Ebook Handbook of clinical anesthesia (7/E): Part 2

(BQ) Part 2 book “Handbook of clinical anesthesia” has contents: Peripheral nerve blockade, anesthesia for neurosurgery, neonatal anesthesia, obstetrical anesthesia, pediatric anesthesia, anesthesia for otolaryngologic surgery, anesthesia for ophthalmologic surgery,…. and other contents.

35

VII

C H A P T E R

Regional anesthesia enables site-specific, long-lasting, and effective

anesthesia and analgesia (Tsui BCH, Rosenquist RW Peripheral nerve

blockade In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Ortega

R, Stock MC, eds Clinical Anesthesia Philadelphia: Lippincott

Williams & Wilkins; 2013:937–995) Peripheral nerve blocks (PNBs)

can be used as the only anesthetic, as a supplement to provide analgesia

and muscle relaxation along with general anesthesia, or as the initial

step in the provision of prolonged postoperative analgesia such as with

intercostal blocks or continuous peripheral nerve catheters The two

most common techniques for nerve localization and block

perfor-mance are nerve stimulation (NS) and ultrasound (US) imaging

I GENERAL PRINCIPLES AND EQUIPMENT. An ing advance in technology in relation to regional anesthesia in recent years has been the introduction of anatomically based

excit-US imaging to visualize the target nerve In many situations, it

is prudent to combine the two technologies of NS and US imaging to achieve the goal of 100% success with all regional blocks

A Setup and Monitoring (Table 35-1)

B Common Techniques: Nerve Stimulation

1 Basics of Technique and Equipment A low-current

electrical impulse applied to a peripheral nerve produces stimulation of motor fibers and theoretically identifies proximity to the nerve without actual needle contact of the nerve or related patient discomfort

2 Practical Guidelines After a low-threshold response is

obtained, 2 to 3 mL of local anesthetic is injected, and the operator watches for disappearance of the motor twitch, which is a signal to inject the remainder of the Peripheral Nerve Blockade

proposed dose in divided aliquots After nerve tion using a stimulating needle, introduction of a stimu-lating catheter with continuous stimulation of the nerve

localiza-is suitable for provlocaliza-ision of continuous analgesia

C Common Techniques: Ultrasound Imaging

1 Basics of Technique and Equipment US images reflect

contours, including those of anatomic structures, based

on differing acoustic impedances of tissue or fluids The Doppler effect can be very useful for identifying blood vessels during nerve localization using US guidance because many nerves are situated in close proximity to vascular structures

2 Practical Guidelines

a Probe sterility is paramount when performing

real-time US guidance For nerve localization during

A selection of sedatives, hypnotics, and intravenous anesthetics should be immediately available to prepare patients for regional anesthesia

Emergency drugs (atropine, epinephrine, phenylephrine, ephedrine, propofol, thiopental, succinylcholine, amrinone, intralipid) should also be immediately available

Monitoring

During the performance of regional anesthesia, it is vital to have skilled personnel monitor the patient at all times (electrocardiogra-phy, noninvasive blood pressure, pulse oximetry, and level of con-sciousness of the patient should be gauged frequently using verbal contact because vasovagal episodes are common with many regional procedures)

The patient should be closely observed for systematic toxicity (within

2 minutes for at least 30 minutes after the procedure)

Before performing blocks with significant sympathetic effects, a line blood pressure reading should be obtained

b After one observes that the needle is seen to be close

to the nerve(s), a 1- to 2-mL test dose of local thetic or dextrose 5% in water (D5W) can be injected

anes-to visualize the spread The solution will be seen as a hypoechoic expansion and often illuminates the sur-rounding area, enabling better visibility of the nerves and block needle

D other Related Equipment

1 Needles used for regional techniques are often modified

from standard injection needles (Continuous blocks require larger bore needles to facilitate catheter introduction.)

2 Catheters amenable to stimulation (with an electrode

placed into the catheter tip) may enable more accurate advancement of catheters for substantial distances to provide continuous analgesia

E Avoiding Complications Despite the excellent safety

record of regional anesthesia, the incidence of some cations may be higher in PNB than other regional anesthesia

compli-or analgesia techniques, and these complications can be devastating Choosing a suitable patient and applying the right dose of local anesthetic in the correct location are the primary considerations Follow-up before and after discharge is equally important

II SPECIfIC TECHNIQUES: HEAD AND NECk, UPPER

EXTREMITIES, CHEST, AND ABDoMEN

A Head and Neck (Figs 35-1 to 35-4)

1 Cervical Plexus Blocks Anesthesia of the deep or

super-ficial cervical plexus or both can be used for procedures

of the lateral or anterior neck such as parathyroidectomy and carotid endarterectomy In carotid surgery, local infiltration of the carotid bifurcation may be necessary to block reflex hemodynamic changes associated with glos-sopharyngeal stimulation

2 occipital Nerve Blocks The greater and lesser occipital

nerves can be blocked by superficial injection at the points

Peripheral Nerves Median nerve at the antecubital fossa

The large anechoic artery lies immediately lateral to the nerve.

Radial nerve at the anterior elbowHumerus at spiral groove Deep brachial arteryTrace the nerve proximally and posteriorly toward the spiral groove of the humerus, just inferior to the deltoid muscle insertion (the nerve is adjacent to the deep brachial artery).

538

The nerve lies lateral to the artery (vein most medial) See Fig 35-11.

Sciatic Classical or Labat

Ischial bone and inferior gluteal or pudendal vesselsThe nerve lies lateral to the thinnest aspect of the ischial bone. The inferior gluteal artery lies medial to and at the same depth as the nerve.

