The monitoring of heparin induced thrombocytopenia following surgery: an audit and international survey.
Low-molecular-weight heparin (LMWH) is widely used in the prevention of thromboembolism in orthopaedic patients, particularly those undergoing lower limb joint arthroplasty (Leyvraz et al 1991, Mohr et al 1993, Wolf 1994). Several types of LMWH are commonly used including enoxaparin (Clexane[R], Rhone-Poulenc Rorer), dalteparin (Fragmin[R], Pharmacia) and tinzaparin (Innohep[R], LEO), with bleeding and thrombocytopenia having been known complications (BNF 2008). Bleeding may occur at various locations: operative site, epidural, intrahepatic, and retroperitoneal sites, gastrointestinal tract (Antonelli et al 2000, Houde & Steinberg 1999, Shaieb et al 1999, Stern et al 2000). Intracerebral haemorrhage following the use of LMWH has occurred following neurosurgical and orthopaedic procedures, with serious consequences (Dickinson et al 1998, Lilikakis et al 2006).
Heparin-induced thrombocytopenia (HIT) is associated with thrombosis, independent of heparin type, dose or route of administration (Boshkov et al 1993, Chong 1995, King et al 1984). It results from an antibody-mediated response to heparin triggering a reduction in the platelet count (Burgess et al 1995, Gerhard-Herman 2001, Warkentin 1999). The British Society for Haematology (BSH) has produced evidence based guidelines for the identification and management of heparin-induced thrombocytopenia (Baglin et al 2006). In summary the guidelines advocate:
1. All patients require a platelet count on day of starting treatment.
2. Repeat platelet counts should be repeated every 2-4 days from days 4-14.
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This study audits the implementation and awareness of these guidelines within an orthopaedic unit and compares current practice both in the UK and internationally.
An audit loop consisting of two sequential surveys detailing the monitoring of at-risk patients was performed before and after the introduction of an evidence based protocol for the monitoring of heparin induced thrombocytopenia--see figure 1. Enoxaparin (Clexane[R], Rhone-Poulenc Rorer) was the only LMWH prescribed for patients in this study. Hospital and departmental approval was obtained prior to commencing this audit. Patients who were medically unwell or commenced on warfarin were excluded since their inclusion would not accurately reflect routine HIT monitoring.
Figure 2: Protocol implemented following initial survey Guidelines on management of heparin-induced thrombocytopenia 1. All patients who receive heparin (of any sort) should have a platelet count on day of starting treatment 2. All surgical patients receiving LMWH, platelet counts should be performed every 2-4 days from days 4--14 3. If platelet count falls by over 50% or below normal lab limits consider HIT, stop heparin and inform haematologist
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The initial 48 patients who received LMWH for longer than 4 days included 35 operative fixations of proximal femoral fractures, one open reduction and internal fixation of a distal femoral fracture, and 12 lower limb joint arthroplasties. The mean average age was 78 years (range 64-93 years), with 29 female and 16 male. The results of the initial survey were compared with the evidence based British Society for Haematology guidelines (Baglin et al 2006) and discussed at a departmental meeting. A protocol recommending a platelet count every 2-4 days in at-risk patients was implemented (see figure 2). A subsequent survey of 53 patients was conducted, with a mean age of 76 years (range 52--89 years), with 20 male and 28 female.
A telephone survey questioning awareness of heparin induced thrombocytopenia and the recent BSH guidelines was conducted. Statistical analysis of the results was carried out using a chi-square test with SPSS v12.0 for Windows.
The initial patient survey demonstrated that only 2 out of 48 at-risk patients (4%) had a full blood count (FBC) performed more than four days after commencing LMWH--see figure 3.
The second survey demonstrated a significant improvement (p<0.05), with 23 out of 40 (57.5%) at-risk patients having a FBC performed more than four days after commencing LMWH--see figure 4.
The secondary survey demonstrated a significant improvement (p<0.05) in the monitoring of HIT compared with the primary survey (57.5% compared to 4%)see figure 5.
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From the secondary survey, 23 out of 40 patients had platelet count monitoring as outlined by the BSH guidelines. The quantitative change in the platelet count seen in these patients is shown in Figure 6. The postoperative platelet count dropped below 75% of the preoperative level in 13 out of the 23. Two patients demonstrated a reduction of over 50% in the platelet count that responded with the subsequent cessation of LMWH.
A telephone survey of registrars/interns from 46 orthopaedic units (34 district general/community hospitals, 12 teaching hospitals) in 5 countries (England, France, Scotland, Canada and USA) was conducted. There was a low awareness of both the condition of heparin-induced thrombocytopenia and the BSH guidelines and no units routinely monitored for HIT (see Table 1).
Low molecular weight heparins have been used to reduce thromboembolic risk in both primary care and the hospital setting for at least twenty years (Clagett et al 1995, Imberti et al 2006, Mohr et al 1993, Wolf 1994). Whilst providing an effective pharmacological thromboprophylaxsis, their use in orthopaedic surgery is not without risk (Bickler et al 2006, Lilikakis et al 2006, Stern et al 2000).
This clinical audit demonstrates a significant improvement in platelet count monitoring for patients at risk of heparin-induced thrombocytopenia by the implementation of a simple protocol and an additional full blood count (approximately 1 [pounds sterling] per test). However, with nearly 50% of at-risk patients still not being monitored, improvements are still needed. The international survey highlights an ongoing lack of awareness regarding heparin-induced thrombocytopenia and the necessary monitoring of platelet counts.
All prescribers of prescription only medications should be aware not only of the common side effects but also of the rare adverse reactions that may have serious consequences. Following the publication of case reports showing intracranial haemorrhages as a consequence of heparin-induced thrombocytopenia (Lilikakis et al 2006) and evidence based guidelines (Baglin et al 2006), failure to routinely monitor for thrombocytopenia in patients receiving LMWHs may have medico-legal implications.
The conclusions of this study are:
1. Heparin-induced thrombocytopenia is a rare but potentially fatal complication of low molecular weight heparin.
2. Few orthopaedic units are currently aware of the risk of heparin-induced thrombocytopenia when prescribing LMWH.
3. The introduction of a simple monitoring protocol can facilitate its early identification and treatment.
KEYWORDS Heparin induced thrombocytopenia (HIT) / Monitoring / Survey
Provenance and Peer review: Unsolicited contribution; Peer reviewed; Accepted for publication September 2009.
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Mr Benedict A Rogers MA, MSc, MRCGP, FRCS(Orth)
Specialist Registrar, Trauma and Orthopaedics, East Surrey Hospital, Redhill, Surrey
Mr Andrew Stuart Cowie MBBS BSc(Hons) MRCS(Eng)
Specialist Registrar, General Surgical Rotation, Wessex Deanery, Poole Hospital NHS Foundation Trust
No competing interests declared
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Table 1: Survey assessing the awareness of the BSH guidelines for heparin-induced thrombocytopenia Aware Aware of Monitor platelet of HIT BSH HIT count for patients guidelines on LMWH District general/ 5/34 1/34 0/34 community hospital Teaching hospital 6/12 1/12 0/12
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|Title Annotation:||RESEARCH & AUDIT|
|Author:||Rogers, Benedict A.; Cowie, Andrew S.|
|Publication:||Journal of Perioperative Practice|
|Date:||Feb 1, 2010|
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