Principles of Positioning

Foundations IKrista Yoder

February 16, 2009

Shared responsibility:

Anesthesia team Surgeon OR nurses

West et al. / Perfusion Zones in Pulmonary Circulation

Zone I – alveolar > arteriolar > venule

Zone II – arteriolar > alveolar > venule

Zone III – venule > arteriole > alveolar

Zone I : alveolar > arteriole > venule

Rarely occurs in healthy pts. (normal lung) Caused by:

– Pulmonary HTN– Excessive PEEP– Over distention of alveolar units during

positive pressure ventilation (excessive tidal volume)

Zone II - arteriole > alveolar > venule

Observed in non-dependant lung segments

Perfusion of Zone II areas is dependant on fluctuation/balance between arteriole and alveolar pressure.

Zone III – arteriole/venule > alveolara. Normal blood flow pattern occurs

1. flow is proportional to difference between arterial and venous pressure.

2. hydrostatic forces in dependent portions of the lung produce venous congestion.

Compartment Syndrome -Compartment Syndrome -

- pathologic process at the tissue level due to inadequate perfusion to an extremity

- extensive and potentially lasting damage to muscles and nerves in the compartment

- ferrihemate, results from myoglobin destruction and exerts a direct toxic effect on renal tubular epithelium and renal failure is likely.

Causes of Compartment Syndrome -Causes of Compartment Syndrome -

Systemic hypotension with loss of driving pressure to extremity

Vascular obstruction of major leg vessels by intra-pelvic retractors or excessive flexion

External compression of elevated extremity by straps, leg wrappings, or surgical assistant leaning on extremity

Signs and symptoms:Signs and symptoms:

Ischemia Hypoxic edemaElevated tissue perfusion pressureExtensive rhabdomyolysisMay occur

– Lithotomy >5hrs. (legs)– Lateral > 5 hrs. (arms)

Undesirable Physiologic Changes Associated with Positioning.

• Interference with ventilation - perfusion relationships in the lungs.

• Impaired venous return to the heart.

• Postural hypotension

• abrupt changes in position

• hypovolemia

Positioning and Hypotension:

General anesthesia blunts the compensatory sympathetic nervous system response that would normally minimize BP changes associated with abrupt position changes.

- When positioning a patient take frequent measurement of the BP to determine if the patient is tolerating the new position.

- If hypotension occurs avoid further changes until BP returns to an acceptable level.

• A. bolus IV fluids

• B. administer vasopressor

• 1. Ephedrine 5-10mg dose

• 2. Neosynephrine 50-100 mcg dose

• C. decrease concentration of inhaled anesthesia

Supine Position• Horizontal

• Trendelenburg

• Reverse Trendelenburg

1.1.

Supine – HorizontalSupine – Horizontalcardiaccardiac1. influence of gravity on vascular 1. influence of gravity on vascular system is minimalsystem is minimal2. intravscular pressures from head to 2. intravscular pressures from head to foot vary little from mean pressures at foot vary little from mean pressures at the level of the heartthe level of the heart

a. almost no perfusion a. almost no perfusion gradient gradient between the heart between the heart and arteries in and arteries in head or head or lower extremitylower extremity

Supine - HorizontalSupine - Horizontal cardiaccardiac

– If a patient in supine position is tilted head high or head low, the effects of gravity can become quite significant.

– Pressures may change by 2mm Hg for each 2.5 cm that a given point varies in vertical height above or below the reference point of the heart.

Supine Horizontal

Respiratory

• A. Gravity increases perfusion of dependent (posterior) lung segments.

• B. Abdominal viscera displace diaphragm cephalad.

• C. Spontaneous ventilation favors dependent lung segments while controlled ventilation favors independent (anterior) segments.

Supine - Horizontal• Respiratory - (continued)

• D. Functional residual capacity decreases and may fall below closing volume in older patients.

Supine - Trendelenburg• 1. Cardiac

• A. Activation of baroreceptors, generally causes decreased:

• cardiac output

• peripheral vascular resistance

• heart rate

• blood pressure

Supine - trendelenburg (continued)

• 2. Respiratory

• A. Marked decreases in lung capacities from shift of abdominal viscera.

• B. Increased ventilation/perfusion mismatching and atelectasis.

• C. Increased likelihood of regurgitation.

Supine - trendelenburg Supine - trendelenburg (continued)(continued) 3. Other

A. Increase in intracranial pressure and decrease in cerebral blood flow d/t cerebral venous congestion.

B. Increased intraocular pressure in patients with glaucoma.

Supine - Reverse Trendelenburg• 1. Cardiac

• A. There is a decrease in preload, cardiac output, and arterial pressure.

