Airway AnesthesiaPREFLOW2NCT06736132
Comparison of Different Oxygen Flow Rates During Preoxygenation Using High-Flow Nasal Oxygen
A study testing High-flow nasal oxygen in people with Airway Anesthesia and Preoxygenation, run by Region Stockholm at 1 site in Sweden.
Trial summary
High-flow nasal oxygen (HFNO) has been used for many years to help people with breathing difficulties in the intensive care and after surgery. More recently, it has become a helpful tool during induction of anaesthesia to prevent oxygen levels from dropping when managing the airway. Read more about this study
- Who is it for?
- Ages 18 to 84 yearsHealthy volunteers can take part
- Conditions the study is for
- Airway Anesthesia, Preoxygenation, High Flow Nasal Canula
- What is being tested?
- High-flow nasal oxygen
- Type of treatment
- Medical device
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 75 participants
- Where
- 1 siteSweden
- Study dates
- 13 Jan 2025to Dec 2026
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 84 years
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- Adult, 18-84 years old
- ASA 1-3
- BMI < 35
- Planned for elective surgery
Who cannot join
- Cardiac disease (ischemic heart disease, heart failure (NYHA ≥2), ongoing arrhythmias, pulmonary hypertension)
- Severe asthma, moderate to severe COPD
- Pregnancy
- Smokers or former smoker last finished 1 year before inclusion
- Baseline oxygen saturation < 95%
- Nasal obstruction
Show all 9Show fewer
- Known or anticipated difficult airway
- Patients with electrical active implants where lung impedance analysis is contraindicated
- Not capable of understanding study information and signing a written consent
Trial locations and contacts
1 site in 1 country.
About this study
High-flow nasal oxygen (HFNO) has been used for many years to help people with breathing difficulties in the intensive care and after surgery. More recently, it has become a helpful tool during induction of anaesthesia to prevent oxygen levels from dropping when managing the airway. HFNO is particularly effective at delivering oxygen even when a patient is not breathing (apnoea), making it useful during surgeries on the voice box (larynx) because it eliminates the need for a breathing tube, giving surgeons a clear view.
HFNO is now also being used to prepare patients for anaesthesia (preoxygenation). Research shows that it works just as well as traditional tight-fitting oxygen masks while offering added benefits like better comfort for patients, easier handling for anaesthetists, and a smooth transition to oxygen delivery during apnoea.
Read more
One reason HFNO is effective is that it creates a mild pressure in the lungs, called positive end-expiratory pressure (PEEP), which improves oxygen storage in the lungs. This pressure depends on the flow rate of oxygen and is higher when the patient keeps their mouth closed. For every increase of 10 liters per minute in flow rate, HFNO generates 1 cmH2O of PEEP. This pressure helps increase the lung's capacity to hold oxygen, making the process of preoxygenation more efficient.
Most studies on HFNO for preoxygenation have used flow rates of up to 60 liters per minute. However, we don't yet know if higher flow rates could further improve preoxygenation or extend the time patients can safely go without breathing.
Read the detailed description
High-flow nasal oxygen (HFNO) has long been employed to address respiratory distress in both the intensive care unit and post-anaesthesia unit. Over the past decade, HFNO has emerged as a valuable tool for preventing oxygen desaturation during airway management in the operating theatre. Notably, HFNO demonstrates effectiveness in oxygenating patients during extended periods of apnoea, providing a reliable method for apnoeic oxygenation. This technique serves as an alternative to mechanical ventilation in laryngeal surgical procedures, offering potential advantages such as a clear operating field for surgeons without the interference of a tracheal tube.
More recently, HFNO has found application in preoxygenation before anaesthesia induction. Studies indicate that the preoxygenation efficacy of HFNO is comparable to that of a standard tight-fitting facemask, with added benefits including enhanced patient comfort, improved ease of use as assessed by anaesthetists, and the potential for a seamless transition to apnoeic oxygenation.