Greater trochanter and ischial tuberosity

Ankle Tibial (posterior tibial) Deep peroneal

Posterior tibial artery Anterior tibial arteryThe nerve lies posterior to the artery The nerve lies lateral to the artery

539

Figure 35-1 Schematic of the cervical plexus, which arises from the anterior

primary rami of C2–C4 The motor branches (including the phrenic nerve) curl

anteriorly around the anterior scalene muscle and travel caudad and medially to

supply the deep muscles of the neck The sensory branches exit at the lateral

bor-der of the sternocleidomastoid muscle to supply the skin of the neck and shoulbor-der.

on the posterior skull where they emerge from below the muscles of the neck This block is rarely used for surgical procedures; it is more often applied as a diagnostic step in evaluating complaints of head and neck pain

B Upper Extremity (Figs 35-5 to 35-7) The four anatomic

locations where local anesthetics are placed are the (1) scalene groove near the cervical transverse processes, (2) subclavian sheath at the first rib, (3) near the coracoid pro-cess in the infraclavicular fossa, and (4) surrounding the axillary artery in the axilla US imaging and NS have greatly facilitated the use of upper extremity regional anesthesia

Figure 35-2 Needle insertion points and angles for the deep cervical plexus

blockade The nerve roots exit the vertebral column via the troughs formed by the

transverse processes The needle is inserted at each nerve roots of C2–C4 in a

caudad and posterior direction.

Figure 35-3 The cervical, thoracic, lumbar, and sacral dermatomes of the body.

Figure 35-4 Greater and lesser occipital nerve distribution, supply, and block

needle insertion sites.

Figure 35-5 Schematic of the brachial plexus Many branches, including the

medial cutaneous nerves of the forearm and arm, which arise from the medial

cord, are not shown here.

Figure 35-6 Courses of the terminal nerves of the upper extremity The

poste-rior view (A) illustrates the branches from the posteposte-rior cord (axillary and radial

nerves), and the anterior view (B) illustrates the branches from the lateral

(musculo-cutaneous and median nerves) and medial (median and ulnar nerves) cords.

B

Figure 35-7 Cutaneous innervation of the upper extremity nerves.

The terminal branches can also be anesthetized by local anesthetic injection along their peripheral course as they cross joint spaces, where they lie in close proximity to easily identifiable structures or by the injection of a dilute local anesthetic solution intravenously below a pneumatic tour-niquet on the upper arm (“intravenous regional” or Bier block) (see Table 38-2)

C Brachial Plexus Blockade (Table 35-3)

D Terminal Upper Extremity Nerve Blocks PNBs in the

upper extremity are of particular value as rescue blocks to supplement incomplete surgical anesthesia and to provide long-lasting selective analgesia in the postoperative period

The peripheral nerves may be individually blocked at humeral, elbow, or wrist locations, depending on the specific nerve If using US guidance, the elbow and forearm regions appear to be the most suitable block regions, and blocks at these sites may improve the accuracy of nerve localization and local anesthetic spread The wrist is highly populated with tendons and fascial tissues (flexor and extensor retinac-ulae), which can be difficult to distinguish from, and may obscure the images of, the nerves Color Doppler combined with US imaging can be used to clearly identify the nerves at many desirable locations because they are often situated near blood vessels (see Table 35-1 and Figs 35-7 and 35-8)

mid-E Intravenous Regional Anesthesia (Bier Block) Arm

anes-thesia can be provided by the injection of local anesthetic into the venous system below an occluding tourniquet with-out using US imaging or NS (Table 35-4)

f Intercostal Nerve Blockade Anesthesia of the intercostal

nerves provides both motor and sensory anesthesia of the abdominal wall from the xiphoid to the pubis These nerve blocks involve injections along the easily palpated abrupt pos-terior angulation of the ribs, which occurs between 5 and 7 cm from the midline in the back The anesthesiologist’s other hand inserts a needle (22 gauge, 3.75 cm) directly onto the rib, maintaining a constant 10° cephalad angulation After contact

is made with the rib, the cephalad traction is slowly released, the cephalad hand takes over the needle and syringe, and the

Interscalene Block

This block frequently spares the lowest branches of the plexus, the C8 and T1 fibers (which innervate the caudad [ulnar] border of the forearm)

Pneumothorax should be considered if cough or chest pain is produced while exploring for the nerve (cupola of the lung near block site)

Direct injection into the vertebral artery can rapidly produce central nervous system toxicity and convulsions

Supraclavicular Block

The midpoint of the clavicle is identified The subclavian artery pulse serves as a reliable landmark in thinner individuals because the plexus lies immediately cephaloposterior to the subclavian artery

Ultrasound imaging and nerve stimulation help avoid puncturing the pleura There is a risk of pneumothorax because the cupola of the lung lies just medial to the first rib; risk of pneumothorax is greater

on the right side because the cupola of the lung is higher on that side; the risk is also greater in tall, thin patients

Infraclavicular Block

This block provides excellent analgesia of the entire arm (blocks the musculocutaneous and axillary nerves more consistently) and allows introduction of continuous catheters to provide prolonged postoperative pain relief

There is a lower risk of blocking the phrenic nerve or stellate ganglion

Vessel puncture is a potential complication

Lateral needle insertion helps avoid the risk of pneumothorax

B

Figure 35-8 Probe placement (A) and ultrasound image (B) during

paraverte-bral block in the thoracic spine The probe is first placed in the midline of the spine

to capture a transverse view of the vertebral and costal (if thoracic spine) elements

L = lamina; S = spinous process; T = transverse process; US = ultrasound.

A small-gauge (20- or 22-gauge) intravenous catheter is placed and taped on the dorsum of the hand in the arm to be blocked.

The arm is elevated to promote venous drainage (an Esmarch bandage

Beyond 45 min of surgery, many patients experience discomfort at the level of the tourniquet (double-cuff tourniquets alleviate this problem)

If surgery is completed in <20 min, the tourniquet is left inflated for

at least that total period of time

If 40 minutes has elapsed, the tourniquet can be deflated as a single maneuver

Between 20 and 40 min, the cuff can be deflated, reinflated ately, and finally deflated after 1 min to delay the sudden absorption

immedi-of anesthetic into the systemic circulation

The duration of anesthesia is minimal beyond the time of tourniquet release

needle is allowed to “walk” down to below the rib at the same angle The needle is then advanced approximately 4 mm under the rib After it is in the groove, aspiration is per-formed, and 3 to 5 mL of a local anesthetic solution is injected Generally, the intercostal nerves are well localized with the blind landmark-based technique Alternatively, the rib can be easily visualized with the use of US imaging

G Paravertebral Block This block technique is useful for

mental anesthesia, particularly of the upper thoracic ments It is also useful if a more proximal (central) blockade than that of the intercostal nerves is needed, such as to relieve the pain of herpes zoster or of a proximal rib fracture

seg-H Inguinal Nerve Block This block is performed easily with

blind technique, although US imaging may be performed to help improve the success rate Side effects include systemic toxicity and transient femoral nerve palsy

I Transversus Abdominis Plane (TAP) block is

predomi-nantly a muscular plane block (three layers of abdominal muscles are separated by hyperechoic fascia) TAP blocks provide effective analgesia for obstetrics and general surgery

J Penile block is used in children and adults for surgical

pro-cedures of the glens and shaft of the penis US may be used

to improve the efficacy of this block

III SPECIfIC TECHNIQUES: LoWER EXTREMITY.

