Regarding Acute Pulmonary Edema

Regarding Acute Pulmonary Edema, answer the following questions:

1. What are the two most common underlying mechanisms of pulmonary edema?
2. What are the most common causes of acute cardiogenic pulmonary edema?
3. What is the immediate treatment of acute cardiogenic pulmonary edema?

Answers:

1. What are the two most common underlying mechanisms of pulmonary edema?
Acute pulmonary edema can have a cardiogenic or noncardiogenic etiology.
In cardiogenic pulmonary edema, a high pulmonary capillary pressure is responsible for the transudation of protein-poor fluid into the lungs caused by an imbalance of Starling's forces. With acute rises in pulmonary capillary pressure, the pulmonary lymphatics cannot rapidly increase the rate of fluid removal; as a result, pulmonary edema occurs.

Noncardiogenic pulmonary edema is caused by altered alveolar capillary permeability due to acute lung injury. Transudation of fluid into the alveolar space is not dependent on an elevated pulmonary capillary wedge pressure but is exacerbated by an elevated pulmonary capillary pressure.
The disorders most frequently resulting in increased permeability pulmonary edema are the acute respiratory distress syndrome (ARDS) and, less commonly, high altitude and neurogenic pulmonary edema.

2. What are the most common causes of acute cardiogenic pulmonary edema?
The most common causes of acute cardiogenic pulmonary edema are :

• Acute ischemia and 
• Accelerated hypertension, 

both causing a sudden increase in left ventricular end-diastolic pressure. Both etiologies result in a stiff left ventricle and decreased diastolic ventricular compliance, impairing ventricular filling during diastole (diastolic dysfunction). Systolic dysfunction may also occur.

Other causes of acute cardiogenic pulmonary edema include

• Acute mitral regurgitation such as might result from acute ischemia or a ruptured chordae tendinea Infectious endocarditis, 
• Discontinuation of antihypertensive medications. 

Acute pulmonary edema may be precipitated by rapid atrial fibrillation or other dysrhythmias. Infection, physical or environmental stresses, changes or noncompliance w ith medical therapy, dietary indiscretion, or iatrogenic volume overload are less common, but important, causes.

3. What is the immediate treatment of acute cardiogenic pulmonary edema?
The immediate treatment of acute cardiogenic pulmonary edema should consist of oxygen therapy to maintain an oxygen saturation within the normal range (95% to 98%), noninvasive positive-pressure ventilation if oxygen saturation remains low [i.e., continuous positive airw ay pressure (CPAP) or bi-level positive airway pressure (BiPAP)], IV diuresis with furosemide or other loop diuretics, IV morphine, and IV vasodilators with NTG, nitroprusside, or angiotensin-converting enzyme (ACE) inhibitors.
The patient should be sitting upright unless hypotension is present. If the patient has an ACS, therapy should be dominated by intervention to minimize ischemic injury. If the acute pulmonary edema is associated with shock, IV inotropic drugs such as milrinone or dobutamine may be necessary.
If severe hypertension is present, IV nitroprusside or other rapidly acting agents such as labetalol should be given to low er systemic blood pressure. Noninvasive positive-pressure ventilation with CPAP or BiPAP has been shown to reduce the need for invasive mechanical ventilation in patients with acute cardiogenic pulmonary edema and even to reduce mortality compared with standard therapy (oxygen by face mask, diuretics, and nitrates); the same has been show n in a recent meta-analysis study.