Effect of Dexmeditomidine on Isofluorane Consumption in Middle Ear Surgery

Background: With the introduction of intentional hypotensive anesthesia in the surgical field to achieve a relatively bloodless surgical field along with the use of the operative microscope, it has revolutionized the middle ear surgery practice. Dexmedetomidine is a relatively new and potent α2 agonist prototype found efficient in rendering bloodless intra-surgical field and inducing controlled hypotension during the surgeries of the middle ear. The objective is to present prospective study was aimed at evaluating with and without dexmedetomidine infusion effect on end-tidal isoflurane concentration for lowering blood pressure by 30%, awakening time and quality of bloodless surgical field during middle ear surgical procedure. Subjects and Methods:54 patients who were to undergo middle ear surgery and had ASA I and II were randomly divided into the two groups. In Group I Dexmedetomidine was used and in Group II Normal saline. Effect of Dexmedetomidine infusion on end-tidal isoflurane concentration for lowering blood pressure by 30%, awakening time, quality of bloodless surgical field during middle ear surgical procedure, heart rate was evaluated. The data collected were statistically analyzed. Results: The mean values of the heart rate were statistically non-significant between the groups when recorded at the baseline, whereas, a statistically significant difference was seen in the values for heart rate intra-operatively. The mean values for heart rates were significantly higher for the placebo group. A significant difference in Isoflurane concentration was found with dexmedetomidine requiring a percentage of 0.6 0.4 and normal saline 1.8 0.5. Less bleeding was seen with dexmedetomidine. Conclusion: Dexmedetomidine is a potent hypotensive agent which also reduces the requirement of Isoflurane compared to the normal saline placebo. The use of dexmedetomidine is relatively safe and provide a relatively bloodless surgical field, hence, increasing efficacy, and improving visibility at the surgical site.

Effects of Standard and Sustained-release Buprenorphine on the Minimum Alveolar Concentration of Isoflurane in C57BL/6 Mice

Both standard and sustained-release injectable formulations of buprenorphine (Bup and BupSR, respectively) are used as preemptive analgesics, potentially affecting gas anesthetic requirements. This study tested the effects of Bup and BupSR on isoflurane requirements and confirmed that buprenorphine could reduce isoflurane requirements during a laparotomy in mice. We hypothesized that both Bup and BupSR would significantly decrease the required minimum alveolar concentration (MAC) of isoflurane. C57BL/6 mice received either isotonic crystalloid fluid (control), Bup (0.1 mg/kg), or BupSR (1.2 mg/kg) subcutaneously 10 min prior to the induction of anesthesia. Each anesthetized mouse was tested at 2 isoflurane concentrations. A 300-g noxious stimulus was applied at each isoflurane concentration, alternating between hindfeet. In addition, a subset of mice underwent terminal laparotomy or 60 min of anesthesia after injection with Bup, BupSR, or saline to ensure an appropriate surgical plane of anesthesia. Mice were maintained at the lowest isoflurane concentration that resulted in 100% of mice at a surgical plane from the aforementioned MAC experiments (control, 2.0%; Bup and BupSR, 1.7%). Analysis showed that both Bup and BupSR significantly decreased isoflurane requirements by 25.5% and 14.4%, respectively. The isoflurane MAC for the control injection was 1.80% ± 0.09%; whereas Bup and BupSR decreased MAC to 1.34% ± 0.08% and 1.54% ± 0.09%, respectively. Sex was not a significantly different between the injection groups during MAC determination. All of the mice that underwent surgery achieved a surgical plane of anesthesia on the prescribed regimen and recovered normally after discontinuation of isoflurane. Lastly, heart and respiratory rates did not differ between mice that underwent surgery and those that were anesthetized only. Bup and BupSR are MAC-sparing in male and female C57BL/6 mice and can be used for effective multimodal anesthesia.

The depth of anaesthesia associated with the administration of isoflurane 2.5% during cardiopulmonary bypass

Background:Administering isoflurane 2.5% into the oxygenator during cardiopulmonary bypass results in no patient movement. However, doing so may result in an excessive depth of anaesthesia particularly, when hypothermia is induced. Bispectral index and arterial blood and oxygenator exhaust concentrations of volatile anaesthetics should be related to depth of anaesthesia. The primary aim of this study was to measure the depth of anaesthesia using bispectral index, resulting from administering isoflurane 2.5% into the oxygenator during cardiopulmonary bypass, and secondary aims were to examine the relationships between blood and oxygenator exhaust isoflurane concentrations and bispectral index.Methods:Arterial and mixed-venous blood samples were aspirated at three time points during cardiopulmonary bypass and measured for isoflurane concentration using mass spectrometry. Simultaneously, oxygenator exhaust isoflurane concentration, nasopharyngeal temperature and bispectral index were recorded.Results:When averaged across the three time points, all patients had a bispectral index score below 40 (binomial test, p < 0.001). There were no significant correlations between bispectral index score and arterial or mixed-venous blood isoflurane concentrations (r = –0.082, p = 0.715; r = –0.036, p = 0.874) and oxygenator exhaust gas concentration of isoflurane (r = –0.369, p = 0.091).Conclusion:When 2.5% isoflurane was administered into the sweep gas supply to the oxygenator during cardiopulmonary bypass, all patients experienced a bispectral index score less than 40 and no significant relationship was found between either arterial or mixed-venous blood or oxygenator exhaust concentrations of isoflurane and bispectral index.

