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Pathophysiology

병태생리학

Increased hydrostatic pressure in the pulmonary vessels creates an imbalance in the starling forces, resulting in an increase of fluid filtration into the interstitial spaces of the lung that exceeds the lymphatic capacity to drain the fluid away. Increasing volumes of fluid leak into the alveolar spaces (Figure 65-1). The lymphatic system at volume through the hilar lymph nodes and back into the vascular system. If this pathway becomes overwhelmed, fluid moves from the pleural interstitium into the alveolar walls. If the alveolar epithelium is damaged, the fluid begins to accumulate in the alveoli. Alveolar edema is a serious late manifestation in the progression of fluid imbalance.

Hypoxemia develops when alveolar membrane is thickened by fluid that impairs the exchange of oxygen and CO₂. As fluid fills the interstitium and alveolar spaces, lung compliance decreases and oxygen diffusion is impaired. If pulmonary edema has developed because of left ventricular failure, right ventricular failure may occur because the pulmonary artery pressure is elevated. This elevation increase afterload for the right ventricle, resulting in manifestations of right ventricular failure.

Clinical Manifestations

The manifestations of pulmonary edema are due to failure of the regulatory factors guiding fluid movement. Most manifestations are seen in the respiratory system and include marked dyspnea, tachypnea, weak and thready tachycardia, hypertension (if cardiogenic), orthopnea at less than 90 degrees, and the use of accessory muscles.

 The client's frequent coughing is an attempt to rid the chest of fluid. The sputum is thin and frothy because it is combined with water. If the hydrostatic pressure is very high, small capillaries break and sputum becomes pink tinged. The client may be anxious from dyspnea and restless from hypoxemia. Chest auscultation reveals crackles, wheezes, and the presence of an S₃ heart sound. A heart murmur may be noted if the cause is mitral valve disease. Pulse oximetry readings are commonly less than 85% and arterial blood gas(ABG) determinations may reveal an arterial PaO₂ of less than 50mmHg. Respiratory alkalosis is common because of the tachypnea. Pressure in the pulmonary artery and pulmonary artery wedge pressure (PAWP) are elevated. The chest x-ray shows areas of "whiteout" where fluid has replaced air-filled lung tissue, which normally appears black. Right ventricular failure may also be noted, with manifestations of hepatomegaly, jugular venous distention, and peripheral edema.

Outcome Management

■ Medical Management

Medical management concentrates on four areas:

(1) correction of hypoxemia, (2) reduction in preload,

(3) reduction of afterload, and (4) support of prefusion.

Correct Hypoxemia. It is imperative to maintain adequate oxygenation. Client with severe pulmonary edema commonly require oxygen therapy at high Fio₂ levels and may require noninvasive positive pressure ventilation (NPPV) such as continuous positive airway pressure (CPAP) or mechanical ventilation if they cannot meet the work of breathing. NPPV is any type of respiratory support that does not require endotracheal tube (ET) intubation.

Reduce Preload. The client is placed in an upright position. Usually, the client does not lie down because of orthopnea and a feeling of choking when supine. Diuretics are prescribed to promote fluid excretion. Nitrates, such as nitroglycerin, are used for their vasodilating properties. Other management strategies consist of treating the underlying condition.

Reduce Afterload. Afterload is reduced to  diminish workload on the left ventricle. Antihypertensive agents, including potent agents such nitroprusside, are prescribed. Morphine is prescribed to reduce the sympathetic nervous system response and to reduce anxiety from the dyspnea.

Support Perfusion. The left ventricle is supported by using inotropic medications such as dobutamine. Urine output is monitored closely to determine whether renal (IABP)  may be required with severe heart failure and pulmonary edema (see Chapter 57)

■ Nursing Management

Assessment

The client with pulmonary edema is assessed quickly on admission, concentrating on only the information and assessment findings essential to begin treatment. The client is typically anxious and having significant shortness of breath. Managing the client's anxiety and reducing the dyspnea is imperative. A complete assessment is carried out over the following hours, when the client can baseline weight and lung assessment is essential, because these parameters will assist in determining treatment effectiveness.

Diagnosis, Outcomes, Interventions

Diagnosis: Impaired Gas Exchange. The fluid-filled alveoli retard the exchange of gases. Use the nursing diagnosis Impaired Gas Exchange related to capillary membrane obstruction from fluid to plan care.

Outcomes. The client will demonstrate improved gas exchange, as evidenced by rising PaO₂to 55 or 60 mmHg, oxygen saturation above 90%, normalizing pH, decreasing anxiety and dyspnea, and fewer crackles and wheezing within 12 hours.

Interventions. Monitor vital signs every 15 minutes initially, until the client is stable. Administer oxygen as ordered using a high-flow rebreather bag to maintain oxygenation. Titrate the actual liter flow of oxygen to maintain saturation above 90%. Continuous assessment is needed because the client may require NPPV or endotracheal (ET) intubation and mechanical ventilation. NPPV, mechanical ventilation, and intubation equipment should readily available. To reduce preload, position the client with the legs in a dependent position. Raising edematous legs increases venous return and will stress the overtraxed left ventricle. Preload is reduced with morphine and nitroglycerin. Because perfusion to the skin is often compromised, repositioning is important.

 Air hunger can lead to panic and feelings of suffocation. Administering opioids (morphine) and anxiolytics and improve breathing. Stay with the client and use breathing techniques to support the client.

Diagnosis: Excess Fluid Volume. Accumulation of fluid from several causes leads to fluid from several causes leads to fluid overload. Use the nursing diagnosis Excess Fluid Volume related to excess preload.

Outcomes. The client will demonstrate improved fluid balance, as evidenced by diuresis (input less than output), decreased number of crackles and wheeze, eupnea, weight loss, resolving peripheral edema, and decreased anxiety.

Interventions. Administer a diuretic (furosemide) as prescribed to promote diuresis. Place an indwelling catheter to monitor response to diuretics. Monitor urine output, weight, and potassium levels (potassium loss is a side effect of furosemide). Monitor blood pressure to determine whether the client can maintain perfusion without inotropic support. Because oral fluids are restricted, oral care is completed every 2 hour.

e-valuation

평가

If the previously described interventions are implemented immediately, a fairly rapid response to diuresis and oxygen therapy should be seen.

이전에 기술된 내정간섭이 즉각 실행되는 경우에, 이뇨와 산소 치료에 상당히 급속한 응답은 보여야 한다.

■ Self-Care

Consider the reasons for development of pulmonary edema when developing a plan for self-care. Clients may need further education on daily weight, dietary choices, and scheduling of medications. Instruct the client and family members on the early manifestations of fluid overload so that early intervention is possible.