Introduction Flashcards
What is anesthesia
Drug induced reversible CNS depression
- loss of response and perception of external stimuli
- low therapeutic index
- combines pharmacology, physiology, clin path, medicine, surgery
Anesthetic
Compound or element that by itself can produce general anesthesia
- ex: isoflurane, propofol, alfaxalone
Anesthesia
State achieved by combination of agents, none of which alone produces anesthesia
- ex: combo of alpha2-agnoist, opioid, dissociative
Anesthetic agents are used for
- exam
- diagnostics
- surgery
- seizure control
- euthanasia
Anesthetic agents are administered
- IV, IM, SC, IN
- inhaled
- topically
- epidural
- subarachnoid
- infiltration
Inhaled anesthetics
- volatile hydrocarbons
- noble gases
- carbon dioxide
- nitrous oxide
Injectable anesthetics
- barbiturates
- chloral hydrate/chloralose
- imidazoles
- phenolics
- steroids
- benzodiazepines
- cyclohexamines
- Na+ channel blockers
Where do anesthetics work?
Subcellular target is synaptic function via ligand-gated ion channels
- n-methyl-d-aspartate (NMDA) antagonists –> dissociatives (ketamine_
- gamma aminoibutyric acid (GABA) agnoists –> inhalants
_______ is primary site where anesthetics act to inhibit purposeful responses
Spinal cord
- brainstem, cerebral cortex involved in conscious perception and memroy
What are the 4 components of general anesthesia
- amnesia
- unconsciousness
- immobility (dose-dependent)
- analgesia: attenuation of autonomic responses to noxious stimuli
Unresponsiveness _____ unconsciousness
Does NOT equal to!!
Consciousness
Subjective experience
Connectedness
Awareness of the environment
Responsiveness
Spontaneous or goal-directed movement
____ likely depends on integrity of the corticothalamic networks
Consciousness
Spontaneous _______ may depend on subcortical and spinal cord networks
Responsiveness
______ may depend on continued information integration in corticothalamic circuits and unperturbed norepinephrinergic signaling
Connectedness
What takes the highest anesthetic concentration to block?
Blocked autonomic response
Loss of righting reflex associated with onset of unconsciousness is _____
Drug dependent
- memory and awareness ablated at anesthetic concentration <50% of that needed to abolish movement
Anesthetized animals may move in response to ______
Noxious stimuli
- unconscious animals can produce complex movements at the level of the brainstem or spinal cord
- connection to cerebral cortex not required
Pain
Unpleasant sensory and emotional experience associated with actual or potential tissue injury
- conscious awreness of nociception
- response to nociception
Nociception
Activation of nociceptors by noxious stimulus
Analgesia is absence of _____
Pain
- pain is a conscious experience
Anesthetized patients ____ experience pain
Do Not
- may respond physiologically, autonomically and reflexively to noxious stimuli
- supplemental analgesia useful to reduce anesthetic requirement, improve comfort at recovery
Analgesia
- conscious: reduced pain perception
- unconscious: reduced autonomic response to nociception
Preventive analgesia
Use analgesic drugs and techniques before, during, and after pain begins
- prevents plastic wind up of pain pathways
Anesthetic care plan
Meets unique medical needs of the individual patient
- consists of patient evaluation and patient preparation
- informed anesthetic choices
Anesthetic sequence of events
- preanesthetic evaluation, preparation, medication
- anesthetic induction
- maintenance of anesthesia
- recovery phase (24 hr following awakening)
50% of anesthetic deaths occur ______
Post-op
Patient evaluation
- positive patient identification
- history
- physical exam findings
- lab data
Lab tests should be chosen based on ________
Physical exam and history
- extensive non-directed pre-anesthetic lab screening does not improve patient outcome!!
ASA status assignment
- class 1: no systemic dz
- class 2: mild compensated systemic dz
- class 3: serious systemic dz, stable vital signs
- class 4: serious systemic dz, decompensated
- class 5: moribund, requires intensive life support
Why hospitalize patient overnight?
- acclimatize to clinic
- time for evaluation
- time for stabilization, if needed
Fasting
May decrease aspiration risk
- improves abdominal access
- may improve ventilatory function
- species differences
- not recommended in young patients
Monogastrics vs ruminants
- monogastrics: water access up to time of premedication
- ruminants: usually recommended (associated with increased parasympathetic tone)
Patient stabilization
Very important!
- provide analgesia
- treat blood, fluid, or electrolyte deficits ahead of time
- decreases anesthetic risk
Equipment
- venous catheterization
- fluid therapy
- patient monitoring
- materials for treatment of anticipated complications (anesthetic and surgical)
- induction and maintenance
Awake EEG
- low voltage ampllitude
- many high frequency components (fast) –> desenchronized
Deep anesthesia EEG
- higher voltage
- slow oscillations
- synchronized, dose dependent
EEG does not determine _______
Onset of consciousness
- limited ability to indicate presence or absense of unconsciousness around the transition point
- unclear which patterns are indicators of activation by stress or pain
Wakefulness
State of being awake
- implies brain physiological state that differs from that found with sleep or anesthesia
- does not by itself signify presence of consciousness
