Compartment Pressure Measurement Technique

With the patient positioned as previously described, determine needle placement. To avoid introduction of bacteria into deep tissues, avoid placing the needle in areas where the overlying skin may be infected. If an overlying cast is present, it should be bivalved, and if necessary, a window overlying the desired area of needle penetration should be cut from the cast. Prepare the skin at the needle insertion site as for any sterile procedure. Administer local anesthesia.

The lower leg has four compartments, as follows:

• Anterior
• Lateral
• Deep posterior
• Superficial posterior

The anterior lower leg is especially predisposed to compartment syndrome because of its high vulnerability to injury and its relatively limited compartment compliance. ^[10]

The easiest cross-sectional level for needle placement for access to all four compartments is approximately 3 cm on either side of a transverse line drawn at the junction of the proximal and middle thirds of the lower leg.

Anterior compartment

With the patient supine, palpate the anterior border of the tibia at the level of the junction of the proximal and middle thirds of the lower leg. Identify the needle entry point 1 cm lateral to the anterior border of the tibia. Orient the needle so that it is perpendicular to the skin, and insert it to a depth of 1-3 cm (see the image below).

Proper needle placement can be confirmed by measuring the pressure during the following:

• Digital compression of the anterior compartment just proximal or distal to the needle insertion site
• Plantarflexion of the foot
• Dorsiflexion of the foot

These maneuvers should produce a severalfold rise in pressure on the monitor.

Note that the most common error with both the Stryker monitor set and the arterial line transducer system is depressing the syringe plunger too quickly. This may give a transient falsely elevated reading. Another source of error with either system is obstruction of the needle with a plug of tissue if the syringe plunger is pulled back.

Deep posterior compartment

With the patient supine, elevate the leg slightly, if possible. Palpate the medial border of the tibia at the level of the junction of the proximal and middle thirds of the lower leg. Identify the entry point just posterior to the medial border of the tibia (see the image below). Palpate the posterior border of the fibula on the lateral aspect of the leg at the same level. Orient the needle so that it is perpendicular to the skin, and advance it toward the posterior fibular border to a depth of 2-4 cm, depending on the amount of subcutaneous fat.

Proper needle placement can be confirmed by seeing a rise in pressure during the following:

• Toe extension
• Ankle eversion

Lateral compartment

With the patient supine, elevate the leg slightly, if possible. Palpate the posterior border of the fibula at the level of the junction of the proximal and middle thirds of the lower leg. Identify the needle entry point just anterior to the posterior border of the fibula. Orient the needle so that it is perpendicular to the skin, and advance it toward the fibula to a depth of 1-1.5 cm (see the image below). If the needle contacts bone, retract it 0.5 cm.

Proper needle placement can be confirmed by seeing a rise in pressure during the following:

• Digital compression of the lateral compartment just inferior or superior to the needle entrance site
• Inversion of the foot and ankle

Superficial posterior compartment

With the patient prone and the leg at the level of the heart, identify a transverse line at the level of the junction of the proximal and middle thirds of the lower leg. Identify the needle entry point at this level and 3-5 cm on either side of a vertical line drawn down the middle of the calf. Orient the needle so that it is perpendicular to the skin, and advance it toward the center of the lower leg to a depth of 2-4 cm (see the image below).

Proper needle placement can be confirmed by seeing a rise in pressure during the following:

• Digital compression of the superficial posterior compartment just inferior or superior to the needle entrance site
• Dorsiflexion of the foot

According to Mubarak and Hargens, an absolute pressure measurement of 30 mm Hg in the compartment should be the “critical pressure” for recommending fasciotomy. ^{[11, 12]} However, even though this tissue pressure is abnormal and corresponds to the onset of pain and paresthesias, ^[11] it does not necessarily precipitate a compartment syndrome in the absence of other factors.

Some variability exists among patients with regard to tolerance of increased pressures. Specifically, clinical scenarios in which the mean arterial pressure is lowered (eg, hypovolemia, sepsis, and thermal injury) may compromise a patient’s ability to tolerate even mildly elevated compartment pressures.

The duration of increased compartment pressure is another important factor. The effects of early fasciotomy (ie, before 12 hours) versus those of late fasciotomy (ie, after 12 hours) on the management of compartment syndrome, especially in trauma patients, are currently subject to debate. Limb salvage may be possible for up to 10-12 hours; however, with high pressures, the salvage period may be as short as 4-6 hours. ^[13]

Compartment pressure must be interpreted within the context of the overall clinical picture. Falsely elevated pressures may be a result of needles placed into tendons or fascia, plugged catheters, or faulty monitoring systems. Falsely low readings may result from bubbles in the lines or transducer, plugged catheters, or faulty monitoring systems. Awareness of the possible causes for falsely elevated or low compartment pressures is paramount for making the proper treatment choice.

Infrared imaging to measure the surface skin temperature of the affected extremity is another technique that is being evaluated for the diagnosis of compartment syndrome; the rationale is based on the known correlation between skin temperature and limb blood flow. Infrared imaging is a noninvasive technology that may hold future promise as a supportive tool for the early detection of compartment syndrome in the legs of patients who sustain blunt trauma. ^[14]

All of the approaches to compartment pressure measurement carry a low risk of infection. Strict adherence to aseptic technique, careful sterilization of catheters, and use of sterile disposable components whenever possible help to minimize this risk.

All monitoring procedures cause some pain. Generally, the pain associated with the actual insertion of needles and catheters is reduced by local anesthesia.