Motor system

Spinal cord

Components of spinal motor control system

• Spinal neurons

• Motor unit

• Muscle spindles • Golgi tendon organs

Muscle spindle

muscle

Dorsal root ganglion cell

Upper motor neuron of

corticospinal tract

α-motor neuron in the spinal cord

Neuro muscular junction

Golgi Tendon organ

α-mn is directly responsible for generation of

force by muscle

Upper motor neuron of extrapyramidal tract

Figure 5.28Page 173

Cervical cord

Thoracic cord

Lumbar cord

Sacral cord

VertebraeCervical nerves

Thoracic nerves

Lumbar nerves

Sacral nerves

Coccygealnerve

Cauda equina

50 muscles of the arm innervated

from spinal segments C3-T1

Muscles of the leg innervated from spinal segments

L1-S3

Figure 5.29Page 174

Cell body ofefferent neuron

Cell body ofafferent neuron

Efferent fiber

From receptors

To effectors

Spinal nerve

White matter Gray matter

Interneuron

Dorsal root

Dorsal root ganglion

Ventral root

Figure 5.31 Page 176

Centralcanal

Dorsal horn (cell bodies of interneuronson which afferent neurons terminate)

Lateral horn (cell bodies of autonomicefferent nerve fibers)

Ventral horn (cell bodies of somaticefferent neurons)

Motor neuron pool of a muscle.

• Those motor neurons innervating a single muscle

• The motor neuron pools are segregated into longitudinal columns extending through two to four spinal segments.

• The longitudinal orientation of motor neurons and their dendrites matches that of primary afferent terminals in that zone.

• Thus impulses in a given afferent axon tend to be distributed to motor neurons innervating the same muscle or muscles with similar function.

Figure 8.15Page 269

Spinal cord

= Motor unit 1

= Motor unit 2

= Motor unit 3

A motor unit is one motor neuron and the muscle

fibers it innervates

The size principle: the orderly recruitment of motor units

• The first motor units to be activated are those with smallest motor axons; – these motor units generate the smallest contractile

forces – and allow the initial contraction to be finely graded.

• As more motor units are recruited, – the alpha motor neurons with progressively larger

axons become involved – and generate progressively larger amounts of tension

Motor unit and motor neuron pool

Figure 5.29Page 174

Dorsal root

Dorsal root ganglion

Ventral root

Whole muscle tension depends on • the size of the muscle, • the extent of motor unit recruitment,• the size of each motor unit.

• The number of muscle fibers varies among different motor units.– Muscles performing refined, delicate movements 

have few muscle fibers per motor unit. – Muscles performing coarse, controlled movements 

have a large number of fibers per motor unit.– The asynchronous recruitment of motor units 

delays or prevents muscle fatigue.

• One group of motor neuron pools is located in the medial part of the ventral horn, and the other much larger group lies more laterally.

Somatotopic organization of spinal cord motor neuron

trunk extremities

flexors

extensorsThe ventral root

α-mn: the final common

pathway

Functional rule• The motor neurons located medially project to

axial muscles (muscles of the neck and back): those located more laterally project to limb muscles (arms and legs).

• Within the lateral group the most medial motor neuron pools tend to innervate the muscles of the shoulder and pelvic girdles, while motor neurons located more laterally project to distal muscles of the extremities and digits.

• In addition the motor neurons innervating the extensor muscles tend to lie ventral to those innervating flexors.

Figure 5.30 (1)Page 174

Descending tracts

Dorsal surface

Gray matter

Ventral surface

Lateral corticospinal

Rubrospinal

Ventral corticospinal

Vestibulospinal

Motor neurons

• Alpha motor neuron– Thick myelinated fast conducting axons– Motor end plate of extrafusal skeletal muscle

fibers

• Gamma motor neuron– Thin myelinated slower conducting axons– Supply the intrafusal fibers of Muscle spindles

in skeletal muscles � γ-static� γ-dynamic

Spinal interneurons

• Points of convergence for– most of the input of the brain descending

tracts– Sensory afferents & collaterals of LMN axons

• Intersegmental; same side of spinal cord

• Commissural: cross midline

Spinal reflexes

• Contribute to

• Muscle tone

• Body posture• Locomotion

Muscle spindles

• Lie parallel to regular muscle fibers

• contain nuclear bag and nuclear chain intrafusal muscle fibers.

