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Tutorial: Pulmonary Function--Dr. Bhutani Clinical Case

Tutorial: Pulmonary Function--Dr. Bhutani Clinical Case. 695 g male neonate with RDS, treated with surfactant and on ventilatory support @ 18 hours age: Settings: 18 / 5 cm H 2 0 x 45 breaths / min; FiO 2 = 0.65 Driving Pressure: 18-5 = 13 cm H 2 0

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Tutorial: Pulmonary Function--Dr. Bhutani Clinical Case

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  1. Tutorial: Pulmonary Function--Dr. Bhutani Clinical Case 695 g male neonate with RDS, treated with surfactant and on ventilatory support @ 18 hours age: Settings: 18 / 5 cm H20 x 45 breaths / min; FiO2 = 0.65 Driving Pressure: 18-5 = 13cm H20 Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg Is this baby a candidate for permissive hypercapnia?

  2. Normocapnia varies? • Maternal:32 -34 mmHg (progesterone effect) • Fetal: 40 -42 mmHg • At birthing: 45 -65 mmHg • First day : 34 mmHg (progesterone effect) • After first week : 35 -42 mmHg • Term PCA: 35 -42 mmHg (RR = 40-60/min) • 52 wks PCA: 35 -42 mmHg (RR = 20-30/min)

  3. Strategies to Prevent Non-Permissive Hypercapnia • Define optimum PaCO2 levels • Level to at which you will intervene • Level to at which you will wean • Ventilate at optimal FRC • Continuous monitoring of tidal volume • Use least pressure for maximal tidal volume • Facilitate spontaneous breathing • Consider “dual wean” of driving pressures • Consider pseudo-adaptive strategies

  4. Alveolar Algebra: Ventilation • Alveolar Ventilation inversely correlated to PaCO2 • Alveolar Ventilation is (VT-VD) x rate • Provided dead space is constant: proportional changes in VT or rate will lead to proportional changes in alveolar ventilation and PaCO2. Based on Pulmonary Gas Law: in a steady state, when inspired CO2 is negligible, then PACO2 = 863 (VCO2 / VA); where, VCO2 is CO2 production; PACO2 is partial pressure of carbon dioxide; 863 is body temp. x std. pressure / standard temperature ( 310 X 760/273 = 863 )

  5. Clinical Case 695 g male neonate with RDS, treated with surfactant and on ventilatory support and is now about 18 hours age and has stable vital signs, normotensive and is normoglycemic: Settings: PIP:18 cm H20; PEEP: 5 cm H20; SIMV: 45 br / min; Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg Is the Alveolar Ventilation compromised? If so, by how much?

  6. Clinical Case 695 g male neonate with RDS, treated with surfactant and on ventilatory support and is now about 18 hours age and has stable vital signs, normotensive and is normoglycemic: Settings: PIP:18 cm H20; PEEP: 5 cm H20; SIMV: 45 br / min; Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg PaCO2 = 55 mmHg is 35% higher than 40 mmHg Alveolar Ventilation is decreased by 35%

  7. Clinical Case 695 g male neonate with RDS, treated with surfactant and on ventilatory support and is now about 18 hours age and has stable vital signs, normotensive and is normoglycemic: Settings: PIP:18 cm H20; PEEP: 5 cm H20; SIMV: 45 br / min; Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg PaCO2 = 54 mmHg is 35% higher than 40 mmHg Questions: Do we wean? Which option?

  8. Clinical Case • OPTIONS: • No Change • Reduce PIP by I cm H20 (17/5) : • Driving Pressure = 12 cm H20 • 3. Reduce PEEP by I cm H20 (18/4): • Driving Pressure = 14 cm H20 • 4. Reduce SIMV: Decrease minute ventilation

  9. Clinical Case: Use of Tidal Volume 695 g male neonate with RDS, treated with surfactant and on ventilatory support: Settings: 18 / 5 cm H20 x 35 breaths / min Driving Pressure: 18-5 = 13cm H20 Tidal Volume (measured): = 4 ml (5.7ml/kg) Effective Compliance: = V /  P ; 5.7 / 13 ml/cm H20/kg Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg

  10. Clinical Case 695 g male neonate with RDS, treated with surfactant and on ventilatory support: Settings: 18 / 5 cm H20 x 35 breaths / min Driving Pressure: 18-5 = 13cm H20 Tidal Volume (measured): = 4.0 ml (5.7 ml/kg) Effective Compliance: = V /  P ; 5.7 /13 = 0.44 ml / cm H20/kg Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg

