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.     

Relationships between a proprietary index, bispectral index, and hemodynamic variables as a means for evaluating depth of anesthesia in dogs anesthetized with sevoflurane

OBJECTIVE: To evaluate relationships among various techniques for monitoring anesthetic depth in sevoflurane-anesthetized dogs undergoing orthopedic surgery. ANIMALS: 10 dogs. PROCEDURE: Dogs were medicated with acepromazine (0.05 mg/kg, IM), buprenorphine (0.01 mg/kg, IM), and atropine (0.04 mg/kg, IM). Anesthesia was induced and maintained with sevoflurane. Cardiovascular and respiratory responses were monitored. Anesthetic depth was monitored by use of the bispectral index (BIS), and a proprietary index was used to monitor activity of the autonomic nervous system. RESULTS: A significant decrease in BIS was seen after induction but concurrent changes were not observed for the other techniques. The proprietary index increased significantly after intubation, but no changes were seen for the other techniques. No significant changes were detected during incision or when higher nociceptive stimuli were applied. We did not identify a correlation between BIS and the proprietary index, the proprietary index and hemodynamic variables, or the BIS and hemodynamic variables during induction and maintenance. A significant increase in the proprietary index and BIS was detected at the time of resumption of reflexes. During anesthetic recovery, a correlation was found between the proprietary index and BIS but not between hemodynamic variables and the other techniques. CONCLUSIONS AND CLINICAL RELEVANCE: A significant increase in the proprietary index, but not the BIS or hemodynamic variables, was detected during intubation. Anesthetic induction with sevoflurane did not prevent the sympathetic stimulus attributable to tracheal intubation. Monitoring of hemodynamic variables does not provide sufficient information to allow clinicians to evaluate stress during anesthetic recovery.     

Pharmacokinetics of vatinoxan in male neutered cats anesthetized with isoflurane

ObjectiveTo characterize the pharmacokinetics of vatinoxan in isoflurane-anesthetized cats.Study designProspective experimental study.AnimalsA group of six adult healthy male neutered cats.MethodsCats were anesthetized using isoflurane in oxygen. Venous catheters were placed to administer the drug and sample blood. Vatinoxan, 1 mg kg^–1, was administered intravenously over 5 minutes. Blood was sampled before and at various times during and up to 8 hours after vatinoxan administration. Plasma vatinoxan concentration was measured using liquid chromatography/tandem mass spectrometry. Compartment models were fitted to the time–concentration data using population methods and nonlinear mixed effect modeling.ResultsA three-compartment model best fitted the data. Typical value (% interindividual variability) for the three volumes (mL kg^–1), the metabolic clearance and two distribution clearances (mL minute^–1 kg^–1) were 34 (55), 151 (35), 306 (18), 2.3 (34), 42.6 (25) and 5.6 (0), respectively. Hypotension increased the second distribution clearance to 10.6.Conclusion and clinical relevanceThe pharmacokinetics of vatinoxan in anesthetized cats were characterized by a small volume of distribution and a low clearance. An intravenous bolus of 100 μg kg^–1 of vatinoxan followed by constant rate infusions of 55 μg kg^–1 minute^–1 for 20 minutes, then 22 μg kg^–1 minute^–1 for 60 minutes and finally 10 μg kg^–1 minute^–1 for the remainder of the infusion time is expected to maintain the plasma concentration within 90%–110% of the plasma vatinoxan concentration previously shown to attenuate the cardiovascular effects of dexmedetomidine (25 μg kg^–1) in conscious cats.     