Capsule

Alpha motorneuron axon

Gamma motorneuron axon

Secondary (flower-spray)endings of afferentfibers

Extrafusal (“ordinary”)muscle fibers

Intrafusal (spindle)muscle fibers

Noncontractilecentral portionof intrafusalfiber

Contractile end portionsof intrafusal fiber

Primary (annulospiral)endings of afferent fibers

Muscle spindles

• Can be stimulated by 2 ways

• Stretching the entire muscle

• Causing contraction of intrafusal fibers while extrafusal fibers remain at the same length.

Muscle spindles

• Group Ia afferent fibers form primary endings on nuclear bag and chain fibers,

• Group II fibers form secondary endings on nuclear chain fibers.

• Dynamic motor axons end on nuclear bag fibers and static motor axons on nuclear chain fibers.

Muscle spindles

• Primary endings demonstrate both static and dynamic responses, which signal muscle length and rate of change in muscle length.

• Secondary endings demonstrate only static responses and signal only muscle length.

• Motor neurons cause muscle spindles to shorten, which prevents the unloading effect of muscle contraction.

Golgi tendon organs

• Located in the tendons of muscles and are arranged in series.

• They are supplied by group Ib afferent fibers and are excited both by stretch and by contraction of the muscle (very sensitive to changes in muscle tension)

Figure 8.26 (1)

Page 287

Extrafusalskeletalmuscle fiber

Intrafusalmusclespindle fiber

Spinalcord

Afferent input from sensory endings of muscle spindle fiber

Alpha motor neuron output to regular skeletal-muscle fiber

Stretch reflex pathway

γ motor-neuron output to contractile end portions of spindle fiber

Descending pathways coactivating α and γ motor neurons

Relaxed muscle; spindlefiber sensitive to stretchof muscle

Contracted muscle inhypothetical situation ofno spindle coactivation;slackened spindle fibernot sensitive to stretchof muscle

Contracted muscle innormal situation of spindle coactivation;contracted spindle fibersensitive to stretch ofmuscle

Primary endings Signal Velocity and amount of change in muscle length

• Nuclear bag fibers• Ia fibers• Show a dynamic

response:– Discharge most rapidly

while the muscle is being stretched & less rapidly during sustained contraction

• Nuclear chain fibers • Ia fibers• Show a Static

response– Discharge at an

increased rate throughout the period when a muscle is stretched

• Signal the amount of displacement

Alpha-gamma linkage

Enhancement of voluntary muscle contraction by co-activation of gamma and alpha motor neurons

The stretch reflex includes

• a monosynaptic excitatory pathway from group Ia (and II) muscle spindle afferent fibers to a motor neurons that supply the same and synergistic muscles and

• a disynaptic inhibitory pathway to antagonistic motor neurons.

Myotatic stretch reflex

• The simplest reflex

• Monosynaptic

• Physiological significance: – Resting muscle tone and thus A key reflex in

maintenance of posture

The tonic stretch reflex

• Physiological significance: Resting muscle tone– Judged by the resistance that a joint offers to

bending

– Receptors: Ia & II from muscle spindle– Triggered by the static responses of group Ia

and II afferents.

– Any slight extension or flexion (during standing) will elicit a tonic stretch reflex in muscles required to oppose the movement, thus helping an individual to stand upright.