  11. Relationship to FRC

  12. Least Intervention or Barotrauma Ventilate at Optimal FRC • Increase Lung Volume : CPAP • Adequate Lung Inflation : T insp. • Adequate Lung Deflation : T exp. • Adjust T insp. / T exp. : by estimating Time Constants

  13. Clinical Case 695 g male neonate with RDS, treated with surfactant and on ventilatory support: Settings: 18 / 5 cm H20 x 45 breaths / min Driving Pressure: 18-5 = 13cm H20 Tidal Volume (measured): = 4.0 ml (5.7 ml/kg) Effective Compliance: = V /  P ; 5.7 /13 = 0.44 ml / cm H20 Arterial Gas: pH = 7.3; PaO2 = 74; PaCO2 = 55 mmHg

  14. Graphic Representation of Ventilator Settings  V = 5.7ml/kg (PEEP) 5 18 (PIP)  P = 13 cm H20

  15. Graphic Representation of Ventilator Settings  V /  P = 5.7/ 13 = 0.44 ml/cm H20 /kg  V = 5.7ml/kg (PEEP) 5 18 (PIP)  P = 13 cm H20

  16. Linear Change in  V/  P 19 18 17  V /  P = 5.7/ 13 = 0.44 ml/cm H20 TLC  V VOLUME 5 PEEP Peak Inflating Pressure RV  P = Driving pressure PRESSURE (cmH20)

  17. Imaginary P-V relationship 19 18 17 TLC  V VOLUME PEEP 5 Peak Inflating Pressure RV  P = Driving pressure PRESSURE (cmH20)

  18. Clinical Case • OPTIONS: • No Change • Reduce PIP by I cm H20 (17/5) : • Driving Pressure = 12 cm H20 • 3. Reduce PEEP by I cm H20 (18/4): • Driving Pressure = 14 cm H20 • 4. Reduce SIMV: Decrease minute ventilation

  19. Wean Peak Inflating Pressure Peak Inflating Pressure 19 16 TLC Tidal Volume decreases with weaning  V VOLUME 5 18 PEEP 17  P = 12 Driving pressure decreased RV PRESSURE (cmH20)

  20. Clinical Case • OPTIONS: • No Change • Reduce PIP by I cm H20 (17/5) : • Driving Pressure = 12 cm H20 • 3. Reduce PEEP by I cm H20 (18/4): • Driving Pressure = 14 cm H20 • 4. Reduce SIMV: Decrease minute ventilation

  21. Wean PEEP Peak Inflating Pressure 19 17 TLC Tidal Volume increases with weaning  V VOLUME 5 PEEP 4 18  P = 14 Driving pressure increased RV PRESSURE (cmH20)

  22. Circuit Airflow • Airflow that is set, at operator’s discretion, to flow from inspiratory to expiratory circuits. • Magnitude dependent on patient’s minute ventilation • Excessive circuit airflow can lead to turbulence and may impede expiratory flow from the patient • Low flow may limit inspiratory airflow • Optimal circuit flow is about 5 to 8 fold minute ventilation

  23. Clinical Case • OPTIONS: • Dual Wean: Reduce both PIP/PEEP • Dual Wean: 18/5 to 17/4 cm H20 • = Driving Pressure • = 13 cm H20

  24. DUAL WEAN: concurrent wean of both PIP and PEEP Peak Inflating Pressure 19 16 TLC Tidal Volume increases with weaning Tidal Volume increases with weaning  V VOLUME 5 18 PEEP 4 17 Driving pressure unchanged RV  P = 13 PRESSURE (cmH20)

  25. DUAL WEAN that allows for permissive hypercapnia 18 Peak Inflating Pressure TLC 14 Tidal Volume unchanged with weaning  V VOLUME 5 PEEP 4 Driving pressure decreased RV  P = 10 PRESSURE (cmH20)

  26. Clinical Case • PaCO2 = 55 torr at 18/5: • IATROGENIC HYPERCAPNIA secondary to ventilation at “flattened” portion of the P-V relationship • After Dual Wean, PaCO2 will be lowered provided ventilation is occurring closer to total lung capacity. • Subsequent weaning to 14/4 may result in a PaCO2 = 55 torr • PERMISSIVE HYPERCAPNIA

  27. Iatrogenic hypercapnia with inappropriate Dual Wean 19 TLC 16 Tidal Volume decreases with weaning VOLUME  V PEEP 18 5 4 Peak Inflating Pressure RV 17  P PRESSURE (cmH20)

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