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.

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