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![Flow…
The need for a high peak flow rate is particularly common
among patients who have obstructive airways disease with
acute respiratory acidosis.
In such patients, a higher peak flow rate shortens inspiratory
time and increases expiratory time (ie, decreases the
inspiratory to expiratory [I:E] ratio).
These alterations increase carbon dioxide elimination and
improve respiratory acidosis, while also decreasing the
likelihood of dynamic hyperinflation (auto-PEEP)
10/18/2020
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Mechanical ventilatory support
- 1. P R ES E N TO R : M E L A K U Y E T B A R E K ( R I ) M O D E R ATO R S : D R . E N D A S H AW ( I N T E R N I S T, A S S I S TA N T P R O F E S S O R ) D R . D E J E N E ( A N E S T H E S I O L O G I S T, A S S I S TA N T P R O F E S S O R ) Mechanical Ventilatory Support 10/18/2020 1
- 2. Outline Introduction Indications Ventilator Circuit Types Modes MV Settings MV alarm setting and troubleshooting Complications Weaning 10/18/2020 2
- 3. Introduction Mechanical ventilation(MV) is used to assist or replace spontaneous breathing It is implemented with special devices that can support ventilatory function and improve oxygenation through the application of high-oxygen-content gas and positive pressure. 10/18/2020 3
- 4. Introduction History: Galen, 2ndcentury A.D, Greek physician, may have been the first to describe mechanical ventilation Vesalius 1543, De Humani Corporis Fabric. “But that life may be restored to the animal, an opening must be attempted in the trunk of the trachea, into which a tube of reed or cane should be put; you will then blow into this, so that the lung may rise again and take air” George Poe 1908, demonstrated his mechanical respirator by asphyxiating dogs and seemingly bringing them back to life. 10/18/2020 4
- 5. Intro… Negative pressure ventilators Developedin 1929. Used widely in 1940 polio epidemic. The patient’s body was encased in an iron cylinder and negative pressure was generated 10/18/2020 5
- 6. Intro… Positive Pressure Ventilation Polio epidemic in Scandinavia and the United States in the early 1950s. Decrease in mortality rate from >80% to 40% 10/18/2020 6
- 7. Indications The most commonreasons for instituting MV are acute respiratory failure with hypoxemia which accounts for ~65% of all ventilated cases, and hypercarbic ventilatory failure—e.g., due to coma (15%), exacerbations of chronic obstructive pulmonary disease (COPD; 13%), and neuromuscular diseases (5%). 10/18/2020 7
- 8. Indications… MV alsois used frequently in conjunction with endotracheal intubation for airway protection to prevent aspiration In critically ill patients, intubation and MV may be indicated before the performance of essential diagnostic or therapeutic studies 10/18/2020 8
- 9. Types There are twobasic methods of MV: Noninvasive ventilation (NIV) Invasive (or conventional mechanical) ventilation (MV) 10/18/2020 9
- 10. Non invasive mechanicalVentilation(NIV) Uses a completely sealed system in which air cannot be entrained, CPAP/ BiPAP circuits are able to deliver a truly accurate high concentration (FiO2=1.0) and are thus effective at treating hypoxia. CPAP is indicated when alveolar recruitment may occur BiPAP/ NIV is required when work of breathing requires augmentation. 10/18/2020 10
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- 12. Indications(NIV) Pulmonary edema Asthma COPD Cardiogenic Pulmonary edema Chest trauma Assisting in early extubation Respiratory failure in Immunocompromised patients 10/18/2020 12
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- 15. Invasive Mechanical Ventilation(Conventional) Delivers conditioned gas (warmed, oxygenated, and humidified) through ETT to the airways and lungs at pressures above atmospheric pressure 10/18/2020 15
- 16. Invasive Mechanical Ventilation Mechanicalventilators are comprised of four main elements: A source of pressurized gas including a blender for air and O2. An inspiratory valve, expiratory valve and ventilator circuit. A control system, including control panel, monitoring and alarms. A system to sense when the patient is trying to take breath. 10/18/2020 16
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- 18. Invasive Mechanical… ET Tubes: They are equipped with an inflatable balloon at the distal end (the cuff). The proximal end has a standard 15 mm connector, the tubes vary in length from 25 to 35 cm and are sized according to their internal diameter. Size 8-9 mm will fit to most men and size 7-8 mm to most women. 10/18/2020 18
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- 22. Invasive Mechanical… Thedepth of the tube on the average is 21-23 from the teeth for male and 19-21 for female patients Cuff pressure – 18-25mmHg >25mmHg pressure necrosis at contact area <18 mmHg air leak around ETT 10/18/2020 22
