Volume-Targeted Ventilation in

Newborn Respiratory Support

Martin Keszler, MD

Professor of Pediatrics

Brown University

Women and Infants Hospital

Providence, RI

Ventilatory Support in Neonatology:

State-of-the-Art 2011

PSV ?

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Outline of Lecture:

Basic Concepts of Mechanical

Ventilation and Lung Injury

Pros-cons of Volume vs. Pressure

Volume -Targeted vs. Volume-

Controlled Ventilation

Evidence base for VG

Practical aspects of VG ventilation

Unique Challenges in NB Ventilation Children ≠ Small Adults!

Newborns ≠ Small Children!

Transitional circulation

Compliant chest wall, stiff lungs

Unfavorable chest wall mechanics

Limited muscle strength and endurance

Immature respiratory control

Rapid RR, short time constants

Small trachea, high ETT resistance

Uncuffed ETT

Location of flow sensor

Need for a specialty Neonatal Ventilator

Volume or Pressure Ventilation?

Bourns LS104 BP 200

Volume vs. Pressure Ventilation Volume Ventilation

- Controls the set flow rate

- Cycles when set volume is delivered

- Pressure rises passively

Pressure Ventilation - Controls the set pressure

- Cycles when set time or flow is

reached

- Volume depends on compliance

Volume vs. Pressure Ventilation Volume Ventilation

- Controls the set flow rate

- Cycles when set volume is delivered

- Pressure rises passively

Pressure Ventilation - Controls the set pressure

- Cycles when set time or flow is

reached

- Volume depends on compliance

Pressure-limited IMV

Patient Patient

Spont.

breath

Continuous flow Continuous flow

Pressure

limit

Expiration Inspiration

Leak

PEEP

valve

Limitations of Volume - Controlled Ventilation in Newborns

Tubing System and Humidifier

Respiratory

System

VTLung = VT set CT

CRS

1

1 + *

Actual tidal volume is influenced by:

1) Ratio of circuit compliance to

respiratory system compliance

Flow Sensor

C T V .

Vent

V .

CRS

Humid

C RS

2) compressible volume of the circuit, including humidifier

Leak

Why Volume-Targeted

Ventilation?

Volutrauma not Barotrauma

Inadvertent hyperventilation is common (Luyt

2001)

Hypocarbia is bad for the brain and the lungs

Adult-type volume controlled ventilation

doesn’t work well in NB

Effect of Pressure v. Volume on Lung Injury Hernandez, et al, J Appl Physiol 1989

Capillary

filtration

coefficient:

measure of

acute lung

injury

Dreyfuss D et al. Am Rev Respir Dis. 1988;137:1159-1164.

10

8

6

4

2

0

Qwl/BW

(mL/kg)

DLW/BW

(g/kg)

Albumin space

(%)

* * 1.2

0.9

0.6

0.3

0

100

0

80

60

40

20

Ventilator-Induced Lung Injury:

Volutrauma, not Barotrauma

Rodents ventilated

with 3 modes:

- High pressure

(45 cm H2O),

high volume

- Low (negative)

pressure, high

volume

- High pressure

(45 cm H2O), low

volume (strapped

chest & abdomen) *P<0.01.

*

PIP is Excessive Relative to Compliance!

!

P

VT

FRC

E

I

!!

Hypocarbia in First 3 Days of Life Proportion of infants with PaCO2 < 25 mm Hg

0%

5%

10%

15%

20%

25%

30%

35%

Day 1 Day 2 Day 3

IMV

PTV

Luyt, et al 2001

Both High and Low PCO2 Increase Risk of IVH Fabres, et al, Pediatrics 2007

Modalities of Volume -Targeted Ventilation

Controls Adjusts Based on

Servo (PRVC) VT to circuit PIP Inspiratory VT

of last breath

VIP Bird (VAPS) Minimum VT

to patient Inspiratory time ( )

Inspiratory VT

Bear Cub 750 (Volume Limit)

Max. VT to patient

Inspiratory time ( )

Inspiratory VT

Avea (VAPS + VL)

Min/Max VT

to circuit/pt Inspiratory time ( )

Inspiratory VT

P. Bennett 840 (Volume Vent +)

VT to circuit Inspiratory time / flow

Inspiratory VT

Babylog 8000+ & VN 500 (VG)

VT to patient

PIP Exhaled VT of

last breath

Comparison between ventilator and Bicore CP-100

Tidal Volume Measurement Chow, et al, Pediatr Pulmonol 2002

PRVC/VG Control Algorithm

Volume Limit

PRESSURE

FLOW

VOLUME

Volume Limit

Pressure limited breaths

Volume limited breath

Decreased

compliance

or decreased

patient effort

Increased compliance or increased patient effort

Volume Limit

Volume Guarantee Principles of Operation

Pressure limit Working Pressure

VT = VT set by user

The PIP (“working

pressure”) is servo-

regulated within preset

limits (“pressure limit”)

to achieve VT that is

set by the user.

Regulation of PIP is in

response to exhaled VT

to minimize artifact

due to ETT leak.

