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Electrical Wiring in the Dialysis Unit

Electrical Wiring in the Dialysis Unit. ‘A Shocking State of Affairs!’ Ian Morgan ART October 2010. Discussion. Are we providing a safe environment in which to dialyse our patients? Are we protecting them from electric shocks?

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Electrical Wiring in the Dialysis Unit

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  1. Electrical Wiring in the Dialysis Unit ‘A Shocking State of Affairs!’ Ian Morgan ART October 2010

  2. Discussion • Are we providing a safe environment in which to dialyse our patients? • Are we protecting them from electric shocks? • Should we understand the DoH building guidelines covering electrical wiring (Health Technical Memorandum 06-01)? • Are those building our dialysis units interpreting these guidelines correctly?

  3. Hazard: Something that has the potential do harm. Using mains powered electrical equipment in the patient environment. Placing a conductor in or near the heart. Micro shock to the myocardium. Risk: The likelihood of the hazard occurring & the consequence. Prevalence of catheters. High impedance or open circuit in the mains flex earth conductor. Patient touching conductive objects. Ventricular fibrillation leading to death. Hazards & Risks

  4. Catheter in Heart

  5. Heart Impulse Conduction

  6. Leakage current Infusion pump ECG monitor Dialysis chair BP monitor Heater Lamp Infusion pump ECG monitor Dialysis chair BP monitor TV Phone charger Wicker and Svensson, 2006

  7. BS EN 60601-1 Limits

  8. What is a Safe Current? • The HD machine chassis current in normal operation could be 100μA and up to 500μA if the earth conductor breaks. • The allowable current for equipment connected to the heart is 50μA in a single fault condition. • Even this may be enough to cause VF as Laks et al (1996) commented that the minimum current shown to cause VF in a human was 15μA. • Deller (1979) commented “(HD) Equipment that has been constructed to BS 5724 should not, by its design, give rise to primary electrical hazards”. • Is that statement correct?

  9. Lets try to kill a dog Are you £µçЌing mad! • Historical acceptance of Type B limits for HD equipment is shown in experiments done by Frize et al. (1978), where a leakage current of 85mA was passed through a 14 gauge needle in the left front leg of a dog to earth via the right rear leg & did not induce VF or heart failure; concluding “…50μA, implies a large margin of safety”. Are you mad!

  10. HD Machine Leakage Current? • Jonsson & Stegmayr (2000) measured patient leakage currents of four machines (Gambro AK10, AK100 & Fresenius 2008 (C&E) & 4008E with values from 1 to 20μA in normal condition and 60 to 140μA with a broken earth conductor; measure at dialyser connectors. • Main on applied part produced 3,500μA leakage current. • Jonsson et al, (2005) then measure in vitro patient leakage current in single fault condition at the tip of a vascular catheter primed with blood; median 68μA (range 35-118μA ). • When mains was applied to the catheter tip a dangerous leakage current was measured; median 610μA (range 441-662μA).

  11. Assessing the Risks • “At least 65% of patients presenting more than three months before initiation of dialysis should start HD with a usable native arteriovenous fistula” Clinical Practice Guidelines Vascular Access for Haemodialysis (2007). • 20-35% of patients are dialysed with a central venous catheter. • Roy (2001) concluded that 10% of deaths on dialysis are most likely caused by technical failure. • “Faults in detachable power cords account for 80-90% of all earth bond failures as … moulded power cables are prone to stress when … dropped” Backes (2006). • Many non-medical electronic devices are present in the patient environment; TV’s PC’s etc.

  12. Assessing the Risks Unacceptable, stop activity and make immediate improvements Tolerable, look to improve within specified timescale Adequate, look to improve @ next review Consequence Acceptable, no further action but ensure controls are maintained Likelihood

  13. Assessing the Risks • The consequence is life threatening and the likelihood is not insignificant. • “This (micro) shock causes no tissue damage, which makes it unlikely that the true cause of death is found in autopsy” Polaschegg • Law requires that we put in place control measures to reduce the risks – so far as is reasonably practical.

  14. Risk Reduction Hierarchy • Eliminate the hazard- This cannot be achieved, the potential to electrocute the patient will always be present. • Reduce the hazard- Electricity will always be in the patient environment. Increase the number of fistulas and grafts used as access. • Prevent contact with the hazard- Bond all conductive surfaces to earth & remove faulty equipment. • Introduce safe system of work- Ensure devices are tested and potential equalisation leads are used at all times. • Protective equipment- Ensure earth equalisation sockets & leads are available.