Hemodynamic effects of intravenous lidocaine in isoflurane anesthetized cats

Lidocaine dose‐dependently decreases the minimum alveolar concentration (MAC) of isoflurane in cats. The purpose of this study was to determine the hemodynamic effects of six lidocaine plasma concentrations in isoflurane anesthetized cats. Six cats were studied. After instrumentation, end‐tidal isoflurane concentration was set at 1.25 times the individual minimum alveolar concentration (MAC), which was determined in a previous study. Lidocaine was administered intravenously to target pseudo‐steady state plasma concentrations of 0, 3, 5, 7, 9, and 11 μg ml^–1, and isoflurane concentration was reduced to an equipotent concentration, determined in a previous study. Cardiovascular variables; blood gases; PCV; total protein and lactate concentrations; and lidocaine and monoethylglycinexylidide concentrations were measured at each lidocaine target concentration, before and during noxious stimulation. Derived variables were calculated. Data were analyzed using a repeated measures anova , followed by a Tukey test for pairwise comparisons where appropriate. One cat was excluded from analysis because the study was aborted at 7 μg ml^–1 due to severe cardiorespiratory depression. Heart rate, cardiac index, stroke index, right ventricular stroke work index, total protein concentration, mixed‐venous PO₂ and hemoglobin oxygen saturation, arterial and mixed‐venous bicarbonate concentrations, and oxygen delivery were significantly lower during lidocaine administration than when no lidocaine was administered. Mean arterial pressure, central venous pressure, pulmonary artery pressure, systemic and pulmonary vascular resistance indices, PCV, arterial and mixed‐venous hemoglobin concentrations, lactate concentration, arterial oxygen concentration, and oxygen extraction ratio were significantly higher during administration of lidocaine than when no lidocaine was administered. Most changes were significant at lidocaine target plasma concentrations of 7 μg ml^–1 and above. Noxious stimulation did not significantly affect most variables. Despite significantly decreasing in inhalant requirements, when combined with isoflurane, lidocaine produces greater cardiovascular depression than an equipotent dose of isoflurane alone. The use of lidocaine to reduce isoflurane requirements is not recommended in cats.     

Ketamine and the arrhythmogenic dose of epinephrine in cats anesthetized with halothane and isoflurane

Epinephrine-induced arrhythmias were studied in 4 cats (group A), using a 4 X 4 Latin square design. Each cat was anesthetized 4 times, 1 week apart, with halothane (1.5% end expired), isoflurane (2.0% end expired), and halothane or isoflurane preceded by ketamine administered IM (8.8 mg/kg). Lead II of the ECG and femoral artery pressure were recorded. Epinephrine was infused in progressively doubled rates (initial rate = 0.125 micrograms/kg/min) for a maximum of 2.5 minutes or until at least 4 ventricular premature depolarizations occurred within 15 s of each other. The arrhythmogenic dose of epinephrine (ADE; micrograms/kg) was calculated as the product of infusion rate and time to arrhythmia. The ADE (means +/- SD) during anesthesia with halothane alone and with ketamine-halothane anesthesia were 1.33 +/- 0.65 and 1.37 +/- 0.59 micrograms/kg, respectively; during anesthesia with isoflurane alone and ketamine-isoflurane anesthesia, the ADE were 9.34 +/- 1.29 and 16.16 +/- 3.63 micrograms/kg, respectively. The ADE was significantly greater (P less than 0.05) during isoflurane anesthesia and ketamine-isoflurane anesthesia than during halothane anesthesia. The percentages of change in systolic blood pressure (means +/- SD) at the ADE during halothane, ketamine-halothane, isoflurane, and ketamine-isoflurane were 31 +/- 34, 41 +/- 17, 127 +/- 27, and 148 +/- 57, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of morphine on the bispectral index during isoflurane anesthesia in dogs

