all analyses, p < 0.05 was considered significant. RESULTS: Dexmedetomidine reduced sevoflurane MAC by 67% (0.64 ± 0.1%), mean ± standard deviation in dogs. The addition of vatinoxan attenuated this to 57% (0.81 ± 0.1%) and 43% (1.1 ± 0.1%) with low and high doses, respectively, and caused a reduction in plasma dexmedetomidine concentrations. Heart rate and CO decreased while systemic vascular resistance increased with dexmedetomidine regardless of ventilation mode. The co-administration of vatinoxan dose-dependently modified these effects such that cardiovascular variables approached baseline. CONCLUSIONS AND CLINICAL RELEVANCE: IV infusions of 90 and 180 µg kg-1 hour-1 of vatinoxan combined with 4.5 µg kg-1 hour-1 dexmedetomidine provide a meaningful reduction in sevoflurane requirement in dogs. Although sevoflurane MAC-sparing properties of dexmedetomidine in dogs are attenuated by vatinoxan, the cardiovascular function is improved. Doses of vatinoxan >180 µg kg-1 hour-1 might improve cardiovascular function further in combination with this dose of dexmedetomidine, but beneficial effects on anesthesia plane and recovery quality may be lost.

Recovery quality following a single post-anaesthetic dose of dexmedetomidine or romifidine in sevoflurane anaesthetised horses.

BACKGROUND: Post-anaesthetic sedation is administered to horses to improve recovery quality from inhalant anaesthesia and reduce the risk of catastrophic injury. A single dose of dexmedetomidine for this purpose has not been evaluated clinically. OBJECTIVES: To determine whether dexmedetomidine improves recovery quality from sevoflurane anaesthesia compared to a previously studied dose of romifidine. STUDY DESIGN: Prospective, randomised, masked clinical trial. METHODS: Ninety-nine, adult, client-owned horses anaesthetised for elective procedures completed the trial. Anaesthetic protocol was standardised. Horses were randomly assigned to receive either dexmedetomidine 1 mcg/kg bwt (D) or romifidine 20 mcg/kg bwt (R) intravenously at their first spontaneous breath in recovery. Recoveries were reviewed and independently assigned subjective visual analogue scale (VAS) scores (0-100 mm, worst to best) for overall quality and standing ataxia scores (1-4, none to severe) by two anaesthesiologists blinded to treatment group. Objective anaesthesia and recovery data were also recorded. Comparisons were made using the Chi-square, Wilcoxon rank sum, linear models or Welch-Satterthwaite two-sample t-test (P ≤ .05). Predictors of VAS score were analysed independent of treatment group. RESULTS: There were no significant differences between groups except end-tidal sevoflurane (FE´Sevo) concentration and post-induction extra ketamine dosing. Including FE´Sevo and additional ketamine in the analysis as covariates, VAS scores and time to standing were not significantly different between groups. Increased age, not receiving a nerve block, increased duration of hypotension, and having a nervous temperament were significant predictors of VAS score. MAIN LIMITATIONS: No universal recovery scale exists for inter-study comparisons. CONCLUSIONS: After sevoflurane anaesthesia, sedation with dexmedetomidine or romifidine provides clinically similar recovery time and quality.

Efficacy of Manual Ventilation Techniques During Cardiopulmonary Resuscitation in Dogs.

The efficacy of ventilation of dogs during cardiopulmonary resuscitation (CPR) with a tight fitting face mask or mouth-to-nose rescue breathing has not been evaluated. Twenty-four purpose bred research dogs: Dogs were randomized to be ventilated by cuffed orotracheal tube, tight fitting face mask, mouth-to-nose breathing or compressions only during CPR (n = 6 in all groups). Orotracheal tube and face mask ventilation was performed on room air. Chest compressions were performed during the experimental procedure. Arterial blood gases were performed prior to euthanasia (baseline), at 3 min and at 6 min of CPR. PaO2 and PaCO2 were compared for each time point and each group. There was no difference in PaO2 or PaCO2 between groups at baseline. At 6 min all groups had a significantly higher PaCO2 (P ≤ 0.005) and the facemask and compression only groups had a significantly lower PaO2 (P < 0.02) when compared to the orotracheal tube group. There was no difference between the PaO2 of the mouth-to-nose group compared to the orotracheal tube group at 3 or 6 min. Gastric distension, regurgitation, gas leakage around the mouth, and ineffective breaths were all noted in both the face mask and mouth-to-nose group. The results of this study supports that orotracheal intubation is the preferred technique for ventilation during CPR in dogs. When orotracheal intubation is not possible, face mask ventilation or mouth-to-nose ventilation would be reasonable alternatives. When oxygen supplementation is available, face mask ventilation is likely to be superior. Appropriate training for both face mask and mouth-to-nose ventilation techniques is recommended.

