Michael S. Shuler

What's new in acute compartment syndrome?

Summary: Acute compartment syndrome (ACS) after trauma is often the result of increased size of the damaged tissues after acute crush injury or from reperfusion of ischemic areas. It usually is not solely caused by accumulation of free blood or fluid in the compartment, although that can contribute in some cases. There is no reliable and reproducible test that confirms the diagnosis of ACS. A missed diagnosis or failure to cut the fascia to release pressure within a few hours can result in severe intractable pain, paralysis, and sensory deficits. Reduced blood circulation leads to oxygen and nutrient deprivation, muscle necrosis, and permanent disability. Currently, the diagnosis of ACS is made on the basis of physical examination and repeated needle sticks over a short time frame to measure intracompartmental pressures. Missed compartment syndromes continue to be one of most common causes of malpractice lawsuits. Existing technology for continuous pressure measurements are insensitive, particularly in the deep tissues and compartments, and their use is restricted to highly trained personnel. Newer concepts of the pathophysiology accompanied by new diagnostic and therapeutic modalities have recently been advanced. Among these are the concept of inflammatory mediators as markers and anti-inflammatories as medical adjunct therapy. New diagnostic modalities include near-infrared spectroscopy, ultrafiltration catheters, and radio-frequency identification implants. These all address current shortcomings in the diagnostic armamentarium that trauma surgeons can use. The strengths and weaknesses of these new concepts are discussed to allow the trauma surgeon to follow current evolution of the field.

Ability of Near Infrared Spectroscopy to Measure Oxygenation in Isolated Upper Extremity Muscle Compartments

PURPOSE Near infrared spectroscopy (NIRS), a noninvasive means for monitoring muscle oxygenation, may be useful in the diagnosis of acute compartment syndrome, a condition characterized by poor tissue perfusion. This study used the decrease in muscle oxygenation caused by exercise to investigate the ability of anatomic placement of NIRS sensor pads over compartments of the forearm to isolate perfusion values of a specific compartment. METHODS We recruited 63 uninjured volunteers from a private clinic-based setting and placed NIRS sensor pads over the dorsal, volar, and mobile wad compartments of 1 forearm. A total of 49 participants also had the contralateral forearm monitored, which served as an internal control. Participants performed a series of 3 exercises designed to sequentially activate the muscles of each compartment. A washout period separated each exercise to allow perfusion to return to baseline. We compared NIRS values of each compartment recorded during muscle contraction with baseline values. RESULTS Mean NIRS values decreased significantly from baseline during muscle contraction for all compartments, whereas mean NIRS values of muscle compartments that remained at rest showed little or no change. We observed no changes in NIRS values of the contralateral arm, which remained at rest during the entire data collection period. CONCLUSIONS Although lack of an existing method for quantifying muscle perfusion precludes validation of this technique against a reference standard, this study suggests that NIRS can provide oxygenation values that are both sensitive and specific to muscle compartments of the forearm. Future studies should investigate NIRS among patients with upper extremity injuries. TYPE OF STUDY/LEVEL OF EVIDENCE Diagnostic III.

Near-infrared spectroscopy in acute compartment syndrome: Case report

A 44-year-old Caucasian male was treated with external fixation to stabilise a proximal tibia fracture with an articular split. Postoperatively, the patient became hypersensitive to pain in both the injured and uninjured legs. Intramuscular pressures (IMPs) were measured in all four compartments of the injured extremity resulting in 40-mmHg perfusion pressure in all four compartments. (Perfusion pressure was defined as diastolic blood pressure minus IMP.) Tissue oxygenation was measured using two near-infrared spectroscopy (NIRS) pads (INVOS, Somanetics, Troy, MI, USA). NIRS pads were placed on the lateral and deep posterior compartments for continual monitoring as described by Shuler et al. (All clinical decisions were based on the clinical symptoms and pressure measurements and not on the NIRS information.) Repeat IMPs were obtained 2 h later and confirmed adequate perfusion gradients of at least 40 mmHg in all four compartments. Approximately 24 h after the initial injury and 18 h after external fixation, the patient began requiring more pain medication. IMP measurements were repeated a third time. The perfusion gradients for the posterior compartments were 11 mmHg, whilst the anterior and lateral were maintained over 20 mmHg of perfusion gradient. A four-compartment fasciotomy was performed. During the release, no gross evidence of muscle necrosis was found.