ObjectiveTo assess the effect of morphine on the bispectral index (BIS) in dogs during isoflurane anesthesia maintained at a constant end–tidal concentration.Study designProspective, randomized, experimental trial.AnimalsEight adult Beagle dogs, weighing between 7.1 and 9.8 kg.MethodsAnesthesia was induced with isoflurane via a face mask. Dog's tracheas were intubated and anesthesia maintained with isoflurane at a constant end–tidal concentration (e′Iso) of 1.81% for a 30–minute equilibration period. Pulmonary ventilation was controlled to normocapnia. After equilibration, baseline values were recorded prior to intravenous administration of morphine sulfate (0.5 mg kg^?1) (MT) or an equal volume of saline (CT). Measurements for heart rate, systolic, diastolic and mean arterial pressure (SAP, DAP and MAP) were recorded at 10, 20, 30, 45, 60, 75, 90, 105 and 120 minutes after treatment. Bispectral index was recorded every 10 seconds for 3 minutes for each time measurement. Venous blood samples were collected at baseline, 10, 20, 30, 45, 60 and 120 minutes for determination of morphine serum concentrations. Anesthesia was discontinued after the last measurement and dogs were allowed to recover.ResultsBaseline BIS for MT and CT at 1.81%e′Iso were 63 ± 10 and 58 ± 9, respectively. Bispectral index in MT was 4–8% lower at 20, 75, 90 and 105 minutes compared with CT. There were no differences in BIS between baseline and any subsequent measurement within either MT or CT. Heart rate, SAP, MAP, and DAP decreased after morphine administration.Conclusion and clinical relevanceIntravenous administration of 0.5 mg kg^?1 morphine sulfate did not cause clinically significant changes in the BIS of unstimulated dogs during isoflurane anesthesia at an e′Iso of 1.81%.     

The cardiac anesthetic index of isoflurane in green iguanas

OBJECTIVE: To determine the cardiac anesthetic index (CAI) of isoflurane in green iguanas and whether butorphanol affected the CAI. DESIGN: Prospective randomized controlled trial. ANIMALS: 7 healthy mature iguanas. PROCEDURE: In 5 iguanas, CAI was determined after induction of anesthesia with isoflurane alone, and in 5 iguanas, CAI was determined after induction of anesthesia with isoflurane and IM administration of butorphanol (1 mg/kg [0.45 mg/lb]). Three iguanas underwent both treatments. Animals were equilibrated for 20 minutes at 1.5 times the minimum alveolar concentration (MAC) of isoflurane and observed for evidence of cardiovascular arrest. If there was no evidence of cardiovascular arrest, end-tidal isoflurane concentration was increased by 20%, and animals were allowed to equilibrate for another 20 minutes. This process was repeated until cardiovascular arrest occurred or vaporizer output could no longer be consistently increased. The CAI was calculated by dividing the highest end-tidal isoflurane concentration by the MAC. RESULTS: None of the iguanas developed cardiovascular arrest and all survived. Mean +/- SD highest end-tidal isoflurane concentration during anesthesia with isoflurane alone (9.2 +/- 0.60%) was not significantly different from mean concentration during anesthesia with isoflurane and butorphanol (9.0 +/- 0.43%). The CAI was > 4.32. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the CAI of isoflurane in green iguanas is > 4.32 and not affected by administration of butorphanol. Isoflurane appears to be a safe anesthetic in green iguanas.     

Pharmacokinetics of dexmedetomidine during administration of vatinoxan in male neutered cats anesthetized with isoflurane

Dexmedetomidine is an alpha-2 adrenoceptor agonist, and vatinoxan is an alpha-2 antagonist believed to poorly cross the blood–brain barrier in cats. Dexmedetomidine–vatinoxan combinations are of interest in anesthetized cats because the anesthetic sparing effect of dexmedetomidine may be preserved while vatinoxan attenuates the adverse cardiovascular effects of dexmedetomidine. The aim of this study was to characterize the pharmacokinetics of dexmedetomidine in cats during administration of isoflurane and vatinoxan. Six healthy adult male castrated cats were anesthetized with isoflurane in oxygen. Vatinoxan was administered using a target-controlled infusion system intended to maintain a plasma concentration of 4 µg/ml. Dexmedetomidine, 35 µg/kg was administered intravenously over 5 min. Plasma dexmedetomidine and vatinoxan concentrations were measured at selected time points ranging from prior to 8 hr after dexmedetomidine administration using liquid chromatography/tandem mass spectrometry. Compartment models were fitted to the time-concentration data using nonlinear mixed-effect modeling. A three-compartment model best fitted the data. Typical value (% interindividual variability) for the three-compartment volumes (ml/kg), the metabolic clearance and the two intercompartment distribution clearances (ml min⁻¹kg⁻¹) were 168 (259), 318 (35), 1,425 (18), 12.4 (31), 39.1 (18), and 29.6 (17), respectively. Mean ± standard deviation plasma vatinoxan concentration was 2.6 ± 0.6 µg/ml.     

