Inhalational Agents Flashcards
Name 2 inhalational agents
Isoflurane and Sevoflurane
Name 2 carrier gases
Oxygen and Nitrous oxide
In what patients should 100% o2 be given?
- anaemia
- pulmonary pathology
- hypoventilation
- those recovering from N2O anaesthesia
What animals tend to breath-hold and benefit from pre-oxygenation?
Rabbits
What are some benefits of nitrous oxide as a carrier gas?
Analgesic properties at concentrations over 20%
Non-irritant
Anaesthetic sparing effect - using 66% lowers the need for high levels of volatile agent
What 2 things MUST be done when using Nitrous oxide as a carrier gas? Why?
- Must be mixed with oxygen at least 33% o2
- Must give 5-10 minutes of pure o2 after N20 is switched off - N20 has low solubility in blood so when the N20 supply is stopped, the N20 in the blood diffuses back into alveoli and dilutes the alveolar air. So if the patient is breathing room air, there may not be enough o2
What happens if over 80% Nitrous oxide is used?
Will lower o2 levels below normal causing hypoxia
When is using nitrous oxide as a carrier gas contraindicated?
N20 diffuses into gas-filled spaces and accumulates and can worsen some conditions. Should be avoided in cases of pathological abdominal or thoracic distension e.g. GDV or pneumothorax
What are the advantages of using inhalational agents?
- Can rapidly alter the depth of anaesthesia
- Advantageous in a patient with kidney or liver issues as it is eliminated via the lungs
- Allows constant delivery alongside an agent
- IPPV may be performed as the anaesthetic is safer
What are the disadvantages of using inhalational agents?
- need anaesthetic machine and range of equipment (cost)
- hazard to personnel
- Knowledge of equipment required to be able to deliver safely
- Induction and recovery could be delayed due to lung pathology
What is MAC?
Minimum alveolar concentration
- a measure of anaesthetic potency i.e. the volume of anaesthetic needed to immobilise half of patients.
Those agents with the lowest MAC value have the greatest potency
What is Blood Gas Solubility?
It is a measure of how readily the volatile agent dissolves into plasma.
Agents with a high BGS take longer to work as they can build a reservoir in the plasma and are therefore less available for uptake
Agents with a low BGS are more rapidly available for uptake and therefore tend to have a faster induction and recovery time
What should an ‘ideal’ agent have in terms of BGS and MAC?
Ideally, should have a low MAC value and a low BGS
What do all inhalational agents cause?
Some degree of respiratory and cardiovascular depression which is dose dependant
What do inhalational agents NOT cause?
Analgesia
