Sequential Compression Devices (SCDs) are non-invasive medical tools used to enhance blood flow, particularly in the lower limbs. These devices apply external, rhythmic pressure to the extremities, which improves circulation in patients who are immobile or have limited mobility. SCDs provide a mechanical method for maintaining vascular health when natural movement is restricted. They are an important component of preventative care for many patients in acute care facilities.
Anatomy of a Sequential Compression Device
The Sequential Compression Device system is composed of interconnected parts. The central unit is the pneumatic pump, which controls the inflation and deflation cycles. This pump is connected to the sleeves via air tubes, which transmit the controlled pulses of air pressure. The tubes must remain unkinked and clear for proper function.
The compression sleeves are inflatable wraps that fit around the patient’s legs, or sometimes the arms. These sleeves are constructed with multiple internal air chambers, often two or three, designed to inflate in a specific, timed sequence. The sleeves are secured around the limb with Velcro or similar fasteners to ensure a snug fit.
The Mechanism of Action
The sequential nature of the device’s operation distinguishes it from simple pneumatic compression. The chambers within the sleeve inflate starting from the most distal point of the limb, such as the ankle or foot, and then progress upward toward the knee or thigh. This action creates a pressure gradient that “milks” the blood upward through the deep veins. This physiological process mimics the natural skeletal muscle pump, which activates when a person walks or moves their calf muscles.
By applying this gradient compression, the device forces static blood out of the lower extremities and back toward the heart. The rapid increase in blood flow velocity prevents blood from pooling, a condition known as stasis, which is a major factor in clot formation. After a short period of compression, the chambers quickly deflate, allowing the veins to refill before the cycle repeats. This continuous, rhythmic action maintains active circulation, which is crucial for immobile patients.
Primary Role in Preventing Blood Clots
The primary medical purpose of SCDs is to prevent the formation of blood clots, specifically Deep Vein Thrombosis (DVT), which typically occurs in the deep veins of the legs. Immobility, such as during surgery, prolonged bed rest, or recovery from trauma, slows blood flow and increases the risk of DVT. If a DVT clot breaks free, it can travel through the bloodstream and lodge in the lungs, causing a potentially fatal condition called Pulmonary Embolism (PE). SCDs mitigate this risk by actively preventing blood stasis, which is a key component in DVT development.
These devices are used for patients who face restricted movement. Patients undergoing major surgery, especially orthopedic or abdominal procedures, are often prescribed SCDs both during and after their operation. They are also standard for trauma patients, individuals with spinal cord injuries, and those in critical care units who are bedridden for extended periods. SCDs are a mechanical form of prophylaxis that can be used alone or in conjunction with blood-thinning medications to reduce the chance of developing a dangerous clot.
Practical Application and Important Considerations
For the SCD to be effective and safe, proper application and fit are necessary, which involves selecting the correct sleeve size for the patient’s limb circumference. The tubing connecting the sleeve to the pump must be free of kinks or twists, as any obstruction can compromise the pressure delivery and cycle timing. Patients and caregivers should regularly check the skin beneath the sleeves for signs of irritation or pressure sores, especially in those with fragile skin integrity.
Contraindications are situations where the use of SCDs is not recommended and can be harmful. A known or suspected Deep Vein Thrombosis is a major contraindication, as compression could potentially dislodge the existing clot and cause a pulmonary embolism. SCDs should also be avoided in limbs with severe peripheral arterial disease, where compression could further impair compromised blood flow. Other situations, such as severe edema (swelling) or acute skin infections, also warrant avoiding the device to prevent worsening the condition or causing tissue damage.