Just Point & Click

     Your ALS service is called to evaluate a 47-year-old female with epigastric pain that came on suddenly about six hours ago; she has vomited once. She thought it was the flu and that it would subside, but it has not. She smokes, is overweight and has a family history of early cardiac disease. Her vital signs are unremarkable and her belly is nontender. You perform a 12-lead ECG that shows nonspecific ST-T wave changes inferiorly. You place a few drops of blood obtained as part of your field-drawn bloods into an i-STAT cartridge. The result surprises you: Her cardiac enzyme (troponin I) is markedly elevated. Should she be transported to the closer facility without primary coronary intervention (PCI) capability or further down the road to a facility that has it?

     EMS has been performing point-of-care (POC) testing for years. Blood glucose determination is just one example of this concept. In the last few years, many EMS systems have expanded their ability to provide more definitive diagnostic information to the emergency departments they serve. What difference does it make? This is a legitimate question. EMS has been accused of not fully supporting its activities with quality research. This article will outline current uses of POC testing, limitations and future directions of this technology.

     One of the most commonly used POC testing instruments is the i-STAT (Abbott Point of Care, East Windsor, NJ). This is an easily operated, hand-held, battery-operated device with different insertable cartridges that run the various tests with a few drops of whole blood. The cartridges can test for electrolytes (sodium, potassium, calcium and chloride), glucose, blood urea nitrogen and creatinine (tests for kidney function), hematocrit and bicarbonate. Special cartridges test for beta natriuretic peptide (a test that aids in diagnosing heart failure) and troponin I (a cardiac-specific enzyme elevated in ACS). The device is easy to use and is as accurate as hospital laboratory testing.^1,2

POC TESTING By EMS

ELECTROLYTE EMERGENCIES
     One of the first research papers to look at this technology came from Grand Canyon National Park EMS providers, who showed the device could be used in a hot environment (daily temperatures of 107°F).3 They were able to identify seven out of 29 patients evacuated to their clinic with suspected heat-related illness who were actually hyponatremic (low serum sodium level). The device aided in field triage decisions and assisted in overnight management at ranger stations for visitors suffering from heat-related illnesses and hyponatremia when evacuation was impossible. The authors were one of the early groups to recognize that hyponatremia often presents similar to, and coexists with, heat illnesses.

     Sodium imbalances are potentially lethal electrolyte disturbances that can result in central nervous system symptoms (confusion, agitation, psychosis, trouble walking and weakness), as well as seizures. Hyponatremia can be divided into three main groups relative to the patient's overall hydration state: hypovolemic, euvolemic and hypervolemic. Hypovolemic hyponatremia occurs when the body loses sodium and water. Common reasons include vomiting and diarrhea, along with so-called "third spacing" of fluids from burns, pancreatitis and even bowel obstructions. Euvolemic patients often have a hormone imbalance (syndrome of inappropriate secretion of anti-diuretic hormone—SIADH). This is a complicated entity that can be caused by various lung or CNS infections and drugs. Lastly, the body can hold onto sodium (and then water) thinking it is dehydrated. This is found in congestive heart failure, liver failure and kidney failure.

     Recent research has highlighted the importance of identifying sodium abnormalities in high-risk populations, such as marathoners, endurance athletes and those exercising in hot environments. These patients are thought to suffer from a dilutional hyponatremia, owing to excess hypotonic fluid intake from sports drinks or water. A study of randomly sampled runners at the 2002 Boston Marathon found 13% had a sodium less than 135 (the lower limit of normal), and 0.6% of those were dangerously below 120.⁴ Recent guidelines have highlighted the danger of worsening hyponatremia by random use of isotonic (typical EMS 0.9% normal saline) boluses in these patients.⁵ These fluids act to lower sodium levels, which could provoke mental status changes and seizures.

     Potassium imbalances can create life-threatening dysrhythmias. The list of possible causes of increased serum potassium or hyperkalemia is long and includes kidney failure (the most common cause), certain medications (ACE inhibitors, non-steroidal drugs like ibuprofen, and digitalis toxicity), acidotic states, rhabdomyolysis, burn and crush injuries.

     Dialysis patients are notorious for having potassium imbalances. If they have missed a dialysis session or two, they are more likely to be hyperkalemic. This knowledge in the field, coupled with appropriate medical command involvement, can allow for quicker treatment with modalities like calcium agents and albuterol. Early knowledge of severe hyperkalemia may even prompt online medical control to divert you to a facility capable of emergent dialysis. Lastly, it is important to realize that an ECG may not manifest any of the classic signs of hyperkalemia and is not always a good test for mild to moderate hyperkalemia.⁶

     We are involved in the care of many high-risk populations where EMS-identified electrolyte abnormalities can speed diagnosis, treatment and recovery (see Table I).