Relationship between Near Infrared Spectroscopy and Intra-compartmental Pressures

BACKGROUND Near infrared spectroscopy (NIRS) has been suggested as a possible means for detecting perfusion deficits in patients with acute compartment syndrome (ACS). STUDY OBJECTIVES To longitudinally examine NIRS in an ACS model to determine its responsiveness to decreasing perfusion pressure. METHODS A NIRS sensor pad was placed under a tourniquet over the anterior compartment in the mid-tibia region on 20 volunteers. Initial perfusion pressures and NIRS values were recorded. The tourniquet pressure was sequentially raised by 10 mm Hg in 10-min intervals until systolic pressure was surpassed. NIRS values and perfusion pressure were determined at the end of each 10-min interval. RESULTS There was no change in mean NIRS values from the initial baseline until 30 mm Hg of perfusion pressure was reached. Additionally, a statistically significant drop in mean NIRS values was observed as perfusion pressures dropped from 10 mm Hg to 0 mm Hg, and again with subsequent decreases of 10 mm Hg perfusion pressure until systolic pressure was surpassed. CONCLUSIONS These results coincide with previously published studies using alternative methods of measuring blood flow or perfusion. NIRS values were responsive to decreasing perfusion pressures over a longitudinal period of time in an ACS model. These results suggest that NIRS may be useful for continuous, non-invasive monitoring of patients for whom ACS is a concern. Additional studies on traumatized patients are required.

Correlation of near-infrared spectroscopy and direct pressure monitoring in an acute porcine compartmental syndrome model.

Objective: To correlate near-infrared spectroscopy (NIRS) and the tibial intracompartmental perfusion pressure (TIPP) in an acute limb compartmental syndrome. Methods: Landrace swine were subdivided into 2 groups: plasma infusion (n = 16) and blunt trauma plus plasma infusion (n = 15). NIRS sensors were placed over the craniolateral muscle compartment of proximal both tibiae. Albumin infusion elevated tibial intracompartmental pressures (TICP). Time-synchronized measures of systolic, diastolic, and mean arterial pressures, TICP, and percent oxygenation from each leg were collected. For the blunt trauma group, trauma was induced by dropping a 2-kg weight 30 times from 100 cm directly on the muscle compartment. For each group, a repeated-measures analysis of variance model was used to test differences in the TICP, TIPP, and oxygenation values. Pearson correlations were calculated between TICP and oxygenation and between TIPP and oxygenation. Results: Both models created reproducible increases in TICP and decreases in TIPP. Trauma did not alter TICP, TIPP, or percent oxygenation in the model. NIRS was able to detect significant changes in tissue oxygenation at all the same time points. NIRS was able to detect decreased oxygenation at every TIPP decrease and subsequent increase after fasciotomies. An increase in percent oxygenation was seen in all cases once fasciotomy was performed and TICP was reduced. Conclusions: NIRS provided a sensitive measure correlating to both an increase and decrease in TICP and TIPP, respectively, in this infusion model. The addition of blunt trauma to the model did not alter the correlations of NIRS values with TICP and TIPP. Fasciotomy produced a rebound in oxygenation values.

Subcutaneous depth in a traumatized lower extremity.

