How I use ventilator waveformsat the bedside ?

Alain Mercat

Conflicts of interests

• Fundings for clinical researchs

• Covidien (PAV+)

• GE (EELV/PEEP/ARDS)

• Maquet (NAVA)

• Fisher-Paykel (Optiflow)

• Patent

• GE (EELV/PEEP/recruitment)

• Fees for lectures

• Covidien

• Fisher Paykel

• Fees for consulting

• Faron Pharmaceuticals

• Air Liquide Medical Systems

• Passive patient

Mechanics of the respiratory system ?

• Actively breathing patient

Patient – ventilator synchrony ?

Respiratory efforts ?

• Supposed to be passive patient

Really passive ?

Ventilator waveforms in ARDS

Passive respiratory mechanics

• ∆P = 29 – 17 = 12 cmH2O

• Crs = 380 / 12 = 32 ml/cmH2O

• Rrs = (40 – 29) / 1

= 11 cmH2O/L/sec

• Ppeak = 40 cmH2O / Plat = 29 cmH2O / PEEP = 17 cmH2O

• Inspiratory flow = 60 L/min = 1 L/sec

• No flow at the end of expiration No PEEPi

Passive respiratory mechanics

• Volume controlled, constant inspiratory flow

Paw

Flow

• Volume controlled

• Constant inspiratory flow

• No inspiratory activity

• Analyse of the shape of the Paw-

time curve during insufflation

• Paw = (V’x R) + (V x E) + PEEP

• Change of the shape during

insufflation is indicative of

change of elastance

Ranieri et al. AJRCCM 1994

Passive respiratory mechanics : Stress index

Ranieri et al. AJRCCM 1994

Passive respiratory mechanics : Stress index

Recruitment Overdistension

Ranieri et al. AJRCCM 1994

Passive respiratory mechanics : Stress index

Passive respiratory mechanics

• Volume controlled, constant inspiratory flow

Paw

Flow

• ARDS, volume A-C : VT 440 ml (6 ml/kg PBW), RR 28/min, PEEP 10

• Midazolam 5 mg/h, Fentanyl 100 μg/h Ramsay 5

The actively breathing patient

Inspiratory efforts during ACV

• ARDS, volume A-C : VT 440 ml (6 ml/kg PBW), RR 28/min, PEEP 10

• Midazolam 5 mg/h, Fentanyl 100 μg/h Ramsay 5

Actively breathing patient

Double triggerings

0

5

10

15

20

25

0 4 8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

0 4 8

0

2

4

6

8

0 4 8

1 effort

Flow (L/s)

Airway Pressure

(cm H2O)

Esophageal

Pressure (cm H2O)

2 cycles

6 + 6 = 12 ml/kg PBW !!

Double triggering

• Caused by :

• High respiratory drive

• Low tidal volume

• Short inspiratory time

• Solutions :

• Increased Ti : plateau, decelerating flow

• Increased VT (?)

• VAC PAC or PS (monitor VT)

• Sedation - paralysis

Flow

(L/s)

0

1

Paw

(cmH2O)

0

40

Peso

(cmH2O)

• ACV : VT 400ml, PEEP 5. Midazolam-Fentanyl, Ramsay 5.

• Measured RR = set RR = 24/min

Curare

The “supposed to be passive patient”

Flow

(L/s)

0

1

Paw

(cmH2O)

0

40

Peso

(cmH2O)

• ACV : VT 400ml, PEEP 5. Midazolam-Fentanyl, Ramsay 5.

• Measured RR = set RR = 24/min

Curare

The “supposed to be passive patient”

Flow

(L/s)

0

1

Paw

(cmH2O)

0

40

Peso

(cmH2O)

• ACV : VT 400ml, PEEP 5. Midazolam-Fentanyl, Ramsay 5.

• Measured RR = set RR = 24/min

Curare

The “supposed to be passive patient”

Reverse triggering

Akoumaniaki et al. Chest 2013

The color may help

Triggered breaths

Reverse triggering : the color may help

Thank you !

alain.mercat@univ-angers.fr