BCIT Module 4 Flashcards
What are the characteristics of ARDS?
- noncardiogenic pulmonary edema
- severe hypoxemia (often resistant to O2 therapy)
- characteristic x ray changes (bilateral opacities)
- decreased lung compliance
What are examples of direct insults that lead to ARDS?
Pneumonia, aspiration, pulmonary contusion
What are examples of indirect insults that may result in ARDS?
Sepsis, pancreatitis, nonthoracic trauma
Who are the patients most at risk for developing ARDS?
Elderly
Severe acute illness
What is the clinical criteria for diagnosing ARDS?
- within 1 week of known clinical insult or worsening respiratory symptoms
- bilateral opacities on X-ray not fully explained by effusions, lung collapse or nodules
- respiratory failure not explained by heart failure or fluid overload
- P:F < 300
What are the 3 phases of ARDS?
- Exudative phase
- Fibroproliferative phase
- Resolution phase
What is the exudative phase of ARDS?
First 72 hours, mediators (neutrophils, macrophages, platelets) cause injury to pulmonary capillaries leading to micro thromboemboli, increased pulmonary artery pressures and interstitial edema.
What is the fibroproliferative phase of ARDS?
Disordered healing in the lungs characterized by fibrosis of the AC membrane resulting in pulmonary hypertension and hypoxemia
What is the resolution phase of ARDS?
Structural and vascular remodeling reestablish AC membrane and intraalveolar fluid is transported out of the alveoli back into the interstitium
What kind of V/Q mismatch is characteristic of ARDS?
Shunt
What is shunt?
Adequate alveolar perfusion with with inadequate ventilation
What causes hypoxemia in ARDS?
- shunt
- impaired diffusion
What is a normal P:F ratio?
> 300
How do you calculate P:F?
PaO2 / FiO2
What is the P:F in mild, moderate and severe ARDS?
Mild = 200-300 Moderate = 100-200 Severe = <100
What are typical ABGs in ARDS?
Initial = respiratory alkalosis
As fatigue sets in = respiratory acidosis
Progressing = metabolic acidosis (mixed acidosis)
What are the PA catheter changes in ARDS?
Increased PADP (8-15 normal) Normal PCWP (8-12) PADP > PCWP by >4 (I.e. pulmonary HTN)
What are typical ARDS ventilation strategies?
- low tidal volumes (6 ml/kg, max PPlat of 30)
- permissive hypercapnia (PaCO2 < 80, pH > 7.2)
- use of pressure modes to limit barotrauma
- PEEP to maintain PO2 > 90%
What are fluid administration strategies in ARDS?
- PCWP 5-8
- fluid restriction
- diuretics
- use vasoactive inotropes to support CO instead
What is static compliance?
Compliance that is only influenced by compliance of the lung (represented by PPlat in a no-flow state)
What is dynamic compliance?
Compliance that is influenced by flow rate, airway diameter and lung compliance (PIP measures dynamic compliance)
What is one of the consequences of increasing a patient’s respiratory rate to compensate for low tidal volumes?
- higher PPlats (less time to reach PIP = increased flow)
- potential for breath stacking with shortened expiratory time
What are the benefits of using pressure mode ventilation over volume in ARDS?
- allow you to control PPlats to prevent barotrauma
- provides laminar flow which helps to open up collapsed airways
What are the benefits of PEEP in ARDS?
- minimizes alveolar collapse
- reduces WOB (especially at the beginning of inspiration)
- thins AC membrane
- lengthens time period during which gas exchange can occur