- 23. Invasive Mechanical… Confirm tubeposition: Bilateral chest rise Auscultation of the chest Tube location at the teeth Co2 detector (Capnography) 10/18/2020 23
- 24. Principles Once thepatient has been intubated, the basic goals of MV are to optimize oxygenation while avoiding ventilator-induced lung injury This concept, known as the “protective ventilatory strategy” 10/18/2020 24
- 25. Principles… Although normalizationof pH through elimination of CO2 is desirable, the risk of lung damage associated with the large volume and high pressures needed to achieve this goal has led to the acceptance of permissive hypercapnia. This condition is well tolerated when care is taken to avoid excess acidosis by pH buffering 10/18/2020 25
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- 27. Modes Mode refersto the manner in which ventilator breaths are triggered, cycled, and limited The trigger, either an inspiratory effort or a time based signal, defines what the ventilator senses to initiate an assisted breath. Cycle refers to the factors that determine the end of inspiration. Other types of cycling include pressure cycling and time cycling. 10/18/2020 27
- 28. Variables that governhow a ventilator functions and interacts with the patient Control variable ‘The Mode of Ventilation’ Pressure, flow, or volume controlled Triggering variable pressure, flow or volume sensing that initiates the vent cycle Cycle variable Pressure, volume, flow, or time that ends the inspiratory phase Limit Variable Volume, pressure or flow can be set to be constant or reach a maximum 10/18/2020 28
- 29. Modes… The limitingfactors are operator-specified values, such as airway pressure, that are monitored by transducers internal to the ventilator circuit throughout the respiratory cycle; If the specified values are exceeded, inspiratory flow is terminated, and the ventilator circuit is vented to atmospheric pressure or the specified pressure at the end of expiration (positive end-expiratory pressure, or PEEP). Most patients are ventilated with assist-control ventilation (ACMV), intermittent mandatory ventilation (IMV), or PSV, with the latter two modes often used simultaneously 10/18/2020 29
- 30. Assist-control ventilation (ACV)or volume control (VC) Every breath is delivered with a pre-set tidal volume and rate or minute ventilation Extra controlled breaths may be triggered by patient effort; if no effort is detected within a specified amount of time the ventilator will initiate the breath 10/18/2020 30
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- 33. Pressure control ventilation(PCV) A minimum frequency is set and patient may trigger additional breaths above the ventilator All breaths delivered at a preset constant inspiratory pressure In traditional PCV, tidal volume is not guaranteed thus changes in compliance and resistance affect tidal volume 10/18/2020 33
- 34. Synchronous intermittent mandatoryventilation (SIMV) Ventilator provides controlled breaths (either at a set volume or pressure depending on whether in VC or PCV, respectively) Patient can breathe spontaneously (these breaths may be pressure supported) between controlled breaths 10/18/2020 34
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- 37. Pressure support ventilation(PSV) Patient initiates all breaths and the ventilator supports each breath with a pre-set inspiratory pressure Useful for weaning off ventilator 10/18/2020 37
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- 39. High-frequency oscillatory ventilation(HFOV) High breathing rate &very low tidal volumes Used commonly in neonatal and pediatric respiratory failure Occasionally used in adults when conventional mechanical ventilation is failing 10/18/2020 39
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- 43. Mechanical Ventilator Settings Trigger Tidal Volume Respiratory Rate PEEP Flow rate Fraction of Inspired oxygen(Fio2) Flow Pattern 10/18/2020 43
- 44. Trigger There aretwo ways to initiate a ventilator-delivered breath: pressure triggering or flow-by triggering. When pressure triggering is used, a ventilator-delivered breath is initiated if the demand valve senses a negative airway pressure deflection The trigger sensitivity should allow the patient to trigger the ventilator easily. Patient-ventilator asynchrony 10/18/2020 44
- 45. Trigger… Pressure triggeringcan be used with the assist control or synchronized intermittent mandatory ventilation modes of mechanical ventilation. Auto-PEEP (intrinsic positive end-expiratory pressure) interferes with pressure triggering. When flow-by triggering is used, a continuous flow of gas through the ventilator circuit is monitored. A ventilator-delivered breath is initiated when the return flow is less than the delivered flow, a consequence of the patient's effort to initiate a breath 10/18/2020 45
