28 Jun 2022

More accurately measuring the difficulty of an operation in advance with NASA technology

The NASA TLX is a multi-item questionnaire which is used in a
variety of fields. TLX stands for Task Load Index, and is a measure
of perceived workload. Image: MeasuringU

Surgery is not an exact science. No surgeon truly knows the complexity of an individual operation until after it is over, and this is difficult to accurately measure.

A group of Melbourne surgeons, led by Dr Stephen Bell, in Monash University’s Department of Surgery and also a surgeon at The Alfred, has adapted an index used by the National Aeronautics and Space Administration (NASA) as a way to measure an operation’s difficulty. 

The research found that the NASA TLX Index accurately measured the technical difficulty of an operation, and therefore may be useful to gauge a trainee’s proficiency over time, which currently relies on self reporting. It can also be used to assess changes in surgical techniques and new technologies.

The study, published in the Australian and New Zealand Journal of Surgery, asked seven surgeons across a number of metropolitan Australian hospitals to use the NASA Task Load Index to gauge the difficulty of 127pre-defined operations.

These scores were then compared to various clinical parameters together with the subjective measure that the surgeons had categorized the operations as easy, moderate or difficult. The operations were minimally invasive right hemicolectomy or a re-do bariatric surgery.

According to Dr Bell, the NASA Index was found to be significantly predictive with:

  • Operation duration
  • Blood loss
  • Pervious abdominal surgery
  • Surgeon’s assessment of difficulty

However, the Index did not predict:

  • Intra-operative or post-operative complications
  • Conversion to open surgery
  • Length of stay in hospital

“In a research or teaching setting it would be valuable to be able to objectively and quantitatively measure the degree of difficulty of an operation as a way to evaluate any new surgical technique, new surgical technology and to measure any improvement in technical expertise in a surgeon or trainee,” Dr Bell said.

“The NASA index is significantly better than the current parameters used to assess operative difficulty, which are imprecise and are largely subjective. The NASA Index offers a single numerical score for an operation that reflects the technical difficulty experienced by a surgeon.”


Bell SW, Kong JCH, Clark DA, Carne P, Skinner S, Pillinger S, Burton P, Brown W. The National Aeronautics and Space Administration-task load index: NASA-TLX: evaluation of its use in surgery. ANZ J Surg. 2022 Jun 8. doi: 10.1111/ans.17830. Epub ahead of print. PMID: 35674407.

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