Acute Respiratory Disorders
-Shunt (o2 not getting in), Dead Space ( Good ventilation, not good perfusion - PNA, Asthma, CHF
Dead space causes: hypovolemia, low cardiac output, pulmonary embolus, high airway pressures
A-a gradient (Alveolar-arterial O2): Tells you if it’s an issue at the level of the lung or just a ventilation issue
Formula: PAO2 (from formula below) - PaO2 (from ABG) = gradient
PAO2 = [FiO2 x (Pb-47)] - [1.25x PaCO2]
***rough guide to whether there is a significant A-a gradient present: PaO2 should = FiO2 x 500 (e.g. 0.21 x 500 = 105 mmHg)
Normal A-a gradient; 10mmHg - if >10 = V/Q Mismatch, lung issue
Determine if ARDS: Pa02:FI02 ratio; >300 = normal
ARDS Severity PaO2/FiO2
Mild 200 – 300
Moderate 100 – 200
Severe < 100
IPAP/EPAP = Pressure Support/Peep (increases oxygenation)
If you have an O2 issue: increase EPAP to bring it closer to IPAP #, titrate by 2cm increments.
Lung Injury / ARDS / COPD: 6-8cc/kg of IDEAL body weight
Normal: 8-10/kg of IDEAL body weight
For every 10mm increase in CO2 = pH change of 0.08
Ventilatory failure: adjust TV, increase difference between IPAP & EPAP
Normal min volume (RR x TV) : 5-10
Plateau Pressure - peak pressure: Normal 5-10
Normal Plateau pressure <30, if higher at risk for barotrauma
Low diff: restrictive process - pneumo, Right main stem, acute pulmonary edema
High diff: obstructive process - biting tube, needs suction, bronchospasm
Interventions to decrease auto-peep:
Decrease respiratory rate
Increase gas flow rate or Increase I:E ratio
Determinants of Oxygenation:
For Obstructive Airway Disease:
Set initial tidal volume 6-8cc/kg
Adjust min. ventilation to low normal pH
