Induction and Maintenance of Anaesthesia Flashcards
Name the 5 routes of drug administration/delivery
IM
IV
SC
Inhaled
Across mucous membranes
Name the 3 things that general anaesthesia includes
- Amnesia
- Loss of consciousness (hypnosis)
- Immobility, often associated with analgesia and suppression of autonomic reflexes
Name the main pharmacokinetic properties of propofol (absorption, solubility, distribution, metabolism, elimination)
Absorption - minimal oral bioavailability therefore inject IV
Solubility - Minimally soluble in water therefore injected as an emulsion
Distribution - 98% protein bound
Metabolism - liver, process of glucuronidation
Elimination - renal
Name the main pharmacodynamic properties of propofol
Anaesthesia in 5-8 mins
Respiratory and cardiovascular depression
Decreased cerebral metabolic rate of oxygen (CMRO2)
Haemodynamic effects due to sympathetic depression
- Decreased HR, MAP, SVR and CVP
- Stable cardiac output
Why do we need to intubate ASAP when using propofol
Apnoea is common
Name the main pharmacokinetic properties of alfaxalone (absorption, solubility, distribution, metabolism, elimination)
Absorption - good bioavailability
Solubility - soluble in water - can give IM or IV
Distribution - 30-50% protein bound
Metabolism - liver, rapid (also lungs and kidney)
Elimination - renal (small % bile)
Name the main pharmacodynamic properties of alfaxalone
Anaesthesia
Decreased cerebral metabolic rate of oxygen (CMRO2)
Haemodynamic effects minimal
- Stable cardiac output
- Stable HR, MAP, SVR, CVP
How should you administer alfaxalone and propofol
Titrate to effect - over 60 seconds
What are the haemodynamic effects of ketamine
Minimal
Stable cardiac output
Increased HR, MAP, SVR, CVP
What effects does ketamine have on the cardiovascular system, and what patients is it contraindicated in
Increases arterial pressure, HR and cardiac output - due to stimulation of SNS
Increases pulmonary arterial pressure
Contraindicated in patients with coronary artery disease and poorly controlled hypertension
What effects does ketamine have on the respiratory system
Minimal effect on ventilatory drive
Bronchodilator - preserves upper airway reflexes
Patients with an increased risk of aspiration may require airway protection
What effects does ketamine have on the cerebral system
Increased cerebral blood flow, intracranial pressure and cerebral oxygen requirements
Dissociative anaesthesia - patent may appear conscious e.g. eye-opening, swallowing
Analgesia and opioid sparing
Which drug can you use to minimise the unpleasant dream/hallucinations following administration of ketamine
Benzodiazepines
Name the main pharmacokinetic properties of ketamine (availability, solubility, distribution, metabolism, elimination)
Availability - Good bioavailability - IV, IM, squirted into mouth
Solubility - soluble in water
Distribution - 12% protein bound
Metabolism - liver => norketamine
Elimination - renal, small % bile
Name the 2 main volatile agents used in maintenance of anaesthesia
Isofluorane
Sevofluorane
Name the main pharmacodynamic properties of volatile agents
Anaesthesia
Cardiopulmonary depression
- Reduced cardiac output, HR, MAP, SVR, CVP
Name the main pharmacokinetic properties of the volatile agents (absorption, solubility, distribution, metabolism, elimination)
Absorption - lungs
Solubility - in tissues/blood varies
Distribution - Via blood to brain
Metabolism - minimal
Elimination - lungs
How is the speed of induction with volatile agents related to cardiac output and why
Speed of induction is inversely proportional to cardiac output
Due to negative effects of cardiac output on alveolar partial pressure
Name 3 ways anaesthesia can be maintained
- Inhalational anaesthesia
- Total intravenous anaesthesia (TIVA)
- Mix of the two - Partial intravenous anaesthesia (PIVA)
Are volatile/inhalational agents vapours or gasses
Vapours
Which gasses can be used to carry volatile agents to the patient
Oxygen - most common
Medical air?
