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Respiratory support and respiratory outcome in preterm infants

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

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Respiratory support and respiratory outcome in preterm infants

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  1. 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

  2. Topics • Sequelae of lung injury • Conventional ventilation strategies • Synchronized ventilation • Volume-controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  3. Topics • Sequelae of lung injury • Acute lung injury (air leaks) • Bronchopulmonary dysplasia (BPD) • Conventional ventilation strategies • Synchronized ventilation • Volume-controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  4. BPD • 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

  5. Topics • Sequelae of lung injury • Conventional ventilation strategies • Avoiding volutrauma • Avoiding atelectotrauma • Synchronised ventilation • Volume controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  6. Mechanical ventilation is harmful! Operator • 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”

  7. Which volumes cause lung injury? Volutrauma Zone overdistention atelectasis Volutrauma Zone Time → B C D A DOptimal AHigh VT low PEEP BNormal VT, high PEEP CNormal VT low PEEP W. A. Carlo

  8. Effect of 6 inadequately large breaths

  9. Respiratory minute ventilation MV = VT * f Reduced tidal volume can be compensated by increase of rate

  10. NNT Pneu: 11 NNT PIE: 5 Trend towards reduced mortality However: no reduction in BPD

  11. Which volumes cause lung injury? Volutrauma Zone overdistention atelectasis Volutrauma Zone Time → B C D A DOptimal AHigh VT low PEEP BNormal VT, high PEEP CNormal VT low PEEP W. A. Carlo

  12. Optimal PEEP level • 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

  13. Topics • Sequelae of lung injury • Conventional ventilation strategies • Synchronised ventilation • Volume controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  14. Why synchronize? 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

  15. Synchronized Ventilation BPD at 28 days postnatal age BPD at 36 weeks postmenstrual age

  16. Air leaks Death

  17. Topics • Sequelae of lung injury • Conventional ventilation strategies • Synchronized ventilation • Volume controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  18. Volume controlled ventilation • 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)

  19. Volume controlled ventilation

  20. Topics • Sequelae of lung injury • Conventional ventilation strategies • Synchronized ventilation • Volume controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  21. Features of HFV • 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

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

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

  24. Topics • Sequelae of lung injury • Conventional ventilation strategies • Synchronised ventilation • Volume controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation

  25. Why maintain a PaCO2 of 40 mmHg? • 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

  26. Randomised trials

  27. Topics • Sequelae of lung injury • Conventional ventilation strategies • Synchronised ventilation • Volume controlled ventilation • High frequency ventilation • Permissive hypercapnia • Non-invasive ventilation • Nasal CPAP • Nasal IMV

  28. nCPAP or CNP for RDS NNT Failure: 4.0; NNT Mortality: 4.5; NNH Pneumotx. : 8 CDP n=71, standard care n=74

  29. nCPAP after Extubation NNT Failure: 6 nCPAP n=239, headbox n=240

  30. nIPPV vs nCPAP after Extubation

  31. Summary • 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

  32. Recommendation for ventilation • 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

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