Basics of Mechanical Ventilation

For Medical Officer, Residents, Critical care Nursing

1. Mechanical Ventilation: Part –I(Basics and Modes) Presenter: Dr. Tirtha Raj Bhandari Anesthesiologist Dadeldhura Hospital, Dadeldhura 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 1

2. Objectives Basic physiology and physics of lung and ventilator To discuss indication of mechanical ventilation To discuss different modes for mechanical ventilation To discuss Troubleshooting during mechanical ventilation To discuss Weaning 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 2

3. CLASSIFICATION MECHANICAL VENTILATION 3 Airway pressure Negative pressure ventilation Positive pressure ventilation Invasiveness Invasive Ventilation Non-invasive mechanical ventilation

4. CLASSIFICATION MECHANICAL VENTILATION 4 1. Negative Pressure Ventilators ( Extrathoracic ) Applied to the outside of the chest which causes chest to rise and expand (inspiration). Indicated for intermittent use, home care and patients with neuromuscular pathologies. Examples:          a. lron Lung (Body Tank).          b. Chest Cuirass 2. Positive Pressure Ventilators ( lntrapulmonary Pressure) Creates a positive pressure that will push air into the patient's lungs and increase intrapulmonary pressure Exhalation is passive and begins when the pressure is terminated and the exhalation valve opens.

5. AIRWAY RESISTANCE 5 Occurs as a result of the friction between the air molecules and the walls of the tracheobronchial tree, and to some extent, as a result of the friction between the air molecules themselves Poiseuille’s law states that the resistance (Raw) to the flow of fluids through a long and narrow tube is: ►Proportional to the length of the tube (l) and the viscosity of the fluid (η) ► Inversely proportional to the fourth power of the radius (r) . This means small changes in the radius can have inordinate effects on airway resistance More than 90% of the normal airway resistance originates in airways which are more than 2.0 mm in diameter

6. AIRWAY RESISTANCE 6 Normal Raw ranges from 0.6 to 2.4 cm H2O/L/s. With an endotracheal tube in situ The driving pressure across a tube in ventilated patient is a function of the difference between the pressures at its ends In a patient who is not being given positive pressure breaths is dependent upon the difference between the atmospheric pressure ( Patm ) and the alveolar pressure ( PALV) (Raw) in a Spontaneous breathing Patient

7. AIRWAY RESISTANCE 7 Clinical conditions that increase airway resistance are:

8. AIRWAY RESISTANCE 8 The airflow resistance of a patient-ventilator system may be monitored using the pressure-volume (P-V) loop An increased bowing of the P-V loop suggests an overall increase in airflow resistance When the inspiratory flow exceeds a patient’s tidal volume and inspiratory time requirement, bowing of the inspiratory limb may result (line A2) When the expiratory airflow resistance is increased (e.g., bronchospasm ), bowing of the expiratory limb (line B2) may occur

9. LUNG COMPLIANCE 9 Measure of distensibility of Lung and calculated by: If a large change in volume is achieved by applying a relatively small amount of airway pressure, the lung is easily distensible and is said to be highly compliant A stiff and poorly compliant lung resists expansion and only a small change in volume occurs with a relatively large change in pressure Compliance has two components A) static B) Dynamic C = ∆V/∆P

10. STATIC LUNG COMPLIANCE 10 Static compliance is the true measure of distensibility of the respiratory system (lung + chest wall) Static compliance can be measured on the ventilator as follows: where V t = Tidal Volume P pl = Plateau pressure PEEP = Positive end-expiratory pressure Measured when the flow is momentarily stopped C stat = V t ( P pl – PEEP)

11. STATIC LUNG COMPLIANCE 11 In mechanically ventilated patient with an essentially normal chest wall and lungs, the static compliance of the respiratory system is usually in the range of 70–100 mL /cm H2O

12. DYNAMIC LUNG COMPLIANCE 12 It is measured while air is still flowing through the bronchial tree It reflects not only the lung and chest wall stiffness, but also the airway resistance, against which distending forces have to act It measure of both static compliance and airflow resistance and can be regarded as a measure of impedance Dynamic compliance falls when either lung stiffness or airway resistance increases Dynamic compliance can be measured as: V t = tidal volume, P P k = peak airway pressure, PEEP = positive end-expiratory pressure. C dyn = V t ( P pk – PEEP)

