Principles of mechanical ventilation

mechanical ventilation

1. Presented by : Dr. Himanshu Jangid Principles of mechanical ventilation

2. Patients requiring mechanical ventilation : 1. Ventilatory Failure : Pt Minute ventilation cannot keep up with CO 2 production. 2. Oxygenation Failure : Pt’s pulmonary system cannot provide adequate oxygen for metabolism. Introduction

3. 1. ed Airway Resistance 2. Changes in Lung Compliance 3. Hypoventilation 4. V/Q Mismatch 5. Intrapulmonary Shunting 6. Diffusion Defect Pathophysiological Factors in Respiratory Failure

4. In Mechanical Ventilation it Depends upon: Length Airway Size ET Tube Patency Ventilator Circuit Airway Resistance

5. Obstrution in airway : 1. Inside the Airway( e.g. Retained secretions) 2. In the Wall of Airway( e.g. Bronchial muscle Neoplasm) 3.Outside the Airway(e.g. Tumour Compression) Poiseuille’s Law : P = V r 4 Airway Resistance

6. Resistance in ET Tube : Directly Proportional to: Length. Inversely Proportional to : Diameter and Patency. Resistance by Ventilator Circuit : Amount of water in circuit due to condensation Airway Resistance

7. Clinical conditions : 1. COPD : Emphysema Chronic Bronchitis Asthma Bronchiectasis 2. Mechanical obstruction : Postintubation Obstruction Foreign Body Aspiration Endotracheal Tube Condensation in Ventilator 3. Infection : Laryngotracheobronchitis Epiglottitis Broncholitis Airway Resistance

8. Airway Resistance(Raw) = ∆P V ∆P = Pressure change( Peak Inspiratory Pressure – Plateau Pressure) V = Flow Increased Raw = Increased work of breathing. Obstructive Disorders = Deeper and Slower Breathing. Restrictive Disorders = Shallow and Faster Breathing. Airway Resistance

9. Defination : Degree of lung expansion per unit pressure change. C = ∆P ∆V Lung Compliance

10. Low Compliance(high elastance ) : Stiff or Noncompliant lungs. High amount of work of breathing. Can be responsible for Refractory Hypoxemia. Occurs in Restrictive Lung diseases. Low lung volumes and Low minute ventilation. Increased Respiratory Rate. Variations in compliance

11. High Compliance : Increased FRC. Occurs in Obstructive Lung diseases. Incomplete Exhalation. Lack of elastic recoil. Emphysema: Chronic air trapping Destruction of lung tissue Enlargement of terminal and respiratory bronchioles Impaired gas exchange Lung Compliance

12. Pressure-Volume Loop 20 40 60 20 40 -60 0.2 LITERS 0.4 0.6 P aw cmH 2 O V T

13. Mandatory Breath Inspiration 20 40 60 20 40 -60 0.2 LITERS 0.4 0.6 P aw cmH 2 O V T

14. Mandatory Breath Expiration 20 40 60 20 40 -60 0.2 LITERS 0.4 0.6 P aw cmH 2 O Inspiration V T Counterclockwise

15. Pressure-Volume Loop Changes 20 40 60 -20 -40 -60 0.2 0.4 0.6 LITERS P aw cmH 2 O V T

16. Changes in Compliances Indicates a drop in compliance (higher pressure for the same volume) 20 40 60 20 40 -60 0.2 0.4 0.6 LITERS P aw cmH 2 O V T

17. Static Compliance : Measured when there is no air flow. Airway resistance is not a determing factor. Reflects the elastic resistance of lungs and chest wall. Lung Compliance

18. Dynamic Compliance : Measured when air flow is present. Airway resistance is a critical factor. Shows both the airway resistance and elastic resistance. Lung Compliance

19. 1.Obtain corrected expired tidal volume. 2.Obtain Plateau Pressure by applying inspiratory hold or occluding the Exhalation port at end expiration. 3.Obtain Peak Inspiratory Pressure. 4.Obtain Positive End Expiratory Pressure(PEEP) level. Method to measure Static and Dynamic Compliance

20. Static Compliance : Corrected Tidal Volumae ( PleateuPressure – PEEP) Dynamic Compliance : Corrected Tidal Volume (peak Inspiratory Pressure – PEEP) Method to measure Static and Dynamic Compliance

21. Static Compliance : Atelectasis ARDS Tension pnemothorax Obesity Retained Secretions Dyanamic Compliance : Bronchospasm Kinking of ET Tube Airway Obstruction Lung Compliance

