Stages of Anesthesia

Ether

• BIS number < 60: Patient unable to respond to verbal commands
• BIS number > 70: Corresponds to a higher likelihood of awareness
• BIS number of 90- 100: Awake

BIS numbers between 45 and 60 are, in general, considered to be optimal for a relatively healthy patient undergoing a routine general anesthetic and surgery.

Ref:Clinical Anesthesiology By G. Edward Morgan, 4th Edition, Chapter 6

A i.e. Ether

Ans:D.)Both a and b.) Stages of Anesthesia and Oropharyngeal Airway.

The image shown is of Anesthesiologist: Arther Guedel

Arther Guedel

• Arthur Ernest Guedel (June 13, 1883 – June 10, 1956) was an American anesthesiologist.
• He designed Stages of Anesthesia and oropharyngeal Airway.
• Guedel’s classification is a means of assessing of depth of general anesthesia 

Stages of Anaesthesia

• Stage I (Stage of Analgesia or the stage of Disorientation): from the beginning of induction of anesthesia to loss of consciousness.
• Stage II (Stage of Excitement or the stage of Delirium): from loss of consciousness to onset of automatic breathing. Eyelash reflex disappears but other reflexes remain intact and coughing, vomiting and struggling may occur; respiration can be irregular with breath-holding.
•  Stage III (Stage of Surgical anesthesia): from the onset of automatic respiration to respiratory paralysis. It is divided into four planes:
• “Plane I” – from the onset of automatic respiration to the cessation of eyeball movements. 
• “Plane II” – from the cessation of eyeball movements to the beginning of paralysis of intercostal muscles. 
• “Plane III” (Surgical Anaesthesia) from beginning to completion of intercostal muscle paralysis. 
• “Plane IV” – from complete intercostal paralysis to diaphragmatic paralysis (apnoea). 
•  Stage IV: from the stoppage of respiration till death. Anaesthetic overdose causes medullary paralysis with respiratory arrest and vasomotor collapse. Pupils are widely dilated and muscles are relaxed.

Oropharyngeal airway (also known as an oral airway, OPA or Guedel pattern airway)

• It is a medical device called an airway adjunct used to maintain or open a patient’s airway.
• It does this by preventing the tongue from covering the epiglottis, which could prevent the person from breathing.
• When a person becomes unconscious, the muscles in their jaw relax and allow the tongue to obstruct the airway.

Ans: B.) Stage of Excitement.

Guedel’s Stages of Anesthesia Stages of Anesthesia is shown in the image.

Stages of Anaesthesia:

• Guedel described four stages of ether anesthesia during the III stage into 4 planes.

• With faster-acting gas, these clear-cut stages are not seen nowadays as induction with these agents is too fast.

1. Stage I / Stage of analgesia:

• Extends from the beginning of anesthetic inhalation to the loss of consciousness.

2. Stage 2 / Stage of delirium or excitement: 

• From the loss of consciousness to the beginning of regular respiration.

• There is roving eyeball (maximum movement of the eye).

• The pupil is partially dilated. Eyelash reflex is lost—> First reflex to be lost. However eyelid reflex remains present.

3. Stage 3 / Stage of surgical anesthesia:

• From the beginning of regular respiration to the cessation of spontaneous breathing.

• Most surgeries are done at this stage.

• It is divided into 4 planes:

• Plane I:
• From the beginning of the regular respiration to the cessation of eye movement.

• There is a roving eyeball.

• Eyelid reflex is lost. This plane ends when eyeball becomes fixed.

• Pupil size is normal.

• Plane II:
• From the cessation of eye movement to respiratory Paresis.

• The eyeball is fixed.

• There is a loss of corneal reflex.

• Pupil starts dilating (1/2 dilated).

• Plane III:

• • From respiratory paresis to respiratory paralysis. Pupil 3/4 dilated. Swallowing reflex and laryngeal reflexes are lost.

• Plane IV:
• Intercostal paralysis, there is only abdominal respiration.

• The pupil is fully dilated.

• Carinal reflex (Cough reflex) is lost —–> Lost reflcx to be lost.

• Lacrimation is present in plane II & In and absent in Plane III, IV.

4. Stage 4 / Stage of medullary paralysis:

• There are respiratory arrest and apnea.

• The pupil is fully dilated & fixed.

Recovery period:

• During recovery, the return of reflexes is in opposite sequence, i.e., first to come is carinal reflex and last is eyelash.

• So theoretically it is a cough which should come first but swallowing comes first than coughing because coughing also requires diaphragm and respiratory muscles effort.

Ans. b. Bispectral index monitoring

Use of the bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease the incidence of anesthesia awareness when the BIS value is maintained below

Bispectral Index Scale (BIS)

• It is based on the principle of EEG°
• Bispectral imaging analyses EEG date and quantitate anesthetic effects on the brain, specifically the hypnotic component.
• It is a composite numerical index, which represents a dimensionless numerical value that has been correlated with the patient’s current hypnotic state or depth of anaesthesia and provides some assurance that paralyzed (anesthetized) patient is also asleep (unaware
• BIS analysis may reduce chances of patient awareness during anesthesia. It may also reduce resource utilization because lesser drug is required to ensure amnesia, facilitating a faster wake up time and a shorter stay in recovery room.

The BIS number decreases with increasing hypnosis

• The BIS is derived from complex EEG analysis incorporating weighted information derived from the degree of burst suppression, spectral (b band) power and the bispectrum coherence^Q.
• To make the EEG signals easier to interpret it uses 2 principles which are, which are, spectral analysis (power) and fast fourier analysis.^Q
• It uses 3 EEG electrodes placed on frontal, parietal and temporal lobes^Q
• IS is used to monitor: Intraoperative awareness°, Depth of anesthesia^Q
• Its value ranges from 0-100 (0: coma; 100: awake)^Q

• Target intra-operative BIS: 40-60^Q
• Target sedation BIS: 60-80^Q

Methods used for Assessing Consciousness Intraoperatively

• Bispectral index (BIS) analysis
• Narcotrend monitor (Monitor Technique)
• Patient state index (PSI, Physiometrix) is based on quantitative EEG signal relationship between frontal and occipital brain regions
• Entropy monitors measure state entropy (response over the range of 0.8-32 Hz, reflecting EEG dominant spectrum and response entropy (response over range of 0.8-47 Hz, reflecting both EEG and EMG spectra)
• Stimulus-response technique of auditory evoked potential

Ans. is ‘a’ i.e., Stage-1