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Incident Rate of Postoperative DVT/PE

Basic Facts

Stage of development


Potential or current usage

Postoperative DVT/PE is associated with a range of complications following surgery, including higher mortality among those with postoperative DVTPE compared to surgical patients with similar patient characteristics. This measure is suitable as a marker of healthcare quality and safety, particularly to assess the impact of interventions to reduce postoperative harm.

Brief overview of the measure

General description

This measure was selected to provide baseline information about the national incidence rate of postoperative DVT/PE, enabling the calculation of changes over time in this number.

Rationale for selection

Postoperative DVT/PE has been shown to result in, among other things, increased mortality rates and increased hospital stay among surgical patients. A range of factors determine the risk of postoperative DVT/PE including patient characteristics, including any predisposing factors, as well as the type of surgery being performed. Prophylaxis for postoperative DVT/PE should be routinely performed for most types of surgery, with mechanical and pharmacological prophylactic methods shown to be safe and effective.

Type of measure


Domain(s) of quality


Application and interpretation of the measure

Stated intent of the measure

To measure national, regional and possibly local incidence rates of postoperative DVT/PE in order to measure the impact of the nation-wide implementation of the surgical safety checklist in DHBs.

Caveats - Considerations

The main caveat of this measure is the sparseness of numerator data, or in other words, the number of events with postoperative DVT/PE. There are too few events to present meaningful postoperative DVT/PE data at the local level using standard approaches. However, the use of statistical process control charts, with a Poisson distribution (useful for examining count data), is being explored for presenting local-level data.

Links to other measures

This measure is part of a set of postoperative harm outcome measures looking at the incidence, excess in-hospital deaths and excess LOS for postoperative sepsis and postoperative DVT/PE.

Level of health care delivery/setting

This measure is focused on postoperative harm following an operating room or anesthetic procedure.

Target population

This measure focuses on the total population.

Stratification by vulnerable populations

There can be wide variation in hospital stay outcomes by admission type, the type of healthcare received, and by patient factors such as co-morbidities. However, the purpose of this analysis was on estimating a national incidence rate to establish a baseline for postoperative sepsis. Therefore only a crude incidence rate was calculated for baseline purposes.

Calculation of the measure

Output of calculation

The output of the calculation is a national incidence rate, with 95% confidence intervals, of postoperative DVT/PE. Incidence rate Calculated using the formula ir = (n/d) x 1000 where ir is the incidence rate, n is the numerator, d is the denominator and 1000 is the number of hospital admissions.

Numerator description

The numerator group, derived from the denominator group, was any hospital events with any secondary diagnosis of DVT/PE. The ICD-10 codes used to define DVT/PE were I260, I269, I801, I802, I803, I809, I828, I829, and O882. An event was included in this numerator group if any of these codes were identified in the 2nd to 25th diagnostic fields.

Numerator exclusions

See denominator description

Denominator description

The denominator group was any hospital event for those aged 18 years and above and where: • those events that had a primary operating room or anesthetic procedure* recorded were included; • those with a primary diagnosis of DVT/PE were excluded; • those with a primary procedure code for interruption of vena cava (3480000, 3533000, and 3533001) were excluded; and • those with a major diagnostic category 14 (pregnancy, childbirth and puerperium) were excluded. * It was identified that not all procedures were recorded in the dataset were ‘surgical’ procedures. A Look-Up Table was created to define which procedures were operating room or anesthetic procedures. The list of operating room procedures using ICD-10 coding was extracted from the Victorian government’s document “Patient Safety Translated Technical Specifications”.

Denominator exclusions

See denominator description

Time period

12 months

Criteria/standard for optimal performance

There is large variation internationally in the ICD codes used to define patients with DVT/PE, including those with postoperative DVT/PE. The codes given above are extracted from the Victoria government’s technical specifications for patient safety. These codes are also being used by researchers at the Christchurch School of Medicine to estimate trends in postoperative harm in New Zealand, 2001-2009.

Data source

National minimum dataset (NMDS) 2010/11, available from the Ministry of Health.

Method of extraction

Method of extraction NMDS data were imported into Microsoft Access 2010. Queries were developed separately for extracting denominator data and numerator data. Calculations of incidence rates and 95% confidence intervals were undertaken in Microsoft Excel 2010.

Appraisal of the measure

Availability of evidence to support application of the measure

Measure is formulated on and underpinned by an evidence based clinical practice guideline.

Evidence of feasibility and reliability of implementation

Reliability - The measure has been demonstrated to be reliable (i.e. free from random error)., Interpretation - The measure allows unambiguous interpretation of better or worse performance., Data extraction - Data collection specifications for the measure are well defined., Data sources - Required data elements for the measure can be obtained from existing data sources., Availability of data - Required data elements for the measure can be gathered during routine practice activities, IT software - Existing IT software is sufficient for data collection., Validity - The measure has been demonstrated to be valid (i.e. it measures what it purports to).

Development approach

Availability of evidence to support application of the measure Postoperative DVT/PE is a substantial topic of interest both to clinicians, healthcare organisations and to researchers. Postoperative DVT/PE is a quality and safety measure that is formulated and underpinned by research by Haynes et al. (NEJM, 2009) that showed that implementation of a surgical checklist is associated with a reduction in complication and mortality rates among patients undergoing most types of surgery. Furthermore, postoperative DVT/PE is a measure of healthcare quality and safety commonly reported by agencies such as the OECD, the Agency for Healthcare Research and Quality (AHRQ), the Health Roundtable (Australia and New Zealand), the Australian Victorian government, and in New Zealand by researchers examining adverse hospital outcomes (P Hider, personal communication, August 2012). Evidence of feasibility and reliability of implementation The feasibility testing showed that it was possible using group numerator and denominator data derived from NDMS data to estimate national incidence rates of postoperative DVT/PE. Similar analyses have been undertaken in New Zealand by researchers at the Christchurch School of Medicine and the Health Roundtable, with similar rates per 1,000 hospital admissions estimated. Future analyses will focus on testing the use of statistical process control charts to present local level data in order to help drive quality improvement initiatives at the district health board level.

Other items

Owner details

Reference number


Date of entry to library

2012-10-29 16:39:54

Owner (Organisation name)

Health Quality and Safety Commission

Owner (Email contact)


Creator (Organisation name)

Health Quality and Safety Commission

Creator (Email contact)