One of the suggested mechanisms contributing to the favourable outcomes observed with HFNO in managing patients with respiratory distress is a flow-dependent positive end-expiratory pressure (PEEP) effect. When patients breathe with a closed mouth, HFNO appears to generate a PEEP effect of 1 cmH2O for every 10 l.min-1 of flow. Prior data has demonstrated that an elevated PEEP leads to a greater functional residual capacity (FRC) and improved preoxygenation effectiveness.
Previous studies investigating HFNO for preoxygenation have used flow rates ≤ 60 l.min-1. Consequently, the impact of higher flow rates on preoxygenation effectiveness and the extension of safe apnoea time remains uncertain.
In this randomised prospective study, we aim to investigate the effectiveness of preoxygenation from HFNO using different flow rates. Seventy-five patients (25 per group) scheduled for elective surgery at the Karolinska University Hospital, will be recruited. After a signed consent, the subject will be enrolled and randomised to preoxygenation using HFNO at flow rates of 45 l/min, 70 l/min or 95 l/min.
Routine perioperative monitoring, such as peripheral oxygen saturation (SpO2) and non-invasive blood pressure will be performed. Preoperatively, an arterial catheter will be inserted. An arterial blood gas will be attained before preoxygenation for base line data regarding PaCO2, PaO2 and pH.
To enable lung impedance measurement, all subjects will be applied an appropriately sized circumferential 16-electrode belt around the torso between the fourth and sixth intercostal spaces.
Patients will be positioned supine with the head elevated at 15 degrees. All groups will undergo preoxygenation using HFNO with the flow rate determined by the randomisation. All groups will be preoxygenated for 3 minutes using 100% oxygen and closed-mouth breathing. Immediately prior to anaesthesia induction, patients will evaluate the level of discomfort of preoxygenation. Thereafter, anaesthesia is induced.
Preoxygenation will be administered to all patients until the onset of apnoea, at which point oxygen delivery via HFNO will be immediately discontinued. The patient will then undergo intubation, with apnoea maintained until their oxygen saturation drops to 93%. Once this threshold is reached, mechanical ventilation with 100% oxygen will be initiated.
- Conditions
- Airway Anesthesia, Preoxygenation, High Flow Nasal Canula
- Being tested
- High-flow nasal oxygen
- Keywords
- Preoxygenation, High-flow nasal oxygen, Anaesthesia induction
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
High-flow nasal oxygenDevice
In this study, we will use high-flow nasal oxygen for preoxygenation in patients undergoing elective anaesthesia. Preoxygenation with high-flow nasal oxygen is most often performed at flow rates of <50 l/min. In this study, patients will be randomised to preoxygenation using high-flow nasal oxygen and flow rates of 45 l/min, 70 l/min or 95 /min.
| Study group | Role | What they receive |
|---|---|---|
| High-flow nasal oxygen, flow rate 45 l/min | Active comparator | Preoxygenation using high-flow nasal oxygen with a flow rate of 45 l/min Receives: Device: High-flow nasal oxygen |
| High-flow nasal oxygen, flow rate 70 l/min | Experimental | Preoxygenation using high-flow nasal oxygen with a flow rate of 70 l/min Receives: Device: High-flow nasal oxygen |
| High-flow nasal oxygen, flow rate 95 l/min | Experimental | Preoxygenation using high-flow nasal oxygen with a flow rate of 95 l/min Receives: Device: High-flow nasal oxygen |
What is being measured
The primary outcome is the main question the study is designed to answer.
Safe apnoea time
Comparison of the time from start of apnoea until reaching a SpO2 = 93% between the different flow rates
Measured: From start of apnoea after anaesthesia induction until peripheral oxygen saturation drops to 93%. This time fram will probably be between 5 and 15 minutes.
