PATIENT POSITIONING IN NEUROANAESTHESIA.

Dr. Rahul NorawatDr. Rahul Norawat

University College of Medical Sciences & GTB Hospital, Delhi

C. Prone Position

» Post. fossa, suboccipital region» Post. approaches to spine.

• Characteristic challenges : Disconnection leads to hypoventilation, desaturation, hemodynamic instability & altered anesthetic depth.

• Pulse oximetry & art. line should be left connected during turn.

• Pressure sores - breasts, penis, soft tissue at the boney points.

• The eyes, nose & ear - periodically checked for lack of pressure.

• Blindness is rare (0.2%), • Optic n. ischemia, CRAO, CRVO.• Risk factors: Prolonged surgery, blood loss,

hypotension, anemia.

Special frames :

Wilson frame: Abdomen is partially compressed, pelvis is partially supported, legs are positioned below the trunk, head rest on pillow.

Wilson frame

Andrews frame : Abdomen hangs free, pelvis is partiallysupported, legs are positioned below heart, head is positioned on pillow or headrest.

Relton Hall frame : Abdomen hangs free, pelvis is supported, legs are positioned below heart, head is positioned on pillow or headrest.

Jackson table : Provides most stable hemodynamic & does not increase dynamic lung compliance.

Concorde position • Modification of prone position,• Best for transtentorial, supracerebellar, infratentorial

area,• Head is flexed, arms are tucked to the trunk & legs are

flexed at knees. • Specific complications - necrosis of chin & obstruction of

cerebral venous outflow.

Hemodynamic and Ventilation.

• Oxygenation improve with prone positioning because

of improved VQ matching.

1) Perfusion of the entire lungs improves,

2) I/A pressure, chest wall compliance, which under positive-pressure ventilation, improves ventilation of the dependent zones of the lung,

3) Previously atelectatic dorsal zones of lungs open.

CVS Respiratory   

CNS Benefits  Risks

Prone                 

Compared to supine, awake:  

VR↓, SV↓

HR↑ ↔, SVR↑, PVR↑, SBP↑↔, MAP↑↔

In anesthetized patient:

VR↓, SV↓, CO↓↔, HR↑, SVR↑, PVR↑, SBP↓↔, MAP↓↔

Compared to supine: increase in upper airway resistance (Wilson frame and chest rolls)  

FRC↑ ↔,

TLC↑ ↔ 

V/Q mismatch ↓

less atelectasis in lungs  

Compared to supine:

a) neutral to the heart

JVF ↑ ↔

JVR↓ ↔

b) lower than heart

JVF↑

JVR↓

Venous Congestion

ICP↑

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)                        

Modification:

Concorde

Best positioning for transtentorial, supracerebellar, infratentorial area

Neck and head hyperflexion: 

venous congestion of the face, nose, and tongue, chin necrosis, cerebral venous obstruction, increase ICP,  

Quadriplegia.

D. Sitting Position

• Posterior fossa surgery, cervical laminectomy.

• Relative contraindications : – Patent ventriculoatrial shunt, – R-L shunt, patent foramen ovale (PFO), – Signs of cerebral ischemia, – Cardiac instability.

• Head holder support is attached to back section of table so the pt. back can be adjusted or lowered emergently without first detaching the head holder.

Semirecumbent position :

• Modified sitting, • Less hemodynamic instability. • Head-up tilt ( venous drainage via IJV - ICP).

Hemodynamic and Ventilation

• Postural hypotension (1/3 of pt.)

• Wrapping of legs with elastic bandages prevents pooling of blood.

• Avoid hyperflexion and hyperextension of neck.

• Maintain at least 2 fingers distance between mandible &

sternum.

• Ventilation improved than supine position due to downward shift of the diaphragm,– I/A pressure, – Ventilation of the dependent zones & V/Q mismatch.

• Prevent hypovolemia & maintain normal pul. perfusion pressure are crucial for maintaining an adequate oxygenation.

CVS Respiratory   

CNS Benefits  Risks

Sitting  Compared to supine, awake: 

VR ↓, SV ↓, CO↓, HR↑, SVR↑, PVR↑

SBP↑↔↓,

MAP↓ ↔↑

In anesthetized patient:

VR↓↓, SV↓, CO↓, HR↑, SVR↑, PVR↑, SBP↓, MAP↓

Compared to supine:  

TLC ↑, FRC ↑

Qs/Qt↓

V/Q mismatch↓

Less atelectasis in lungs 

Compared to supine: 

JVF ↓,

JVR ↑

ICP↓↓

CPP ↔ 

Good cerebral venous and CSF drainage

Optimal approach to posterior fossa

Low ICP  

Minimal bleeding (compared to prone)

Access to airway

Venous air embolism (VAE).

Paradoxical air embolism,

Hypotension,   

Pneumocephalus, SDH,

Paraplegia,

Quadriplegia,

Macroglossia,

Bradycardia or cardiac arrest due to brain stem manipulations.

E. Three-Quarter Prone Position

(Lateral Oblique, or Semiprone)

• Post fossa and parieto-occipital surgery.

• Benefit: VAE is lower. • Risks: Bleeding, brachial plexus injury, pressure sores, &

macroglossia.

• Hemodynamic and ventilation are similar to those with lat & prone positioning.

• Principles resemble those for lat position,

• Dependent arm placed behind the body (coma or sleeping position).

• For suboccipital approach, the nondependent shoulder should be taped down towards the foot.

CVS Respiratory   

CNS Benefits  Risks

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,

AIR EMBOLISM – PATHOPHYSIOLOGY, DETECTION

AND MANAGEMENT