Phasic stretch reflex

• Physiological significance:

• Receptors: Ia from muscle spindle

• Triggered by the dynamic responses of group Ia fibers

• Enhancement of voluntary muscle contraction by co-activation of gamma and alpha motor neurons

Myotatic stretch reflex

• Clinical significance in diagnosis of diseases – tendon jerks

– muscle tone

Muscle stretch reflex

Figure 8.27Page 288

Patellar tendon

Extensor muscle of knee(quadriceps femoris)

Musclespindle

Alpha motorneuron

Inverse stretch reflex• Disynaptic (inhibitory interneuron+ α-mn )• Inhibition of α-mn of same muscle• Receptor: Golgi tendon organ (in series with

muscle fibers)

• Stimulus: increase in muscle tension by – excessive stretch – excessive active muscle contraction

• Result: relaxation (sudden stop in contraction)• Safety:

– regulates muscle tension– protects the tendon from tearing

Withdrawal reflex

• Polysynaptic

• Protective

• Painful stimulation of skin, subcutaneous tissue or muscle

• Stimulation of flexorscontraction

• Reciprocal innervation

• Simultaneous inhibition of antagonists relaxation

Figure 5.33Page 178

Stimulus

Biceps(flexor)contracts

Handwithdrawn

Triceps(extensor)relaxes

Ascending pathwayto brain

Response

Components of areflex arc

ReceptorAfferent pathwayIntegrating centerEfferent pathwayEffector organs

Integrating center(spinal cord)

Thermalpain receptor

in finger

Efferent pathway

Effectororgans

= Inhibitory interneuron= Excitatory interneuron= Synapse= Inhibits= Stimulates

AfferentPathway

Crossed extensor reflex

• Supporting reflex, serves to maintain posture

• Polysynaptic • Irradiation of stimulation• Reciprocal innervation

• Flexion and withdrawal of the painfully stimulated limb

• + extension of the other limb

Figure 5.34Page 179

Efferent pathway

Afferentpathway Efferent

pathway

Flexormusclecontracts

Extensormusclerelaxes

Flexormusclerelaxes

Extensormusclecontracts

StimulusResponse

Painreceptorin heel

Injured extremity(effector organ)

Integrating center(spinal cord)

Opposite extremity(effector organ)

Response

Receptor

Effector

Dorsal root ganglion cell Interneuron in

the spinal cord

Upper motor neuron of

corticospinal tract

α-motor neuron in the spinal cord

XU

T

S

V

Y

Z

W

The motor control system

Overview

The Motor system 1

• Cortex

• The Corticospinal tract

• Alpha motor neuron

• Muscles

Motor ControlMotor Cortex

UMN

Corticospinal tract (UMN)

Alpha motor neuron,

LMNMuscle

Alpha motor neuron

axon, LMN

Four Hierarchical Components that Control Movements

• Motor systems consist of separate neural circuits that are linked.

• Ultimately, whether directly or indirectly distributed, all motor processing is focused on a single target ‘the motor neuron’ constituting the ‘final common pathway’ of motor system.

Four Hierarchical Components that Control Movements

Spinal cord BrainstemSubcortical (basal nuclei, thalamus,

cerebellum)Cortical –(primary motor cortex, premotor

and supplementary motor areas)

Motor system 2

• Cortex• corticospinal tract• Alpha motor neuron• Muscles

• Two control circuits that influence the activity of corticospinal tract– Cerebellum – Basal Ganglia

Motor system 2two control circuits

Motor system 3• Cortex• corticospinal tract• Alpha motor neuron• Muscles• + two control circuits influence the corticospinal tract• Cerebellum and BG

• The Indirect brainstem motor control centers and pathways which tonically activate the Lower Motor Neurons especially those that innervate the Axial and Antigravity muscles

Motor system 3

Upper Motor Neuron • The corticospinal tract has its main influence on

LMN that innervate the muscles of the distal extremities, i.e., the hand and the foot

• The corticospinal tract has collaterals that modulate the control of indirect brainstem motor centers, so that we are not as a statue opposing gravity and can move at will and have the right amount of supporting tone

• When there is lesion of UMN, clinical findings are a combination of both direct + indirect effects

Figure

8.24Page 285

Cortical level

Subcortical level

Brain stem level

Spinal cord level

Periphery

Premotor and supplementary motor areas

Sensory areas of cortex

Primary motor cortex

Basal nuclei Thalamus

Brain stem nuclei

Cerebellum

Afferent neuronterminals

Motor neurons

Muscle fibers

Movement

“To move things is all that mankind can do… for such the sole executant is muscle,

whether in whispering a syllable or in felling a forest”.. Charles Sherrington

• The spinal cord contains certain motor programs for the generation of coordinated movements and that these programs are accessed, executed, and modified by descending commands from the brain.

