Comparison between pulse pressure variation and systolic pressure variation measured from a peripheral artery for accurately predicting fluid responsiveness in mechanically ventilated dogs.

OBJECTIVE: To compare pulse pressure variation (PPV) and systolic pressure variation (SPV) measured from a peripheral artery to predict fluid responsiveness in anesthetized healthy dogs. STUDY DESIGN: Prospective study. ANIMALS: A total of 39 dogs (13.8-26.8 kg) anesthetized with isoflurane for elective ovariohysterectomy. METHODS: Ventilation was controlled (tidal volume 12 mL kg-1; 40% inspiratory pause). PPV and SPV were recorded from a dorsal pedal artery catheter using an automated algorithm. A fluid challenge (FC) with lactated Ringer's solution (20 mL kg-1 over 15 minutes) was administered once (21 animals) or twice (18 animals) before surgery. Increases in transpulmonary thermodilution stroke volume index > 15% from values recorded before each FC defined responders to volume expansion. Final fluid responsiveness status was based on the response to single FC or second FC. Predictive ability of PPV and SPV was compared by receiver operating characteristic (ROC) curve analysis and by the range of cut-off values associated with uncertain results (gray zone). RESULTS: All animals after the single FC were responders; all animals administered two FCs were nonresponders after the second FC. The area under the ROC curve (AUROC) of PPV (0.968) did not differ from that of SPV (0.937) (p = 0.45). Best cut-off thresholds to discriminate responders from nonresponders were >11.7% (PPV) and >7.4 mmHg (SPV). The gray zone of PPV and SPV was 8.2-14.6% and 7.0-7.4 mmHg, respectively. The percentage of animals with PPV and SPV values within the gray zone was less for SPV (10.2%) than for PPV (30.8%). CONCLUSIONS AND CLINICAL RELEVANCE: PPV and SPV obtained from the dorsal pedal artery are useful predictors of fluid responsiveness in dogs. Using an automated algorithm, SPV may more accurately predict fluid responsiveness than PPV, with responders identifiable by PPV > 14.6% and SPV > 7.4 mmHg.

Use of aortic flow indexes derived from transthoracic echocardiography to evaluate response to a fluid challenge in anesthetized dogs.

OBJECTIVE: To evaluate the ability of transthoracic echocardiographic aortic flow measurements to discriminate response to a fluid challenge (FC) in healthy anesthetized dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: A total of 48 isoflurane-anesthetized dogs (14.2-35.0 kg) undergoing elective surgery. METHODS: Fluid responsiveness was evaluated before surgery by FC (lactated Ringer's 10 mL kg-1 intravenously over 5 minutes). Percentage increases in transpulmonary thermodilution stroke volume (ΔSVTPTD) >15% from values recorded before FC defined responders to volume expansion. A group of 24 animals were assigned as nonresponders (ΔSVTPTD ≤15%). When ΔSVTPTD was >15% after the first FC, additional FC were administered until ΔSVTPTD was ≤15%. Final fluid responsiveness status was based on the response to the last FC. Percentage increases after FC in aortic flow indexes [velocity time integral (ΔVTIFC) and maximum acceleration (ΔVmaxFC)] and in mean arterial pressure (ΔMAPFC) were compared with ΔSVTPTD. RESULTS: After one FC, 24 animals were responders. For nonresponders, ΔSVTPTD was ≤15% after one, two and three FCs in eight/24, 15/24 and one/24 animals, respectively. The FC that defined responsiveness increased ΔSVTPTD by 29 (18-53)% in responders and by 8 (-3 to 15)% in nonresponders [mean (range)]. The area under the receiver operating characteristics curve (AUROC) of ΔVTIFC (0.901) was larger than the AUROCs of ΔVmaxFC (0.774, p = 0.041) and ΔMAPFC (0.519, p < 0.0001). ΔMAPFC did not predict responsiveness (p = 0.826). Best cut-off thresholds for discriminating responders, with respective zones of diagnostic uncertainty (gray zones) were >14.7 (10.8-17.6)% for ΔVTIFC and >8.6 (-0.3 to 14.7)% for ΔVmaxFC. Animals within the gray zone were 17% (ΔVTIFC) and 50% (ΔVmaxFC). CONCLUSIONS AND CLINICAL RELEVANCE: Changes in VTI induced by FC can determine responsiveness with reasonable accuracy in dogs and could play an important role in goal-directed fluid therapy.

EVALUATION OF A LARYNGEAL MASK AIRWAY AS AN ALTERNATIVE TO OROTRACHEAL INTUBATION FOR MAINTAINING AIRWAY PATENCY DURING INHALANT ANESTHESIA UNDER SPONTANEOUS VENTILATION IN CAPYBARAS (HYDROCHOERUS HYDROCHAERIS).