Psoas compartment and sacral plexus block via electrostimulation for pelvic limb amputation in dogs.

OBJECTIVE: To assess the efficacy of psoas compartment and sacral plexus block for pelvic limb amputation in dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: A total of 16 dogs aged 8±3 years and weighing 35±14 kg (mean±standard deviation). METHODS: Dogs were administered morphine (0.5 mg kg-1) and atropine (0.02 mg kg-1); anesthesia was induced with propofol and maintained with isoflurane. Regional blocks were performed before surgery in eight dogs with bupivacaine (2.2 mg kg-1) and eight dogs were administered an equivalent volume of saline. The lumbar plexus within the psoas compartment was identified using electrolocation lateral to the lumbar vertebrae at the fourth-fifth, fifth-sixth and sixth-seventh vertebral interspaces. The sacral plexus, ventrolateral to the sacrum, was identified using electrolocation. Anesthesia was monitored using heart rate (HR), invasive blood pressure, electrocardiography, expired gases, respiratory frequency and esophageal temperature by an investigator unaware of the group allocation. Pelvic limb amputation by coxofemoral disarticulation was performed. Dogs that responded to surgical stimulation (>10% increase in HR or arterial pressure) were administered fentanyl (2 µg kg-1) intravenously for rescue analgesia. Postoperative pain was assessed at extubation; 30, 60 and 120 minutes; and the morning after surgery using a visual analog scale (VAS). RESULTS: The number of intraoperative fentanyl doses was fewer in the bupivacaine group (2.7±1.1 versus 6.0±2.2; p<0.01). Differences in physiologic variables were not clinically significant. VAS scores were lower in bupivacaine dogs at extubation (0.8±1.9 versus 3.8±2.5) and at 30 minutes (1.0±1.4 versus 4.3±2.1; p<0.05). CONCLUSIONS AND CLINICAL RELEVANCE: Psoas compartment (lumbar plexus) and sacral plexus block provided analgesia during pelvic limb amputation in dogs.

Effects of constant rate infusions of dexmedetomidine or MK-467 on the minimum alveolar concentration of sevoflurane in dogs.

OBJECTIVE: To determine the effects of low and high dose infusions of dexmedetomidine and a peripheral α2-adrenoceptor antagonist, MK-467, on sevoflurane minimum alveolar concentration (MAC) in dogs. STUDY DESIGN: Crossover experimental study. ANIMALS: Six healthy, adult Beagle dogs weighing 12.6±0.9 kg (mean±standard deviation). METHODS: Dogs were anesthetized with sevoflurane in oxygen. After a 60-minute instrumentation and equilibration period, the MAC of sevoflurane was determined in triplicate using the tail clamp technique. PaCO2 and temperature were maintained at 40±5 mmHg (5.3±0.7 kPa) and 38±0.5 ºC, respectively. After baseline MAC determination, dogs were administered two incremental loading and infusion doses of either dexmedetomidine (1.5 µg kg-1 then 1.5 µg kg-1 hour-1 and 4.5 µg kg-1 then 4.5 µg kg-1 hour-1) or MK-467 (90 µg kg-1 then 90 µg kg-1 hour-1 and 180 µg kg-1 then 180 µg kg-1 hour-1); loading doses were administered over 10 minutes. MAC was redetermined in duplicate starting 30 minutes after the start of drug administration at each dose. End-tidal sevoflurane concentrations were corrected for calibration and adjusted to sea level. A repeated-measures analysis was performed and comparisons between doses were conducted using Tukey's method. Statistical significance was considered at p<0.05. RESULTS: Sevoflurane MAC decreased significantly from 1.86±0.3% to 1.04±0.1% and 0.57±0.1% with incremental doses of dexmedetomidine. Sevoflurane MAC significantly increased with high dose MK-467, from 1.93±0.3% to 2.29±0.5%. CONCLUSIONS AND CLINICAL RELEVANCE: Dexmedetomidine caused a dose-dependent decrease in sevoflurane MAC, whereas MK-467 caused an increase in MAC at the higher infusion dose. Further studies evaluating the combined effects of dexmedetomidine and MK-467 on MAC and cardiovascular function may elucidate potential benefits of the addition of a peripheral α2-adrenergic antagonist to inhalation anesthesia in dogs.

