End-tidal Isoflurane Concentration Research Articles

The effect of intra‐articular mepivacaine administration prior to carpal arthroscopy on anesthesia management and recovery characteristics in horses

To evaluate the effects of intra-articular (IA) mepivacaine administration prior to carpal arthroscopy on anesthetic drug requirements, blood pressure support, hemodynamic variables, and quality of recovery in horses. Experimental, analytical, cohort study. Twenty-two horses (n = 11 horses/group). Horses were anesthetized by using the same protocol, but an IA injection of mepivacaine or saline was performed before carpal arthroscopy. End-tidal isoflurane concentration, heart rate, and mean arterial pressure were recorded at specific time points. Quality of recovery was scored by the anesthetist, who was unaware of group assignment. Data were analyzed by using two-way repeated-measures analysis of variance. Mean arterial pressure was higher during joint distension in the control group compared with baseline (7% higher, P = .02) and with the treatment group (10% higher, P = .04). Heart rate was higher in the control group compared with the treatment group during joint distension (8% higher, P = .04) and chip removal (11% higher, P = .03). Heart rate was higher in the control group compared with baseline during chip removal (5.5% higher, P = .04). Two horses in the control group required additional ketamine vs none in the treatment group. Quality of recovery was not different between groups. Intra-articular mepivacaine resulted in fewer detectable reactions to surgical stimulation, with similar recovery scores and blood pressure support requirements. Intra-articular anesthesia prior to arthroscopy can be used safely in the horse and should be considered as a part of balanced anesthetic protocols.

Frontal electroencephalogram reveals emergence-like brain activity occurring during transition periods in cardiac surgery

BackgroundCardiac surgery has one of the highest incidences of intraoperative awareness. The periods of initiation and discontinuation of cardiopulmonary bypass could be high-risk periods. Certain frontal EEG patterns might plausibly occur with unintended intraoperative awareness. This study sought to quantify the incidence of these pre-specified patterns during cardiac surgery. MethodsTwo-channel bihemispheric frontal EEG was recorded in 1072 patients undergoing cardiac surgery as part of a prospective observational study. Spectrograms were created, and mean theta (4–7 Hz) power and peak alpha (7–17 Hz) frequency were measured in patients under general anaesthesia with isoflurane. Emergence-like EEG activity in the spectrogram during surgery was classified as an alpha peak frequency increase by 2 Hz or more, and a theta power decrease by 5 dB or more in comparison with the median pre-bypass values. ResultsData from 1002 patients were available for analysis. Fifty-five of those patients (5.5%) showed emergence-like EEG activity at least once during surgery with a median duration of 13.2 min. These patients were younger (median age, 59 vs 67 yr; P<0.001) and the median end-tidal isoflurane concentration before cardiopulmonary bypass was higher (0.82 vs 0.75 minimum alveolar concentration [MAC]; P=0.013). There was no significant difference between those with or without emergence-like EEG activity in sex, lowest core temperature, or duration of surgery. Forty-six of these EEG changes (84%) occurred within a 1 h time window centred on separation from cardiopulmonary bypass. ConclusionThe findings of this study suggest that approximately one in 20 patients undergoing cardiac surgery with a volatile anaesthetic agent have a sustained EEG pattern while surgery is ongoing that is often seen with emergence from general anaesthesia. Monitoring the frontal EEG during cardiopulmonary bypass may identify these events and potentially reduce the incidence of unintended awareness. Clinical trial registrationNCT 02976584.

Effects of fentanyl–lidocaine–ketamine versus sufentanil–lidocaine–ketamine on the isoflurane requirements in dogs undergoing total ear canal ablation and lateral bulla osteotomy