Breath terminates if

130% of TVT reached.

Separate algorithm for

spontaneous and

machine breaths.

Working Pressure

VOLUME

Target tidal volume

Pressure Limit

PRESSURE

Benefits of VG

Maintenance of (relatively) constant tidal volumes / avoidance of hypocapnia

Prevention of overdistention and volutrauma due to

• Surfactant administration

• Lung volume recruitment

• Clearance of lung fluid

Automatic lowering of pressure support level during weaning – weans in “real-time”

Compensation for variable respiratory drive

• stabilization of tidal volume and minute ventilation due to changes of respiratory drive (periodic breathing)

The benefits of VTV can not be

realized without ensuring that the

tidal volume is evenly distributed

throughout an “open lung”!!!

Expiration

Inspiration Ventilated

Stable

Ventilated

Unstable Unventilated

“Atelectotrauma”

Non-Homogenous Aeration in RDS Recruitment/ de-

recruitment injury

Shear

forces

Adequate PIP, Adequate PEEP

COP CCP

FRC

P

V

VT

P

Good oxygenation, low FiO2, minimal lung injury

CCP = critical closing pressure; COP = critical opening pressure

OLC Prevents Lung Injury

0%

10%

20%

30%

40%

50%

60%

VT>6/kg PaCO2<35

A/C

A/C+VG

* *

Proportion of Values Outside the

Target Range

Keszler, et al. Ped Pulmonol ‘04 * p < 0.001

Spontaneous Hyperventilation and VG

0

2

4

6

8

10

12

14

16

18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0

2

4

6

8

10

12

14

16

18

PIP

PIP limit

PEEP

VT

Set VT

Breath #

PIP (cm H2O) VT (ml)

Note the large VT, generated by the infant, while the PIP

drops near the PEEP level as the ventilator in VG mode

responds appropriately to the large VT by reducing PIP.

VG Combined with A/C v. SIMV

0

2

4

6

8

10

12

VT variance SpO2 variance

A/C + VG

SIMV + VG

* P < 0.001

*

*

Variance of VT and SpO2

Abubakar, et al, J Perinatol 2005

VG Combined with A/C v. SIMV Ventilator Variables – Mechanical Breaths

0

2

4

6

8

10

12

14

16

18

PIP MAP VT MV (L/min x

10)

A/C + VG

SIMV + VG

# P < 0.005

#

#

Abubakar, et al, J Perinatol 2005

Lung Volume

Patient’s

Pleural

Pressure

Machine

Generated

Pressure

Lung Volume

SIMV vs. A/Cor PSV: Work of Breathing and VT

CPAP/SIMV (unsupported) A/C or PSV

Machine

Generated

Pressure

Patient’s

Pleural

Pressure

Lung Volume

SIMV (supported)

Patient’s

Pleural

Pressure

Machine

Generated

Pressure

0

1

2

3

4

5

6

7

ml/

kg

SIMV SIMV+PS3 SIMV SIMV+PS6

VT SIMV VT spont

SIMV: Uneven VT (Osorio, et al. J Perinat Apr 05)

VG Combined with A/C v. SIMV Cardio-Respiratory Variables

0

20

40

60

80

100

120

140

160

180

HR RR SpO2

A/C + VG

SIMV + VG

*

*

*

* P < 0.001 Abubakar,et al, J Perinatol 2005

VG vs NAVA or PAV

Extreme Periodic Breathing Owen, et al, ADC 2010

Cochrane Review: Duration of MV Wheeler, et al 2010

Cochrane Review: Death or BPD @ 36 wk Wheeler, et al 2010

Cochrane Review: Pneumothorax Wheeler, et al 2010

Effect of VG on Markers of Lung Inflammation Lista, et al 2005 & 2006

Two prospective randomized trials

A/C vs. A/C + VG

BAL on days 1,3,5

VG @ 5 mL/kg reduced pro-

inflammatory cytokine levels and

decreased duration of ventilation

VG @ 3 mL/kg increased pro-

inflammatory cytokine levels

Low PEEP (3-4 cm H2O)

Summary of VG Studies

When compared to PLV, VG results in:

Same or lower PIP 1,2,3

More stable VT 1,3

Less hypocapnia 3

Faster recovery from forced exhalation episodes3

Works better with A/C than SIMV 4

Faster recovery from suctioning 4

Pro-inflammatory cytokines decreased @ 5 ml/kg5

Faster weaning from mechanical ventilation5

Higher VT needed in RLBW* infants 6

Higher VT needed with advancing post-natal age 3

1 Herrera et al, 2 Cheema, et al, 3 Keszler, et al, 4 Abubakar, et al, 5 Lista, et al

6 Montazami, et al * RLBW = Ridiculously low birth weight infant (<600g)

VG-Clinical Guidelines Initiation

VG should be implemented immediately upon initiation of mechanical ventilation.

The usual starting target VT is 4 - 5 mL/kg during the acute phase of the illness.

