9 - ARDS

acute respiratory distress syndrome (ARDS)

diffuse damage to alveolar-capillary membrane

• causes non-cardiac pulmonary edema and hypoxemia

• bilateral opacities not explained by other pathology

• respiratory failure not explained by HF or fluid overload

onset of ARDS

within 1 week of other clinical manifestation or worsening respiratory symptoms

etiology of ARDS

• direct

• pneumonia

• toxins/irritants

• O₂ toxicity

• pulmonary ischemia

• radiation

• pulmonary contusion

• fat/air emboli

• post-cardiac bypass edema

etiology of ARDS

• indirect

• infection

• trauma

• drug overdose

• immune reaction

• CNS disease

• DIC

• acute pancreatitis

pathology of ARDS

1. inflammation

2. neutrophil proliferation

3. capillary engorgement

4. increased permeability

   • type I cell damage

   • hemorrhage

   • hyaline membrane formation

   • type II cell swelling and hyperplasia

   • microthrombi

   • decreased surfactant

   • atelectasis

manifestations of ARDS

• progressive dyspnea

• tachycardia

• tachypnea

• hypertension

• decreased lung compliance

• retractions

• cyanosis

• dull percussion

• bronchial sounds

• crackles

clinical findings for ARDS

PFTs

• restrictive pattern

• decreased diffusion

hemodynamics

• PHTN

• normal/decreased BP

categories of ARDS based on P_aO₂/F_iO₂ (p/F) ratio

mild	201-300
moderate	101-200
severe	≤ 100

formula for O₂ index

\frac{MAP\cdot F_{i}O_2}{P_{a}O_2}\cdot100

stages of ARDS injury

1. exudative

• interstitial edema

• inflammation

• hyaline membrane

stages of ARDS injury

2. proliferative

• edema resolution

• reproduction of type II alveolar cells

• restoration of epithelial and endothelial barriers

stages of ARDS injury

3. fibrotic (does not always occur)

• fibrosis

• cyst formation

ARDSNet (now TULIP)

organization that creates ARDS protocol

general management of ARDS

• treat cause

• support hemodynamics

• O₂

• lung expansion (PEEP/CPAP)

• ventilation

  • low V_T (4-6 mL/kg)

  • RR < 35

  • P_plat < 30

  • permissive hypercapnia

other treatments for ARDS

• ECMO

• medication

  • anti-inflammatories

  • antioxidants

  • vasodilators (ie, iNO)

  • neuromuscular blockers

• proning

• fluids

• nutrition

• mobility

outcomes for ARDS

• 40% mortality

  • 1/3 within 72 hours

  • usually due to sepsis or multi-system organ failure

• 1 year post-ARDS

  • PFT normal/mild restriction

  • diffusion defects

• low quality of life

  • cognitive issues

  • PTSD?