What is the pathophysiology of neurogenic pulmonary edema (NPE)?

From the Guidelines

Neurogenic pulmonary edema (NPE) should be managed with mechanical ventilation and supportive respiratory care, focusing on treating the underlying neurological condition, as it occurs in up to 20% of aneurysmal subarachnoid hemorrhage (aSAH) patients, with a high risk of requiring mechanical ventilation 1. The condition is characterized by acute fluid accumulation in the lungs following a central nervous system injury, such as aSAH, and typically occurs within minutes to hours after the insult. Key aspects of management include:

• Supplemental oxygen
• Mechanical ventilation if needed, with positive end-expiratory pressure (PEEP) of 5-15 cmH2O to improve oxygenation
• Maintaining the head of bed elevated at 30-45 degrees
• Diuretics like furosemide (20-40mg IV) to reduce fluid overload, used cautiously to avoid hypotension
• Blood pressure management, with mean arterial pressure maintained between 65-110 mmHg using vasopressors or antihypertensives as needed. The pathophysiology of NPE involves a massive sympathetic discharge following the neurological injury, causing increased pulmonary vascular permeability and hydrostatic pressure from systemic vasoconstriction, leading to protein-rich fluid leaking into the alveoli and impairing gas exchange 1. Most cases of NPE resolve within 48-72 hours with appropriate management of the underlying neurological condition, though mortality remains high due to the severity of the precipitating neurological event, with 18-50% of patients with aSAH experiencing acute respiratory distress syndrome (ARDS) 1.

From the Research

Definition and Characteristics of Neurogenic Pulmonary Edema

• Neurogenic pulmonary edema (NPE) is characterized by acute respiratory distress triggered by acute, severe compromise of the central nervous system (CNS) 2.
• It is defined as acute respiratory distress triggered by severe sympathetic discharge from acute compromise in the central nervous system 3.
• NPE produces a capillary-aveolar block resulting in hypoxia complicating the underlying neurologic condition 4.

Causes and Triggers of Neurogenic Pulmonary Edema

• The most common cerebral triggers of NPE include enterovirus-71-associated brainstem encephalitis, subarachnoid bleeding, intracerebral bleeding, traumatic brain injury, epilepsy, ischemic stroke, intracranial/spinal surgery, multiple sclerosis, electroconvulsive therapy, subdural/epidural hematoma, intoxication, hypoxia, and hydrocephalus 2.
• Head injuries and craniotomy can also cause NPE 5.
• Traumatic brain injury is a significant cause of NPE 3, 6.

Clinical Symptoms and Diagnosis of Neurogenic Pulmonary Edema

• Clinical symptoms of NPE include the sudden onset of coughing, tachypnea, tachycardia, and pink bubbly sputum 5.
• Patients may also suffer from cyanosis, confusion, or respiratory failure 5.
• Diagnosis involves identifying signs of pulmonary edema in patients who experienced a neurologic insult 6.
• NPE is diagnosed in the presence of pink, frothy sputum, pulmonary edema, bilateral opacities on X-ray, PaO2:PiO2 <200 mm Hg, acute CNS compromise with increased intra-cranial pressure, rapid resolution within 48-72 h, and the absence of alternative causes of respiratory distress 2.

Treatment and Management of Neurogenic Pulmonary Edema

• Treatment of NPE includes reducing intracranial pressure, diuresis, narcotics, and blocking the peripheral effect of sympathetic reflex activity 5.
• Mechanical ventilation support and controlled hyperventilation may also be necessary 5.
• Positive end-expiratory pressure (PEEP) should be carefully applied to balance recruitment of alveoli and minimisation of ICP 3.
• Management strategies aim to address both brain and lung injury, and treatment modalities appear to work best when balanced toward maintaining a normal physiologic state 6.

Outcome and Prognosis of Neurogenic Pulmonary Edema

• The outcome of NPE has improved with the application of intensive care measures 2.
• However, prognosis is generally poor due to the severity of the underlying brain injury, with estimated mortality rates of between 60 and 100% 3.
• Early diagnosis and intensive care of the pulmonary edema may have a significant bearing on the recovery of lung functions 5.