POSITIONING IN NEUROSURGICAL PROCEDURES

POSITIONING IN NEUROSURGICAL PROCEDURESPRESENTER DR. SAIKAT MITRA MODERATOR DR. SHOBHA PUROHITSMS MEDICAL COLLEGE, JAIPUR

INTRODUCTIONAim of optimal positioning is to provide best surgical access & potential risk to the patient.

Safe positioning requires planning and good communication between anaesthetist and surgeon.

Skilled personnel are required at the beginning & end of surgical procedure to facilitate safe positioning.

Knowledge of physiological changes associated with positioning can help predict potential problems.

All equipments should be secured and rechecked after every change in position.

Head-up posturing (150 - 200) to improve cerebral venous drainage.

Many complications do not reveal themselves for up to several days after surgery.

POSITIONING AIDS/ SUPPORTSPin (Mayfield) head holder

Radiolucent pin head holder

Horseshoe head rest

Foam head support (e.g., Voss, O.S.I., Prone-View)

Vacuum mattress (bean bag)

Wilson-type frame

Andrews (hinder binder)-type frame

Relton-Hall (four-poster) frame

Mayfield head holderRadiolucent pin head holderVacuum mattressHorseshoe head restFoam head support

FRAMESSpinal surgery frames optimizes venous return. risk of air embolism.

Relton-Hall (four-poster)frame

Wilson-type frame

POSITIONSSupine

Lateral (Park bench)

Semi-lateral (Jannetta)

Prone

Sitting

SUPINE POSITION

INTRODUCTIONCommonest position; also known as dorsal decubitus position.

Used for cranial procedures, carotid end-arterectomies & anterior approaches to cervical and lumbar spine.

Haemodynamic reserve best maintained (as entire body is close to the heart level).

Variations: a) Lawn chair position, b) Frog-leg position, c) Trendelenburg & d) Reverse Trendelenburg position.

As compensatory mechanisms are blunted by anaesthesia Trendelenburg or Reverse Trendelenburg positions cause significant cardiovascular alterations.

PRESSURE POINTS

ARM POSITIONMay be abducted or adducted (tucked).

Abduction limited < 900 to minimize brachial plexus injury by caudad pressure in axilla from humerus head.

Hand and forearm are kept supinated or in neutral position with palm toward body to reduce external pressure on spiral groove of humerus and ulnar nerve.

When arms are adducted, they are usually held alongside the body with a draw sheet that passes under the body, over the arm, and is then tucked directly under the torso (not the mattress).

Elbows and any protruding objects (i.v. fluid lines and stopcocks) are padded.

ARM POSITIONArm position using the arm board. Abduction of arm is limited to < 900. Arm is supinated and elbow is padded.Arm tucked at patient side and is in neutral position with palm to hip. Elbow is padded and arm is well supported by the mattress.

VARIATIONS OF SUPINE POSITION

LAWN CHAIR POSITIONHead-up posture accomplished by adjusting operating table to a chaise lounge (lawn chair) position.

Advantages:Promotes cerebral venous drainageDecreases stress on back, hips and knees.Venous drainage from lower extremity improves (legs are slightly above heart level).FLEXION + PILLOW UNDER KNEES + SLIGHT REV. TRENDELENBERG

LAWN CHAIR POSITION

TRENDELENBURG POSITIONAssociated with tilting a supine patient head down.Often used to increase venous return during hypotension.Named after 19th century German surgeon Friedrich Trendelenburg.

Trendelenburg position and reverse Trendelenburg position

HARMFUL EFFECTS CVP, ICP, IOP.

Respiratory system Abdominal viscera moves cephalad against diaphragm FRC & pulmonary compliance V/P mismatch.

CVS VR C.O.Central redistribution of blood may lead to volume overload in the failing heart.

Stomach lies above glottis Aspiration.

Prolonged head-down lead to swelling of face, conjunctiva, larynx & tongue postoperative upper airway obstruction.

PRECAUTIONSExtra-care to prevent from slipping cephalad on the surgical table due to effect of gravity. Techniques Antiskid beddingKnee flexionShoulder bracesBeanbag cradling &Padded cross-torso straps.To avoid compression of brachial plexus by torso against shoulder girdle.Shoulder braces & beanbag pads risk of injury to upper & middle trunk of brachial plexus.Due to risk of upper airway obstruction air leak test or visualizing larynx before extubation must be carried out.