Types of Movements

• Involuntary motor acts– Reflex: the most automatic behaviors (such

as reflexes-organized at spinal cord level)

• Voluntary motor acts– The maintenance of position (posture)– Goal directed movements- skilled voluntary

movements- organized at higher centers

Somatic musculature in relation to the joint they act on

• Axial muscles:– For movements of the trunk

• Proximal muscles (or girdle muscles)– For movements of the shoulder, elbow, pelvis

and knee

• Distal muscles– That move the hands, feet, and digits (fingers

and toes)

Important aspects of hierarchical organization:

• Somatotopic maps – preserved in interconnections at different levels

• each hierarchical level receives information from periphery so that sensory input can modify the action of descending commands

• The higher levels have capacity to control the information that reaches them, allowing or suppressing the transmission of afferent volleys through sensory relays.

Important aspects of hierarchical organization:

• The various motor control levels are also organized in parallel: so that each level can act independently on the final common pathway.

• This allows commands from higher levels either to modify or to supersede lower order reflex behavior.

Upper Motor Neuron Lesion

UMNL loss of direct effect of UMN

UMNL loss of indirect effect of UMN

UMNL is a combination of Loss of regulation

of indirect brainstem motor control centers

Loss of direct CST control

of LM neurons

Upper Motor Neuron Lesion

• Loss of distal extremity strength

• Loss of distal extremity dexterity

• Babinski sign

Loss of direct effect

• Increased tone

• Hyperreflexia

• Clasp-knife phenomenon

Loss of indirect effect

UMNL on opposite side of clinical findings if lesion is above the decussation

UMNL on same side of clinical findings if lesion in the spinal cord after decussation

Figure 9: The brain of a recovered stroke patient relies

on a compensatory neural pathway (dark blue) as

substitution for the damaged neuralpathway (blue dashed).

The cerebello-thalamo -cortical pathway (green) is “teaching” the

supplementary motor area its new function, which is indicated

by abnormal activity in the cerebellum and thalamus.

(Freely adapted from Azari & Seitz, 2000)

Airway Management in the Emergency Department

and ICUMehdi Khosravi, MD Pulmonary/CCM Fellow

Giuditta Angelini, MD Assistant Professor

Jonathan T. Ketzler, MD Associate Professor

Douglas B. Coursin, MD Professor

Departments of Anesthesiology & MedicineUniversity of Wisconsin, Madison

Global Assessment

Assess underlying need for airway control• Duration of intubation

- Nasal intubation less advantageous for potentially prolonged ventilator requirements

• Permanent support- Underlying advanced intrinsic lung or neuromuscular disease

• Temporary support• Anesthesia• Presence of reversible intrinsic lung or neuromuscular disease• Protection of the airway due to depressed mental status • Presence of reversible upper airway pathology• Patient care needs (e.g., transport, CT scan, etc.)• Significant comorbidities

Aspiration potential or increased respiratory secretions Hemodynamic issues such as cardiac disease or sepsis Renal or liver failure

Global Assessment

Pathophysiology of the respiratory failure• Hypoxic respiratory failure

- In case of hypoxic respiratory failure, different noninvasive oxygen delivery devices can be used.

- The severity of hypoxia and presence or absence of underlying disease (such as COPD) will dictate the device of choice.

• Hypercapnic respiratory failure- The noninvasive device of choice for hypercapnic respiratory failure is BIPAP.

Assessment of above mentioned patient characteristics in conjunction with the mechanism of respiratory distress leads the clinician to proper choice and duration of invasive or noninvasive options for airway management.

Code status should be clarified prior to proceeding.

Global AssessmentOxygenation• Respiratory rate and use of accessory muscles

- Is the patient in respiratory distress?• Amount of supplemental oxygen

- What is the patient’s oxygen demand?• Pulse oximeter or arterial blood gas

- Is the patient physiologically capable of providing appropriate supply?

Airway• Anatomy

- Will this patient be difficult to intubate?• Patency

- Is there a reversible anatomical cause of respiratory failure as opposed to intrinsic lung dysfunction?

