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Proper pressures in the DR Proper FiO2 in the DR (blended) Surfactant in the DR CPAP in the DR Consistent CPAP i

‘Golden Hour’ Lung Protective Strategy from Birth. Proper pressures in the DR Proper FiO2 in the DR (blended) Surfactant in the DR CPAP in the DR Consistent CPAP in the NICU Reduced SIMV in the NICU. good judgement. informed jugement. Neo-Puff in the DR.

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Proper pressures in the DR Proper FiO2 in the DR (blended) Surfactant in the DR CPAP in the DR Consistent CPAP i

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  1. ‘Golden Hour’ Lung Protective Strategy from Birth • Proper pressures in the DR • Proper FiO2 in the DR (blended) • Surfactant in the DR • CPAP in the DR • Consistent CPAP in the NICU • Reduced SIMV in the NICU

  2. good judgement informed jugement

  3. Neo-Puff in the DR • manual ventilation of babies <30 weeks gest. • Used for all transport ventilation for all babies

  4. Neo-Puff Infant Resuscitator • easy to use, • manually operated • gas-powered.

  5. Controlled and Precise Peak Inspiratory Pressure (PIP) The Neopuff™ Infant Resuscitator will inflate the baby’s lungs & provide optimum oxygenation by delivering consistent PIP with each breath, limiting the risks associated with under or over inflation at uncontrolled pressures. Consistent and Precise Positive End Expiratory Pressure (PEEP) The Neopuff™ Infant Resuscitator maintains Functional Residual Capacity (FRC) by providing a consistent PEEP throughout the resuscitation process.

  6. The desired PIP is set by turning the inspiratory pressure control. The desired PEEP is set by adjusting the T-piece aperture.

  7. Pressure/Volume

  8. Over Weaning damages too

  9. Ventilator-Associated Lung Injury • Barotrauma (air leak) • Oxygen toxicity • Ventilator associated pneumonia • Over-distention • De-recruitment

  10. Biochemical Injury Biophysical Injury • Shear • Overdistention • Cyclic stretch • Inc. intrathoracic pressure Cytokines, prostanoids, Leukotrienes, reactive oxygen species, protease • Inc alveolar cap permeability • Dec cardiac output • Dec organ perfusion • Tissue injury secondary to • Inflamatory mediators/cells • Impaired O2 delivery • bacteremia Distal Organs neutrophil Slutsky and Tremblay Am J Respir Crit Care Med 1998; 157: 1721-1725 Death MOSF

  11. normal lungs 20 min of 45 cm H2O 5 min of 45 cm H2O Dreyfuss, Am J Respir Crit Care Med 1998;157:294-323

  12. 14/0 45/10 45/0 Webb and Tierney, Am Rev Respir Dis 1974; 110:556-565

  13. esophagealintubation

  14. Pulmonary • Interstitial • Emphesema • to Pneumo-

  15. Assessment • Chest x-ray AP • 8 rib conventional • 9-10 rib Hi-Fi • Rise & fall of chest (slight per NRP) • Listen to breath sounds • Vt 5-7 ml/kg (3-5 spont.) • follow ABGs

  16. Pressure Wave To Increase Mean Airway Pressure 1. Increase flow 2. Increase peak pressure 3. Lengthen inspiratory time 4. Increase PEEP 5. Increase Rate

  17. TYPES OF MECHANICAL VENTILATION • negative pressure ventilation • positive pressure ventilation • high-frequency ventilation • non-invasive positive pressure ventilation

  18. Body Box:

  19. Outline • Respiratory mechanics and gas exchange • Factors affecting oxygenation and carbon dioxide elimination during mechanical ventilation • Blood gas analysis • Ventilatory management: basics and specifics • High frequency ventilation: the basics

  20. Overview • Mechanical ventilation is an integral part of neonatal intensive care, and has led to increased survival of neonates over the last 3 decades • Advances in knowledge of neonatal respiratory physiology have led to optimization of techniques and strategies • Conventional mechanical ventilation (CMV) is most often used, despite the advent of HFV and SIMV

  21. Overview • Respiratory failure in neonates has significant morbidity and mortality (although less than in the past) • Optimal ventilatory management will reduce the risk of chronic lung disease • Optimal ventilatory management should be individualized and be based upon the pathophysiology and certain basic concepts of mechanical ventilation

  22. Concepts • Goal of mechanical ventilation: to improve gas exchange and to sustain life without inducing lung injury • Factors that should influence ventilator adjustment decisions: • Pulmonary mechanics • Gas exchange • Control of breathing • Lung injury

  23. Pulmonary mechanics • Compliance • Property of distensibility of the lungs and chest wall • Change in volume per unit change in pressure • C = D Volume D Pressure • Neonatal lung • Normal 0.003-0.006 L/cm H2O • with RDS 0.0005-0.001 L/cm H2O

  24. Pulmonary mechanics • Resistance: • inherent capacity of the air conducting system (airways and ETT) and tissues to resist airflow • Change in pressure per unit change in flow • R = D Pressure D Flow Total cross-sectional area of airways ResistanceLength of the airways Flow rate Density and viscosity of gas

  25. Pulmonary mechanics • Location of airway resistance: 0 5 10 15 20 • Distal airways contribute less to resistance due to increased total cross-sectional area • Small ETT and high flow rates can increase resistance markedly Resistance Distal --> Airway Generation

  26. Pulmonary mechanics • Laminar flow (Distal airways) • Driving pressure proportional to flow • R= 8 n l (n = viscosity ; l = length; r = radius) p r4 • Turbulent flow (Proximal airways) • Driving pressure proportional to square of flow • Reynolds number (Re) = 2 r V d (d = density) n

