Minimum Alveolar Concentration of Sevoflurane With Nitrous Oxide Inducing Isoelectric EEG

Huazhong University of Science and Technology

Status and phase: Completed; Phase 4

Conditions: Middle Aged Patients; General Anesthesia

Treatments: Drug: Sevoflurane; Drug: Sevoflurane+Nitrous oxide

Study type: Interventional

Funder types: Other

Identifiers

NCT01705743

TJMZK20120903

Details and patient eligibility

About

In order to investigate the effect of a combination effect of sevoflurane and nitrous oxide on cerebral electrical activity, the investigators determined the MAC of sevoflurane combined with nitrous oxide inducing isoelectric electroencephalogram (EEG) in 50% of the subjects (MACie) in middle aged subjects.

Full description

Anaesthesia was induced by sevoflurane in oxygen. Cisatracurium 0.15 mg kg-1 was administered after loss of the lash reflex, then ventilated manually until the amplitude of T1 decreased to 0. Intubation was performed and switched to mechanical ventilation with a fresh gas flow of 2 L min-1. Anesthesia was maintained by sevoflurane or sevoflurane+60% nitrous oxide respectively. The surgical incision was performed at least 30 min after tracheal intubation, provided that the predetermined end-tidal sevoflurane concentration had been constant for at least 30 min and that the difference between inspired and end-tidal concentrations was less than 10%.

Brain electrical activity was measured using Narcotrend Monitor and S/5 Compact Anaesthesia Monitor, which displayed unprocessed EEG and burst suppression ratio, respectively. The design of the experiment is referred to the "Dixon up-and-down" method. To avid anaesthesia awareness, the first subject was designed to receive end-tidal sevoflurane concentration of 2.5 %. The presence or absence of isoelectric EEG (Entropy Module) of the preceding patient determined the end-tidal concentration of sevoflurane given to the next patient (with an increment size of 0.2%). The isoelectric EEG was considered as significant when the isoelectric state last for more than 1 min. The maximal burst suppression rate was recorded if isoelectric EEG was not reached.

Enrollment: 76 patients

Sex: All

Ages: 45 to 64 years old

Volunteers: No Healthy Volunteers

Inclusion criteria

• between 45 to 64 years old
• ASA physical status class 1 or 2
• elective abdominal surgery
• Informed Consent

Exclusion criteria

• history of neurological disease
• received central nervous system-active drugs
• cardiac ejection fraction less than 40%
• history of difficult intubation or anticipated difficult intubation
• daily alcohol consumption
• obesity, defined as a body-mass index of more than 30
• without informed consent
• others judged inappropriate as subjects for the study by the Study Chair

Trial design

Primary purpose: Treatment

Allocation: Randomized

Interventional model: Parallel Assignment

Masking: Double Blind

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76 participants in 2 patient groups

Group 1 Sevoflurane+Nitrous oxide

Active Comparator group

Treatment:

Drug: Sevoflurane+Nitrous oxide

Group 2 Sevoflurane

Active Comparator group

Treatment:

Drug: Sevoflurane