13. LUNG COMPLIANCE 13

14. LUNG COMPLIANCE 14 Static and dynamic compliance in various lung conditions

15. Alveolar Ventilation & Dead-Space The total surface area of the alveolar epithelium is about 72–80 m2 Approximately 85–95% (about 70 m2) of this is in contact with pulmonary capillaries: this constitutes the alveolocapillary interface The part of the inspired gas that does not come into contact with the pulmonary capillary bed is termed the dead-space Dead space can be: 1)Anatomical 2 )Alveolar 3 ) Physiological

16. Alveolar Ventilation & Dead-Space

17. Alveolar Ventilation & Dead-Space Minute ventilation is the product of the tidal volume times the respiratory rate It is inversely proportional to the PaCO2. It also affects the PaO2 in a nonlinear fashion; however, manipulating the minute volume for the change in PaO2 is undesirable, as only small changes in PaO2 can be brought about by large alterations in minute ventilation. Such large changes in minute ventilation can have a profound and unwanted effect on PaCO2.

18. EXAMPLE: A set tidal volume of 500 mL and a RR of 10 breaths/min results in a minute ventilation of 500 × 10 = 5,000 mL /min The same minute ventilation can be produced by a tidal volume of 250 mL delivered at a RR of 20 breaths/min 250 × 20 = 5,000 mL /min When dead-space 150ML is taken the alveolar ventilation In the first example would be (500 – 150) × 10 = 3,500, In the second example would be (250 – 150) × 20 = 2,000 The alveolar ventilation in the first instance would vastly exceed the alveolar ventilation in the second example The PaCO2 is inversely proportional not to all of the minute ventilation, but to that part of the ventilation that is independent of dead-space Alveolar Ventilation & Dead-Space

19. Alveolar Ventilation & Dead-Space

20. Peak Inspiratory Pressure ( P peak ) During a ventilator-driven tidal breath, the airway pressure rises rapidly to a peak which is called as Peak Inspiratory Pressure It is influenced both by airway resistance and compliance It can be high either on account of narrowed airways or stiff lung It is used to deliver the tidal volume by overcoming non-elastic (airways) and elastic(lung parenchyma) resistance

21. Plateau Pressure ( P plateau ) At the end of inspiration, the airway pressure falls to a plateau as the air diffuses out to the periphery of tracheobronchial tree This pressure within the airway during no airflow period is called the pause pressure or the plateau pressure It is a reflection of the static compliance Any condition that stiffens the lung will increase the pause pressure.

22. Plateau Pressure ( P plateau )

23. POSITIVE END-EXPIRATORY PRESSURE (PEEP) PEEP is alveolar pressure above atmospheric pressure that exist at the end of expiration Types of PEEP: A)Extrinsic PEEP PEEP provided by mechanical ventilator B)Intrinsic PEEP Secondary to incomplete expiration Also known as auto PEEP

24. Baseline Pressure PEEP/CPAP Physiological effects of positive end-expiratory pressure (PEEP)

25. Mean Airway Pressure( P mean ) Average pressure within the airway over the entire respiratory cycle Is significantly affected by: PEEP Inspiratory time (T I ) Is affected to a lesser degree by: Peak pressure Has significant affect on oxygenation

26. AIRWAY OPENING PRESSURE

27. PLEURAL & ALVEOLAR PRESSURE

28. Pressure, volume and flow relationship is described by equation of motion for the respiratory system. (stems from Newton’s third law of motion) P TR = P E +P R P TR Transrespiratory pressure(P at the airway opening minus pressure at the body surface) P E pressure caused by elastic resistance, P R Resistance due to airflow 29 Physics

29. Volume Compliance A (P AW ) Flow x resistance + Physics Only possible to set one of: Pressure Flow Volume Other variables become a dependent variable +PEEP

30. Indications Can not oxygenate (low PaO2/SpO2)- Hypoxemic respiratory failure Can not ventilate (high PCO2)- Hypercarbic Respiratory failure Both Can not protect airway/ secure airway( Low GCS) When clinician/ physician confused, either patient need or not, needs mechanical ventilation Elective ventilation for GA 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 31