ObjectiveTo compare the isoflurane-sparing effects of sufentanil–lidocaine–ketamine (SLK) and fentanyl–lidocaine–ketamine (FLK) infusions in dogs undergoing total ear canal ablation and lateral bulla osteotomy (TECA–LBO). Study designRandomized blinded clinical study. AnimalsA group of 20 client-owned dogs undergoing TECA–LBO. MethodsIntravenous (IV) administration of lidocaine (3 mg kg–1) and ketamine (0.6 mg kg–1) with fentanyl (5.4 μg kg–1; n = 10; FLK group) or sufentanil (0.72 μg kg–1; n = 10; SLK group) was immediately followed by the corresponding constant rate infusion (CRI) (lidocaine 3 mg kg–1 hour–1; ketamine 0.6 mg kg–1 hour–1; either fentanyl 5.4 μg kg–1 hour–1 or sufentanil 0.72 μg kg–1 hour–1). Anaesthesia was induced with propofol 3–5 mg kg–1 IV and was maintained with isoflurane. End-tidal isoflurane concentration (Fe′Iso) was decreased in 0.2% steps every 15 minutes until spontaneous movements were observed (treated with propofol 1 mg kg–1 IV) or an increase of > 30% in heart rate or mean arterial pressure from baseline occurred (treated with rescue fentanyl or sufentanil). Quality of recovery and pain were assessed at extubation using the short-form Glasgow Composite Pain Scale (SF-GCPS), Colorado State University Canine Acute Pain scale (CSU-CAP), and visual analogue scale (VAS). Data were analysed with analysis of variance, t tests, Fisher test and Spearman coefficient (p < 0.05). ResultsFe′Iso decreased significantly in SLK group (45%; p = 0.0006) but not in FLK (15%; p = 0.1135) (p = 0.0136). SLK group had lower scores for recovery quality (p = 0.0204), SF-GCPS (p = 0.0071) and CSU-CAP (p = 0.0273) than FLK at extubation. Intraoperative rescue analgesia and VAS were not significantly different between groups. Conclusions and clinical relevanceCompared with FLK infusion, CRI of SLK at these doses decreased isoflurane requirements, decreased pain scores and improved recovery quality at extubation in dogs undergoing TECA–LBO.

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

BackgroundInfiltration 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.ResultsArea 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.ConclusionsLocal 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.

Minimum anesthetic concentration of isoflurane and sparing effect of midazolam in Quaker parrots (Myiopsitta monachus)

ObjectiveTo determine the effects of midazolam on the minimum anesthetic concentration (MAC) reduction of end-tidal isoflurane concentration (Fe′Iso) measured using an electrical stimulus in Quaker parrots (Myiopsitta monachus). Study designRandomized crossover experimental study. AnimalsA group of six adult Quaker parrots, weighing 98–124 g. MethodsBirds were anesthetized with isoflurane in oxygen delivered by mask, then tracheally intubated and mechanically ventilated. Three treatments were applied with a 4 day interval between anesthetic events. Each anesthetized bird was administered midazolam (1 mg kg−1; treatment MID1), midazolam (2 mg kg−1; treatment MID2) or electrolyte solution (control) intramuscularly. The treatments were administered using a replicated Latin square design and the observers were blinded. Based on a pilot bird, the starting Fe′Iso was 1.8%. After equilibration for 10 minutes, a supramaximal stimulus was delivered using an electrical current (20 V and 50 Hz for 10 ms) and birds were observed for non-reflex movement. The Fe′Iso was titrated by 0.1% until a crossover event was observed. The MAC was estimated using logistic regression. ResultsThe MAC of isoflurane (MACISO) was estimated at 2.52% [95% confidence interval (CI), 2.19–2.85] with a range of 1.85–2.65%. MACISO in MID1 was 2.04% (95% CI, 1.71–2.37) and in MID2 was 1.81% (95% CI, 1.48–2.14); reductions in MACISO from control of 19% (p = 0.001) and 28% (p < 0.001), respectively. Heart rate, temperature, sex and anesthetic time were not different among treatments. ConclusionsMidazolam (1–2 mg kg−1) intramuscularly resulted in a significant isoflurane-sparing effect in response to a noxious stimulus in Quaker parrots without observable adverse effects. Clinical relevanceMidazolam can be used as part of a balanced anesthetic approach using isoflurane in Quaker parrots, and potentially in other psittacine species.

Combined ultrasound/electrostimulation-guided block of the lumbosacral plexus in a cat undergoing pelvic limb amputation

A cat was anaesthetised with midazolam and alfaxalone for a pelvic limb amputation due to a metatarsal fracture complicated with soft tissue necrosis. The femoral nerve and lumbosacral trunk were...

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

ObjectiveTo 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 designProspective study. AnimalsA total of eight cats (3.0–3.8 kg) for neutering. MethodsDuring 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. ResultsMean 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 relevanceThe 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.