Orotracheal intubation carries greater difficulty in rodents than in most domestic species. The human laryngeal mask airway (LMA) was compared with an endotracheal tube (ETtube) for maintaining airway patency in anesthetized capybaras (Hydrochoerus hydrochaeris). Six capybaras (24-52 kg) were remotely darted with intramuscular ketamine, midazolam, and acepromazine on two occasions (≥7-day intervals). After isoflurane mask induction for random placement of an ETtube or a LMA during each episode, anesthesia was maintained with isoflurane in oxygen under spontaneous ventilation for 90-120 min. Computed tomography of the pharynx and larynx was performed in two of six animals and three of six animals with the ETtube and LMA, respectively. End-tidal isoflurane [median (range)] was not significantly different between ETtube [0.6% (0.5-1.5%)] and LMA [0.6% (0.4-0.9%)]. Heart rate [67 ± 11 beats/min (ETtube) and 67 ± 18 beats/min (LMA)], mean arterial pressure [74 ± 13 mm Hg (ETtube) and 74 ± 14 mm Hg (LMA)], arterial CO2 tension [41 ± 2 mm Hg (ETtube) and 43 ± 4 mm Hg (LMA)], and arterial O2 tension [360 ± 59 mm Hg (ETtube) and 360 ± 63 mm Hg (LMA)] were not significantly different between treatment groups. Computed tomography showed gas in the esophagus with the LMA (three of three animals); the fit of the LMA to the larynx was adequate in two of three animals and fair in one of three animals. Recovery from anesthesia was uneventful. The LMA is a feasible alternative to the ETtube for maintaining airway patency during inhalant anesthesia in spontaneously breathing capybaras. However, the LMA may be dislodged during movement of the animal.

Comparison of perioperative analgesia using the infiltration of the surgical site with ropivacaine alone and in combination with meloxicam in cats undergoing ovariohysterectomy.

BACKGROUND: Infiltration of the surgical site with local anesthetics combined with nonsteroidal anti-inflammatory drugs may play an important role in improving perioperative pain control. This prospective, randomized, blinded, controlled clinical trial aimed to evaluate intraoperative isoflurane requirements, postoperative analgesia, and adverse events of infiltration of the surgical site with ropivacaine alone and combined with meloxicam in cats undergoing ovariohysterectomy. Forty-five cats premedicated with acepromazine/meperidine and anesthetized with propofol/isoflurane were randomly distributed into three treatments (n = 15 per group): physiological saline (group S), ropivacaine alone (1 mg/kg, group R) or combined with meloxicam (0.2 mg/kg, group RM) infiltrated at the surgical site (incision line, ovarian pedicles and uterus). End-tidal isoflurane concentration (FE'ISO), recorded at specific time points during surgery, was adjusted to inhibit autonomic responses to surgical stimulation. Pain was assessed using an Interactive Visual Analog Scale (IVAS), UNESP-Botucatu Multidimensional Composite Pain Scale (MCPS), and mechanical nociceptive thresholds (MNT) up to 24 h post-extubation. Rescue analgesia was provided with intramuscular morphine (0.1 mg/kg) when MCPS was ≥6. RESULTS: Area under the curve (AUC) of FE'ISO was significantly lower (P < 0.0001) in the RM (17.8 ± 3.1) compared to S (23.1 ± 2.2) and R groups (22.8 ± 1.1). Hypertension (systolic arterial pressure > 160 mmHg) coinciding with surgical manipulation was observed only in cats treated with S and R (4/15 cats, P = 0.08). The number of cats receiving rescue analgesia (4 cats in the S group and 1 cat in the R and RM groups) did not differ among groups (P = 0.17). The AUC of IVAS, MCPS and MNT did not differ among groups (P = 0.56, 0.64, and 0.18, respectively). Significantly lower IVAS pain scores were recorded at 1 h in the RM compared to the R and S groups (P = 0.021-0.018). There were no significant adverse effects during the study period. CONCLUSIONS: Local infiltration with RM decreased intraoperative isoflurane requirements and resulted in some evidence of improved analgesia during the early postoperative period. Neither R nor RM infiltration appeared to result in long term analgesia in cats undergoing ovariohysterectomy.

Addition of magnesium sulfate to intraperitoneal ropivacaine for perioperative analgesia in canine ovariohysterectomy.

Magnesium may be used as an adjunctive analgesic for perioperative pain management because of its antinociceptive properties. This study investigated the analgesic efficacy of intraperitoneal ropivacaine combined with magnesium sulfate in canine ovariohysterectomy. Forty-five dogs sedated with acepromazine/meperidine and anesthetized with propofol/isoflurane were randomly distributed into three treatments, administered intraperitoneally (n = 15 per group): saline solution (group S), 0.25% ropivacaine (3 mg/kg) alone (group R), or in combination with magnesium sulfate (20 mg/kg, group R-Mg). Intravenous fentanyl was given to control cardiovascular responses to surgical stimulation. Postoperative pain was assessed using an Interactive Visual Analog Scale (IVAS), the short form of the Glasgow Composite Pain Scale, and mechanical nociceptive thresholds. Morphine/meloxicam was administered as rescue analgesia. Intraoperatively, the R-Mg group required less fentanyl (p = .02) and exhibited higher incidence of hypotension (systolic arterial pressure <90 mm Hg, p = .006) compared with the S group. Lower IVAS pain scores were recorded during the first hour in the R-Mg group than the other groups (p = .007-.045). Postoperative rescue analgesia did not differ between groups. Intraperitoneal magnesium sulfate administration, in spite of decreasing intraoperative opioid requirements, increased the incidence of hypotension with minimal evidence of postoperative analgesic benefits.

