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Ventilation of Patients with COPD and Asthma

Ventilation of Patients with COPD and Asthma. Chronic lung diseases with airflow obstruction. Chronic lung diseases with airflow obstruction. Asthma Emphysema Bronchitis. COPD CXR. Near fatal asthma. Near fatal asthma. Mechanical Venitlation of COPD & Asthma Exacerbations.

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Ventilation of Patients with COPD and Asthma

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  1. Ventilation of Patients with COPD and Asthma

  2. Chronic lung diseases with airflow obstruction

  3. Chronic lung diseases with airflow obstruction

  4. Asthma Emphysema Bronchitis

  5. COPD CXR

  6. Near fatal asthma

  7. Near fatal asthma

  8. Mechanical Venitlation ofCOPD & Asthma Exacerbations Objectives  Pathophysiology - PaCO2 dederminants- Gas trapping - Work of breathing - Auto-PEEP  NIPPV - IPAP - EPAP  Mechanical ventilation - FIO2- PEEP - VT

  9. Pathohysiology ofAsthma/COPD Exacerbations Airway narrowing & obstruction IPAP Airway Inflammation ­ Frictional WOB MV Auto- PEEP Shortened muscles, ¯ curvature ­ Elastic WOB Gas trapping ¯ muscle strength ­ VCO2 VT ­ VE • PaCO2 • pH • PaO2 VA Steroids Abx? PEEP BDs MV? IPAP MV?

  10. Determinants of PaCO2 PaCO2VCO2 VA  VA   VE -  RR -  VT - VD (without  VE)  VCO2   Work - Agitation - Seizures -  WOB   Metabolism - Fever - CHO -  T4

  11. Oxygen Cost of Breathing Roussos, JCI 1959

  12. PV Curve in COPD and Asthma(Stable) Emphysema 6 Normal/ Asthma VL (L) VT 4 2 VT -10 -20 -30 -40 Ptp (cm H2O) Macklem and Becklake, 1963

  13. PV Curve in COPD & Asthma(Acute Exacerbtion) Emphysema 6 Asthma VL (L) 4 VT 2 VT -10 -20 -30 -40 Ptp (cm H2O)

  14. Implication VT falls because FRC encroaches on TLC  Limited ability to  VT with MV/IPAP Best way to  PaCO2 is to  VCO2   WOB (frictional and/or elastic)  PaCO2 even if VT, VE and VA are constant

  15. Work of Breathing Total Work Elastic Work Work of Breathing Frictional Work RV FRC TLC

  16. Effect of VA/Q on PaCO2(Normal) PAO2 = 100 PACO2 = 40 PAO2 = 100 PACO2 = 40 DCO2 = 100 ml/min VCO2 = 100 ml/min VCO2 = 100 ml/min DCO2 = 100 ml/min PvCO2 = 46 PvCO2 = 46 PcCO2 = 40 PcCO2 = 40 PaCO2 = 40

  17. Effect of VA/Q on PaCO2(Low VA/Q, Normal) PAO2 = 50 PACO2 = 40 PAO2 = 100 PACO2 = 40 50%  VE 50%  VE DCO2 = 50 ml/min DCO2 = 150 ml/min VCO2 = 50 ml/min VCO2 = 150 ml/min PvCO2 = 46 PvCO2 = 46 PcCO2 = 40 PcCO2 = 40 HPV PaCO2 = 40

  18. Effect of VA/Q on PaCO2(Low VA/Q,, AECOPD) PAO2 = 50 PACO2 = 40 PAO2 = 100 PACO2 = 40 50%  VE VE at max DCO2 = 150 ml/min DCO2 = 50 ml/min VCO2 = 50 ml/min VCO2 = 100 ml/min PvCO2 = 46 PvCO2 = 46 PcCO2 = 40 PcCO2 = 44 HPV PaCO2 = 42

  19. Effect of VA/Q on PaCO2(Low VA/Q,, AECOPD,  FIO2) PAO2 = 100 PACO2 = 44 PAO2 = 100 PACO2 = 44  FIO2 50%  VE VE constant DCO2 = 100 ml/min DCO2 = 100 ml/min VCO2 = 50 ml/min VCO2 = 50 ml/min PvCO2 = 46 PvCO2 = 46 PcCO2 = 44 PcCO2 = 44 HPV PaCO2 = 44

  20. Ventilation in COPD/Asthma

  21. Ventilation in COPD/Asthma

  22. Which Patients with COPD benefit from NIV ?

  23. NIPPV Pathophysiology of AECOPD & Asthma is amenable to Rx with NIPPV ·EPAP for auto-PEEP ·IPAP for inspiratory Raw Will work of breathing ·  VCO2 · At constant VA,  PaCO2 and  pH May  VA May mortality and intubation rate