Combined blocks of the lumbar and sciatic plexuses provide effective surgical anesthesia to the entire lower extremity (Figs 35-3 to 35-10)

A Terminal Nerves of the Lumbar Plexus (Table 35-5)

B Sacral Plexus: formation and Branches The anterior

pri-mary rami of S1–S4 join the lumbosacral trunk to form the sacral plexus (see Fig 35-9)

1 Sciatic, Tibial, and Common Peroneal Nerves At a

variable distance within the posterior thigh (often high

in the popliteal fossa), the sciatic nerve bifurcates into common peroneal and tibial nerves

2 Nerves at the Ankle By the time the femoral, tibial, and

common peroneal nerves reach the ankle, five branches cross this joint to provide innervation for the skin and muscles of the foot (Table 35-6; see Fig 35-10)

C Psoas Compartment Block This block has the advantage of

blocking the entire lumbar plexus and therefore provides anesthesia/analgesia of the anterolateral and medial thigh, the knee, and the cutaneous distribution of the saphenous nerve below the knee

D Separate Blocks of the Terminal Nerves of the Lumbar Plexus Anesthesia can be performed for four terminal

nerves (lateral femoral cutaneous, femoral, obturator, and saphenous), although a lumbar plexus block is preferable if anesthesia of all these nerves is required

1 Anesthesia of the lateral femoral cutaneous nerve is sionally used to provide sensory anesthesia for obtaining a skin graft from the lateral thigh It can also be blocked as

occa-a diocca-agnostic tool to identify cocca-ases of merocca-algiocca-a pocca-arestheticocca-a

2 Obturator nerve block can be effective to prevent rator reflex during transurethral bladder tumor resec-tions, for treatment of pain in the hip area, for adductor spasm (as seen in multiple sclerosis patients), or as a diagnostic tool when studying hip mobility

obtu-3 Procedures on the knee require anesthesia of the femoral and obturator nerves, although postoperative analgesia of the knee can usually be provided by femoral nerve block alone

4 Femoral nerve block is used extensively for analgesia (Fig 35-11)

Figure 35-9 The lumbar (A; L1–L4) and sacral (B; L4–S4) plexuses.

T a b l e 3 5 - 6 NERvES AT THE ANkLE

Deep peroneal nerve (L5–S1)Tibial nerve (posterior tibial nerve, (S1–S3)Superficial peroneal nerve

Sural nerveSaphenous nerve

Figure 35-10 Cutaneous innervation from the terminal nerves of the lower

obturator Nerve (L2–L4)

Divides into its anterior and posterior branches near the obturator foramen

Figure 35-11 Ultrasound-guided femoral nerve block A The probe is placed in

a slightly oblique plane (at the level of and parallel to the inguinal crease) to capture

the nerve in short-axis lateral to the femoral artery (FA) B The needle is seen (not

shown) as it transects the fascia lata and iliaca The dotted line indicates the

femo-ral nerve.

Figure 35-12 Landmarks for the sciatic nerve block using a posterior gluteal

approach when a nerve stimulation procedure is used This location will serve as a

reference point when applying ultrasound imaging The asterisk indicates the

approximate location of the sciatic nerve PSIS = posterior superior iliac spine.

E Sciatic Nerve Blockade Using Posterior, Anterior, and Posterior Popliteal Approaches A sciatic nerve block can

be used with lumbar plexus block for anesthesia of the lower extremity Together with a saphenous nerve block, the block produces adequate anesthesia to the sole of the foot and the lower leg

1 The sciatic nerve is deep within the gluteal region and may be difficult to locate blindly or with US imaging Of benefit during US-guided blockade of the sciatic nerve and its terminal branches (tibial and common peroneal nerves) are the numerous bony and vascular landmarks that can be used for ease of identification (Fig 35-12)

2 US guidance, either alone or in conjunction with NS, improves success

f Ankle Block All five nerves of the foot can be blocked at the

level of the ankle The superficial nerves (sural, superficial peroneal, and saphenous nerves) can be blocked by simple infiltration techniques US guidance can be useful for block-ing the posterior tibial and deep peroneal (fibular) nerves because their locations can be easily identified next to reli-able landmarks (bones and vessels) that are clearly visible

36

Anesthesia for Neurosurgery

An understanding of neuroanatomy is essential for all who care for

patients with disease of the central nervous system (CNS) (Dagal A,

Lam AM Anesthesia for neurosurgery In: Barash PG, Cullen BF,

Stoelting RK, Cahalan MK, Ortega R, Stock MC, eds Clinical Anesthesia

Philadelphia: Lippincott Williams & Wilkins; 2013:996–1029)

I NEUROANATOMY

A The brain and spinal cord are surrounded by protective but nondistensible bony structures that surround them and provide protection

B The intracranial volume is fixed, thereby providing little room for anything other than the brain, cerebrospinal fluid (CSF), and blood contained in the cerebral vasculature It is

in the context of the restrictive nature of the space in which the CNS is housed that all interventions must be considered

C The anterior cerebral circulation originates from the carotid artery, the posterior circulation results from the vertebral arteries, and the system of collateralization is known as the circle of Willis (Fig 36-1)

D The spinal column is the bony structure made up of the seven cervical, 12 thoracic, and five lumbar vertebrae, as well as the sacrum

