Local Warming to Improve Pulse Oximetry Accuracy in Critically Ill Patients

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.

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) \