• Airway device in place- Is there a nasopharyngeal airway or combitube in place?

Oxygen Delivery Devices(In order of degree of support)

Nasal Cannula• 4% increase in FiO2 for each 1 L of flow (e.g., 4 L flow = 37% or 6 L flow

= 45%)

Face tent• At most delivers 40% at 10-15 L flow

Ventimask• Small amount of rebreathing• 8 L flow = 40%, 15 L flow = 60%

Nonrebreather mask• Attached reservoir bag allows 100% oxygen to enter mask with

inlet/outlet ports to allow exhalation to escape - does not guarantee 100% delivery.

Oxygen Delivery DevicesNoninvasive Positive Pressure

CPAP is a continuous positive pressure• Indicated in hypoxic respiratory failure and obstructive sleep apnea

BiPAP allows for an inspiratory and expiratory pressure to support and improve spontaneous ventilation

• Mainly indicated in hypercapnic respiratory failure and obstructive sleep apnea

If use of noninvasive modes of ventilation does not result in improved ventilation or oxygenation in two to three hours, intubation should be considered

These devices can be used if following conditions are met:• Patient is cooperative with appropriate level of consciousness• Patient does not have increased respiratory secretions or aspiration potential• Concurrent enteral feeding is contraindicated.

Facilitates early extubation, especially in COPD patients

Some devices allow respiratory rate to be set.

Up to 10 L of oxygen can be delivered into the mask for 100% oxygen delivery.

Nasal or oral (full face) mask can be used; less aspiration potential with nasal.

Degree of Respiratory DistressRespiratory pattern• Accessory muscle use is an indication of distress.• Rate > 30 can indicate need for more support by noninvasive positive

pressure or intubation

Need for artificial airway• Tongue and epiglottis fall back against posterior pharyngeal wall• Nasopharyngeal airway better tolerated

Pulse oximetry• O2 saturation less than 92% on 60 - 100% oxygen can suggest the need

for intubation based on whether there is anything immediately reversible which could improve ventilation.

Arterial blood gas• pH < 7.3 can indicate need for more support by noninvasive positive

pressure or intubation.

Temporizing Measures

Naloxone for narcotic overdose• 40 mcg every minute up to 200 mcg with:

- 45 minutes to one hour duration of action• 0.4 - 2 mg of naloxone is indicated in patients with respiratory arrest and

history suggestive of narcotic overdose- There is a potential for pulmonary edema, so large dose is reserved

for known overdose and respiratory arrest• Caution in patients with history of narcotic dependence• Naloxone drip can be titrated starting at half the bolus dose used to

obtain an effect- Manufacturer recommended 2 mg in 500 ml of normal saline or D5

gives 0.004 mg/ml concentration

Temporizing Measures (cont'd)

Flumazenil for benzodiazepine overdose• 0.2 mg every minute up to 1 mg• Caution in patients with history of benzodiazepine or alcohol dependence• Caution in patients with history of seizure disorder as it will decrease the

seizure threshold

Artificial airway for upper airway obstruction in patients with oversedation• May be necessary in patients with sleep apnea despite judicious sedation

100% oxygen and maintenance of spontaneous ventilation in patients with pneumothorax• Washout of nitrogen may decrease size of pneumothorax• Positive pressure may cause conversion to tension pneumothorax

Oral/Nasal Airways

Indications for Intubation

Depressed mental status• Head trauma patients with GCS 8 or less is an indication for intubation

- Associated with increased intracranial pressure- Associated with need for operative intervention- Avoid hypoxemia and hypercarbia which can increase morbidity and

mortality• Drug overdose patients may require 24 - 48 hours airway control.

Upper airway edema• Inhalation injuries• Ludwig’s angina• Epiglottitis

Underlying Lung Disease

Chronic obstructive lung disease• Application of controlled ventilation may interfere with complete

exhalation, overdistend alveoli, and impair right heart and pulmonary venous return.

Pulmonary embolus• Pulmonary artery and right ventricle already have high pressure and

dependent on preload• Application of controlled ventilation may deteriorate oxygenation and

systemic pressure.

