Condition category
Injury, Occupational Diseases, Poisoning
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status
No longer recruiting

Plain English Summary

Background and study aims
Very fat (obese) people have a large belly that presses the lungs upwards and squeezes them, making the lungs smaller. When a person is unconscious due to anesthesia, their breathing is less efficient. This is why obese people have a risk of low oxygen levels in the blood when they are put to sleep before surgery, compared to people with normal weight. The risk of low oxygen continues after the surgery has been completed, when the person is being cared for in the post-operative ward.
This study will compare two different ways of improving oxygen levels in patients undergoing weight loss (bariatric) surgery. The usual way is for the patient to breathe extra oxygen using a face mask. Another way is to deliver the oxygen into the nose. This study aims to recruit 40 patients to compare the two methods. The study’s findings should help to find the best way of preventing low oxygen levels.

Who can participate
Adult between 18 and 60 years without serious diseases undergoing weight loss surgery.

What does the study involve?
Participants are asked to join this study before their planned operation. Participants are randomly allocated to one of the two groups. All patients will have an arterial line (needle and tube that stays in the artery) placed in the wrist to make it possible to get blood samples to measure the oxygen content in the blood. Before the start of anesthesia, the participant will breathe oxygen for 5-10 minutes. Blood samples are collected during this time. After surgery blood samples are collected during the first hour at the post-operative ward.

What are the possible benefits and risks of participating?
Placing the arterial line can cause some pain and occasionally minor bleeding. Possible benefits could be a more comfortable way of oxygenating and more careful monitoring in routine practice.

Where is the study run from?
The study is run from Uppsala University Hospital, Sweden and takes place at Samariterhemmets Hospital in Uppsala, Sweden.

When is the study starting and how long is it expected to run for?
October 2018 to December 2019 (updated 03/07/2019, previously: June 2019)

Who is funding the study?
Uppsala Regional Council

Who is the main contact?
1. Associate Professor Peter Frykholm (scientific contact)
2. Dr. Diddi Fors (public contact)

Trial website

Contact information



Primary contact

Dr Diddi Fors


Contact details

Dept. of Anaesthesia and Intensive Care
Uppsala University Hospital.



Additional contact

Prof Peter Frykholm


Contact details

Dept. of Anaesthesia and Intensive Care
Uppsala University Hospital

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

Trans-nasal humidified high flow oxygen for preoxygenation in bariatric surgery. A randomized controlled trial



Study hypothesis

Morbidly obese patients are more likely to have significant impairment of pulmonary gas exchange and respiratory mechanics. Furthermore, they are at risk of oxygen desaturation more rapidly than non-obese patients during apnea, which occurs when the patient is anesthetized before the trachea is intubated. We hypothesize that high flow humidified nasal oxygen (HFNO) may increase the efficacy of preoxygenation compared to spontaneous breathing though a face mask.

Ethics approval

Uppsala Regional Ethics Review Board, 04/04/2018, Dnr 2018-007

Study design

Randomized controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use contact details to request a participant information sheet.


Pre-intubation apnea following anesthesia in obese patients undergoing bariatric surgery


Normally in bariatric surgery, the patient is pre-oxygenated during anesthetic induction with 100% oxygen through a face mask until anesthetic induction is completed and the trachea is intubated. After surgery, at the postoperative ward they receive nasal oxygen supply of 2-4 l/min. Half of the patients will be block randomized to be pre-oxygenated with high flow (70 l/min) nasal 100% oxygen during anesthetic induction and postoperatively with 40 l/min 30% oxygen using Armstrong Medical's Peri-Operative Insufflatory Nasal Therapy (POINT) system. The other half will receive the usual oxygenation.

Intervention type



Drug names

Primary outcome measure

1. End-tidal oxygen concentration (EtO2) in breath measured at baseline, every 2.5 min until 10 min and after tracheal intubation by the ventilator (Maquet FLOW-i®)
2. Blood gases measured at baseline, every 2.5 minutes until 10 minutes and after tracheal intubation using Abbott's i-STAT®1 portable blood gas analyser. Blood gases are also measured on arrival at the postoperative ward and at 30 and 60 min after arrival.

Secondary outcome measures

1. End-tidal carbon dioxide concentration (EtCO2) in breath measured by the ventilator (Maquet FLOW-i®)
2. Peripheral capillary oxygen saturation (SpO2; a measure of haemoglobin oxygenation in blood) measured using the Draeger Infinity® Delta monitor
3. Heart rate measured using the Draeger Infinity® Delta monitor
4. Blood pressure measured using the Draeger Infinity® Delta monitor
All secondary outcome measures are measured at baseline, every 2.5 min until 10 min and after tracheal intubation.

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Patients undergoing bariatric surgery due to morbid obesity
2. American Society of Anesthesiologists (ASA) Classification I or II
3. Able to understand participant information sheet and give written consent

Participant type


Age group




Target number of participants


Total final enrolment


Participant exclusion criteria

1. New York Heart Association (NYHA) Functional Classification >II
2. COPD or asthma causing restrictions in daily activities
3. Restrictive lung disease associated with a reduction of total lung capacity (TLC) of >20%
4. Allergy to any of the anesthetic agents used in the study

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Uppsala University Hospital
Dept. of Anaesthesiology and Intensive Care

Sponsor information


Uppsala Regional Council

Sponsor details

P.O. Box 602

Sponsor type




Funder type


Funder name

Uppsala Regional Council

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Planned publication in a high-impact peer-reviewed journal.

IPD sharing statement:
The datasets generated and/or analysed during the current study during this study will be included in the subsequent results publication.

Intention to publish date


Participant level data

Not expected to be available

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes

06/03/2020: The recruitment end date was changed from 29/02/2020 to 11/02/2020. 05/03/2020: The total final enrolment was added. 15/01/2020: The following changes have been made: 1. The recruitment end date has been changed from 31/12/2019 to 29/02/2020. 2. The overall trial end date has been changed from 31/12/2019 to 15/03/2020. 03/07/2019: The following changes were made to the trial record: 1. The recruitment end date was changed from 25/06/2019 to 31/12/2019. 2. The overall end date was changed from 30/06/2019 to 31/12/2019. 3. The intention to publish date was changed from 30/06/2020 to 21/12/2020. 4. The plain English summary was updated to reflect these changes.