Pharmacokinetics and pharmacodynamics of propofol with or without 2% benzyl alcohol following a single induction dose administered intravenously in cats.

OBJECTIVE: To compare the pharmacokinetics and pharmacodynamics of propofol with or without 2% benzyl alcohol administered intravenously (IV) as a single induction dose in cats. STUDY DESIGN: Prospective experimental study. ANIMALS: Six healthy adult cats, three female intact, three male castrated, weighing 4.8 ± 1.8 kg. METHODS: Cats received 8 mg kg(-1) IV of propofol (P) or propofol with 2% benzyl alcohol (P28) using a randomized crossover design. Venous blood samples were collected at predetermined time points to 24 hours after drug administration to determine drug plasma concentrations. Physiologic and behavioral variables were also recorded. Propofol and benzyl alcohol concentrations were determined using high pressure liquid chromatography with fluorescence detection. Pharmacokinetic parameters were described using a 2-compartment model. Pharmacokinetic and pharmacodynamic parameters were analyzed using repeated measures anova (p < 0.05). RESULTS: Plasma concentrations of benzyl alcohol were below the lower limits of quantification (LLOQ) at all time points for two of the six cats (33%), and by 30 minutes for the remaining four cats. Propofol pharmacokinetics, with or without 2% benzyl alcohol, were characterized by rapid distribution, a long elimination phase, and a large volume of distribution. No differences were noted between treatments with the exception of clearance from the second compartment (CLD2), which was 23.6 and 38.8 mL kg(-1)  minute(-1) in the P and P28 treatments, respectively. Physiologic and behavioral variables were not different between treatments with the exception of heart rate at 4 hours post administration. CONCLUSIONS AND CLINICAL RELEVANCE: The addition of 2% benzyl alcohol as a preservative minimally altered the pharmacokinetics and pharmacodynamics of propofol 1% emulsion when administered as a single IV bolus in this group of cats. These data support the cautious use of propofol with 2% benzyl alcohol for induction of anesthesia in healthy cats.

Prevalence and risk factors for canine post-anesthetic aspiration pneumonia (1999-2009): a multicenter study.

OBJECTIVE: To determine the incidence of canine post-anesthetic aspiration pneumonia (AP) and to identify anesthetic agents, procedures and management factors associated with the development of AP. STUDY DESIGN: Multicenter, randomized, case-controlled retrospective study. ANIMALS: Two hundred and forty dogs affected with AP and 488 unaffected control dogs. METHODS: Electronic medical record databases at six Veterinary colleges were searched for dogs, coded for anesthesia or sedation and pneumonia from January 1999 to December 2009. The resultant 2158 records were hand-searched to determine eligibility for inclusion. Diagnosis of AP was made radiographically. Two unaffected control dogs were randomly selected for each affected dog, from a list of dogs that underwent sedation or anesthesia in the same time period and did not develop aspiration pneumonia. Fifty-seven factors were then evaluated for association with aspiration pneumonia. Data analysis was performed using univariate Chi-square or student t-tests, then multivariate logistic regression. RESULTS: Incidence of post-anesthetic AP was 0.17%, from 140,711 cases anesthetized or sedated over the 10 year period. Two anesthesia-related events were significantly associated with development of AP: regurgitation and administration of hydromorphone at induction. Administration of anticholinergics was not associated with AP. Procedures associated with increased odds of aspiration pneumonia included laparotomy, upper airway surgery, neurosurgery, thoracotomy and endoscopy. Orthopedic surgery, ophthalmologic surgery, dental procedures, MRI, CT, bronchoscopy, cystoscopy, tracheoscopy and neutering were not associated with development of AP. Three patient factors were associated with the development of AP: megaesophagus, and a history of pre-existing respiratory or neurologic disease. Sixty-nine% of dogs with two or more of the above independent predictive variables developed AP. CONCLUSION AND CLINICAL RELEVANCE: Most anesthetic agents and procedures were not associated with the development of AP. We need to devise and evaluate strategies to protect at risk patients.

