1.2 Surgical Positioning: Supine, Prone, Trendelenburg, and Lateral

Surgical Positioning: Supine, Prone, Trendelenburg, and Lateral

Quick Answer: Proper surgical positioning is a delicate balance between providing the surgeon with optimal access to the operative site and protecting the anesthetized patient from physiological harm. The CSFA plays a hands-on role in moving and padding the patient to prevent nerve injuries (neuropathies), preserve skin integrity, and maintain adequate respiration and circulation.

An anesthetized patient lacks normal pain responses and muscle tone. They cannot complain about a limb being overstretched or a hard surface digging into a nerve. Consequently, the surgical team, including the CSFA, bears the full responsibility for maintaining anatomical alignment and protecting vulnerable structures.

General Principles of Positioning

• Nerve Protection: Nerves are vulnerable to stretch (tension) and compression. The most frequently injured nerves in the OR are the ulnar nerve and the brachial plexus.
• Pressure Ulcers: Bony prominences (heels, sacrum, elbows, occiput) must be well-padded to prevent tissue ischemia and necrosis.
• Circulation: Extreme flexion or extension of joints can kink blood vessels. Straps should be snug but not tight enough to act as tourniquets.
• Respiration: The chest and abdomen must be free to expand. Compression restricts diaphragmatic excursion, leading to hypoxia.
• Team Coordination: Movements must be slow, coordinated, and directed by the anesthesia provider, who controls the patient's airway.

The Supine Position (Dorsal Decubitus)

The supine position is the most common surgical position, used for abdominal, anterior neck, cardiac, and some orthopedic procedures. The patient lies flat on their back with legs uncrossed.

Key Considerations for Supine

• Arm Placement: Arms can be tucked at the sides or placed on armboards. If on armboards, the arms must never be abducted more than 90 degrees. Abduction beyond 90 degrees stretches the brachial plexus, leading to severe nerve damage.
• Ulnar Nerve Protection: The palms should face upward (supinated) when on armboards. If the palms face downward (pronated), the ulnar nerve (located at the medial epicondyle of the elbow) is rotated downward and compressed against the firm surface of the armboard.
• Legs: Legs must remain uncrossed to prevent compression of the peroneal nerve and blood vessels. A pillow is placed under the knees to relieve strain on the lower back.

The Trendelenburg Position

The Trendelenburg position is a modification of the supine position where the head of the bed is tilted downward. It is frequently used for lower abdominal and pelvic surgeries (e.g., prostatectomy, hysterectomy) because gravity pulls the abdominal viscera toward the head, improving visualization of the pelvic organs.

Physiological Risks of Trendelenburg

• Respiratory Compromise: The weight of the abdominal organs rests on the diaphragm, making ventilation more difficult. The anesthesia provider must use higher airway pressures.
• Hemodynamic Changes: Blood pools in the upper body, increasing intracranial pressure (ICP) and intraocular pressure. It can also cause facial and conjunctival edema.
• Shearing Forces: The patient may slide toward the head of the bed. Padded shoulder braces may be used, but they must be placed over the acromioclavicular joint, not the soft tissues of the neck, to prevent massive brachial plexus injury. Non-slip mattresses are preferred.

Reverse Trendelenburg

In Reverse Trendelenburg, the head is elevated, and the feet are lowered. This is used for upper abdominal surgeries (e.g., cholecystectomy, hiatal hernia repair) to displace organs downward. A padded footboard is required to prevent the patient from sliding down the table.

The Prone Position

In the prone position, the patient lies face down. This provides access to the posterior spine, dorsal cranium, and posterior lower extremities (e.g., Achilles tendon repair). The patient is usually intubated in the supine position on the stretcher, then carefully log-rolled onto the operating table.

Key Considerations for Prone

• Chest and Abdominal Support: The patient must be placed on longitudinal chest rolls (e.g., Wilson frame or Jackson table). These rolls span from the clavicle to the iliac crest. Their purpose is twofold: they allow the chest to expand for ventilation, and they prevent compression of the inferior vena cava (IVC) and aorta. IVC compression reduces venous return to the heart, causing profound hypotension.
• Head and Neck: The head is supported by a specialized face piece (e.g., prone view helmet) to keep the cervical spine neutral and to ensure no pressure is placed on the eyes. Direct pressure on the eyes can cause central retinal artery occlusion and permanent blindness.
• Arms: Arms are typically extended forward and placed on armboards alongside the head. The elbows must be padded to protect the ulnar nerve.

The Lateral Position (Lateral Decubitus)

The lateral position involves the patient lying on their side. It is used for thoracic, renal, and hip procedures. It is named for the side resting on the table (e.g., a left lateral position means the patient is lying on their left side, exposing the right side for surgery).

Key Considerations for Lateral

• Axillary Roll: This is the most critical protective measure in the lateral position. A padded roll is placed under the dependent thorax, slightly caudal (inferior) to the axilla. It must never be placed directly into the armpit. The goal is to lift the weight of the torso off the shoulder, preventing compression of the dependent brachial plexus and axillary artery.
• Legs: The dependent (bottom) leg is flexed at the hip and knee to provide stability. The upper leg is kept straight. Pillows must be placed between the knees and ankles to prevent pressure on the peroneal nerve (outer aspect of the knee) and bony prominences.
• Support: The patient is secured with a beanbag positioner or padded pegs (e.g., for hip arthroplasty) to maintain the strict lateral posture. A wide safety strap is placed over the hip.

Mastering these positions is essential for the CSFA, as improper positioning is a leading cause of preventable intraoperative morbidity.