31. Goals/Principles of mechanical Ventilation To provide adequate ventilation and oxygenation To achieve adequate lung volume and recruitment To improve lung compliance To reduce work of breathing To limit lung injury 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 32

32. Assessment for MV We should know 1)History and physical examination 2) Laboratory and radiological finding of patient 3) Anatomical size and structure of airway and lungs 4) Disease severity 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 33

33. Classification Both on inferior airway invasion 1 ) Non- invasive : No inferior airway invasion 2) Invasive : Invasion by endotracheal tube Based on modes 1 ) Controlled Mechanical Ventilation : PCV, VCV, PRVC, HFV, CMV, IMV 2) Supported spontaneous breathing : PSV, VSV 3) Mixed Respiratory Support : SIMV/ or +PS 4) Assisted spontaneous breathing : CPAP, APRV 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 34

34. VCV Volume is independent variable Pressure varies with compliance of lung Expiration is passive not affected by ventilator mode, rather affected by compliance and resistance Not a weaning mode Peak airway Pressure= R*F+ Vt/compliance+ PEEP Plateau Pressure= Vt/compliance+ PEEP 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 35

35. VCV What do we set?? Vt and RR for Minute Ventilation  For PaCO2 Management PEEP and FiO2  For Pao2 Management Flow/ I:E ratio- for both 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 36

36. PCV Pressure is independent variable Volume is dependent variable  Depends on: level of pressure, I-time also it is the function of compliance and airway resistance. That’s why volume deliver can vary breath to breath. Ventilator adjust flow to maintain pressure. Flow decreases throughout the inspiratory cycle. Good mode to use if patient has large air leak, the ventilator will increase the flow to compensate it. Not a weaning mode 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 37

37. PCV What do we set?? Pressure limit, T- Insp , RR,FIO2,PEEP P and RR  for Minute ventilation PaCO2 management FiO2 and PEEP for PaO2 management 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 38

38. VCV and PCV 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 39

39. Pressure Support=PS Supports each spontaneous breath with supplemental flow to achieve preset pressure All breath are triggered by patient Preset value  PIP, PEEP, FiO2 Patient determine Rate, Ti , I/E ratio, TV 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 40

40. PS Needs intact respiratory drive Helps to overcome airway resistance/ tube resistance, so that spontaneous breathing will be easier Can not be use in patient not having spontaneous breathing(i.e. muscle relaxant) 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 41

41. SIMV= Synchronized intermittent mandatory ventilation Preset mechanical breath delivered within interval acc to preset and wait for spontaneous in between, which it will use as a trigger to deliver full breath. If not sensed it will automatically give a breath Vt on spontaneous breaths depends entirely upon the patient effort and lung mechanics, can be pressure or volume controlled. 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 42

42. SIMV Tb(time for breathing) = Tm(mandatory)+ Ts (spontaneous) If patient tries to breath during Tm, ventilator gives a fully assisted breath If Patient tries to breath during Ts , the ventilator will allow the patient to take breath 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 43

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46. SIMV+PS SIMV+PS= provides assistance for spontaneous breath to overcome tube resistance 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 47

47. CPAP Provides continuous positive pressure throughout the respiratory cycle So gives supports to inspiration and resistance to expiration Can be use both in invasive and non-invasive form. Very similar to PEEP 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 48

48. PEEP PEEP is a residual pressure above atmospheric pressure maintained at the end of expiration. PEEP can be added to any mode PEEP helps to recruit alveoli, increase FRC , Redistribute pulmonary edema, Decrease intrapulmonary shunt, Increase PaO2.(GOOD) PEEP , decreases venous return/CO, increase ICP/intensify cerebral ischemia/ risk of barotrauma(Bad) 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 49

