Excess Length of Stay Associated with Postoperative DVT/PE
- 1 Basic Facts
- 2 Brief overview of the measure
- 3 Application and interpretation of the measure
- 4 Calculation of the measure
- 5 Appraisal of the measure
- 6 Other items
- 7 Owner details
Stage of development
Potential or current usage
Postoperative DVT/PE is associated with a range of complications following surgery, including greater length of stay among those with postoperative DVT/PE compared to surgical patients with the same 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
This measure was selected to provide baseline information about the excess length of stay (LOS) associated with postoperative DVT/PE, enabling the calculation of changes over time in this measure.
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, such as the presence of 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 the number of excess length of stay associated with postoperative DVT/PE in order to assess the impact of healthcare quality and safety initiatives in New Zealand.
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.
Links to other measures
This measure uses the numerator and denominator data assembled to calculate incidence rates of postoperative DVT/PE. This measure is also linked to the Health Quality and Safety Commission’s broader set of postoperative harm Quality and
Level of health care delivery/setting
This measure is focused on postoperative harm following an operating room or anesthetic procedure.
This measure focuses on the total population.
Stratification by vulnerable populations
In order to adjust for risks associated with adverse surgical outcomes, the calculation of the excess length of stay requires the stratification of data by age, sex, admission type and diagnostic related group.
Possible sources of bias or confounding
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. These are referred to as risks, and need to be adjusted for when assessing postoperative harm. Statistical methods such as regression modeling are commonly used to risk-adjust estimates of adverse healthcare outcomes. However, these methods can produce results that are negatively influenced by small numerator counts, lack of clinical data, and misclassification of the adverse outcomes associated with healthcare. An approach more recently used is to match individual cases and controls by these risk adjustment variables. In the analyses described here, confounding has been controlled for by grouping (stratifying) observed and expected data by these risk adjustment variables and then matching these observed and expected grouped data to estimate the excess number of deaths. Regression modeling maybe used in future analyses once larger count data are available.
Calculation of the measure
Output of calculation
The output of this calculation is the excess LOS associated with postoperative DVT/PE. The calculation of this measure is described below.
This measure uses the numerator and denominator data assembled to calculate incidence rates of postoperative DVT/PE (see the specifications for incidence rates of postoperative DVT/PE). This was calculated by using the formula E = o – e where E is the excess LOS associated with postoperative DVT/PE, o is the average LOS observed in the postoperative DVT/PE group, and e is the average LOS expected in the postoperative DVT/PE group. A number of steps were taken to calculate the excess LOS. First, total LOS data for postoperative DVT/PE group (i.e. numerator data) were grouped by age, sex, admission type and diagnostic related group (DRG) variables. The total number of events in the postoperative DVT/PE group for each stratified group was also calculated. Second, total LOS data for the non-postoperative DVT/PE group (i.e. denominator data) were grouped by age, sex, admission type and DRG variables. The total number of events in this denominator set for each stratified group was also calculated. Then, a national average was calculated for each stratified group by dividing the total LOS by the total number of events in each stratified group. Third, the grouped data for patients with DVT/PE were matched by age, sex, admission type and DRG to those patients without DVT/PE. Then, the expected total LOS for patients with postoperative DVT/PE was then calculated by multiplying the national average for each stratified group with the total number of events of postoperative DVT/PE (from the numerator data) in each stratified group. Fourth, the average observed and expected LOS for patients with postoperative DVT/PE was calculated. Fifth, the excess LOS was calculated as the difference between the average observed LOS and the average expected LOS for patients with postoperative DVT/PE.
National minimum dataset (NMDS) 2010/11, available from the Ministry of Health.
Method of extraction
NMDS data were imported into Microsoft Access 2010. Queries were developed separately for extracting denominator data and numerator data. Calculations of expected LOS and the matching of grouped data 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).
There is currently limited knowledge internationally on the adverse effects of postoperative harm, including examination of excess length of stay and excess mortality. However, a number of recent patient safety studies and reports have assessed the excess LOS associated with postoperative DVT/PE. These studies have estimated excess LOS for postoperative DVT/PE at approximately 5. 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 the excess LOS associated with postoperative DVT/PE. Few similar analyses have been undertaken in New Zealand to compare findings. Future analyses will focus on testing the selection of risk-adjustment variables to provide a best estimate of excess LOS associated with postoperative DVT/PE.
Date of entry to library
Owner (Organisation name)
Health Quality and Safety Commission
Owner (Email contact)
Creator (Organisation name)
Health Quality and Safety Commission