Clinical comparison of sevoflurane and isoflurane when administered with nitrous oxide for surgical procedures of intermediate duration

Effect of charcoal filter on the emergence from sevoflurane anesthesia in a semi-closed rebreathing circuit

PURPOSE

A charcoal filter attached within the anesthetic circuit has been shown to efficiently adsorb halothane or isoflurane, thus hastening anesthetic recovery in low or minimal flow system. This study was intended to demonstrate whether the charcoal filter enhances the recovery time from sevoflurane anesthesia using a semi-closed circuit system.

MATERIALS AND METHODS

Thirty healthy patients scheduled for elective surgery under sevoflurane anesthesia were randomly assigned to the charcoal filter or control group. Upon completion of surgery, the end-tidal concentration of sevoflurane was maintained at 2.0 vol%. A charcoal filter was attached to the expiratory limb of the breathing circuit of charcoal filter group subjects. After sevoflurane was discontinued, ventilation was controlled with the same minute volume as the intra-operative period at a fresh gas flow rate of 5 L·min⁻¹ with 100% O₂. The elimination kinetics of sevoflurane from end-tidal concentration, Bispectral index and times of eye opening and extubation were obtained.

RESULTS

The exponential time constant (τ) of alveolar sevoflurane concentration in the charcoal filter group was significantly shorter than that in the control group (1.7±0.5 vs. 2.5±1.1 min, p=0.008). The charcoal filter hastened rapid eye opening (11.1±3.8 vs. 14.8±3.0 min, p=0.007) and extubation (11.9±3.9 vs. 15.3±3.2 min, p=0.014), compared to the control group.

CONCLUSION

A charcoal filter enhances the recovery from sevoflurane anesthesia with a semi-closed rebreathing circuit.

Pharmacoeconomics of Volatile Inhalational Anaesthetic Agents: An 11-Year Retrospective Analysis

With continuously increasing expenditure on health care resources, various cost containment strategies have been suggested in regard to controlling the cost of inhalational anaesthetic agents. We performed a cost identification analysis assessing inhalational anaesthetic agent expenditure at a tertiary level hospital, along with an evaluation of strategies to contain the cost of these agents.

The number of bottles of isoflurane, sevoflurane and desflurane used during the financial years 1997 to 2007 was retrospectively determined and the acquisition costs and cumulative drug expenditure calculated. Pharmacoeconomic modelling using low fresh gas flow anaesthesia was performed to evaluate practical methods of cost reduction.

The use of isoflurane decreased from 384 bottles during 1997 to 204 in 2007. In contrast, use of sevoflurane increased from 226 bottles during 1998 to 875 during 2007. Desflurane use increased from 34 bottles per year during 2002 (its year of introduction) to 163 bottles per year in 2007. While the inflation-adjusted cumulative expenditure for these inhalational agents (Australian dollars) increased from $132,000 in 1997 to over $326,000 in 2007, an increase of 168%, patient workload over the same period increased by only 11%. Pharmacoeconomic modelling demonstrated that sevoflurane at 2 l/minute costs 19 times more than isoflurane at 0.5 l/minute.

For the financial years 1997 to 2007, we found a progressive shift from the cheaper isoflurane to the more expensive agents, sevoflurane and desflurane, a shift associated with marked increases in costs. Low flow anaesthesia with isoflurane is one strategy to reduce costs.

Sevoflurane provides better recovery as compared with isoflurane in children undergoing spinal surgery

Rapid recovery is desirable in pediatric neurosurgical patients to obtain an early neurologic assessment. We compared the recovery characteristics of 2 commonly used anesthetic agents, sevoflurane and isoflurane, under bispectral index-guided anesthesia in children undergoing spinal surgery. Eighty children who underwent surgery for occult spinal dysraphism at the lumbar and sacral level were randomized to anesthesia with sevoflurane or isoflurane in oxygen and nitrous oxide. Anesthesia depth was guided by a bispectral index monitor kept between 40 and 60. In addition to time at emergence, extubation and discharge, recovery (modified Aldrete) score, and hemodynamics were compared. The 2 groups did not differ significantly with respect to demographics, duration of surgery and anesthesia, and intraoperative hemodynamic changes. Extubation (6.4+/-3.3 vs. 10.7+/-4.6) and emergence (7.8+/-3.4 vs. 12.8+/-5.6) times (minutes) were significantly shorter with sevoflurane (P<0.001). Time (minutes) to achieve full Aldrete (modified) scores was less with sevoflurane (13.9+/-5.3 vs. 20.3+/-6.5) than isoflurane (P<0.001). However, the time (minutes) to achieve discharge criteria from postanesthesia care unit (140.7+/-49.3 vs. 146+/-43.3) and first dose of postoperative analgesic (60+/-24.1 vs. 72+/-33.4) in addition to incidence of postoperative agitation were similar in both groups (P>0.05). Sevoflurane results in an earlier recovery and assessment of modified Aldrete score when compared with isoflurane.