49. CPAP 5/21/21 Dadeldhura Hospital Dadeldhura 50

50. CPAP 5/21/21 Dadeldhura Hospital Dadeldhura 51

51. CPAP 5/21/21 Dadeldhura Hospital Dadeldhura 52

52. BiPAP 5/21/21 Dadeldhura Hospital Dadeldhura 53

53. BiPAP 5/21/21 Dadeldhura Hospital Dadeldhura 54

54. CPAP Vs BiPAP 5/21/21 Dadeldhura Hospital Dadeldhura 55

55. CPAP Vs BiPAP 5/21/21 Dadeldhura Hospital Dadeldhura 56

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60. IPAP/EPAP 5/21/21 Dadeldhura Hospital Dadeldhura 61

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68. NASAL CPAP FOR NEONATE/INFANT Nasal prong/ Nasopharyngral tube/ET tube can be use for nasal cpap 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 69

69. Indication Disease condition; 1)Retained lung fluid 2)Post- extubation (if risk of airway collapse) 3)Atelectasis 4)Respiratory distress syndrome 5) For administration of controlled concentration of nitric oxide 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 70

70. CONTD Physical findings : 1)Increase WOB ,indicated by increase RR by 30-40% 2)Sub-sternal/suprasternal retraction 3)Grunting and nasal flaring 4)Pale or cyanotic skin color 5)Agitation 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 71

71. Contraindication/ Should 'Not Try C/I: Choanal atresia Untreated diaphragmatic hernia Cleft palate TEF Should 'not try: Cardiovascular instability Severe ventilatory impairment Severe hypoxemia Frequent apnea High level of sedation 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 72

72. How it Helps?? Reduces grunting and tachypnea Increases FRC and PaO2 Decreases intrapulmonary shunting Improves lung compliance Aids in stabilization of floppy infant chest wall 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 73

73. CONTD Improves distribution of ventilation Reduce WOB Reduces central and obstructive sleep apnea by mechanically splinting the upper airway. Better recruitment and oxygenation Stimulation of infant/neonate for breathing 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 74

74. Mechanical Ventilation: Part -II(Troubleshooting and Weaning) Presenter: Dr.Tirtha Raj Bhandari Anesthesiologist Dadeldhura Hospital,dadeldhura 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 75

75. Troubleshooting and Weaning 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 76

76. Common Troubleshooting Ventilator alarms Hypoxia(Desaturation) Hypotension Patient ventilator dysynchrony 77

77. Assessment Is the chest moving and is it moving symmetrically? Is the patient cyanosed? What is the arterial saturation? Is the patient haemo -dynamically stable ? -Do not forget to observe respiratory pattern and feature of respiratory distress 78

78. High Airway Pressure Why does this matter?? -Risk of barotrauma -Hypoventilation(premature termination by high airway pressure) 79

79. Causes of high airway pressure; 80

80. CONTD Ventilator malfunction/setting circuits problems Endotracheal tube obstruction Increase airway resistance Decrease compliance of lung 81

81. Dynamic Compliance Static compliance(lung) Bronchospasm Obesity Kinking of tubes Atelectasis, ARDS Airway obstruction(mucus, secretions) Pneumothorax Retained secretion 82

82. Dynamic compliance  PIP 83

83. Static Compliance  Both PIP and PLAT 84

84. Low Airway Pressure/volume Why it is important?? -Risk of hypoventilation  hypoxia and hypercarbia (Lactic and respiratory acidosis)  Deasaturation  Bradycardia Cardiac Arrest 85

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86. Auto-peep 87

87. Causes of Auto-peep formation Inadequate time for expiration, either by flow limitation or development of resistance in airway or endotracheal tube More time for inspiration Obstructive airway disease High minute ventilation( High Tidal Volume, High Frequency) Dysynchrony 88

88. Pathophysiological Consequences of air trapping Air-trapping Dynamic hyperinflation  Autopeep leads following consequences, 1) Increase intra-thoracic pressure 2) Increase work of breathing 3) Decrease preload  Hypotension 4) Worsened V/Q mismatch 5) Increase risk of barotrauma 89

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92. Management of Auto-PEEP Depends upon cause -decrease MV -allow sufficient time for expiration -bronchodilator -use higher size tube -remove obstruction in airway -increase sedation 93

93. Desaturation(Hypoxia) Ventilatory Malfunction ET tube disconnection(circuit malfunction), cuff leak Oxygen failure Any causes of hypoxic respiratory failure Special consideration: endobronchial intubation, pneumothorax, collapse of part of lung, pulmonary edema, bronchospasm and pulmonary embolis m 94

