The 312 bed Royal Brompton Hospital in West London has an international reputation for the treatment of lung diseases. It conducts around 24,500 lung function tests a year on in-patients, out-patients, direct referrals from GPs and from other hospitals.
One of the challenges in lung function testing is working with seriously ill patients who do not have the strength to perform the standard test, which consists of exhaling until the lungs are completely empty, then inhaling a lungful of a gas mixture and breath holding for 10 seconds.
An earlier system built by the hospital to conduct a rebreathing rather than breath holding test had become obsolete and in need of replacement. Although similar systems are available from medical manufacturers, they are not suitable for the most seriously ill patients.
In identifying a suitable replacement, Steven Phillips, senior technical support specialist in the clinical engineering department, needed a solution that allows the lung capacity of these patients to be measured accurately.
“The application is the measurement of lung volume and the transfer of gases, using the helium dilution method and CO uptake” says Phillips. This test measures the size of the patient’s lungs and how air is distributed through them. The test can determine if disease is causing lung tissue to become distorted or under-used, or if the disease is causing the gas diffusion across the lung membrane to be affected.”
The patient breathes a gas mixture containing a percentage of helium, into which is dissolved a small amount of carbon monoxide (CO). “The patient rebreathes the gas from a bag, with their airway sealed to the bag to produce a closed environment” says Phillips. “The test measures the start concentration of carbon monoxide and compares it with the end concentration. This difference in the two figures is a measure of gas transfer across the lung membrane and the Helium dilution allows for measurement of accessible lung volume.”
The hospital found that very few manufacturers could supply a helium / carbon monoxide analyzer with the required accuracy. “The helium forms up to 15 percent of the air and needs to be read with an accuracy of two decimal places. The carbon monoxide forms up to 0.3 percent of the air and needs to be read with an accuracy of three decimal places,” explains Phillips. “For example, the initial concentration for carbon monoxide might be 0.285 percent. The accuracy of the machine reflects the accuracy of the results, so it is very important for the health of the patient that we have an analyzer that has the specified accuracy. We also required a fast response time from the analyzer in order to get a stable measurement.”
Phillips opted for ABB’s EasyLine 3000 analyzer. This continuous gas analyzer can be supplied with various measurement principles for numerous process and emission monitoring applications. The version used by Royal Brompton is the EL3030 analyzer, with a Caldos 27 0-15% Helium in Air detector and a Uras 26 0-0.3% Carbon Monoxide infrared photometer.
Designed for simple, intuitive operation, the unit’s backlit display is menu-driven via five buttons. Information can be presented in several languages, while each input and output can be configured individually.
“As well as providing the accuracy we wanted, the ABB EL3000 also provides other benefits,” says Phillips. “With its modern digital display, it is easy to calibrate through the front panel. It is also easy to link to a PC to get the data, which we are analysing with a DDE sample interface program.”
A major deciding factor in choosing the ABB solution was ABB’s willingness to adapt its standard service agreement to match the needs and budget of the hospital. They are calibrated using standard gases to ensure they are maintaining the required degree of accuracy. This is backed up with a call out service to deal with unexpected failures.