L8 General Anaesthesia Flashcards
Definition of GA
A controlled, reversible state of unconsciousness produced by anesthetic agents from which a patient cannot be aroused by an external stimuli
4 characteristics of GA
- Pt in a controlled state of unconscious
- Complete loss of protective reflexes
- Cannot maintain airway independently
- There is no purposeful response to verbal commands
Takes longer to come back from compared to IV sedation
4 stages of GA
Stage 1 - induction
Between initial administration of induction meds and loss of consciousness
Stage 2 - excitement
Period following loss of consciousness and marked by excited and delirious activity. Cannot work in this stage
Stage 3 - surgical anesthesia
Skeletal muscles relax, pt’s breathing becomes regular. Eye movements slow, then stop, surgery begins.
Stage 4 - overdose
Too much medication has been given and pt has severe medullary depression. Lethal without cardiovascular/resp support
Indications of GA
- Longer procedures
- Acute infections
- Allergy to LA
- Infants/children
- Learning disability
- Anxiety
- Pt’s difficult to do under IV sedation
Contraindications of GA
- Lack of training/equipment/facility
- Unescorted patient and patient eating!
- Pregnancy?
- ASA IV & certain ASA III
Advantages of GA
- Pt is unconscious
- Patient cooperation is not essential
- Analgesia, amnesia
- Muscle relaxation
- Airway is protected
- Rapid onset
- Can be titrated
LA is always safer, but it pt is very anxious this may be even safer
Disadvantages of GA
- Pt is unconscious
- Depressed protective reflexes/vital signs
- Advanced training needed
- Anesthesia team must be there
- Special equipments
- Recovery area is required
- Higher risk vs LA
3 types of GA
- Totally IV-GA (TIVA)
- Totally GA inhalation
- Mixed IV and inhalation
2 IV Agents
- Propofol
2. Ketamine
Inhalation Agents
- Halogenated ethers (common - especially in kids)
ex. enflurane, isoflurane, desflurance, sevoflurane - Halogenated ethane (uncommon)
ex. Nitrous oxide (has to be combined with other gasses), halothane (less common from liver toxicity)
Out-patient GA (IV)
Indication: short procedure Requirement: fasting, escort, consent ASA: I/II Cost: cheaper Patients: lots of children
Other: reduced contact with hospital hazards, parental preference
MOA of propofol
Enhanced GABA, enhancing inhibition
Uses of propofol
Short acting GA & sedative
Weak analgesic & antiemetic
Constituents of propofol
10% soya beans oil
2.25% clycerol
1.2% egg phosphatide
1% isopropylephenol
Side effects of propofol
Inhibition of sympathetic vasoconstrictor nerve activity –> decreased vascular resistance
- hypotension
- lower brain metabolism
- decreased respiration
Onset of propofol, and duration
30s with quick recovery, duration <5-10 mn
Location of metabolism and excretion of propofol
Metabolized: liver
Excreted: in urine
Induction and maintenance doses of propofol
Induction: 1-2 mg/kg
Maintenance: 0.1 - 0.2 mg/kg/mn
MOA of ketamine
Dissociation anesthesia - pt is in neuroleptic state by blocking NMDA receptors in nerve cells and other receptors
Location of metabolism and excretion of propofol
Metabolized: liver
Excreted: in urine
Side effects of ketamine
- Tachycardia
- hypertension
- hallucination on recovery
- bronchial secretions
Induction doses of ketamine
IV 1-2 mg/kg (30-60s)
or
IM 5-10 mg/kg (5min)
Results of ketamine
- Amnesia
- Analgesia
- Unconscious
- Open eyed and swallow un-purposefully
- Bronchodilation (with more secretions - useful for COPD pt)
What are the uses of halogenated ethers vs ethanes?
Ethers: Induction and maintenance of anesthesia
- less liver toxicity and blood solubility
Ethane: induction only
- liver toxicity is highest among GA gases (metabolized in liver)
- sweet smelling drug, so good for induction
- soluble in blood (slower induction & recovery)
What about nitrous oxide in general anesthesia?
Has to be combined with other gases because it is a weak anesthetic
W/ other gasses –> induction & maintenance
Would never be used alone - has to be combined with other gases because it is too weak
What is the benefit in terms of nitrous use as an inhalation agent?
it is excreted by lungs –> no liver toxicity
How do we maintain the airway?
- Endotracheal intubation - oral/nasal
- laryngeal mask & fiber optic intubation are used in difficult intubation
- surgical airway are used in emergencies and impossible oro-naso-endotracheal intubation
Muscle relaxants prior to intubation
Remove skeletal muscle responses to painful stimuli/tracheal intubation & reduce muscle tone
What types of muscle relaxants are used?
Depolarising agents: suxamethonium, succenyl coline = short acting (3-5 mn)
Non-depolarising agents: recoronium, sistracurium, moderate and long acting (15-19)
What is the sequence for tracheal intubation for GA?
- ventilation
- sedation
- IV GA induction
- Muscle relaxation
- Intubation
Opioids and steroids may also be used to blunt parasympathetic effects + reduce nausea and inflammation
LA used for hemostasis and pain control