  15. Risk Reduction • Dialysis machines are constructed to meet Type CF requirement. Unlikely in the near future. • Exclude all non-medical electrical equipment from the patient environment. Impractical. • Supply power in the patient environment through an isolated power supply. Impractical & costly. • Use earth potential equalisation leads on all medical devices. • This reduces the risk of a fault in the mains power cord but not excessive patient auxiliary current from non-medical devices & other conductive surfaces.

  16. Isolated Power supply Leakage current Dialysis Machine L X N X

  17. Earth Potential Equalisation

  18. Creating a Safer Environment • All medical devices are constructed to comply with the Medical Devices Directive (93/42/EEC): Procurement. • Routinely perform earth bonding, earth leakage and patient leakage current tests: Renal Technologist/MEP. • Routinely perform portable appliance electrical safety tests on non-medical devices: Estates/Facilities. • The electrical distribution within the clinical environment is designed to comply with DoH Estates & Facilities Division, Health Technical Memorandum 06-01 (HTM 06-01) published 2007: Estates/Facilities. • Routine inspection (6 monthly) and service (2 yearly) of earth & power distribution system (HTM 06-01): Estates/Facilities. • Connect all medical equipment to an earth potential equalisation socket: End users.

  19. HTM 06-01 Electrical service supply & distribution • Provides guidance for all works on fixed wiring within healthcare premises. • Provides guidance to managers on how European and British Standards relating to electrical safety can be used to fulfil their duty relating to the H & S at Work Act 1974. • Understanding & ownership of risk.

  20. Risk Category Comparison

  21. Reverse Mains Dialysis Machine L N

  22. Engaging the Design Team • Make your self familiar with the relevant sections of HTM 06-01. • Ask if those designing & modifying your dialysis units are familiar with it as the previous version HTM 2007 published in 1993 was very vague. • Do they understand dialysis and the risks? • Do they realise that providing earth potential equalisation sockets is mandatory?

  23. The Future • More dialysis equipment manufacturers are recommending the use of earth potential equalisation when dialysing patient with a catheter. • The MHRA are looking into providing additional guidance on this subject similar to the MEIGaN (Medical Electrical Installation Guidance Notes) they produced for diagnostic imaging & x-ray installations.

  24. References • Backes J 2006 A Practical Guide to IEC60601-1. Rigel Medical • Deller AG 1979 Electrical safety in dialysis J Med Eng Technol 3(4):186-191 • Department of Health 2007 Health technical Memorandum 06-01: Electrical service supply and distribution. https://estatesknowledge.dh.gov.uk/index.php?option=com_documents&Itemid=1&sdocid=49(registration required) • Frize M, Scott J, Durie N, Park G (1978) Fibrillation caused by leakage current from dialysis machines – What is the danger? Med. & Biol. Eng. & Comput16:124 • Johnsson P, Eliasson G, Stegmayr B (2005) Blood lines conduct leakage current during haemodialysis: a potential safety risk during first failure, especially for patients with dialysis catheter as access. Med. Biol. Eng. Comput43:731-38 • Jonsson P, Stegmayr B (2000) Current Leakage in Hemodialysis Machines May Be a safety Risk for Patients. Artificial Organs24(12):977-87 • Laks M, Arzbaecher R, Bailey J, Geselowitz D, Berson A (1996) Recommendations for Safe Current Limits for Electrocardiographs Circulation93:837-39 • MHRA 2007 Medical Electrical Installation Guidance Notes http://www.mhra.gov.uk/home/idcplg?IdcService=GET_FILE&dDocName=CON2018069&RevisionSelectionMethod=Latest&noSaveAs=0&Rendition=WEB • Polaschegg H-D Neglected Safety Aspects in Hemodialysis Machines and Their Related Problems. http://www.aami.org/publications/hh/Neglected.Polaschegg.pdf Accessed 20 July 2010 • Roy T 2001 Patients’ safety and haemodialysis devices Nephrol Dial Transplant16:2138-2142 • Wicker PO, Svennson R (2006) Is potential equalization in HD treatments necessary? J Ren Care32(3):136-40

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