May include NO
How do inhalational agents work (cause anaesthesia)
Fresh gas + volatile agent are inhaled => alveoli
The agent is soluble in blood, plasma conc. increases
Agent => brain
What factors does the rate of plasma increase of volatile agents depend on and how
The concentration of the agent
- Increase in conc => quicker increase of plasma conc.
Patient’s ventilation
- Increased ventilation => faster increase in plasma conc.
Cardiac output
- Increased CO => slower increase
Solubility of the agent in the blood
- increased solubility => slower increase
- Poorly soluble agents diffuse out of blood to tissues more quickly
What 3 receptors do we think volatile agents act on
- GABA
- NMDA
- Ach
Name the different types of anaesthetic scavenging
Passive scavenging - can use charcoal to absorb
Active scavenging
Define the minimum alveolar concentration (MAC)
The concentration of a vapour in the alveoli of the lungs that is needed to prevent movement in 50% of subjects in response to surgical stimulus.
Name 3 factors which affect MAC
- Individual variation
- Body temperature, age, etc.
- Drugs given premed or intraoperatively (MAC sparing often)
Out of isoflurane and sevoflurane, which has a higher MAC across all species
Sevoflurane
Which species are isoflurane and sevoflurane licensed in
Iso - dogs, cats, horses
Sevo - Dogs and cats
What are the advantages and disadvantages of sevoflurane
Higher MAC and lower blood gas solubility => diffuses into the brain quicker than iso => quicker change in anaesthetic depth
More expensive than iso
Higher MAC - use more of it
More suitable for mask induction - doesn’t taste/smell and quicker to effect
What are the main disadvantages of inhalational anaesthetic agents
Profound dose-dependant cardiovascular and respiratory depression
Cardiovascular depression leads to:
- Peripheral vasodilation
- Decrease in vascular reactivity
- Reduction in BP and cardiac output
Respiratory depression due to:
- Depressed response to CO2
- Depressed hypoxic pulmonary vasoconstriction
- Almost complete suppression of ventilatory response to hypoxia
- Bronchodilation => increased dead space
What are the negatives of nitrous oxide (N2O)
Persists in atmosphere for 100 years
Ozone-depleting
Very high MAC - can’t use on its own
Poor solubility In blood - can lead to diffusion hypoxia
What are the positives of Nitrous oxide (N2O)
MAC sparing
Can spare the cardiovascular effects of iso or sevo
Anaesthetic and analgesia due to NMDA receptor antagonism
What are the main contraindications of Nitrous oxide
N2O quickly diffuses into gas-filled spaces - any condition with a gas filled space = bad
GDV
Pneumothorax
Horses and rabbits
Endoscopy - inflate areas with air
ocular procedures where there is a risk of bubbles forming in the eye
Why are there environmental concerns regarding anaesthetic inhalation agents
Considered greenhouse gasses
Some of which, e.g. N2O, are ozone depleting
What controls are anaesthetic inhalation agents subject to and why
COSHH (control of substances hazardous to health)
They are volatile and not metabolised by the patient => potential for personnel exposure
How is exposure to inhalation anaesthetic agents measured
Dosimeter
What is TIVA and what does it stand for
TIVA = total intravenous anaesthesia
Where anaesthesia is induced and maintained by IV administration of drugs
Simply - no inhaled agents are used
Which drugs are licensed for TIVA in small animals
Propofol
Alfaxalone
(can also use repeated boluses of ketamine)
Why should you be careful if using propofol for TIVA in cats
Potential for oxidative damage and Heinz body formation if propofol is used repeatedly or over a long period of time
Which 3 drugs are in the ‘triple drip’ used for TIVA in horses
Detomidine (or Xylazine)
Ketamine
Guafenesin
What is PIVA and what does it stand for
PIVA = partial intravenous anaesthesia
Combination of IV and inhalational anaesthesia
The rationale is that using IV drugs reduces the amount of inhalation agent used
Give 2 examples of drugs which improve cardiovascular stability under anaesthesia
Ketamine
Lidocaine