1 The spinal cord exits the skull through the foramen num and enters the canal formed by the vertebral bodies

mag-In adults, the spinal cord typically ends at the lower aspect of the first lumbar vertebral body

2 The anterior spinal artery arises from the vertebral ies and supplies the anterior two thirds of the spinal cord This vessel runs the length of the cord, receiving contribution from radicular arteries via intercostal ves-sels The artery of Adamkiewicz is the most important radicular vessel

arter-3 The posterior third of the cord is supplied by two posterior spinal arteries, which arise from the vertebral arteries and also receive contribution from radicular arteries

AnteriorChoroidal Artery

PosteriorCerebral Artery

SuperiorCerebellar Artery

Basilar Artery

Anterior InferiorCerebellarArtery

Vertebral Artery

Anterior SpinalArtery

Posterior InferiorCerebellar Artery

Ophthalmic Artery

Anterior CerebralArtery

InternalCarotid ArteryPosterior

Communicating

Artery

PontineArteries

AnteriorCommunicatingArtery

MiddleCerebralArtery

Figure 36-1 The circle of Willis, which supplies blood flow to the brain.

II NEUROPHYSIOLOGY

A Cerebral metabolism is directly related to the number and frequency of neuron depolarizations (activity or stimulation increases the metabolic rate) Cerebral blood flow (CBF) is tightly coupled to metabolism

pro-C Intracranial pressure (ICP) is low except in pathologic states The volume of blood, CSF, and brain tissue must be

in equilibrium An increase in one of these three elements,

or the addition of a space-occupying lesion, can be modated initially through displacement of CSF into the the-cal sac but only to a small extent Further increases, as with significant cerebral edema or accumulation of an extradural hematoma, quickly lead to a marked increase in ICP because of the low intracranial compliance (Fig 36-2)

accom-D Many factors affect CBF because of their effect on lism (Stimulation, arousal, nociception, and mild hyper-thermia elevate metabolism and flow, and sedative–hypnotic agents and hypothermia decrease metabolism and flow.)

metabo-E A number of other factors govern CBF directly without changing metabolism

1 A potent determinant of CBF is PaCO2 CBF changes by approximately 3% of baseline for each 1 mm Hg of change in PaCO2 (Fig 36-3)

Intracranial Mass

Figure 36-2 Intracranial compliance (elastance) curve.

Arterial Carbon Dioxide Partial Pressure

Figure 36-3 Cerebrovascular response to a change in arterial carbon dioxide

partial pressure (PaCO2) from 25 to 65 mm Hg.

2 As CBF changes, so does cerebral blood volume (CBV), which is the reason hyperventilation can be used for short periods of time to relax the brain or to decrease ICP This effect is thought to be short lived (minutes to hours) because the pH of CSF normalizes over time and vessel caliber returns to baseline

F In contrast to PaCO2, PaO2 has little effect on CBF except at abnormally low levels (Fig 36-4) When PaO2 decreases below 50 mm Hg, CBF begins to increase sharply

G CBF remains approximately constant despite modest swings

in arterial blood pressure (autoregulation) (Fig 36-5)

1 As cerebral perfusion pressure (CPP), defined as the ference of mean arterial pressure (MAP) and ICP, changes, cerebrovascular resistance (CVR) adjusts in order to maintain stable flow

dif-2 The range of CPP over which autoregulation is

main-tained is termed the autoregulatory plateau Although

this range is frequently quoted as a MAP range of 60 to

150 mm Hg, there is significant variability between viduals, and these numbers are only approximate

indi-a At the low end of the plateau, CVR is at a minimum,

and any further decrease in CPP compromises CBF

Figure 36-4 Cerebrovascular response to a change in arterial oxygen partial

pressure (PaO2) The response of cerebral blood flow to change in PaO2 is flat until

the PaO 2 decreases below about 50 mm Hg.

Cerebral Perfusion Pressure

w Autoregulatory Plateau

Figure 36-5 Cerebral autoregulation maintains cerebral blood flow constant

between 60 to 160 mm Hg These are average values, and there is considerable

variation in both the lower and upper limit of cerebral autoregulation among

normal individuals.

b At the high end of the plateau, CVR is at a maximum,

and any further increase in CPP results in hyperemia

3 The resultant effect is that during low-dose inhalation anesthesia, CBF is either unchanged or slightly increased

Compared with other inhaled agents, sevoflurane in clinically relevant doses does not increase CBF

Furthermore, sevoflurane is associated with profound regional and global reductions in cerebral metabolic rate

4 Intravenous (IV) agents, including thiopental and pofol, cause vasoconstriction coupled with a reduction

pro-in metabolism Ketampro-ine, on the other hand, pro-increases CBF and metabolism

5 Cerebrovascular carbon dioxide reactivity is a robust mechanism and is preserved under all anesthetic condi-tions Cerebral autoregulation, on the other hand, is abolished by inhalation agents in a dose-related manner but is preserved during propofol anesthesia

III PATHOPHYSIOLOGY. The homeostatic mechanisms that

ensure protection of the brain and spinal cord, removal of waste, and delivery of adequate oxygen and substrate to the tissue can

be interrupted through a multitude of mechanisms (Table 36-1)

MECHANISMS FOR BRAIN PROTECTION

Traumatic Insults

Contusion with edema formationDepressed skull fracturesRapid deceleration

Mass Lesions

Tumors (compress adjacent structures, increase ICP, and obstruct normal flow of CSF)

Hemorrhage (spontaneous or traumatic)

CSF = cerebrospinal fluid; ICP = intracranial pressure.