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in dogs.

To determine the effect of oral administration of gabapentin (20 mg/kg) on the minimum alveolar concentration (MAC) of isoflurane in dogs. 6 healthy adult dogs (3 males and 3 females with a mean ± SD body weight of 24.8 ± 1.3 kg). Each dog was anesthetized twice. Dogs were initially assigned to 1 of 2 treatments (gabapentin [20 mg/kg, PO] followed 2 hours later by anesthesia maintained with isoflurane or anesthesia maintained with isoflurane alone). A minimum of 7 days later, dogs received the other treatment. The MAC of isoflurane was determined by use of an iterative bracketing technique with stimulating electrodes placed in the maxillary buccal mucosa. Hemodynamic variables and vital parameters were recorded at the lowest end-tidal isoflurane concentration at which dogs did not respond to the stimulus. Effect of treatment on outcome variables was analyzed by use of a paired t test. Mean ± SD MAC of isoflurane was significantly lower when dogs received gabapentin and isoflurane (0.71 ± 0.12%) than when dogs received isoflurane alone (0.91 ± 0.26%). Mean reduction in MAC of isoflurane was 20 ± 14%. Hemodynamic variables did not differ significantly between treatments. Mean time to extubation was significantly less when dogs received gabapentin and isoflurane (6 ± 4 minutes) than when dogs received isoflurane alone (23 ± 15 minutes). Oral administration of gabapentin 2 hours before anesthesia maintained with isoflurane had a MAC-sparing effect with no effect on hemodynamic variables or vital parameters of dogs.

A preoperative bupivacaine retrobulbar block offers superior antinociception compared with an intraoperative splash block in dogs undergoing enucleation.

Investigate nociception differences in dogs undergoing enucleation administered bupivacaine either via preoperative retrobulbar block (pRB) or intraoperative splash block (iSB). Prospective, randomized, double-masked, clinical comparison study. Dogs undergoing unilateral enucleation were randomized to two groups: one received bupivacaine pRB and saline iSB of the same volume, and the other received saline pRB and bupivacaine iSB. The following intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO2 (EtCO2 ); systolic, mean, and diastolic arterial blood pressure (SAP, MAP, and DAP respectively); inspired end-tidal isoflurane concentration (EtISOIns), and expired end-tidal isoflurane concentration (EtISOExp). Pain scores were recorded pre- and postoperatively. Analgesic rescue was documented. Surgical hemorrhage and postoperative bruising and swelling were graded subjectively by the surgeon (HDW) and study coordinator (AEZ). A significant (P=.0399) increase from baseline in overall mean heart rate was recorded in iSB bupivacaine patients (n=11) compared with pRB bupivacaine patients (n=11), with no significant differences in other intraoperative physiologic parameters, or pain scores. More analgesic rescue events occurred in iSB bupivacaine patients compared to pRB bupivacaine patients. A near-significant increase in intraoperative bleeding (P=.0519), and a significant increase in bruising (P=.0382) and swelling (P=.0223) was noted in the iSB bupivacaine group. Preoperative retrobulbar block bupivacaine is more effective than an iSB bupivacaine at controlling both intraoperative and postoperative nociception in dogs undergoing enucleation. Additionally, iSB causes more postoperative bruising and swelling and may be associated with increased intraoperative hemorrhage.

Effects of midazolam and nitrous oxide on the minimum anesthetic concentration of isoflurane in the ball python (Python regius)

