Flashcards in Anaesthetics - Perioperative prescribing Deck (32)
What are the important things to ask in a perioperative drug history?
1) Current medications
- don't forget over the counter medicines
- non oral medicines
- oral contraceptives
- illicit substances
2) Drug allergies
- Contraception - pregnancy, risk of VTE
- Anticoagulation - risk of bleeding
- Steroids - requirement for steroids in surgery to prevent Addisonian crisis
- Ethanol - risk of alcohol withdrawel, interaction with anaesthetic
- Smoking - lung disease
What are the general rules about continuing or discontinuing medication prior to surgery?
Continue medication that can cause withdrawal symptoms postoperatively
Stop non essential medicines that can increase risk during surgery pre operatively
Use clinical judgement in other cases
When should antiplatelet drugs used for primary prevention be discontinued preoperatively?
Antiplatelet drugs (e.g. aspirin, diprydamole, clopidogrel) for primary prophylaxis should be stopped 7 days prior to surgery to reduce the risk of bleeding complications. But evidence is less clear and individual practices vary. It is important to ascertain the reason for antiplatelet medication as the risk of thromboembolic events is different for primary prophylaxis and percutaneous coronary revascularisation.
Does the contraceptive pill need to be stopped prior to surgery?
The contraceptive pill only needs to be discontinued prior to surgery if there is a high risk of thromboembolism. Always consider the potential drug interactions, particularly with broad spectrum antibiotics. Additional contraception may be required.
When should patients be NBM prior to surgery?
For elective surgery in healthy adults without gastrointestinal disease:
- restrict oral solids for 6 hours before surgery
- allow water and clear fluids until 2 hours before surgery
- allow routine medications with these clear fluids until 2 hours before the operation
If your patient has gastrointestinal disease, or will be starved postoperatively, you will need to use alternative routes of administration (e.g. parenteral preparations).
It is important to note that the absorption of oral medications in this period may be affected by diminished blood flow to the gut.
How should insulin and oral hypoglycaemic agents be altered in the day prior to surgery?
This can depend on the type of insulin used:
- dose of long acting insulin should be reduced by 20% prior to surgery. This advice is the same for those patients who administer a once daily dose in the morning or at night
- if the patient divides their long acting insulin into a BD regime then a dose adjustment is not necessary
- Metformin can be continued as normal
Under what circumstances should metformin be omitted the day before surgery?
1) Metformin should be omitted the day before surgery and for the following 48 hours if the eGFR is <60ml/min/1.73m2
2) If radiocontrast media is used or or if a VRII is used
3) Metformin should be stopped once a variable rate insulin infusion is started. It should only be started once the patient is eating and drinking normally
If a VRII needs to be started during surgery, how would a patients long acting daily insulin need to be adjusted?
This only applies if the patient is taking an once daily insulin regime. The long acting insulin (e.g. determir) should be continued at 80% of the dose (i.e. reduced by 20%). If the patient divides their long acting insulin into a twice daily regime, this should be stopped until the patient is eating and drinking normally.
Which patients require a variable rate insulin infusion during surgery?
Not all diabetic patients require a variable rate insulin infusion when they undergo surgery. Tight glycaemic control preoperatively can reduce the incidence of infection.
Patients who are more likely to need a VRII are:
- prolonged periods of starvation (i.e. more than one meal missed)
- no or unknown post op enteral absorption
- labile blood sugars
- type 1 DM undergoing major surgery
- type 1 DM who have not received their background insulin
- emergency surgery in diabetics
Can normal insulin regimes be restarted whilst the patient is on a VRII?
Twice daily regimes (i.e. bisphasic or long acting insulins given twice daily) and short acting regimes must be stopped whilst a VRII is being used. Long acting OD regimes should be continued at 80% of their normal dose whilst on a VRII.
The VRII can be withdrawn when the patient is able to eat and drink without nausea and vomiting. You should never discontinue a VRII without giving a bolus of background insulin first.
Should oral hypoglycaemic agents be given as normal on the morning of surgery?
This depends, and the following assumes that a VRII is not being prescribed:
- Gliclazide - omit the dose
- Piolgitazone - take as normal
- Sitagliptin - take as normal
- Metformin - take the day before
What are the direct oral anticoagulants?
DOACs are alternative drugs to anticoagulants such as warfarin. They are licensed for several indications including the prevention of thromboembolic events in AF and treatment of thromboembolism. They have a more predictable anticoagulant effect with minimal or no monitoring required, fewer drug interactions and a shorter plasma half life. However, concomittant use with anti-platelet therapy will increase the risk of bleeding by 60%.
What is dabigatran?
This is a direct thrombin inhibitor, with a half life of 12-24 hours. It is poorly protein bound and 80% renally excreted. It is contraindicated in patients with a creatinine clearance of less than 30ml/min.