ACUTE CORONARY SYNDROME
     One of the hallmarks for early identification of patients suffering from ACS is cardiac enzyme determination. The diagnosis of a myocardial infarction is based upon positive findings in two of three criteria: a history suggestive of ischemic chest pain, 12-lead ECG changes and elevated cardiac enzymes. The traditional enzymes measured are the cardiac-specific markers, such as creatine kinase (CK-MB) and cardiac-specific troponins. There are now several POC tests available for EMS to rapidly determine cardiac enzyme levels.

     What impact might this have on EMS management of ACS patients? As the case at the beginning illustrates, knowing about abnormal cardiac enzymes can influence treatment and destination decisions. The American College of Cardiology/American Heart Association 2007 guidelines for management of patients with unstable angina and non-ST-segment elevation myocardial infarction (non-STEMI) recommend enzyme determination be done as soon as possible, including the use of POC.⁸ The cardiology community has divergent views on whether these patients should have early PCI performed, which illustrates the importance of coordinating acute coronary care in your community and knowing whether your cardiologists prefer an early or late PCI strategy. Obviously, if the preference is for early intervention, EMS POC testing could have an important role in caring for these patients.

     The importance of field determination of enzymes has yet to be realized. We know the impact EMS-acquired 12-leads have had on reducing time to reperfusion for ST-elevation MI (STEMI) patients. What about patients with non-STEMI? Could early determination of cardiac enzymes speed time through the ED? Do patients without STEMI benefit from early management by interventional cardiologists? The effects on outcome by use of this technology are not clear. What is obvious is that patients will be identified and treated with appropriate agents more quickly, can be moved through the ED faster, and have the chance, as part of a coordinated community care system, to be triaged to facilities more skilled at non-STEMI management.

SPECIAL POPULATIONS
     Seasoned paramedics will recognize another potential application of POC testing: anion gap determination. The anion gap is a calculated determination of unmeasured ions or electrolytes. A value above 20 usually indicates the presence of an acidosis-causing substance and helps identify causes of poisoning such as aspirin, methanol and anti-freeze. It may also indicate a metabolic acidosis from such things as ketones from ketoacidosis (both diabetic and alcoholic). The mnemonic MUDPILES is used to help sort out causes of anion gap acidosis: methanol, uremia, DKA, paraldehyde, iron/INH, lactic acid, ethanol, salicylates. Being familiar with these abnormalities can help paramedics guide patient therapies.

     Patients with gastrointestinal or other forms of internal bleeding may also be field-identified with rapid determination of hematocrit via POC testing. Patients with severely lowered hemoglobin and hematocrit levels often receive blood products in the hospital. If EMS can identify these patients before arrival, the ED can more rapidly begin the process to obtain appropriate blood products.

     Several authors have demonstrated the ability of POC testing to shorten ED lengths of stay. There are many clinical examples of how EMS POC could potentially speed ED decision-making. Patients who need CT scans that require contrast (possible appendicitis or pulmonary embolus) usually need evidence of normal kidney function before scanning. If your patient needs these types of studies and you can document a normal creatinine, the patient gets scanned and dispositioned faster.

LIMITATIONS

     What would be the reason to not consider this technology? Simply stated, it has not been shown to improve survival outcomes. There was a similar argument against acquiring 12-leads in the field. It is plausible that earlier identification of important, abnormal laboratory values would improve mortality. EMS systems have been cautioned in the past to demonstrate the effectiveness of interventions we undertake in the field before widespread use.

     The devices are also not without significant operating costs, including initial purchase of the testing device and ongoing costs of the cartridges themselves. Initial and ongoing education for EMS providers is another cost, and the issue of possible reimbursements from insurance groups is poorly understood. Given the current crisis with EMS delays in transferring patients to EDs, one has to wonder if this technology, coupled with cost-sharing for the devices, could lead to shorter ED times.

     The devices require daily quality-control checks. The most comprehensive cartridge for the i-STAT has been granted a Clinical Laboratory Improvement Amendment of 1988 (CLIA) waiver. The nuances of this requirement are complicated, but EMS systems can and do abide by it. Either way, the implementation requires that an appropriate laboratory officer be in place to oversee the use of the devices.

     The tests themselves have many limitations. For example, troponins collected early on in the course of ACS are often negative, and there are many reasons for false elevations (renal failure, sepsis and a variety of non-ischemic stresses to the heart). A complete discussion of test limitations is beyond the scope of this article.

Point-of-Care Testing In Action
     The paramedics with the Gig Harbor (WA) Fire Department have been using the i-STAT device for several years. I spoke with two of their paramedics, EMS Chief Paul Berlin and i-STAT program manager Geoff North, about their experiences.

1. How have the medics taken to the i-STAT?

        The medics are all on board with the program, at least on a basic level. Some are more gung-ho than others about really learning what all of the different lab values mean, but all have a good basic working knowledge. Medic buy-in was an issue that we tried to address before we spent the money and started the program, because it was going to be a potential roadblock to our success.

2. How long is the training for its use?

        The initial training is about four hours including phlebotomy, sample handling and basic lab value interpretation. This is followed by ongoing monthly training in the form of run reviews, with emphasis on certain lab values and what they mean. We have integrated the i-STAT labs into our ACLS-EP recertification process, with an emphasis on fluid and electrolyte imbalances. We also do annual skills competency review and monitor the analyzer logs for common operator errors.

