Noninvasive Multimodal Imaging to Predict Recovery of Locomotion after Extended Limb Ischemia

Abstract

Acute limb ischemia is a common cause of morbidity and mortality following trauma both in civilian centers and in combat related injuries. Rapid determination of tissue viability and surgical restoration of blood flow are desirable, but not always possible. We sought to characterize the response to increasing periods of hind limb ischemia in a porcine model such that we could define a period of critical ischemia (the point after which irreversible neuromuscular injury occurs), evaluate non-invasive methods for characterizing that ischemia, and establish a model by which we could predict whether or not the animal’s locomotion would return to baselines levels post-operatively. Ischemia was induced by either application of a pneumatic tourniquet or vessel occlusion (performed by clamping the proximal iliac artery and vein at the level of the inguinal ligament). The limb was monitored for the duration of the procedure with both 3-charge coupled device (3CCD) and infrared (IR) imaging for tissue oxygenation and perfusion, respectively. The experimental arms of this model are effective at inducing histologically evident muscle injury with some evidence of expected secondary organ damage, particularly in animals with longer ischemia times. Noninvasive imaging data shows excellent correlation with post-operative functional outcomes, validating its use as a non-invasive means of viability assessment, and directly monitors post-occlusive reactive hyperemia. A classification model, based on partial-least squares discriminant analysis (PLSDA) of imaging variables only, successfully classified animals as “returned to normal locomotion” or “did not return to normal locomotion” with 87.5% sensitivity and 66.7% specificity after cross-validation. PLSDA models generated from non-imaging data were not as accurate (AUC of 0.53) compared the PLSDA model generated from only imaging data (AUC of 0.76). With some modification, this limb ischemia model could also serve as a means on which to test therapies designed to prolong the time before critical ischemia.

In vitro development and in vivo application of a platinum-based electrochemical device for continuous measurements of peripheral tissue oxygen

“…Furthermore, there was no significant variation in the maximum response times (p = 0.58, one-way ANOVA, n = 6), indicating that a comparable level of ischaemia was induced followed tourniquet application across all Pt-Pt configurations and animal species investigated. These findings corroborate recent work using noninvasive imaging in porcine limb that measured an immediate drop in oxygenated haemoglobin (within the first 10 min) after induction of ischaemia that continued to decrease over the course of the insult (3-4 h), albeit at a much slower rate [10]. Their objective was to measure locomotion recovery and required significantly longer durations of ischaemia to achieve this.…”

“…Compartment syndrome is a time-critical medical emergency, in which irreversible nerve and muscle damage can occur after just six hours of increased intra-compartmental pressure. Recovery from tissue ischaemia complications is largely dependent on tissue microcirculation [10] in the smallest blood vessels, including arterioles, capillaries, and venules, which are responsible for tissue oxygenation and, ultimately, tissue (and organ) health [11].…”

“…Blood perfusion is commonly assessed by non-invasive Laser Doppler Imaging (LDI), which measures blood flow through backscattering a laser beam that interacts with moving red blood cells [12,13]. While the non-invasive nature of LDI is highly desirable, it suffers from a lack of standardisation, poor temporal resolution, and can only penetrate tissue to a maximum depth of 10 mm [10]. More recently, near infrared spectroscopy (NIRS) has demonstrated excellent clinical utility that has facilitated clinical diagnoses [14][15][16].…”

Preclosure spectroscopic differences between healed and dehisced traumatic wounds

“…In previous studies, increases in R-B values indicated increased oxygenation of the wounds through more robust microvasculature. [ 14 – 16 ] This is likely secondary to the increases in angiogenesis in wounds that heal compared with those that dehisce. In this study, however, we had to explore more robust normalization techniques to exploit the small differences in the R-B values between healed and dehisced wounds.…”

“…Recent advances in image processing allow for the immediate assessment of tissue viability, something the authors believe beneficial when treating large, heterogeneous extremity wounds. In fact, previous studies utilized a 3CCD (three charge-coupled device) camera to evaluate changes in oxygenation in red blood cells[ 12 ], vessels[ 13 ], ischemic limbs[ 14 – 16 ], during pediatric appendectomies[ 17 ], and in partial and donor nephrectomies[ 18 , 19 ]. The present study seeks to ascertain the imaging characteristics of a heterogeneous population of extremity wounds prior to closure using a 3CCD camera, a commercially available and inexpensive device that records the levels of each of the three primary colors (red, green, and blue) to form a high-resolution image.…”