REVERSE TRENDELENBURG POSITIONAlso known as head-up tilt.

Precautions -Preventing the patients from slipping on the table.Frequent monitoring of arterial blood pressure hypotension may result from VR. Head is positioned above heart perfusion pressure to brain.

Complications HypotensionVenous air embolism

HEAD DURING SUPINE POSITIONNeutral or rotated frontal, temporal or parietal access.

Neutral Bifrontal craniotomy and transsphenoidal approach to pituitary.

Flexion interhemispheric approach to lateral or third ventricle.

Slight extension subfrontal approach.

PRECAUTIONSExtremes of head rotation impairs jugular venous drainage shoulder roll attenuate this problem.

Extreme flexion causes kinking of ET tube airway pressures (keep a distance of 1 or 2 finger breadths between chin & chest during flexion).

Flexion + reverse Trendelenburg position risk of VAE {esp. in bifrontal craniotomy which traverses SSS}

COMPLICATIONS OF SUPINE POSITIONPressure alopecia -Cause Ischemia of hair follicles due to prolonged head immobilization with its full weight falling on a limited area (usually occiput).

Precautions Lumps such as those caused by monitoring cable connectors should not be placed under the head.Prevention of hypothermia and hypotension during surgery.Ample cushioning of head & periodic rotation of head to redistribute the weight.

COMPLICATIONSBackache -Cause Normal lumbar lordotic curvature is lost during general anaesthesia with muscle relaxation due to their effects on tone of paraspinous muscles.

Precautions Patients with extensive kyphosis, scoliosis or h/o back pain extra padding of spine/slight flexion at hip and knee.

Peripheral nerve injury Ulnar neuropathy is most common.

risk of aspiration of gastric contents.

PERIPHERAL NERVE INJURYAs per ASA Closed Claims database (1970 2010): Ulnar neuropathy (21%)Brachial plexus (20%)Spinal cord (19%)Lumbosacral nerve roots or cord (17%)

Ulnar neuropathy

Classic site of injury exposed ulnar groove behind medial epicondyle of humerus.

Here nerve is exposed to both direct trauma from sides of operating table and indirect trauma from stretch.

Precaution - Pronation makes ulnar nerve very vulnerable, while supination keeps it in a more protected position.

BRACHIAL PLEXUS INJURYBrachial plexus (primarily C8 and T1 nerve roots) susceptible to injury because:-

Long superficial course via axilla with 2 points of fixation - cervical vertebrae and axillary fascia.

Lies in close proximity to relatively fixed first rib, clavicle and humerus and get compressed between these structures.

Precautions Arm abduction limited < 900Avoid shoulder bracesHead in midline

LATERAL POSITION

INTRODUCTIONUsed for access to posterior parietal lobes, occipital lobes and lateral posterior fossa, including tumors at CP angle and vertebral/basilar arteries aneurysms.

Patient rests on non-operative side; balanced with anterior and posterior support (bedding rolls or deflatable beanbag) with flexed dependent leg.

ARM POSITIONArms are kept in front of the patient.

Dependent arm rests on a padded arm board perpendicular to the torso.

Non-dependent arm is supported over folded bedding or suspended with armrest or foam cradle.

Neither arm should be abducted > 900.

Axillary roll is placed between chest wall and bed just caudal to dependent axilla to prevent compression of dependent neurovascular bundle (should never be placed in the axilla).

Axillary roll is placed well away fromaxilla to prevent compression of axillary artery and brachial plexus.

POSTIONINGHead must be in neutral position to prevent excessive lateral rotation of neck and stretch injuries to brachial plexus this requires additional head support.

Dependent ear should be checked to avoid folding and undue pressure.

Eyes should be securely taped before repositioning.

Dependent eye must be checked for external compression frequently.

A pillow or other padding is placed between knees with dependent leg flexed to minimize excessive pressure on bony prominences & stretch of lower extremity nerves.

Picture showing placement of arms and head. Additional padding is under headrest to ensure alignment of head with spine. Headrest is kept away from dependent eye.

PRECAUTIONSPulse should be monitored in dependent arm to detect early compression of axillary neurovascular structures. Vascular compression and venous engorgement in the dependent arm may affect pulse oximetry reading.

SpO2 is an early warning sign of compromised circulation.

Hypotension measured in dependent arm may be due to axillary arterial compression.

