BAC - Chapter 5: Anaesthetic Drugs Flashcards
Advantages of IV induction agents:
- Rapid onset
- Smooth induction
- More pleasant for patient
- Less theatre pollution
Disadvantages of IV induction agents:
- Venipuncture needed
- Easily overloaded
- No elimination by lungs - needs metabolism and excretion
- Sudden loss of normal protective mechanisms & apnoea
Sodium Thiopentone - indications:
- Induction
- Maintenance
- Rx of status epilepticus
- Reduce ICP
Sodium Thiopentone - CIs:
- Allergy
- Porphyria
- CVS disorders - CCF, fixed CO, hypovolaemia
- Asthma - relative
Special precaution in Sodium Thiopentone:
- Intra-arterial injection
- Causes arterial spasm & thrombosis
- Prevention: don’t used veins next to arteries/ use 2.5% solution
- Rx: Inject papaverine 80 mg in 20 ml N/S.
- Anticoagulation
Propofol - precautions:
- Good culture medium
- CVS depression so beware in:
Hypovolemia
HPT
Fixed CO
Elderly
Propofol - Indications:
- Favoured IV induction agent - rapid return of consciousness
- Most suitable for TIVA - minimal accumulation
- Sedation for regional anaesthesia
- Sedation in ICU
- Agent for porphyria
PRIS - risky dose?
- > 5mg/kg/hr for > 48 hrs
PRIS - features:
- Lipaemia
- Metabolic acidosis
- Cardiomyopathy
- Cardiac failure
- Skeletal myopathy
- Death
Etomidate - Indications:
- Induction with CVS compromise
Etomidate - precautions:
- Suppress cortisol synthesis
2. Long infusion - Reduce immunological competence
Ketamine - features of induction:
- Dissociative anaesthesia:
Catatonia
Amnesia
Analgesia
Ketamine - precautions:
- Distressing emergence phenomena
- Increased secretions - pre-med with anticholinergic
- Avoid in IHD/ HPT
Ketamine - Indications:
- Shocked pts
- Severe asthmatics - potent bronchodilator
- Paeds
- Difficult locations - accident scene
- Short procedures
- Analgesia + sedation - wound dressings
Ketamine - CIs:
- CVS disorders - HPT, IHD, AA
- Raised ICP
- Open eye injuries - raised IOP
- Psych pts.
- Pts. on TAD
- Thyrotoxicosis
- Early pregnancy
- Epileptics
Thiopentone - dose:
- Induction: 3-5 mg/kg
2. Infusion: 4mg/kg/hr
Thiopentone - preparation:
500 mg amp in 20 ml = 25mg/ml
Thiopentone - CVS affects:
- Decreases myocardial contractility
- Decreases CO by 10-20% d/t peripheral vasodilation
- Reflex tachycardia
Thiopentone - Resp affects:
- Central depression
- Potent apnoea
- A/W reflexes not abolished - risk of L/G or bronchospasm
Thiopentone - CNS affects:
- Decreased ICP
- Anticonvulsant
- Cerebral protection in focal ischemia
- Commonly used in neuroanaesthesia
Propofol - dose:
- Induction: 2-3 mg/kg
2. Infusion: 6-8 mg/kg/hr
Propofol - how to reduce pain when giving IV:
- Mixing with 10 mg lignocaine in syringe
Propofol - effect on emesis:
- Thought to be anti-emetic
Propofol - CVS affects:
- Up to 40% decrease in BP d/t:
Myocardial depression
Decreased PVR - Tachycardia
Propofol - Resp affects:
- Apnoea common with induction
- Decreased TV w/ infusion
- Increased RR w/ infusion
- Laryngeal reflexes suppressed - reduced risk of laryngospasm
- Drug of choice for LMA
Propofol - CNS affects:
- Anticonvulsant
2. Reduces ICP
Etomidate - dose:
- Induction: 0.2 - 0.3 mg/kg
2. Maintenance: 10-20 ug/kg/min (generally not used for infusion d/t adrenal suppression)
Etomidate - effect on emesis:
- 30% increased risk - “vomidate”
Etomidate - CVS affects:
- Minimal CVS depression
Etomidate - Resp affects:
- Ventilation affected less
- No apnoea with induction
- No histamine release
- Good for asthmatics
Etomidate - CNS affects:
- Reduces ICP
Ketamine - dose:
- Induction: 2 mg/kg IVI
- Infusion: 4-6 mg/kg/hr
- Analgesia: 0.5 mg/kg
Ketamine - analgesic affect:
- Intense visceral & somatic analgesia
Ketamine - emergence phenomena:
- Delirium
- Agitation
- Nightmares
Ketamine - CVS effects:
- Increases arterial BP by 25%
- Increases HR by 20%
- Increases myocardial O2 consumption
Ketamine - Resp effects:
- Upper A/W reflexes remain largely intact
- No histamine release
- Potent Bronchodilator
- Increases secretions
Ketamine - CNS effects:
- Increases ICP
2. Dissociative amnesia
Midazolam - dose:
- Induction: 0.2 mg/kg
- Sedation: 2.5 - 7.5 mg
- Pre-med: 5mg IMI
- ICU:
- 1 Initial bolus of 5mg/kg
- 2 Then infusion of 1-20 mg/hr titrated to response
Midazolam - affect on emesis:
- Incidence of PONV
Midazolam - CVS affects:
- Slight decrease in BP
2. Slight increase in PR
Midazolam - Resp affects:
- Risk of resp depression/ apnoea
Ways to create faster gas induction:
- Increase concentration of gas
- Increase flow rate
- Use non-rebreathing circuit