Secondary outcomes (4)
Tolerance of 360 seconds of apnoea
Comparison between the three groups of the proportion of patients tolerating 360 seconds of apnoea
Measured: From apnoea start until 5 minutes of apnoea
Arterial oxygen levels during preoxygenation
Comparison between the groups in PaO2 at 1 minute and 2 minutes of preoxygenation and at the start of apnoea
Measured: From start of preoxygenation until end of preoxygenation (approximately 3 to 4 minutes)
Discomfort assessment
Comparision between the groups in the level of discomfort during preoxygenation. Discomfort will be assessed on a scale from 1 to 10 (0 = no discomfort, 10 = maximal discomfort)
Measured: From start of preoxygenation until the end of preoxygenation, this time fram will be three minutes.
Lung impedance changes
Lung impedance measurement will be conducted before preoxygenation (baseline) after three minutes of pre-oxygenation and at the end of apnoea. Comparisons of these values, at the different time points, will be conducted between the three groups.
Measured: From start of preoxygenation until end of apnoea (approximately 5 to 15 minutes)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted16 Dec 2024
- Study start13 Jan 2025
- Primary completionJun 2026 (estimated)
- Study completionDec 2026 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for Airway AnesthesiaStudies of the same condition, open and under way.
- More trials run by Region StockholmThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Randomised controlled trial
- Masking
- Double blind
- Who is masked
- Participant, Care provider
- Enrolment
- 75 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Region Stockholm
- Sponsor type
- Other government
- Collaborators
- Karolinska Institutet
- Responsible party
- Principal investigator, Albin Sjöblom, Region Stockholm
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06736132
- Sponsor's protocol ID
- DNR: 2024-04565-01
- Other IDs
- SLS-1000363 & SLS-999871
- Acronym
- PREFLOW2
- Status last verified
- Dec 2024
- First submitted
- 9 Dec 2024
- Last updated
- 27 Jun 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No: The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available because they contain information that could compromise the privacy of research participants.
Publications
Sjoblom A, Hoffman F, Hedberg M, Forsberg IM, Jonsson Fagerlund M. Preoxygenation with high-flow nasal oxygen at various flow rates in elective surgical patients: a prospective, randomised, single-blind clinical trial. Br J Anaesth. 2026 Mar;136(3):983-990. doi: 10.1016/j.bja.2025.11.017. Epub 2025 Dec 18.
PubMed 41419379
Study at a glance
From the registry record, last updated by the sponsor on 27 Jun 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Comparison of Different Oxygen Flow Rates During Preoxygenation Using High-Flow Nasal Oxygen
- ClinicalTrials.gov ID
- NCT06736132
- Acronym / sponsor ID
- PREFLOW2 / DNR: 2024-04565-01
- Conditions
- Airway Anesthesia, Preoxygenation, High Flow Nasal Canula
- Keywords
- Preoxygenation, High-flow nasal oxygen, Anaesthesia induction
- Study type
- Interventional
- Recruitment status
- Active, not recruiting
- Enrolment
- 75 participants (estimated)
- Lead sponsor
- Region StockholmOther government
- Collaborators
- Karolinska Institutet
- Study start
- 13 Jan 2025 (actual)
- Primary completion
- Jun 2026 (estimated)
- Study completion
- Dec 2026 (estimated)
- First posted
- 16 Dec 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
High-flow nasal oxygen (HFNO) has been used for many years to help people with breathing difficulties in the intensive care and after surgery. More recently, it has become a helpful tool during induction of anaesthesia to prevent oxygen levels from dropping when managing the airway. HFNO is particularly effective at delivering oxygen even when a patient is not breathing (apnoea), making it useful during surgeries on the voice box (larynx) because it eliminates the need for a breathing tube, giving surgeons a clear view.
HFNO is now also being used to prepare patients for anaesthesia (preoxygenation). Research shows that it works just as well as traditional tight-fitting oxygen masks while offering added benefits like better comfort for patients, easier handling for anaesthetists, and a smooth transition to oxygen delivery during apnoea.
One reason HFNO is effective is that it creates a mild pressure in the lungs, called positive end-expiratory pressure (PEEP), which improves oxygen storage in the lungs. This pressure depends on the flow rate of oxygen and is higher when the patient keeps their mouth closed. For every increase of 10 liters per minute in flow rate, HFNO generates 1 cmH2O of PEEP. This pressure helps increase the lung's capacity to hold oxygen, making the process of preoxygenation more efficient.
