Journalist Miles O’Brien earlier this week related a harrowing experience that began when a piece of TV equipment fell on his left forearm, leaving it sore and swollen but not enough for him to seek medical treatment. Two days later, after the pain and swelling had increased, a doctor delivered some terrible news to O’Brien. A sharp increase in pressure inside the journalist’s injured forearm was killing the nerve cells and damaging the arteries and veins. Hours later doctors amputated the dying limb.
O’Brien had experienced a medical condition known as acute compartment syndrome in his lower arm as a result of his injury. The condition—which can affect the arms, hands, legs, feet and buttocks—develops when pressure builds up within groups of muscles, nerves and blood vessels that together comprise compartments in different areas of the body. Sheets of relatively inflexible connective tissue called fascia cover these compartments. Too much pressure within these fascia-bound compartments disrupts blood flow, damaging vessels and tissue.
To better understand what happened to O’Brien, Scientific American spoke with Brett Cascio, head of the Department of Surgery at Lake Charles Memorial Hospital in Louisiana.
[An edited transcript of the interview follows.]
What causes acute compartment syndrome?
A person’s body is divided into compartments, which help your muscles return venous blood back to your heart. Your forearm, calf and thigh muscles all have compartments. In order for your muscles to act like pumps, they need something to work against—a tough fascia that covers all the muscle compartments you have creates pressure. When you have an injury to one of your limbs—either a blunt force trauma or a broken bone, for example—cells in that limb start to die and swell and rupture. The fascia covering that limb’s muscles has very minimal elasticity—it’s very tough and does not give way. Now you have an increase in pressure inside the compartment, to the point where it can impede capillary flow.
Acute compartment syndrome occurs when there’s not enough blood flow at the microscopic level through the capillaries and the cells start to die. It becomes a vicious circle—more cells die and swelling increases. If you don't release the pressure at that point, you risk everything in that limb dying, including the muscles and nerves.
What parts of the body does this condition typically affect?
There are four compartments in the leg between the knee and the ankle, and that’s where it happens the most. Probably at least 50 percent of compartment syndrome cases happen in that area of the body. Other common areas are the forearm and the thigh.
How common is acute compartment syndrome?
Compartment syndrome is a well-described, well-documented entity that orthopedic and vascular surgeons run into on a regular basis. One of the statistics that I’m aware of is that there’s about a 5 percent incidence of acute compartment syndrome as a result of tibia fractures. You’re going to see this condition more often in trauma centers, during wartime or in major disasters. You’ll also see it happen in drug overdose victims if they fall with their head on their arm and stay that way for hours. In those cases it’s not a lot of pressure at once, but over time a lower amount of pressure can cause a compartment syndrome.
Who is most at risk?
Acute compartment syndrome usually happens in young, muscular males. In young people the fascia fits perfectly around the muscle. There’s little room for swelling and the muscles squeeze tight against the venous return and get the blood back up into the heart. It’s a perfectly balanced system. As you get older you start to lose muscle mass and you have slack in the system.
How does a physician know when a patient is experiencing acute compartment syndrome?
There are no technologies that can tell a physician this is happening. This is a clinical diagnosis based on the five “P”s of compartment syndrome: 1) Is the pain out of proportion? That means the patient doesn’t have a bad injury but is screaming and clawing at the ceiling because they’re in so much pain. 2) Is there pain on a passive stretch? In the case of a leg, if you take the patient’s toe and bend it up or down it will make the pain that much worse. The patient will yell or writhe in pain; more pain than you would expect. 3) Is there pallor? Does the injured limb’s coloring look different from the healthy one? Are the capillaries under the skin under pressure and not getting as much blood flow? 4) Is the patient experiencing "pulselessness" in their limb, or a change in pulse in that limb? 5) And is the patient experiencing paresthesia [a burning or prickling sensation]? When that nerve starts to die the patient will experience numbness and tingling. Once the limb is completely numb and weak, it’s often too late to save the limb.
How often is this serious enough to require cutting open the fascia or amputating a limb?
There are situations where a patient has an impending compartment syndrome and then there are situations where the patient is actually having a compartment syndrome. Doctors differ in how aggressive they are in treating these situations. If a person has an impending compartment syndrome, a doctor will admit them to the hospital and monitor the pressure [in the injured limb] below the fascia and compare those readings to the diastolic pressure [the pressure in the arteries when the heart rests between beats]. If the pressure readings below the fascia get high enough, the doctor will pull the trigger and do the fasciotomy [which involves making incisions in the fascia to relieve pressure].
If the patient is experiencing compartment syndrome already—they’re having numbness and weakness and pain out of proportion with the severity of their injury and the compartment is swollen and tense—I don’t even really measure pressures a lot in that case, I just move to release the pressure right away.
Response time is critical—you try to release the fascia as soon as possible [via a fasciotomy]. [Extra] minutes mean muscle and nerve damage, just the way when you’re treating a stroke, extra minutes mean more damaged brain cells or, in the case of a heart attack, damaged heart muscle.  
Can a patient die as a result of acute compartment syndrome?
In some cases a victim of an earthquake or an accident will experience compartment syndrome in multiple areas of [his or her] body. That’s very dangerous because the cells in the crushed limbs spill potassium and muscle enzymes into the blood-stream when they die. This can lead to kidney failure or can affect the heart’s electrophysiology, leading to arrhythmias [irregular heartbeats]. When you have millions of cells spilling their contents into the blood-stream, it really affects the body’s physiology.
If the patient is suffering from compartment syndrome in one area, it’s not usually life-threatening and can be managed. In those cases it could become life-threatening if the limb gets infected.