Inhalational Anaesthetics Flashcards
What are the 3 carrier gases?
Oxygen
Nitrous oxide
Carbon dioxide
What are the characteristics of oxygen?
-odourless
-allows combustion
-explosive if near sparks or naked flame
What are the uses of 100% 02?
-pulmonary pathology
-hypoventilation
-animals recovering from N20 anaesthesia
-supplied during recovery period if needed
-may be used pre-operatively
Delivery of oxygen in special patients?
-delivery of oxygen before anaesthetic period is desirable in debilitated patients, brachycephalics and small furries
-oxygen may be continued in recovery for some patients
What are the characteristics of nitrous oxide?
-delivered from compressed air tanks
-odourless
-combined with oxygen as a carrier gas
-analgesic properties
-non irritant
-used in conjunction with other anaesthetics
-second gas effect
Nitrous oxide has an anaesthetic sparing effect, what does this mean?
-uses 66%
-this lowers the need for high volatile agent levels
Nitrous oxide has a second gas effect, what does this mean?
-it enhances the uptake of volatile therefore allowing faster induction of anaesthesia
What care must be taken when using nitrous oxide?
-cannot use more than 80% as this will lower oxygen below normal levels
-it might compromise some patients as it diffuses into gas-filled spaces and accumulates
-must be avoided in cases with pathological abdominal or thoracic distension
Describe what does diffusion hypoxia means?
-due to the fact that nitrous oxide has low solubility in blood, at the end of anaesthesia when administration of N20 ceases the N20 present in blood diffuses back into the alveoli and “dilutes” the alveolar air so less 02 is available
-if the animal is breathing room air hypoxia may occur as a result of this
-this effect is mitigated by ensuring that patients receiving N20 have 10 mins of pure oxygen after cessation of nitrous administration
What are the characteristics of carbon dioxide?
-not routinely used
-may be used occasionally to maintain normal levels of C02
-best used with blood gas analysis
What are the 4 inhaled anaesthetics?
Halothane
Isoflurane
Sevoflurane
Desflurane
What are advantages of using inhaled anaesthetics?
-depth of anaesthesia readily altered
-concentration of anaesthetic in blood or brain may be altered rapidly by changing vaporiser setting
-elimination of inhaled agents occurs mainly via lungs so benefits liver/kidney patients
-allows constant delivery of oxygen alongside agent
-most patients intubated so IPPV may be performed
What are disadvantages of using inhaled anaesthetics?
-need for anaesthetic machine and range of equipment (cost)
-hazards, personal health risk and explosion risk
-knowledge required of circuits and machine
-induction and recovery possibly delayed due to lung pathology
What are volatile anaesthetic agents, how are the delivered?
-inhaled anaesthetics
-delivered by carrier gases
How is the level of agent determined in inhaled anaesthetics, side effects?
-determined by dial up on vaporiser
-all cause some degree of respiratory and cardiovascular depression which is dose dependent
Do inhaled anaesthetics provide analgesia?
No
What are the characteristics of isoflurane?
-liquid
-without additives or preservatives
What are the advantages of using isoflurane?
-greater margin of safety than halothane
-relatively fast induction and recovery
-good muscle relaxation
What are the disadvantages of using isoflurane?
-hypotension can occur due to CVS depression
-does not sensitise the heart to arrhythmias
-potential respiratory depressant
-poorly tolerated for mask induction, as has pungent smell and irritates airways
What are the advantages of using sevoflurane?
-rapid induction and rapid recovery when compared to isoflurane as has a lower blood;gas solubility
-pleasant non irritant odour
-well tolerated for mask induction
What are the disadvantages of using sevoflurane?
-hypotension (dose dependant)
-respiratory depression (dose dependant)