Most studies on HFNO for preoxygenation have used flow rates of up to 60 liters per minute. However, we don't yet know if higher flow rates could further improve preoxygenation or extend the time patients can safely go without breathing.
Detailed description
High-flow nasal oxygen (HFNO) has long been employed to address respiratory distress in both the intensive care unit and post-anaesthesia unit. Over the past decade, HFNO has emerged as a valuable tool for preventing oxygen desaturation during airway management in the operating theatre. Notably, HFNO demonstrates effectiveness in oxygenating patients during extended periods of apnoea, providing a reliable method for apnoeic oxygenation. This technique serves as an alternative to mechanical ventilation in laryngeal surgical procedures, offering potential advantages such as a clear operating field for surgeons without the interference of a tracheal tube.
More recently, HFNO has found application in preoxygenation before anaesthesia induction. Studies indicate that the preoxygenation efficacy of HFNO is comparable to that of a standard tight-fitting facemask, with added benefits including enhanced patient comfort, improved ease of use as assessed by anaesthetists, and the potential for a seamless transition to apnoeic oxygenation.
One of the suggested mechanisms contributing to the favourable outcomes observed with HFNO in managing patients with respiratory distress is a flow-dependent positive end-expiratory pressure (PEEP) effect. When patients breathe with a closed mouth, HFNO appears to generate a PEEP effect of 1 cmH2O for every 10 l.min-1 of flow. Prior data has demonstrated that an elevated PEEP leads to a greater functional residual capacity (FRC) and improved preoxygenation effectiveness.
Previous studies investigating HFNO for preoxygenation have used flow rates ≤ 60 l.min-1. Consequently, the impact of higher flow rates on preoxygenation effectiveness and the extension of safe apnoea time remains uncertain.
In this randomised prospective study, we aim to investigate the effectiveness of preoxygenation from HFNO using different flow rates. Seventy-five patients (25 per group) scheduled for elective surgery at the Karolinska University Hospital, will be recruited. After a signed consent, the subject will be enrolled and randomised to preoxygenation using HFNO at flow rates of 45 l/min, 70 l/min or 95 l/min.
Routine perioperative monitoring, such as peripheral oxygen saturation (SpO2) and non-invasive blood pressure will be performed. Preoperatively, an arterial catheter will be inserted. An arterial blood gas will be attained before preoxygenation for base line data regarding PaCO2, PaO2 and pH.
To enable lung impedance measurement, all subjects will be applied an appropriately sized circumferential 16-electrode belt around the torso between the fourth and sixth intercostal spaces.
Patients will be positioned supine with the head elevated at 15 degrees. All groups will undergo preoxygenation using HFNO with the flow rate determined by the randomisation. All groups will be preoxygenated for 3 minutes using 100% oxygen and closed-mouth breathing. Immediately prior to anaesthesia induction, patients will evaluate the level of discomfort of preoxygenation. Thereafter, anaesthesia is induced.