Iv MONITORING. The integrity of the CNS needs to be

evalu-ated intraoperatively with monitors that specifically detect CNS function, perfusion, or metabolism

A Central Nervous System Function (Tables 36-2 to 36-4)

B Influence of Anesthetic Technique (Table 36-5)

v CEREBRAL PERFUSION. Although adequate CBF does not

guarantee the well-being of the CNS, it is an essential factor in its integrity

A Laser Doppler flowmetry requires a burr hole and

mea-sures flow in only a small region of the brain

B Transcranial Doppler ultrasonography (TCD) is a

nonin-vasive monitor for evaluating relative changes in flow through the large basal arteries of the brain (often flow velocity in the middle cerebral artery) (Fig 36-6)

num-Evoked potential monitoring detects signals that result from a specific stimuli

SSEP requires intact sensory pathway, spine surgery when the dorsal column of the spinal cord may be at risk

BAEP: acoustic neuroma surgery VEP: difficult to record during anesthesia MEP monitors descending motor pathways, complements SSEP during spine surgery, signals sensitive to volatile anesthetics and

IV anesthetics may be preferredsEMG detects injury to nerve roots in the surgical area; muscle relaxants must be avoided

Electromyography: cranial nerve monitoringBAEP = brain stem auditory evoked potential; BIS = bispectral index; EEG = electro-

encephalography; IV = intravenous; MEP = motor evoked potential; sEMG =

sponta-neous electromyography; SSEP = somatosensory evoked potential; VEP = visual

evoked potential.

T a b l e 3 6 - 4 INDICATIONS FOR

ELECTROENCEPHALOGRAPHIC MONITORING

During anesthesia Carotid endarterectomy

Cardiopulmonary bypassCerebrovascular surgery (temporary clipping, vascular bypass)

Intensive care unit Barbiturate coma for patients with traumatic

brain injurySubclinical seizures suspected

Frequency (Hz) Description

Delta 0–3 Low frequency, high amplitude

Present in deep coma, encephalopathy, deep anesthesia

Theta 4–7 Not prominent in adults

May be seen in encephalopathyAlpha 8–12 Prominent in the posterior region during

relaxation with the eyes closedBeta >12 High frequency, low amplitude

Dominant frequency during arousal

1 In addition to the measurement of flow velocity, TCD is useful for detecting emboli (Fig 36-7)

2 Specific applications for intraoperative use of TCD include carotid endarterectomy (CEA), nonneurologic surgery and cerebral autoregulation in patients with traumatic brain injury (TBI), and surgical procedures requiring cardiopulmonary bypass

3 An important use of TCD is to monitor the development

of vasospasm in patients who have experiences a arachnoid hemorrhage (SAH)

sub-C Intracranial Pressure Monitoring

1 Although monitoring ICP does not provide direct mation about CBF, it allows calculations of CPP (the dif-ference between MAP and ICP)

infor-2 Within a physiologic range of CPP, CBF should remain approximately constant A CPP that is too low results in

CENTRAL NERvOUS SYSTEM MONITORING

Inhalation agents (including nitrous oxide) generally have more depressant effects on evoked potential monitoring than IV agents

Whereas cortical evoked potentials with long latency involving ple synapses (SSEP, VEP) are exquisitely sensitive to the influence

multi-of anesthetic, short-latency brain stem (BAEP) and spinal nents are resistant to anesthetic influence

compo-Monitoring of MEP and cranial nerve EMG in general preclude the use of muscle relaxants Use of a short-acting neuromuscular blocking agent for the purpose of tracheal intubation is acceptable

MEP is exquisitely sensitive to the depressant effects of inhalation anesthetics, including nitrous oxide Total IV anesthesia without nitrous oxide is the recommended anesthetic technique for moni-toring of MEP

Opioids and benzodiazepines have negligible effects on recording of evoked potentials

Propofol and thiopental attenuate the amplitude of virtually all modalities of evoked potentials but do not obliterate them

During crucial events when part of the central neural pathway is cifically placed at risk by surgical manipulation, as in placement of

spe-a temporspe-ary clip during spe-aneurysm surgery, chspe-ange in “spe-anesthetic depth” should be minimized to avoid misinterpretation of the changes in evoked potential

BAEP = brain stem auditory evoked potential; IV = intravenous; MEP = motor evoked

potential; SSEP = somatosensory evoked potential; VEP = visual evoked potential.

RT MCA

MedaSonics//CDS MedaSonics//CDS

100 CM/S

ID#

Ref DR : None Vessel : RMCA

Range : 19 dB Angle : 0 deg Sample : 13 mm

Mean

Figure 36-6 Transcranial Doppler tracing with release of the cross-clamp during

carotid endarterectomy The resultant hyperemia is accompanied by evidence of air

embolism (vertical streaks in the tracing) ICA = internal carotid artery; MCA = middle

cerebral artery; RT = right.

Figure 36-7 Particulate emboli seen on transcranial Doppler in a patient with

symptoms of transient ischemic attacks consistent with right carotid artery territory

embolization The emboli are denoted by the arrows L = left; MCA = middle cerebral

tar-a ftar-avortar-able btar-altar-ance of the two (Ttar-ables 36-6 tar-and 36-7)

MAP is increased via adequate intravascular tion and with a vasopressor as needed The goal CPP in TBI is >50 to 60 mm Hg

vI CEREBRAL PROTECTION. Efforts to avert neurologic

insult using medications or through the manipulation of ologic parameters have met with meager results Although recent advances are intriguing, no maneuver matches the cere-bral protection provided by mild to moderate hypothermia

physi-The operating room is unique in that an opportunity exists to intervene before the ischemic event occurs (Use of a temporary aneurysm clip on the middle cerebral artery is an example of a

T a b l e 3 6 - 6 INTERvENTIONS TO LOwER INTRACRANIAL

PRESSURE

Suppression of cerebral metabolic activityPositional changes to decrease cerebral venous blood volumeDrainage of CSF

Removal of brain water with osmotic agents (mannitol)Mild to moderate hyperventilation to further decrease CBVCBV = cerebral blood volume; CSF = cerebrospinal fluid.

INADEqUATE CEREBRAL PERFUSION PRESSURE

Reduce brain water Mannitol

Hypertonic salineFurosemideRemove CSF External ventricular drain

Lumbar drainDecrease CBV Head-up tilt

Neutral neck positionMetabolic suppression: propofol, barbiturateMild to moderate hyperventilationElevate MAP Adequate intravascular volume resuscitation

VasopressorCBV = cerebral blood volume; CSF = cerebrospinal fluid; MAP = mean arterial pressure.