- 46. Tidal Volume Thetidal volume is the amount of air delivered with each breath. The appropriate initial tidal volume depends on numerous factors, most notably the disease for which the patient requires mechanical ventilation. As an example, randomized trials found that mechanical ventilation using tidal volumes of ≤6 mL per kg of predicted body weight (PBW) improved mortality in patients with acute respiratory distress syndrome (ARDS) 10/18/2020 46
- 47. Tidal… An initialtidal volume of approximately 8 mL per kg of predicted body weight (PBW, which is the same as ideal body weight) seems reasonable, albeit unproven and based only on clinical experience. The tidal volume can then be increased or decreased incrementally to achieve the desired pH and arterial carbon dioxide tension (PaCO 2 ), while monitoring the auto-PEEP and airway pressure. Return to the previous tidal volume is indicated if the patient develops auto-PEEP >5 cm H 2 O or a plateau airway pressure >30 cm H 2 O following an increase in the tidal volume. During volume-limited ventilation, the tidal volume is set by the clinician and remains constant. 10/18/2020 47
- 48. Respiratory Rate(RR) Anoptimal method for setting the respiratory rate has not been established. For most patients, an initial respiratory rate between 12 and 16 breaths per minute is reasonable, although it may be modified according to the mode For patients receiving assist control, the respiratory rate is typically set four breaths per minute below the patient's native rate For patients receiving synchronized intermittent mandatory ventilation, the rate is set to ensure that at least 80 percent of the patient's total minute ventilation is delivered by the ventilator 10/18/2020 48
- 49. RR… Once thetidal volume has been established, the respiratory rate can be incrementally increased or decreased to achieve the desired pH and PaCO 2 , while monitoring auto-PEEP. Return to the previous respiratory rate is indicated if the patient develops auto-PEEP >5 cm H 2 O. For patients with ARDS, the required respiratory rate is higher (up to 35 breaths per minute), in order to facilitate low tidal volume ventilation. Increasing the inspiratory flow rate and the respiratory rate simultaneously may mitigate the development of auto-PEEP. 10/18/2020 49
- 50. Positive end expiratorypressure(PEEP) Applied PEEP (extrinsic positive end-expiratory pressure) is generally added to mitigate end-expiratory alveolar collapse. A typical initial applied PEEP is 5 cm H 2 O. However, up to 20 cm H 2 O may be used in patients undergoing low tidal volume ventilation for acute respiratory distress syndrome (ARDS). 10/18/2020 50
- 51. PEEP… Elevated levels ofapplied PEEP can have adverse consequences, such as Reduced preload (decreases cardiac output), Elevated plateau airway pressure (increases risk of barotrauma), Impaired cerebral venous outflow (increases intracranial pressure). 10/18/2020 51
- 52. Flow rate Thepeak flow rate is the maximum flow delivered by the ventilator during inspiration. Peak flow rates of 60 L per minute may be sufficient, although higher rates are frequently necessary. An insufficient peak flow rate is characterized by dyspnea, spuriously low peak inspiratory pressures, and scalloping of the inspiratory pressure tracing 10/18/2020 52
- 53. Flow… The needfor a high peak flow rate is particularly common among patients who have obstructive airways disease with acute respiratory acidosis. In such patients, a higher peak flow rate shortens inspiratory time and increases expiratory time (ie, decreases the inspiratory to expiratory [I:E] ratio). These alterations increase carbon dioxide elimination and improve respiratory acidosis, while also decreasing the likelihood of dynamic hyperinflation (auto-PEEP) 10/18/2020 53
- 54. Flow Pattern Microprocessor-controlledmechanical ventilators can deliver several inspiratory flow patterns, including a square wave (constant flow), a ramp wave (decelerating flow), and a sinusoidal wave The ramp wave may distribute ventilation more evenly than other patterns of flow, particularly when airway obstruction is present This decreases the peak airway pressure, physiologic dead space, and PaCO 2 , while leaving oxygenation unaltered The effects of the different flow patterns on potential complications of mechanical ventilation (eg, hemodynamic impairment, pulmonary barotrauma, ventilator-associated lung injury) are unpredictable 10/18/2020 54
