Bispectral Index Guided Sevoflurane Titration

Electroencephalographic (EEG)-based monitoring systems, for example the bispectral index [(BIS); BIS monitor, Covidien, Boulder, Colorado, USA], were designed to prevent anaesthesia underdosage with the risk of awareness and to reduce the time to awakening after terminating general anaesthesia. However, little is known about the consequences of anaesthetic overdose. The investigators assume that high doses of anaesthetics result in cardiocirculatory depression and the necessity for high-dose vasopressor therapy, followed by microcirculation disorder and organ dysfunction.

The investigators hypothesised that in on-pump cardiac-surgery, goaldirected administration of sevoflurane guided by BIS monitoring reduces excessive sevoflurane plasma concentration (SPC) and the need for an intraoperative vasopressor. To test this hypothesis, the current study compared BIS-guided sevoflurane administration with the constant delivery of an inspired sevoflurane concentration of 1.8% during on-pump cardiac surgery and analysed its effect on the SPC and the required intraoperative dosage of norepinephrine.

The study population was divided into two patient groups: Thirty-three on-pump cardiac surgery patients enrolled in the study were allocated to a conventionally treated control group, with the constant administration of an inspired concentration of sevoflurane 1.8% (group Sevo1.8%). Thirty-four patients were sequentially allocated to an interventional group with BIS-guided administration of sevoflurane (group SevoBIS).

Vasoactive drugs were administered according to the following protocol in both groups. If the mean arterial blood pressure decreased below 50 mmHg, a continuous infusion of norepinephrine was given to maintain a perfusion pressure between 50 and 60 mmHg during cardiopulmonary bypass. If the mean arterial pressure increased above 75 mmHg, nitroglycerine was used in boluses of 0.1 mg until arterial pressure returned to a mean of less than 75 mmHg. If mean arterial pressure persisted above 75 mmHg after a cumulative administration of nitroglycerine 1.0 mg, urapidil was administered in boluses of 0.1 mg/kg until the perfusion pressure decreased below 75 mmHg.

At the end of the surgical procedure, all patients were transferred to the ICU.

Inclusion criteria

• Undergoing elective on-pump cardiac surgery and an American Society of Anesthesiologists' (ASA) physical status of 3 to 4

Exclusion criteria

• A contraindication to the administration of volatile anaesthetics, an active infection with a temperature more than 38°C and any history of neurological disease