The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been endorsed by the ANZCTR. Before participating in a study, talk to your health care provider and refer to this information for consumers
Trial details imported from

For full trial details, please see the original record at

Registration number
Ethics application status
Date submitted
Date registered
Date last updated

Titles & IDs
Public title
Physiological Effects of Nitrous Oxide on Anaesthesia
Scientific title
Nitrous Oxide and Inhalational Agent Pharmacokinetics During Anaesthetic Induction and Emergence
Secondary ID [1] 0 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Anesthesia 0 0
Condition category
Condition code

Study type
Description of intervention(s) / exposure
Treatment: Drugs - sevoflurane on air/O2
Treatment: Drugs - sevoflurane in N2O/O2

Experimental: Air/Oxygen - Sevoflurane with Air/Oxygen Mix

Experimental: sevoflurane in N2O/O2 -

Treatment: Drugs: sevoflurane on air/O2
sevoflurane on air/O2

Treatment: Drugs: sevoflurane in N2O/O2
sevoflurane in N2O/O2

Intervention code [1] 0 0
Treatment: Drugs
Comparator / control treatment
Control group

Primary outcome [1] 0 0
Pa t/Pa0 Sevo (Arterial Partial Pressure of Sevoflurane), t=Time(Minutes) - Rate of fall in the arterial partial pressure of sevoflurane relative to baseline at 2 minutes (Pa 2/Pa0 Sevo), 5 minutes (Pa 5/Pa0 Sevo, and 30 minutes (Pa 30/Pa0 Sevo)
Timepoint [1] 0 0
Baseline, 2 minutes, 5 minutes, and 30 minutes after emergence
Primary outcome [2] 0 0
PA t/PA0 Sevo (End Tidal Partial Pressure of Sevoflurane), t=Time (Minutes) - Rate of fall in the end-tidal partial pressure of sevoflurane relative to baseline at 2 minutes (PA2/PA0 sevo) and 5 minutes (PA5/PA0 sevo)
Timepoint [2] 0 0
Baseline, 2 minutes, and 5 minutes after emergence
Secondary outcome [1] 0 0
Time to Eye Opening - The time to eye opening to command after cessation of inhalational anaesthetic administration
Timepoint [1] 0 0
20 Minutes

Key inclusion criteria
- Adult patients undergoing elective general or orthopaedic surgery under relaxant
general anaesthesia anticipated to take >1 hour
Minimum age
18 Years
Maximum age
No limit
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
- Age under 18 years

- Morbid obesity BMI > 35

- Severe or moderately severe lung disease (FEV1 < 1.0L, FEV1/FVC < 50%)

- Past history of severe post-operative nausea and vomiting

- Pregnancy

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s

Intervention assignment
Other design features
Phase 4
Type of endpoint(s)
Statistical methods / analysis

Recruitment status
Data analysis
Reason for early stopping/withdrawal
Other reasons
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment hospital [1] 0 0
Austin Health - Melbourne
Recruitment postcode(s) [1] 0 0
3084 - Melbourne

Funding & Sponsors
Primary sponsor type
Austin Health

Ethics approval
Ethics application status

Brief summary
Nitrous oxide is the oldest anaesthetic agent still in routine use today. Despite huge
changes in the pharmacology of volatile anaesthetic agents and intravenous anaesthetics, the
unique properties of nitrous oxide have maintained its place in modern practice, where it is
used in combination with other, more powerful inhaled agents, such as sevoflurane. It has
useful analgesic properties, unlike the other agents used today, and its inclusion reduces
the concentration of other agents required to maintain an adequate depth of anaesthesia for

In particular, its low solubility in body tissues gives it a unique pharmacokinetic profile,
with rapid washin and washout from the body. It has been shown to have a similar effect on
the speed of uptake of accompanying agents like sevoflurane (the "second gas effect"), which
have much slower pharmacokinetics. A recent study by us suggested that this promotes faster
and smoother onset of anaesthesia, as measured using the standard monitor of depth of
anaesthesia (the BIS monitor). This finding requires confirmation prospectively in a larger
group of patients. The investigators further hypothesise that a similar effect also exists on
washout of sevoflurane at the end of the procedure, promoting quicker recovery (emergence)
from anaesthesia. This has never been previously demonstrated. This information will help
better define the place of nitrous oxide in achieving optimal outcomes in modern anaesthetic
practice. The investigators propose to conduct a simple study to measure the effects of
nitrous oxide washin and washout on exhaled concentrations of accompanying sevoflurane during
both induction of anaesthesia and emergence, and identify any accompanying effect on the rate
of change in depth of anaesthesia using BIS. The investigators hypothesise that the rate of
fall of exhaled sevoflurane concentration at the end of anaesthesia will be more rapid in the
group of patients breathing a gas mixture containing nitrous oxide, and that the rate of fall
of BIS on induction and the rate of rise of BIS on emergence will be faster in the nitrous
oxide group.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 0 0
Phil Peyton, MBBS
Address 0 0
Austin Health
Country 0 0
Phone 0 0
Fax 0 0
Email 0 0
Contact person for public queries
Name 0 0
Address 0 0
Country 0 0
Phone 0 0
Fax 0 0
Email 0 0
Contact person for scientific queries

Summary results
Other publications