ANAESTHETICS : General Anesthetics | Basic Concepts in Pharmacology

 Reversible state of CNS depression, resulting in loss of response to & perception of External stimuli.
Pre-anaesthetics medicines

calm the patient , relieve pain & protected against undesirable effects of anaesthetics or surgical procedure
STAGES & DEPTH OF ANAESTHESIA

1) Induction=Period of time from onset of Administration to development of surgical anaesthesia. Propofol produce induction in 30-40sec...For Childern Halothane or Sevoflurane induce general anaesthesia

2) Maintenance=Sustained surgical anaesthesia

3) Recovery= Time from discontinuation of anaesthesia until consciousness & protective physiological reflexes.
Depth of Anaesthesia= Four stages ...each stage characterized by CNS depression
Stage l-Analgesia= Loss of pain sensation
Stage ll-Excitement= Dilirium....increase BP...increase risk of Laryngospasm
Stage lll-Surgical Anaesthesia= Loss of muscle tone...decrease CNS reflexes ...Regular respiration
Stage IV-Medullary paralysis= Severe depression of Respiratory & CNS
INHALATION ANAESTHETICS
Mostly used for maintenance.. Narrow Therapeutic Index...Nonflammable..

Potency= potency is MAC(Minimum Alveolar Conc.)...MAC is the median effective dose ED50 of the anaesthetic...High MAC-Low Potency
MAC useful in comparing pharmacologic effect of different anaesthetic
More Lipid drug lowerconc. Needed to produce anesthesia, high potency of drug
Sevoflurane have Small ED50....N2O have large ED50
Alveolar wash-in= replacement of normal lung gases with Inspired Anaesthetic mixture..... time required for Alveolar wash-in ∞ Residual Lung Capacity... and inversely proportional to Ventilatory Rate
Wash –out=body moves anaesthetic into Alveolar space..NO exit faster than Halothane.
MOA

 Activate GABA receptor...inhibit Glutamate Activated NMDA receptor..activate the inhibitory Glycine receptor...inhalation anesthetics also block the excitatory presynaptic neurons
Halothane

prototype...Potent anesthetic...weak analgesic...usually coadminister with opioid,NO,Local anesthetic
T.E

used in Obstetrics to relax uterine & skeletal muscle..DOC for Inhalation induction
S.E

Hepatotoxic but not in children..Bradycardia..Hypercapnia(increased CO2)...
Malignant Hyperthermia more susceptible in Patients with Burn, Duchenne Muscular Dystrophy, Myotonia, Osteogenesis imperfect...
Dantrolene used to relieve from HYPERTHERMIA
Isoflurane

not hepatotoxic, cardiac toxicity...Dose-Dependent Hypotension due to
vasodilation..topically used

Desflurane

 rapid onset & recovery than all inhaled anesthetic..for out patient surgery
Sevoflurane

suitable for anesthesia induction in Pediaterics
Nitrous Oxide(NO)

Laughing gas...nonIrritating...Potent analgesic..Weak Anesthetic...
Applied with 30-50% conc. In combination with O2 for Analgesia in Dental Surgery..
Nitrous oxide at 80% not used for Surgical anesthesia
Second-Gas Effect: NO b/c of its fast uptake from alveolar gas, can concentrate
halogenated Anesthetics in Alveoli when they concomitantly used
Cause” Diffusion Hypoxia” retard O2 uptake during recovery
Contraindicated in Pernicious Anemia b/c it cause Hypoxia
INTRAVENOUS ANESTHESIA
Propofol= I/v anesthesia..replaced THIOPENTALas first choice for Anesthesia
Induction & sedation b/c it produce Euphoric effect...Does not cause postanesthesia vomiting
Actions

Depression of CNS..Muscle twitching..Hiccups..Vasodilation..DOC in
“Ambulatory Surgery”
Fospropofol

 Prodrug of Propofol...only for sedation

Etomidate

Hypnotic agent lack analgesic activity..water soluble formed in PEG soln..
used for Patients with Coronory Artery disease
S.E

 decrease Cortisol & Aldosterone level due to Inhibition of 11-β Hydroxylase
Ketamine

Non-Barbiturate...for Dissociative anesthesia for Cardiogenic Patients..
increase BP& CO in Patients with Hypovolemic or Cardiogenic shock & in Asthma..
cross B.B.B causes Postoperative Hallucination(Nightmare) in adults