Clin Med - ARDS Flashcards
ARDS is also known as
- non-cardiogenic pulmonary edema
- adult hyaline membrane dz
- capillary leak syndrome
- shock lung
ALI (acute lung injury)
a syndrome of inflammation and increased permeability that is associated w/ a constellation of clinical, radiographic and physiologic abnormalities that cannot be explained, but may co-exist w/ left arterial or pulmonary htn
ARDS relation to ALI
- ARDS is a severe form of ALI
- more hypoxic
ARDS classification
- acute
- bilateral
- no left sided heart failure
Epidemiology of ARDS
- annual incidence 60/10k
- 20% of pts in ICU meet criteria for ARDS
- moridity and mortality:
- 26-48% (over 80% of deaths attributed to non-pulm organ failure
risk factors for ARDS
- extrems of age, pre-existing organ dysfunction, chronic medical illnesses
- pts w/ ARDS from a direct lung injury have a higher incidence of death
Causes of ARDS (in order of most common to least)
- pneumonia
- severe sepsis
- aspiration
- other (drowning, smoke/chemical inhalation)
- trauma
Pathophys of ARDS
- direct/indirect injury to alveolus causes macrophages to release pro-inflammatory cytokines
- cytokines attract neutrophils into alveolus and interstitum where they damage the alveolar-capillary membrane
- ACM integrity is lost, alveolus fills w/ fluid, surfactant can no longer support alveolus
Consequences of lung injury include? (3)
- impaired gas exchange (reduced perfusion and diffusion)
- decreased compliance (decreased ventilation)
- increased pulmonary arterial pressure
impaired gas exchange caused by ARDS
- V/Q mismatch
- shunting: mixed blood = hypoxemia
- increased dead space: impairs CO2 elimination; higher minute vent needs
decreased compliance caused by ARDS
- hallmark of ARDS
- consequence of stiff, non or poorly aerated lung
- fluid filled lung becomes stiff and boggy
- requires increasing pressure to deliver Vt
increased pulmonary arterial pressure caused by ARDS
- about 25% of patients
- result of hypoxic vasoconstriction
- can result in right ventricular failure
- not routinely measured
treatment of ARDS
- treat the underlying cause!
- low tidal volume ventilation
- use PEEP
- monitor airway pressures
- conservative fluid management
- reduce potential complications
tidal volume hypothesis in tx of ARDS
-ventilation w/ smaller tidal volumes (6mL/kg) will result in better clinical outcomes than traditional tidal volumes ventilation
when compared to larger tidal volumes, Vt of 6ml/kg of ideal body weight:
- decreased mortality
- increased number of ventilator free days
- decreased extrapulmonary organ failure
mortality is decrease in low tidal volumes despite the patients having:
- worse oxygenation
- increased pCO2
- lower pH
Explain how ARDS effects the lungs differently
- normal alveoli
- injured alveoli: can potentially participate in gas exchange, susceptible to damage from opening and closing
- damaged alveoli: filled w/ fluid, do not participate in gas exchange
protective measures to avoid over distention of normal alveoli:
- use low (normal) tidal volumes
- minimize airway pressures
- use PEEP (positive end expiratory pressure)
PEEP hypothesis in ARDS treatment
pts ventilated w/ 6ml/kg, higher levels of PEEP will result in better clinical outcomes than lower levels of PEEP
PEEP
- every ARDS pt needs it
- goal is to maximize alveolar recruitment and prevent cycles of recruitment/derecruitment
what is most predictive of lung injury?
-plateau pressure
plateau pressure
- goal is <30, the lower the better
- decreases alveolar over-distension and reduces risk of lung strain
- refer to graph if needed
fluid management in ARDS
-conservative fluid management improved lung function and shortened mechanical ventilation times and ICU days w/o increasing nonpulmonary organ
things to remember w/ fluid managment in ARDS
- increased lung water is the underlying cause of many of the clinical abnormalitites in ARDS
- after shock is resolved, effort should be made to diuresis
- shortens time on vent and ICU length
prone positioning in ARDS
-early application of prolonged prone positioning significantly decreased 28 day and 90 (day?) mortality in pts w/ severe ARDS
to summarize:
- recognize ALI early
- intervene in the dz process early
- limit fluids to physiologic necessity, diurese as able
- ventilate w/ low tidal volumes (6cc per ideal body weight) and high PEEP (keep O2 sat > 88%)
