7/28/2019 Sleep and Anaesthesia(June 1999)

1/4

Write down the physiology of sleep. How does it differ from

anaesthesia? What phases occur in various stages of anaesthesia?

-Normal Sleep-1] NREM-N1/N2/N3 (delta)

-2] REM-a) Tonic-parasympathetically driven state

-no eye movement

b) Phasic-Sympathetically driven state

-rapid eye movement

-muscle twitches

-respiratory variables

-Sleep is a state of unconsciousness in which the brain is relatively more

responsive to internal than external stimuli. It is a heightened anabolic

state; accentuating the growth and rejuvenation of the immune,

nervous, skeletal and muscular system.

-Sleep proceeds in cycles of REM and NREM, the order normally being

N1->N2->N3->N2->NREM

-Sleep and other characteristics of sleep are commonly assessed by

Polysomnography in a specialized sleep lab.

-Measurements taken include

i) EEG of brain waves

ii) EOG of eye movements

iii) EMG of skeletal muscles

-In humans, each sleep cycle lasts from 90 to 110 minutes on average

7/28/2019 Sleep and Anaesthesia(June 1999)

2/4

-NREM-N1-alpha waves-8-13 Hz to theta waves 4-74 Hz, myoclonus

-N2-sleep spindle-11 to 16 Hz, K-Complexes, muscular activity as

measured by EMG decreases

-occupies 45-55% of total sleep

-N3-deep or slow wave sleep-theta wave-0.5 to 2Hz

-parasomnia, nocturnal enuresis, sleep walking and

somniloquy

Occur

-REM-20-25%of total sleep

-rapid eye movement

-rapid low voltage EEG

DIFFERENCE BETWEEN GA AND SLEEP

SLEEP GA

Distinctive EEG

patterns

GA EEG most similar to that of a comatose

brain

Emergence from GA parallels recovery from

coma

Controlled by sleep

wake cycle, circadian

rhythm, switch of

sleep is the

ventriculolateral

Preoptic nucleus of

the anterior

Hypothalamus

Controlled by anaesthetic

7/28/2019 Sleep and Anaesthesia(June 1999)

3/4

The predictable cycling of sleep, the reversal of relative external

unresponsiveness are features that assist in distinguishing sleep from

other states of consciousness.

STAGES OF ANAESTHESIA

-Four stages of anaesthesia

-Stage 1-Induction

-period between initial administration of the induction agents

and loss of consciousness.

-patient can carry on a conversation.

-Stage 2-excitement stage

-period following loss of consciousness

-marked by excited and delirious activities

-RR and HR become irregular

-there may be vomiting, breath holding, and pupillary dilatation

-since these may lead to airway compromise, rapidly acting

drugs

are used to minimize time in this stage and reach stage 3 as far

as possible.

-Stage 3-Surgical anaesthesia

-skeletal muscle relaxation, patients breathing becomes

7/28/2019 Sleep and Anaesthesia(June 1999)

4/4

regular, eye movements slow and then stop

-divided into 4 planes

Plane 1-eyes initially rolling, and then become fixed

Plane 2-loss of corneal and laryngeal reflexes

Plane 3-pupils dilate and loss of light reflex

Plane 4-intercostal paralysis, shallow abdominal respiration,

dilated

Pupils.

-Stage 4-overdose

-stage where too much medication given relative to the amount

of surgical stimulation and the patient has severe brain stem

or medullary depression.

-this results in a cessation of respiration and potential

cardiovascular collapse.

-this stage is lethal, without cardiovascular and respiratory

support