Early prediction of pressure injury development using diffuse correlation spectroscopy

Pressure injuries (PIs) are a serious secondary complication for patients with prolonged immobility that are often caused by prolonged ischemia and reperfusion injury. The cost to manage a single full-thickness pressure injury is estimated to be as high as $120,000 and hospitals are not reimbursed for treatment of PIs that are not documented as "present on admission." Detection of early pressure injuries is currently performed through visual inspection. However, these methods are inadequate because they only evaluate the surface of the skin and provide no information to the underlying health of deep tissue, where PIs often manifest. For this reason, deep tissue pressure injury (DTPI) is often not evident until the injury has evolved to an advanced PI and tissue breakdown. Therefore, there is a well-defined need to develop a method to noninvasively examine tissue below the surface of the skin to identify deep tissue pressure injury earlier than it can be detected by current methods. The goals of this research were to enable early detection of PI in high risk patients and to develop a procedure capable of differentiating between patients who develop advanced pressure injuries and those who do not. Diffuse correlation spectroscopy (DCS), a noninvasive optical method, was used to measure microcirculatory blood flow in skin and subcutaneous tissue. Data was collected from the DCS device and analyzed in the form of [tau]_exp, which is a value calculated directly from the measured temporal correlation function (TCF) of scattered light intensity. In addition a multi-distance DCS algorithm was developed in order to calculate the optical properties from multiple TCFs, thereby providing more information on the health of underlying tissue. This method was validated in vitro through the use of optical phantoms and later applied to human data. The DCS device was first tested in a clinical study that included 16 spinal cord injury patients with erythema in the sacrum from a rehabilitation hospital. Patients were measured in a three-step protocol to monitor blood flow during baseline, applied pressure, and released pressure stages. Four of the 16 patients developed an open ulcer (Advanced PIs) while the other 12 patients did not develop an open ulcer (No PIs). The baseline results showed that Advanced PIs had [tau]_exp values 7-8 times lower than No PIs, suggesting Advanced PIs had significantly faster blood flow than that of No PIs. Patients from an acute care setting were also measured, including individuals in the surgical intensive care unit (SICU), individuals in the trauma and surgical step-down units, and surgical patients in the post-anesthesia care unit (PACU). During these studies, several modifications were made to the device in order to increase the efficiency of the protocol and usability for a layperson. The results from these studies showed the same trends found from the rehab study. The patient who developed a PI from the SICU had an average [tau]_exp value about two times lower than that of other SICU patients who did not develop a PI, suggesting faster blood flow. Also the patient who developed a PI from the surgical study had a [tau]_exp value ~2.5 times lower post-op compared to pre-op, the highest ratio among all patients. Furthermore, when applying the multi-distance DCS algorithm to the data collected from surgical patients and showed a difference of 6.5 times between post-op and pre-op blood flow for the patient who developed an Advanced PI. The successful implementation of DCS technology as a pressure injury assessment method would result in improved and personalized patient care. It would permit clinicians to immediately assess the severity and extent of a subcutaneous injury and change the preventive treatment, if needed. It would also decrease morbidity and minimize the hospital's liability to patients who develop PIs in their care.