Unit 2: Acute Respiratory Distress Syndrome (ARDS) Flashcards
Epidemiology: Acute Respiratory Distress Syndrome
- high mortality rate
- life-threatening
- death d/t multiple organ dysfunction bought on by hypoxia and/or infection
Most Common cause of ARDS
sepsis
Direct Causes of ARDS
damage or disruption of the respiratory system
- aspiration
- chest trauma
- pneumonia (infectious or aspiration)
- pulmonary contusion
- inhalation injury (smoke; toxins)
- pulmonary embolus
Indirect Causes of ARDS
processes or disorders that occur outside the respiratory system but have deleterious effect on the lungs
- sepsis, shock
- pancreatitis
- multiple blood-transfusions; transfusion-related acute lung injury (TRALI)
- cardiopulmonary bypass
- drug/alcohol overdose
How is ARDS Defined?
- acute onset of less than 7 days
- refractory hypoxemia
- bilateral infiltrates ruling out cardiac pulmonary edema as the cause
ARDS Severity
based on PaO2/FIO2 ratio
- Mild ARDS
- Moderate ARDS
- Severe ARDS
Mild ARDS
PaO2/FIO2 ratio: 200-300 on ventilator settings that include positive end-expiratory pressure (PEEP) or continuous positive airway pressure (CPAP) >5 cm H2O
Moderate ARDS
PaO2/FIO2: 100-200 on ventilator settings that include positive end-expiratory pressure (PEEP) >5 cm H2O
Severe ARDS
PaO2/PIO2: less than 100 on ventilator settings that include PEEP >5 cm H20
-if patient has a PaO2 of 70 mmHg while receiving 70% (0.7) FIO2, the ratio (PaO2/FIO2) is 100, which is diagnostic for severe ARDS
ARDS Severity: PaO2/FIO2 ratio
ratio of the partial pressure of oxygen over the fraction of inspired oxygen
-divide fraction
How to determine PaO2/PIO2 ratio
divide PaO2 by FIO2
-Normal Average PaO2: 90 mm Hg
(normal is 80 to 100)
-Breathing room air, FIO2 is 21% (or 0.21)
>Equation: 90/.21 or a PaO2/FIO2 ratio of approximately 428
How to determine PaO2/PIO2 ratio
divide PaO2 by FIO2
-Normal Average PaO2: 90 mm Hg
(normal is 80 to 100)
-Breathing room air, FIO2 is 21% (or 0.21)
>Equation: 90/.21 or a PaO2/FIO2 ratio of approximately 428
Normal PaO2 Level
80 to 100 mmHg
-Average: 90 mmHg
Breathing room air (RA), What is the normal FIO2 level?
21% (0.21)
3 Phases of ARDS
- Exudative
- Proliferative
- Fibrotic
Exudative Phase
- occurs within 24 to 48 hours after injury
- there is a disruption of the alveolar-capillary membrane (ACM) as a result of the activation and release of inflammatory mediators
- ACM becomes dilated d/t inflammatory mediators; allows fluid to move from capillaries into interstitial space and alveoli
- Disruption of ACM allows protein to move from the vascular space; loss of protein from vascular space lessens the oncotic forces, worsening the movement of fluid into the alveoli
- The alveolar and interstitial edema results in a severe V/Q mismatch (ventilation/perfusion; inadequate ventilation occurring in the face of adequate perfusion or blood flow) which results in hypoxemia; blood is shunted past the fluid-filled alveoli w/o being oxygenated
- there is damage to the alveolar cells that produce surfactant; at risk for atelectasis
Surfactant
responsible for maintaining alveolar surface tension
-alveolar surface tension keeps the alveoli from fully collapsing at the end of expiration
-if alveolar surface tension is lost, then the alveoli collapse; atelectasis
>there is damage to cells that produce surfactant in the exudative phase of ARDS
Clinical Manifestations Shown During the Exudative Phase
-Hyperventilation and Tachycardia as a compensatory response to hypoxemia
-ABGs reveal Respiratory Alkalosis d.t hyperventilation
-Cardiac Output increases; attempt to increase blood flow through the lungs
-Chest x-ray reveals the increased alveolar fluid as bilateral infiltrates (pulmonary edema)
>there would be no evidence of increased left atrial or ventricular pressure, which indicates left heart failure (noncardiogenic pulmonary edema)
Proliferative Phase
neutrophils and other inflammatory mediators cross the damaged alveolar-capillary membrane (ACM) and release toxic mediators that further damage both the alveolar and capillary endothelium
- diffusion defects
- V/Q mismatch worsens
- pulmonary hypertension b/c of locally occurring vasoconstriction in the lung caused by hypoxemia; right sided heart failure d/t increase in PVR or high vascular pressures in the lung
- widespread fibrotic changes; lungs become stiff and non-compliant; increases work of breathing
Clinical Manifestations Shown in Proliferative Stage
- Hypercarbia (High CO2) and worsening hypoxemia
- PaCO2 begins to rise despite hyperventilation
- Refractory hypoxemia (in spite of increasing oxygen delivery (DO2) to the patient, the hypoxemia does not improve and will eventually worsen)
- Lung compliance continues to deteriorate; increasing work of breathing
Fibrotic Phase
- diffuse and fibrotic scarring, results in impaired gas exchange and compliance
- pulmonary hypertension worsens
- accompanying right sided heart failure worsens
Clinical Manifestations Shown in the Fibrotic Stage
- decreased left-heart preload d/t the right heart failure and reduced capacity of the right ventricle to deliver blood to the lungs and on the left side of the heart
- decreased BP
- decreased CO
- severe V/Q mismatch, diffusion defects, and intrapulmonary shunting result in refractory hypoxemia
- severe tissue hypoxia and lactic acidosis
Refractory Hypoxemia
in spite of increasing oxygen delivery to the patient, the hypoxemia does not improve and will eventually worsen
Connection Check: The pulmonary edema associated with ARDS is caused by?
A. increased permeability of the ACM
B. right ventricular failure w/ pulmonary hypertension
C. left ventricular failure d/t poor oxygenation
D. fluid overload r/t resuscitation in the first phase
A. Increased permeability of the ACM
Diagnosis: Imaging Studies
> Chest x-ray
- to identify bilateral infiltrates in the early stages that are the hallmark sign of ARDS
- “ground-glass appearance”
- “snow screen effect” or whiteout effect on chest x-ray
Diagnosis: Laboratory Testing
- ABGs
- Complete blood count (CBC) w/ differential
- Sputum
- Blood
- Urine cultures
- Coagulation Studies
- Electrolyte panels
- Liver Function Tests
Laboratory Tests: Arterial Blood Gases (ABGs)
initially show hypoxemia and hypocapnia as alveolar compromise develops