The use of Lean and Six Sigma methodologies in surgery: A systematic review

Abstract

Background

Lean and Six Sigma are improvement methodologies developed in the manufacturing industry and have been applied to healthcare settings since the 1990s. They use a systematic and reproducible approach to provide Quality Improvement (QI), with a flexible process that can be applied to a range of outcomes across different patient groups. This review assesses the literature with regard to the use and utility of Lean and Six Sigma methodologies in surgery.

Methods

MEDLINE, Embase, PsycINFO, Allied and Complementary Medicine Database, British Nursing Index, Cumulative Index to Nursing and Allied Health Literature, Health Business Elite and the Health Management Information Consortium were searched in January 2014. Experimental studies were included if they assessed the use of Lean or Six Sigma on the ability to improve specified outcomes in surgical patients.

Results

Of the 124 studies returned, 23 were suitable for inclusion with 11 assessing Lean, 6 Six Sigma and 6 Lean Six Sigma. The broad range of outcomes can be collated into six common aims: to optimise outpatient efficiency, to improve operating theatre efficiency, to decrease operative complications, to reduce ward-based harms, to reduce mortality and to limit unnecessary cost and length of stay. The majority of studies (88%) demonstrate improvement; however high levels of systematic bias and imprecision were evident.

Conclusion

Lean and Six Sigma QI methodologies have the potential to produce clinically significant improvement for surgical patients. However there is a need to conduct high-quality studies with low risk of systematic bias in order to further understand their role.

Introduction

The National Health Service (NHS) is undergoing a challenging period - it is faced with increasing patient expectation, a demand to improve quality of care and yet has been asked to save £20bn within four years.1, 2, 3 Political and healthcare groups have expressed concern that limitation of NHS resources will inevitably result in a detrimental effect on patient care, however this belief is not necessarily true.4, 5 It has been shown that quality of care delivered is not solely proportional to financial expenditure but of equal importance is how the system is organised and in particular it's efficiency - the effectiveness of scarce resource allocation to best achieve the intended outcome.6, 7

These challenges are not unique to the UK healthcare system⁸ but are relatively new in comparison with the manufacturing industry, which has demonstrated since the 1930s that systematic, reproducible and evidence-based methodologies are beneficial in achieving quality improvement.⁹ The strengths of these strategies are fourfold when applied within the complex environment of healthcare. First, they objectively set out the processes the investigators need to follow to understand the problem and to guide decision-making when identifying potential aspects for improvement. Second, these processes are flexible and can be focussed at improving a wide range of quality measures. Third, a framework is provided to analyse whether interventions are providing an improvement whilst simultaneously having the capability of identifying further problem areas. Lastly, they promote continual assessment and re-assessment, cyclically creating improvement within a system that may have changing needs and resources over time.

Six Sigma (SS) and Lean are two prominent Quality Improvement (QI) methodologies that have been demonstrated across several areas of healthcare since 1998.9, 10 Despite a slow initial uptake within surgery,¹¹ the use of Lean and Six Sigma has increased markedly with more than half of studies published within the past four years (Fig. 1).

Six Sigma is a process developed by the Motorola Corporation in 1986, which aims to improve quality by identifying and correcting the causes of errors and in doing so reduce the rate to a six sigma level - 3.4 defects per million opportunities (DPMO). Applying the concept of DPMO to a healthcare context, Sedlack et al.¹² described that if the aviation industry operated to the 95 DPMO (5.25 sigma) level that is seen in bile duct injury during laparoscopic cholecystectomy, there would be 20 commercial aeroplane crashes each day in the United States of America alone.

Lean is a QI methodology evolved from the Toyota Production System in 1990,¹³ which uses an on-going cycle of improvement to focus on mapping out and adapting process pathways to preserve the steps which provide 'value' and to eliminate sources of waste. This concept is complimentary to Six Sigma and they can be combined to create Lean Six Sigma (LSS), where a 5-stage system known as DMAIC (Define, Measure, Analyse, Improve, Control) is employed. This methodology benefits from the statistical rigor of SS as well as the cyclical waste reduction seen in Lean.⁹

The aim of this systematic review is to assess the literature with regard to the use and utility of both Lean and Six Sigma QI methodologies in the improvement of patient care within surgery.