Comparison of the analgesic efficacy of oral ABT-116 administration with that of transmucosal buprenorphine administration in dogs.

OBJECTIVE: To evaluate the analgesic efficacy of ABT-116, a transient receptor potential cation channel vanilloid subfamily V member 1 antagonist, and compare it with that of buprenorphine by measurement of mechanical and thermal nociceptive thresholds in dogs. ANIMALS: Six 7- to 8-month-old dogs (3 males and 3 females). PROCEDURES: In a crossover study design, all dogs received ABT-116 (30 mg/kg, PO) and buprenorphine (0.03 mg/kg, orotransmucosally), with each treatment separated by 1 week. Physiologic variables were recorded prior to and 1, 6, and 24 hours after drug administration. Thermal (thoracic) and mechanical (dorsolateral aspect of the radius [proximal] and dorsopalmar aspect of the forefoot [distal]) nociceptive thresholds were assessed prior to (baseline) and 15 minutes and 1, 2, 4, 6, 12, 18, and 24 hours after treatment. RESULTS: Buprenorphine administration resulted in higher overall thermal and proximal mechanical nociceptive thresholds, compared with ABT-116. Distal mechanical nociceptive thresholds after treatment were higher than baseline values for both treatments, but the magnitude of change was greater for buprenorphine at 1 hour after administration. Whereas HR and RR sporadically differed from baseline values after ABT-116 administration, rectal temperature increased from a baseline value of 39 ± 0.2°C (mean ± SD) to a peak of 40.6 ± 0.2°C at 6 hours. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs without inflammation or nerve injury, PO administration of ABT-116 did not consistently result in an increase in nociceptive thresholds. However, clinically relevant increases in rectal temperature were identified after ABT-116 administration.

Correlation between jugular and central venous pressures in laterally recumbent horses.

OBJECTIVE: To compare and correlate right atrial pressure, which represents central venous pressure (CVP) to jugular vein pressure (JVP) in laterally recumbent horses under anesthesia. STUDY DESIGN: Retrospective clinical trial. ANIMALS: Seven adult healthy horses (411 ± 8.7 kg). METHODS: Horses were sedated with IV xylazine and anesthesia was obtained with IV ketamine and diazepam. Anesthesia was maintained with sevoflurane in oxygen. All horses were positioned in left lateral recumbency. An 8F catheter introducer was inserted into the right jugular vein to measure JVP. An 8F catheter introducer was inserted into the left jugular vein to be used as the port for a 7F 110 cm catheter that reached the right atrium to measure CVP. Both, CVP and JVP were measured simultaneously with a water calibrated aneroid manometer using the sternum as the 0 cmH(2) O reference point. Measurements were compared using Spearman correlation and the Bland-Altman plot. RESULTS: Twenty paired samples were obtained over a period of 2 hours. The CVP ranged from 7 to 31 cmH(2) O, while the JVP ranged from 5 to 30 cmH(2) O. The Spearman correlation coefficient indicated that CVP and JVP had a strong correlation with r = 0.88. The Bland-Altman plot showed a bias of 0.7 cmH(2) O. CONCLUSION AND CLINICAL RELEVANCE: Jugular vein pressure showed a strong correlation with CVP in healthy, euvolemic, laterally recumbent anesthetized adult horses. Thus, JVP cannot replace CVP but it may be used clinically to monitor CVP in laterally recumbent horses.

Hemodynamic effects of butorphanol in desflurane-anesthetized dogs.

