Term
| When is IM anaes. induction preferred? |
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Definition
| for difficult to handle animals |
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Term
| why is IM anaes. induction inherently unsafe? |
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Definition
| no way to remove the agent once administered |
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Term
| Examples of ket-combos used for IM induction |
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Definition
-dexmedetomidine + ketamine
-xyaline + ketamine
-midazolam + ketamine
-ACP + ketamine
-alphaxalone can be used but need large vol. and some muscle twitching /rigidity observed |
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Term
| Why is ketamine not used alone to induce anaesthesia? |
|
Definition
-poor muscle relaxation
-often exciteable "stormy" recovery |
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Term
|
Definition
-absorption claimed to be best from quadriceps muscle but often more painful
-epaxial muscles common (lumbar or cervical)
NB: ketamine combinations sting so good restraint is important |
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Term
|
Definition
-can ge given 'off the needle' or via pre-placed catheter
-'over-the-needle' catheters are usually used for peripheral vessel canulation
-cephalic most common in D+Cm, lateral saphenous and jugular also poss. |
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Term
| Thiopental IV induction admin |
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Definition
- have a calculated dose ready(depending on premed. etc)
-give a portion of this rapidly - usually 1/3 - 2/3, depending on sedation
-then the remainder given to effect, until suitable conditions for intubation
-very slow delivery tends to result in an excitement phase and then a larger dose of drug being required |
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Term
| Propofol IV induction admin |
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Definition
-given slowly and gradually - so only required amount given (may be more or less than calculated) and side effects decr.
-rapid admin is likely to lead to post-induction apnoea and more marked CV effects i.e. hypotension |
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Term
| Problems associated w. attempted IV injection |
|
Definition
-incorrect agent used
-contaminated or deteriorated agent used
-perivasc. injection
-intra-arterial inj. |
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Term
|
Definition
-often painful - suspect if there is marked reaction to the injection
-thiopental may cause severe sloughing and pain |
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Term
| Treatment of perivascular inj. |
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Definition
-if poss, leave catheter / needle in place and flush w. saline
-if thiopentane, some people use small amount of local anaesthetic e.g. lidocaine - decr. the pain and neutralises the pH of the alkaine drug
-use a different site for induction of anaesthesia |
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Term
| Consequences of intra-arterial injection |
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Definition
-may cause spasm of artery (cold, pale extremity) and pain (if conscious)
-in horses, the carotid a. is most commonly injected
- if an alpha-2-agonist injected into carotid then get wild excitement, animal may fall over but may survive
-inj of an induction agent such as thiopental into carotid will often result in death before tx is poss |
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Term
| Treatment of intra-arterial injection |
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Definition
| dilute the drug w. saline, heparin and poss. agents to dilate the b.v. |
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Term
| Decr. risk of intra-arterial injection |
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Definition
-venous cannulation is recommended
-ensure blood flow is non-pulsatile and flow rate venous not arterial
-sedate the animal if necessary - intra-art. inj more likely if animal is struggling |
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Term
| Why is IV maintenance of anaesthesia more common than IM? |
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Definition
-IM access if often difficult in surgery
-IM doses may be difficult to calculate - have to predict because slower onset and so give before necessary |
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Term
| Why is cannulation of a vein preferable to injection is IV anaes maintenance? |
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Definition
-avoid damage to the vv. with repeated inj.
-also more rapid reaction in event of anaes. lightening
-decr. risk of intra-arterial or peri-vascular injection |
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Term
| If using IV injections to maintain anaesthesia, why must the top-ups often be given further apart as time progresses? |
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Definition
in many drugs the duration of action inc. w. longer admin. so each top up lasts longer
-plus accumulation of drug |
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Term
| Context sensitive half life |
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Definition
| if a drug has been infused or administered over time, the half life increases i.e. does not stay constant |
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Term
| Describe the context sensitive half time of fentanyl |
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Definition
-half time incr. slowly until 2 hours then massive incr.
-therefore need to change the rate of admin once over 2 hours |
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Term
| Describe the context sensitive half time of thiopental |
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Definition
| massive incr. in half time in first 30 mins - hence not used repeatedly / as only anaes. agent |
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Term
| Describe the context sensitive half time of propofol |
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Definition
| half time increases slightly at beginning then plateus and remains contstant despite amount of drug infused |
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Term
|
Definition
Total Intravenous Anaesthesia
-involves maintaining anaesthesia using continuous infusion of anaesthetic agents rather than boluses (which will result in gr. fluctuations in plasma drug conc) or inhalation anaesthetics
-generally use a bolus to induce then follow w. infusion at a set rate
-usually involves guaiphenesin combinations, oft. w. ketamin and alpha-2-agonist |
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Term
| Advantages of TIVA in horses |
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Definition
-does not require expensive equipment (although O2 supplementation is beneficial)
-maintains BP
-causes little resp. depression |
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Term
| Disadvantages of TIVA in horses |
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Definition
-difficult to gauge depth of anaesthesia
-may caused prolonged, ataxin recovery is excessive guaiphenesin (GGE) |
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