Local Warming to Improve Pulse Oximetry Accuracy in Critically Ill Patients (PULSEWARM)

Effect of Local Warming on Pulse Oximetry Accuracy in Critically Ill Patients With Low Peripheral Perfusion: A Multicenter Randomized Controlled Trial

Pulse oximeters are widely used in intensive care to continuously estimate the oxygen level in the blood. However, pulse oximeter measurements may be less accurate when blood flow to the fingers is poor, which is common in critically ill patients.

This study will investigate whether warming the hand and lower part of the forearm can improve the accuracy of pulse oximeter measurements in mechanically ventilated adult intensive care patients with low blood flow to the fingers.

Participants will be randomly assigned to either a local warming strategy or usual care without warming. In the warming group, the hand and lower forearm will be warmed for 15 minutes to a target temperature of 41-42°C. Pulse oximeter measurements will be compared with oxygen saturation measured from an arterial blood sample before and after the intervention.

The main objective is to determine whether local warming reduces the difference between pulse oximeter oxygen saturation (SpO₂) and arterial oxygen saturation (SaO₂) 15 minutes after the start of the assigned strategy. The study will also assess whether any improvement persists at 60 minutes, how peripheral blood flow changes during 4 hours of follow-up, whether repeat warming is effective when blood flow decreases again, and whether the effect differs according to skin phototype. Safety related to the warming intervention will also be evaluated.

Study Overview

• Status: Not yet recruiting
• Conditions: Critical Illness; Low Peripheral Perfusion; Pulse Oximetry Accuracy
• Intervention / Treatment: Other: Protocolized Local Warming

Detailed Description

Pulse oximetry is a fundamental component of monitoring and oxygen titration in critically ill patients. Its accuracy may, however, be impaired by reduced peripheral perfusion. Low peripheral perfusion is common in mechanically ventilated intensive care patients and may contribute to clinically relevant differences between peripheral oxygen saturation measured by pulse oximetry (SpO₂) and arterial oxygen saturation measured by blood gas analysis (SaO₂).

Local warming increases cutaneous blood flow and is routinely used to improve peripheral perfusion during procedures such as capillary blood sampling. Preliminary single-center data suggest that local warming may also improve pulse oximetry accuracy in critically ill patients with low peripheral perfusion. Whether this effect is present when evaluated in a randomized controlled trial is unknown.

This is a prospective, multicenter, parallel-group randomized controlled strategy trial conducted in four intensive care units. Mechanically ventilated adult ICU patients with an arterial catheter and a finger perfusion index (PFI) <1.0 will be randomized in a 1:1 ratio to a protocolized local warming strategy or usual care without protocolized warming. Randomization will be stratified by study site and Fitzpatrick skin phototype.

In the intervention group, local warming will be applied to the dorsum of the hand and distal forearm for 15 minutes, with a target interface temperature of 41-42°C. Repeat warming is permitted during follow-up if finger PFI decreases below 0.5 according to the prespecified study strategy. The control group will receive usual care without protocolized local warming.

SpO₂, finger PFI, earlobe PFI, and arterial SaO₂ will be assessed at baseline, 15 minutes, and 60 minutes. Additional PFI measurements will be obtained at 120 and 240 minutes. Oxygen therapy will otherwise be managed according to standard clinical care.

The primary objective is to compare pulse oximetry bias between the randomized groups at 15 minutes. Bias is defined as SpO₂ minus SaO₂, expressed in percentage points. The primary analysis will compare the groups using an analysis of covariance adjusted for baseline SpO₂-SaO₂ bias and study site.

Secondary objectives include assessment of pulse oximetry accuracy at 60 minutes, the proportion of measurements within ±2 percentage points of SaO₂, changes in peripheral perfusion during 4 hours of follow-up, the local versus systemic perfusion response assessed using finger and earlobe PFI, the response to repeat warming, safety outcomes, and possible treatment-effect modification according to Fitzpatrick skin phototype.

The planned sample size is 240 participants, with 120 participants allocated to each study group.

• Study Type: Interventional
• Enrollment (Estimated): 240
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Carl Sjödin, PhD student; Phone Number: 0707163277; Email: carl.sjodin@vgregion.se

Study Locations

• Sweden
  • Gothenburg, Sweden
    • Sahlgrenska University Hospital
    • Contact: Carl Sjödin, PhD student; Phone Number: 0707163277; Email: carl.sjodin@vgregion.se
  • Kungälv, Sweden
    • Kungälvs Sjukhus
  • Skövde, Sweden
    • Skaraborgs Sjukhus
  • Trollhättan, Sweden
    • Norra Älvsborgs Sjukhus

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age 18 years or older.
• Admitted to an intensive care unit.
• Receiving invasive mechanical ventilation via endotracheal tube or tracheostomy.
• Existing arterial catheter placed for a clinical indication.
• Objectively verified low peripheral perfusion, defined as finger perfusion index (PFI) <1.0 at screening.
• Stable baseline pulse oximetry signal permitting calculation of the SpO2-SaO2 difference.
• Clinical condition considered sufficiently stable to allow study measurements without interfering with ongoing treatment.

