[Long-term medication with acetylsalicylic acid--a problem in regional anesthesia?]

In patients medicated with acetylsalicylic acid (ASA) and undergoing regional anaesthesia there is a risk of traumatically induced haematoma, particularly near the spinal cord. The increased bleeding tendency following aspirin administration is due to a change in thrombocyte aggregation caused by irreversible inhibition of prostaglandin synthesis. In order to assess the bleeding risk, it was investigated whether and how much subaqueous bleeding time (SBT) and aggregation inhibition (AGI) change under low-dose medication, and when these values return to normal after the end of administration. RESULTS. 1. SBT increased significantly with daily ASA medication of 100 mg or of 300 mg. However, only 4.5% of the values measured were within a pathologic range. After discontinuation of the medication SBT significantly dropped on the 2nd day, reaching the initial level on the 4th day at the latest. 2. AGI was significantly reduced, to 20% of the normal value. Depending on the dosage, the 100-mg group reached full aggregation capacity on the 4th day and the 300-mg group on the 7th day following discontinuation of medication. 3. AGI returned to normal 2-3 days later than SBT. CONCLUSIONS. 1. In the case of pathologically increased values (greater than 6 min), the determination of SBT may indicate an increased bleeding risk. 2. If SBT is within the normal range during or shortly after ASA administration, thrombocytic function is still disturbed. Whether there is a correlation between inhibition of thrombocyte aggregation and the occurrence of spinal haematomas is not yet known. 3. In view of these results, the effect of ASA should be investigated by determining SBT prior to scheduled regional anaesthetic procedures near the spinal cord. 4. If SBT is increased (greater than 6 min) and regional anaesthesia near the spinal cord is indicated, the procedure involving the slightest trauma (spinal anaesthesia) should be chosen [31]. Careful postoperative follow-up (1-2 days) should be guaranteed with regard to neurological disorders.