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Cumulative Sum (CUSUM) charts for medical student peripheral venous cannulation; development of a difficulty-adjusted C

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Cumulative Sum (CUSUM) charts for medical student peripheral venous cannulation; development of a difficulty-adjusted CUSUM. Dr Harry Murgatroyd SpR Anaesthesia Leeds Teaching Hospitals Trust Sumaiyah Kola Medical Student Leeds University Medical School.

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slide1

Cumulative Sum (CUSUM) charts for medical student peripheral venous cannulation; development of a difficulty-adjusted CUSUM

Dr Harry Murgatroyd

SpR Anaesthesia

Leeds Teaching Hospitals Trust

Sumaiyah Kola

Medical Student

Leeds University Medical School

slide2

Runcie CJ. Assessing the performance of a consultant anaesthetist by control chart methodology. Anaesthesia. 2009; 64(3): 293-296

slide3

Developed initially to look at industrial processes

CUSUM Chart

Learning Curves

Monitors performance

Audit of quality clinical practice

Graphical presentation over time

Used to determine competency

theory
Theory

Set:

definition of success / failure

acceptable failure rate

unacceptable failure rate

error

Collect:

binary data

Algorithm:

Score falls with success

Score increases with failure

Graph

Boundary Lines

slide5

Sequential cannulation attempts

Success is seen as a fall in the graph

Failure seen as a rise in the graph

Each point represents a single cannulation attempt

Score derived using the CUSUM formula

problems
Problems
  • Patient variability
    • Standard CUSUM
      • Constant failure and success rates
    • Risk adjusted CUSUM
      • Complicated
      • Not intuitive
  • Failure rates
    • Set by user
    • Can affect results considerably
medical student project
Medical student project
  • Aims
    • Proficiency at intravenous cannulation
    • Plot individual CUSUM charts
    • Develop a ‘difficulty-adjusted’ CUSUM technique
  • Time Scale:
    • 5 weeks
methodology
Methodology
  • Setting
    • Teaching hospital
    • Elective surgical lists
  • Procedures
    • Verbal consent
    • Peripheral venous cannulation
      • Standard technique
      • Size of cannula appropriate to surgical procedure
    • Data collection
      • Success or failure
      • Appearance of vein
      • Size of cannula
      • Patient awake or anaesthetised
conventional cusum
Conventional CUSUM
  • Definition of ‘success and failure’
  • Acceptable and unacceptable failure rates
    • Consultant consensus
    • Literature
    • 0.2 and 0.4 respectively
  • Calculation
    • Published formulae
    • Error rates = 0.1
    • MS Excel

de Oliveira. Anesth Analg 2002;95:411-6.

Williams et al. BMJ 1992;304:1359-61.

conventional cusum12
Conventional CUSUM

Failure rates

Upper and lower boundries

0= failure,1= success

Data is plotted sequentially

Running total, CUSUM

Example if “IF” formula in Excel

difficulty adjusted cusum
Difficulty Adjusted CUSUM
  • Difficulty score
    • Appearance of vein
    • Cannula size
    • Awake or anaesthetised
  • Different failure rates
    • Two stages
      • Vein adjusted
      • All three variables
    • Intervention line
      • Average of all prior lines
slide15

Three variable methodology

Table shows the scoring of each of the recorded variables. These are then added up to give the total score for the cannulation attempt

Shows the standard CUSUM formula, whilst incorporating different failure rates and scores dependent on the difficulty of the variables recorded.

Spreadsheet showing the final added up scores of the different variables. Hence including the vein, consciousness and cannula size. Using “IF” formulas the correct value of S is selected from the table above and the CUSUM then plotted in the same way as before.

difficulty adjusted cusum16
Difficulty Adjusted CUSUM
  • Successful difficult cannulation
    • Large fall in score
  • Failed difficult cannulation
    • Small rise in score
  • Successful easy cannulation
    • Small fall in score
  • Failed easy cannulation
    • Large rise in score
slide20

POSITIVES of CUSUM

  • Objective
  • Simple Calculations
  • Shows improvement in learners
  • Early detection of poor performance
  • Allows comparisons between students
  • LIMITATIONS of CUSUM
  • Only technical skills
  • Must have binary outcome
  • Relies on logbooks and honesty of user
  • Time consuming
  • Open to manipulation
  • Does not show improvements that do not change binary outcome

Bolson S, Colon M. Int J Health Care Qual Assur 2000;12:433-438.

Kestin IG. BJA 1995;75:805-809.

difficulty adjusted cusum21
POSITIVES

Potentially corrects for patient variability

Easier and more intuitive than other methods of adjustment

LIMITATIONS

Failure rates set by the user

The more variables ‘corrected’ for, the more layers of estimation and inaccuracy

Loss of statistical element of conventional CUSUM

Difficulty adjusted CUSUM
summary
Summary
  • Easy technique
    • Handheld devices
    • Electronic logbooks
  • Objective
  • Can be adjusted for patient variability
  • Allows
    • Charting of ‘learning curve’
    • Comparison between practitioners
    • Identification of poor performance
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