Use corrected VT if ETT leak (VN 500)

Larger VT is needed with SIMV, in ELBW infants, those with MAS and older infants with BPD!

PIP limit should be set 20% above the PIP currently needed to deliver the target VT in order to give the device adequate room to adjust PIP.

Record both the PIP limit and the working pressure.

VT in infants with MAS Sharma, et al ESPR 2011

Relationship of Birthweight and VT

Montazami,et al, Ped Pulmonol 2009

3

3.5

4

4.5

5

5.5

6

6.5

0.3 0.4 0.5 0.6 0.7 0.8 0.9

Weight (kg)

VT

(m

l/k

g)

R= -0.563 p<0.001

ELBW RLBW *

*RLBW = Ridiculously LBW

Conventional Physiology Anatomical dead-space = 2mL/kg. Instrumental dead-space is fixed.

Anatomical + Instrumental dead-space = 3mL in a typical 1 kg infant

Anatomical + Instrumental dead-space = 2.5mL in a typical 0.5 kg infant

Alveolar ventilation = tidal volume – dead-space volume) x RR

VT = 5mL , DS=3mL VT = 4mL , DS=3mL VT = 3mL , DS=3mL

Alveolar ventilation = X Alveolar ventilation

= 0.5 X

Alveolar ventilation

= 0

Time to Eliminate CO2 from Test Lung 2.5 mm ETT, DS = 3.5 ml

0

50

100

150

200

250

300

350

400

450

500

DS + 2 DS+ 1 DS DS -0.5 DS - 1 DS -1.5Tidal Volume (ml)

Seconds

Keszler, et al. ADC FN in print (Published Online 18 November 2011)

Fresh gas inflow spikes through DS gas

Mixing when flow abruptly stops

Exhaled gas spikes through mixed DS gas

Gas Flow Through Narrow ETT

Henderson’s Experiment 1915

Relationship of Post-Natal

Age and VT (mL/Kg)

Keszler,et al, Arch Dis Child ‘09

Day 1-2

n = 251

Day 5-7

n = 185

Day 14-17

n = 216

Day 18-21

n = 176

VT (mL/kg) 5.15 + 0.6 5.24 + 0.7 5.63 + 1.0 6.07 + 1.4

PCO2 (torr) 44.0 + 5.4 46.3 + 5.2 53.9 + 7.3 53.9 + 6.2

MV and Anatomical Dead Space

in ELBW Infants

As gas is delivered under pressure to the newborn lung, the airway expands in proportion to its compliance.1

Over time, elasticity is lost and airway becomes larger than normal.

Preterm infants who are mechanically ventilated have larger tracheal widths than nonventilated neonates (Figure)2

1. Greenspan JS, et al. Neonatal Netw. 2006;25:159-166.

2. Bhutani VK, et al. Am J Dis Child. 1986;140:449-452.

750 1,000 1,250 1,500

Study Weight, g

Tra

chea

l Wid

th, m

m

0

1.0

2.0

3.0

4.0

5.0

Ventilated

Non-ventilated

VG Clinical Guidelines: Subsequent Adjustments

Adjustment to target VT may be made, based on

PaCO2. Usual increment is 0.5 mL/kg.

PIP limit needs to be adjusted from time to time to

keep the PIP limit close to the actual PIP.

PIP will default to the limit if sensor is out or when

giving a manual breath!

Consider light sedation if infant is agitated despite

good support

Pay attention to alarms, graphics (beware of leaks)!

If the low VT alarm sounds repeatedly, increase the

pressure limit AND INVESTIGATE THE CAUSE

VG Clinical Guidelines: Weaning

If target VT is set at low normal (usually ~4 mL/kg in first few days, higher later on) and PaCO2 is allowed to rise to the mid - high 40s (pH <7.35), weaning occurs automatically (“self-weaning”). Avoid VT <4 mL/kg.

If VT is set too high and/or the pH is too high, the baby will not have a respiratory drive and will not “self-wean”.

Avoid sedation during the weaning phase!

If significant oxygen requirement persists, PEEP may need to be increased to maintain mean airway pressure as PIP is automatically lowered.

Most infants can be extubated when they consistently maintain VT at or above the target value with working PIP < 10-12 cm H2O (< 12-15 cm H2O in infants > 1 kg) with FiO2 < 0.35 and good sustained respiratory effort.

Work of Breathing @ Different VT target Patel, et al Pediatrics 2009

VG-SIMV: Minute Ventilation Herrera, et al, Pediatr 2002

0

50

100

150

200

250

SIMV SIMV+VG4.5 SIMV+VG3

Total

Mech

Spont

ml/kg/min

Troubleshooting

There will be more alarms (interactive mode, gives useful information, pay attention to it)

Avoid excessive alarms (they get ignored!

Common causes: - Limits are too tight (most often pressure limit)

- Excessive ETT leak (change ETT if leak > 40% (Much less of a problem with the VN 500)

- Forced exhalation episodes

- Agitation • Excessive noise

• handling

• lack of boundaries

mkeszler@WIHRI.org

Thank You