Noninvasive Measurements of Pressure for Detecting Compartment Syndromes

Samantha Lee

doi:10.13188/2334-2846.1000005

Abstract

We tested a noninvasive ultrasound, Pulse Phase Locked Loop (PPLL) technique for estimating Intramuscular Pressure (IMP) in a model Acute Compartment Syndrome (ACS); and compared it to a Near-Infrared Spectroscopy (NIRS) method. We wanted to validate our model compartment syndrome, and to compare and validate the PPLL and NIRS methods of detecting compartment syndrome. To simulate the tamponade of an ACS, external-pressure levels from 10 to 70 mm Hg were applied to the legs of 15 healthy adult subjects to raise their IMP. Receiver Operator Characteristic (ROC) curves were used to determine the sensitivity and specificity of diagnosing elevated IMP by the two noninvasive techniques. NIRS data varied significantly with compression (p=0.003) with large subject-to-subject variability (p<0.001). PPLL data also varied significantly with compression (p=0.004), but subject-to-subject variation was not significant (p=0.47), suggesting that individual variation does not affect the diagnostic accuracy of the PPLL technique. Sensitivity and specificity for diagnosing normal IMP by the PPLL (<30 mm Hg from a slit catheter reading) from elevated IMP (>30 mm Hg) were 0.75 and 0.75, respectively, and the area under the curve (AUC) was 0.78. For the NIRS, the sensitivity and specificity were 0.65 and 0.65, respectively, and the AUC was 0.68. Both NIRS and PPLL recordings are able to differentiate a simulated ACS up to 70 mm Hg. However, the PPLL technique is a slightly better diagnostic predictor than NIRS with less subject-to-subject variability and slightly better sensitivity and specificity. Level II, Diagnostic test.

Highlights

Acute compartment syndrome (ACS) is a condition which occurs when increased intramuscular pressure (IMP) within a closed fascial space impairs vascular perfusion to a point below the level necessary for muscle and nerve viability
We have developed a novel way to simulate elevated Intramuscular Pressure (IMP) based on previous models including Styf and co-worker’s leg elevation [6] and Reneman’s leg chamber pressure [7]
In the process of the designing the experiment, the reproducibility of measurement with digital implementation of the PPLL (dPPLL) was noted to increase with the clamp compared to one probe, as the placement of one probe caused significant differences in data, while with two probes in a clamp, the placement of the two probes could vary but still produced the same data

Summary

Introduction

Acute compartment syndrome (ACS) is a condition which occurs when increased intramuscular pressure (IMP) within a closed fascial space impairs vascular perfusion to a point below the level necessary for muscle and nerve viability. ACS can be diagnosed based on clinical findings such as the 6 Ps: pressure, pain, paresthesias, paresis, pink skin, and presence of a distal pulse [1]. These clinical findings have a low positive predictive value and a high negative predictive value, so the absence of the clinical findings is more useful in excluding the diagnosis of ACS than in making a diagnosis [2]. We tested a noninvasive ultrasound, Pulse Phase Locked Loop (PPLL) technique for estimating Intramuscular Pressure (IMP) in a model Acute Compartment Syndrome (ACS); and compared it to a Near-Infrared Spectroscopy (NIRS) method.

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Conclusion