BACKGROUND Acute compartment syndrome is a rare but serious consequence of traumatic leg injury. Near-infrared spectroscopy (NIRS) is able to measure oxygenation to a depth of 2 cm to 3 cm below the skin, raising concerns over the ability of NIRS to accurately determine oxygenation of injured leg compartments in the presence of swelling and in the obese. The purpose of this study was to measure the thickness of the subcutaneous tissue overlying the posterior muscle compartment in subjects with tibia fractures to determine if it might compromise rSO2 measurement in the muscle. METHODS Data were analyzed on 50 patients with severe leg injuries. Distance from the skin to the fascia in the superficial posterior compartment of both legs was measured on each patient using a portable ultrasound device. RESULTS Subject age ranged from 18 years to 65 years (mean, 39 years), with 43 male and 7 female patients. The mean (SD) subcutaneous adipose tissue thickness (ATT) was 6.98 (3.17) mm for the injured leg and 7.06 (3.37) mm for the uninjured leg, and the mean body mass index for the group was 27.08 kg/m2. No significant correlation was found between the ATT of the injured or uninjured legs and body mass index. Mean comparison testing revealed no difference in ATT between the injured and uninjured legs (null hypothesis: equal means, p > 0.05). Of the 50 subjects analyzed, no subject had a subcutaneous depth of more than 2 cm on the injured or uninjured leg. CONCLUSION These data suggest that, within this traumatically injured population, symptoms associated with leg injury (such as swelling and edema) do not significantly affect the distance from the skin to the fascia. It is also notable that subcutaneous depth beyond the 2-cm mark (validated in previous studies) is a rare occurrence in this population. These results further support the use of continuous NIRS monitoring for diagnosis of acute compartment syndrome. LEVEL OF EVIDENCE Therapeutic study, level IV.

Depth Penetration of Near Infrared Spectroscopy in the Obese

Near-Infrared Spectroscopy (NIRS) measures to a depth of 2 to 3 cm below the skin, raising concern over the utility of NIRS in the obese patient. The purpose of this prospective study is to investigate the effect of overlying adipose tissue thickness (ATT) on NIRS oxygenation measurements of skeletal muscle. ATT was measured by ultrasound. NIRS sensors were placed over the anterior and superficial posterior compartments of one leg during exercise and the change in regional oxygen saturation was calculated for each compartment. There was a decreasing trend in change of rSO2 from baseline with increasing ATT. Extremely obese patients (BMI >40) had significantly smaller changes in rSO2 from baseline as compared to otherwise similar patients in both the compartments (p<0.01). As ATT increased, the change of the NIRS values from baseline decreased. There was not a specific BMI or ATT determined to be incapable of being monitored.

SpO2 and Pulse Rate Data: A Comparison of Current Technologies duringSustained Shivering in Post-Operative Patients

Pulse oximetry is a noninvasive method of measuring the oxygen saturation (SpO2) of the arterial blood and is considered standard-of-care in post-operative settings. Patient motion or low perfusion can present challenges in obtaining accurate readings. Postoperative shivering occurs in anywhere from 5-65% of patients who have received general anesthesia and can manifest as continuous tremors and/or sporadic muscle movements. Objective: Compare the effect of post-operative shivering on functioning capabilities of two commercially available pulse oximeters. Methods: Two additional pulse oximeter sensors (Nonin 7500 Pulse Oximeter with 8000AA Sensor and Masimo Rad-8 with Rainbow DCI SC-200 Adult Reusable Sensor) were added to 40 shivering patients who met eligibility criteria. Shivering episodes were documented by recording the start and stop times for each episode as it occurred. Dropout rates for each device were calculated by dividing the amount of time that each instrument displayed no SpO2 or pulse rate value by the total time of the test. A 2-sample T-test was performed to compare dropout times of the devices and dropout rates were compared using a z-test for 2 proportions. Results: Drops in signal occurred in fourteen subjects. The Masimo sensor dropped 21 times, for an average of 40 seconds per drop and Nonins dropped 16 times averaging 29 seconds per drop. Nonins dropout rate of 0.108 was less than that of Masimos at 0.149, however this difference was not found to be statistically significant (p=0.87). Conclusion: The incidence of shivering was very low among patients in this particular study setting (0.1%) For 5 different subjects, both sensors experienced drops during identical time intervals indicating that motion artifact may impact readings regardless of specific technology. Clinically significant shivering varied in duration among subjects therefore individual shiver rates varied as well. This preliminary analysis shows no significant difference between Nonin and Masimo sensors.

