Multicentre analysis of 7-bar surgical air provision and use across NHS Scotland

Abstract

Historically, surgical air powered a range of surgical tools, particularly in orthopaedics. Advances in technology have enabled widespread adoption of battery-operated and electric cable tools, reducing reliance on compressed air. Scottish Health Technical Memorandum 02-01 states that surgical air is only required where air-driven surgical tools are used [1]. With decreasing clinical use, decommissioning of existing surgical 7-bar air plants may be appropriate where standalone systems are installed. However, many sites have combined 7 and 4-bar medical air plants, making decommissioning difficult. In new-build hospitals, consideration should be given to replacing 7-bar systems with modern alternative tools or local cylinder supply where necessary.

We investigated the use of surgical air across NHS Scotland to assess whether centralised piped systems remain necessary.

Surgical air (7-bar) was used to power tools in several surgical specialities. The configuration of plant varies from combined systems, typical in small to medium hospitals, where compressed air is generated at 9–10-bar and then regulated to 7 and 4-bar, to separate systems used where consumption justifies independent plants. Higher pressure systems consume more energy with an approximately 7% increase in energy use per additional bar of pressure meaning approximately 21% higher energy consumption for 7- vs. 4-bar systems [2].

An overview of compressed air systems at 29 acute hospitals in NHS Scotland revealed that 24 sites have combined medical air systems, two have separate 7- and 4-bar compressed air systems and three provide 4-bar systems only. One hospital recently decommissioned its 7 bar air plant in favour of local cylinder provision for the only identified clinical use in orthopaedics.

Analysis of clinical use found that 28/36 orthopaedic surgeons report no use of 7-bar air for hand tools, with others indicating only occasional or limited use and, of those, all were willing to trial battery or electric alternatives. Cement mixing remains the main indication for 7-bar air, but accounts for just 30 s of use per cement mix. This equates to 4 min of use for an arthroplasty list of four cases or 0.28% utilisation. Measurement of one Venturi cement mixing vacuum pump driven by 7-bar air revealed an average flow rate of 20 l.min^-1, meaning that cylinder supply of 80–100 l.day^-1 of compressed air should suffice. Use in plastic surgery was limited to dermatomes and drills, estimated at 5–10 min per case (0.35–0.7% utilisation), but with a number of units already using electric alternatives. There was no use of 7-bar tools in cardiothoracic or neurosurgery, with all centres now using electric tools and a mix of air and mains tools in oral and maxillofacial surgery. Dental services utilise a separate system of a lower standard compared with surgical use [3] and most clinics are supplied by local compressors rather than a central system.

Decision-making requires detailed knowledge of compressed air plant configuration and how this provision matches with clinical need. For the provision of compressed air, where deemed clinically necessary, local teams should consider the volumes required and select the most efficient method of provision, such as a local cylinder manifold. This assessment also requires measurement of pipeline leak and energy expenditure, alongside installation and maintenance costs. Evidence of 80–95% leak in nitrous oxide pipelines led to the decommissioning of nitrous oxide manifolds [4], and possible leaks may also be present in pressurised gas pipeline systems. Ultrasonic metering of flow in 7-bar air pipelines at a 450-bed district general hospital found that 46,798 l of air passed through the pipeline in 21 days, but with evidence of limited clinical use. There were only 36 dento-alveolar cases with an estimated total of 360–540 min of drill use but a continuous leak of around 1.5 l.min^-1, adding up to > 800,000 l.y^-1.

Energy use and carbon savings can be difficult to measure in combined plant systems, but logbook examination of a standalone 7-bar compressor records 7535 kWh annual energy use, emitting 1333 kg of carbon dioxide equivalent (CO₂e) [5] and at a financial cost of £2185 (US$2936, €2526). Based on 123,000 acute beds across the UK [6], this results in an estimated 333 tonnes of CO₂e emissions and costs of over £500,000 ($672,000, €578,000) annually. Installation of a 7 bar air unit in a planned 450-bed district general site has been costed at £163,000 ($219,000, €188,501) not including annual maintenance.

Preliminary findings indicate that 7-bar surgical air is no longer used widely across NHS Scotland. Plastic and oral surgery may be amenable to electric replacement tools or local cylinder provision. Decommissioning offers substantial carbon and financial savings, so depending on local use there may be a strong case for removing 7-bar air systems. Assessment of provision and clinical use of compressed air informs future hospital design, potentially eliminating central surgical air systems in new-build hospitals, creating financial savings and supporting sustainability objectives.