When kidney rest is used, it must be properly placed under dependent iliac crest to prevent inadvertent compression of IVC.

PHYSIOLOGICAL CHANGESRespiratory system:-Non-dependent lung well ventilated, poorly perfused.&Dependent lung well perfused, poorly ventilated (due to lateral weight of mediatinum & disproportionate cephalad displacement of abdominal contents)

V/Q mismatch

Cardiovascular system:- Minimal decrease in MAP; HR unchanged.

POTENTIAL PRESSURE POINTS

PARK-BENCH ORTHREE QUARTER PRONE POSITIONModification of lateral position.

Provides better access to posterior fossa (compared to lateral position).

Placing patient sufficiently superiorly on operating table such that dependent arm hangs over edge of table & secured with a sling.

Trunk is rotated 15 from lateral position into semiprone position & supported with pillows.

Lower extremities should be slightly flexed and pillow placed between legs.

Head is flexed at neck and then rotated to look toward the floor (120 from vertical & laterally flexed 20 ).

SEMILATERAL OR JANETTA POSITION

SEMILATERAL POSITIONNamed after the neurosurgeon who popularized its use for microvascular decompression of 5th cranial nerve.

Used for petrosal, retromastoid & U/L frontotemporal approaches.

Achieved by lateral tilting of table 100 to 200 combined with a generous shoulder roll.

Extreme head rotation should be avoided (to prevent compression of contralateral jugular vein by the chin).

Excessive traction on shoulder should be avoided.

PRONE POSITION

INTRODUCTIONAlso known as ventral decubitus position.

Used for spinal cord, occipital lobe, craniosynostosis & posterior fossa procedures.

Physiological changes:-If legs are in plane with torso haemodynamic reserve is well maintained.

Pulmonary function is superior to supine or lateral decubitus positions if the patient is properly positioned with no abdominal pressure.

POSITIONING

POSITIONING

POSITIONING

POSITIONING

ARMS POSITIONBoth arms may be kept along the patients sides and tucked in neutral position or placed in the stick-em up position.

In stick-em up position, arms should not be abducted > 90 & elbows should not be extended > 90 (90-90 position) to prevent excessive stretching of brachial plexus, especially in patients with head turned.

Elbow should be anterior to the shoulder to prevent wrapping of brachial plexus around head of humerus.

Extra padding under the elbow may be needed to prevent compression of ulnar nerve.

Prone position with Wilson frame

HEAD POSITIONHead may be turned laterally, if neck mobility is adequate.

Patients with cervical arthritis or cerebrovascular disease lateral rotation of neck may carotid or vertebral arterial blood flow or jugular venous drainage.

Head is kept in neutral position (most common) using a) Surgical pillow, b) Horseshoe headrest or c) Mayfield head pins.

Disadvantage with pillows face is not always visible making eye checks more difficult.

Mirror systems are available to facilitate intermittent visual confirmation that eyes are not compressed.

Horseshoe headrest supports only forehead and malar regions and allows excellent access to the airway.Mayfield rigid pins firmly hold the head in one position without any direct pressure on face & allow access to the airway.HEAD POSITION

Mirror system for prone positionProne position with horseshoe adapter

TAKE CARE OF ABDOMEN & THORAXAim of posterior spinal surgery - venous pressure to minimize bleeding and facilitate surgical exposure.

External pressure on abdomen intra-abdominal and intra-thoracic pressures.

Abdominal pressure venous pressure of valveless abdominal & spine vessels (including epidural veins) and causes compression of IVC VR, cardiac output.

External pressure on abdomen pushes diaphragm cephalad FRC & pulmonary compliance; PIP.

Firm rolls or bolsters placed along each side from clavicle to iliac crest to support the torso abdominal, thoracic pressures.

PRESSURE POINTS

PRECAUTIONSUse of wire-reinforced ET tube to avoid kinking and obstruction as it exits patients mouth during prone position.

Dependent eye must be frequently checked for external compression.

Abdomen should hang relatively free and move with respiration.

Breasts should be placed medial to gel bolsters.

Lower portion of each roll or bolster must be placed under its respective iliac crest to prevent pressure injury to genitalia and femoral vasculature.

Prevention of patient movement when head is held in rigid pins skidding out of pins can result in scalp lacerations/cervical spine injury.

Horseshoe and pin headrests attach to adjustable articulating supports any slippage or failure of this bracketing device may lead to complications due to sudden dropping of head.

