DIAGNOSTIC TOOLS
ACS is diagnosed based on the previously mentioned clinical signs, along with objective evidence of decreased tissue perfusion in the affected limbs.24 Direct intracompartmental pressure measurements, obtained using a needle- or catheter-based technique, are the most common means of identifying ACS.7 However, near infrared spectroscopy and infrared imaging have also been found helpful.7, 25
Direct Intracompartmental Pressure Monitoring
Supported by clinical findings, direct measurement of the intracompartmental pressure (ICP) using a needle transducer is the most accurate method for detecting ACS and guiding treatment choices. Several measurement options are available, including a handheld needle manometer, which records single-pressure readings, or a wick or slit catheter, which can record continuous pressures.13 The choice between devices is based on facility/provider preference, as any commercial pressure device can be used with similar accuracies. When no such device is available, an 18-gauge needle with a set-up resembling an arterial line is another option.1
When using these instruments, it is essential for the provider to implement proper sterile technique and to record pressures from compartments within a 5-cm radius of the injury site.17 Furthermore, clinicians should be aware that the ICP can vary greatly and that tolerance to increased pressure varies with the patient’s diastolic blood pressure.
Normal capillary perfusion pressure (diastolic blood pressure minus compartment pressure) is approximately 30 mm Hg. Therefore, absolute ICP readings above 30 mm Hg can be diagnostic of ACS and indicative of fasciotomy. Likewise, a perfusion pressure below 30 mm Hg is also diagnostic. Based on consensus, either calculation can be used.16,17
Infrared Spectroscopy and Imaging
Barker and colleagues7 describe use of near infrared spectroscopy (NIRS) as a method to diagnose lower-extremity ACS. Noninvasive skin probes can detect the absorption spectra of mixed venous hemoglobin levels beneath the skin to determine oxygen saturation (StO2). StO2 measured by NIRS is location dependent, enabling the clinician to monitor oxygenation levels in any illuminated tissue. NIRS has great potential for use in confirming a diagnosis of ACS since decreased perfusion pressure from elevated ICP correlates well with decreased StO2. However, this technique has limitations that currently prevent its widespread use as a diagnostic tool.7
Use of noninvasive infrared imaging has also been investigated. Katz and colleagues25 describe the use of a long-wave infrared camera and thermographic imaging analysis software to detect differences in surface temperatures in patients’ limbs after blunt trauma. The researchers were able to correlate declines in temperature with decreased blood flow. They proposed that this modality be used to make the diagnosis of ACS before the development of muscle ischemia and necrosis. This software is still being investigated.25
Imaging Studies
CT or MRI can be helpful in identifying swelling, hematomas, or areas of necrosis, but their specificity is not sufficient to confirm elevated compartmental pressures24; additionally, MRI cannot distinguish between swelling resulting from soft-tissue injury and swelling in muscles affected by ACS.26, 27
Ultrasound also has potential as a diagnostic tool, as it helps clinicians visualize soft-tissue structures and assess the patency of large arteries and veins; the absence of venous outflow may suggest ACS. However, the efficacy of ultrasound in diagnosing ACS has proven inconsistent, and it is not recommended over direct ICP measurements. Instead, ultrasound can be relied on as an adjunctive modality.13
Blood Tests
Laboratory tests cannot contribute toward the diagnosis of ACS, but assessment of renal function and skeletal muscle breakdown is important to identify potential complications of ACS. Obtaining baseline levels in blood urea nitrogen and creatinine will help identify changes in kidney function, while potassium, urates, creatine phosphokinase (CPK), and myoglobin can be measured to assess for muscle breakdown. Findings of myoglobinuria with elevated CPK are strongly indicative of rhabdomyolysis, which can easily precipitate acute renal failure.8
Results from a complete blood count or prothrombin time/partial thromboplastin time may facilitate monitoring for blood loss or identification of contributing bleeding disorders. Because surgery remains the definitive treatment for ACS, a type and screen is essential in the workup, as blood products and transfusion are likely to be required during treatment.
MANAGEMENT
Fasciotomy remains the standard of care for patients presenting with the clinical signs and symptoms of increased compartment pressure consistent with ACS.16 Researchers engaged in animal studies and human case reports have shown that fasciotomy must be performed within six hours of injury to prevent adverse outcomes.8,16,28
As definitive treatment for ACS, a complete fasciotomy of all compartments in the vicinity of the injury should be performed. The most effective approach for fasciotomy consists of two long skin incisions (ie, double-incision radical dissection, to prevent concomitant increased pressure within the boundary of the skin), on opposite aspects of the affected limb, to ensure that all compartmental fascia can be decompressed.17,26,28