In medical settings, SCD most commonly stands for sequential compression device, an inflatable sleeve worn on the legs to prevent blood clots in hospitalized patients. Less frequently, SCD can refer to superior canal dehiscence syndrome, an inner ear condition. Since most people encounter this abbreviation during or after a hospital stay, this article covers both meanings, starting with the compression device.
Sequential Compression Devices: The Basics
A sequential compression device is a set of inflatable sleeves that wrap around your lower legs (and sometimes thighs) and connect to a small bedside pump. The pump inflates different chambers in the sleeve one after another, squeezing from the ankle upward. This mimics what your calf muscles normally do when you walk: push blood back up toward the heart. When you’re stuck in bed after surgery, during a long illness, or following an injury, your leg muscles aren’t contracting enough to keep blood moving efficiently. Blood pools in the deep veins of the legs, and that stagnant blood is where dangerous clots can form. SCDs solve this by mechanically reproducing that pumping action.
The sleeves typically inflate to around 50 mmHg of pressure, roughly equivalent to a firm blood pressure cuff squeeze. They cycle on and off throughout the day, creating rhythmic compression that keeps venous blood flowing.
Why Hospitals Use Them
Deep vein thrombosis (DVT), a blood clot in the leg, is one of the most common preventable complications of hospitalization. A clot that breaks loose and travels to the lungs becomes a pulmonary embolism, which can be fatal. Hospitals use two main strategies to prevent this: blood-thinning medications and mechanical devices like SCDs.
SCDs are especially useful for patients who can’t safely take blood thinners, such as people with active bleeding, recent brain surgery, or a high fall risk. They’re also used alongside blood thinners for patients at very high risk of clotting, like those recovering from major orthopedic procedures. For best results, clinical guidelines recommend wearing the sleeves 18 to 21 hours per day. Compliance is a known challenge; patients often remove them to walk to the bathroom or simply because they’re uncomfortable, and nurses may not always reapply them promptly.
The evidence on how well SCDs work on their own is mixed. A retrospective study of medically ill hospitalized patients published in the Turkish Journal of Hematology found no significant difference in clot rates between patients who used SCDs alone and those who used no prevention at all. This doesn’t mean SCDs are useless, but it does suggest they work best as part of a combined approach rather than as a sole preventive measure.
SCDs vs. Compression Stockings
You may also see TED hose or graduated compression stockings used in hospitals. These are passive, tight-fitting stockings that squeeze the legs at a constant pressure. They work mainly by preventing veins from expanding and pooling blood, rather than actively pushing blood upward. They’re cheaper and simpler than SCDs, which is why they remain popular.
However, compression stockings are generally considered less effective than either blood thinners or intermittent compression devices like SCDs. Combining the two, stockings plus SCDs, has been shown to reduce clot and pulmonary embolism rates more than stockings alone. One practical concern with stockings: studies have found that the vast majority of compression stockings in clinical settings don’t produce the pressure profile they’re designed for. In one study, 98% of calf-length stockings failed to deliver the intended compression, and more than half created a “reverse gradient” where pressure was highest at the top of the stocking rather than the ankle, potentially acting like a tourniquet and increasing clot risk rather than reducing it.
Who Should Not Use SCDs
SCDs are not appropriate for everyone. They should not be used in patients with:
- Severe peripheral artery disease: poor blood flow to the legs means compression could worsen circulation to the tissues
- Severe heart failure: pushing extra blood back toward the heart can overload a heart that’s already struggling
- Severe diabetic neuropathy: loss of sensation in the legs means the patient can’t feel if the device is causing skin damage
- Allergy to the sleeve material
- Skin infections, open wounds, or recent skin grafts on the legs
Interestingly, the old belief that compression devices should never be used on a leg with an existing blood clot has softened. An international consensus statement notes that this concern was based on the theory that compression might dislodge a clot and send it to the lungs, but no data actually support that theory. Current guidance suggests compression can be used cautiously even with an acute clot.
What It Feels Like to Wear Them
If you’re a patient, SCDs feel like a rhythmic squeezing that starts at your ankle and rolls up your calf every few seconds, then releases. Most people describe it as mildly uncomfortable but not painful. The sleeves can feel warm, and your legs may get sweaty underneath them, which is why nurses periodically check the skin for irritation or breakdown. The tubing connecting the sleeves to the pump can make getting in and out of bed awkward, and the pump itself makes a quiet humming and hissing sound as it inflates and deflates.
The most important thing you can do as a patient is keep them on as much as possible. Every hour they’re off is an hour your blood is pooling. If you need to get up, call your nurse so the sleeves can be removed and reapplied properly when you return to bed.
The Other SCD: Superior Canal Dehiscence Syndrome
SCDS (with the extra “S”) is a completely different condition. Superior canal dehiscence syndrome is a rare inner ear disorder where a tiny opening develops in the bone covering the superior semicircular canal, one of the structures deep in the ear that helps you balance.
That small hole has outsized consequences. Sounds from inside your body, like your own voice, heartbeat, or even your eyes moving, become abnormally loud in the affected ear. This phenomenon, called autophony, is one of the hallmark symptoms. People with SCDS may also hear their stomach digesting food or feel like their surroundings are bouncing in sync with their pulse.
Loud external sounds can also push pressure through that opening and disturb the fluid in the semicircular canal. Your brain interprets this moving fluid as head movement, so a sudden loud noise can trigger dizziness or a feeling of imbalance. Changes in skull pressure from sneezing, straining, or coughing can do the same thing.
Beyond the direct ear symptoms, many people with SCDS experience significant “brain fog,” difficulty with thinking, concentration, and memory. This is thought to result from the constant mental effort of processing distorted sound, communicating, and maintaining balance with conflicting signals from the inner ear. Fatigue is extremely common for the same reason. SCDS can affect one or both ears, and symptoms may be constant or come and go, though they typically don’t worsen over time.
How SCDS Is Diagnosed
Diagnosis involves a specialized CT scan of the temporal bone (the bone surrounding the ear) to look for the opening in the superior canal. Doctors also test hearing with an audiogram and evaluate the balance system through a series of eye movement and vestibular tests. Because the symptoms overlap with other ear and balance disorders, SCDS is often misdiagnosed initially. If your symptoms match this pattern, particularly the autophony and sound-triggered dizziness, asking specifically about SCDS can help move the diagnostic process along.