Effects of cuff size and position on the agreement between arterial blood pressure measured by Doppler ultrasound and through a dorsal pedal artery catheter in anesthetized cats.

OBJECTIVE: To compare the effects of cuff size/position on the agreement between arterial blood pressure measured by Doppler ultrasound (ABPDoppler) and dorsal pedal artery catheter measurements of systolic (SAPinvasive) and mean arterial pressure (MAPinvasive) in anesthetized cats. STUDY DESIGN: Prospective study. ANIMALS: A total of eight cats (3.0-3.8 kg) for neutering. METHODS: During isoflurane anesthesia, before surgery, changes in end-tidal isoflurane concentrations and/or administration of dopamine were performed to achieve SAPinvasive within 60-150 mmHg. Cuff sizes 1, 2 and 3 (bladder width: 20, 25 and 35 mm, respectively) were placed on distal third of the antebrachium, above the tarsus and below the tarsus for ABPDoppler measurements. Agreement between ABPDoppler and SAPinvasive or between ABPDoppler and MAPinvasive was compared with reference standards for noninvasive blood pressure devices used in humans and small animals. RESULTS: Mean bias and precision (±standard deviation) between ABPDoppler and SAPinvasive met veterinary standards (≤10 ± 15 mmHg), but not human standards (≤5 ± 8 mmHg), with cuffs 1 and 2 placed on the thoracic limb (7.4 ± 13.9 and -5.8 ± 9.5 mmHg, respectively), and with cuff 2 placed proximal to the tarsus (7.2 ± 12.4 mmHg). Cuff width-to-limb circumference ratios resulting in acceptable agreement between ABPDoppler and SAPinvasive were 0.31 ± 0.04 (cuff 1) and 0.42 ± 0.05 (cuff 2) on the thoracic limb, and 0.43 ± 0.05 (cuff 2) above the tarsus. ABPDoppler showed no acceptable agreement with MAPinvasive by any reference standard. CONCLUSIONS AND CLINICAL RELEVANCE: The agreement between ABPDoppler and SAPinvasive can be optimized by placing the occlusive cuff on the distal third of the antebrachium and above the tarsus. In these locations, cuff width should approach 40% of limb circumference to provide clinically acceptable estimations of SAPinvasive. Doppler ultrasound cannot be used to estimate MAPinvasive in cats.

Comparison of the diagnostic accuracy of dynamic and static preload indexes to predict fluid responsiveness in mechanically ventilated, isoflurane anesthetized dogs.

OBJECTIVE: To compare the diagnostic accuracy of pulse pressure variation (PPV), stroke volume variation from pulse contour analysis (SVVPCA), plethysmographic variability index (PVI), central venous pressure (CVP) and global end-diastolic volume index measured by transpulmonary thermodilution (GEDVITPTD) to predict fluid responsiveness (FR) in dogs. STUDY DESIGN: Prospective study. ANIMALS: A group of 40 bitches (13.8-26.8 kg) undergoing ovariohysterectomy. METHODS: Anesthesia was maintained with isoflurane under volume-controlled ventilation (tidal volume 12 mL kg-1; inspiratory pause during 40% of inspiratory time; inspiration:expiration ratio 1:1.5). Transpulmonary thermodilution cardiac output was recorded through a femoral artery catheter. FR was evaluated by a fluid challenge (lactated Ringer's, 20 mL kg-1 over 15 minutes) administered once (n = 21) or twice (n = 18) before surgery. Individuals were responders if stroke volume index measured by transpulmonary thermodilution increased >15% after the last fluid challenge. RESULTS: Of the 39 animals studied, 21 were responders and 18 were nonresponders. Area under the receiver operating characteristics curve (AUROC) was 0.976, 0.906, 0.868 and 0.821 for PPV, PVI, CVP and SVVPCA, respectively (p < 0.0001 from AUROC = 0.5). GEDVITPTD failed to predict FR (AUROC: 0.660, p = 0.078). Best cut-off thresholds discriminating responders and nonresponders, with respective zones of diagnostic uncertainty (gray zones) were: PPV >16% (15-16%), PVI >11% (10-13%), SVVPCA >10% (9-18%) and CVP ≤1 mmHg (0-3 mmHg). Percentage of animals within gray zone limits was 13% (PPV), 28% (PVI), 51% (SVVPCA) and 67% (CVP). CONCLUSIONS AND CLINICAL RELEVANCE: PPV has better diagnostic accuracy to predict FR (conclusive results in nearly 90% of population) than other preload indexes in healthy dogs. When invasive blood pressure is unavailable, PVI will predict FR with reasonable accuracy (conclusive results in approximately 70% of the population). PPV and PVI values above gray zone limits (>16% and >13%, respectively) can reliably predict responders to volume expansion.