AND METABOLISM

Near-infrared spectroscopy is a noninvasive method of evaluating

the oxygenation of cerebral blood and balance between flow and metabolism

Brain tissue PO 2 probe is placed through a burr hole It is commonly used in patients with TBI (<15 mm Hg warrants intervention, including treatment of anemia)

Jugular venous oximetry provides the same information as the brain

tissue PO2 probe but over a larger portion of the brain Normal jugular venous saturation is 65% to 75%; saturation below 50% in TBI is associated with a poor outcome

TBI = traumatic brain injury.

of a basilar artery aneurysm is an example of a global insult.)

A Ischemia and Reperfusion

1 It is reasonable to attempt to minimize ischemic insult

by lowering the cerebral metabolic rate, thus decreasing the likelihood of exhausting adenosine triphosphate reserves during the period of ischemia (the traditional paradigm for approaching the subject of intraoperative neuroprotection)

2 Unfortunately, further damage occurs as a result of cesses that are initiated during the reperfusion stage

pro-3 A shift in the focus of neuroprotection from metabolic suppression to targeting ischemic cascades has recently been advocated

B Hypothermia

1 Profound hypothermia is well known for its tective effects When core body temperature decreases below 20°C, circulatory arrest of <30 minutes appears to

neuropro-be well tolerated

2 Mild hypothermia (33°C–35°C) not only decreases bral metabolism but likely also modulates the immune and inflammatory response to ischemia, thus affecting the reperfusion portion of the injury as well Although considerable evidence in rats suggests that mild hypo-thermia is beneficial, there is a paucity of evidence in humans Nevertheless, hypothermia remains the most promising intervention for cerebral protection

cere-3 There is ample evidence that hyperthermia is associated with worse outcome in the setting of ischemic stroke, SAH, cardiac arrest, and TBI

4 In the operating room during neurosurgical procedures during which the brain is at risk for ischemic insult, a goal temperature of 35°C to 36°C is reasonable Mild hypothermia (33°C–35°C) may be appropriate in many patients, recognizing that there may be no benefit to this therapy

C Medical Therapy for Cerebral Protection

1 Volatile and IV anesthetic agents decrease cerebral metabolism Animal studies have found protective effects of volatile anesthetics, particularly isoflurane, in mitigating a mild to moderate ischemic insult, although this effect may only be short lived

2 Barbiturates, such as thiopental, have been shown

to have at least short-term benefits on focal cerebral

ischemia, but the benefit in global ischemia remains controversial Propofol likely has similar protective effects.

3 Current opinion is that anesthetic neuroprotection is primarily mediated through prevention of excitotoxic injury, not through termination of apoptotic pathways

(It thus delays neuronal death and leaves a greater poral window for intervention.)

tem-4 Clinically, barbiturates and propofol are used atively to achieve burst suppression on the electroen-cephalogram, although their neuroprotective action does not appear to be metabolically mediated

intraoper-D Glucose and Cerebral Ischemia

1 Although considerable evidence has accumulated gesting harm from hyperglycemia, evidence for benefit with normalization of serum glucose concentrations using insulin has been controversial

sug-2 Despite a reluctance to embrace intraoperative tight cemic control given the current literature, it is worth-while to consider for patients undergoing cerebrovascu-lar surgery Given the preponderance of evidence that hyperglycemia and cerebral ischemia in combination are harmful, changing practice in these patients may be war-ranted Tight glycemic control is a reasonable goal in these patients (It cannot be stated that this intervention

gly-is neuroprotective.)

E A Practical Approach

1 For patients undergoing surgical procedures with an anticipated period of cerebral ischemia such as cerebral aneurysm surgery or cerebrovascular bypass procedures, either volatile anesthesia or an IV technique is appropri-ate It is reasonable to administer additional propofol or thiopental before vessel occlusion

2 Euglycemia before vessel occlusion is desirable, but quent glucose checks are essential during anesthesia to avoid episodes of hypoglycemia if insulin is administered

fre-3 Hyperthermia should be avoided during this time, with the temperature kept at or below 36°C

vII ANESTHETIC MANAGEMENT

A Preoperative Evaluation

1 It is prudent to consider the nature of the patient’s ease that brings him or her to the operating room in the context of the patient’s medical and surgical history

2 Preoperative risk stratification for a cardiac complication

is important to consider Current guidelines include delaying surgery for at least 2 weeks after simple balloon angioplasty, 4 to 6 weeks after placement of a bare metal stent, and 1 year after placement of a drug-eluting stent

3 Many patients presenting for spine surgery have ness or paralysis that may present a contraindication to the use of succinylcholine (Sch)

weak-4 Many neurosurgical patients have been exposed to ileptic medications Previous allergies or reactions to these medications, especially phenytoin, should be elucidated

antiep-B Induction and Airway Management

1 During induction of anesthesia, three iatrogenic consequences (hypotension, hypertension, apnea) may

be significant hazards for neurosurgical patients

a Hypertension caused by laryngoscopy is poorly

toler-ated by patients after aneurysmal SAH because tolic hypertension is thought to be a cause of recur-rent hemorrhage from the aneurysm

sys-b Hypertension may worsen elevated ICP and possibly

lead to herniation of cranial contents into the men magnum

fora-c Apnea results in a predictable increase in PaCO2 and corresponding cerebral vasodilation

2 A cervical collar for known or suspected cervical spine injury may make tracheal intubation more difficult

These patients are also particularly harmed by periods of hypotension or hypertension

3 Because patients with SAH are at risk for harm from hypertension, it is reasonable to place an arterial catheter for hemodynamic monitoring before induction

of anesthesia

4 Many neurosurgical and spine surgery patients have conditions in which Sch is contraindicated

a In the setting of acute stroke or spinal cord injury

(SCI), it remains safe to use Sch for approximately

48 hours from the time of injury

b Alternatively, a rapid-acting nondepolarizing muscle

relaxant is appropriate in many neurosurgical patients

to achieve acceptable intubating conditions

C Maintenance of Anesthesia

1 The primary considerations for maintenance of sia include the type of monitoring planned for the proce-dure, brain relaxation, and the desired level of analgesia

anesthe-at the end of the surgical procedure

2 Remifentanil is appropriate for neurosurgical procedures

in which tracheal extubation is planned at the end of the surgery and minimal residual sedation is desired to facil-itate the neurologic examination

