Week 1 - Neurophysiology for Anesthesia Flashcards
What is the purpose of Anesthesia?
To reduce anxiety – Anxiolysis
To relieve pain – Analgesia
To provide a stable surgical field – Paralysis
To produce Hypnosis (don’t want awareness)
Autonomic supression
Somatic suppression
Physiologic Patterns of Sleep and Wake
Wakefulness: norepinephrine, histamine, serotonin, dopamine, orexin
Non REM Sleep: firing decreases
REM Sleep: firing virtually quiescent
Anesthesia Affect on Sleep
Anesthetic effect on the thalamus resemble the naturally occurring thalamocortical inhibition characteristic of NREM sleep
Somnogens reduce amount of GA needed
Adenosinergic Antagonists increase amount of GA needed
Sites in the brain where anesthesia affects sleep
Thalamic Sites: during NREM sleep and anesthesia, the cortex is deprived of input (Thalamic Gates)
Hypothalamic Sites: histaminergic and orexenergic neurons in the hypothalamus stimulate the thalamus
Brainstem Sites: Locus Ceruleus, Mesopontine Tegentum, and VLPO stabilization
Limbic System: Hippocampus, medial septum, amygdala
Chemicals that Act at Synapses as Neurotransmitters (Table 3-2)
Glutamate — Oxytocin — Acetylcholine — Cholecystokinin — Norepinephrine — Gastrin — Glycine — GABA — Endorphins — Dopamine — Serotonin — Epinephrine — Histamine — Substance P — Vasopressin — Prolactin — Glucagon — Vasoactive intestinal Peptide
Inotropic Receptors vs Metabotropic Receptors
Ionotropic: ligand-gated ion channels that pass + or - ions and excite or inhibit
Metabotropic: can be excited or inhibited by the same neurotransmitter depending on which type of G-protein is coupled to the transmitter
Glutamate?
Excitatory in the brain and spinal cord
KA, AMPA, NMDA ionotropic receptors
NDMA blocked by Mg at normal extracellular levels
Open NMDA allow Ca into the cell
GABA
Inhibitory primarily in the brain
GABAa - ionotropic (Chloride/Bicarb)
GABAb - metabotropic open K+ channels
Glycine
Inhibitory primarily in the spinal cord
Requires 3 glycine to activate Chloride channels
It is a co-agonist at the NMDA receptor
What type of receptors are the Acetylcholine Receptors in the CNS?
Nicotinic are ionotropic
Muscarinic are G protein coupled
ACh regulated wakefulness, attention, learning, and motivation
What is critical in memory formation and storage?
Alteration in the strength of neuronal connections
Phases of memory
Short-Term Memory - seconds to hours
Long-Term Memory - hours to months
Long-Lasting (months to lifetime)
What phase of memory do Benzodiazepines and IV Anesthetics affect?
Primarily long term memory storage or retrieval
At what MAC do volatile agents impair memory formation?
25% to 50%
What is Long Term Plasticity and what inhibits it?
A form of synaptic plasticity important in memory formation
Inhibited by barbiturates, benzodiazepines, propofol, and Isoflurane
What is a BIS monitor and its limitations?
Algorithmic EEG analysis – range 0-100
General Anesthesia = 40-60
Gives an indication of how “deep” under anesthesia the pt is
Limitations of a BIS monitor
Ketamine and N2O increase BIS (False high)
Neuromuscular blockers decrease BIS in awake pts (False low)
Multiple BIS sensors on same pt give different values
Low BIS values may result in a reduction in delivered anesthesia concentration and resulting awareness
Types of Procedures with Incidence of Awareness
Highest in OB
General Surgery with ETT (1%)
Cardiac Surgery (pure narcotic)
Trauma (shock and severe injury does not equal unconsciousness)
Reasons for Intraoperative Awareness
Equipment Failure Inadequate Anesthesia Patient Factors (age, health status, alcohol/drug use, obesity, pharmacokinetic/pharmacodynamic) Inability to assess depth of anesthesia Inappropriate anesthesia technique
Likely times for recall in anesthesia
Preinduction (light induction for various reasons)
After Intubation (paralyzed but not anesthetized)
Intraoperative (light anesthesia w/ paralysis, wakeup test well tolerated)
Postoperative (residual paralysis during emergence)
What are Guedels Signs and Stages?
Stage I Analgesia or Disorientation
Stage II Excitement or Delirium
Stage III Surgical Anesthesia
Stage IV Overdose
Guedels Signs and Stages - Stage I
Analgesia or Disorientation
From beginning of induction of anesthesia to loss of consciousness
Guedels Signs and Stages - Stage II
Excitement or Delirium
From loss of consciousness to onset of automatic breathing
Eyelash reflex disappears but other reflexes remain intact, pupils dilated but reactive, tearing, coughing, vomiting and strugglilng may occur; respiration can be irregular with breath-holding
Guedels Signs and Stages - Stage III
Surgical Anesthesia
Begins with onset of regular respiratory pattern and ends with loss of respiration
Guedels Signs and Stages - Stage III Phane I
Onset of automatic respiration to cessation of eyeball movements
Eyelid reflex is lost, swallowing reflex disappears, marked eyeball movement may occur but conjunctival reflex is lost at the bottom at the bottom of the plane
Guedels Signs and Stages - Stage III Phane II
Cessation of eyeball movements to beginning of paralysis of intercostal muscles
Laryngeal reflex is lost although inflammation of the upper resp tract increases reflex irritability, corneal reflex disappears, secretion of tears increases, respiration is automatic and regular, movement and deep breathing as a response to skin simulation disappears
Guedels Signs and Stages - Stage III Phane III
From beginning to completion of intercostal muscle paralysis
Diaphragmatic respiration persists but there is progressive intercostal paralysis, pupils dilated and light reflex is abolished. Laryngeal reflex lost in plane II can still be initiated by painful stimuli arising from the dilatation of anus or cervix.
Desired plane for surgery when muscle relaxants were not used
Guedels Signs and Stages - Stage III Plane IV
From complete intercostal paralysis to diaphragmatic paralysis (apnea)