OBJECTIVE: To evaluate the effects of butorphanol on cardiopulmonary parameters in dogs anesthetized with desflurane and breathing spontaneously. STUDY DESIGN: Prospective, randomized experimental trial. ANIMALS: Twenty dogs weighing 12 ± 3 kg. METHODS: Animals were distributed into two groups: a control group (CG) and butorphanol group (BG). Propofol was used for induction and anesthesia was maintained with desflurane (10%). Forty minutes after induction, the dogs in the CG received sodium chloride 0.9% (0.05 mL kg(-1) IM), and dogs in the BG received butorphanol (0.4 mg kg(-1) IM). The first measurements of body temperature (BT), heart rate (HR), arterial pressures (AP), cardiac output (CO), cardiac index (CI), central venous pressure (CVP), stroke volume index (SVI), pulmonary arterial occlusion pressure (PAOP), mean pulmonary arterial pressure (mPAP), left ventricular stroke work (LVSW), systemic (SVR) and pulmonary (PVR) vascular resistances, respiratory rate (f(R) ), and arterial oxygen (PaO(2) ) and carbon dioxide (PaCO(2) ) partial pressures were taken immediately before the administration of butorphanol or sodium chloride solution (T0) and then at 15-minute intervals (T15-T75). RESULTS: In the BG, HR, AP, mPAP and SVR decreased significantly from T15 to T75 compared to baseline. f(R) was lower at T30 than at T0 in the BG. AP and f(R) were significantly lower than in the CG from T15 to T75. PVR was lower in the BG than in the CG at T30, while PaCO(2) was higher compared with T0 from T30 to T75 in the BG and significantly higher than in the CG at T30 to T75. CONCLUSIONS AND CLINICAL RELEVANCE: At the studied dose, butorphanol caused hypotension and decreased ventilation during desflurane anesthesia in dogs. The hypotension (from 86 ± 10 to 64 ± 10 mmHg) is clinically relevant, despite the maintenance of cardiac index.

Plasma concentrations and behavioral, antinociceptive, and physiologic effects of methadone after intravenous and oral transmucosal administration in cats.

OBJECTIVE: To determine plasma concentrations and behavioral, antinociceptive, and physiologic effects of methadone administered via IV and oral transmucosal (OTM) routes in cats. ANIMALS: 8 healthy adult cats. PROCEDURES: Methadone was administered via IV (0.3 mg/kg) and OTM (0.6 mg/kg) routes to each cat in a balanced crossover design. On the days of drug administration, jugular catheters were placed in all cats under anesthesia; a cephalic catheter was also placed in cats that received methadone IV. Baseline measurements were obtained ≥ 90 minutes after extubation, and methadone was administered via the predetermined route. Heart and respiratory rates were measured; sedation, behavior, and antinociception were evaluated, and blood samples were collected for methadone concentration analysis at predetermined intervals for 24 hours after methadone administration. Data were summarized and evaluated statistically. RESULTS: Plasma concentrations of methadone were detected rapidly after administration via either route. Peak concentration was detected 2 hours after OTM administration and 10 minutes after IV administration. Mean ± SD peak concentration was lower after OTM administration (81.2 ± 14.5 ng/mL) than after IV administration (112.9 ± 28.5 ng/mL). Sedation was greater and lasted longer after OTM administration. Antinociceptive effects were detected 10 minutes after administration in both groups; these persisted ≥ 2 hours after IV administration and ≥ 4 hours after OTM administration. CONCLUSIONS AND CLINICAL RELEVANCE: Despite lower mean peak plasma concentrations, duration of antinociceptive effects of methadone was longer after OTM administration than after IV administration. Methadone administered via either route may be useful for perioperative pain management in cats.

Determination of the sevoflurane sparing effect of methadone in cats.

OBJECTIVE: To determine the magnitude and duration of sevoflurane minimum alveolar concentration (MAC) reduction following a single intravenous (IV) dose of methadone in cats. STUDY DESIGN: Prospective experimental study. ANIMALS: Eight (four females and four males) healthy mixed-breed adult (1-2 years) cats weighing 5.82 ± 0.42 kg. METHODS: Anesthesia was induced and maintained with sevoflurane. Intravenous catheters facilitated administration of methadone and lactated Ringer's solution. After baseline MAC determination in triplicate using a tail clamp technique, 0.3 mg kg(-1) of methadone was administered IV. End-tidal sevoflurane concentration (e'SEVO) was reduced and MAC was redetermined. In an effort to determine the duration of MAC reduction, measurements were repeated in a stepwise manner until MAC values returned to baseline. After the last stimulation, the e'SEVO was increased to 1.2 individual MAC for 15 minutes, then sevoflurane was discontinued and cats were allowed to recover from anesthesia. RESULTS: Baseline sevoflurane MAC was 3.18 ± 0.06%. When compared with baseline the sevoflurane MAC after methadone administration was significantly reduced by 25, 15 and 7% at 26, 76 and 122 minutes, respectively. The final MAC value (3.09 ± 0.07%) determined 156 minutes after methadone administration was not significantly different from baseline. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous methadone (0.3 mg kg(-1)) significantly decreased MAC of sevoflurane in cats but the effect was short-lived.

Effects of intravenous administration of lidocaine on the minimum alveolar concentration of sevoflurane in horses.