3 Replacement of a volatile anesthetic with a continuous infusion of propofol is desirable with motor evoked potential (MEP) monitoring and when brain relaxation

is inadequate with a volatile anesthetic

4 The use of intraoperative muscle relaxants should be avoided during MEP, spontaneous electromyography, and cranial nerve monitoring Muscle relaxants may be used during isolated somatosensory evoked potential monitoring

D ventilation Management

1 Hypocapnic cerebral vasoconstriction provides siologists with a powerful tool for manipulating CBF and CBV

anesthe-2 Hyperventilation is routinely used to provide brain relaxation and optimize surgical conditions

3 Because hyperventilation decreases CBF, it has the retical potential for causing or exacerbating cerebral ischemia Clinically, hyperventilation has been associated with harm only in the early period of TBI, but it is still recommended to be avoided in all patients with TBI except when necessary for a brief period to manage acute increases in ICP

theo-4 During neurosurgical procedures, it is reasonable to tain the PaCO2 between 30 and 35 mm Hg Further brain relaxation should be accomplished with other modalities, such as mannitol, hypertonic saline, or IV anesthesia If hyperventilation to a PaCO2 below 30 mm Hg is required,

main-it is appropriate to guide this therapy wmain-ith jugular venous oximetry and the arterial–jugular lactate gradient

5 The duration of effectiveness of hyperventilation is ited Normalization of CBF and consequently CBV has been reported to occur within minutes Clinically, the beneficial effects of hyperventilation appear to be sus-tained during most neurosurgical procedures of modest duration

lim-E Fluids and Electrolytes

1 To maintain adequate cerebral perfusion, adequate intravascular volume should be maintained (euvolemia

to slight hypervolemia)

2 To minimize brain edema, it is important to maintain serum tonicity It is prudent to check serum sodium

levels on a regular basis in prolonged surgical procedures

in which mannitol has been given

3 In addition to osmotic dehydration of the brain tium, other proposed benefits of hypertonic solutions include a reduction in blood viscosity, increasing eryth-rocyte deformability, and improving cardiac output and microcirculatory flow

intersti-F Transfusion Therapy The lower limit of acceptable

hemo-globin or hematocrit has not been well defined (Evidence supports avoidance of transfusion for a hematocrit above 21% except in the context of ongoing hemorrhage and possibly the early phase of resuscitation for septic patients.)

G Glucose Management

1 The combination of hyperglycemia and cerebral emia appears to be particularly deleterious Nevertheless, tight glycemic control (80–110 mg/dL) with insulin may

isch-be associated with an increased mortality rate at 90 days

2 In the neurosurgical population, intensive insulin ment results in increased variability in the blood glucose concentration, leading to cerebral osmotic shifts and higher incidences of hypoglycemia, leading to worse outcomes

treat-H Emergence

1 The decisions that need to be made regarding emergence from anesthesia for neurosurgical and spine surgery patients hinge on whether the patient is an appropriate candidate for tracheal extubation

2 For extensive spine surgeries in the prone position, nificant dependent edema frequently occurs Although the predictive value of an air leak from around the endo-tracheal tube cuff is poor, the combination of pro-nounced facial edema and an absent cuff leak after prone surgery should make one suspicious of upper airway edema Delaying extubation of the trachea under these circumstances may be appropriate

sig-3 Avoiding coughing and hemodynamic changes with emergence is important for all neurosurgical patients

vIII COMMON SURGICAL PROCEDURES

A Surgery for Tumors

1 The fundamental anesthetic considerations in tumor surgery are proper positioning of the patient to facilitate the surgical approach; providing adequate relaxation of the brain to optimize surgical conditions; and avoiding

well-known devastating complications, such as venous air embolism.

2 Preoperative assessment of the level of consciousness and a review of relevant radiologic studies should be performed, and the results should be taken into consid-eration in the anesthetic plan

3 Adequate brain relaxation is typically achieved with a standard anesthetic, including sub-MAC volatile anes-thesia, an opioid infusion, mild to moderate hyperventi-lation, and mannitol

B Pituitary Surgery

1 These patients should undergo a preoperative evaluation

of their hormonal function to detect hypersecretion of pituitary hormones, which is common in patients with pituitary adenomas, as well as panhypopituitarism

Patients with panhypopituitarism need hormone replacement, including cortisol, levothyroxine, and possibly desmopressin These medications should be continued in the perioperative period

2 Small pituitary tumors can be resected by a noidal approach, but larger tumors may require a crani-otomy

transsphe-3 Intraoperative monitoring of glucose and electrolytes is essential, particularly if the patient has pre-existing dia-betes insipidus (DI) or if the patient develops signs of DI during surgery

a DI is a common complication of pituitary surgery

because of the loss of antidiuretic hormone tion It may be temporary or permanent and may occur either in the intraoperative or postoperative period

produc-b DI is initially suspected on the basis of copious urine

output, as well as increased serum sodium tion A urine specific gravity 1.005 or below is confir-mative

concentra-C Cerebral Aneurysm Surgery and Endovascular Treatment

1 For patients who survive hemorrhage, surgical or vascular intervention to secure the aneurysm is essential

endo-to prevent further hemorrhage

2 Patients with aneurysmal SAH are at risk for numerous complications that may affect the anesthetic plan These complications include cardiac dysfunction, neurogenic

or cardiogenic pulmonary edema, and hydrocephalus, as well as further hemorrhage from the aneurysm

3 A patient presenting for the elective correction of

an intracranial aneurysm typically has good brain

per-to cure the lesion.