ObjectiveTo evaluate the effects of midazolam and nitrous oxide (N2O) on the minimum anesthetic concentration of isoflurane (MACISO) in ball pythons. Study designProspective, crossover, randomized, semi-blinded study. AnimalsA total of nine healthy adult female ball pythons (Python regius) weighing 2.76 ± 0.73 kg. MethodsIn each snake, three protocols were evaluated with 2 week washouts: treatment MID–O2, midazolam (1 mg kg−1) administered intramuscularly (IM) and anesthesia induced with isoflurane–oxygen; treatment SAL–O2, saline (0.2 mL kg−1) IM and anesthesia with isoflurane–oxygen; and treatment SAL–N2O, saline IM and anesthesia with isoflurane and 50% nitrous oxide (N2O):50% oxygen. In each treatment, isoflurane was administered by face mask immediately after premedication. Snakes were endotracheally intubated and inspired and end-tidal isoflurane concentrations were monitored. The study design followed a standard bracketing technique, and the MACISO was determined using logistic regression. Electrical stimulation using a Grass stimulator connected to the base of the tail (50 V, 50 Hz, 6.5 ms pulse−1) was used as the supramaximal stimulus. Blood-gas analysis was performed on cardiac blood collected immediately following intubation and after the last stimulation. Blood-gas variables were compared over time and between treatments using linear mixed models. ResultsMACISO at a body temperature of 30.1 ± 0.4 °C was 1.11% (95% confidence interval, 0.94–1.28%) in SAL–O2 and was significantly decreased to 0.48% (0.29–0.67%) in MID–O2 (p < 0.001) and to 0.92% (0.74–1.09%) in SAL–N2O (p = 0.016). PO2 was significantly lower in MID–O2 and SAL–N2O than in SAL–O2. Conclusions and clinical relevanceMidazolam significantly decreased the MACISO by 57% in ball pythons, whereas addition of N2O resulted in a modest, although significant, decrease (17%). MACISO in ball pythons was lower than those previously reported in reptiles.

Cardiopulmonary effects of dexmedetomidine, with and without vatinoxan, in isoflurane-anesthetized cats

ObjectiveTo characterize the cardiopulmonary effects of dexmedetomidine, with or without vatinoxan, in isoflurane-anesthetized cats. Study designRandomized, crossover experimental study. AnimalsA group of six adult healthy male neutered cats. MethodsCats were instrumented during anesthesia with isoflurane in oxygen. Isoflurane end-tidal concentration was set to 1.25 minimum alveolar concentration (MAC). Dexmedetomidine was administered using a target-controlled infusion system to achieve and maintain 10 target plasma concentrations ranging from 0 to 40 ng mL–1. Furthermore, vatinoxan or an equivalent volume of saline was administered using a target-controlled infusion system to achieve and maintain a target plasma concentration of 4 μg mL–1. Isoflurane concentration was adjusted after each change in dexmedetomidine concentration to maintain a concentration equivalent to 1.25 MAC. Heart rate (HR), arterial blood pressure, central venous pressure (CVP), pulmonary artery pressure (PAP), pulmonary artery occlusion pressure (PAOP), body temperature, cardiac output, arterial and mixed-venous blood gas and pH and drug concentrations were measured. Additional variables were calculated from the measurements. ResultsDexmedetomidine alone resulted in decreased HR, cardiac index, stroke index and oxygen delivery, and increased systolic, mean (MAP) and diastolic arterial pressure, CVP, PAP, PAOP, systemic vascular resistance index, rate-pressure product, left ventricular stroke work index and oxygen extraction ratio. Vatinoxan resulted in severe hypotension at target plasma dexmedetomidine concentrations <10 ng mL–1. Vatinoxan attenuated the cardiovascular effects of dexmedetomidine at the 10 and 20 ng mL–1 targets, but MAP could be maintained above 60 mmHg only when isoflurane concentration was <1.25 MAC. Less improvement in cardiovascular function was seen with vatinoxan at the 40 ng mL–1 target plasma dexmedetomidine concentration. Conclusions and clinical relevanceVatinoxan, at the plasma concentration maintained in this study, attenuated the cardiovascular effects of dexmedetomidine in isoflurane-anesthetized cats. However, its administration resulted in hypotension, which may limit its clinical usefulness.

Recovery characteristics of dogs following anesthesia induced with tiletamine-zolazepam, alfaxalone, ketamine-diazepam, or propofol and maintained with isoflurane.

