Anesthetic Pre-medications - Sedatives Flashcards
what is the purpose of anesthesia
to numb pain and/or induce inconsiousness
how does anesthesia work
blocks nerve signals at the level of the CNS (general anesthesia)
block nerve signals at thevel of PNS at a specific location (local anesthesia)
what are the main steps in anesthesia protocol
- Premedication: to reduce anxiety and pain before anesthesia
- Induction: to rapidly and smoothly produce state of unconiusness - IV
- Maintenance: keep patient unconscious - inhaled
- Recovery: emergance from general anesthetic
what are different types of premeducations
- sedatives/anxiolytics/neuroleptics
- analgesics
- muscle relaxants
- anticholinergics
role of sedatives as premedication
- inhibit irritabiliy and excitement
- cause some degree of sleepiness
role of anxiolytics as premedication
- inhibit apprehension and fear
- does not induce sleepiness/hypnosis
- formerly known as “minor tranquilizers”
role of neuroleptics as premedication
- results in emotional detachment (apathy) and suppress agitation-related movement
- also known as anti-psychotics or “major tranquilizers”
- many have sedation properties too
what are the benefits of using sedative/anxiolitic drugs before surgery as premedication
- easier surgical preperation
- reduces anesthetic dose needed and therefore chance of side-effects
- smoother recovery for patients
3 classes of pre-medications - sedative and anxiolytics
phenothiazines: neuroleptic/sedative
alpha-2 agonists: sedative
benzodiazepines: sedative/anxiolytic
clinical effects of Chlorpromazine - a Phenothiazine
- reduction of fear and anxiety
- sedation
- muscle relaxation
clinical indications of Chlorpromazine - a Phenothiazine
- reduction of agitation before surgery
- *also main use to treat schizophrenia
Phenothiazine’s mechanism of action
- block dopamine D2 receptors in the brain
- D2 blockade causes sedation, reduced agitation
- also blocj peripheral a1 receptors - side effects
side effects of Phenothiazine’s
- have to do with peripheral a1 receptor blockade
- vasodilation and hypotension
how do phenothiazines (chlorpromazine) cause hypotension
- when they bind to a1 they block NE from binding to carry out vasoconstriction
clinical effects of Dexmedetomidine - an Alpha2 agonist
- sedation/hypnosis (sleepiness)
- analgesia (pain relief)
- muscle relaxation
clinical indications of dexmedetomidine - an Alpha2 agonist
- for seation in adults prior to and/or during surgical procedures
Alpha2 agonists mechanism of action
- selective for a2 receptors
- in presynaptic neurons cause K+ channels to open and Ca2+ channel suppression (inhibitory)
- leads to membrane hyperpolarization and inhibits NT release
Inhibiting NT release by dexmedetomidine binding a2 receptors leads to…
- sedation (instead of wakefulness)
- analgesia (instead of pain)
- hypotension (instead of SNS outflow)
- muscle relaxation (instead of motor activity)
Dexmedetomidine is a selective a2 agonist if…
injectled SLOWLY and at LOW DOSES
Dexmedetomidine can also stimulate a1 and a2b receptors when…
drug is injected RAPIDLY pr at HIGH DOSES causing transient hypertension
how does dexmedetomidine cause transient hypertension when it binds a1 receptors
- drug binds a1 at BV (SNS) first if injected rapidly causing hypertension
- then binds receptors on brain (CNS) to inhibit SNS outflow - relaxes BV
side effects of dexmedetomidine
- hypotension, bradycardia, heart block
- casued by inhibition of SNS outflow from the CNS via a2a receptor
effects of Alpha2-agonists (e.g. Dexmedetomidine) on HR and BP
HR = decreased
BP = increased if injected rapidly at high dose
BP = decreased if injected slowly at low dose
clinical effects of Midazolam - a Benzodiazapine
- reduce anxiety
- drowsiness/fatigue
- muscle relaxation
- amnesia
- anti-seizure effects
clinical indications of Midazolam - a Benzodiazapine
- for releif of anxiety and tension in patients about to undergo surgery
- diminish patients recall of procedure (administered 5-10 minutes before anesthesia)
Midazolam mechanism of action
- facilitates binding of GABA to its receptor through allosteric binding site
- hyper polarizes cell and inhibits excitation
safety profile of Midazolam
- safe when administered alone because little effect on CV and respiratory systems
- overdose can be reversed by flumazenil - competitive inhibitor of the benzo binding site
adverse effects of midazolam
- dose-dependent respiratory depression if co-administered with other CNS depressants
benzodiazepines vs alpha-2 antagonists when preparing a patient for general anesthesia
- a2 = lighter sedation, benzo = deeper sedation
- a2 = analgesic properties, benzo = reduce anxiety
- a2 = CV effects, benzo = respiratory effects