3 After resection of large AVMs or those in the posterior fossa, it may be appropriate to take the patient to the intensive care unit mechanically ventilated and sedated

If the decision is made by the surgeon and gist to allow emergence and extubation of the trachea, aggressive management of blood pressure should be instituted, and coughing should be avoided

anesthesiolo-E Carotid Surgery

1 Carotid stenosis is a common cause of transient ischemic attack and ischemic stroke It is amenable to surgical intervention and endovascular stenting

2 Surgery is associated with a risk of stroke, myocardial infarction, and wound infection With recent advances

in medical therapy, including more effective ing drugs, antiplatelet agents, and antihypertensive ther-apy, the margin of benefit of surgery may be even lower

lipid-lower-3 Both general and regional anesthesia may be used for CEA (There is no difference in outcomes based on the anesthetic technique.) Regional anesthesia is accom-plished with a superficial cervical plexus block or a com-bination of superficial and deep cervical plexus block

4 Several CNS monitors may be used during CEA under general anesthesia

5 Rapid emergence and tracheal extubation at the end of the procedure are desirable because they allow immedi-ate neurologic assessment

6 Carotid artery stenting (CAS) is minimally invasive and may be performed under sedation (may need to convert

to general anesthesia) There is no difference in outcome (stroke, myocardial infarction, death) comparing CAS and CEA

F Epilepsy Surgery and Awake Craniotomy Some

intracra-nial neurosurgical procedures are performed on “awake”

(sedated and pain free yet able to respond to verbal or visual

command) patients to facilitate monitoring of the region of the brain on which the surgeon is operating (epileptic focus) Patients with a difficult airway, obstructive sleep apnea, or orthopnea may have relative contraindications to

an “awake” craniotomy Patients with severe anxiety, trophobia, or other psychiatric disorders may be particu-larly inappropriate candidates for this type of procedure

claus-1 Intraoperative Management Direct visual and verbal

contact with the patient should be maintained out the procedure

through-2 Conscious Sedation Technique Propofol is one of the

most frequently used drugs either alone or in tion with remifentanil Dexmedetomidine may be the ideal sedative (minimal respiratory depression) for awake procedures (0.3–0.6 μg/kg/hr)

combina-3 “Asleep–Awake–Asleep” Technique This is often the

pre-ferred method for epilepsy surgery (general anesthesia for the initial craniotomy and closure and awake in the mid-dle to identify the precise location of the epileptic focus)

4 General anesthesia is selected for children, patients with

continuous movement disorders, and patients with an increased ICP

Ix ANESTHESIA AND TRAUMATIC BRAIN INJURY

A Overview of Traumatic Brain Injury

1 The presence of TBI is the primary determinant in ity of outcome for patients with traumatic injuries

qual-2 Airway and breathing are of paramount importance in any critically ill patient but even more so in patients with head injuries given the sensitivity of the brain to hypox-emia and hypercapnia

3 Patients with TBI have up to a 10% incidence of an unstable cervical spine injury

a Risk factors include a motor vehicle accident

and Glasgow Coma Scale (GCS) score below 8 (Table 36-9) Therefore, all attempts at intubation should include in-line neck stabilization to decrease the chance of worsening a neurologic injury

b Patients with TBI should generally be intubated orally

because the potential presence of a basilar skull fracture may increase the risk associated with a nasal intubation

4 Minimizing the risk of aspiration during airway dures is essential The effectiveness and correct applica-tion of cricoid pressure have been questioned

6 Administering muscle relaxants prevents coughing and the resultant spikes of ICP The main choice is between Sch and rocuronium The main drawback to rocuronium

is the prolonged effect when a rapid sequence dose (1.2 mg/kg) is used The argument against Sch is the potential increase in ICP (This is not supported by clinical data.)

7. The overwhelming evidence of harm from hypotension necessitates restoration of intravascular volume The goal is to maintain CPP in the range of 50 to 70 mm Hg

8. In the absence of ICP monitoring but with known TBI,

an ICP of at least 20 mm Hg should be assumed, and MAP should be kept above 60 mm Hg

9. Patients with TBI are typically described by their GCS score (see Table 36-9) This simple test provides prog-nostic information and facilitates communication among providers

10 The presence of a unilateral dilated pupil suggests brain stem compression and is a surgical emergency The presence of bilateral dilated pupils portends a dismal prognosis

11 Intracranial hypertension predisposes patients to poor outcomes, and elevated ICP refractory to therapy is associated with a worse prognosis

2 Opens to painful stimulation

2 Extension to painful stimulus

3 Abnormal flexion to painful stimulus

4 Withdrawal from painful stimulus

5 Localization of painful stimulus

12 CPP goals are 50 to 70 mm Hg.

13 Reduction of ICP in patients with head injuries can be accomplished effectively using osmotic diuretics

a Mannitol is the most commonly used agent and is

available for IV administration in either a 20% or 25% solution Common doses range from 0.25 to

1 g/kg of body weight Mannitol may be used on a repeated schedule, but the serum osmolarity should not be allowed to exceed 320 mOsm Intravascular volume depletion should be avoided

b The mechanism of ICP reduction by mannitol may be

related to its osmotic effect in shifting fluid from the brain tissue compartment to the intravascular compart-ment as well as its ability to decrease blood viscosity

c Hyperventilation is an effective way to reduce ICP It

is useful in the setting of an acutely increased ICP that needs to be controlled until more definitive therapy can be initiated Current recommendations are that patients with TBI should be maintained at normocapnia except when hypocapnia is necessary

to control acute increases in ICP Chronic tilation should be avoided if possible

hyperven-14 There is no evidence that hypothermia is beneficial in the treatment of patients with TBI

15 Barbiturates may be used as an adjunct to other therapy for controlling ICP Barbiturate therapy is appropriate only in patients who are hemodynamically stable and have been adequately resuscitated Propofol is a reason-able alternative to barbiturates for ICP management

Prolonged use of high-dose propofol is not recommended because it may cause a propofol infusion syndrome

B Anesthetic Management Patients with TBI requiring

sur-gery can be subdivided into those who require emergent surgery and those who require nonemergent surgery

1 Emergent Surgery These patients commonly arrive in the

operating room with an endotracheal tube in place The neurologic condition of the patient can be determined rapidly by obtaining the GCS score, examining the pupils, and reviewing the computed tomography (CT) scan

a The patient’s hemodynamic status is also extremely

important Patients may demonstrate a Cushing’s response (hypertension and bradycardia), which sig-nifies brain stem compression from increased ICP

These classic findings may be masked by mia, and their absence does not rule out brain stem compression