Clinical trial NCT02471950: Isoflurane During Cardiopulmonary Bypass
Official title: The Depth of Anaesthesia Associated With the Use of 2.5% Isoflurane During Cardiopulmonary Bypass
Study type: OBSERVATIONAL
Overall status: COMPLETED
Conditions: Cardiopulmonary Bypass
Consciousness Monitors
Isoflurane
Lead sponsor: University of Edinburgh
Sponsor class: OTHER
First posted: 2015-06-15
Enrollment: 22
Sex: ALL
Minimum age (years): 18
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: no
Observational model: COHORT
Time perspective: PROSPECTIVE
Sampling method: NON_PROBABILITY_SAMPLE
Study population: Those patients scheduled for elective heart surgery over the age of 18 requiring cardiopulmonary bypass

Brief summary: There is no clinical way of assessing the depth of anaesthesia while patients are on the heart-lung machine. A new method of measuring the depth of anaesthesia using brainwaves called the Bispectral index (BIS) has been developed and its use in cardiac surgery is now widespread. However BIS is also altered by patients body temperature. As cooling is common during heart surgery the use of BIS to measure the depth of anaesthesia during heart-lung bypass remains controversial. This study aims to find out what depth of anaesthesia is produced according to BIS during heart lung bypass using a standard anaesthetic technique that utilises the anaesthetic isoflurane.

Detailed description: There is no clinical way of assessing patients' depth of anaesthesia on the heart-lung machine. For this reason, the amount of volatile anaesthetic agent like isoflurane, that is administered has traditionally been determined by anaesthetists' clinical experience. Recently, a device that assesses depth of anaesthesia by analysing the electrical brain waves called the Bispectral index (BIS) has been introduced. The study aims to determine whether the level of anaesthesia produced by isoflurane using the traditional approach is more than required simply to maintain unconsciousness according to BIS. In addition, the study will determine whether the concentration of isoflurane in exhaust gases from the heart-lung machine can be used as an estimate arterial blood concentration and so, depth of anaesthesia.

The study will recruit patients who are scheduled for heart surgery using a heart-lung machine. Patients will be anaesthetised using a long established balanced technique including the administration of isoflurane 2.5% whilst supported on the heart-lung machine. Measurements of exhaust gas concentration of isoflurane from the heart-lung machine and level of BIS will be recorded at three time points. Simultaneously, three arterial blood samples will be taken and the isoflurane concentration measured in these samples. The BIS levels will be averaged and the proportion of patients with a BIS below 40 (lower limit of normal) will be calculated. Concentrations of isoflurane in the exhaust gas of the heart-lung machine will be compared with blood concentrations of isoflurane and the both concentrations will be compared with the level of BIS to establish whether they can be used to assess depth of anaesthesia.

If this study finds that a large proportion of patients have more than adequate levels of anaesthesia, then future studies could explore whether administering lower concentrations of isoflurane improves outcome whilst maintaining anaesthesia.

Eligibility criteria: Inclusion Criteria:

* Participants over the age of 18
* Scheduled for elective cardiac surgery under the care of trial anaesthetists
* Patient has provided informed consent to participate

Exclusion Criteria:

* Patients presenting for emergency cardiac surgery
* Patients who will have cardiac surgery that does not require cardiopulmonary bypass
* Unwilling/unable to provide informed consent
* Patients under the age of 18
* Anaesthesia undertaken by anaesthetists not involved in trial

Primary outcomes:
measure: Depth of anesthesia according to BIS
timeFrame: Intraoperative
Secondary outcomes:
measure: Comparison of exhaust gas and blood concentration of isoflurane
timeFrame: Intraoperative
measure: Comparison of blood isoflurane concentration and BIS score
timeFrame: Intraoperative
measure: Comparison of exhaust isoflurane Concentration and BIS score
timeFrame: Intraoperative
Other outcomes:
Locations:
city: Edinburgh
country: United Kingdom
facility: Royal Infirmary of Edinburgh
state: Scotland
Study officials:
affiliation: University of Edinburgh
name: Peter Alston, MBChB
role: PRINCIPAL_INVESTIGATOR
References:
citation: Alston RP, Connelly M, MacKenzie C, Just G, Homer N. The depth of anaesthesia associated with the administration of isoflurane 2.5% during cardiopulmonary bypass. Perfusion. 2019 Jul;34(5):392-398. doi: 10.1177/0267659118822946. Epub 2019 Jan 12.