Pharmacokinetics of buprenorphine and its metabolite norbuprenorphine in neutered male cats anesthetized with isoflurane

ObjectiveTo characterize the pharmacokinetics of buprenorphine and norbuprenorphine in isoflurane-anesthetized cats.Study designProspective experimental study.AnimalsA group of six healthy adult male neutered cats.MethodsCats were anesthetized with isoflurane in oxygen. Catheters were placed in a jugular vein for blood sampling and in a medial saphenous vein for buprenorphine and lactated Ringer’s solution administration. Buprenorphine hydrochloride (40 μg kg^–1 over 5 minutes) was administered intravenously. Blood samples were collected before buprenorphine administration and at various times up to 12 hours after administration. Plasma buprenorphine and norbuprenorphine concentrations were measured using liquid chromatography/tandem mass spectrometry. Compartment models were fitted to the time-concentration data using nonlinear mixed effect (population) modeling.ResultsA five-compartment model (three compartments for buprenorphine and two compartments for norbuprenorphine) best fitted the data. Typical value (% interindividual variability) for the three buprenorphine volumes of distribution, and the metabolic clearance to norbuprenorphine, the remaining metabolic clearance and the two distribution clearances were 157 (33), 759 (34) and 1432 (43) mL kg^–1, and 5.3 (33), 16.4 (11), 58.7 (27) and 6.0 (not estimated) mL minute^–1 kg^–1, respectively. Typical values (% interindividual variability) for the two norbuprenorphine volumes of distribution, and the norbuprenorphine metabolic and distribution clearances were 1437 (30) and 8428 (not estimated) mL kg^–1 and 48.4 (68) and 235.9 (not estimated) mL minute^–1 kg^–1, respectively.Conclusions and clinical relevanceThe pharmacokinetics of buprenorphine in isoflurane-anesthetized cats were characterized by a medium clearance.     

Bispectral index as an indicator of anaesthetic depth during isoflurane anaesthesia in the pig

The objective of the study was to examine the relationship between the ‘depth’ of anaesthesia - as determined by clinical signs - and the bispectral index (BIS). Electroencephalograms (EEG)s were recorded in 8 female and 8 castrated male, healthy Norwegian landrace pigs undergoing isoflurane anaesthesia, from which the bispectral index (BIS) was calculated. Isoflurane was delivered in pure oxygen at end-tidal concentrations of 1.6, 1.9, 2.2 and 2.5%, in randomised order, for 30 min after which the EEG was recorded over a 5 min period. Anaesthetic depth was evaluated on a visual analogue scale (VAS) by an experienced anaesthetist. The 95% confidence interval for the mean correlation coefficient between BIS and VAS was calculated to be -0.52–0.30. Confidence intervals (95%) for the mean change in the BIS obtained during the conscious state and that obtained during anaesthesia at different isoflurane concentrations was also calculated. There was a significant decrease in the BIS recorded during consciousness and after 1.6% isoflurane anaesthesia, and between readings after inhalation of 2.2% and 2.5% isoflurane. This indicates that BIS does not accurately reflect ‘depth’ at surgical levels of isoflurane anaesthesia in the pig, and is of no use for this purpose.     