A Comparison of Wireless Pulse Oximetry Technologies during SustainedShivering in Post-Operative Patients

Background: Pulse oximetry measures oxygen saturation in arterial blood non-invasively and is routinely practiced in many clinical settings. Technological advancements have expanded the performance capabilities of these devices to operate wirelessly, making pulse oximetry measures more convenient to obtain. Factors such as patient motion however can potentially complicate the ability to retrieve these measures. We examined the performance of two wireless pulse oximeters in patients who shiver postoperatively. Methods: Two additional pulse oximeter sensors (Masimo and Nonin) were added to 30 patients who shivered post-operatively and met eligibility criteria. Dropout rates were calculated by dividing the number of times that each instrument displayed no SpO2 or pulse rate value by the total time both sensors were in camera view for that subject. We used Wilcoxon matched pairs tests to compare the average time until the first reading displayed on the sensor for each device as well as dropout times. Dropout events were also compared using McNemars test. Results: Drops in signal occurred in thirteen subjects. The Masimo sensor had more dropouts and a longer average drop duration, which was found to be statistically significant (p=0.02). Masimos sensor required more s on average than Nonins (8.86>8.78) to display the first reading, but this was not found to be statistically significant (p=0.90). Masimo also had a higher percentage of drops however this was not statistically significant (p=0.07). Conclusion: Overall incidence of shivering was low among patients in this setting (0.1%). More than 1/3 of subjects experienced drops during identical time intervals indicating that motion artifact may impact results regardless of technology. Additionally, Masimos sensor is not meant for clinical use thereby raising questions regarding our statistically significant result in this particular setting. Combined with results from part I of this study, we cannot confidently detect a statistically significant difference between manufacturers.

Comparison of NIRS, serum biomarkers, and muscle damage in a porcine balloon compression model of acute compartment syndrome.

BACKGROUND Near-infrared spectroscopy (NIRS) has been shown to aid in the diagnosis of extremity acute compartment syndrome (ACS), offering continuous real-time capability to monitor perfusion in extremities. Porcine models of ACS have been developed to attempt to aid in the understanding of the development of ACS and provide better methods of diagnosing ACS. The objective of the present study was to assess and correlate NIRS, tibial intracompartmental pressure (TICP), tibial intracompartmental perfusion pressure (TIPP), serum markers of inflammation and muscle injury in a balloon compression model of ACS. METHODS Six swine were used. Balloon catheters were inflated below the cranial tibial muscle. Systolic, diastolic, and mean arterial pressures; compartmental pressures; and oximetry were measured before, during, and after balloon inflation/deflation. Cranial tibial muscle was collected for muscle damage scoring. Serum creatine kinase, myoglobin, tumor necrosis factor &agr;, IL-1&bgr;, and IL-6 were measured. Data analysis included comparing differences in TICP, NIRS, and TIPP measurements as well as creatine kinase, myoglobin, tumor necrosis factor &agr;, IL-1&bgr;, and IL-6 levels between time points. Pearson correlations were calculated for muscle degeneration and edema and NIRS. RESULTS Increases in TICP and decreases in TIPP were found. Near-infrared spectroscopy detected significant changes in tissue oxygenation at all the same time points. Myoglobin significantly increased from 45.7 ± 13.0 ng/mL (baseline) to 219.5 ± 57.3-ng/mL (balloon deflation) and continued to increase over the duration of the study. Creatine kinase significantly increased 2 hours after balloon deflation. Cranial tibial muscle degeneration, necrosis, and edema scores were higher in the test than the control legs. CONCLUSIONS Near-infrared spectroscopy of the compartment provided a reliable, sensitive measure of both an increase and decrease in TICP and TIPP in this porcine balloon model of ACS. Creatine kinase and myoglobin significantly increased following balloon removal. Significant correlations between muscle degeneration, edema, hemorrhage, and NIRS were found.