Capillary Refill Index with Rewarming

A new technology, capillary refill index (CRI) can be useful for assessing peripheral perfusion status quantitatively, but this value can be influenced by fingertip temperature. The aim of this study is to evaluate the predictive accuracy of CRI after a temperature control (warming) procedure in predicting 30-day mortality among ICU/CCU patients. The investigators hypothesized that lowered fingertip temperature can lead prolonged CRI values which are considered as false positives in detection of high-risk patients for mortality, because it causes poor peripheral perfusion which does not reflect hemodynamic instability. The investigators will use the warming procedure to remove or reduce the effect of the fingertip temperature on the CRI measurement and will analyze whether it contributes to reduction of false positives in detection of high-risk patients for mortality.

Capillary refill time (CRT) test is a simple and noninvasive method typically used to assess peripheral blood perfusion at the bedside. CRT is defined as the time required for a distal capillary bed (e.g., fingertip) to regain its color after having received enough compression to cause blanching \[1\]. Because a prolonged CRT suggests a decrease in peripheral perfusion and poor peripheral perfusion is strongly associated with patients' mortality, several studies reported the clinical usefulness of CRT for predicting patients' mortality in the critical care setting \[2,3\]. However, because the conventional CRT test depends on clinicians' subjective visual assessment, the inter-rater agreement of it has been questioned, and substantial clinical experience is needed to acquire the reliable skill to measure CRT \[4, 5, 6, 7\]. Therefore, there is great demand for the creation of objective methods to easily assess peripheral blood perfusion.

Previously, the investigators developed a new mechanical device by using pulse oximetry waveforms, which can enable us to measure CRT easily and objectively. The measurement obtained with this device is called Capillary Refill Index (CRI) to differentiate it from traditional visual assessment of CRT \[8\]. The method calculates the time it takes for blood to return to the fingertip after release from compression by algorithmically analyzing the light intensity waveform of a normal pulse oximeter sensor attached to a patient's fingertip. The investigators' previous study showed that CRI can be an alternative to traditional CRT for assessing peripheral blood perfusion \[8, 9, 10\].

In the investigators previous study with healthy volunteer subjects \[11\], the investigators found that lowered fingertip temperature is a critical component that affects measurement values of CRI, which is the same phenomena with the traditional CRT. Since lowered skin temperature causes poor peripheral perfusion, the patients with lower fingertip temperature can show prolonged CRI without reflecting hemodynamic instability, which means lower skin temperature can increase false positives when using CRI to detect patients at high risk for mortality. The investigators hypothesize that the predictive accuracy of CRI for detecting patients at increased risk for mortality may be improved if the patients' skin temperature is warmed up before the measurement.

Eligibility Criteria:
Inclusion Criteria:

* 18 years of age or older;
* Admitted to any ICU of North Shore University Hospital (NSUH) within 24 hours

Exclusion Criteria:

* Pregnant
* Prisoners
* Finger, hand or forearm anatomical anomaly or disease that may interfere with attaching a pulse oximeter sensor
* Patients who are not deemed clinically stable by the clinical team
* Wearing nail polish, nail gel, or nail decorations