Restrictive lung disease• May require less than 6 cc/kg Vt to prevent elevated intrapulmonary

pressure• Application of positive pressure may result in barotrauma in addition to

impaired preload.

Airway Anatomy Suggesting Difficult Intubation

Length of upper incisors and overriding maxillary teeth

Interincisor (between front teeth) distance < 3 cm (two finger tips)

Thyromental distance < 7 cm• tip of mandible to hyoid bone (three finger breaths)

Neck extension < 35 degrees

Sternomental distance < 12.5 cm• With the head fully extended and mouth closed

Narrow palate (less than three finger breaths)

Mallampati score class III or IV

Stiff joint syndrome• About one third of diabetics characterized by short stature, joint rigidity, and tight waxy skin• Positive prayer sign with an inability to oppose fingers

No sign is foolproof to indicate intubation difficulty

Erden V, et al. Brit J Anesth. 2003;91:159-160.

Prayer Sign

Mallampati Score

Class I: Uvula/tonsillar pillars visibleClass II: Tip of uvula/pillars hidden by tongueClass III: Only soft palate visibleClass IV: Only hard palate visible

Den Herder, et al. Laryngoscope. 2005;115(4):735-739.

ComorbiditiesPotential for aspiration requires rapid sequence intubation with cricoid pressure• Clear liquids < 4 hours• Particulate or solids < 8 hours• Acute injury with sympathetic stimulation and diabetics may have

prolonged gastric emptying time.

Potential for hypotension• Cardiac dysfunction, hypovolemia, and sepsis• May need to consider awake intubation with topical anesthesia

(aerosolized lidocaine) as sedation may precipitate hemodynamic compromise and even arrest.

Organ failure• Renal and hepatic failure will limit medication used.• Potential for preexisting pulmonary edema and airway bleeding from

manipulation

Induction Agents

Sodium Thiopental• 3 - 5 mg/kg IV• Profound hypotension in patients with hypovolemia, histamine release,

arteritis • Dose should be decreased in both renal and hepatic failure.

Etomidate• 0.1 - 0.3 mg/kg IV• Lower dose range for elderly and hypovolemic patients• Hemodynamic stability, myoclonus• Caution should be exercised as even one dose causes adrenal

suppression due to similar steroid hormone structure.• Unlikely to have prolonged effect in organ failure

Induction Agents (cont'd)

Propofol• 2 - 3 mg/kg IV• Hypotension, especially in patients with systolic heart dysfunction,

bradycardia, and even heart block• Unlikely to have prolonged effect in organ failure

Ketamine• 1 - 4 mg/kg IV, 5 - 10 mg/kg IM• Stimulates sympathetic nervous system• Requires atropine due to stimulated salivation and midazolam for

potential of dysphoria• Avoid in patients with loss of autoregulation and closed head injury

Neuromuscular Blockers

Succinylcholine• 1 - 2 mg/kg IV, 4 mg/kg IM• Avoid in patients with malignant hyperthermia, > 24 hours out from burn or

trauma injury, upper motor neuron injury, and preexisting hyperkalemia

Rocuronium • 0.6 - 1.2 mg/kg, highest dose required for rapid sequence• Hemodynamically stable, 10% renal elimination

Vecuronium• 0.1 mg/kg• Hemodynamically stable, 10% renal elimination

Cisatricurium• 0.2 mg/kg• Mild histamine release, Hoffman degradation, not prolonged in renal or

hepatic failure

Rapid Sequence Intubation

Preoxygenate for three to five minutes prior to induction• Wash out nitrogen to avoid premature desaturation during intubation.

Crycoid pressure should be applied from prior to induction until confirmation of appropriate placement.

Succinylcholine 1 - 2 mg/kg IV will achieve intubation conditions in 30 seconds; Rocuronium 1.2 mg/kg IV will achieve intubation conditions in 45 seconds.• Other muscle relaxants do not produce intubation conditions in less than

60 seconds.

Avoid mask ventilation after induction.• Potentially can inflate stomach• Use only if necessary to ensure appropriate oxygenation during

prolonged intubation.