OBJECTIVE: To determine effects of a continuous rate infusion of lidocaine on the minimum alveolar concentration (MAC) of sevoflurane in horses. ANIMALS: 8 healthy adult horses. PROCEDURES: Horses were anesthetized via IV administration of xylazine, ketamine, and diazepam; anesthesia was maintained with sevoflurane in oxygen. Approximately 1 hour after induction, sevoflurane MAC determination was initiated via standard techniques. Following sevoflurane MAC determination, lidocaine was administered as a bolus (1.3 mg/kg, IV, over 15 minutes), followed by constant rate infusion at 50 µg/kg/min. Determination of MAC for the lidocaine-sevoflurane combination was started 30 minutes after lidocaine infusion was initiated. Arterial blood samples were collected after the lidocaine bolus, at 30-minute intervals, and at the end of the infusion for measurement of plasma lidocaine concentrations. RESULTS: IV administration of lidocaine decreased mean ± SD sevoflurane MAC from 2.42 ± 0.24% to 1.78 ± 0.38% (mean MAC reduction, 26.7 ± 12%). Plasma lidocaine concentrations were 2,589 ± 811 ng/mL at the end of the bolus; 2,065 ± 441 ng/mL, 2,243 ± 699 ng/mL, 2,168 ± 339 ng/mL, and 2,254 ± 215 ng/mL at 30, 60, 90, and 120 minutes of infusion, respectively; and 2,206 ± 329 ng/mL at the end of the infusion. Plasma concentrations did not differ significantly among time points. CONCLUSIONS AND CLINICAL RELEVANCE: Lidocaine could be useful for providing a more balanced anesthetic technique in horses. A detailed cardiovascular study on the effects of IV infusion of lidocaine during anesthesia with sevoflurane is required before this combination can be recommended.

Comparison of the cardiovascular effects of equipotent anesthetic doses of sevoflurane alone and sevoflurane plus an intravenous infusion of lidocaine in horses.

OBJECTIVE: To compare cardiovascular effects of sevoflurane alone and sevoflurane plus an IV infusion of lidocaine in horses. Animals-8 adult horses. PROCEDURES: Each horse was anesthetized twice via IV administration of xylazine, diazepam, and ketamine. During 1 anesthetic episode, anesthesia was maintained by administration of sevoflurane in oxygen at 1.0 and 1.5 times the minimum alveolar concentration (MAC). During the other episode, anesthesia was maintained at the same MAC multiples via a reduced concentration of sevoflurane plus an IV infusion of lidocaine. Heart rate, arterial blood pressures, blood gas analyses, and cardiac output were measured during mechanical (controlled) ventilation at both 1.0 and 1.5 MAC for each anesthetic protocol and during spontaneous ventilation at 1 of the 2 MAC multiples. RESULTS: Cardiorespiratory variables did not differ significantly between anesthetic protocols. Blood pressures were highest at 1.0 MAC during spontaneous ventilation and lowest at 1.5 MAC during controlled ventilation for either anesthetic protocol. Cardiac output was significantly higher during 1.0 MAC than during 1.5 MAC for sevoflurane plus lidocaine but was not affected by anesthetic protocol or mode of ventilation. Clinically important hypotension was detected at 1.5 MAC for both anesthetic protocols. CONCLUSIONS AND CLINICAL RELEVANCE: Lidocaine infusion did not alter cardiorespiratory variables during anesthesia in horses, provided anesthetic depth was maintained constant. The IV administration of lidocaine to anesthetized nonstimulated horses should be used for reasons other than to improve cardiovascular performance. Severe hypotension can be expected in nonstimulated horses at 1.5 MAC sevoflurane, regardless of whether lidocaine is administered.

Evaluation of cardiovascular, respiratory and biochemical effects, and anesthetic induction and recovery behavior in horses anesthetized with a 5% micellar microemulsion propofol formulation.