  27. Pulmonary mechanics • A pressure gradient between the upper airway and alveoli is necessary for gas flow during inspiration and expiration • The pressure gradient is required to overcome the elasticity, resistance, and inertance of the respiratory system • Equation of motion: P = 1 V + R V + I V C Elasticity+Resistance+Inertance

  28. Pulmonary mechanics • Time constant • The time taken for the airway pressure (and volume) changes to equilibrate throughout the lung is proportional to the compliance and resistance of the respiratory system • Time constant = Compliance x Resistance

  29. Pulmonary mechanics 99 98 95 • % change in pressure in relation to time • Almost full equilibration: 3-5 time constants 100 86 80 63 Change in pressure (%) 60 40 20 0 1 2 3 4 5 Time constants

  30. Pulmonary mechanics • Healthy term neonate: • C = 0.004 L/cm H2O; R = 30 cm H2O/L/sec • T = 0.004 x 30 = 0.12 sec • Time constants Time (sec) % equilibration 1 0.12 63 2 0.24 86 3 0.36 95 5 0.60 99 • RDS: Shorter time constant

  31. Pulmonary mechanics • Application of the concept of time constant • Short TI : decreased tidal volume delivery • Inadequate TE: Gas trapping ( FRC, inadvertent PEEP) • Heterogeneous lung disease (BPD): different regions of the lung have different time constants; tendency for atelectasis and hyperexpansion to co-exist

  32. Gas exchange • Total minute ventilation = tidal vol x freq • VE = VT x f • Alveolar ventilation (VA) = Useful (fresh gas) portion of minute ventilation that reaches gas exchange units; excludes dead space (VD) • VA = (VT-VD) x f • Alveolar ventilation equation: VA (L/min) = VCO2 (ml/min) x 0.863 (BTPS PACO2 (mm Hg) corr.)

  33. Gas exchange • Alveolar gas equation: • If R=1, each molecule of O2 removed from alveoli is replaced by one molecule of CO2 PAO2 = PIO2 -PACO2 • Average normal value for R = 0.8 PAO2 = FIO2 x (PB-PH2O)- PACO2x FIO2+ 1- FIO2 R • PaCO2 = effective PACO2 • True PACO2 = PETCO2

  34. Gas exchange • Ventilation-Perfusion matching: matching of gas flow and blood flow required for successful gas exchange • VA = Alveolar ventilation Q Pulmonary blood flow (Fick method: O2) = 0.863 x R x (CaO2 - CVO2) PACO2 • V/Q mismatching usually relevant to effect on alveolar-arterial PO2 difference: (A-a)DPO2

  35. Gas exchange • O2-CO2 diagram v 0.2 0.5 1.0 V/Q = 0 1.5 PCO2 Ideal V/Q = 0.84 0 20 40 60 I 8 V/Q = 40 60 80 100 120 140 160 P O2 (mm Hg)

  36. Gas exchange • Causes of hypoxemia • V/Q mismatch • Right to left shunt (venous admixture) • Hypoventilation (e.g. in apnea) • Diffusion abnormalities • Causes of hypercapnia • Hypoventilation • Severe V/Q mismatch

  37. Gas exchange • Factors involved in gas exchange during mechanical ventilation • Oxygenation • Carbon dioxide elimination • Gas transport mechanisms • Patient - ventilator interactions

  38. Gas exchange • Factors affecting oxygenation • Mean airway pressure (MAP): affects V/Q matching. MAP is theaverage airway pressure during respiratory cycle MAP = K (PIP-PEEP) [TI / (TI+TE)] + PEEP • Oxygen concentration of inspired gas (FIO2)

  39. Gas exchange • MAP increases with increasing PIP, PEEP, TI to TE ratio, rate, and flow PIP Pressure Flow Rate TI PIP PEEP PEEP Time TI TE

  40. Gas exchange • Relation of MAP to PaO2 not linear; is like an inverted “U”: • Low MAP: • Atelectasis-->very low PaO2 • High MAP: • hyperinflation--> V/Q mismatch; intrapulmonary shunt, hypoventilation due to distended alveoli • decreased cardiac output --> decreased oxygen transport despite adequate PaO2

  41. Gas exchange • For the same change in MAP, changes in PIP and PEEP improve oxygenation more than changes in I:E ratio • Reversed I:E ratios increase risk of air-trapping • PEEP levels higher than 6 cm H2O may not improve oxygenation in neonates • Attainment of optimal MAP may allow weaning of FIO2 • Atelectasis may lead to sudden increase in required FIO2

  42. Gas exchange • Carbon dioxide elimination • Proportional to alveolar ventilation (VA) which depends on tidal volume (VT) and frequency (rate) • VT changes more effective (but more barotrauma) : dead space constant, so proportion of VT that is alveolar ventilation increases to a greater degree with increases in VT • VT 4 --> 6cc/kg (50% ) with dead space of 2 cc/kg increases VA from 2 (4-2) to 4 (6-2) cc/kg/breath (100% )

  43. Gas exchange Short TI Optimal TILong TI • Clinical estimation of optimal TI and TE: Inadeq VT Short insp. plateau Long plateau Chest Wall Motion Time Short TE Optimal TELong TE Air trapping Short exp. plateau Long exp. plateau Chest Wall Motion

  44. Gas exchange • Synchrony vs. Asynchrony + “fighting” • Synchrony augments ventilation, improves CO2 elimination, decreases hypoxic episodes • Asynchrony leads to poor tidal volume delivery, and impairs gas exchange • Active exhalation (exhalation during ventilator breath) increases risk of hypoxic episodes

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