This article first appeared on FireRehab.com, sponsored by Masimo.
By Jay MacNeal with Todd Daniello, Ken Hanson, Mitch Li, Sean Marquis, John Pakiela, Matt Smetana and Chris Wistrom
The ability to rapidly and reliably perform laboratory testing at the patient bedside has taken huge leaps in recent years. There are devices to quickly check a patient's blood sugar, electrolytes, INR, cardiac enzymes, lactic acid and other biomarkers.
Do these devices have a role in the rehab area, or are they only suited for in-hospital care" Glucometers, pulse oximetry, end-tidal carbon dioxide and carbon monoxide (CO) oximetry are all common in EMS, but the use of i-STAT or other point-of-care testing devices is a bit outside the norm of most EMS operations.
To examine the appropriateness of these point-of-care testing options, we must consider the costs and human resources it will require to maintain the processing device, sampling equipment and replacement cartridges, perform calibration and training, obtain CLIA waivers, apply interpretation of the results to immediate patient care and other challenges important to EMS.
With all of that in mind, let's explore some available point-of-care testing tools and their potential usefulness or application for on-scene rehab of firefighters and other emergency personnel.
ECG and 12-lead EKG
Probably the least frequently used point-of-care test in the rehab environment is the one that has been around the longest. An EKG is an excellent tool in analysis of the person with chest pain or persistent shortness of breath, but it is much more versatile.
By using intervals and morphology of QRS, QTc and T waves we can glean insight into severe electrolyte disturbance, including hypo- or hyperkalemia and hypo- or hypernatremia. Both of these are significant concerns in sports medicine, and it makes sense that we would have the same issues in heat-stressed responders.
One of the steps in risk stratifying patients who have chest pain in the hospital is to subject them to a stress test. This involves exercising or stressing the heart to ensure its ability to maintain adequate perfusion and oxygenation during high demand periods.
Any degree of active or even passive firefighting involves the release of adrenaline and generation and sometimes impaired loss of heat, as well as significant exertion, which all equate to stress on the heart.
Firefighters are at a higher than average risk for heart disease and sudden death than the general population. The complaint of chest pain on the fire scene should most certainly be taken seriously and prompt an appropriate evaluation, including the performance of an on-site 12-lead EKG and timely transport to the hospital for further evaluation.
Lactate levels
The measurement of point-of-care lactic acid levels is an interesting notion. We know that lactic acid is a product of aerobic and anaerobic metabolism. It is found in high levels in those who are hypoperfused, such as sepsis and shock patients [1].
This biomarker as a prehospital point-of-care test is not widely used, but it may become an important assessment tool as mobile integrated health care progresses. Its utility in rehab is uncertain.
CO exposure
Carbon monoxide and cyanide are commonly found in the air on scene of active fires. CO needs to be a concern in confined-space operations as well. Any worker with headache, nausea, vomiting, weakness or altered mental status must be considered for CO exposure.
The Rad-57 is a commonly carried oximeter that will read O2 and CO saturations. It is important to note that whether using Rad-57 for routine CO screening or COHb blood testing in the hospital, a level of CO means almost nothing without a correlating physical examination.
Any patient with symptoms consistent with CO poisoning should be placed on high-flow oxygen and transported for formal laboratory evaluation and thorough workup at the emergency department. Any fire victims or exposed responders with altered mental status should be assumed to have high CO and cyanide levels and need to be aggressively treated.
ETCO2
Carbon dioxide along with water and ATP are produced as a byproduct of cellular metabolism as our bodies consume oxygen and glucose. Following its production, CO2 is transported in the blood and is exhaled through the lungs, where it provides a convenient source to be measured. CO2 measured at the end of an exhaled breath is known as ETCO2.
Basic physiology dictates that as the body becomes more acidic, the carbonic acid buffering system balance shifts toward producing more CO2. A normal ETCO2 is between 35-45 mm Hg. Quantitative ETCO2 is directly related to cardiac perfusion, with a decrease in perfusion leading to a lower ETCO2. A patient with low cardiac output from any number of shock states does not deliver as much CO2 back from the bloodstream to the lungs to be exhaled, which subsequently results in decreased ETCO2 levels.
The use of capnography to measure ETCO2 has been gaining popularity in EMS, with applications from intubation confirmation to sepsis detection. Use of ETCO2 has long been the standard for ventillatory monitoring during anesthesia and procedural sedation.
It is not unrealistic to see ETCO2 utility in firefighter rehab as more and more ALS and BLS services use this technology on a routine basis.
In addition to the quantitative number that is generated, the capnography waveform can also be used to assist in diagnosis of the firefighter in rehab. A bronchospasm waveform is characterized by changes in the ascending phase with loss of the sharp upslope resulting in a shark fin appearance. This is due to uneven emptying of CO2 by the alveoli during exhalation. Correlated with a physical exam, this measurement can also be used to guide treatment and the response to treatment in the firefighter with bronchospasm.
Finally, when using quantitative capnography a respiratory rate is displayed, which can assist in quickly gathering and trending vital signs of firefighters who present to rehab. This saves time and resources over counting respirations, which is frequently inaccurate and time-consuming.
Use of ETCO2 can be an excellent diagnostic aid in the rehab sector of firefighting operations, but remember that diagnostic tests, regardless of their ability and value, must be interpreted in the context of the patient's clinical picture.
Conclusion
The assessment of anyone going through the rehab process should be dictated primarily by patient history, physical exam and field-proven point-of-care testing. It is unlikely that on-scene labs will be used routinely in the rehab sector unless costs decrease considerably. Pulse oximetry, EKG, ETCO2 and CO oximetry will likely continue to be the mainstays of rehab operations for some time to come.
Having formal rehab protocols, sign-in sheets, individual accountability and the support of incident commanders is crucial to rehab operations. Once in rehab, the responders become the responsibility of those running rehab.
EMS providers who are responsible for rehab operations should be familiar with local EMS protocols and NFPA 1584. In the event that a specific protocol does not cover a condition encountered on scene, medical direction should be contacted and transport initiated. We need to take a conservative approach to protecting the well-being and lives of our responders.
References
1. Hunter et al: End-tidal carbon dioxide is associated with mortality and lactate in patients with suspected sepsis. American Journal of Emergency Medicine (2013) 31, 64–71
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