- 55. Fraction of InspiredOxygen (FiO 2 ) The lowest possible fraction of inspired oxygen (FiO 2 ) necessary to meet oxygenation goals should be used. This will decrease the likelihood that adverse consequences of supplemental oxygen, Typical oxygenation goals include an arterial oxygen tension (PaO 2 ) above 60 mmHg and an oxyhemoglobin saturation (SpO 2 ) above 90 percent. In patients with ARDS, targeting a PaO 2 of 55 to 80 mmHg and a SpO 2 of 88 to 95 percent is acceptable when the trade off would be higher plateau pressures and an increased risk of lung injury due to alveolar overdistension (ie, volutrauma) 10/18/2020 55
- 56. MV Alarm Setting&Troubleshooting ventilator inoperative (vent INOP) power failure, no gas delivery to the patient, low peak inspiratory pressure (PIP), low tidal volume (VT), low or high minute volume (MV), 10/18/2020 56
- 57. Alarm… low positiveend-expiratory pressure and continuous positive airway pressure (PEEP/CPAP), apnea, inspiratory:expiratory (I:E) ratio, High pressure limit, high respiratory rate, and low or high fraction of inspired oxygen (FIO2) 10/18/2020 57
- 58. Alarms… 10/18/2020 58 High Peak InspiratoryPressure: Secretions Patient biting ETT Patient coughing Low Pressure Alarm or low PEEP alarm: Disconnect (check all connections) Apnea Low Tidal Volume Spontaneous: Circuit disconnect Secretions
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- 60. Desaturation or Hypoxia 1.Attendthe patient promptly. 2. Increase the FiO2 appropriately (to 100% O2 if necessary 3. Is the patient ventilating? Check for chest wall movement (and its synergy) visually and manually while looking at the ventilator (for low tidal volumes/ alarms from high pressures) 10/18/2020 60
- 61. Desaturation… 4.If inadequate ventilation,disconnect from the ventilator, and bag manually on 100% O2. Then ascertain which of the possible causes Blocked or displaced tracheostomy or ET tube Tension Pneumothorax Mucus Plug Endobronchial intubation Massive acute Pulmonary alveolar ‘flooding’ 10/18/2020 61
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- 63. Patient Ventilator Asynchrony Asynchronyoccurs when there is a discrepancy between patient and ventilator in one or more of the breathing phases The trigger mechanism The Inspiratory flow phase Breath termination Expiratory phase 10/18/2020 63
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- 65. Patient Management Oncethe patient’s gas exchange has been stabilized, definitive therapy for the underlying process responsible for respiratory failure is continued. Subsequent modifications in ventilator therapy must be provided in parallel with changes in the patient’s clinical status. As improvement in respiratory function is noted, the first priority is to reduce the level of mechanical ventilatory support. 10/18/2020 65
- 66. Patient… Patients onfull ventilatory support should be monitored frequently, with the goal of switching to a mode that allows for weaning as soon as possible Patients whose condition continues to deteriorate after ventilatory support is initiated may require increased O2, PEEP, or one of the alternative modes of ventilation 10/18/2020 66
- 67. Patient… Oversedation mustbe avoided in the ICU because most studies show that daily interruption of sedation in patients with improved ventilatory status results in a shorter time on the ventilator and a shorter ICU stay Immobilized patients receiving mechanical ventilatory support are at risk for deep venous thrombosis and decubitus ulcers. 10/18/2020 67
- 68. Patient… Patients forwhom MV has been initiated usually require sedation and analgesia Combination of a benzodiazepine and an opiate administered intravenously. Medications commonly used for this purpose include lorazepam, midazolam, diazepam, morphine, and fentanyl. 10/18/2020 68
- 69. Patient… Venous thrombosisshould be prevented with the use of subcutaneous heparin and/ or pneumatic compression boots. Fractionated low-molecular-weight heparin appears to be equally effective for this purpose. To help prevent decubitus ulcers, frequent changes in body position and the use of soft mattress overlays and air mattresses are employed. Early mobilization is recommended for patients on MV, since this approach is associated with better outcomes. 10/18/2020 69
- 70. Patient… Prophylaxis againstdiffuse gastrointestinal mucosal injury is indicated for patients undergoing MV. Histamine-receptor (H2-receptor) antagonists, antacids, and cytoprotective agents such as sucralfate have all been used and appear to be effective 10/18/2020 70
- 71. Patient… Nutritional supportby enteral feeding through either a nasogastric or an orogastric tube Promotility agents such as metoclopramide. Parenteral nutrition is an alternative to enteral nutrition in patients with severe gastrointestinal pathology who need prolonged MV 10/18/2020 71
