Decontamination of ultrasound probes requires a strict adherence to national and local guidance to prevent any risk of cross contamination between patients. The level of decontamination required depends on how the ultrasound probe is used. Essentially if an ultrasound Probe is used invasively or if the skin is not intact then High-Level Disinfection (HLD) is required. If ultrasound probes are used on intact skin, then Low Level Disinfection (LLD) is required.
Ultrasound probes cannot be re-processed using conventional surgical instrument washers and sterilisers due to excessive heat and pressures but can be processed using a fully automatic endoscope washer disinfector EWD; it is important that a watertight capsule is used for sealing and protecting the plug socket end. Ultrasound probes can also be disinfected using a semi-automatic disinfector or by an approved manual cleaning and disinfection process.
Types of Ultrasound Probes
Convex Transducers – A convex transducer has a curved probe; this allows for wide and deep imaging. These probes are generally used for abdominal examinations, nerve and vascular examinations, Musculoskeletal Examinations and Obstetrics Examinations.
Linear Transducers – A linear transducer has a flat rectangle shaped probe and provides a good near field resolution. These probes used for breast examinations, thyroid examinations, vascular examinations and venipuncture or blood vessel visualisation.
Endocavity Transducers – Endocavity transducers are designed to fit inside body orifices. They are primarily used for examination of female reproductive organs through the vagina using a Transvaginal Ultrasound Probe (TVUS) and for the examination for prostate cancer through the rectum using a Transrectal Ultrasound Probe (TRUS). Some TRUS probes have a biopsy channel included within the probe, these must be carefully re-processed in a similar way to a flexible endoscope, ensuring the biopsy channel has been fully cleaned and disinfected. Other types of endocavity transducers include Transoesophageal Echocardiography Probes (TOE probe) used for examining the heart via the oesophagus.
Phased Array Transducers – Phased Array Transducers have a small working end. These probes are generally used for abdominal examinations, brain examinations and cardiac examinations.
Spaulding Classification
Spaulding Classification identifies the risk and level of decontamination required for medical procedures using medical devices. The Spaulding Classification identifies three levels of risk depending on the type of procedure: noncritical, semi critical and critical devices. Ultrasound probes used on intact skin such as an obstetric ultrasound scan require local cleaning followed by disinfecting using an intermediate disinfectant wipe.
If ultrasound probes such as Transrectal, Transvaginal or a TOA probe comes into contact with intact mucous membrane, or Linear or Phased Linear probe is used on non-intact skin, wounds or when inserting lines; then High-level Disinfection is required to minimise any risk of cross contamination. High Level Disinfection is still required even if the probe is sheathed as no guarantee can be given with integrity of the sheath.
Ultrasound scopes used for sterile procedures should theoretically be sterilised, however, due to the high temperatures this is not always possible. The current recommendation is High level Disinfection with sterile sheath. However, some hospitals are utilising Low temperature hydrogen peroxide vapour or low temperature hydrogen peroxide gas plasma sterilisers to re-process heat liable ultrasound probes for sterile procedures.
How to safely Clean and Disinfect Ultrasound Probes
The decontamination of ultrasound probes involves several important stages. The most important part of any decontamination stage is a pre-clean process to remove any gross soiling and debris which will hinder the disinfection process. Following pre-cleaning the ultrasound probe can be disinfected using a compatible High-Level Disinfectant such as Chlorine Dioxide. The ultrasound probe is then rinsed using a sterile rinse wipe to remove any remaining chemistry, completing the full decontamination process.
Alternatively, the ultrasound probe can be inserted into a semi-automatic disinfector which utilises hydrogen peroxide or Ultraviolet (UV Disinfection), however, it is still essential to ensure a satisfactory pre-clean and rinse takes place to complete the whole decontamination process.
Each stage relating to the decontamination of ultrasound probes must be fully recorded via an electronic or manual traceability system, providing assurance that all processes have been followed minimising any cross-contamination risks to patients. It is also, essential that all staff involved are trained in using PPE Personal Protective Equipment and the correct decontamination procedures.
The Journal of Hospital Infection has published: “Guidance for the decontamination of intracavity medical devices: the report of a working group of the Healthcare Infection Society 2018” highlighting the need to ensure the whole ultrasound probe including the cable and socket (Plug) is High level Disinfected. Consideration and care must also be given for the sonographer’s workstation including disinfecting the keyboard, ultrasound probe holders and mouse takes place in between patient use.
How does an Ultrasound Probe work?
The ultrasound probe works via a transducer that emits ultrasound waves through the body until it reaches soft tissue or bone, the ultrasound wave will then echo back, which is also detected by the transducer.
Soundwaves are produced by ceramic crystals called Piezoelectrics Crystals, when electricity is applied these crystal rapidly expand and vibrate creating sound waves which travel outwards, when the soundwaves bounce back hitting the same Piezoelctric Crystals, they will emit electrical currents.
The time taken between the soundwaves leaving and bouncing back onto the transducer inside the ultrasound probe, is captured by the scanner machine which calculates and creates a 2 dimensional visual image of soft tissue and organs this image is referred to as a Sonogram.
The technology is similar as to an echo sounder on a ship, sound waves are emitted from the ships eco sounder transducer, sound waves bounce off the seabed, the echo is then received by the ships receiver. The time taken between emitting the sound and receiving the signal back will give an indication of the sea depth.
Prior to an examination the sonographer will apply gel to the skin surface, gel is used to ensure all air between the transducer and skin is removed providing close contact with the skin. Gel can be a breeding ground for bacteria and careful control must be observed to minimise any cross contamination risks. Sterile gel sachets must be used for Neonates at all times.