OBJECTIVE To compare characteristics of recovery from isoflurane anesthesia in healthy nonpremedicated dogs after anesthetic induction by IV administration of tiletamine-zolazepam with those observed after induction by IV administration of alfaxalone, ketamine-diazepam, or propofol. DESIGN Prospective, randomized crossover study. ANIMALS 6 healthy adult hounds. PROCEDURES Each dog underwent the 4 treatments in random order with a ≥ 7-day washout period between anesthetic episodes. Anesthesia was induced by IV administration of the assigned induction drug or combination (each to effect in 25% increments of calculated dose) and maintained with isoflurane in oxygen for 60 minutes. Cardiorespiratory variables and end-tidal isoflurane concentration (ETISO) were measured just before isoflurane administration was discontinued. Dogs were observed and video recorded during recovery. Recovery characteristics were retrospectively scored from recordings by 3 raters. Interrater and intrarater reliability of scoring was assessed by intraclass correlation coefficient calculation. Linear and mixed ANOVAs were used to compare extubation times, recovery scores, and body temperature among treatments. RESULTS Most cardiorespiratory variables, body temperature, ETISO, and time to extubation did not differ between tiletamine-zolazepam and other induction treatments. Recovery scores were lower (indicating better recovery characteristics) with propofol or alfaxalone than with tiletamine-zolazepam but did not differ between tiletamine-zolazepam and ketamine-diazepam treatments. Anesthetic episode number and ETISO had no effect on extubation time or recovery score. Intrarater and interrater correlations for recovery scores were excellent. CONCLUSIONS AND CLINICAL RELEVANCE Recovery of healthy dogs from anesthesia with isoflurane after induction with tiletamine-zolazepam was uncomplicated and had characteristics comparable to those observed following induction with ketamine-diazepam. However, recovery characteristics were improved when anesthesia was induced with propofol or alfaxalone.

Dexmedetomidine versus lidocaine as an adjuvant to general anesthesia for elective abdominal gynecological surgeries

Study objectiveThe current study was conducted to compare the effect of perioperative administration of intravenous dexmedetomidine versus lidocaine on the perioperative hemodynamic changes, anesthetic consumption, anesthesia induction, and recovery times in patients undergoing elective abdominal gynecological surgeries under general anesthesia.Materials and methodsNinety female patients undergoing elective abdominal gynecological surgeries were enrolled in the current study. Patients were randomly distributed to one of three equal groups: group L received lidocaine (1.5 mg/kg loading, 2 mg/kg/h infusion), group D received dexmedetomidine (1 μg/kg loading, 0.5 μg/kg/h infusion), and group C received isotonic saline 0.9% in the same volume and pattern as the study drugs. Hemodynamic parameters including mean arterial pressure (MAP) and heart rate (HR), anesthetic consumption and induction, recovery times, and time to the first postoperative analgesic demand were recorded.ResultsThe MAP and HR after endotracheal intubation and in the subsequent recordings were significantly lower in group L and D when compared with group C with no significant difference between group D and L. The propofol induction dose and mean end-tidal isoflurane concentration were significantly lower in group L and D when compared with group C and were also significantly lower in group D when compared with group L. The intraoperative fentanyl consumption was significantly lower in group L and D when compared with group C with no significant difference between group D and L. The anesthesia induction time was significantly shorter in group L and D when compared with group C; it was also significantly shorter in group D when compared with group L with no significant difference as regards the anesthesia recovery time and the response time between the three study groups. The time to the first postoperative analgesic requirement was significantly longer in group D and L when compared with group C; it was also significantly longer in group D when compared with group L.ConclusionBoth dexmedetomidine and lidocaine could be a useful adjuvant to general anesthesia in patients undergoing abdominal gynecological surgeries. However, dexmedetomidine has a better sparing effect on intraoperative anesthetic consumption and longer time to the first postoperative analgesic demand than that of lidocaine with no significant difference between both agents on intraoperative analgesic demand.

Effects of midazolam on cardiovascular responses and isoflurane requirement during elective ovariohysterectomy in dogs

