respiratory support and respiratory outcome in preterm infants pd dr. med. ulrich thome division of...

Respiratory support and respiratory outcome

in preterm infants

PD Dr. med. Ulrich Thome

Division of Neonatolgy and Pediatric Critical Care

University Children’s Hospital

Ulm, Germany

Topics

• Sequelae of lung injury

• Conventional ventilation strategies

• Synchronized ventilation

• Volume-controlled ventilation

• High frequency ventilation

• Permissive hypercapnia

• Non-invasive ventilation

• Sequelae of lung injury– Acute lung injury (air leaks)– Bronchopulmonary dysplasia (BPD)



• Volume-controlled ventilation




Topics

• Bronchopulmonary dysplasia (Northway 1967)– Epithelial metaplasia– Fibrosis– Smooth muscle hypertrophy– Heterogenous inflation

• “New BPD“ (Jobe 1999)– Extremely immature preterm infants, surfactant-treated– Arrested lung development

• Reduced alveolar formation • Reduced gas exchange area• Reduced microvascular development

• Definition: Oxygen or ventilator support needed at 36 weeks PMA

BPD


• Conventional ventilation strategies– Avoiding volutrauma– Avoiding atelectotrauma

• Synchronised ventilation

• Volume controlled ventilation




Topics

• ventilator-induced lung injury• Volutrauma rather than barotrauma

(Dreyfuss D et al. AJRCCM 1998)

• Multicenter trial in adults: Lower VT reduced mortality, lung injury and multi-organ failure (N Engl J Med 2000; 342:1301-8)

=>↓ Tidal volume:• Decreases lung injury• May result in “permissive hypercapnia”

Operator

Mechanical ventilation is harmful!

B Normal VT, high PEEP

A High VT

low PEEPD Optimal

A BTime →

Volutrauma Zone

C

Volutrauma Zone atelectasis

overdistention

D

C Normal VT

low PEEPW. A. Carlo

Which volumes cause lung injury?

Effect of 6 inadequately large breaths

MV = VT * f

Reduced tidal volume can be compensated by increase of rate

Respiratory minute ventilation

NNT Pneu: 11 NNT PIE: 5Trend towards reduced mortalityHowever: no reduction in BPD

B Normal VT, high PEEP

A High VT

low PEEPD Optimal

A BTime →

Volutrauma Zone

C

Volutrauma Zone atelectasis

overdistention

D

C Normal VT

low PEEPW. A. Carlo

Which volumes cause lung injury?

• Animal studies indicate increased lung injury at too low or too high PEEP levels

• Multicenter trial of two PEEP levels in adults with ARDS: no difference

(N Engl J Med 2004; 351:327-336)

• No randomized studies on preterm infants available

Optimal PEEP level








Topics

Possible advantages:

• higher patient comfort

• more stable gas exchange because of the patients’ own regulatory mechanisms

Possible disadvantage: increased volutrauma

• Flow sensors used for triggering: – 1 ml of dead space = 33% of VT in 500g infant

• More frequent occurrence of Head’s reflex Pediatr Pulmonol. 1997, 24:195-203

Why synchronize?

BPD at 28 days postnatal age

BPD at 36 weeks postmenstrual age

Synchronized Ventilation

Air leaks

Death








Topics

• Two forms– Volume controlled– Volume guarantee

• Automatically adjusts peak pressure to ensure correct tidal volume– Immediately responds to inadvertent changes in

lung mechanics

• Requires a flow sensor– Increased deadspace may lead to increased

volutrauma in extremely small infants (< 1000g)

Volume controlled ventilation

0.1 1 10

Volume controlled

Mortality

Pneumothorax

BPD 28d

BPD 36w

Volume guarantee

Mortality

Pneumothorax

BPD 28d

BPD 36w

volume ctrl better | conventional better

Volume controlled ventilation








Topics

• High frequency (300-1200/min = 5-20 Hz)

• Very small tidal volumes

• Incomplete inspiration and expiration

• Dampening of oscillations in the airways

=> Very small intra-alveolar pressure amplitude

Features of HFV

0,5 1 1,5

#Stud.| #Pts

Mortality 17 3776

BPD28 12 2104

BPD28/D 12 2305

BPD36 14 2869

BPD36/D 14 2969

Air leaks 16 3721

IVH°3-4 17 3733

PVL 14 3570

HFV better | conventional better

NNH = 28

Thome U et al.: ADC F&N ed., in press

0.5 1 1.5

BPD36/D

all 14 2969

HFV / HLVS 12 2771

SM3100 7 1270

CMV / LPVS 7 2232

HFPPV 3 1381

IVH°3-4

all 17 3733

HFV / HLVS 13 2822

SM3100 7 1252

CMV / LPVS 7 2217

HFPPV 3 1366

#Stud.| #Pts

HFV better | conventional better

NNT = 16

NNT = 26

Thome U et al.: ADC F&N ed., in press








Topics

• Less than normal PaCO2 requires higher work of breathing.

• Higher than normal PaCO2 impairs oxygenation

Mechanical ventilation - normal PaCO2 not needed:

• Impaired oxygenation can be easily compensated by ↑FiO2

• Increased PACO2 improves CO2 removal

• Higher PaCO2 goal provides a greater margin of safety against hypocapnia

Why maintain a PaCO2 of 40 mmHg?

0.1 1 10

BPD36w/death

Mariani 1999

Carlo 2002

Thome 2005

Total

IVH °3-4

Mariani 1999

Carlo 2002

Thome 2005

Total

hypercapnia better | normocapnia better

Randomised trials







• Non-invasive ventilation– Nasal CPAP– Nasal IMV

Topics

NNT Failure: 4.0; NNT Mortality: 4.5; NNH Pneumotx. : 8

CDP n=71, standard care n=74

nCPAP or CNP for RDS

NNT Failure: 6 nCPAP n=239, headbox n=240

nCPAP after Extubation

0.1 1 10

Post extubation failure

short prongs

Barrington 2001

Khalaf 2000

long prongs

Friedlich 1999

Total

BPD at 36 weeks PMA

Barrington 2001

Khalaf 2000

Total

nIPPV better | nCPAP better

nIPPV vs nCPAP after Extubation

• High rate (60/min) low tidal volume ventilation: – better short-term results than low rate ventilation

• Synchronized and volume controlled ventilation: – not shown to improve long-term outcome– need dead space increasing flow sensors– may be associated with increased VT

• High frequency ventilation:– no better outcome than high rate low tidal volume ventilation

• Permissive hypercapnia:– not shown to improve long-term outcome – moderately high PaCO2 goals safe

• Non-invasive ventilation:– reduces the need for intubation and invasive ventilation– increases success rate after extubation: nIMV > nCPAP– increased incidence of air leaks compared to no ventilation

Summary

• Use only when absolutely necessary• Machine: any• Rate: high (>60/min)• PEEP: sufficient (3-6 mbar)• Tidal volume: as small as possible (don’t measure)• Synchronization, volume-controlled, volume-

guarantee: use under special circumstances, flow sensor contraindicated <1000g

• HFOV: not necessary for usual infants• Permissive hypercapnia: moderately high PaCO2 g • Non-invasive ventilation: use instead of invasive vent.

whenever possible, don’t use in too healthy pts

Recommendation for ventilation

respiratory support and respiratory outcome in preterm infants pd dr. med. ulrich thome division of...

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