Sitting/Beach chair

This position may be used for posterior fossa and cervical spine procedures. It provides excellent surgical exposure, facilitates blood and cerebral spinal fluid drainage, and decreases blood in the field. 

Note the risk of jugular venous obstruction with excessive neck flexion. 

Shoulder surgery is another option. The sitting position decreases the brachial plexus stretch and helps manipulate the joint.

MAP increases or decreases by 0.75mmHg for each cm change in height between the heart and a body region. Therefore, elevated areas above the heart in the sitting, head-up, or lithotomy position may be at risk for hypoperfusion and ischemia, especially with hypotension.

45-degree head-up: minimal hemodynamic changes

90-degree head-up: cardiac output decreases by 20% due to venous blood pooling in the legs. Try to elevate the torso in increments, giving the body time to adjust.

Horseshoe headrest is often used to support the head using straps or tape to secure the head to the headrest - note the risk of brachial plexus injury with manipulation of limbs/head.

There are serious complications associated with the sitting position, such as Venous Air Embolism (VAE), pneumocephalus, quadriplegia, and peripheral nerve injuries.

Venous air embolism (VAE)

  • Cardiac dysrhythmias, arterial oxygen desaturation
  • Any position where a negative pressure gradient exists between the right atrium and the veins at the operative site
  • Complications vary with inspired volumes
    • No effect with minimum amounts of air
    • Hypotension, arrhythmias, cardiac arrest, and death with larger volumes
  • Air that enters the right side of the heart can limit gas exchange as it displaces blood in the pulmonary vasculature
  • PFO increases the risk for a paradoxical air embolism, causing severe cardiac and neurologic complications
  • Transesophageal echocardiography( TEE) is the most sensitive monitor
  • VAE will increase dead space and contain nitrogen
    • End-tidal CO2 will drop, and end-tidal nitrogen will increase

Anesthetic considerations

  • Decreased CI, CVP, PCWP, and increased SVR
  • Consider A-line in seated procedures where cerebral perfusion is a concern with the transducer at the level of the circle of Willis
  • Excessive flexion of the neck can impede arterial and venous blood flow and cause hypoperfusion and inadequate drainage of the brain
  • The kinked tube is due to neck flexion, and there is a risk of tube pressure on the tongue leading to macroglossia. Keep two fingerbreadths between the chin and sternum.
  • The sitting position interferes the least with ventilation and has less influence on lung volumes
    • With flexion of the hips and elevation of the legs, abdominal contents may shift caudally and limit the diaphragm, which will decrease FRC
  • Arm support to prevent stretching of brachial plexus
  • Leg support/flexion of knees to avoid stretching of sciatic nerve

A 4-patient case series describing catastrophic cerebral ischemia in patients undergoing shoulder surgery in the beach chair position can be accessed at the following APSF page: Sitting/Beach chair position