BackgroundA prospective, randomized, placebo-controlled, blinded clinical study was conducted to determine whether a single dose of midazolam affects the cardiovascular response to surgical manipulation of the ovaries during elective ovariohysterectomy. Thirty-nine client-owned dogs undergoing elective ovariohysterectomy were recruited. After scoring cage demeanour, dogs were premedicated with acepromazine (0.03 mg kg-1) and pethidine (3 mg kg-1) intramuscularly into the quadriceps muscle and 20 min later sedation was scored. Anaesthesia was induced with propofol intravenously (IV) to effect. The study treatment (group M: midazolam (0.25 mg kg-1); or group P: placebo (Hartmann’s solution) (0.125 ml kg-1)) was administered IV before the intra-operative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Morphine (0.3 mg kg-1 IV) was administered prior to the start of surgery. The vaporizer setting was adjusted according to the depth of anaesthesia. If an end-tidal isoflurane concentration (FE’Iso) above 1.6% was required additional analgesia was provided with fentanyl (2 μg kg-1). Dogs received meloxicam (0.2 mg kg-1 IV) at the end of procedure. Heart rate, mean arterial blood pressure, respiratory rate and end-tidal partial pressure of carbon dioxide as well as FE’Iso were recorded and analysed.ResultsA statistical significant difference between groups was detected in FE’Iso, with group M requiring a significantly lower FE’Iso than group P (14.3%) after administration of midazolam. No differences between groups was shown for percentage change in heart rate and mean arterial blood pressure, or end-tidal carbon dioxide and requirement for mechanical ventilation, or rescue analgesia. There was no statistically significant difference in the incidence of complications in group M and P. Group M received significantly more succinylated gelatin solution pre-administration of midazolam than group P, but no differences in fluid administration post-administration of the study treatment (midazolam/placebo) were detected. No statistical significant difference was demonstrated for the use of anticholinergic agents, dobutamine or noradrenaline.ConclusionNo significant effect on cardiovascular parameters could be observed with administration of midazolam, but a modest (14.3%) isoflurane-sparing effect was detected.

Effect of three opioid-based analgesic protocols on the perioperative autonomic-mediated cardiovascular response in sheep.

Few reports evaluate the clinical effects of opioids in sheep during experimental surgical procedures. Catecholamine-mediated haemodynamic changes resulting from surgical noxious stimulation are blunted by opioids. The aim of this study was to evaluate the efficacy of three opioid-based analgesic protocols in avoiding a 20% increase in heart rate (HR) and/or mean arterial blood pressure (MAP) during experimental intervertebral disk nucleotomy in sheep. Eighteen female Brogna sheep were anaesthetized with propofol and maintained with a fixed end-tidal isoflurane concentration of 1.5 ± 0.1%. Sheep were assigned to one of three groups that intravenously received methadone 0.3 mg/kg (group M), fentanyl 2 µg/kg followed by 10 µg/kg/h (group F), or buprenorphine 10 µg/kg and 30 minutes later ketamine 1 mg/kg followed by 5 mg/kg/h (group BK). Intravenous fentanyl at 2 µg/kg would have been used for rescue analgesia in case HR and/or MAP had increased. During surgery, HR and MAP values did not increase over 20% in all groups. All animals maintained the percentage change between -4 and 7% for both variables; only one sheep in group BK had an increase in MAP superior to 20% after ketamine administration before surgical stimulation. In group M, HR decreased over time and in group BK, MAP tended to increase during surgery. All the opioid-based protocols tested were able to control the cardiovascular response to noxious stimulation in sheep undergoing spinal surgery, although ketamine may have represented a confounding factor.

Caffeine Accelerates Emergence from Isoflurane Anesthesia in Humans: A Randomized, Double-blind, Crossover Study.

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: There are currently no drugs clinically available to reverse general anesthesia. We previously reported that caffeine is able to accelerate emergence from anesthesia in rodents. This study was carried out to test the hypothesis that caffeine accelerates emergence from anesthesia in humans. We conducted a single-center, randomized, double-blind crossover study with eight healthy males. Each subject was anesthetized twice with 1.2% isoflurane for 1 h. During the final 10 min of each session, participants received an IV infusion of either caffeine citrate (15 mg/kg, equivalent to 7.5 mg/kg of caffeine base) or saline placebo. The primary outcome was the average difference in time to emergence after isoflurane discontinuation between caffeine and saline sessions. Secondary outcomes included the end-tidal isoflurane concentration at emergence, vital signs, and Bispectral Index values measured throughout anesthesia and emergence. Additional endpoints related to data gathered from postanesthesia psychomotor testing. All randomized participants were included in the analysis. The mean time to emergence with saline was 16.5 ± 3.9 (SD) min compared to 9.6 ± 5.1 (SD) min with caffeine (P = 0.002), a difference of 6.9 min (99% CI, 1.8 to 12), a 42% reduction. Participants emerged at a higher expired isoflurane concentration, manifested more rapid return to baseline Bispectral Index values, and were able to participate in psychomotor testing sooner when receiving caffeine. There were no statistically significant differences in vital signs with caffeine administration and caffeine-related adverse events. Intravenous caffeine is able to accelerate emergence from isoflurane anesthesia in healthy males without any apparent adverse effects.