How should dabigatran be restarted following surgery?
Reinitiation should be considered on a case by case basis depending on the bleeding risk of the procedure and the patients renal function. This is typically 48-72 hours following surgery.
Renal function should be checked at baseline. There is no other routine monitoring required. In an actively bleeding patient, haemodialysis can actively filter out dabigatran. Idarucizimab is now available as an antidote to dabigatran (specialist only).
What are the factor Xa inhibitors? How long after surgery can they be restarted?
These are also a type of DOAC/NOAC and include rivaroxiban, apixiban, and edoxaban. Edoaxban has the longest half life, rivaroxiban the shortest. They are generally strongly protein bound drugs and excreted renally.
The rules for restarting factor Xa inhibitors is the same for dabigatran. Check the patients renal function, consider operative blood loss and haemostasis. Most of them are re-started within 48-72 hours post operatively.
How long before surgery should anticoagulants be stopped?
1) Vitamin K antagonists should be stopped at least 3-4 days prior to surgery
- stop these for a minimum of 24 hours prior to surgery, or 48 hours if the patient is high risk (defined as a creatinine clearance of 15-29 ml/min or less)
- Dabigatran omission is dependent on renal function so in patients with a poor renal function, CrCl 30-49 ml/min and a high risk of bleeding, then stop this 4 days prior to elective surgery
What anticoagulation cover should be given for patients whose normal anticoagulant medications need stopping prior to surgery?
The aim of stopping anticoagulants is to reduce the risk of bleeding during surgery, but these patients are also at risk of venous thromboembolism. Low molecular weight heparin (LMWH) is used until oral anticoagulation can be reinstated post operatively AND the INR is therapeutic again (between 2-3). Occasionally unfractionated heparin is given, particularly to those patients with artificial heart valves.
Why should patients who are maintained on long term corticosteroids NOT have their medication discontinued perioperatively?
1) Underlying condition being managed with steroids may flare following withdrawal
2) The patients HPA axis will be suppressed with maintenance doses of steroids equivalent to 10mg of prednisolone or more daily
The stress of surgery may increase the need for steroid replacement. Supplementation may also be required for those patients who are no longer taking steroids but have taken them within the last 3 months.
A patients has been taking 10mg of prednisolone for PMR for the past 6 months and is attending for major elective surgery. How should there steroids be managed perioperatively?
On the morning of surgery the usual dose of prednisolone should be given.
+ 25mg i.v. hydrocortisone at induction
+ 100mg i.v. hydrocortisone in 2-3 doses for 48-72 hours
Recommence usual oral regime after 2-3 days or when gastrointestinal function has been restored.
The only difference with moderate surgery is that the 100mg i.v. hydrocortisone is given as divided doses over 24 hours.
How should a patient who has taken regular 10mg prednisolone for the past few months have their steroids managed for minor surgery?
Usual corticosteroid dose on the morning of surgery, or 25-50mg hydrocortisone (as sodium succinate) i.v. at induction.
Recommence usual oral regime after surgery.
How long before surgery should MAOIs be stopped?
14 days - due to the risk of hypo and hypertension
How long before surgery should lithium salts, ACEi and short acting sulphonylureas be discontinued before surgery?
ACEi are stopped because they have potent vasodilating properties and there is some concern about their use immediately prior to anaesthesia.
Lithium can be started 24 hours after surgery provided U&Es are normal.
Should beta blockers be discontinued perioperatively?
No, if prescribed for ischaemic heart disease. They should not be stopped abruptly because the patient will be at higher risk of perioperative cardiac events if stopped.
What drug causes a risk of ventricular arrhythmias if used with suxamethonium?
If prophylactic antimicrobials are needed, how long before knife to skin should they be administered?
What drugs are known to interact with neuromuscular blocking agents?
- effect of competitive neuromuscular blockers are reduced with long term use of phenytoin and carbamazepine
Aminoglycosides and vancomycin
- neuromuscular blockade prolonged and increased
- risk of ventricular arrhythmias with suxamethonium
- effect of neuromuscular blockade enhanced
What drugs are known to interact with anaesthetic agents?
CCBs - enhanced hypotensive effect an AV delay with verapamil
Lithium - enhanced effect of muscle relaxants
How long should patients continue to receive VTE prophylaxis after surgery?
This depends on the risk of surgery, but prophylaxis may continue for some weeks postoperatively. Just because the patient is mobile does not mean that prophylaxis is not needed.
How is VTE prophylaxis with LMWH calculated?
Dose is based on weight. Haematological monitoring dose not aid dose manipulation. Remember that renal impairment may necessitate dose adjustment. There is also a lower risk of HIT with LMWH compared to UH. Platelets should still be monitored during therapy, particularly in the first 21 days.