Preoxygenation will be administered to all patients until the onset of apnoea, at which point oxygen delivery via HFNO will be immediately discontinued. The patient will then undergo intubation, with apnoea maintained until their oxygen saturation drops to 93%. Once this threshold is reached, mechanical ventilation with 100% oxygen will be initiated.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Double blind (participant, care provider)
- Number of arms
- 3
- Model description
- Randomised controlled trial
| Arm | Type | Receives |
|---|---|---|
| High-flow nasal oxygen, flow rate 45 l/min | Active comparator | Device: High-flow nasal oxygenPreoxygenation using high-flow nasal oxygen with a flow rate of 45 l/min |
| High-flow nasal oxygen, flow rate 70 l/min | Experimental | Device: High-flow nasal oxygenPreoxygenation using high-flow nasal oxygen with a flow rate of 70 l/min |
| High-flow nasal oxygen, flow rate 95 l/min | Experimental | Device: High-flow nasal oxygenPreoxygenation using high-flow nasal oxygen with a flow rate of 95 l/min |
Who may qualify
- Ages
- 18 to 84 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (4 listed)
- Adult, 18-84 years old
- ASA 1-3
- BMI < 35
- Planned for elective surgery
Key exclusion criteria (9 listed)
- Cardiac disease (ischemic heart disease, heart failure (NYHA ≥2), ongoing arrhythmias, pulmonary hypertension)
- Severe asthma, moderate to severe COPD
- Pregnancy
- Smokers or former smoker last finished 1 year before inclusion
- Baseline oxygen saturation < 95%
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| High-flow nasal oxygenIn this study, we will use high-flow nasal oxygen for preoxygenation in patients undergoing elective anaesthesia. Preoxygenation with high-flow nasal oxygen is most often performed at flow rates of <50 l/min. In this study, patients will be randomised to preoxygenation using high-flow nasal oxygen and flow rates of 45 l/min, 70 l/min or 95 /min. | Device | High-flow nasal oxygen, flow rate 45 l/min, High-flow nasal oxygen, flow rate 70 l/min, High-flow nasal oxygen, flow rate 95 l/min |
Primary outcome
Safe apnoea time
Time frame: From start of apnoea after anaesthesia induction until peripheral oxygen saturation drops to 93%. This time fram will probably be between 5 and 15 minutes.
Comparison of the time from start of apnoea until reaching a SpO2 = 93% between the different flow rates
4 secondary outcomes
Tolerance of 360 seconds of apnoea
Time frame: From apnoea start until 5 minutes of apnoea
Arterial oxygen levels during preoxygenation
Time frame: From start of preoxygenation until end of preoxygenation (approximately 3 to 4 minutes)
Discomfort assessment
Time frame: From start of preoxygenation until the end of preoxygenation, this time fram will be three minutes.
Lung impedance changes
Time frame: From start of preoxygenation until end of apnoea (approximately 5 to 15 minutes)
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 27 Jun 2025.
- Derived from this study: PubMed 41419379Sjoblom A, Hoffman F, Hedberg M, Forsberg IM, Jonsson Fagerlund M. Preoxygenation with high-flow nasal oxygen at various flow rates in elective surgical patients: a prospective, randomised, single-blind clinical trial. Br J Anaesth. 2026 Mar;136(3):983-990. doi: 10.1016/j.bja.2025.11.017. Epub 2025 Dec 18.
- Individual participant dataSharing planned: No. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available because they contain information that could compromise the privacy of research participants.
Related trials for Airway Anesthesia
Recruiting
Hyperangulated vs. Macintosh Style Blades for Intubation in Obstetric Patients
Obstetric, Cesarean Birth
Not yet recruitingPhase 4
Effect of Neuromuscular Blocking Agent Use on Video Laryngeal Mask Airway Insertion
Airway Management, Supraglottic Airway Device Insertion
Not yet recruiting
Video Laryngeal Mask SaCoVLM Versus LMA Supreme and Ambu AuraGain in Children
Airway Management, Anesthesia, General
Enrolling by invitationObservational study
ETCO₂ Targeting and Cerebral Oxygenation
Airway Reactivity, Hemodynamic Stability During Anesthesia
Not yet recruiting
Pharyngeal Mucosal Conditioning to Prevent Postoperative Sore Throat in Septoplasty Patients With Severe Nasal Obstruction
Postoperative Sore Throat, Nasal Obstruction
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing High-flow nasal oxygen in people with Airway Anesthesia and Preoxygenation, run by Region Stockholm at 1 site in Sweden.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 9 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: under way, not looking for participants, as of the sponsor's last update on 27 Jun 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Sweden. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Safe apnoea time (time frame: From start of apnoea after anaesthesia induction until peripheral oxygen saturation drops to 93%. This time fram will probably be between 5 and 15 minutes.). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT06736132, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 27 Jun 2025.