• B. There is a baroreflex mediated increase in sympathetic tone, heart rate, and blood pressure.

Supine Reverse Trendlenberg - continued

•2. Respiratory

• A. Spontaneous respiration requires less work.

• B. FRC increases.

• 3. Other

•A. Cerebral perfusion pressure and blood flow may decrease

Lithotomy • 1. Cardiac

• A. An autotransfusion effect occurs with placing of the legs in stirrups. This increases the circulating blood volume and preload.

• B. Returning the patients legs to the supine position at the end of the case has the opposite effect, decreasing circulating blood volume and preload.

• C. Effect on blood pressure and cardiac output depends on volume status.

Variations of Lithotomy Variations of Lithotomy

Standard – a patient’s thighs and legs are flexed approximately 90* on the trunkLower leg is nearly parallel to the floor

Low – a patient’s thighs and legs are flexed approximately 30-45* on the trunkUrologic procedures

Reduces perfusion gradients to and from the legs

Lithotomy ContinuedLithotomy Continued

High – a patient’s thighs are flexed 90* or more on the trunk

• Significant uphill gradient for arterial perfusion into the feet

• Exaggerated – a patient’s thighs are forcibly flexed on the trunk, and the lower legs are aimed skyward.

•long axis of synphysis pubis almost parallel to the floor.

Lithotomy - continued2. Respiratory

• A. Decreases vital capacity.• B. Increases likelihood of aspiration.

Prone• 1. Cardiac

• A. Pooling of blood in the extremities and compression of abdominal muscles may decrease preload, cardiac output, and blood pressure.

• 2. Respiratory

• A. Compression of abdomen and thorax decreases total lung compliance.

• B. Increased work of breathing.

• 3. Other

• A. Extreme head rotation may decrease cerebral venous drainage and cerebral blood flow.

Lateral Decubitus• 1. Cardiac

• A. Cardiac output unchanged unless venous return is obstructed.

• Kidney rest

• B. Arterial blood pressure may fall as a result of decreased vascular resistance.

• 2. Respiratory

• A. Decreased ventilation of dependent lung; increased perfusion of dependent lung. V/Q mismatch

• Further decreases in dependent lung ventilation with paralysis and an open chest.

Sitting• 1. Cardiac

• A. Pooling of blood in lower extremities decreases central blood volume.

• B. Cardiac output and arterial blood pressure decrease despite rise in heart rate and systemic vascular resistance.

• 2. Respiratory

• A. Increase in lung volumes and functional residual capacity.

• B. Increase in work of breathing.

• 3. Other

• A. Cerebral blood flow decreases.

Complications of Positioning

Complications associated with patient positioning.

• Complication - Air embolism

• Positions of concern - Sitting, prone, reverse trendelenburg

• Prevention - Maintain venous pressure above 0 at the wound.

Complications continued -

• Complication - Alopecia

• Positions of concern - Supine, lithotomy, trendelenburg

• Prevention -

• maintain normotension

• padding of occiput

• turn the patient’s head intermittently

Complications continued-

• Complication - Backache

• Position of concern - any

• Prevention -

• lumbar support

• padding of OR table

• slight hip flexion

Complications continued-

• Complication - Compartment syndrome

• Position of concern - Especially lithotomy

• Prevention -

• Maintain perfusion pressure

• Avoid external compression

• See Stoelting pg. 294

Complications continued -

• Complication - corneal abrasion

• Position of concern - any, especially prone

• Prevention - lubricate and tape the eyes

• Complication - digit amputation

• Position of concern - any

• Prevention - check for protruding digits prior to changing OR table configuration.

Complications continued -

• Complication - retinal ischemia

• Position of concern - prone or sitting

• Prevention - avoid pressure on globe of eye

• Complication - skin necrosis

• Position of concern - Any

• Prevention - padding over bony prominences

Complications Continued - Peripheral Nerve Injuries

Causes of Peripheral Nerve Injury• Positioning that compresses or stretches nerves

• Co-existing diseases

• diabetes mellitus

• Vitamin deficiency

• Alcoholism

• Cancer

• Type of surgery

• Anticoagulant therapy and hematoma

Causes of Peripheral Nerve Injury - continued

• Hypothermia

• Hypotension

• Prolonged tourniquet application (greater than 3 hours)

Brachial Plexus InjuryBrachial Plexus Injury

Radial nerve injuryRadial nerve injury

Ulnar nerve injury Ulnar nerve injury

Cubital tunnel nerve injuryCubital tunnel nerve injury

Saphenous Nerve injurySaphenous Nerve injury

Mask Strap Injury:

Tissue Necrosis from ETT :

Vigilance = PreventionVigilance = Prevention