Exclusion Criteria:

• Absence of a stable baseline pulse oximetry signal on all available sensors, preventing calculation of the SpO2-SaO2 difference.
• Skin injury, burn, infection, or other local skin condition of the hand or forearm that prevents safe application of the warming pad or pulse oximetry sensor.
• Clinical instability for which the treating physician considers study participation likely to interfere with acute treatment or patient safety.
• Known hypersensitivity to materials used in the warming pad or sensors.
• Participation in another ongoing interventional study that could affect the primary outcome.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Supportive Care
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Protocolized Local Warming; Participants receive protocolized local warming applied to the dorsum of the hand and distal forearm for 15 minutes, targeting an interface temperature of 41-42°C. Repeat warming is permitted during follow-up if finger perfusion index decreases below 0.5.	Other: Protocolized Local Warming; Local warming is applied to the dorsum of the hand and distal forearm for 15 minutes using a warming device adjusted to achieve a target interface temperature of 41-42°C. During follow-up, repeat warming is permitted if finger perfusion index decreases below 0.5.
No Intervention: Usual Care Without Protocolized Warming; Participants receive usual care without protocolized local warming. Oxygen therapy and all other clinical management are provided according to standard intensive care practice.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
SpO2-SaO2 Bias at 15 Minutes	Pulse oximetry bias is defined as peripheral oxygen saturation measured by pulse oximetry (SpO2) minus arterial oxygen saturation measured by blood gas analysis (SaO2), expressed in percentage points. The primary analysis will compare SpO2-SaO2 bias between the local warming and control groups at 15 minutes, adjusted for baseline bias and study site.	15 minutes after initiation of the randomized strategy

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
SpO2-SaO2 Bias at 60 Minutes	Pulse oximetry bias is defined as SpO2 minus SaO2, expressed in percentage points. Bias at 60 minutes will be compared between randomized groups to evaluate durability of the effect of the warming strategy.	60 minutes after initiation of the randomized strategy
Proportion of SpO2 Measurements Within ±2 Percentage Points of SaO2	The proportion of participants with an absolute difference between SpO2 and SaO2 of 2 percentage points or less will be determined at 15 and 60 minutes and compared between randomized groups.	15 and 60 minutes after initiation of the randomized strategy
Change in Finger Perfusion Index	Finger perfusion index (PFI) will be measured serially to assess the peripheral perfusion response to the randomized strategy and its durability during 4 hours of follow-up.	Baseline and 15, 60, 120, and 240 minutes
Difference Between Finger and Earlobe Perfusion Index Response	Changes in perfusion index measured at the finger and earlobe will be compared to assess whether the perfusion response to local warming is predominantly local rather than systemic.	Baseline, 15 minutes, and 60 minutes
Perfusion Index Response to Repeat Local Warming	Among participants in the warming group who undergo repeat warming because finger PFI decreases below 0.5 during follow-up, the change in finger PFI following repeat warming will be assessed to evaluate repeatability of the perfusion response.	Up to 240 minutes after randomization
Warming-Related Adverse Events	Number of participants experiencing adverse events considered related to local warming, including skin injury, erythema requiring discontinuation of warming, or other prespecified adverse reactions during the study period.	From initiation of the randomized strategy through 240 minutes

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Treatment Effect on SpO2-SaO2 Bias According to Fitzpatrick Skin Phototype	Prespecified analysis of treatment-effect modification according to Fitzpatrick skin phototype. The interaction between randomized treatment group and Fitzpatrick skin phototype will be evaluated for the primary outcome of SpO2-SaO2 bias at 15 minutes.	15 minutes after initiation of the randomized strategy

Collaborators and Investigators

• Sponsor: Vastra Gotaland Region
• Collaborators: Skaraborg Hospital; North Älvsborg County Hospital, Trollhättan

Study record dates

Study Major Dates

• Study Start (Estimated): October 1, 2026
• Primary Completion (Estimated): October 1, 2028
• Study Completion (Estimated): December 1, 2028

Study Registration Dates

• First Submitted: August 24, 2026
• First Submitted That Met QC Criteria: August 24, 2026
• First Posted (Actual): August 28, 2026

Study Record Updates

• Last Update Posted (Actual): August 28, 2026
• Last Update Submitted That Met QC Criteria: August 24, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Keywords: Arterial blood gas; Mechanical ventilation; Critically ill patients; Skin pigmentation; Pulse oximetry Oxygen saturation; SpO₂; SaO₂; Peripheral perfusion Perfusion index; Local warming; Fitzpatrick skin phototype
• Additional Relevant MeSH Terms: Pathologic Processes; Disease Attributes; Skin Diseases; Pathological Conditions, Signs and Symptoms; Skin and Connective Tissue Diseases; Critical Illness; Pigmentation Disorders
• Other Study ID Numbers: PULSEWARM-RCT-01

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED
• IPD Plan Description: The feasibility and conditions for sharing de-identified individual participant data have not yet been determined. Any future data sharing will be subject to applicable ethical approvals, data protection regulations, institutional policies, and appropriate data-sharing agreements.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No