Effect of medetomidine administration on bispectral index measurements in dogs during anesthesia with isoflurane

OBJECTIVE: To determine the relationship between bispectral index (BIS) and minimum alveolar concentration (MAC) multiples of isoflurane after IM injection of medetomidine or saline (0.9% NaCl) solution in anesthetized dogs. ANIMALS: 6 dogs. PROCEDURE: Each dog was anesthetized 3 times with isoflurane. First, the MAC of isoflurane for each dog was determined by use of the tail clamp method. Second, anesthetized dogs were randomly assigned to receive an IM injection of medetomidine (8 microg x kg(-1)) or an equal volume of isotonic saline (0.9% NaCl) solution 30 minutes prior to beginning BIS measurements. Last, anesthetized dogs received the remaining treatment (medetomidine or isotonic saline solution). Dogs were anesthetized at each of 4 MAC multiples of isoflurane. Ventilation was controlled and atracurium (0.2 mg/kg followed by 6 microg/kg/min as a continuous infusion, IV) administered. After a 20-minute equilibration period at each MAC multiple of isoflurane, BIS data were collected for 5 minutes and median values of BIS calculated. RESULTS: BIS significantly decreased with increasing MAC multiples of isoflurane over the range of 0.8 to 2.0 MAC. Mean (+/- SD) MAC of isoflurane was 1.3 +/- 0.2%. During isoflurane-saline anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 65 +/- 8, 60 +/- 7 52 +/- 3, and 31 +/- 28, respectively. During isoflurane-medetomidine anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 77 +/- 4, 53 +/- 7, 31 +/- 24, and 9 +/- 20, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: BIS monitoring in dogs anesthetized with isoflurane has a predictive value in regard to degree of CNS depression. During isoflurane anesthesia, our results support a MAC-reducing effect of medetomidine.     

Minimum alveolar concentration measures of central nervous system activation in cats anesthetized with isoflurane

OBJECTIVE: To compare the minimum alveolar concentration (MAC) of isoflurane required to prevent corticocerebral activation, autonomic responses, and purposeful movements after somatic or visceral stimulation in cats anesthetized with isoflurane. ANIMALS: 17 healthy spayed female cats. PROCEDURE: Bispectral index (BIS), autonomic parameters, and purposeful movements were monitored before and after somatic or visceral stimuli in cats anesthetized with isoflurane. End-tidal (ET) isoflurane concentration was varied to determine MAC values for cortical arousal (MAC(BIS)), autonomic responsiveness (MAC(BAR)), and purposeful movement (MAC). Bispectral index values > or = 60 were considered to represent corticocerebral activation. RESULTS: Minimum alveolar concentration for purposeful movement was significantly less than MAC(BIS) and MAC(BAR) for both somatic and visceral stimulation. Individual MAC values for somatic stimulation were not significantly different from respective MAC values for visceral stimulation. The percentage of cats that had a BIS response > or = 60 was inversely related to the end-tidal isoflurane concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Corticocerebral arousal and subcortical autonomic reflexes occured at isoflurane anesthetic concentrations at which reflexive or purposeful movements were absent. These results suggested that isoflurane had a preferential effect on voluntary motor output at low end-tidal isoflurane concentrations, and that sensory pathways, subcortical sympathetic output, and cortical responsiveness are less susceptible to the anesthetic effects of isoflurane. Bispectral index values obtained after somatic or visceral stimulation were sensitive for the detection of early changes in cortical excitability.     

Quantitative characteristics of anesthetic induction with and recovery from isoflurane and sevoflurane in cats