- 72. Complications Endotracheal intubation andMV have direct and indirect effects on The lung and upper airways, The cardiovascular The gastrointestinal system. 10/18/2020 72
- 73. Pulmonary complications Barotrauma, Nosocomial pneumonia, Oxygen toxicity, Tracheal stenosis, Deconditioning of respiratory muscles 10/18/2020 73
- 74. Pulmonary complications Barotraumaand volutrauma overdistend and disrupt lung tissue; may be clinically manifest by pneumomediastinum, interstitial and subcutaneous emphysema, or pneumothorax Clinically significant pneumothorax requires tube thoracostomy. 10/18/2020 74
- 75. Complications Hypotension resultingfrom elevated intrathoracic pressures with decreased venous return Gastrointestinal effects of positive-pressure ventilation include stress ulceration and mild to moderate cholestasis 10/18/2020 75
- 76. Weaning The Decision toWean It is important to consider discontinuation of MV once the underlying respiratory disease begins to reverse. Although the predictive capacities of multiple clinical and physiologic variables have been explored, the following conditions indicate amenability to weaning: 10/18/2020 76
- 77. Weaning… Lung injuryis stable or resolving; Gas exchange is adequate, with low PEEP (<8 cmH2O) and Fio2 (<0.5); Hemodynamic variables are stable, and the patient is no longer receiving vasopressors; The patient is capable of initiating spontaneous breaths. 10/18/2020 77
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- 79. Weaning… A “weanscreen” should be done at least daily. If the patient is deemed capable of beginning to wean, the recommendation is to perform a spontaneous breathing trial (SBT) 10/18/2020 79
- 80. Weaning… The SBTinvolves an integrated patient assessment during spontaneous breathing with little or no ventilatory support. The SBT is usually implemented with a T-piece using 1– 5 cmH2O CPAP with 5–7 cmH2O or PSV from the ventilator to offset resistance from the endotracheal tube. Decide on extubation,once patient has the ability to protect the airway, is able to cough and clear secretions, and is alert enough to follow commands. 10/18/2020 80
- 81. Weaning… In addition,other factors must be taken into account, such as the possible difficulty of replacing the tube if that maneuver is required If upper airway difficulty is suspected, an evaluation using a “cuff-leak” test (assessing the presence of air movement around a deflated endotracheal tube cuff) is supported by current evidence If the “cuff-leak test” suggests a risk of post-extubation stridor, the administration of systemic corticosteroids should be considered prior to extubation 10/18/2020 81
- 82. Weaning… Despite allprecautions, ~10–15% of extubated patients require reintubation Several studies suggest that NIV can be used to obviate reintubation, particularly in patients with ventilatory failure secondary to COPD exacerbation or congestive heart failure 10/18/2020 82
- 83. Weaning… Prolonged MV andTracheostomy From 5 to 13% of patients undergoing MV will go on to require prolonged MV (>21 days) In these instances, critical care personnel must decide whether and when to perform a tracheostomy. 10/18/2020 83
- 84. Weaning… This decisionis individualized and is based on the risk and benefits of tracheostomy and prolonged intubation as well as the patient’s preferences and expected outcomes. A tracheostomy is thought to be more comfortable, to require less sedation, and to provide a more secure airway and may also reduce weaning time. 10/18/2020 84
- 85. Weaning… However, tracheostomycarries the risk of complications, which occur in 5–40% of these procedures In patients with long-term tracheostomy, complex complications include tracheal stenosis, granulation, and erosion of the innominate artery. 10/18/2020 85
- 86. Weaning… In general,if a patient needs MV for >10–14 days, a tracheostomy, planned under optimal conditions, is indicated Whether it is completed at the bedside or as an operative procedure depends on local resources and experience. 10/18/2020 86
- 87. Weaning… Some 5–10%of patients are deemed unable to wean in the ICU These patients may benefit from transfer to special units 10/18/2020 87
- 88. Weaning… Unfortunately, closeto 2% of ventilated patients may ultimately become dependent on ventilatory support to maintain life Most of these patients remain in chronic care institutions, although some with strong social, economic, and family support may live a relatively fulfilling life with at-home ventilation 10/18/2020 88
- 89. References Uptodate,2018 Harrison’sPrinciples of Internal Medicine,2018 Hand book of Mechanical Ventilation, User’s guide Practical Guide for Mechanical Ventilation,4th edition 10/18/2020 89