  24. Which Patients with COPD benefit from NIV ?Hospital Mortality 12% NNT 8 2%

  25. NIV in Severe Asthma • 17 Episodes of ARF due to asthma • 2 patients required intubation for worsening PaC02 • Duration of NPPV was 16±21 h. • All patients survived. Length of hospital stay was 5±4 days

  26. Ventilation in COPD/Asthma

  27.  Peak Airway Pressure & Normal Plateau Resistance Resistance Compliance Pressure Pressure Time Time

  28. Air-trapping in Asthma/COPD Patients on Mechanical Ventilation I :E 1:1 I : E 1: 6 Lung volume Tidal ventilation VEI V VT T V EE FRC Time

  29. Assessment of Mechanics Raw= Peak - Plateau Auto-PEEP

  30. Obstructive Airway Disease • Beware of auto-PEEP!

  31. After the third breath, the airway was occluded at end-expiration using the end-expiratory hold function on the ventilator. During the period of zero flow, pressure in the alveoli and ventilator circuit equilibrate, and the plateau pressure reflects auto or intrinsic positive end-expiratory pressure (PEEPi), indicated by the arrow.

  32. Giving CPAP to a patient who has auto-PEEP The increased work of breathing associated with auto-PEEP can be offloaded by applying CPAP to the trachea/mouth, and splinting open the connecting airways.

  33. The use of external PEEP in the setting of auto-PEEP may be conceptualized by the "waterfall over a dam" analogy. In this analogy, the presence of dynamic hyperinflation and 10 cmH20 of auto-PEEP is represented in the top panel by the reservoir of water trickling over the dam represented by the solid block. In the middle panel, as long as the external PEEP is less than or equal to the amount of auto-PEEP, the amount of water in the upstream reservoir, representing dynamic hyperinflation, does not increase. However, once the amount of water in the reservoir does increase (bottom panel), dynamic hyperinflation worsens.

  34. Excessive Inspiratory Time Air Trapping Auto-PEEP Normal Patient Inspiration Increase WOB and “Fighting” of the ventilator Time (sec) Flow (L/min) } Expiration

  35. Ventilation in COPD/Asthma

  36. Pressure or Volume Mode? Volume • Predictable TV • Peak-Plat gradient • Monitor Plat • Better acidosis control Pressure • Minimise over-distension • Monitor Tidal volume • Excess volumes as airway resistance improves

  37. Mechanical Ventilation ofCOPD & Asthma Exacerbations Mode: AC vs IMV  PS  ? rest respiratory muscles: CMV  Better sleep with AC vs. IMV-PS Ventilator-induced diaphragm changes (?) Triggering: key issue with either mode PEEP to counter auto-PEEP  Major cause of patient-ventilator dissynchrony

  38. Initial Ventilator Settings • Inspiratory time 0.8 – 1.2 secs • RR 10-12 • TV 6-8 ml/Kg • Pplat < 30 cm H2O • PEEP ??

  39. Assessment of Hyperinflation

  40. Reducing Hyperinflation I : E 1: 6 I : E 1: 2 • Reduce rate • Reduce tidal volume • Increase expiratory time • Increase inspiratory flow rate • Increased Peak Airway Pressure • Monitor (Pplat) • Tolerate increased CO2 (minimise dead space)

  41. COPD flow and frequency As flow increased from 30 to 60 and 90 L/min (from right to left), frequency increased from (18 to 23 and 26 breaths/min, respectively), Auto-PEEP decreased (from 15.6 to 14.4 and 13.3 cm H2O, respectively) and end-expiratory chest volume also fell. Increases in flow from 30 L/min to 60 and 90 L/min also led to decreases in the swings in Pes from 21.5 to 19.5 and 16.8 cm H2O.

  42. Hypercapnia: How permissive? • Defence of intracellular pH • Apnoeic oxygenation in dogs to pH 6.5 and PaCO2 of 55kPa • Anaesthetic mishap with PaCO2 of > 300 mmHg (40 kPa) and pH of 6.6 survived without sequelae Am J Respir Crit Care Med 1994; 150:1722-37

  43. Ventilation in COPD/Asthma

  44. External & Internal PEEP Waterfall Concept Pao 0 Pao 0 10 10 EPP EPP 10 +10 10 Palv Palv 10 10 10 Pel Ppl Ppl

  45. Effect of Auto-PEEP Normal airway resistance (end-exhalation) Ptp = 5 - 5 PA = 0 Patm = 0 Ppl = - 5 Pel = 5 - 5 D Ppl needed to initiate inhalation: - 1 PA drops to - 1 relative to Patm

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