22. Anatomical Dead space : The volume of conducting airways which doesn’t take part in gas exchange. About 1ml/lb in ideal body weight. ed Tidal volume = Increase in anatomic dead space % Example: 150/500 = 0.3 or 30% 150/300 = 0.5 or 50% Dead space Ventilation

23. Aleoolar Deadspace : When a % of alveoli ventilated are not adequately perfused . Causes: Decreased Cardiac Output Obstruction of pulmonary vessels Dead space Ventilation

24. Physiologic Deadspace : Anatomic + Alveolar Deadspace In Normally , PhysioDS = Anatomic Deadspace Physiologic Deadspace to tidal volume ratio can be calculated by : V(d) = PaCO2 – PeCO2 V(t) PaCO2 PaCO2 = Arterial CO2, PeCO2 = Mixed expired sample V(d)/V(t) < 60% predicts normal ventilatory function upon weaning from mechanical ventilation. Dead space Ventilation

25. Physiological Dead space in Health and Disease

26. Inability to maintain proper removal of CO2 from lungs. Five mechanisms: 1. Hypoventilation 2. Persistent V/Q mismatch 3. Persistent Intrapulmonary Shunting 4. Persistent Diffusion Defect 5. Persistent reduction of inspired oxygen tension. Ventilatory Failure

27. Causes: CNS Depression Neuromuscular diseases Airway obstruction Characterized by : Decreased Alveolar Ventilation Increased Arterial CO2 Tension Hypoventilation

28. Causes of Hypoventilation

29. Alveolar Volume: Volume of tidal volume that takes part in gas exchange. Va = V(t) – V(d) Proportional to Tidal volume Inversely proportional to Deadspace volume Minute Alveolar Ventilation : Va = ( Vt – Vd ) x RR Alveolar ventilation

30. Amount of Ventilation Amount of Perfusion V/Q Ratio = 0.4 ( in lower lung zone) Because of Gravity = 0.3 ( in upper lung zone) V/Q Ratio Pulmonary Embolism V/Q Ratio Airway Obstruction ILD Hypoxemia due to mismatch can be corrected by : Increasing the Rate , Tidal volume and FiO2 on ventilator. V/Q Mismatch

31. Shunting refers to perfusion in excess of ventilation. Causes Refractory Hypoxemia Poor response to O2 Therapy Normally ; Physiologic Shunt = Anatomic Shunt < 5% NonCritical Patients = < 10% Critical Patients = > 30% Intra Pulmonary Shunting

32. .

33. Estimated Physiologic Shunt Equation : NonCritical pts : Estimated Qsp = ( CcO2 – CaO2) Qt 5 + ( CcO2 – CaO2) Critical pts : Estimated Qsp = ( CcO2 – CaO2) Qt 3.5 + (CcO2 – CaO2) Classical PS Equation : Classic Qsp = CcO2 – CaO2 Qt CcO2 – CvO2 Shunt Equation

34. Decrease P(A-a) gradient High Altitude Fire Combustion Thickening of A-C membrane Pul . Edema Retained secretions Decrease surface area of A-C Emphysema membrane Pul . Fibrosis Insufficient time for diffusion Tachycardia Diffusion Defects

35. Hypoxemia : Reduced O2 in blood. PaO2 : Reflects the dissolved O2 in blood not that carried by hemoglobin . Precise measurement by Oxygen Content ( CaO2). Hypoxemia Levels in term of PaO2 Normal 80 – 100 mmHg Mild 60 – 79 mmHg Moderate 40 – 59 mmHg Severe < 40 mmHg Oxygenation Failure

36. Hypoxia : Reduced O2 in Organs and tissues. Can occur with a normal PaO2. Four types : 1. Hypoxic Hypoxia 2. Histotoxic Hypoxia 3. Stagnant Hypoxia 4. Anemic Hypoxia Oxygenation Failure

37. Three Distinct Groups: 1.Depressed Respiratory Drive 2.Excessive Ventilatory Work load 3.Failure of Ventilatory pump Clinical conditions leading to mechanical ventilation

38. Depressed Respiratory Drive : Drug Overdose Acute Spinal cord injury Head trauma Neurological Dysfunction Sleep Disorders Metabolic Alkalosis Clinical conditions leading to mechanical ventilation

39. Excessive Ventilatory Work load : Acute Airflow Obstruction Deadspace ventilation Acute Lung Injury Congenital Heart Diseases Cardiovascular decompensation Shock Increased Metabolic Rate Decreased Compliance Drugs Clinical conditions leading to mechanical ventilation

40. Failure of Ventilatory pump : Chest Trauma Premature Birth Electrolyte Imbalance Geriatric Patients Clinical conditions leading to mechanical ventilation

41. Thank You To be Continued …….