ACUTE RESPIRATORY DISTRES SYNDROME (ARDS)
الدكتور خلدون ذنون- كلية طب نينوى- المرحلة الرابعةObjectives
Concentrate on the following:1. ARDS is an acute medical emergency that needs ventilatory support.
2. Pathology: acute lung tissue inflammation.
3. Diagnosis: hypoxia and normal left atrial pressure.
4. Causes: aspiration, gases, infection, trauma, drugs, embolism etc....
5. Features: dyspnea and cyanosis.
6. Management: supportive and mechanical ventilation.
7. Mortality: 40%
Definition
Acute condition characterized by bilateral pulmonary infiltrates and severe hypoxemia in the absence of evidence for cardiogenic pulmonary edema.Frequently associated with other organ dysfunction e.g kidney, heart, gut, liver, coagulation, CNS.
Patients with ARDS require ventilatory support on ICU.
Conditions predisposing to ARDS
A. Inhalation (Direct)Aspiration of gastric content
Toxic gases / burn injury
Pneumonia
Blunt chest trauma
Near drowning
B. Blood borne (Indirect)
Sepsis
Necrotic tissue (particularly bowel)
Multiple trauma
Pancreatitis
Cardiopulmonary bypass
Severe burns
Drugs e.g heroin ,barbiturates , thiazides
Major blood transfusion reaction
Anaphylaxis ( wasp, bee & snake venom)
Fat embolism
Carcinomatosis
obstetric crises (amniotic fluid embolism, eclampsia)
Pathophysiology
A. Exudative phase:
Injury to alveolar-capillary endothelial cells & type 2
Pneumocytes leading to surfactant depletion,(inflammatory cytokines,
pulmonary vascular injury, alveolar edema, neutrophil infiltration,
formation of hyaline membrane from diffuse alveolar damage,
atelectasis, may last 7 days.
B. Proliferative phase:
prominent interstitial inflammation&early fibrotic changes, most
patient recover rapidly, last from day 7-day 21.
C. Fibrotic phase
After 3 weeks, substantial fibrosis & bullae formation.
Clinical features
Underlying conditions.
Dyspnea, cyanosis, chest crepitations.
Features of organ dysfunction.
Diagnosis (Criteria defining ARDS)
Hypoxaemia pa02(mm Hg)/Fi02 =< 200 mm Hg (26.7 kpa)Chest radiograph: diffuse bilateral infiltration.
Left atrial filling pressure ( PAWP) < 15 mm Hg.
Impaired lung compliance.
Management
Treatment of underlying condition (sepsis, aspiration, trauma)Prophylaxis against venous thromboembolism, GIT bleed, CNS catheter infection.
Recognition of nosocomial infection.
Adequate nutrition: Enteral nutrition via a feeding tube is preferable to IV hyperalimentation unless it is contraindicated because of an acute abdomen, ileus, GI bleeding, or other conditions
HYPERLINK "https://emedicine.medscape.com/article/165139-treatment" Noninvasive Ventilation and High- HYPERLINK "https://emedicine.medscape.com/article/165139-treatment" Flow Nasal Cannula, provided that patient is alert, has no vomiting or hematemesis.
Mechanical ventilation 1. PEEP (positive end expiratory pressure): use minimal amount of pressure (12-15 mm Hg) to avoid further lung injury, keep FI02 ( 0.6, Pa02 55-80 mm Hg saturation 88-95%. 2. PEEP prevent alveolar collapse, minimize FI02 , avoid high
conc. 02 toxicity, maximize pa02.
3. Low tidal volume 6ml / kg of ideal body wt., (mortality to 31%,
with 12 ml mortality 40%.4. High frequency ventilation & extracorporeal membrane
oxygenation (ECMO): improves survival in neonatal and
selected adult patients with ARDS.
Fluid management Maintain normal or low left atrial filling pressure < 15 mm Hg, which minimize pulmonary edema, prevent (in arterial 02 & lung compliance.
Some 70% of patients with ARDS have significantly improved oxygenation when turned from the supine to the prone position.
Corticosteroid Current evidence does not support their use. If patient fails to respond after 1 week of supportive therapy & have no c/i to steroid, then it can be used empirically.
Prognosis
Mortality 40% in best centers.Death mainly due to non-pulmonary causes e.g sepsis, organ failure, advanced age, chronic medical conditions, chronic alcoholism, and immunosuppression.
Experience prolonged respiratory failure & depend on mechanical ventilation.
Majority of survivors recover normal lung function with in 6 months.
Significant rate of depression & post traumatic stress disorder.