Y BAG PEOPLE (Reference #6)

Cricoid Pressure

Cricoid is circumferential cartilage

Pressure obstructs esophagus to prevent escape of gastric contents

Maintains airway patency

Koziol C, et al. AORN. 2000;72(6):1018-1030.

Sniffing PositionAlign oral, pharyngeal, and laryngeal axes to

bring epiglottis and vocal cords into view.

Hirsch N, et al. Anesthesiology. 2000;93(5):1366.

Mask Ventilation

Mask ventilation crucial, especially in patients who are difficult to intubate

Sniffing position with tight mask fit optimal

May require two hands

Mask ventilation crucial, especially in patients who are difficult to intubate

Sniffing position with tight mask fit optimal

May require two hands

Laryngoscope Blades and Endotracheal Tubes

Miller blade: End of blade should be under epiglottis

Mac blade: End of blade should be placed in front of epiglottis in valecula

ETT for Fastrach LMA

Pediatric uncuffed ETT

ETT for blind nasal

Standard ETT

Graded Views on Intubation

Grade 1: Full glottis visibleGrade 2: Only posterior commissureGrade 3: Only epiglottisGrade 4: No glottis structures are visible

Yarnamoto K, et al. Anesthesiology. 1997;86(2):316.

Confirmation of PlacementDirect visualization

Humidity fogging the endotracheal tube

End tidal CO2 which is maintained after > 5 breaths• Low cardiac output results in decreased delivery of CO2

Refill in 5 seconds of self-inflating bulb at the end of the endotracheal tube

Symmetrical chest wall movement

Bilateral breath sounds

Maintenance of oxygenation by pulse oximetry

Absence of epigastric auscultation during ventilation

Additional Considerations

Always have additional personnel and an experienced provider as backup available for potential failed intubation

Always have suction available

Never give a muscle relaxant if difficult mask ventilation is demonstrated or expected

Awake intubation should be considered in the following:• If patient is so hemodynamically unstable that induction drugs cannot be

tolerated (topicalize airway)• If patient has a history or an exam which suggests difficult mask

ventilation and/or direct laryngoscopy

American Society of Anesthesiologistswww.asahq.org

Alternative MethodsBlind nasal intubation

• Bleeding may cause problems with subsequent attempts.• Contraindicated in patients with facial trauma due to cribiform plate disruption or

CSF leak• Avoid in immune suppressed (i.e., bone marrow transplant)

Eschmann styletFiber optic bronchoscopic intubation

• Awake vs. asleep

Laryngeal mask airway• Allows ventilation while bridging to more definitive airway

Light wandRetrograde intubation

• Through cricothyrotomy

Surgical tracheostomyCombitube

Eschman Stylet

Use especially if Grade III view achievedDirect laryngoscopy is performedPlace Eschman where trachea is anticipatedMay feel tracheal rings against stiffness of styletThread 7.0 or 7.5 ETT over stylet with the laryngoscope still in place

Fiberoptic Scope

Essentially what is used to do a bronchoscopyCan be used to thread an endotracheal tube into the trachea either while the patient is asleep or on an awake patient with a topicalized airwayVia laryngeal mask airway in place due to inability to intubate with DL:

• Aintree (airway exchange catheter) can be threaded over the FOB to be placed into trachea upon visualization

• Wire-guided airway exchange catheter can also be used with one more step

The Laryngeal Mask Airway (LMA)

LMA Placement

Guide the LMA along the palate

Eventual position should be underneath the epiglottis, in front of the tracheal opening, with the tip in the esophagus

FOB placement through LMA positions in front of trachea

Martin S, et al. J Trauma Injury, Infection Crit Care. 1999;47(2):352-357.

The FastrachTM Laryngeal Mask Airway

Reinforced LMA allows for passage of ETT without visualization of trachea.

10% failure rate in experienced hands

20% failure rate in inexperienced

The Light WandTransillumination of trachea with light at distal endTrachea not visualized directlyShould not be used with tumors, trauma, or foreign bodies of upper airwayMinimal complication except for mucosal bleed10% failure rate on first attempt in experienced hands

Retrograde Intubation

Puncture of the cricothyroid membrane with retrograde passage of a wire to the trachea

Endotracheal tube guided endoscopically over the wire through the trachea

Catheter through the cricothyroid can be used for jet ventilation if necessary.

