Evaluating methoxyflurane (Penthrox) as an alternative to Entonox for colonoscopy in the Scottish Highlands

Project completed as part of the 2026 Green Gastroenterology Challenge 

Team members

Mr George Neelankavil Davis (Registrar, General Surgery)

Ms Sumathi Nadikuditi (Registrar, General Surgery)

Ms Leila Chandler (Clinical Endoscopist)

Mr Alan Grant (Consultant Surgeon)

Dr Kenneth Barker (Consultant Anaesthetist)

Setting / patent group: 

Endoscopy Department at Raigmore Hospital, NHS Highland. Adult patients undergoing elective outpatient colonoscopy who were suitable for methoxyflurane according to local prescribing guidance

Issue:

Entonox is commonly used as patient-controlled analgesia during colonoscopy, but nitrous oxide is a potent greenhouse gas with a high global warming potential and a long atmospheric lifetime. The project sought to assess whether low-dose methoxyflurane (Penthrox) could provide a lower-carbon alternative while maintaining procedural effectiveness, patient comfort, safety and service delivery. 

Intervention: 

A self-administered 3 mL Penthrox inhaler was introduced for appropriate patients undergoing elective colonoscopy. Standard monitoring, escalation procedures and existing colonoscopy pathways were maintained. Staff training, governance approvals, patient information materials and standardised documentation were developed before implementation. Outcomes were evaluated during a single PDSA cycle between September 2025 and July 2026 using routinely collected clinical, environmental, economic and social data.

Outcomes:

Clinical: 

57 procedures were performed using Penthrox alone and 554 using Entonox alone. Procedure completion rates were similar with 91.2% with Penthrox and 95.8% with Entonox. Procedure duration (37.0 vs 39.3 minutes) and recovery time (15.2 vs 18.4 minutes) were similar between groups. Patient comfort was maintained, with no patients in the Penthrox group reported moderate or severe discomfort (compared to 17 in the Entonox group). No drug-related adverse events were reported in either group. 

Environmental: 

Modelled emissions were 1.12 kgCO2e per procedure with Penthrox compared with 28.29 kgCO2e with Entonox. Modelling based on 742 procedures per year suggested a potential annual reduction of approximately 20,163 kgCO2e, representing a 96% reduction in carbon emissions. 

Financial: 

Penthrox was associated with higher direct organisational costs than Entonox. Estimated costs were £16.02 per procedure for Penthrox and £2.58 per procedure for Entonox. At a modelled annual activity of 742 procedures, full conversion to Penthrox would increase projected annual expenditure from approximately £1,914 to £11,887, an additional cost of approximately £9,973 per year. The marginal reduction in procedure and recovery time could offset this cost with a £80-£118 reduction in procedure time cost per case but requires further evaluation. No additional implementation or training costs were incurred.

Social: 

Patient-reported experience was highly favourable. Positive responses exceeded 87% across all domains surveyed, with an overall mean score of 4.6/5. Overall satisfaction was high, with 90.3% stating they would choose Penthrox again. Among patients with previous colonoscopy experience, 92.9% preferred Penthrox for a future procedure. Staff feedback was also positive, with 90% willing to offer Penthrox again. 

Key learning point 

Successful implementation depended on multidisciplinary and cross-department communication, the development of a structured pathway, and sustained staff engagement. Although initial resistance to change was encountered, governance approval, standardised documentation, staff education and gradual implementation enabled safe integration of Penthrox into practice. The project demonstrated that substantial carbon reductions may be achievable while maintaining clinical quality and patient acceptability, although larger prospective evaluations are needed to establish comparative effectiveness, safety and economic value.