Background: Shock is defined as the condition where there is inadequate tissue perfusion to support cellular function. Currently, there are no methods to help the medic identify when s/he has provided adequate resuscitation from shock. The gut and skeletal muscles are affected earliest in shock and are the last organs to be functionally restored as a result of resuscitation. It has been previously demonstrated that muscle pH is an indicator for the severity of shock and insufficient resuscitation. We have previously shown that muscle pH, muscle PO2 and blood hematocrit, measures of tissue perfusion, can be simultaneously and noninvasively determined using near infrared spectroscopy; however, no portable field instrument exists to perform these measurements on or near the battlefield.

Objective/Hypothesis: This proposal will develop and demonstrate a prototype, portable sensor system based on near infrared spectroscopy to noninvasively measure tissue perfusion on a group of human subjects experiencing hemodilution, hypothermia, and hypotension.

Specific Aims: (1) Design and build novel prototype miniature sensor system for robust collection of spectra. (2) Develop new methodology to transfer calibration equations developed in vivo on a laboratory instrument to the new miniature sensor system. (3) Validate the new miniature sensor system and calibration methods on human subjects. (4) Deliver four systems to the Army for future testing.

Study Design: We will partner with a local and highly respected medical optics company (Luxtec Corp.) to design the miniature sensor system. The sensor and control electronics will be designed and tested to assure that (a) there is control for light source and detector instabilities; (b) the sensor is insensitive to motion and placement; and (c) the sensor can meet the Army¿s requirements for weight, power, and ease of use (Objective 1). Concurrently, we will develop test samples for documentation and correction of spectral differences between new instruments. These samples will be used to develop new methods to transfer calibration equations previously developed from human subjects on a laboratory instrument (Objective 2). We will transfer the calibration equations to the miniature sensor system and demonstrate that it has acceptable accuracy for measurement of tissue pH and PO2 on cardiac surgery patients experiencing hemodilution, hypothermia, and hypotension. We will then build nine more miniature sensors and demonstrate their accuracy for measuring blood hematocrit (Objective 3). Four of the miniature sensor systems will be delivered to the Combat Casualty Care Program for future testing.

Relevance: The proposed device will be robust and portable. The medic could easily carry it to the battlefield for monitoring during patient evacuation. It will provide three parameters that will assist in the triage of multiple casualties and help guide their resuscitation. It is anticipated that the device will find immediate application in assessing new types of resuscitation fluids and strategies being developed by Combat Casualty Care..