Sacral Skin Temperature Assessed by Thermal Imaging: Role of Patient Vascular Attributes

The purpose of this study was to test the hypothesis that temperature differentials measured by thermal imaging of sacral versus a remote skin area in critically ill patients differentiate those with significant vascular disease and risk for pressure injury of the sacral area.

Prospective cohort study.

The sample comprised 100 patients (58 men, 42 women) with mean ± SD ages of 70.4 ± 14.4 and 74.0 ± 14.5 years, respectively, who were admitted to a cardiovascular intermediate care unit or a neurosurgical intensive care unit in the southeastern region of the United States.

A commercially available thermal imaging system was used to obtain simultaneous standard photographic and infrared thermal images (11 × 14 inches) that included the patient's buttocks and a remote skin area after the patient was off-loaded for about 4 minutes. Images were processed to determine temperature differences between the sacral region (deemed to have an elevated risk for pressure injury) and a remote region of the skin located at least 10-cm proximal to the sacrum, with an average sacrum-to-remote distance of 17.9 ± 3.0 cm that was deemed to be at minimal risk. Prior measurements of healthy subjects showed that sacral skin was on average 0.75°C less than the remote skin site (ΔT =-0.75°C). For the present analysis, a threshold ΔTTH of twice that amount (ΔT =-1.5°C) or more was considered to put a patient at greater than normal risk based on the hypothesis that low sacral temperatures were associated with lowered blood perfusion issues of various clinical conditions. The vascular status of patients who equaled or exceeded this threshold was compared to the other patients.

Thirty-two patients exceeded ΔTTH, with an average ΔT of -1.92°C ± 0.62°C. In 6 patients, ΔT was greater than +1.5°C, with average of +1.98°C ± 0.49°C. The remaining 63 patients had an average ΔT of 0.13°C ± 0.58°C. Chi-square analysis of the proportions of patients exceeding or not exceeding thresholds in relation to their known vascular disease status revealed no significant difference between these subgroups.

Although infrared thermal screening may provide visually impressive and potentially useful images in some cases, the use of temperature differentials to detect patients at particularly high risk for pressure injury owing to local blood flow is not supported by results of this study.