Face must be periodically checked to ensure weight is borne only by bony structures, airway is uncompromised and no pressure on the eyes.

PRECAUTIONS

Modification of prone position.

Used for cervical spine & posterior fossa procedures.

Neck flexion, reverse Trendelenburg, arms tucked alongside to trunk & elevation of legs this orientation brings surgical field to a horizontal position.

Complication 1) necrosis of chin & 2) obstruction of cerebral venous outflow.THE CONCORDE POSITION

Postoperative vision loss (POVL)

Retinal ischemia Ischemic optic neuropathy (ION) (more common)COMPLICATIONSBlindnessCause - Orbital compression causing central retinal vessel occlusion.Precaution - must be intermittently confirmed (every 15 min) & after any surgery-related head or neck movement that eyes are not impingedCause BP, hematocrit, lengthy surgical procedures, i.v. fluid administration, poor collateralization or absence of autoregulation of vasculature of optic nerve head, small and anatomically crowded optic nerve head, impaired cerebral venous drainage, IOP.

Macroglossia Flexion of neck frequently required to facilitate surgical access AP dimension of hypopharynx compression ischemia of tongue base, soft palate, posterior wall of pharynx occur in presence of foreign bodies (ETT, esophageal stethoscope, oral airway).

Edema accumulates after reperfusion of ischemic tissue Macroglossia post-extubation airway obstruction.

Swollen tongue may protrude between and trap by teeth during prolonged prone procedure.

Rolled gauze bite block may be used instead of oral airway.COMPLICATIONS

SITTING POSITION

INTRODUCTIONUsed for posterior cervical spine and posterior fossa surgeries.

Infrequently used.

Advantages Excellent surgical exposureDrier fieldPerioperative blood lossSuperior access to the airwayFacial swellingImproves ventilationCan see face during cranial nerve stimulation

PHYSIOLOGYCardiovascular system:- VR, Stroke volume, Cardiac output, Cardiac index MAP unchanged SVR, PVR

Respiratory system:- FRC, VC improves V/P mistmatch (hypoperfusion of upper lung)

Other systems:- RBF, CBF

POSITIONINGMore commonly patient positioned in modified recumbent position.

Head may be fixed in Mayfield head pins.

Head holder should be attached to back portion of the table, rather than to the thigh or leg portions makes lowering of head and closed chest massage if necessary, easier.

Arms must be supported (due to gravitational pull) to the point of slight elevation of shoulders to avoid traction on shoulder muscles and neurovascular structures.

Legs should be kept as high as possible (usually with pillows under knees) to promote venous return.

Knees are slightly flexed for balance and to reduce stretching of sciatic nerve.

Feet are supported and padded.

Elastic stockings and active leg compression devices also help to maintain venous return.

POSITIONING

Patient is typically semi-recumbent rather than sitting. A The head-holder support is correctly positioned so that the head can be lowered without the necessity to first detach the head holder.

B This configuration with the support attached to the thigh portion of the table, should be avoided.

PRESSURE POINTS

CARE OF HEAD & NECKExcessive cervical flexion may occur with head fixed in pins

Impede both arterial and venous blood flow hypoperfusion or venous congestion of brain.

Impede normal respiratory excursion.

Obstruct ETT and place significant pressure on tongue leading to macroglossia.

Careful vigilance of BP.

MAP should be corrected to head level zeroing arterial pressure transducer at interaural plane/skull base (CPP maintenance become easier).

If manual BP cuff is used correction (a column of water 32 cm high exerts a pressure of 25 mmHg) for hydrostatic difference between arm and operative field should be applied.

Excessive flexion of knees towards chest should be avoided prevent abdominal compression,lower extremity ischemia and sciatic nerve injury.

PRECAUTIONS

Maintaining at least 2 fingers distance between mandible and sternum is recommended.

Patients should not be positioned at the extreme of their range of motion.

Extra caution with neck flexion is advised if TEE is used for air embolism monitoring (as esophageal probe lies between flexed spine and airway with ETT compression of laryngeal structures and tongue).

Screening contrast echocardiography to investigate the patency of the inter-atrial septum is performed before considering sitting position.

PRECAUTIONS

COMPLICATIONSCardiovascular instability

Venous air embolism

Paradoxical air embolism

Pneumocephalus

Macroglossia

Quadriplegia

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