STAGES OF ANESTHESIA

STAGES OF ANESTHESIA


Introduction:
Order of anesthesia action:
  • An irregular descending CNS depression.

In brain: 

  • Higher functions lost first —> progressively lower brain area involved. 
  • Vital centers located in medulla paralyzed at last as depth of anesthesia increases.

In spinal cord: 

  • Lower segments affected earlier than upper segments. 
Stages of anesthesia:
  • Guedel described 4 stages with reference as ether.
  • Note: IIIrd stage divided into 4 planes.
  • Only observed in slow acting GA.
  • With faster-acting inducing agents, no clear cut stages observed with GA’s. 

Stage 1:

  • Stage of analgesia.
  • Extends from beginning of anesthetic inhalation to loss of conciousness.

Stage 2:

  • Stage of delirium or excitement.
  • Extends from loss of conciousness to beginning of regular respiration.

Features:

  • Presence of roving eye ball (maximum movement of eye).
  • Pupil is partially dilated.
  • Loss of eyelash reflex -> 1st reflex to be lost.
  • No loss of eyelid reflex.

Stage 3:

  • Stage of surgical anesthesia. 
  • Extends from beginning of regular respiration to cessation of spontaneous breathing.
  • Divided into 4 planes.

Plane 1:

  • From beginning of regular respiration to cessation of eye movement.
  • Presence of roving eye ball.
  • Loss of eyelid reflex.
  • Plane ends with eye-ball fixation.
  • Normal pupil size.

Plane 2:

  • From cessation of eye movement to respiratory paresis.
  • Fixed eye ball.
  • Loss of corneal reflex.
  • Pupil starts dilating (1/2 dilated).
  • Lacrimation present.

Plane 3:

  • From respiratory paresis to respiratory paralysis.
  • Pupil 3/4 dilated.
  • Swallowing & laryngeal reflexes are lost.
  • Lacrimation present

Plane 4:

  • Intercostal paralysis.
  • Only abdominal respiration.
  • Fully dilated pupil. 
  • Lost carinal (cough reflex) –> Final reflex to be lost.
  • Note: Lacrimation is present in plane II & III & absent in plane III, IV.

Stage 4:

  • Stage of medullary paralysis.
  • Presence of respiratory arrest & apnea.
  • Fully dilated & fixed pupil.
Recovery from anesthesia:
  • Return of reflexes is in opposite sequence.
  • i.e., 1st – Carinal reflex. 
  • Last – Eyelash reflex.
  • Note: Cough should come first but swallowing comes first.
  • Because coughing requires diaphragm & respiratory muscles effort.

Monitoring the depth of anesthesia:

Done mainly clinically:

  • Tachycardia
  • Hypertension.
  • Lacrimation.
  • Perspiration (sweating).
  • Eye movement.
  • Preserved reflexes (coughing).
  • Movement on painful stimuli.
  • Laryngospasm / Bronchospasm.
  • Tachypnea.
  • 3 waves on EEG.
  • Evoked responses.
  • Bispectral index.
Bispectral index:
  • 1st scientifically validated & commercially available monitor to check depth of anesthesia. 
  • Utilizes parameters like EEG signals, eye blinks for score calculation
  • Adequate depth = score of 45-60.
  • Fully awake state = score of 100.
  • Completely silent brain = 0.

Exam Important

  • Bispectral index is 1st scientifically validated & commercially available monitor to check depth of anesthesia. 
  • Monitoring the depth of anesthesia is done clinically by perspiration (sweating) & bispectral index.
  • During recovery from anesthesia, swallowing comes first.
  • Stage 4 is stage of medullary paralysis.
  • Lacrimation is present in plane II & III & absent in plane III, IV of stage 3 of surgical anesthesia. 
  • Stage 3 is Stage of surgical anesthesia. 
  • Stage of surgical anesthesia extends from beginning of regular respiration to cessation of spontaneous breathing.
  • Stage 3 is divided into 4 planes.
  • Plane 1 of stage 3 ends with eye-ball fixation.
  • Stage 2 is stage of delirium or excitement.
  • In stage 2 there is presence of roving eyeball (maximum movement of eye) & pupil is partially dilated.
  • Stage 1 is stage of analgesia.
  • Guedel described 4 stages of anesthesia with reference as ether.
  • Vital centers located in medulla paralyzed at last as depth of anesthesia increases.
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