[This monograph covers aspirin as a single antiplatelet or aspirin in combination with dipyridamole.
For patients taking Aspirin and Clopidogrel / Prasugrel / Ticagrelor – see Dual Antiplatelet Therapy (DAPT) monograph
For patients taking aspirin for analgesia – see Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) including Cyclo-oxygenase-2 (COX-2) Selective Inhibitors (Oral) monograph]
Issues for Surgery
For prevention of cardiovascular events – risk of major adverse cardiovascular events (MACE) if omitted.
Risk of bleeding and/or complications of bleeding if continued.
Advice in the Perioperative period
Low dose (≤150mg): Continue
In these circumstances consideration should be given to stopping 7 days pre-operatively.
If patient has received doses of aspirin in past 7 days be aware of potential for increased surgical bleeding.
Patient Undergoing Surgery Associated with Unacceptably High Risk of Bleeding
Neuraxial (Spinal/Epidural) Anaesthesia or Lumbar Puncture
If stopped pre-operatively, restart as soon as possible post-operatively once haemostasis secure.
Interaction(s) with Common Anaesthetic Agents
Interaction(s) with other Common Medicines used in the Perioperative Period
Non-Steroidal Anti-inflammatory Drugs (NSAIDs)
NSAIDs may have an additive effect on the risk of bleeding (including gastrointestinal bleeding) when given with aspirin5; consider gastroprotection if other risk factors for gastrointestinal bleeding are present6.
Concomitant administration of standard NSAIDs, which are non-selective reversible cyclooxygenase (COX)-1 inhibitors (e.g. naproxen, ibuprofen), may lead to impaired efficacy of aspirin through competition for binding sites7. The Commission on Human Medicines advises there may be a small increased risk of thrombotic events with non-selective NSAIDs, particularly when used at high doses and for long-term treatment6.
Low Molecular Weight Heparin (LMWH) / Unfractionated Heparin (UFH)
LMWHs and UFH are predicted to increase the risk of bleeding events when given with aspirin; manufacturer advises use with caution5.
Mode of Action
Aspirin exerts its antiplatelet effect by inhibiting cyclo-oxygenase (COX) thus preventing prostaglandin-mediated production of thromboxane A2, which is responsible for platelet activation and aggregation. The irreversible inhibition of cyclo-oxygenase means the pharmacological effects persist until platelets are regenerated. After discontinuation of aspirin intake platelet function can be expected to increase by 10-15% a day as a result of new platelet formation2. Within 3-4 days more than 30% of irreversibly inhibited platelets will be replaced; in patients with a normal platelet count this is usually sufficient to return haemostasis to normal4.
Risk of Major Adverse Cardiovascular Events (MACE)
Non-adherence or withdrawal of aspirin in non-surgical patients is associated with a three-fold increase in MACE; this rises to an 89-fold increased incidence in patients with coronary artery stents8. This increased incidence is thought to be due to rebound increases in thromboxane A2 activity leading to increased platelet aggregation2. Patients with diabetes, acute coronary syndrome or undergoing cardiac surgery are associated with high platelet reactivity2. The time between aspirin withdrawal and adverse event was found to be 8.5 days for acute coronary syndrome and 14.3 days for cerebrovascular events9. It is possible that the risk of discontinuation is further increased in the perioperative period as surgery promotes an inflammatory state that increases platelet reactivity10.
Risk of Bleeding
Pre-operative aspirin continuation increases the baseline rate of bleeding by fifty percent in a large meta-analysis of pooled data from several underpowered studies9. However, whilst the prevalence of bleeding was higher in patients who continued aspirin the severity of bleeding and bleeding associated mortality was not increased, apart from in a study of patients undergoing transurethral resection of the prostate (TURP)9. With recent changes in surgical technique, and the use of isotonic saline rather than glycine irrigation, bleeding complications from TURP may now be lower than in 2005 when this meta-analysis was conducted.