Isoflurane (ISO) is the most commonly administered feline inhalant anesthetic in North America. A newer agent, sevoflurane (SEVO), may provide faster induction and recovery from anesthesia based on its physical characteristics. Accordingly, we compared some induction and recovery characteristics of ISO and SEVO in healthy cats. Six female DSH cats (17.9 ± 9.0 (mean ± SD) months, 3.7 ± 0.3 kg) received four randomly assigned treatments: ISO for 1 hour (IS), SEVO for 1 hour (SS), ISO for 5 hours (IL), and SEVO for 5 hours (SL). Anesthesia was induced in a chamber into which ISO or SEVO was delivered at 2.7 times the individual's MAC (determined previously) in 6 L minute^?1 O₂. Measured (Rascal II, Ohmeda) anesthetic concentration was reported after correction using a multiple gas, standard‐defined calibration curve. For induction, time (seconds) from introduction of inhalant to onset of incoordinated movement (IM), recumbency with movement (RM), recumbency without movement, loss of pedal reflex (PD), and intubation (ET) were recorded. Following intubation, anesthesia was maintained for the required time at 1.25 times the individual's MAC. For recovery, time (seconds) from discontinuation of the inhalant (with continuation of O₂) to first movement, extubation (EXT), start of incoordinated movement, head‐lift, sternal recumbency (SR), crawl, stand/walk with incoordination, and jump without incoordination were recorded. Esophageal normothermia was maintained. Data were analyzed by paired t‐test (induction) or One‐way Repeated Measures anova followed, when appropriate, by Tukey's test (recovery). p < 0.05 was regarded as significant. For induction, IM was not significantly different between ISO and SEVO (118 ± 28 seconds vs. 104 ± 28 seconds). All other induction times were significantly shorter with SEVO vs. ISO, e.g. RM (181 ± 31 seconds vs. 213 ± 31 seconds), PD (426 ± 68 seconds vs. 504 ± 70 seconds), and ET (434 ± 66 seconds vs. 515 ± 69 seconds). For recovery, there were no differences between ISO and SEVO for any stage of recovery, e.g. EXT (IS 588 ± 163 seconds vs. SS 425 ± 109 seconds), SR (IS 735 ± 215 seconds vs. SS 655 ± 337 seconds), and IL (710 ± 658 seconds vs. SL 807 ± 465 seconds). We concluded that quantitative recovery characteristics did not depend on whether cats are anesthetized with equipotent amounts of SEVO or ISO, but some induction end‐points were reached more quickly with SEVO.     

Comparison of anesthetic induction in cats by use of isoflurane in an anesthetic chamber with a conventional vapor or liquid injection technique

OBJECTIVE: To compare 2 techniques for induction of cats by use of isoflurane in an anesthetic chamber. DESIGN: Prospective, randomized study. ANIMALS: 51 healthy cats. PROCEDURES: Cats were randomly allocated to 2 induction techniques. Cats were premedicated with acepromazine (0.1 mg/kg [0.045 mg/lb], SC) and buprenorphine (0.01 mg/kg [0.0045 mg/lb], SC) 30 minutes before induction. Cats were then placed into an induction chamber, and anesthetic induction was initiated. One technique involved a conventional flow-through system that used an oxygen flowmeter and an isoflurane vaporizer to flow vapors into the induction chamber. Alternatively, liquid isoflurane was injected into a vaporization tray that was mounted to the interior surface of the chamber lid. Inductions were videotaped for analysis. Five variables (head bobbing, head swinging side to side, paddling, rotating 180 degrees to 360 degrees, and rolling over or flipping) were scored to assess induction quality. Time variables recorded during induction corresponded to the interval until onset of excitatory motion, duration of excitatory motion, interval until recumbency, and interval until complete induction. RESULTS: Compared with cats anesthetized by use of a conventional vapor chamber technique, cats anesthetized by use of the liquid injection technique had a significantly shorter interval until recumbency and interval until complete induction and lower scores for quality of induction, indicating a smoother induction. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthetic induction in cats by use of a liquid injection technique was more rapid and provided a better quality of induction, compared with results for cats induced by use of a conventional vapor technique.     

