Shoulder surgery is another option and the sitting position decreases brachial plexus stretch and aids in manipulation of the joint.
MAP increases or decreases by 0.75mmHg for each cm change in height between heart and a body region. Therefore regions elevated 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 pooling of blood in legs. Try to elevate torso in increments giving the body time to adjust.
Horse shoe head rest often used to support head using straps or tape to secure head to the headrest - note 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 risk for a paradoxical air embolism causing severe cardiac and neurologic complications
- Trans esophageal echocardiograph( TEE) is the most sensitive monitor
- VAE will increase dead space and contains nitrogen
- End-tidal CO2 will drop and end-tidal nitrogen will increase
- 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 neck can impede arterial and venous blood flow and cause hypoperfusion and inadequate drainage of the brain
- Kinked tube due to neck flexion, risk of tube pressure on tongue leading to macroglossia. Keep two fingerbreadths between 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 prevent 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