Monitoring the anesthetized patient Flashcards
What is anesthesia (4 factors)?
- Lack of awareness of all aspects of environment
- Reversible, neurological depression; unconsciousness
- Lack of sensation; analgesia
- Amnesia
- Muscle relaxation
Anesthesia is the overlap of what 2 things?
Overlap of analgesia and unconsciousness
T/F: Anesthetics are inherently good analgesics
FALSE–anesthetics are not inherently good analgesics
What are the signs (indirect) of neurologic depression?
- Physical signs, somewhat subjective
- Physiologica parameters of the autonomic system
- Quality of pulse
- To avoid “too deep”
How do we know if the patient is adequately anesthetized?
- Adequate neurological depression
- Can we monitor the CNS?
- EEG
- Bi-spectral analysis (BIS)
What is the bispectral analysis? What is it based on and what do low values represent?
- Processed EEG that monitors cortical activity
- Based on an algorithm, the EEG is quantitated to a scale from 0-100
- The lower the number, the more depressed
- Better titration of anesthetics
T/F: Bispectral analysis is a practical monitoring modality in vet med
FALSE–usefulness is uncertain–depends on drugs used; it is not yet a practical monitoring modality in veterinary medicine
What are the physical signs to assess depth of anesthesia?
- Presence/absence of purposeful movement in response to stimuli
- Potency of inhalants based on this fact (MAC [50% subjects] to prevent movement)
- Muscle relaxation
- Eyeball rotation*
- Jaw tone*
- Abdominal mm tone
- Reflexes
- Palpebral*
- Corneal
- Anal
- Pupillary light (not helpful)
- Autonomic signs
- Changes in cardiovascular, respiratory parameters
What are the different stages based on ether anesthesia? What should you avoid (gas anesthetic)? Which is the ideal surgical plane (gas anesthetic)?
- Avoid excitement (stage II–delerium)
- Ideal surgical plane in stage III plane 2
T/F: There is no clear demarcation between stages or planes of ether anesthesia
TRUE
How is movement used to determine adequate/inadequate anesthesia?
- Purposeful movement to a noxious stimulus is a reliable sign of inadequate anesthesia (too light) for that particular stimulus
- Ex: lack of movement to a toe pinch does not mean they won’t move in response to a surgical stimulus
- Useful to test soon after induction or during mask inductions
How are reflexes used to determine adequate/inadequate anesthesia?
- Gag or swallow reflexes, moving tongue are reliable signs that they are too light
- Don’t even try to intubate
- Palpebral reflex–suggests a too light plane of anesthesia for surgery (except horse)–may/may not be adequate anesthesia
- Corneal reflex–should always be present (don’t elicit often)
- Pupillary light reflex–not a reliable sign of adequate depth–can be present at a surgical plane
How is jaw tone used to measure anesthetic depth?
- Reliable sign of relaxation and depth (dog/cat/bird) although subjective
- Test beginning of anesthesia to have ‘baseline’
- Should be easy to move with 2 fingers
- Test intermittently during anesthesia
How is eye position used to determine anesthetic depth?
- Extra-ocular mm relax at different stages
- Generally, we like to see the eyeball rolled ventrally (see some sclera); probably has no palpebral reflex
- A central eyeball may suggest too deep
- The 2 eyes may differ–look at BOTH
- Look at the palpebral fissure
- Lack of palpebral fissure (closed eyelid) reliable sign of light anesthesia; may/may not have palpebral reflex
- Wide palpebral fissure suggests deeper plane
What eye signs in large animals are used to determine anesthetic depth?
- Horse/ruminant tend to roll eyes forward
- Tearing is a sign of light anesthesia–common to see in horse
- Swine–eye signs (nor jaw tone) are not very helpful
Why isn’t pupil size very useful in determining anesthetic depth?
- Autonomic responses (catecholamines) produce dilation, as well as some drugs (atropine, ketamine)
- Pupils can appear pinpoint to mid-sized at light-moderate stages
- FIXED AND DILATED is a BAD sign
T/F: Eye position can change frequently–if so, they are light enough to be responding to stimuli–can be a good thing
TRUE
T/F: A brisk nystagmus seen in ruminants is a reliable sign of a very light stage of surgical anesthesia
FALSE–in HORSES
Watch out–horse may move
T/F: Nystagmus is rarely seen in small animals except in stage 2 or early recovery
TRUE
I can’t remember if we have to memorize this, but here’s the chart for all the reflexes during various planes of anesthesia
T/F: Changes in heart rate, resp rate, or blood pressure may be autonomic responses to stimuli that aid in assessing depth but are not specific for depth
TRUE
What happens with the autonomic system during induction? As anesthesia progresses?
- At induction (if not profoundly sedated) animal usually has more sympathetic activity
- Possible increased HR, RR
- Avoid excessive excitation at induction
- Epinephrines going around–> increased HR, etc. –> could be fatal
- As anesthesia progresses, HR, RR usually levels to more stable parameters
What autonomic responses usually infer to a patient being ‘light’ for that particular stimulus? What else should you check?
- Increasing RR, HR, and BP coinciding to a sudden noxious stimuli (drilling bone, pulling up an ovary); they may not all change together;
- Check physical signs–did the jaw tone get tighter?
What autonomic responses generally suggest that anesthetic depth is adequate (and not necessarily too deep)? What signs signal a serious problem?
- Gradual decreasing of HR or RR = adequate
- Parasympathetic > sympathetic tone
- Decreasing BP may/may not be a sign of too deep anesthesia (CNS depression)
- Side effects of anesthetics
- Corrective measures must still be instituted if BP is getting too low
- Sudden and/or profound decrease in HR/RR/BP = serious problem–turn off anesthetic and investigate
