Rapid Shallow Breathing Index (RSBI)
Respiratory Rate / Tidal Volume ( in L)
Pulmonary mechanic desired for extubation (6)
- RSBI < 105
- Negative inspiratory force > -20
- Vital Capacity > 15 mL/kg
- cuff leak
- Change in RSBI during 2 hour SBT < 20%, 30 min SBT < 5%
- Reason for intubation resolved (mental status, secretions)
Vital Capacity
Inspiratory reserve volume + tidal volume + expiratory reserve volume
ARDS three Classifications and PaO2/FiO2 ratio
- MIld: 200-300 (PEEP > 5)
- Moderate: 100-200 (PEEP > 5)
- Severe: < 100 (PEEP > 5)
Mortality and median duration of mechanical ventilation for
- Mild ARDS
- Moderate ARDS
- Severe ARDS
- Mild ARDS: 27% and 5 days
- Moderate ARDS: 32% and 7 days
- Severe ARDS: 45% and 9 days
Respiratory Equation of Motion
Pmus + Pvent = F x R + TV/C
Transairway pressure
Pressure at mouth opening - alveolar pressure
Transthoracic pressure
Alveolar pressure - body surface pressure
Transpulmonary pressure
alveolar pressure - pleural pressure
Transrespiratory pressure
Pressure at airway opening - body surface pressure
Compliance
Change in volume / change in pressure (normal > 100 ml / cm H2O)
Dynamic Compliance
tidal volume / PIP - PEEP
Static compliance
Tidal volume / Pplateau - PEEP
Resistance
pressure / flow = PIP - Pplateau / flow
Work
Four phases of mechanical ventilation
- Expiratory phase
- Triggering
- Inspiratory phase
- Cycling
ventilation pressure
Resistive pressure x
Time constant
Compliance x resistance
Three ventilator variables that determine the breath
- Trigger variable
- Target or limit variable
- Cycle variable
Three variables that can increase risk of instrinsic PEEP
- Minute ventilation increases
- Expiratory time fraction decreases
- Time constant (compliance x resistance) increases
Way to quantify intrinsic PEEP
Expiratory hold will allow intrinsic PEEP to equilibrate and be quantified.
