Lecture 5: Monitoring Anesthetic Depth (Exam 1) Flashcards
What is general anesthesia
- Both the loss of consciousness & sensation
- Should include muscle relaxation, analgesia, suppression of stress response, & hypnosis
- Reversible process
- May be produced w/ 1 drug or a combo of drugs
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Describe stage 1
- The time from the start of admin of induction drugs until loss of consciousness
- Stage of voluntary movement (able to initially turn or lift head w/out support)
- Some analgesia present
- Progressive ataxia -> lateral recumbency
- Most variable stage
What will stage on look like if the patient is excite
- Struggling
- Breath holding
- Increased HR
- Pupil dilation due to epinephrine release
- Defecation
- Urination
- Salivation
Describe stage two
The stage of delirium & involuntary movement & lasts from loss of consciousness to onset of regular breathing pattern
Describe stage 3
- Stage of surgical anesthesia due to level of unconsciousness w/ progressive depression of reflexes, muscle relaxation, & slow regular breathing pattern
- Vomiting (by plane 1) & swallowing (by plane 2) reflexes abolished
- loss of jaw tone
Describe stage 3 plane 1
- “light” plane of anesthesia
- Persists until eyeball movement stops
- Min invasive/painful procedures
Describe stage 3 plane 2
- “Medium” plane of anesthesia
- Most surgical procedures performed @ this plane
- Characterized by progressive intercostal paralysis
- Respiration & HR have stabilized
- Sluggish palpebral reflex
- Strong corneal reflex
- Adequate muscle relaxation & analgesia
- Abolished laryngeal reflexes
Describe Stage 3 plane 3
- “deep” plane of anesthesia or “deep plane of surgical anesthesia”
- Decrease in HR
- Slow shallow abdominal breathing pattern (“diaphragmatic respiration”)
- Now jaw tone
- No reaction to surgical stimulation profound muscle relaxation
- No palpebral reflex, weak corneal reflex
- Pupil progressively dilated & central
Describe stage 3 plane 4
- Pupils dilated
- Hypotension progressing to shock
- Slow CRT
- Slow irregular respirations
- Lack of muscle tone
- No anal sphincter tone
Describe stage 4
- Extreme CNS depression which leads to anesthetic overdose
- Pale to white mm, CRT > 3 sec
- Respiratory arrest followed by cardiac arrest
- Central widely dilated pupils
- Absent ocular reflexes
- Flaccid muscle tone
- Death unless swift intervention
Why should lubrication ointment be placed in the eyes
Eyes open = dry out= corneal ointment
What ocular signs should be checked to monitor depth
- Palpebral refle
- Eye position
- Lacrimation
- Nystagmus
- Corneal reflex
What other areas should be checked to monitor depth
- Jaw tone
- Anal reflex
- Pedal reflex (tail pinch, ear pinch, or ear-flick reflex)
- Overall muscle tone or degree of px relaxation
What is the goal for a surgical anesthesia plane
- Relaxed jaw tone (easy to open w/ 2 fingers)
- Mild to no palpebral reflex
- Ventral medial eye rotation
- Relaxed anal tonie
- Smooth regular respiratory pattern
- Norm HR
- No swallowing, coughing, vomiting, or laryngospasm
What signs to look for in horses
- lacrimate in light stages of anesthesia
- Eyes stay central instead of ventral medial eye rotation
- Nystagmus in stage 2
- Corneal reflex persists into deeper anesthesia plane
What signs should be looked for in cats
May go into laryngospasm &/or may retain cough, swallow, & vomiting reflex until they reach a deeper plane of anesthesia
What signs should be looked for in cattle
Have consistent reliable eyeball rotation
What signs should be looked for in rodents
*Observe feet, ears, & muzzle for pallor or cyanosis
* Pedal reflex
What signs should be looked for in poultry
- Examine comb &/or wattle for pallor
- Vent reflex
What signs should be looked for in rabbits
Can use the color of light reflected from the eye to determine circulation status
Are there any factors that make monitoring depth difficult
- drugs like ketamine (typical eye signs not produce) & propofol (no analgesia & apnea)
- Oxygenation adequacy
- CO2 retention
- Physical status
Describe anesthetic gas analyzer
- Useful piece of equipment but not commonly ava in general prac
- Used to perform min alveolar concentration (MAC) studies in many species
What other methods can be used to measure depth
- Anesthetic gas analyzer
- Bispectral index (BIS) usually in research
Explain recovery
- Progresses in reverse order
- Every species & px will recovery differently
- Treat post op pain if suspected
- Stage 2 can be a difficult time due to delirium/dysphoria, esp in equine px (horses ae often sedated w/ an alpha2 agonist going into inhalant anesthesia recovery & stimulation is minimized i.e a dark quiet room)