Recovery of older patients undergoing ambulatory anaesthesia with isoflurane or sevoflurane

BACKGROUND

Delayed recovery of cognitive function is a well-recognized phenomenon in older patients. The potential for the volatile anaesthetic used to contribute to alterations in postoperative cognitive function in older patients following minor surgical procedures has not been determined. We compared emergence from isoflurane and sevoflurane anaesthesia in older surgical patients undergoing urological procedures of short duration.

METHODS

Seventy-one patients, 60 yr of age or older, undergoing anaesthesia expected to last less than 60 min for ambulatory surgery, were randomly assigned to receive isoflurane or sevoflurane. A standardized anaesthetic protocol was used, with intravenous fentanyl 1 microg kg(-1) and propofol 1.5-2.0 mg kg(-1) administered to induce anaesthesia. Anaesthesia was maintained with either sevoflurane or isoflurane in 65% nitrous oxide and oxygen. Early and intermediate recovery times were recorded. The Mini Mental State Examination and digit repetition forwards and backwards were administered at baseline, and at 1, 3 and 6 h postoperatively, to assess cognitive function.

RESULTS

There were no between-group differences in (sevoflurane vs. isoflurane, mean +/- standard error of the mean) times to removal of the laryngeal mask airway (7.7 +/- 0.6 vs. 7.1 +/- 0.4 min), verbal response time (10.1 +/- 0.7 vs. 9.9 +/- 0.7 min) and orientation (12.1 +/- 0.7 vs. 12.1 +/- 0.7 min). Intermediate recovery, as measured by time to readiness for discharge from the post anaesthesia care unit (44.9 +/- 1.5 vs. 44.3 +/- 1.5 min), was similar in the two groups. Postoperative indices of cognitive function and attention were comparably reduced at 1 h, but returned to baseline in both groups at 6 h.

CONCLUSIONS

Isoflurane and sevoflurane anaesthesia resulted in similar clinical and neurocognitive recovery profiles in older patients undergoing ambulatory surgical procedures of short duration.

Diastolic blood pressure in patients with tibia fractures under anaesthesia: implications for the diagnosis of compartment syndrome

OBJECTIVE

In the treatment of tibia fractures, is the intraoperative diastolic blood pressure (DBP) less than pre- and postoperative DBP, and how does this relate to the diagnosis of compartment syndrome using DeltaP (diastolic blood pressure [DBP] - intracompartmental pressure)?

DESIGN, SETTING, AND PATIENTS

This was a prospective cohort study in a level 1 trauma center, with a consecutive series of 242 patients with a tibia fracture.

INTERVENTION

Intramedullary nail fixation of tibia fractures under general anesthesia.

MAIN OUTCOME MEASURES

Patient demographics, type and location of fracture, injury severity score, and blood pressures preoperatively, intraoperatively, and postoperatively.

RESULTS

There were 187 male and 55 female patients, whose ages ranged from 16 to 87 years (average, 39 years). There were 123 open and 119 closed tibia fractures. The average injury severity score was 14.7 (range: 9-41). Anesthetized patients had a significant decrease in their DBP and systolic blood pressure (SBP) compared with their preoperative, postanesthesia care unit and postoperative floor measurements. The mean DBP in the operating room was 18 +/- 13 mm Hg lower than the preoperative measurement (P < 0.05), whereas the difference in the preoperative and postoperative mean DBP was only 2 +/- 13 mm Hg.

CONCLUSIONS

There is a predictable response of DBP in patients with tibia fractures treated with intramedullary (IM) nailing under general anesthesia. The preoperative DBP is a good indicator of the postoperative DBP, and the intraoperative DBP is significantly lower (average 18 mm Hg; P < 0.05). The surgeon should recognize that intraoperative DeltaP may be lower than DeltaP once the patient is awakened in deciding whether to perform a fasciotomy or awaken the patient and perform serial examinations and or compartment pressure measurements. Intraoperative DeltaP may be spuriously low compared with that after the patient is awakened.

The effect of nitrous oxide on halothane, isoflurane and sevoflurane requirements in ventilated dogs undergoing ovariohysterectomy

OBJECTIVE

To examine the effect of 64% nitrous oxide (N2O) on halothane (HAL), isoflurane (ISO) or sevoflurane (SEV) requirements in dogs undergoing ovariohysterectomy.

STUDY DESIGN

Prospective, randomized, clinical trial.

ANIMALS

Ninety, healthy dogs of (mean +/- SD) body weight 21.2 +/- 10.0 kg and age 17.8 +/- 22.8 months.