OBJECTIVE: To characterize cardiovascular, respiratory and biochemical effects and recovery behavior associated with a 3-hour continuous infusion of a micellar microemulsion propofol formulation in horses. STUDY DESIGN: Prospective experimental trial. ANIMALS: Six healthy adult horses, 9 +/- 2 years old and weighing 557 +/- 14 kg. METHODS: All horses received xylazine (1 mg kg(-1), IV) 5 minutes prior to anesthetic induction. Each horse was anesthetized on two occasions with a 5% micellar microemulsion propofol formulation (2 mg kg(-1), IV); first as a single bolus (phase I) and then as a 3-hour continuous infusion (phase II). Propofol pharmacokinetics were obtained from phase I and used to determine the starting infusion rates in phase II. Anesthetic induction and recovery characteristics were quantitatively and qualitatively assessed. Cardiovascular, respiratory and biochemical parameters were monitored during anesthesia and recovery. RESULTS: Induction quality varied, ranging from good to poor. Standing and overall recovery quality scores were consistently excellent in phase I but more variability was observed among horses in phase II. Heart rate (HR) and mean arterial pressure (MAP) were adequately maintained but marked hypoventilation developed. There were only minimal changes in blood biochemical analytes following anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: The micellar microemulsion propofol formulation, administered as a 3-hour continuous infusion, showed similar results compared to those previously described with a commercially available propofol preparation. However, based on present findings, use of propofol as a primary anesthetic in horses for prolonged periods of anesthesia requires further study to determine the limits of safety and clinical applicability.

Alterações em variáveis cardiovasculares e intracranianas induzidas pela associação de buprenorfina e sevoflurano em cães

Objetivou-se, com este experimento, estudar possíveis alterações nas variáveis cardiovasculares e intracranianas promovidas pela buprenorfina, em cães anestesiados. Utilizaram-se oito cães adultos, clinicamente saudáveis. Aanestesia foi induzida com propofol (8 mg/kg IV) e eAi $~g.uida ·os ànimais foram erittJbados ~com sonda orotraqueal de Magill,a qual foi conectada ao aparelho de anestesia volátii4Jara,administração de sevoflurano {1,3 CAM). Os animais foram mantidossob ventilação controlada durante o período experimental. Após 20 minutos do posicionamento do cateter de pressãointracraniana (PIC), foi aplicada buprenorfina {0,02 mg/kg IV}. Avaliou-se: PIC; temperatura intracraniana (TIC); pressão deperfusão cerebral (PPC); freqüência cardíaca (FC); pressões arteriais sistólica, média e diastólica (PAS, PAM e PAD, respectivamente);débito cardíaco (DC); pressão venosa central (PVC); pressão da artéria pulmonar (PAP); e temperatura corporal(TC). As colheitas foram feitas nos seguintes momentos: M1 -" 20 minutos após o posicionamento do cateter de PIC; M2 - 15minutos após a administração do opióide; M3, M4 e M5- de 15 em 15 minutos após M2. A avaliação estatística dos dados foiefetuada por meio do Teste de Tukey (P 0,05). A PIC permaneceu estável durante todo o período experimental, sendoobservada discreta elevação em M2, mas sem significado clínico ou estatístico. Entretant

Evaluation of transesophageal echo-Doppler ultrasonography for the measurement of aortic blood flow in anesthetized cats.

OBJECTIVE: To evaluate the use of a transesophageal echo-Doppler ultrasonography (TED) technique for measurement of aortic blood flow (ABF) in relation to cardiac output (CO) measured by use of a thermodilution technique in anesthetized cats. ANIMALS: 6 adult cats (mean +/- SD body weight, 5 +/- 0.7 kg). PROCEDURES: Anesthesia was induced and maintained in cats by administration of isoflurane. A thermodilution catheter was placed in a pulmonary artery. The TED probe was positioned in the esophagus in the region where the aorta and esophagus are almost parallel. Five baseline values for ABF and CO were concurrently recorded. Cats were randomly assigned to a high or low CO state (increase or decrease in CO by at least 25% from baseline, respectively). Baseline conditions were restored, and the other CO state was induced, after which baseline conditions were again restored. For each CO state, ABF and CO were measured 5 times at 5-minute intervals. Correlation and agreement between the techniques were determined by use of the Pearson product-moment correlation and Bland-Altman method. RESULTS: CO ranged from 0.16 to 0.75 L/min and ABF from 0.05 to 0.48 L/min. Overall data analysis revealed a high correlation (r = 0.884) between techniques but poor agreement (limits of agreement, -0.277 to 0.028 L/min). During the low CO state, correlation between techniques was low (r = 0.413). CONCLUSIONS AND CLINICAL RELEVANCE: TED did not accurately measure CO. However, it allowed evaluation of CO patterns and may be useful clinically in anesthetized cats.