Wesler N, et al. Acta Anaes Scan. 2004;48(4):412-416.

CombitubeEmergency airway used mostly by paramedics and emergency physicians for failed endotracheal intubation

Ventilation confirmed through blind blue tube

• Combitube is in the esophagus and salem sump can be placed through white tube

Ventilation confirmed through white (clear) tube with patent distal end

• Combitube is in the trachea and salem sump should be placed outside of combitube into esophagus

• Fiber optic exchange can be accomplished through combitube

Combitube (cont'd)

Should be changed to endotracheal tube (ETT) or tracheostomy to prevent progressive airway edema

If in esophagus, take down pharyngeal cuff and attempt direct laryngoscopy (DL) or fiber optic bronchoscope (FOB) placement around combitube

Failed exchange attempt can be solved with operative tracheostomy

Placement of combitube can produce significant airway trauma

• Removal prior to DL or FOB should be done with caution after thorough airway evaluation

• Cricoid pressure should be maintained and emergency tracheostomy equipment available

Tracheostomy

Surgical airway through the cervical tracheaEmergent procedure carries risk of bleeding due to proximity of innominate arteryCan be difficult and time consuming in emergent situations

Sharpe M, et al. Laryngoscope. 2003;113(3):530-536.

Case Scenario #1

The patient is 70 kg with a 20-year history of diabetes.

On exam, the patient has intercisor distance of 4 cm, thyromental distance is 8 cm, neck extension is 45 degrees, and mallampati score is 1.

Your staff wants to use thiopental and pancuronium.

Do you have any further questions for this patient or would you proceed with your staff?

Case Scenario #1 - Answer

A diabetic for 20 years needs assessment for stiff joint syndrome.

You should have the patient demonstrate the prayer sign.

If the patient is unable to oppose their fingers, you should not give pancuronium.

You may want to proceed with an LMA and FOB at your disposal.

If the patient has a history of gastroparesis, you may want to consider an awake FOB.

Case Scenario #2

43-year-old patient with HIV, likely PCP pneumonia who had been prophylaxed with dapsone

RR is 38, oxygen saturation is 90% on 100% NRB mask

The patient is on his way to get a CT scan.

Is it appropriate to proceed without intubation?

Case Scenario #2 - Answer

Dapsone will produce some degree of methemoglobinemia.

Therefore, some degree of desaturation may not be overcome.

The patient is in significant respiratory distress and will be confined in an area without easy access.

Intubation should be considered as an extra measure of safety, especially as this patient is likely to get worse.

Case Scenario #3

40-year-old, 182-kg man has a history of sleep apnea and systolic ejection fraction of 25%. He has a Strep pneumonia in his left lower lobe and progressive respiratory insufficiency.

He extends his neck to 50 degrees and has a mallampati score of 2.

Would you proceed with an awake FOB?

Case Scenario #3 - Answer

The patient’s airway anatomy is not suggestive of difficulty.

However, with supine position, subcutaneous tissue may impair your ability to visualize or ventilate.

Use of gravity, including a shoulder roll, extreme sniffing position, and reverse trendelenburg may be helpful with asleep DL.

Prudent to have some accessory equipment, including an LMA and FOB, for back up

References

1. Caplan RA, et al. Practice guidelines for management of the difficult airway. Anesthesiology. 1993;78:597-602.

2. Langeron O, et al. Predictors of difficult mask ventilation.Anesthesiology. 2000;92:1229-36.

3. Frerk CM, et al. Predicting difficult intubation. Anaesthesia.1991;46:1005-08.

4. Tse JC, et al. Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia. Anesthesia & Analgesia. 1995;81:254-8.

5. Benumof JL, et al. LMA and the ASA difficult airway algorithm. Anesthesiology. 1996;84:686-99.

6. Reynolds S, Heffner J. Airway management of the critically ill patient. Chest. 2005;127:1397-1412.