MATERIALS AND METHODS

After premedication with acepromazine, hydromorphone and glycopyrrolate, anesthesia was induced with thiopental administered to effect. Dogs received one of six inhalant protocols (n = 15 group): HAL; HAL/N2O; ISO; ISO/N2O; SEV; or SEV/N2O. End-tidal CO2 was maintained at 40 +/- 2 mmHg with intermittent positive pressure ventilation (IPPV). Body temperature, heart rate, indirect systemic arterial blood pressures, inspired and end-tidal CO2, volatile agent, N2O and O2 were recorded every 5 minutes. The vaporizer setting was decreased in 0.25-0.5% decrements to elicit a palpebral reflex, and this level maintained. Statistical analysis included two-way anova for repeated measures with Bonferroni's correction factor and statistical significance assumed when p < 0.05. Percentage reduction in end-tidal volatile agent was calculated at 60 minutes after starting study.

RESULTS

End-tidal HAL, ISO and SEV decreased when N2O was administered. Percentage reduction: HAL (12.4%); ISO (37.1%) and SEV (21.4%). Diastolic, mean and systolic blood pressures increased in ISO/N2O compared with ISO. Heart rate increased in ISO/N2O and SEV/N2O compared with ISO and SEV, respectively. Systolic, mean and diastolic blood pressures increased in SEV compared with HAL and ISO. Systolic, mean, diastolic blood pressures and heart rate increased in SEV/N2O and ISO/N2O compared with HAL/N2O.

CONCLUSIONS

N2O reduces HAL, ISO and SEV requirements in dogs undergoing ovariohysterectomy. Cardiovascular stimulation occurred when N2O was used with ISO, less so with SEV and not with HAL

Tutorial: Context-Sensitive Decrement Times for Inhaled Anesthetics

Context-sensitive decrement times for inhaled anesthetics connect two values: a) the duration of anesthesia (nominally at a constant alveolar concentration)-the "context" and b) the time to decrease the alveolar or vital tissue (e.g., brain, heart, kidney, and liver, collectively called the vessel-rich group of tissues) concentration by some fractional "decrement" of the starting concentration. Increasing duration of anesthesia increases the time to a given decrement in a nonlinear manner that may considerably delay recovery. In the present report we use a commercially available simulation program (Gas Man) to confirm and enlarge on these concepts. In this simulation, increasing duration of anesthesia can markedly delay complete awakening for isoflurane. Increasing anesthesia duration imposes considerably less delay in awakening from sevoflurane compared with isoflurane. For desflurane, only prolonged anesthesia or decrements of 95% and more should delay awakening from anesthesia. These changes are shown to be the result of the relative solubility of each anesthetic in blood and tissue. An increase in cardiac output is also shown to delay awakening.

Comparison of recovery after intermediate duration of anaesthesia with sevoflurane and isoflurane

BACKGROUND

The purpose of this study was to compare recovery from anaesthesia after sevoflurane and isoflurane were administered to children for more than 90 min.

METHODS

After parental informed consent and ethical committee approval, children aged between 2 months and 6 years, ASA I or II, were randomly allocated to sevoflurane (n=20) or isoflurane (n=20) groups. Halogenated agents were discontinued following skin closure and patients were ventilated mechanically with 100% oxygen until minimum alveolar concentration (MAC) values awake were obtained (endtidal concentrations 0.6 MAC for sevoflurane and 0.4 MAC for isoflurane). Effective perioperative analgesia was provided by a caudal block.

RESULTS

The mean (+/- SD) duration of anaesthesia was 132 +/- 38 min and 139 +/- 49 min for sevoflurane and isoflurane, respectively. Early recovery occurred sooner in the isoflurane group (time to extubation was 16 +/- 7 min and 11 +/- 5 min, P<0.01; Aldrete's score at 0 min was 5.5 +/- 1.5 and 7.4 +/- 1.8, P<0.001, respectively). But the time to be fit for discharge from recovery room was similar at 136 +/- 18 min and 140 +/- 20 min, respectively.

CONCLUSIONS

After intermediate duration of anaesthesia administered to children for up to 90 min, isoflurane and sevoflurane allow recovery after approximatively the same lapse of time.

Sevoflurane versus isoflurane in patients undergoing valvular cardiac surgery

OBJECTIVE

To determine if sevoflurane provides hemodynamic and recovery characteristics comparable to isoflurane in patients undergoing surgery for valvular heart disease.

DESIGN

A prospective crossover, dose-response study using sevoflurane and isoflurane before the start of surgery, followed by randomization to sevoflurane or isoflurane for surgery with blinded assessment for recovery.

SETTING

Tertiary referral cardiac center.

PARTICIPANTS

Twenty-seven patients scheduled for elective valve surgery. Surgery consisted of 18 aortic valve and 12 mitral valve replacements, of which 3 patients had 2 valves replaced; 1, tricuspid repair; and 8, coronary artery bypass procedures.

