Compartment Pressure Measurement

Compartment pressure measurement (see the image below) is employed in the assessment of potential compartment syndrome, which is a condition of increased pressure within a nonexpansile space that results in compromised tissue perfusion and ultimate dysfunction of neural and muscular structures contained within that space.[1]

Compartment pressure measurement.

Compartment syndrome has numerous possible causes, including fractures, crush injury, snake bite,[2]  burns, nephrotic syndrome, drug overdose or injection, intravenous (IV) and intraosseous fluid infiltration, and various medications (eg, pressors, anticoagulants, and platelet inhibitors). By far the most common cause, however, is fracture of a long bone. Fractures of the tibia and forearm bones account for most cases. Compressive dressings and casts can also cause compartment syndrome, as in the first case reported by Volkmann.[3]

Compartment syndrome can occur within any semirigid anatomic space within the body. The lower leg is the site most frequently affected, followed by the forearm. However, gluteal,[4] hand, foot,[5] upper arm, thigh, and back compartment syndromes can also occur.

A number of underlying factors may be present that are likely to exacerbate the syndrome and must be treated. These include hypotension, coagulopathy, vascular injury, and artificially created external pressure, such as that imposed by a cast. Definitive intervention is surgical. The clinician must maintain a high index of suspicion in multiply injured, unresponsive, or uncooperative patients so as not to overlook this syndrome and thereby worsen patient outcome.[6, 7]

Fasciotomy is the treatment of choice. This involves opening the skin and muscle fascia at key points overlying the involved compartment or compartments. The release of enclosed muscles causes a decrease in compartment pressure, thereby improving blood flow to the tissues.[6] This procedure is best left to surgeons who have experience in fasciotomy and who will subsequently manage the patient.

A clinical history is the first step in the evaluation of an injury or condition that may produce a compartment syndrome. Clinical examination may confirm the diagnosis in the presence of clear evidence of increased tissue pressure, inadequate tissue perfusion, and loss of tissue function. The diagnosis is less certain when these factors are absent.

Reliance on the presence or absence of the classic five Ps (pain, pallor, pulselessness, paresthesias, and paralysis) may lead to a delay in diagnosis. Patients with a burning quality of pain, delayed onset or increasing severity of pain, or, as classically described, pain on a passive stretch of the compartment must be evaluated for compartment syndrome. As an example, dorsiflexion of the foot causes pain in the posterior calf if its compartment pressure is elevated.

Arterial pulses may persist indefinitely because compartment pressure is almost always less than systolic blood pressure. On examination, the soft tissues are often visibly swollen, and the compartment usually has a tense “woody” feeling on palpation. The presence of fracture blisters suggests increased compartment pressure, but these blisters are not reliably present when compartment pressure is increased. Paresthesias and paralysis tend to be late findings but also merit investigation.

Of the five Ps, the only relatively reliable one is pain. Severe pain that is out of proportion to the injury may be the only early symptom of acute compartment syndrome. Tissue pressure measurements may suggest compartment syndrome, but equivocal measurements still require clinical judgment.

There are three groups of patients in whom clinical findings are difficult to interpret and who may benefit from compartment pressure measurement, as follows (see the image below):

• Unresponsive patients
• Uncooperative patients (eg, children, developmentally delayed, or intoxicated patients)
• Patients with peripheral nerve deficits attributable to other causes (eg, tibial fracture with peroneal nerve injury)

Algorithm for management of a patient with suspected compartment syndrome.

Whitesides et al[8] found that fasciotomy was required when the intracompartmental pressure approached 20 mm Hg below the diastolic pressure, whereas McQueen et al[9] recommended using a differential pressure (ie, diastolic pressure minus compartment pressure) of less than 30 mm Hg as a criterion for fasciotomy.[6]

Compartment pressure measurement has no absolute contraindications. Avoidance of areas with overlying cellulitis is recommended. The procedure itself carries some risk of infection, but this can usually be avoided with appropriate technical practices.

The equipment employed for compartment pressure monitoring includes the following:

• Stryker Intra-Compartmental Pressure Monitor System (Stryker Surgical, Kalamazoo, MI; see the first image below)
• Syringe, prefilled with saline
• Side-port needle
• Diaphragm chamber
• Arterial line transducer system (see the second image below) - This system, used with a simple or side-port needle, provides a high degree of accuracy for simple episodic readings; the commercially available Stryker system (see the first image below) provides consistent accurate readings for episodic and extended monitoring situations; the mercury manometer system is the least accurate measurement system, is no longer available, and therefore is not described here
• Intracompartment needle - Needles available for placement into the compartment for pressure measurement include a simple 18-gauge needle, an 18-gauge spinal needle (for deep compartments), and the side-port needle (Stryker); the side-port needle and slit catheter have comparable efficacy in this setting, whereas a simple 18-gauge needle is less precise
• High-pressure tubing
• Pressure transducer with cable
• Pressure monitor/module
• Sterile saline
• Transducer stand that allows variable height
• Two three-way stopcocks
• Syringe, 20 mL

Stryker.

Arterial line transducer.

Anesthesia

The skin should be anesthetized with a small amount of local anesthetic, with care taken to avoid injection into muscle or fascia. Excessive deep infiltration may falsely elevate the compartment pressure reading. Lidocaine 1-2% without epinephrine is sufficient to provide local anesthesia (see Local Anesthetic Agents, Infiltrative Administration).

Consider procedural sedation and analgesia in any patient who may be uncooperative and unable to hold the extremity still during the procedure. Any struggling or movement that requires restraint of the extremity may falsely elevate the compartment pressure.

Positioning

The positioning of the patient and the extremity for compartment pressure measurement depends on the extremity being studied, the compartment being studied, and the presence or absence of coexisting injury.

Patients should be comfortable, usually in the supine or prone position. The compartment to be measured should be at the same level as the heart. The patient and extremity should be positioned so that the needle can be introduced perpendicularly to the muscular compartment being measured. Remove any obstructions at the needle’s entry point into the skin, as well as all structures that may put pressure on the compartment and falsely elevate the pressure.

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).

Anterior compartment: pressure measurement.

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.

Deep posterior compartment: pressure measurement.

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.

Lateral compartment: pressure measurement.

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).

Superficial posterior compartment: pressure measurement.

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.

The goals of pharmacotherapy are to reduce pain and potential complications.

Class Summary

Local anesthetics block the initiation and conduction of nerve impulses.

Lidocaine (Xylocaine)

Lidocaine is an amide local anesthetic used in 1-2% concentration. The 1% preparation contains 10 mg of lidocaine for each 1 mL of solution; the 2% preparation contains 20 mg of lidocaine for each 1 mL of solution. Lidocaine inhibits depolarization of type C sensory neurons by blocking sodium channels.

To improve local anesthetic injection, cool the skin with ethyl chloride before injection. Use 1-2% without epinephrine to provide local anesthesia. Make sure the solution is at body temperature. Infiltrate very slowly to minimize the pain. Excessive deep infiltration may falsely elevate the compartment pressure reading. The time from administration to onset of action is 2-5 minutes, and the effect lasts for 1.5-2 hours.

Buffering the solution helps reduce the pain of local lidocaine injection. Sodium bicarbonate can be added to injectable lidocaine vials (1 part bicarbonate to 9 parts lidocaine) to produce buffered lidocaine. The shelf-life of buffered lidocaine is approximately 1 week at room temperature. All vials should be marked "buffered," labeled with the time and date, and signed by the person who created the buffered mixture.