title: Maternal anti-factor Xa activity following subcutaneous unfractionated heparin after Caesarean section.
abstract: Unfractionated heparin is widely used for prophylaxis against venous thromboembolism after Caesarean section. We performed a survey of thromboprophylactic methods after elective Caesarean section in 50 maternity units in the United Kingdom. We found that a variety of regimens were used. Thirteen (26%) used subcutaneous unfractionated heparin at standard (non-pregnant) doses. We then studied anti-Xa activity in women following elective Caesarean section under regional anaesthesia. Initially, eight women were given 5000 U unfractionated heparin subcutaneously after surgery and anti-Xa activity was measured 1, 2, 3, 4, 5, 6, 8 and 10 h after administration. There was no detectable anti-Xa activity in any of the samples so the dose was increased to 7500 U in a further five women and a single anti-Xa assay performed at 3 h when peak activity should occur. Again, no activity was detected so the dose was increased to 10 000 U heparin in a final group of 10 women and anti-Xa activity measured at 0.5, 1, 1.5, 2, 3, 4, 5 and 6 h. Although there was some activity after 10 000 U heparin, the level was below that accepted for prophylaxis. If anti-Xa activity is an appropriate monitor of prophylactic unfractionated heparin, doses up to 10 000 U are inadequate. Since there is evidence that enoxaparin is effective at producing adequate prophylactic anti-Xa activity following Caesarean section, we suggest abandoning the use of unfractionated heparin in favour of enoxaparin for this purpose.
authors.affiliation: Magill Department of Anaesthesia, Intensive Care & Pain Management, London SW10 9NH, UK.
authors.forename: C A
authors.initials: CA
authors.lastname: Stirrup
authors.forename: D N
authors.initials: DN
authors.lastname: Lucas
authors.forename: M L
authors.initials: ML
authors.lastname: Cox
authors.forename: M
authors.initials: M
authors.lastname: Rucklidge
authors.forename: M R
authors.initials: MR
authors.lastname: Nel
authors.forename: L J
authors.initials: LJ
authors.lastname: Acton
authors.forename: C
authors.initials: C
authors.lastname: Costello
authors.forename: S M
authors.initials: SM
authors.lastname: Yentis
mesh_terms: D000328:Adult; D000765:Anesthesia, Conduction; D000773:Anesthesia, Obstetrical; D000925:Anticoagulants / Q000627:therapeutic use*; D002585:Cesarean Section; D004305:Dose-Response Relationship, Drug; D065427:Factor Xa Inhibitors; D005260:Female; D006493:Heparin / Q000627:therapeutic use*; D006801:Humans; D011182:Postoperative Care / Q000379:methods; D011183:Postoperative Complications / Q000097:blood / Q000517:prevention & control; D011247:Pregnancy; D011644:Puerperal Disorders / Q000517:prevention & control; D013923:Thromboembolism / Q000097:blood / Q000517:prevention & control*
chemical_list: D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006493:Heparin