INTERVENTIONS

A pulmonary artery catheter was used to obtain a complete hemodynamic profile during the dose-response study before surgery. Transesophageal echocardiography was used to confirm the diagnosis, and electrocardiography monitored for myocardial ischemia.

MEASUREMENTS AND MAIN RESULTS

Both agents showed similar hemodynamic effects at 0.5 and 1.0 minimum alveolar concentration. There was a tendency to decreases in heart rate, blood pressure, and cardiac output, whereas filling pressures remained stable with each volatile agent. Electrocardiography did not detect ischemic changes. Times to eye opening and extubation were similar with both agents, with sevoflurane tending to be earlier than isoflurane.

CONCLUSION

Sevoflurane showed a tendency to lower heart rates and cardiac index compared with isoflurane. Eye opening and extubation were slightly earlier. These findings were not statistically significant, however.

Sevoflurance: approaching the ideal inhalational anesthetic. a pharmacologic, pharmacoeconomic, and clinical review

Sevoflurane is a safe and versatile inhalational anesthetic compared with currently available agents. Sevoflurane is useful in adults and children for both induction and maintenance of anesthesia in inpatient and outpatient surgery. Of all currently used anesthetics, the physical, pharmacodynamic, and pharmacokinetic properties of sevoflurane come closest to that of the ideal anesthetic (200). These characteristics include inherent stability, low flammability, non-pungent odor, lack of irritation to airway passages, low blood:gas solubility allowing rapid induction of and emergence from anesthesia, minimal cardiovascular and respiratory side effects, minimal end-organ effects, minimal effect on cerebral blood flow, low reactivity with other drugs, and a vapor pressure and boiling point that enables delivery using standard vaporization techniques. As a result, sevoflurane has become one of the most widely used agents in its class.

Sevoflurane versus isoflurane in patients undergoing coronary artery bypass grafting: a hemodynamic and recovery study

OBJECTIVE

To determine if sevoflurane provides comparable hemodynamics and recovery characteristics to isoflurane in cardiac anesthesia.

DESIGN

A prospective, crossover, dose-response study using sevoflurane and isoflurane before the start of surgery, followed by randomization to sevoflurane or isoflurane for surgery with blinded assessment for recovery.

SETTING

Tertiary referral cardiac clinic and intensive care.

PARTICIPANTS

Sixteen elective patients scheduled for coronary artery bypass grafting.

INTERVENTIONS

A pulmonary artery catheter was used to obtain a complete hemodynamic profile during the dose response study before surgery. Transesophageal echocardiography (TEE) and an electrocardiogram (ECG) were used to assess myocardial ischemia.

MEASUREMENTS AND MAIN RESULTS

Both agents showed similar hemodynamic effects at 0.5 and 1.0 minimum alveolar concentration (MAC). There was a tendency toward decreases in heart rate, blood pressure, vascular resistance, and cardiac output with a rise in central pressures. Ischemic changes were not detected by TEE or ECG. Times to eye opening and extubation were similar for both agents.

CONCLUSION

At MAC equivalent doses, sevoflurane showed comparable hemodynamics to isoflurane. Both agents when used as the primary anesthetic showed similar recovery characteristics, with no statistical difference between them at any stage of the study.

Target controlled infusion of ketamine as analgesia for TIVA with propofol

PURPOSE

To determine the accuracy of a target controlled infusion system for ketamine and to assess its suitability for the provision of analgesia when used in conjunction with a propofol infusion in spontaneously breathing patients.

METHODS

Nineteen, adult, ASA I-III patients scheduled for elective surgery were studied. After premedication with 20 mg temazepam an appropriate plasma concentration of ketamine was selected and, when the target controlled infusion (TCI) system indicated that this had been achieved, anesthesia was induced and maintained using a propofol infusion. The plasma ketamine concentration was measured at predetermined intervals and cardiovascular and respiratory parameters recorded at 10 min intervals. Patients were reviewed in recovery and 24 hr postoperatively to assess the adequacy of their recovery and the presence of any undesirable side effects.

RESULTS

The TCI system had a median performance error against predicted plasma concentrations of 18.9% (SE 2.5%) and a median absolute performance error of 23.3% (SE 2.3%). Divergence was 20.3% (SE 30.1%) and wobble was 12.9% (SE 2.1%). There was a mean decrease in arterial pressure of 6.4% (SD 19.7%) and a mean increase in heart rate of 4.3% (SD 17.4%). Little respiratory depression occurred and all patients made a rapid postoperative recovery with none describing unpleasant dreams or hallucinations.

CONCLUSION

The TCI system provided a clinically acceptable degree of control of the plasma ketamine concentration although some further improvement should be possible by amending the pharmacokinetic model. Clinically the combination with a propofol infusion proved to be a satisfactory anesthetic technique.