3. What do you see as its biggest impact?

        The biggest impacts have been the ability to better identify non-STEMI patients (which sometimes includes emergent PCI) and better differentiate CHF from COPD, pneumonia and sepsis. And, speed of patient care has improved.

4. What is the most difficult thing about its use?

        The time factor for getting results during a short transport. It takes the analyzer 10 minutes to run a troponin or BNP cartridge. Most of our transports are in the 15- to 30-minute range, so we have time to run the tests and react to the results, but this could be a deterrent to EMS agencies that average 5- to 10-minute transports.

5. Why do you think other services haven't adopted the technology?

        Money is the biggest hurdle. The start-up cost is still relatively high ($5000–$7000 for the analyzer alone), and there is a substantial training commitment.

6. What are the major logistical problems with storage or use?

        The analyzer is pretty rugged, and we have not seen any problems with vibrations or movement while using the analyzer in an ambulance setting. In places that have very warm temperatures, a climate-controlled compartment would be necessary due to operating temperature limitations. We have not seen any problems with cool temperatures. The cartridges can be stored at room temperature for two weeks or in an on-board refrigerator for 12 months.

7. How has the i-STAT been received by ED personnel?

        There are mixed reviews. Some doctors love them; some think it is a complete waste of money and time, like when we first started doing 12-leads. We have had doctors ask the medic to do an i-STAT on an ED patient (that we didn't transport) because they needed the results now to start treatment and not in 90 minutes, which is about the lab turn-around time. So it all depends on whom you ask.

8. How has the i-STAT helped the average medic?

        At each month's run review meeting, we review several charts where the labs made a difference in ED care. Once the medics start seeing this, they want more info. They are encouraged to do i-STAT determinations on patients and learn what treatment plan to expect to begin in the medic unit that will carry into the ED.

FUTURE DIRECTIONS
     The technology for EMS POC testing has been used for many years and has evolved to a higher level of clinical sophistication. Future research should focus on the applicability of the device to various EMS systems. Clearly, it has uses for remote and rural settings. It can aid in more quickly identifying patients who need expedient care for such diverse medical conditions as acute coronary syndrome, internal bleeding, undifferentiated respiratory distress and electrolyte emergencies. What remains to be seen is whether the testing adds value in terms of improved outcomes. Is identifying a patient with a non-STEMI and diverting them to a facility with a cardiac catheterization lab a benefit to that patient? What about early identification of internal bleeding? Is your system ready for POC testing?

References

1. Tortella BJ, Lavery RF, Doran JV, et al. Precision, accuracy, and managed care implications of a hand-held whole blood analyzer in the prehospital setting. Am J Clin Path 106(1):124–127, 1996.
2. Hsiao AL, Santucci KA, Dziura J, et al. A randomized trial to assess the efficacy of point-of-care testing in decreasing length of stay in a pediatric emergency department. Ped Emerg Care 23(7):457–462, 2007.
3. Backer HD, Collins S. Use of a handheld, battery-operated chemistry analyzer for evaluation of heat-related symptoms in the backcountry of Grand Canyon National Park: A brief report. Ann Emerg Med 33(4):418–422, 1999.
4. Almond CS, Shin AY, Fortescue EB, et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med 352:1550–1556, 2005.
5. Hew-Butler T, Almond C, Ayus JC, et al. Consensus statement of the 1st International Exercise-Associated Hyponatremia Consensus Development Conference, Cape Town, South Africa, 2005. Clin J Sport Med 15: 208–213, 2005.
6. Mattu A, Brady WJ, Robinson DA. Electrocardiographic manifestations of hyperkalemia. Am J Emerg Med 18:721–729, 2000.
7. Lowe RA, Arst HF, Ellis BK. Rational ordering of electrolytes in the emergency department. Ann Emerg Med 20(1):16–21, 1991.
8. Available at www.acc.org.

Further Reading
Apple FS, Murakami MM, Christenson RH, et al. Analytical performance of i-STAT cardiac troponin I assay. Clin Chim Acta 345:123–127, 2004.
Caragher TE, Fernandez BB, Jacobs FL, et al. Evaluation of quantitative cardiac biomarker point-of-care testing in the emergency department. J Emer Med 22:1–7, 2002.
Hamm CW, Goldmann BU, Heeschen C, et al. Emergency room triage of patients with acute chest pain by means of rapid testing for cardiac troponin T or troponin I. N Engl J Med 337:1648–1653, 1997.
Schuchert A, Hamm C, Scholz J, et al. Prehospital testing for troponin T in patients with suspected acute myocardial infarction. Am Heart J 138:45–48, 1999.

Fritz Fuller, BS, PA-C, REMT-P, is an emergency medicine physician assistant with the Department of Emergency Medicine at Penn State University Hershey Medical Center. He has over 20 years' experience in EMS and emergency medicine. He can be reached at mtwiens@yahoo.com.