2 - Ventilator Graphics and Alarms

normal pressure, flow, and volume scalars for mechanical ventilation

normal pressure, flow, and volume scalars for spontaneous breathing

positive end-expiratory pressure (PEEP)

pressure at end of expiration that keeps alveoli open

peak inspiratory pressure (PIP)

pressure at end of inspiration

plateau pressure (P_plat)

pressure in the alveoli after inspiration

• can be seen on MV after inspiratory hold

dynamic compliance (C_dyn)

pressure needed to overcome compliance in the lungs with airway resistance

static compliance (C_stat)

pressure needed to overcome compliance in the lungs without airway resistance

airway resistance (R_aw)

pressure needed to overcome resistance in the airways

normal range of C_stat

40-100 mL/cmH₂O

normal range of R_aw

< 10 cmH₂O/L/sec

formula for C_stat

\frac{V_{T}}{P_{plat}-PEEP}

formula for C_dyn

\frac{V_{T}}{PIP-PEEP}

formula for R_aw

\frac{PIP-P_{plat}}{\cdot V}

(.V = L/sec)

mean airway pressure (MAP)

formula for MAP

\left(PIP-PEEP\right)\left(\frac{T_{i}}{T_{tot}}\right)+PEEP

how to increase MAP

• add inspiratory pause

• increase i-time

• increase PEEP

• decrease flow

• increase RR

pressure waveform

• autocycling

how to fix autocycling

• fix leak

• lower sensitivity

pressure waveform

• auto-PEEP

seen with expiratory hold

causes of auto-PEEP

• obstruction

• dynamic hyperinflation (caused by RT due to RR or i-time)

pressure waveform

• leak

causes of leaks

• hole in mask/tube

• valve fails to close properly

square flow waveform

sinusoidal flow waveform

decelerating ramp flow waveform

square flow waveform

• characteristics

• ↓i-time (↑e-time)

• ↑PIP

• ↓MAP

sinusoidal flow waveform

• characteristics

• ↑i-time (↓e-time)

• ↓PIP

• ↑MAP

• most comfortable

decelerating ramp flow waveform

• characteristics

• ↑i-time (↓e-time)

• ↓PIP

• ↑MAP

• best ventilation distribution

flow waveform

• auto-PEEP

flow waveform

• bronchodilator response

flow waveform

• insufficient flow

normal range for flow

30-60 L/min

volume waveform

• normal

volume waveform

• leak

volume waveform

• obstruction

volume waveform

• forced exhalation

pressure-volume loop

• normal

pressure-volume loop

• overcompliance

pressure-volume loop

• noncompliance / decreased compliance

causes of decreased compliance

lungs

• atelectasis

• pulmonary edema

• ARDS

thorax

• pneumothorax

• burns

• (kypho)scoliosis

pressure-volume loop

• trigger sensitivity

pressure-volume loop

• increased work of breathing (spontaneous only)

pressure-volume loop

• leak

pressure-volume loop

• insufficient flow

flow-volume loop

• normal

flow-volume loop

• obstruction

flow-volume loop

• restriction (not seen on MV)

flow-volume loop

• auto-PEEP

flow-volume loop

• leak

flow-volume loop

• water/secretions

high pressure alarms

MV

• 10 above PIP as long as P_plat < 30 and PIP is not > 10 above P_plat

CPAP

• N/A (watch vent settings!)

low pressure alarms

low inspiratory pressure (LIP)

• 3-5 below PIP

low PEEP

• 2-3 below set PEEP

high V_T/V_E alarm

20% over set volume

low V_T/V_E alarm

20% below set volume

I:E alarm

ratio inversion

high RR alarm

10 above average combined rate (set + spontaneous)

• do not go above 35 b/min

F_iO₂ alarm

± 5%