Effects of pneumoperitoneum and of an alveolar recruitment maneuver followed by positive end-expiratory pressure on cardiopulmonary function in sheep anesthetized with isoflurane-fentanyl.

OBJECTIVE: To investigate the effects of pneumoperitoneum alone or combined with an alveolar recruitment maneuver (ARM) followed by positive end-expiratory pressure (PEEP) on cardiopulmonary function in sheep. STUDY DESIGN: Prospective, randomized, crossover study. ANIMALS: A total of nine adult sheep (36-52 kg). METHODS: Sheep were administered three treatments (≥10-day intervals) during isoflurane-fentanyl anesthesia and volume-controlled ventilation (tidal volume: 12 mL kg-1) with oxygen: CONTROL (no intervention); PNEUMO (120 minutes of CO2 pneumoperitoneum); PNEUMOARM/PEEP (PNEUMO protocol with an ARM instituted after 60 minutes of pneumoperitoneum). The ARM (5 cmH2O increases in PEEP of 1 minute duration until 20 cmH2O of PEEP) was followed by 10 cmH2O of PEEP until the end of anesthesia. Cardiopulmonary data were recorded until 30 minutes after abdominal deflation. RESULTS: PaO2 was decreased from 435-462 mmHg (58.0-61.6 kPa) (range of mean values in CONTROL) to 377-397 mmHg (50.3-52.9 kPa) in PNEUMO (p < 0.05). Quasistatic compliance (Cqst, mL cmH2O-1 kg-1) was decreased from 0.85-0.92 in CONTROL to 0.52-0.58 in PNEUMO. PaO2 increased from 383-385 mmHg (51.1-51.3 kPa) in PNEUMO to 429-444 mmHg (57.2-59.2 kPa) in PNEUMOARM/PEEP (p < 0.05) and Cqst increased from 0.52-0.53 in PNEUMO to 0.70-0.74 in PNEUMOARM/PEEP. Abdominal deflation in PNEUMO did not restore PaO2 and Cqst to control values. Cardiac index (L minute-1 m2) decreased from 4.80-4.70 in CONTROL to 3.45-3.74 in PNEUMO and 3.63-3.76 in PNEUMOARM/PEEP. Compared with controls, ARM/PEEP with pneumoperitoneum decreased mean arterial pressure from 81 to 68 mmHg and increased mean pulmonary artery pressure from 10 to 16 mmHg. CONCLUSIONS AND CLINICAL RELEVANCE: Abdominal deflation did not reverse the pulmonary function impairment associated with pneumoperitoneum. The ARM/PEEP improved respiratory compliance and reversed the oxygenation impairment induced by pneumoperitoneum with acceptable hemodynamic changes in healthy sheep.

Reliability and Validity of UNESP-Botucatu Cattle Pain Scale and Cow Pain Scale in Bos taurus and Bos indicus Bulls to Assess Postoperative Pain of Surgical Orchiectomy.

Pain assessment guides decision-making in pain management and improves animal welfare. We aimed to investigate the reliability and validity of the UNESP-Botucatu cattle pain scale (UCAPS) and the cow pain scale (CPS) for postoperative pain assessment in Bos taurus (Angus) and Bos indicus (Nelore) bulls after castration. METHODS: Ten Nelore and nine Angus bulls were anaesthetised with xylazine-ketamine-diazepam-isoflurane-flunixin meglumine. Three-minute videos were recorded at -48 h, preoperative, after surgery, after rescue analgesia and at 24 h. Two evaluators assessed 95 randomised videos twice one month apart. RESULTS: There were no significant differences in the pain scores between breeds. Intra and inter-rater reliability varied from good (>0.70) to very good (>0.81) for all scales. The criterion validity showed a strong correlation (0.76-0.78) between the numerical rating scale and VAS versus UCAPS and CPS, and between UCAPS and CPS (0.76). The UCAPS and CPS were responsive; all items and total scores increased after surgery. Both scales were specific (81-85%) and sensitive (82-87%). The cut-off point for rescue analgesia was >4 for UCAPS and >3 for CPS. CONCLUSIONS: The UCAPS and CPS are valid and reliable to assess postoperative pain in Bos taurus and Bos indicus bulls.

Effect of intraperitoneal or incisional bupivacaine on pain and the analgesic requirement after ovariohysterectomy in dogs.

