Chapter 15 - Anaethesia Flashcards
Why would you stop Phenelzine before surgery?
As a MAOI (other monoamine oxidase inhibitors include Isocarboxazid, Tranylcypromine, and Moclobemide, the latter a reversible type A antagonist) it has many interactions (could potentiate hypotension or hypertension) and so should be stopped 2 weeks before surgery, albeit and ideally in a tapered withdrawal of 4 weeks (can cause movement disorders, insomnia, agitation and even potentially hallucinations)
Why would you stop Yasmin before surgery?
Yasmin is a COC combining ethinylestradiol and drosperidone, other Monophasic COCs include Gedarel, Cilest, Rigevidon, Loestrin, which all vary in their progesterone element. Some biphasic include Logynon, which vary amounts per week.
Ideally COCs should be stopped 4 weeks before all major surgery/ leg surgery/ surgery resulting in prolonged immobilisation due to increases of venous thrombosis. A progesterone only contraceptive, such as Levonogestrel (Cerazette, Cerelle, Zelleta) should be started after a complete cycle (no break) in this case. COC can be restarted 2 weeks after the first menses after mobilisation.
How would you deal with a patient unable to stop COC before major surgery, ie. in emergency trauma?
Recommend a low molecular weight heparin (Enoxaparin, Dalteparin, Tinzaparin) and graduated compression hosiery in order to reduce risk of thrombosis.
Why would you stop Lithium 24 hours before major surgery? Is it different for minor?
Lithium should be stopped 24 hours before surgery due to fluid and electrolyte changes.
In minor surgery, can continue with lithium if fluid and electrolytes are monitored (contraindicated in dehydration and low salt as can change lithium plasma concentration leading to overdose - GI issues, tremor, CNS and cardiac issues).
Why give premedication to patients before surgery?
Use of benzodiazepines (Temazepam, Diazepam. Midazolam) will reduce anxiety/ sleep issues, augment anaesthesia, reduce extraneous movements from drugs like Propofol and Etomidate and potentially give amnesia.
This can be given as dose night before and smaller one just before or just the first dose on day of surgery.
The alpha adrenergic agonist Clonidine is also used when standard treatment does not give enough sedation.
In what situations would the short recovery of Midazolam increase?
May have slower recovery if used repeatedly, if used in the elderly or in patients with low cardiac output.
Increased dose and a large drug combination before surgery could cause profound sedation too.
Why might you use oral Temazepam over IV Diazepam?
Temazepam is fast acting even when oral so less invasive and diazepam can be painful upon injection due to low water solubility (therefore preferable to use emulsion).
Why might you avoid use of Ketamine in anaesthesia?
Psychotic effects can present, albeit transiently, giving rise to hallucinations, nightmares (though benzos can reduce this). Ketamine can also give a slow recovery and extraneous muscle movements.
How would you prevent NO associated hypoxia?
Mixture to have at least 30% oxygen and run the oxygen for several minutes after stopping NO.
Do not give longer than 24 hours and do not use more than once every 4 days without close supervision and haematological monitoring.
Why might you avoid intramuscular injections of Diclofenac and Ketopofen post op?
Patients with cardiac impairments, heart disease/ failure, elderly or with Crohns / UC (may exacerbate)
Why give IV infusion of Remifentanil over repeated IV Alfentanil dosing during surgery as opioid enhancement of anaesthesia?
Remifentanil has a short half life (metabolised by blood and tissue esterases not in the liver) allowing the infusion to be terminated and giving no respiratory depression affects making it far more preferable in cases where ventilation is needed, whereas Alfentanil can give rise to post op respiratory depression.
Please note; all fentanils can lead to muscle rigidity requiring antimuscarinic management.
Why might you switch to Atracuronium from the other non depolarising neuromuscular blockers?
All the others require caution, monitoring a dose changes in renal (impairment = increased duration) and liver impairment
Why should the injection of combination of local anaesthetics + vasoconstrictors take special care not to be given into a vein.
Ex. Lidocaine / Articaine / Bupivicaine and adrenaline
Vasoconstrictors stop the local anaesthetics being taken into the bloodstream therefore prolonging their effect by reducing absorption.
If injected into a vein it may cause ischaemic necrosis, especially if an appendage, and systemic exposure in hypertensive / arrhythmic patients is dangerous.
Why would you not use Neostigmine to reverse Suxamethoniun chloride?
Suxamethoniun works by acting as an acetylcholine mimics at the neuromuscular junction but with a slower hydrolysis, this increases depolarisation and gives neuromuscular blockade (leading to side effects like bradycardia, hypersalivation)
Neostigmine is an anticholinesterase so will reverse competitive (non neuromuscular) blockage of drugs like Vecuronium (coupled with glycopyrroniun to control muscarinic sides) - will inhibit breakdown of acetylcholine and increase signalling however if given with Suxamethoniun it will prolong the depolarisation even more.
Why do you need caution in Flumazenil use?
Half life is shorter than benzos do repeated dosing may be required
It may lead to anxiety conditions, N and V, agitation and tachcardia
Should avoid breastfeeding for 24 hours.
