Acute pulmonary edema, therefore, may likely be less of a fluid volume problem than a fluid distribution problem. There may be no excess accumulation of fluid needing to be diuresed; it is simply in the wrong place and needs to be distributed properly. Some patients are overhydrated, but it is difficult to determine that by physical examination. At any rate, diuretics are now seen as an intervention best saved for those patients who do not respond to nitroglycerin.6
Since APE is a volume distribution problem, administration of furosemide provides no immediate benefit for most patients. Administration of furosemide carries the potential for hypokalemia, arrhythmias and increased systemic vascular resistance through enhancement of the RAAS, all of which may be deleterious to the acute CHF patient. Administration of furosemide to patients who really have COPD or pneumonia, rather than APE, can be especially harmful.
Evolution in APE Treatment
In recent years, intravenous administration of morphine sulfate and furosemide for acute pulmonary edema has given way to aggressive administration of nitrates. Prehospital administration of intravenous nitroglycerin infusion and graduated dosing protocols, allowing much higher doses of sublingual nitroglycerin in severely hypertensive patients (often doses of 1.2 grams or more for patients with systolic BP > 170), have proven highly effective at reversing acute pulmonary edema.
In one comparison of prehospital APE protocols, the study authors concluded that nitroglycerin alone was beneficial, while concomitant administration of morphine and furosemide provided no added benefit, and in some cases was harmful.7
Non-invasive positive pressure ventilation (NIPPV), or as it was once called, CPAP, has long been an effective adjunct in the ED and ICU for emergent treatment of acute pulmonary edema, but until recent years the devices were too expensive and complex to see much prehospital use. However, recent technological advances have resulted in affordable mechanical NIPPV flow generators, which are easy to use and rugged enough for prehospital use. There are even a wide variety of disposable NIPPV/CPAP systems specifically designed for EMS.
Aggressive administration of nitroglycerin, coupled with the rapid proliferation of prehospital NIPPV, has resulted in far less need for morphine and furosemide in treatment of acute CHF. While morphine still has a place as an effective analgesic, furosemide has been pushed to the back of the drug box to gather dust until it reaches its expiration date. Increasingly, EMS systems are relegating furosemide to medical command order only, or removing it from protocols entirely.
While current prehospital treatment of acute CHF, even in those patients suffering from volume overload, focuses on vasodilation with nitrates and alveolar recruitment with NIPPV, there are diagnostic tools and treatment options on the horizon that may creep into prehospital care.
ACE inhibitors such as captopril have shown promise in the emergent treatment of acute CHF, and sublingual captopril given in conjunction with nitroglycerin has been shown to significantly reduce APE distress scores within 40 minutes of administration.3
Administration of furosemide first requires diagnosis of volume overload, which usually requires laboratory testing of renal function and B natriuretic peptide (BNP). BNP is secreted by the myocardial muscle cells in response to excessive stretching of heart muscle cells, and is a definitive diagnostic indicator for congestive heart failure. Measurement of BNP is vital in differentiating CHF from pneumonia or COPD exacerbation.
While traditional laboratory testing is out of the reach of almost all EMS systems, technological advances have resulted in small and rugged point-of-care test meters capable of rapidly yielding quantitative lab results, including those for BNP and renal function. The only issue now is price, and that is steadily falling.
Is There Still a Place for Furosemide?
Diuresis is still indicated for CHF patients suffering from volume overload, so it is unlikely furosemide will disappear entirely. However, while a certain percentage of acute pulmonary edema patients suffer from volume overload, that percentage is fairly small, and treatment with nitrates and NIPPV is usually sufficient to stabilize the patient in the prehospital realm.