Furosemide in the Treatment of Acute Pulmonary Edema
- Jan 22nd, 2014
- Anand Swaminathan
Anand Swaminathan, MD, MPH (@EMSwami) is an assistant professor and assistant program director at the NYU/Bellevue Department of Emergency Medicine in New York City.
A 55-year-old man with a history of congestive heart failure (CHF) and hypertension (HTN) presents with worsening shortness of breath over the last 2 days. Vital signs are:
HR: 132, BP: 210/110, RR: 35, O2Sat: 83%
The patient is in severe respiratory distress. A quick bedside ultrasound reveals numerous B lines. Supplemental oxygen is started and the patients O2 sat increases to 86%. An IV is placed and an EKG reveals sinus tachycardia. A nurse begins to draw up furosemide but you consider other options.
CHF is a common problem in the US with over 5 million patients carrying the diagnosis and 500,000 new diagnoses each year.1 Cardiogenic acute pulmonary edema (APE) occurs when blood backs up into the pulmonary vasculature leading to increased oncotic pressure and leakage of fluid into the alveolar spaces. Essentially, patients are drowning. APE patients suffer from both increased afterload: making it more difficult for the left ventricle to function, and increased preload. As such, the goals of treatment must be directed at both decreasing cardiac filling pressures (preload) and decreasing afterload. Additionally, neurohormonal activation worsens cardiac performance, increases intravascular volume, and increases vascular tone. For decades, the mainstay of treatment in APE has been loop diuretics: mainly furosemide. The continued central role these drugs play highlights a lack of understanding of the underlying pathophysiology of the disease.
Pathophysiology of APE
In the 1940s the cardiorenal model was first put forward as the predominant explanation for APE. It was believed that decreased blood flow to the kidneys led to decreased renal function and fluid retention leading to volume overload. This was the basis for loop diuretics being recommended. However, it was clear that this model was insufficient as it did not explain why the disease progressed or the finding of increased peripheral vasoconstriction from invasive monitoring studies.
The cardiocirculatory model was first put forth in the 1970s. This model argued that peripheral vasoconstriction led to decreased cardiac function and that increased preload and afterload were at the center of the problem. This model explained much of what we see occurring in APE.
Finally, in the 1990s, researchers established the neurohormonal model. In this model neurohormones (norepinephrine, renin, angiotensin, aldosterone) are upregulated in APE. These compounds have vasoactive properties leading to vasoconstriction and increase intravascular volume. Current recommendations for APE treatment are based on the integration of the cardiovascular and the neurohormonal models.
Why Not Loop Diuretics?
The idea of using loop diuretics is based on the idea that patients with vascular congestion are volume overloaded. Let’s look at the actual literature here.
Urban Legend: Patients presenting with APE are volume overloaded.
Zile MR et al. demonstrated that while most patients with APE have increased cardiac filling pressures, most did not have a significant increase from their dry weight on presentation.2
50% of patients had a minimal weight gain (< 2 lbs) on presentation for APE.3
Fallick C et al. argue that it isn’t fluid gain but rather shift in fluids from other compartments, particularly shift from the splanchnic circulation, which is normally very compliant.4
Bottom line: Vascular congestion does note equal volume overload. More than 50% of cases of APE are not associated to significant volume overload.
However, many argue that even in the absence of volume overload, there’s so little downside to giving a dose of furosemide that we should just do it.
Urban Legend: Loop diuretics are not harmful in APE so just give them.
Hoffman JR and Reynolds S showed that patients who got furosemide and or morphine for APE had more complications.5 However, the study was small (n = 57) and had multiple treatment arms.
Francis GS et al. described how administration of furosemide actually led to decreased LV function, increased LV filling pressures, increases in MAP, SVR, plasma renin activity, and plasma norepinephrine levels.6 Essentially, furosemide led to activation of the neurohormonal system instead of turning it off.
Kraus PA et al. demonstrated that PCWP was increased for the first 20 minutes after administration of furosemide.7
Finally, Marik PE et al. summarizes the evidence. Furosemide decreases GFR, activates the renin-angiotensin-aldosterone system, decreases cardiac output, and increases afterload early after administration.8
Bottom Line: Loop diuretics are harmful early in the management of APE.
The first 10 minutes of management for these patients is key so any increases in afterload, preload etc are going to be extremely detrimental.
And let’s not forget that many of our patients with APE have ESRD where no dose of loop diuretic will ever make them diurese. If we aren’t using loop diuretics, what should we be doing?
Non-Invasive Positive Pressure Ventilation (NIPPV)
NIPPV has multifactorial action in APE. It decreases work of breathing, stents open alveoli during the entire respiratory cycle leading to improved gas exchange and, in the case of bilevel NIPPV, decreases afterload.
A number of papers have shown decreased intubation rates and decreased ICU utilization with the use of NIPPV. The most recent study showed a decreased ICU admission from 92% to 38%.9
The key for NIPPV is to start it immediately on presentation to the ED. Even if it doesn’t stave off intubation, it will likely help with preoxygenation.
There are many studies looking at the use of nitroglycerin10, comparing it to fuorsemide11 and looking at high-dose therapy12.
The bottom line is that nitro is recommended for all patients with APE. It reduces preload and at higher doses (> 100 mcg/min) it decreases afterload leading to increased cardiac output and decreased SVR.8
Overall, ACEI have been less studied in APE. The proposed role here is shutting of the renin-angiotensin-aldosterone system and decreasing the neurohormonal drive.
Hamilton RJ et al. found that patients who received sublingual captopril in addition to standard therapy were more comfortable and had a decrease in respiratory failure (not statistically significant).13
Haude M et al. demonstrated in a small study that sublingual captopril improved cardiac index and stroke volume versus nitroglycerin.14
1. There’s minimal or no role for the administration of loop diuretics early in the management of APE. The majority of patients aren’t volume overloaded.
2. Immediate care should focus on NIPPV and administration of nitroglycerin.
3. In patients with ESRD, dialysis is what’s ultimately going to fix the patient.