Caffeine Accelerates Emergence from Isoflurane Anesthesia in Humans

Editor’s Perspective What We Already Know about This Topic 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. Methods 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. Results 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. Conclusions Intravenous caffeine is able to accelerate emergence from isoflurane anesthesia in healthy males without any apparent adverse effects.

Assessing the depth of isoflurane anaesthesia during cardiopulmonary bypass

Introduction: Bispectral index (BIS) and monitoring of end-tidal concentration may be associated with a reduction in the incidence of awareness during volatile-based general anaesthesia. An analogue of end-tidal concentration during cardiopulmonary bypass (CPB) is measuring exhausted isoflurane concentration from the oxygenator as an estimate to blood and, so, brain concentration. The aim of this study was to determine the relationships between oxygenator exhaust and blood concentrations of isoflurane and the BIS score during CPB when administering isoflurane into the sweep gas supply to the oxygenator. Methods: Seventeen patients undergoing elective cardiac surgery using CPB and isoflurane with BIS monitoring were recruited in a single-centre university hospital. Isoflurane gas was delivered via a calibrated vaporiser at the beginning of anaesthetic induction. Radial arterial blood samples were collected after the initiation of CPB and before aortic cross-clamping, which were analysed for isoflurane by gas chromatography and mass spectrometry. The BIS score and the concentration of exhausted isoflurane from the oxygenator membrane, as measured by an anaesthetic gas analyser, were recorded at the time of blood sampling. Results: The mean duration of anaesthetic induction to arterial blood sampling was 90 min (95%CI: 80,100). On CPB, the median BIS was 39 (range, 7-43) and the mean oxygenator exhaust isoflurane concentration was 1.24 ± 0.21%. No significant correlation was demonstrated between BIS with arterial isoflurane concentration (r=-0.19, p=0.47) or oxygenator exhaust isoflurane concentration (r=0.07, p=0.80). Mixed-venous blood temperature was moderately correlated to BIS (r=0.50, p=0.04). Oxygenator exhaust isoflurane concentration was moderately, positively correlated with its arterial concentration (r=0.64, p<0.01). Discussion: In conclusion, in patients undergoing heart surgery with CPB, the findings of this study indicate that, whilst oxygenator exhaust concentrations were significantly associated with arterial concentrations of isoflurane, neither had any association with the BIS scores, whereas body temperature has moderate positive correlation.

Isoflurane sparing effect of diazepam and midazolam to xylazine-ketamine induction and isoflurane maintenance in goats

The clinical study was undertaken to assess the isoflurane sparing effect of diazepam and midazolam during isoflurane anaesthesia in goats. The study was conducted in 12 clinical cases of goats randomly divided into two equal groups. In all the animals, xylazine hydrochloride was administered at the dose rate of 0.05 mg per kg body weight intramuscularly. In group I and II, diazepam and midazolam were administered at the dose rate of 0.5 mg per kg body weight i.v. respectively, prior to induction of anaesthesia. Anaesthesia was induced with ketamine hydrochloride at the dose rate of 5 mg per kg body weight i.v. and was maintained with isoflurane employing rebreathing circuit. The end-tidal isoflurane concentration required to maintain surgical plane of anaesthesia was significantly lower in group II (0.82 ± 0.03 per cent) indicating that inclusion of midazolam in the anaesthetic protocol had significant (28 per cent) isoflurane sparing effect.

Intraoperative end-tidal concentration of isoflurane in cats undergoing ovariectomy that received tramadol, buprenorphine or a combination of both

Objectives The aim of the study was to evaluate the end-tidal concentration of isoflurane required to maintain heart and respiratory rate within ± 20% of basal measurement in cats undergoing ovariectomy that received buprenorphine, tramadol or a combination of both. Methods Thirty cats, divided into three groups, were enrolled in a simple operator-blinded, randomised study. Cats received acepromazine (0.03 mg/kg) and one of the following treatments: buprenorphine (0.02 mg/kg), tramadol (2 mg/kg) or a combination of both. Anaesthesia was induced with propofol and maintained with isoflurane titrated in order to maintain heart and respiratory rate within the target values recorded before premedication. Results Groups were similar for age, weight, dose of propofol administered, sedation and recovery scores. Cats receiving tramadol with buprenorphine were extubated earlier after isoflurane discontinuation. No statistical differences were detected in end-tidal fraction of isoflurane between buprenorphine alone or with tramadol. In cats that received tramadol or buprenorphine alone, ovarian pedicle traction caused a statistical increase in end-tidal isoflurane concentration compared with that measured during incision and suture of the skin. In cats that received the combination of tramadol plus buprenorphine no differences among surgical time points were observed. Conclusions and relevance Tramadol added to buprenorphine did not provide any advantage in decreasing the end-tidal fraction of isoflurane compared with buprenorphine alone, although it is speculated there may be an infra-additive interaction between tramadol and buprenorphine in cats.