OBJECTIVE: To compare the effect of intraperitoneal (IP) or incisional (INC) bupivacaine on pain and the analgesic requirement after ovariohysterectomy in dogs. STUDY DESIGN: Prospective, randomized clinical study. ANIMALS: Thirty female dogs undergoing ovariohysterectomy (OHE). METHODS: Dogs admitted for elective OHE were anesthetized with acepromazine, butorphanol, thiopental and halothane. Animals were randomly assigned to one of three groups (n = 10 per group). The treatments consisted of preincisional infiltration with saline solution (NaCl 0.9%) or bupivacaine with epinephrine and/or IP administration of the same solutions, as follows: INC and IP 0.9% NaCl (control group); INC 0.9% NaCl and IP bupivacaine (5 mg kg(-1), IP group); INC bupivacaine (1 mg kg(-1)) and IP 0.9% NaCl (INC group). Postoperative pain was evaluated by a blinded observer for 24 hours after extubation by means of a visual analog scale (VAS) and a numeric rating scale (NRS). Rescue analgesia (morphine, 0.5 mg kg(-1) , IM) was administered if the VAS was >5/10 or the NRS >10/29. RESULTS: At 1 hour after anesthesia, VAS pain scores were [medians (interquartile range)]: 6.4 (3.1-7.9), 0.3 (0.0-2.6) and 0.0 (0.0-7.0) in control, IP and INC groups, respectively. VAS pain scores were lower in the IP compared to the control group. Over the first 24 hours, rescue analgesia was administered to 7/10, 5/10 and 3/10 dogs of the control, INC and IP groups, respectively. Total number of dogs given rescue analgesia over the first 24 hours did not differ significantly among groups. CONCLUSIONS AND CLINICAL RELEVANCE: Intraperitoneal bupivacaine resulted in lower pain scores during the first hour of the postoperative period and there was a trend towards a decreased need for rescue analgesia after OHE in dogs.

Agreement between direct, oscillometric and Doppler ultrasound blood pressures using three different cuff positions in anesthetized dogs.

OBJECTIVE: To evaluate the agreement between invasive blood pressure (IBP) and Doppler ultrasound blood pressure (DUBP) using three cuff positions and oscillometric blood pressure (OBP) in anesthetized dogs. STUDY DESIGN: Prospective study. ANIMALS: Nine adult dogs weighing 14.5-29.5 kg. METHODS: The cuff was placed above and below the tarsus, and above the carpus with the DUBP and above the carpus with the OBP monitor. Based on IBP recorded via a dorsal pedal artery catheter, conditions of low, normal, and high systolic arterial pressures [SAP (mmHg) <90, between 90 and 140, and >140, respectively] were induced by changes in isoflurane concentrations and/or dopamine administration. Mean biases ± 2 SD (limits of agreement) were determined. RESULTS: At high blood pressures, regardless of cuff position, SAP determinations with the DUBP underestimated invasive SAP values by more than 20 mmHg in most instances. With the DUBP, cuff placement above the tarsus yielded better agreement with invasive SAP during low blood pressures (0.2 ± 16 mmHg). The OBP underestimated SAP during high blood pressures (-42 ± 42 mmHg) and yielded better agreement with IBP for mean (MAP) and diastolic (DAP) arterial pressure measurements [overall bias: 2 ± 15 mmHg (MAP) and 0.2 ± 16 mmHg (DAP)]. CONCLUSIONS: Agreement of SAP determinations with the DUBP is poor at SAP > 140 mmHg, regardless of cuff placement. Measurement error of the DUBP with the cuff placed above the tarsus is clinically acceptable during low blood pressures. Agreement of MAP and DAP measurements with this OBP monitor compared with IBP was clinically acceptable over a wide pressure range. CLINICAL RELEVANCE: With the DUBP device, placing the cuff above the tarsus allows reasonable agreement with IBP obtained via dorsal pedal artery catheterization. Only MAP and DAP provide reasonable estimates of direct blood pressure with the OBP monitor evaluated.

Effects of remifentanil on the minimum alveolar concentration of isoflurane in dogs.

OBJECTIVE: To evaluate the effects of remifentanil on isoflurane minimum alveolar concentration (ISO(MAC)) in dogs. ANIMALS: 6 adult mixed-breed dogs. PROCEDURES: Dogs were anesthetized with isoflurane on 2 occasions. During the first set of experiments, ISO(MAC) was determined before remifentanil infusion (baseline), during constant rate infusion (CRI) of remifentanil (0.15, 0.30, 0.60, and 0.90 microg/kg/min), and 80 minutes after remifentanil infusion. After a 1-week washout period, dogs received a CRI of remifentanil (0.15 microg/kg/min) and ISO(MAC) was redetermined 2, 4, and 6 hours after commencing the infusion. RESULTS: Mean +/- SD baseline ISO(MAC) was 1.24 +/- 0.18%. Remifentanil infusion (0.15, 0.30, 0.60, and 0.90 microg/kg/min) decreased ISO(MAC) by 43 +/- 10%, 59 +/- 10%, 66 +/- 9%, and 71 +/- 9%, respectively. The ISO(MAC) values determined during the 0.30, 0.60, and 0.90 microg/kg/min infusion rates did not differ from each other, but these values were significantly lower, compared with the 0.15 microg/kg/min infusion rate. The ISO(MAC) recorded after remifentanil infusion (1.09 +/- 0.18%) did not differ from baseline ISO(MAC). There was no change in ISO(MAC) throughout the 6-hour period of a CRI of remifentanil. CONCLUSIONS AND CLINICAL RELEVANCE: Remifentanil decreased ISO(MAC) in a dose-related fashion; the reduction in ISO(MAC) was stable over the course of a prolonged CRI (6 hours). A dose of 0.30 microg of remifentanil/kg/min resulted in nearly maximal isoflurane-sparing effect in dogs; a ceiling effect was observed at higher infusion rates.

