In the UK national guidance has been published by the National Institute for Health and Clinical Excellence (NICE), first in 2007 (for surgical inpatients) and more recently in 2010 (for all hospitalised patients).^6,11 It provides ‘high level’ guidance for all hospital specialties about assessing patients for any risk of VTE and bleeding, and about who should receive pharmacological or mechanical prophylaxis. However, it leaves more detailed decisions about types and doses of anticoagulants and about types of mechanical prophylaxis to the discretion of individual hospitals and units.

An important issue for consideration when producing local policies for VTE prophylaxis is risk stratification, in other words whether some patients at risk for VTE are at greater risk than others and therefore should receive different doses of anticoagulant drugs or different mechanical methods – typically intermittent pneumatic compression (IPC) rather than graduated compression stockings (GCS).

Auditing the adequacy of VTE prophylaxis has become an important quality-assurance measure. However, the existence of a variety of different guidelines (including a NICE guideline that rightly accommodates flexibility in practice) can make both auditing and interpreting the results of audit problematic. The different sources of guidance make somewhat different recommendations about which patients should receive what prophylaxis. They also stratify the risks of patients in different ways (or not at all). This study examined the effect of using criteria from different guidelines to evaluate practice.

Audit 1 was performed in November 2008. It included all adult general surgical elective and emergency inpatient admissions to the Royal Devon and Exeter NHS Foundation Trust during a single week. Patients were under the care of two upper gastrointestinal, three lower gastrointestinal, three vascular, two breast and four urological consultant surgeons.

The audit was carried out by LH and DR using the medical and nursing notes and prescription charts, each evening while patients were still in hospital. Data collection was done according to a proforma (Fig 1) that specified aspects of VTE risk, what prophylaxis each patient was prescribed and whether this concurred with three guidance documents current at that time: NICE clinical guideline (CG) 46,⁶ the European consensus (EC) guidelines⁷ and the Department of Health (DH) risk stratification tool.⁸ No local guideline was used; the audit was done in part to guide agreement about a cohesive departmental policy.

The results of Audit 1 were presented at a departmental meeting and to new trainees, and the intention to carry out a second audit was announced. In addition, a cohesive unit policy was agreed and used as one of the standards in Audit 2.

Audit 2 was performed a year after Audit 1, during November 2009. The methods were the same except that the new local policy (Fig 2) was used instead of the EC guidelines⁷ (it included similar risk stratification) and a slightly amended proforma was used (Fig 1).

Table 1 shows the classification of patients for their levels of VTE risk according to each of the guidelines and the numbers for whom prophylaxis was prescribed correctly or incorrectly (note that the DH tool is only a risk assessment instrument and does not stipulate what prophylaxis patients should receive). Table 2 shows a breakdown of the VTE prophylaxis prescribed; compliance with each guidance was estimated from the number of patients expected to be on each modality of prophylaxis divided by the observed numbers. Tables 1 and ​and22 illustrate that compliance in giving particular types of prophylaxis was higher for high-risk patients but generally less concordant with guidance for those requiring less or no prophylaxis.

Table 3 shows numbers of patients stratified into different level of risk according to different guidelines. There were significant differences in the percentages of patients classified as ‘high risk’ by the DH tool and EC guideline in Audit 1 (72% and 40% respectively, p<0.001), and between the DH tool and local guideline in Audit 2 (74% and 33% respectively, p<0.001). However, when high and moderate-risk groups were combined, then the percentages of patients in these combined groups were only dissimilar in Audit 2 (82% for the DH tool compared to 98% for local guidance). There was a significant difference for combined high + moderate risk between the NICE CG46 and our local guideline in Audit 2 (80% and 98% of patients classified as being ‘at risk’ respectively, p<0.001).

Our compliance rates in both audits were significantly higher for the NICE CG46 ‘at risk’ criteria (81% and 90%) than for the EC or local guidelines. In other words, we performed quite well in giving prophylaxis to ‘at risk’ patients but less well when judged for our use of the correct prophylaxis for specified levels of increased risk. The percentages of patients who fell into low, moderate and high risk groups differed between the different sources of guidance. Our local discussions have highlighted the fact that patients at lower risk may pose more difficult decisions in policy making than those at high risk.¹² This is in part because it may be difficult to be sure which of these patients really are at risk (for example, many fit patients become mobile very rapidly after a hernia repair or scrotal surgery but some do not and this is unpredictable).

In addition, the evidence of benefit from prophylaxis for lower-risk patients is more controversial.^13,14 Our local policy, developed after Audit 1, took a particularly risk-averse approach, such that only two patients (2%) were ‘low risk’. This approach was driven by the strong patient safety agenda (both in the UK and internationally) and by other pressures that led the surgeons to agree on a low threshold for using mechanical and/or pharmacological methods of prophylaxis unless there was a good reason not to do so.

In contrast to the low-risk patients, those at particularly high risk are, by and large, easily recognised. Our highest risk patients (those who ought to have been receiving high dose low-molecular-weight heparin (LMWH), most in combination with mechanical prophylaxis) had these prescribed correctly in around 90% of cases, unlike those who required only one modality and/or lower doses of heparin. Especially when patients are at very high risk, the responsible surgeon is likely to make personal judgements about prophylaxis. This is generally accepted as best practice and is implicit in the NICE CG92, which gives recommendations for broad types of prophylaxis rather than any amount of detail about precisely what type of prophylaxis to use in patients at different levels of risk.^11,13

This contrasts with the other sources of guidance used in our audits and with the internationally influential guidelines from the American College of Chest Physicians.^9,10 We had originally considered using the latter in Audit 1 but decided to confine the guidelines used to three in number, relevant to the UK and Europe.