Principles of mechanical ventilation
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The document discusses mechanical ventilation and factors that influence airway resistance. It notes that patients may require mechanical ventilation due to ventilatory or oxygenation failure. Several factors can affect airway resistance, including changes in lung compliance, airway obstructions, and infections. The length and diameter of the endotracheal tube and patency of the ventilator circuit also impact resistance. Clinical conditions like COPD, asthma, and infections can further increase resistance. Proper assessment of compliance, dead space, and causes of hypoxemia are important for effective mechanical ventilation.
Principles of mechanical ventilation
- 1. Presented by : Dr. Himanshu Jangid
- 2. Patients requiring mechanical ventilation : 1. Ventilatory Failure : Pt Minute ventilation cannot keep up with CO2 production. 2. Oxygenation Failure : Pt’s pulmonary system cannot provide adequate oxygen for metabolism.
- 3. 1. ed Airway Resistance 2. Changes in Lung Compliance 3. Hypoventilation 4. V/Q Mismatch 5. Intrapulmonary Shunting 6. Diffusion Defect
- 4. In Mechanical Ventilation it Depends upon: Length Airway Size ET Tube Patency Ventilator Circuit
- 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 r4
- 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
- 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
- 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.
- 9. Defination: Degree of lung expansion per unit pressure change. C = ∆P ∆V
- 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.
- 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
- 12. 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O VT
- 13. Mandatory Breath Inspiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O VT
- 14. Mandatory Breath Expiration 0 20 40 602040-60 0.2 LITERS 0.4 0.6 Paw cmH2O Inspiration VT Counterclockwise
- 15. Pressure-Volume Loop Changes 0 20 40 60-20-40-60 0.2 0.4 0.6 LITERS Paw cmH2O VT
- 16. Changes in Compliances Indicates a drop in compliance (higher pressure for the same volume) 0 20 40 602040-60 0.2 0.4 0.6 LITERS Paw cmH2O VT
- 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.
- 18. Dynamic Compliance: Measured when air flow is present. Airway resistance is a critical factor. Shows both the airway resistance and elastic resistance.
- 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.
- 20. Static Compliance : Corrected Tidal Volumae (PleateuPressure – PEEP) Dynamic Compliance : Corrected Tidal Volume (peak Inspiratory Pressure – PEEP)
- 21. Static Compliance : Atelectasis ARDS Tension pnemothorax Obesity Retained Secretions Dyanamic Compliance: Bronchospasm Kinking of ET Tube Airway Obstruction
- 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%
- 23. Aleoolar Deadspace : When a % of alveoli ventilated are not adequately perfused. Causes: Decreased Cardiac Output Obstruction of pulmonary vessels
- 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.
- 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.
- 27. Causes: CNS Depression Neuromuscular diseases Airway obstruction Characterized by : Decreased Alveolar Ventilation Increased Arterial CO2 Tension
- 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
- 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.
- 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%
- 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
- 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
- 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
- 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
- 37. Three Distinct Groups: 1.Depressed Respiratory Drive 2.Excessive Ventilatory Work load 3.Failure of Ventilatory pump
- 38. Depressed Respiratory Drive : Drug Overdose Acute Spinal cord injury Head trauma Neurological Dysfunction Sleep Disorders Metabolic Alkalosis
- 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
- 40. Failure of Ventilatory pump: Chest Trauma Premature Birth Electrolyte Imbalance Geriatric Patients
- 41. Thank You