Effects of methadone on the minimum alveolar concentration of isoflurane in dogs.

OBJECTIVE: To investigate the effects of methadone on the minimum alveolar concentration of isoflurane (ISO(MAC)) in dogs. STUDY DESIGN: Prospective, randomized cross-over experimental study. ANIMALS: Six adult mongrel dogs, four males and two females, weighing 22.8 +/- 6.6 kg. METHODS: Animals were anesthetized with isoflurane and mechanically ventilated on three separate days, at least 1 week apart. Core temperature was maintained between 37.5 and 38.5 degrees C during ISO(MAC) determinations. On each study day, ISO(MAC) was determined using electrical stimulation of the antebrachium (50 V, 50 Hz, 10 mseconds) at 2.5 and 5 hours after intravenous injection of physiological saline (control) or one of two doses of methadone (0.5 or 1.0 mg kg(-1)). RESULTS: Mean (+/-SD) ISO(MAC) in the control treatment was 1.19 +/- 0.15% and 1.18 +/- 0.15% at 2.5 and 5 hours, respectively. The 1.0 mg kg(-1) dose of methadone reduced ISO(MAC) by 48% (2.5 hours) and by 30% (5 hours), whereas the 0.5 mg kg(-1) dose caused smaller reductions in ISO(MAC) (35% and 15% reductions at 2.5 and 5 hours, respectively). Both doses of methadone decreased heart rate (HR), but the 1.0 mg kg(-1) dose was associated with greater negative chronotropic actions (HR 37% lower than control) and mild metabolic acidosis at 2.5 hours. Mean arterial pressure increased in the MET1.0 treatment (13% higher than control) at 2.5 hours. CONCLUSIONS AND CLINICAL RELEVANCE: Methadone reduces ISO(MAC) in a dose-related fashion and this effect is lessened over time. Although the isoflurane sparing effect of the 0.5 mg kg(-1) dose of methadone was smaller in comparison to the 1.0 mg kg(-1) dose, the lower dose is recommended for clinical use because it results in less evidence of cardiovascular impairment.

Effects of the opioid remifentanil on the arrhythmogenicity of epinephrine in halothane-anesthetized dogs.

Opioids may exert a protective effect against ventricular arrhythmias via a vagally mediated mechanism. This study evaluated the effects of the opioid remifentanil on arrhythmogenicity of epinephrine during halothane anesthesia. Eight dogs were assigned to 2 treatments in a randomized crossover design, with 1-week intervals between treatments. Anesthesia was maintained with 1.3% end-tidal halothane in oxygen and mechanical ventilation to maintain eucapnia. A constant rate infusion of remifentanil (0.72 microg/kg/min) was administered throughout the study in the experimental treatment, while control animals received physiologic saline as placebo. The arrhythmogenic dose of epinephrine (ADE), defined as 4 premature ventricular complexes (PVCs) within 15 s, was determined by administering progressively increasing infusion rates of epinephrine (2.5, 5.0, and 10 microg/kg/min), allowing 20 min intervals between each infusion rate. In both treatments, epinephrine infusions induced bradyarrhythmias and atrioventricular conduction disturbances, which were followed by escape beats and PVCs. In the remifentanil treatment, mean +/- s ADE values (11.3 +/- 4.9 microg/kg) did not differ from values observed in control animals (9.9 +/- 6.1 microg/kg). On the basis of the ADE model for assessing the arrhythmogenity of drugs during halothane anesthesia, the present study did not demonstrate a protective effect of remifentanil (0.72 microg/kg/min) against ventricular arrhythmias in dogs.

Effects of 6% tetrastarch or lactated Ringer's solution on blood coagulation in hemorrhaged dogs.

