Table 1.

Summary of Specific Physiological Changes and Risks and Benefits with Positioning for Neurosurgical Procedures.

	Cardiovascular	Respiratory	Central nervous	Benefits	Risks
Supine	Compared to upright, awake and anesthetized:	Compared to upright: FRC ↓, TLC ↓ atelectasis of the dependent lung zones;	Compared to upright:	The easiest position	Often needs head flexion/extention/rotation Ulnar and peroneal nerve injury
	VR ↑, SV ↑, CO ↑	Qs/Qt ↑	JVF ↑ ↔
	HR ↓	V/Q mismatch ↑	JVR ↓ ↔
	SVR ↓		CPP ↔ ↓
	SBP ↔, MAP↓↔		CSF drainage may be impaired
Modifications: a)lawn-chair b)reverse Trendelenbourg	Improvement of the VR from the lower extremities	Improvement of ventilation of the dependent lung zones	Improvement of the cerebral venous, lymphatic and CSF drainage.
Lateral	Compared to supine, anesthetized:	Compared to supine:	Compared to supine:	Optimal approach to the temporal lobe	Brachial plexus injury
	VR ↓, SV ↓, CO↓	FRC ↓, TLC ↓	JVF↑↔		Ear and eye injury
	HR↑ ↔	Qs/Qt ↑↑	JVR↓↔		Suprascapular nerve injury (of the dependent shoulder)
	SVR↑, PVR↑	V/Q mismatch ↑↑ atelectasis of the dependent lung	with neck flexion:
	SBP↓, MAP↓		JVF↓, JVR↑, ICP↑
Modification: park-bench					Stretch injuries (axillary trauma) Decreased perfusion to the dependent arm
Prone	Compared to supine, awake:	Compared to supine: increase in upper airway resistance (Wilson frame and chest rolls)	Compared to supine: a) neutral to the heart	Optimal posterior approach to spine Less risk for VAE (compared to sitting)	The most difficult position Difficult access to airway Pressure sores of soft tissues Eye injury Blindness Bleeding (compared to sitting)
	VR↓, SV↓
	HR↑ ↔		JVF ↑ ↔
	SVR↑, PVR↑	FRC↑ ↔, TLC↑ ↔	JVR↓ ↔
	SBP↑↔, MAP↑↔	V/Q mismatch ↓	b) lower than heart
	In anesthetized patient:	less atelectasis in lungs	JVF↑, JVR↓, venous congestion
	VR↓, SV↓, CO↓↔		ICP↑
	HR↑, SVR↑, PVR↑
	SBP↓↔, MAP↓↔
Modification: Concorde					Neck and head hyperflexion: venous congestion of the face, nose, and tongue, epystarchis, chin necrosis, cerebral venous obstruction, increase of ICP, quadriplegia
Sitting	Compared to supine, awake:	Compared to supine:	Compared to supine:	Optimal approach to posterior fossa Low ICP	Venous air embolism (VAE) Paradoxical air embolism Arterial Hypotension
	VR ↓, SV ↓, CO↓	TLC ↑, FRC ↑	JVF ↓, JVR ↑
		Qs/Qt↓	ICP↓↓
	HR↑, SVR↑, PVR↑	V/Q mismatch ↓	CPP ↔	Minimal bleeding (compared to prone) Access to airway	Pneumocephalus Paraplegia, Quadriplegia Macroglossia
	SBP↑↔↓, MAP↓ ↔↑	less atelectasis in lungs	Good cerebral venous and CSF drainage
	In anesthetized patient:
	VR↓↓, SV↓, CO↓
	HR↑, SVR↑, PVR↑
	SBP↓, MAP↓
Three - quarters	different changes, resemble lateral or prone	changes, resemble lateral or prone	different changes, resemble lateral or prone	Less risk for VAE (compared to sitting) Better access to airway (compared to prone)	Difficult position Brachial plexus injury Pressure sores Compartment syndrome of the dependent upper extremity Pudendal nerve injury

Changes of physiologic parameters in cardiovascular, respiratory and central nervous system are presented as observed in anesthetized subjects, changes in cardiovascular system presented in awake and anesthetized subjects: HR- heart rate, SV-stroke volume, VR – venous return, CO-cardiac output, SBP- systolic blood pressure, TLC- total lung capacity, FRC- functional residual capacity, Qs/Qt – intrapulmonary shunt, V/Q mismatch- ventilation/perfusion mismatch, ICP- intracranial pressure, JVF – jugular venous flow, JVR – jugular venous resistance, CPP- cerebral perfusion pressure; ↑- increase, ↓ - decrease, ↔ no change.