Rocuronium infusion: A higher rate is needed in diabetic than nondiabetic dogs

ObjectiveTo determine the infusion rates that maintain the train-of-four (TOF) ratio within 20–70% in dogs and compare the infusion rates between diabetic and nondiabetic dogs. Study designProspective clinical study. AnimalsIn total, 47 dogs scheduled for phacoemulsification were included with a median (80% central range) bodyweight of 10.6 (5.7–35.5) kg and age of 7 (1–11) years. Diabetes mellitus was previously diagnosed in nine dogs. MethodsAfter premedication using acepromazine and methadone, anaesthesia was induced by intravenous (IV) propofol and maintained by isoflurane and fentanyl or remifentanil. The TOF ratio was monitored by stimulating the peroneal nerve and the response quantified by accelerometry. Rocuronium 0.5 mg kg−1 was administered IV, and further infused to maintain the TOF ratio between 20% and 70%. The infusion rates of rocuronium were compared by the Mann–Whitney test between diabetic and nondiabetic dogs, and the influence of age, sex, bodyweight, body temperature, end-tidal carbon dioxide, end-tidal isoflurane concentration, mean arterial blood pressure, pulse rate and time from induction and time from rocuronium bolus to stable rocuronium infusion rate were investigated in a stepwise, forward regression model. ResultsA stable infusion rate was found in 42 dogs. A higher median (80% central range) infusion rate was found in diabetic [0.43 (0.35–0.50) mg kg−1 hour−1] compared with nondiabetic dogs [0.30 (0.20–0.50) mg kg−1 hour−1] (p = 0.013). None of the other variables investigated were found to significantly influence the infusion rate. Conclusions and clinical relevanceThere is a quite large individual variation in the infusion rates of rocuronium needed to maintain a stable neuromuscular block in a varied population of dogs. Of the variables investigated, diabetes mellitus was the only one found to significantly influence the infusion rate of rocuronium.

Effect of oral trazodone on the minimum alveolar concentration of isoflurane in dogs

ObjectiveTo determine the effect of oral trazodone on the minimum alveolar concentration (MAC) of isoflurane in dogs. Study designProspective blinded, single-observer, randomized crossover experimental study. AnimalsSix adult (age 6.8 ± 1.6 months) healthy dogs (three males and three females), weighing 24.8 ± 3.4 kg (mean ± standard deviation). MethodsEach dog was anesthetized twice with a minimum of 7 days between anesthetic episodes. Dogs were randomly assigned to be administered two treatments in a crossover design: premedication with trazodone (8 mg kg−1; TRAZ–ISO) orally 2 hours prior to an anesthetic episode or no (ISO). Dogs were anesthetized with intravenous propofol (6 mg kg−1) and isoflurane in >95% oxygen. Isoflurane MAC was determined using an iterative bracketing technique with electrodes placed in the buccal mucosa. Hemodynamic variables were compared at the lowest end-tidal isoflurane concentration at which each dog did not respond. A paired t test was used to assess the effect of treatment on outcome variables with significance set to a value of p < 0.05. ResultsThe MAC concentration (mean ± standard deviation) in dogs administered TRAZ–ISO was 0.85 ± 0.17% compared with 1.02 ± 0.11% in those administered ISO (p = 0.01, 95% confidence interval −0.25 to −0.05), resulting in a mean MAC reduction of 17 ± 12%. There were no differences in hemodynamic variables between treatments. Conclusions and clinical relevancePremedication of dogs with oral trazodone (8 mg kg−1) 2 hours prior to anesthetic induction has a significant isoflurane MAC sparing effect with no significant observed hemodynamic benefit.