Comparison of sevoflurane and isoflurane anesthetic index in unpremedicated dogs

Anesthetic respiratory effects of sevoflurane (SEVO) were compared with isoflurane (ISO) in unpremedicated dogs. Minimum alveolar concentration (MAC), apneic concentration (AC), and anesthetic index (AI) of SEVO and ISO were determined in eight 1‐year‐old healthy dogs, weighing 19 ± 3 kg (mean ± SEM) in a randomized complete block multiple cross‐over design. Dogs were mask‐induced with either SEVO or ISO in 100% oxygen. Following endotracheal intubation, dogs were instrumented, mechanically ventilated, and MAC was determined using a tail‐clamp method. Next, spontaneous ventilation was re‐established, and anesthetic concentration was increased to determine the AC. Throughout the anesthetic event, heart rate (HR), systolic blood pressure (SAP), mean blood pressure (MAP), diastolic blood pressure (DAP), respiratory rate (RR), end‐tidal carbon dioxide (Pe ′CO₂), and oxyhemoglobin saturation (SpO₂) were recorded at 3‐minute intervals. Following AC determination, AI was calculated as AC/MAC, and dogs were allowed to recover. Each dog was anesthetized four times (twice with ISO and SEVO each) at 1‐week intervals. All data were analyzed using the two‐way anova . Multiple comparisons were performed between ISO and SEVO treatments. Statistical significance was set at p < 0.05. Significant differences were noted between agents for MAC (SEVO, 2.13 ± 0.10%; ISO, 1.38 ± 0.14%; p < 0.0001), AC (SEVO, 7.34 ± 0.13%; ISO, 3.60 ± 0.13%; p < 0.0001), and AI (SEVO, 3.46 ± 0.22; ISO, 2.63 ± 0.14; p = 0.0002). Physiologic parameters were compared between SEVO and ISO at 1MAC, 2MAC, 3MAC, and AC. No differences were noted between SEVO and ISO treatments for cardiovascular parameters (HR, SAP, MAP, DAP). Significant differences were noted, favoring SEVO, for all respiratory parameters (RR, Pe ′CO₂, SpO₂) at increasing MAC multiples. Additionally, regression analysis was conducted for physiologic variable data points. Analysis of Pe ′CO₂ data points demonstrated a significant slope difference of ?6.47 ± 1.02 (B_SEVO ? B_ISO; p < 0.0001; r² = 0.6042) favoring SEVO. While expected dose‐related ventilatory depression was noted for both agents, all the respiratory parameters for SEVO demonstrated less respiratory depression than ISO at equipotent doses. These results indicated that SEVO caused less dose‐dependent ventilatory depression than ISO, having a significantly higher AI and causing less detrimental change in pulmonary parameters at increasing levels of MAC.     

Evaluation of an oscillometric blood pressure monitor for use in anesthetized cats

OBJECTIVE: To determine accuracy of an oscillometric blood pressure monitor used over a wide range of pressures in anesthetized cats. DESIGN: Prospective study. ANIMALS: 6 healthy cats. PROCEDURE: 4 female cats and 2 male cats that weighed 2.7 to 4.5 kg (5.9 to 9.9 lb) and were 2 to 8 years old were anesthetized. Blood pressure was measured directly with an arterial catheter placed in the right femoral artery and indirectly from the left antebrachium by use of an oscillometric monitor. A series of diastolic arterial pressure (DAP), mean arterial pressure (MAP), and systolic arterial pressure (SAP) measurements were obtained during hypotension, normotension, and hypertension. Values obtained indirectly and directly were compared. RESULTS: The oscillometric monitor was accurate for DAP and MAP throughout the entire pressure range and met the standards of the Association for the Advancement of Medical Instrumentation (mean +/- SD difference from values obtained directly, < or = 5 +/- 8 mm Hg). The SAP was increasingly underestimated with increasing overall pressure; mean differences from direct measurements were -5.2, -12.1, and -17.7 mm Hg during hypo-, normo-, and hypertension, respectively. Standard deviations for SAP were all < or = 8 mm Hg. The monitor gave readings during all attempts. The direct blood pressure recording system appeared to perform well with neither under- nor overdamping. CONCLUSIONS AND CLINICAL RELEVANCE: Except for a minor underestimation of SAP during normo- and hypertension, the oscillometric monitor yielded reliable and easily obtainable blood pressure measurements in anesthetized cats.