Inhalational Agents Flashcards
List the volatile AA.
Halothane Isoflurane Desflurane Enflurane Sevoflurane
How is N20 (nitrous oxide) controlled and administered?
Flow meter
How are the volatile agents controlled and administered?
Vapourisers
What are the safety features of the vapourisers?
Colour coded
Specific colour coded keyed fillers with individual shapes (like puzzled pieces)
Which volatile gas has a different vapouriser design to the others, and why?
Enflurane
Boiling point near room temperature
Features of the ideal inhalational AA?
Cheap Stable No metabolism (fewer toxic effects) Potent No LT effects Non irritant odour No respiratory or cardiovascular depression Hypnotic and analgesic Readily reversible, neuroprotective and non-excitatory
Which inhalational agents are suitable for a gas induction?
Halothane
Sevoflurane
In which patients are gas inductions mostly used?
Children
Patients with compromised airways where patient continues to breathe spontaenously
Factors affecting fiAA?
Volume of the breathing circuit
Fresh gas flow rate
Absorption of inhalational agent by breathing circuit
Factors affecting alveolar concentration of AA (fA-AA)?
Inspired concentration Uptake of the agent from the alveoli into the blood Alveolar ventilation (RR)
The inhalational AA uptake depends on…
Solubility of the agent in blood (blood to gas partition coefficient - BGPC)
Cardiac output
Alveolar to mixed venous partial pressure difference
Factors affecting arterial concentration of AA (faAA)?
Shunting of blood
e.g. intrapulmonary (atelectasis, bronchial intubation) or intracardiac (ASD, VSD)
Poorly soluble inhalational AA?
Desflurane
Sevoflurane
N20
Highly soluble inhalational AA?
Halothane
How do you assess the potency of an inhalational AA?
Looking at MAC (minimum alveolar concentration)
Definition of MAC?
The steady-state minimum alveolar concentration (at sea level) that prevents movement to a standard surgical stimulus in 50% of non-premedicated adults.
MAC50
Which is the most potent inhalational AA, and why?
Halothane
Highest fat solubility (brain is a fatty tissue)
MACbar?
MAC-blocks autonomic response
Higher than MAC-50
Factors that increase MAC (patient requires higher alveolar concentration to have ideal effect)?
Infancy Hyperthermia Hyperthyroidism Catechloamines and sympathomimetics Chronic opioid use Chronic alcohol intake Acute amphetamine intake Hypernatraemia
Factors that decrease MAC (patient requires lower alveolar concentration to have ideal effect)?
Neonates Elderly Pregnancy Hypotension Hypothermia Hypothyroidism Alpha-2 agonists Sedatives Acute opioid use Acute alcohol intake Chronic amphetamine intake Lithium
Factors that DO NOT affect MAC?
Gender
Duration of anesthesia
Time of day
Hypocarbia
Inhalational AA vapouriser colours?
N20 - Blue (cylinder and pipeline) Isoflurane - Purple Sevoflurane - Yellow Halothane - Red Desflurane - Sky blue Enflurane - Orange
MAC of inhalational AA?
N20 - 105% Isoflurane - 1,2% Sevoflurane - 2% Halothane - 0,75% Desflurane - 6% Enflurane - 1,7%
N20 is also known as…
Laughing Gas
Uses of N20 in anaesthesia?
Potent analgesic (but poor anaesthetic)
Used as carrier gas to deliver volatile agents
Used in reducing concentrations of volatile agents needed
Speeds up inhalational induction with another volatile agent ("second gas effect")What is Etonox?
Mixture of 50% N20 and 50% O2
Used for analgesia in lanour and minor ER procedures
Toxic effects of N20?
PONV
Bone marrow depression is given for long periods
Addictive
3rd most abundant greenhouse gas
Organ effects of Halothane?
Potent
Increases cerebral blood flow and ICP quite markedly compared to other agents
Slow recovery with hangover effect
Hypotension
Dysrythmias
Increased RR, decreases TV
Some muscle relaxation, including uterine
Mild elevation in liver enzymes post-op (Halothane hepatitis is a rare complication)
Describe Halothane hepatitis?
Rare (1:35000)
Allergic phenomenon
Fulminant hepatic necrosis
50-75% mortality
Organ effects of Isoflurane?
Less potent than Halothane
Least CNS effects (agent of choice in neuro-anesthesia)
Rapid recovery compared to Halothane
Good peripheral vasodilator - hypotension
Irritant to airways (not suitable for induction)
Isolated reports of liver enzyme elevation
Reduces total hepatic blood flow, while preserving hepatic arterial blood flow (best agent for patients with liver disease)
Relaxant
Organ effects of Sevoflurane?
Relatively weak agent Low solubility - fast induction Mildly decreases SVR May prolong QT interval Does NOT induce arrythmias Agent of choice for cardiac patients Non-irritant (can be used for induction) Used with caution in renal failure patients
Characteristics of Desflurane?
Newest volatile agent
Expensive
Very small toxic potential
Rapid acting, but highly irritant and unpleasant (not suited for induction)
Most insoluble agent with the most rapid recovery
Rapid increases can lead to transient marked elevated HR, BP and catechloamine levels
Characteristics of Enflurane?
Expensive
Practically obsolete
Unacceptable side effects
High concentrations may provide epileptiform EEG activity (avoid in epileptics)
Contraindicated in neurosurgery and renal problems