BACKGROUND: Tetrastarch solution (TS) can impair coagulation but the clinical relevance of this impairment is unclear in veterinary medicine. OBJECTIVE: Compare the effects of volume replacement (VR) with lactated Ringer's solution (LRS) or 6% TS on coagulation in hemorrhaged dogs. ANIMALS: Six healthy English Pointer dogs (19.7-35.3 kg). METHODS: Prospective crossover study. Dogs were anesthetized without hemorrhage and VR (control). Two weeks later, dogs were hemorrhaged under anesthesia on 2 occasions (8-week washout intervals) and randomly received VR with LRS or TS at 3:1 or 1:1 of shed blood, respectively, aiming to decrease the hematocrit to 33%. Rotational thromboelastometry and other coagulation variables were determined before 0.5, 2, and 4 hours after VR during anesthesia and 24 hours after VR (conscious dogs). RESULTS: Buccal mucosal bleeding time did not differ between treatments after VR. Activated partial thromboplastin time increased from controls 4 hours after TS (P = 0.045). Clot formation time (CFT) and alfa-angle increased from controls from 0.5 to 4 hours after LRS (CFT, P ≤ 0.0001-0.02; alpha angle, P = 0.0001-0.02) and from 0.5 to 2 hours after TS (CFT, P = 0.0002-0.01; alpha angle, P = 0.0005-0.02). The maximum clot firmness decreased from controls from 0.5 to 4 hours after LRS (P ≤ 0.0001-0.01) and TS (P ≤ 0.0001-0.04). CONCLUSIONS AND CLINICAL RELEVANCE: Tetrastarch does not impair primary hemostasis and induces transient dilutional coagulopathy that is similar to LRS because, when compared to a 3 times higher volume of LRS in hemorrhaged dogs, it does not cause greater interference on the viscoelastic properties of the coagulum.

Effects of epidural administration of dexmedetomidine on the minimum alveolar concentration of isoflurane in dogs.

Objective-To evaluate the effects of epidural administration of 3 doses of dexmedetomidine on isoflurane minimum alveolar concentration (MAC) and characterize changes in bispectral index (BIS) induced by nociceptive stimulation used for MAC determination in dogs. Animals-6 adult dogs. Procedures-Isoflurane-anesthetized dogs received physiologic saline (0.9% NaCl) solution (control treatment) or dexmedetomidine (1.5 [DEX1.5], 3.0 [DEX3], or 6.0 [DEX6] mug/kg) epidurally in a crossover study. Isoflurane MAC (determined by use of electrical nociceptive stimulation of the hind limb) was targeted to be accomplished at 2 and 4.5 hours. Changes in BIS attributable to nociceptive stimulation and cardiopulmonary data were recorded at each MAC determination. Results-With the control treatment, mean +/- SD MAC values did not change over time (1.57 +/- 0.23% and 1.55 +/- 0.25% at 2 and 4.5 hours, respectively). Compared with the control treatment, MAC was significantly lower at 2 hours (13% reduction) but not at 4.5 hours (7% reduction) in DEX1.5-treated dogs and significantly lower at 2 hours (29% reduction) and 4.5 hours (13% reduction) in DEX3-treated dogs. The DEX6 treatment yielded the greatest MAC reduction (31% and 22% at 2 and 4.5 hours, respectively). During all treatments, noxious stimulation increased BIS; but changes in BIS were correlated with increases in electromyographic activity. Conclusions and Clinical Relevance-In dogs, epidural administration of dexmedetomidine resulted in dose-dependent decreases in isoflurane MAC and that effect decreased over time. Changes in BIS during MAC determinations may not represent increased awareness because of the possible interference of electromyographic activity.

Use of bispectral index to monitor depth of anesthesia in isoflurane-anesthetized dogs.

OBJECTIVE: To evaluate the correlation between the bispectral index (BIS) and end-tidal isoflurane (ET(ISO)) concentration and compare the use of 3 BIS sensor positions in dogs. ANIMALS: 6 adult dogs. PROCEDURES: Mechanically ventilated dogs received pancuronium, and depth of anesthesia was altered by increasing ET(ISO) concentration from 1.5% to 2.3% and 3.0%. The BIS, suppression ratio (relative percentage of isoelectric electroencephalographic waveforms), and signal quality index (SQI) were recorded at each ET(ISO) concentration for each of 3 BIS sensor positions (frontal-occipital, bifrontal, and frontal-temporal positions). RESULTS: The BIS and ET(ISO) concentration were poorly correlated; regardless of sensor positioning, mean BIS values did not change significantly as ET(ISO) was increased. At 3% isoflurane, regardless of sensor positioning, there was an increase in suppression ratio coincident with BIS < 40 in some dogs, whereas paradoxic increases in BIS (> 60) were recorded in others. Furthermore, at 3.0% isoflurane, the SQI was significantly lower for the bifrontal sensor position (compared with values for the other positions), but low SQI values prevented recording of BIS values from the frontal-occipital sensor position in 2 dogs. Overall, BIS values derived from the 3 sensor positions did not differ. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, BIS values may not reflect changes in depth of isoflurane anesthesia in the absence of noxious stimulation. Of the 3 sensor positions, frontal-temporal positioning provided better correlation with changes in depth of anesthesia induced via changes in isoflurane concentrations. However, the sensor placements yielded similar results at SQI values > 50.

Comparison of two species-specific oscillometric blood pressure monitors with direct blood pressure measurement in anesthetized cats.