Analgesic and isoflurane sparing effect of buprenorphine and butorphanol in cats anaesthetized with midazolam-ketamine-isoflurane

A clinical study was conducted in 18 female cats subjected for ovariohysterectomy to access the analgesic and isoflurane sparing effect of buprenorphine and butorphanol in cats anaesthetized with midazolam-ketamine- isoflurane. The cats were divided into three Groups. In Group I, anaesthesia was induced by midazolam (@0.3mg/kg) ketamine (11mg/kg) mixture. In Group II and Group III cats, butorphanol and buprenorphine were administered intramuscularly @ 0.4 mg/kg and 0.01 mg/kg, 15 minutes prior to induction of anaesthesia as in Group I. Anaesthesia was maintained with isoflurane. Inspired fraction of isoflurane (FiISO) and End-tidal isoflurane (ETISO) in percentage were recorded by main stream infrared spectroscopy analysis. The postoperative antinociceptive efficacy of drugs was studied by four point simple descriptive scale (SDS) scoring system. The study on end-tidal isoflurane concentration revealed both buprenorphine and butorphanol had reduced the use of isoflurane when compared to control group and among that butorphanol had a higher isoflurane sparing effect than buprenorphine. The pain score study revealed buprenorphine produced adequate postoperative analgesia when compared to butorphanol.

Hypotension Aggravated by Dopamine in a Dog Under Isoflurane Anesthesia

Background: Hypotension (MAP &lt; 60 mmHg) is the most common complication in anesthetic practice and has been identified in 38% of canine patients undergoing general anesthesia for variety of procedures. Normalization of arterial pressure can usually be achieved by decreases in inhalant anesthetic concentrations, fluid administration, and use of inotropes/vasopressors in healthy animals (ASA I) or animals with mild systemic disease (ASA anesthetic risk II). The present report shows an ASA II dog with severe hypotensive crisis [mean arterial pressure (MAP) &lt; 50 mmHg] during general anesthesia, in which the procedure was aborted because hypotension was aggravated by dopamine.Case: A 7-year-old male Bull Terrier was anesthetized for magnetic resonance imaging (MRI) of a tumor in the face. After intramuscular acepromazine (0.01 mg/kg) and meperidine (3 mg/kg), anesthesia was induced with intravenous (IV) ketamine (1 mg/kg) and propofol (2.3 mg/kg) and maintained with isoflurane in oxygen. Ten min after induction of anesthesia MAP was 45 mmHg, while end-tidal isoflurane (ETISO) concentration was 0.5%. End-tidal isoflurane was decreased to 0.3% and an IV bolus of Lactated Ringer’s was initiated (15 mL/kg over 10 min), followed by two ephedrine boluses (0.1mg/kg, IV) administered 5 min apart. MAP remained low (&lt; 50 mmHg) and dopamine constant rate infusion (CRI) was initiated (7.5 μg/kg/min). Ten minutes after dopamine CRI was commenced, MAP was further decreased to 25-22 mmHg. Dopamine CRI was increased to 10 μg/kg/min, but MAP remained &lt; 25 mmHg. Infusion drugs and isoflurane anesthesia were stopped. After the animal was extubated MAP returned 60-70 mmHg.Discussion: Among the drugs used, isoflurane is known for decreasing blood pressure in a dose-related manner because of its vasodilating properties. Hypotension is rarely associated with low end-tidal isoflurane concentrations (0.3-0.5%) in animals that do not present previous evidence of circulatory dysfunction. Acepromazine may have contributed to the hypotensive actions of isoflurane in the case reported here because of its vasodilating effects. Acepromazine has prolonged plasma half-life (7 h) and might also have contributed to the lack efficacy of ephedrine to treat hypotension. Aggravation of hypotension (MAP decreased from 45-50 mmHg to approximately 25 mmHg) by dopamine was unexpected. Aggravation of hypotension during administration of vasopressor doses of dopamine could be related to the activation of the cardiopulmonarychemoreflex (CCR), previously known with the eponym Bezold-Jarisch reflex or due to a prevalence of dopamine´s vasodilatory effects (dopaminergic receptor stimulation) and failure of this drug in promiting increased CO and SVR at the dose ranges used (7.5 to 10 μg/kg/min).. The CCR involves activation of mechano and baroreceptors in the heart, by inotropes such as dopamine and dobutamine. This activation originates vagal afferent impulses to the nucleus tractus solitarii of the spinal cord, which in turn originates parasympathetic afferent impulses to the heart. The consequence is an increase in parasympathetic outflow and decreased sympathetic activity, ultimately producing bradycardia, hypotension, or both.Keywords: acepromazine, Bezold-Jarish reflex, cardiopulmonary chemoreflex, canine, inotropes.