acute respiratory distress syndrome (ARDS)

acute respiratory distress syndrome (ARDS)

sudden progressive form of acute respiratory failure

• alveolar capillary membrane becomes damaged and more permeable to intravascular fluid which results in

  • severe dyspnea

  • hypoxemia refractory to supplemental oxygen

  • reduced lung compliance

  • diffuse pulmonary infiltrates

direct causes of ARDS

• aspiration of gastric contents

• fat embolism

• inhalation of toxic gases

• multisystem trauma (chest and/or lung injury)

• pneumonia

• near-drowning

indirect causes of ARDS

• bruns

• cardiopulmonary bypass

• drug overdose

• fractures, especially pelvis/long bones

• multiple transfusions

• multisystem trauma (w/o chest or lung injury)

• pancreatitis

• sepsis

ARDS pathophysiology

lung becomes remodeled by collagenous and fibrous tissues d/t interstitial and alveolar edema resulting in decreased lung compliance and decreased surface area for gas exchange

clinical course of ARDS

• differs between patients

• some recover within a week as lung swelling goes down

• others enter fibrotic stage that leads to

  • need for long-term ventilation

  • has a lower chance of survival

• unclear why some recover while others get worse

ARDS diagnostic studies

• CXR

  • initially → may be normal

  • with progression → often shows diffuse and extensive bilateral interstitial and alveolar infiltrates

• ABGs

  • initially → mild hypoxemia and respiratory alkalosis caused by hyperventilation

  • with progression → refractory hypoxemia key sign of ARDS, increasing CO2 levels indicate muscle fatigue and poor gas exchange

• P/F ratio

  • evaluates severity of hypoxemia in ARDS

  • reflects ratio of patients paO2 to FIO2 that patient is receiving

initial symptoms of ARDS

• mild dyspnea

• tachypnea

• cough

• restlessness

• fine scatter crackles on asucultation

progressive symptoms of ARDS

• increased WOB

• intercostal and suprasternal retractions

• diaphoresis

• mental status changes

• may see cyanosis or pallor

• auscultation reveals scattered to diffuse crackles and course crackles

complications of ARDS

• death r/t MODS/sepsis

• infection - catheter related

• respiratory - O2 toxicity, barotrauma, PE, pulmonary fibrosis, VAP

• GI - paralytic ileus, pneumoperitoneum, ulcer, hemorrhage'

• renal - AKI

• cardiac - decreased CO, dysrhythmias

• hematologic - anemia, DIC, thrombocytopenia, VTE

• endotracheal tube - laryngeal laceration, tracheomalacia, stenosis, or ulceration

• CNS/psychologic - delirium, PTSD, sleep deprivation

abnormal lung function with ARDS

• most patients recover within 6 months

• abnormal lung function can persist years/be permanent

  • scarring and changes within lungs r/t mechanical ventilation, duration of time ventilated, extracorporeal life support

• patients report extreme fatigue, chest pain, SOB after minimal activity, persistent dyspnea

ARDS goals

• paO2 within normal limits for age or baseline values on room air

• O2 sats greater than 90

• patent airway, clear lungs on auscultation

collaborative care of ARDS: respiratory support

• oxygen therapy

  • nasal cannula or facemask with high flow systems that deliver high oxygen concentrations

  • give lowest concentration of required to keep paO2 60 or greater

    • FIO2 >60% for more than 48 hours increases risk of oxygen toxicity

  • patients with severe ARDS and refractory hypoxemia → intubation/mechanical ventilation

• mechanical ventilation

  • endotracheal intubation and PPV → when hypoxemia does not respond to initial treatment

    • use of PEEP keeps lungs partially expanded and prevents total collapse of alveoli

• prone positioning or continuous turning

collaborative care of ARDS: hemodynamic monitoring

• patients receiving PPV and PEEP frequently experience decreased CO, monitoring is essential to see trends, detect changes, and adjust therapy as needed

  • A-line → inserted for continuous monitoring of blood pressure and drawing ABG values

  • use of inotropic drugs → dobutamine or dopamine, may be necessary

collaborative care of ARDS: fluid balance

• parenteral/enteral feedings; fluid restriction due to possible pulmonary edema, monitor fluid status closely

collaborative care of ARDS: analgesia and sedation

• decrease discomfort associated with ET tube, reduce WOB, prevent ventilator dyssynchrony

• asynchronously breathing with mechanical ventilation may benefit from an adjustment of ventilator or may need neuromuscular blocking agent

  • vecuronium → relax skeletal muscles and promote synchrony with mechanical ventilation

    • can appear to be asleep, but still be awake and in pain

    • simultaneous administration of analgesia and sedation with NMBAs is essential

collaborative care of ARDS: maintaining CO and tissue perfusion

• administer fluids/inotropic meds as prescribed

• PRBCs

• closely monitor VS

• hemodynamic monitoring

collaborative care of ARDS: fluid balance and nutrition

• monitor intake and output hourly

• keep ARDS patient on dry side → patients typically have WOB because alveoli, lungs, and spaces between alveoli are partially or completely fluid filled

• maintaining protein and energy stores → nutritional depletion causes loss of muscle mass

• ideally, enteral or parenteral nutrition → initiate within 24-48 hours