One of the most exciting trends in pre-hospital emergency medicine over most of its history has been the transfer of technologies from the hospital to the field. One early example was the advent of portable defibrillators. More recently, the use of thrombolytic medicines as a pre-hospital treatment for acute myocardial infarction has successfully been transferred to the streets.
As a general rule, for a new technology to be useful in the back end of an ambulance it must be durable, relatively small and easy to use. It should be able to withstand changes in temperature and climate as well as being tossed around a moving vehicle. Because there is an almost constant demand for new instruments and procedures inside a small compartment, the size of a new technology is very important. Manpower and time considerations mean that it can not be too intrusive in patient care. Finally, the information yielded must be such that the costs and time associated with it are outweighed by easier or more complete patient treatment.
Portable, hand-held analyzers of whole blood are becoming widely available. Among the clinical parameters that can be assessed are electrolytes, glucose, blood urea nitrogen (BUN) and hematocrit.
"Out-of hospital testing is becoming more prevalent," said Bartholo-mew Tortella, M.D., of the New Jersey Trauma Center at University Hospital in Trenton. "Many diabetics use glucometers at home to monitor glucose levels by finger-stick. The extension of whole blood chemistry determination to the field with paramedics is the next logical progression of this technology."
Tortella and his group used a portable analyzer made by iSTAT of Princeton, NJ. It weighs around a pound, has disposable cartridges for performing its analysis and gives quantitative results from small samples in less than two minutes.
Phase 1 of the study was to assess how well the iSTAT would withstand the rigors of being on the road. A group of six paramedics were trained on the use of the machine. The paramedics were given reference solutions provided by the manufacturer and spent a week performing tests in a moving ambulance. They performed 30 tests with the reference solution over the week. No significant differences were found when comparing values obtained in the ambulance against the reference values found in the machine's manual.
The second arm of the study looked at how the system performed on patients in field conditions. When paramedics started an IV, a sample of blood was drawn into a tube per the EMS systems' routine. Part of the sample was run on the iSTAT analyzer in the ambulance on the way to the hospital. A comparison value was obtained on the same machine when they reached the emergency room. Fifty-seven samples were obtained during the 90-day period. There was an excellent correlation between the tests run in the field and those completed after arrival at the hospital. The correlation (r) values ran from a low of 0.89 for chloride to 0.99 for potassium, BUN and glucose.
"The recent development of a hand-held whole blood analyzer has made rapid, mobile analysis possible, known as point-of-care testing," Tortella said. "We reasoned that if these devices could be shown to reliably function in the hostile pre-hospital environment in ground ambulances, the data may give paramedics and emergency physicians additional information to aid in the treatment of patients. It might, when combined with other clinical indications, permit physicians to triage only those patients who need expensive ED care to that setting while permitting others to be transported to less costly ambulatory care centers."
One problem that had to be faced by the researchers was the narrow temperature range of operation for the iSTAT. The testing, done from March through May, was initially hampered by "out-of-temperature" errors caused by low temperature. This was quickly solved with the addition of an insulated carrying case outfitted with heating elements. However, the group did not know what the effects on the analyzer may be in hot weather. They thought the insulated nature of the carrying bag would make this less likely.
Another concern not specifically addressed by the physicians is the costs associated with placing these in the field. The additional costs of the analysis cassettes was only $10 per sample. However, what it would cost to buy and maintain the iSTAT was not calculated. Expenses surrounding paramedic training, continuing education and quality control paperwork were not addressed. The machine was, according to the paramedics, very easy to use. It performed its job unattended and within two minutes. It has a memory that enables the medics to display results at their convenience. All those involved reported that use of the device did not intrude into patient-care time.
"Armed with the knowledge that blood chemistries and hematocrit can rapidly and reliably be obtained in the field, it is now appropriate to begin considering deployment of this technology on advanced life support ambulances," Tortella said. "Knowledge of the patient's status may permit physicians to triage patients to less costly areas and off-load busy EDs choked with patients waiting for their labs."
For further information see: Tortella, B.J. et al., "Precision, Accuracy and Managed Care Implications of a Handheld Whole Blood Analyzer in the Pre-hospital Setting," American Journal of Clinical Pathology, July 1996.
Kurt Ullman, a Firehouse® contributing editor, is a registered nurse and regional chairman of the volunteer Indiana Arson and Crime Association.