OBJECTIVE: To compare the performance of 2 species-specific oscillometric blood pressure (OBP) monitors (petMAPclassic and petMAPgraphic ) with direct blood pressure measurement in anesthetized cats. DESIGN: Prospective, experimental study. SETTING: Veterinary teaching hospital. ANIMALS: Eight adult cats (3.2-5.5 kg). INTERVENTIONS: During isoflurane anesthesia, OBP cuffs were placed on the thoracic limb and on the base of the tail while invasive blood pressure (IBP) was recorded from a dorsal pedal artery. End-tidal isoflurane concentrations, with or without intravenous dopamine (n = 8), norepinephrine (n = 1), or phenylephrine (n = 1) were adjusted to change invasive mean arterial pressure (MAP) between 40 to 100 mm Hg. Data were analyzed by the Bland-Altman method and 4-quadrant plots. MEASUREMENTS AND MAIN RESULTS: Mean biases and limits of agreement (LOA: ± 1.96 SD) (mm Hg) recorded between the petMAPclassic (thoracic limb) and IBP for systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and MAP were 4.2 ± 28.5, -6.1 ± 13.2, and -1.9 ± 14.6, respectively; mean biases and LOA (mm Hg) recorded with the tail cuff were 7.2 ± 31.3 (SAP), -6.1 ± 11.6 (DAP), and -1.1 ± 11.7 (MAP). Mean biases and LOA (mm Hg) between petMAPgraphic (thoracic limb) and IBP were 7.7 ± 27.0 (SAP), -4.3 ± 11.5 (DAP), 0.2 ± 13.0 (MAP); values recorded with the tail cuff were 10.9 ± 29.6 (SAP), -4.4 ± 11.7 (DAP), and -0.1 ± 12.1 (MAP). Concordance rates after excluding arterial pressure changes ≤ 5 mm Hg was ≥ 93% for both devices. CONCLUSIONS: Although both OBP monitors provide unacceptable SAP estimations, MAP values derived from both monitors and DAP measured by the petMAPgraphic result in acceptable agreement with the reference method according to the Association for the Advancement of Medical Instrumentation (mean bias ≤ 5 mm Hg with LOA ≤ ± 16 mm Hg). Both monitors provide acceptable trending ability for SAP, DAP, and MAP.

An Update on Drugs Used for Lumbosacral Epidural Anesthesia and Analgesia in Dogs.

This review aims to report an update on drugs administered into the epidural space for anesthesia and analgesia in dogs, describing their potential advantages and disadvantages in the clinical setting. Databases searched include Pubmed, Google scholar, and CAB abstracts. Benefits of administering local anesthetics, opioids, and alpha2 agonists into the epidural space include the use of lower doses of general anesthetics (anesthetic "sparing" effect), perioperative analgesia, and reduced side effects associated with systemic administration of drugs. However, the potential for cardiorespiratory compromise, neurotoxicity, and other adverse effects should be considered when using the epidural route of administration. When these variables are considered, the epidural technique is useful as a complementary method of anesthesia for preventive and postoperative analgesia and/or as part of a balanced anesthesia technique.

Evaluation of the isoflurane-sparing effects of lidocaine and fentanyl during surgery in dogs.

OBJECTIVE: To evaluate the isoflurane-sparing effects of lidocaine and fentanyl administered by constant rate infusion (CRI) during surgery in dogs. DESIGN: Randomized prospective study. Animals-24 female dogs undergoing unilateral mastectomy because of mammary neoplasia. PROCEDURES: After premedication with acepromazine and morphine and anesthetic induction with ketamine and diazepam, anesthesia in dogs (n = 8/group) was maintained with isoflurane combined with either saline (0.9% NaCl) solution (control), lidocaine (1.5 mg/kg [0.68 mg/lb], IV bolus, followed by 250 microg/kg/min [113 microg/lb/min], CRI), or fentanyl (5 microg/kg [2.27 microg/lb], IV bolus, followed by 0.5 microg/kg/min [0.23 microg/lb/min], CRI). Positive-pressure ventilation was used to maintain eucapnia. An anesthetist unaware of treatment, endtidal isoflurane (ETiso) concentration, and vaporizer concentrations adjusted a nonprecision vaporizer to maintain surgical depth of anesthesia. Cardiopulmonary variables and ETiso values were monitored before and after beginning surgery. RESULTS: Heart rate was lower in the fentanyl group. Mean arterial pressure did not differ among groups after surgery commenced. In the control group, mean +/- SD ETiso values ranged from 1.16 +/- 0.35% to 1.94 +/- 0.96%. Fentanyl significantly reduced isoflurane requirements during surgical stimulation by 54% to 66%, whereas the reduction in ETiso concentration (34% to 44%) observed in the lidocaine group was not significant. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of fentanyl resulted in greater isoflurane sparing effect than did lidocaine. However, it appeared that the low heart rate induced by fentanyl may partially offset the improvement in mean arterial pressure that would be expected with reduced isoflurane requirements.