94. Management Increase F io2 to 1.0 Check whether the chest is moving or not Briefly examine chest to determine the cause of desaturation If cause is not obvious manually ventilate the patient with 100% oxygen to exclude ventilator malfunction as the cause Treat underlying cause Alter ventilator settings to improve oxygenation Chest x-ray 95

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97. Hypotension Immediately after the initiation of mechanical ventilation hypotension can occur: Causes: Relative Hypovolaemia : reduction in venous return exacerbated by positive intra-thoracic pressure. Drug induced vasodilation and myocardial depression: all induction agents have some short lived vaso -dilatory myocardial depressant effects. Tension pneumothorax Gas trapping ( dyanamic hyperinflation ) Delayed cause may be due to pathological process going on in patient’s body. 98

98. Management Depends upon causes -fluid therapy -decrease positive pressure/peep -treat air trapping -chest tube(if pneumothorax) 99

99. Dysynchrony 100

100. Dysynchrony According to its relationship to specific phases of the delivered breath: breath initiation/trigger, flow delivery and breath cycling/termination . *Asynchrony/ dysynchrony index 101

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102. Ineffective trigger Causes : improper setting of sensitivity, weak patient effort , auto-peep 103

103. Auto-trigger Causes : low trigger sensitivity, circuit leak, water in the circuit, cardiac oscillation. 104

104. Double trigger Causes : unusually high ventilatory demand, low PaO2/FiO2, longer/too short inspiratory time of patient 105

105. Flow Dysynchrony Causes : High respiratory drive, insufficient flow setting 106

106. Premature cycling Causes: Increase neural inspiratory time, earlier termination of inspiration by ventilator 107

107. Delayed cycling 108

108. Management Select the appropriate mode Proper trigger setting Adjust adequate flow Adjust proper cycling Clear airway Treat auto-peep Sedation Neuromuscular blockade 109

109. WEANING W eaning is the process of withdrawing mechanical ventilatory support and transferring the work of breathing from the ventilator to the patient . In most cases, weaning may be accomplished rapidly from full ventilator support to unassisted spontaneous breathing. 110

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112. Formula RSBI= RR(f)/Tidal Volume(L) P/F ratio: PO 2 /FiO 2 :,FiO 2 =1=100% 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 113

113. Formula 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 114

114. Formula 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 115

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116. Weaning success Weaning success is defined as absence of ventilatory support 48 hours following the extubation . T he spontaneous breaths are unassisted by mechanical ventilation , S upplemental oxygen, bronchodilators, pressure support ventilation, or continuous positive airway pressure may be used to support and maintain adequate spontaneous ventilation and oxygenation. 117

117. Weaning In Progress Weaning in progress is an intermediate category (between weaning success and weaning failure) for patients who are extubated but continue to receive ventilatory support by noninvasive ventilation (NIV) 118

118. Weaning Failure Weaning failure is defined as either the failure of spontaneous breathing trial (SBT) or for reintubation within 48 hours following extubation . Patients who fail the SBT often exhibit the following clinical signs: tachypnea, tachycardia, hypertension, hypotension, hypoxemia, acidosis, or arrhythmias. Physical signs of SBT failure may include agitation, distress, diminished mental status, diaphoresis, and increased work of breathing 119

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120. CONTD Causes of failure are Increase airway resistance Decrease in compliance of lungs Respiratory muscle fatigue 121

121. Spontaneous Breathing Trail The patient may be discontinued from full ventilatory support and placed on a spontaneous breathing mode via the ventilator or T-tube ( B rigg’s adaptor) for up to 30 minutes. Oxygen and low level pressure support may be used to supplement oxygenation and augment spontaneous breathing. The criteria for passing an SBT include normal respiratory pattern (i.e., absence of rapid shallow breathing), adequate gas exchange, and hemodynamic stability. 122

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123. Rapid Shallow Breathing Index(RSBI) 124 <100=success of weaning >100=failure of weaning

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125. THANK YOU 5/21/21 Department of Anesthesiology and intensive care, Dadeldhura Hospital 126