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Mechanical ventilation


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Mechanical ventilation

  1. 1. Mechanical ventilation Shilanjan Roy PGT Medicine
  2. 2. Objectives
  3. 3. Objectives • Discuss indications and techniques for non invasive positive pressure ventilation. • Describe characteristics of different types of breath and modes of mechanical ventilation. • Outline basic ventilator settings. • Interactions between ventilatory parameters and modifications needed to avoid harmful effects of mechanical ventilation. • Initial ventilator management that apply to specific clinical situations.
  4. 4. Indications
  5. 5. Indications for Mechanical Ventilation • The work of breathing usually accounts for 5% of oxygen consumption (V02). • In the critically ill patient this may rise to 30%. • Invasive mechanical ventilation eliminates the metabolic cost of breathing.
  6. 6. Indications for Mechanical Ventilation • Inadequate oxygenation (not corrected by supplemental O2 by mask). • Inadequate ventilation (increased PaCO2). • Retention of pulmonary secretions (bronchial toilet). • Airway protection (obtunded patient, depressed gag reflex).
  7. 7. Indications • Ventilation abnormalities: • • • • • Respiratory muscle fatigue Chest wall abnormalities Neuromuscular disease Increased airway resistance and /or obstruction Decreased ventilatory drive • Oxygenation abnormalities: • Refractory Hypoxaemia • Excessive work of breathing • Need for positive end expiratory pressure
  8. 8. Other indications • Need for sedation and / or neuromuscular blockade. • Need to decrease systemic / myocardial oxygen demand. • Use of hyperventilation to reduce Raised ICP. • Facilitation of alveolar recruitment and prevention of atelectasis.
  10. 10. NIV vs. Invasive Mechanical Ventilation •NIV is defined as ventilatory support provided via a tight fitting mask or similar interface as opposed to invasive support, which is provided via a laryngeal mask, endotracheal tube or tracheostomy tube. • Tight fitting masks deliver can CPAP, BIPAP or NIV via the mechanical ventilator.
  11. 11. Advantages of NPPV • • • • Reduced need for sedation Preservation of airway protective reflexes Avoidance of upper airway trauma Decreased incidence of nosocomial sinusitis and pneumonia • Improved patient comfort • Shorter length of ICU and hospital stay • Improved survival
  12. 12. Disadvantages of NPPV • • • • • Claustrophobia Facial /nasal pressure lesions. Unprotected airway Inability to suction deep airway Gastric distension with use of face mask or helmet • Possible upper extremity edema, axillary vein thrombosis, tympanic dysfunction, and intrahelmet noise with use of helmet • Delay in intubation.
  13. 13. Contraindications of NPPV • • • • • • • • Cardiac or respiratory arrest. Haemodynamic instability Uncooperative. Inability to protect the airways. High risk of aspiration. Active upper GI bleed. Severe encephalopathy. Facial trauma, recent surgery &/or burn
  14. 14. Conditions likely to respond to NPPV • Hypoxaemic respiratory failure: – Cardiogenic pulmonary edema without haemodynamic instability – Respiratory failure in IC patients. (haematologic malignacies and transplant patients) – Patients not candidates for intubation
  15. 15. • Hypercapnic respiratory failure: – AECOPD – AE bronchial asthma – Resp failure in patients with cystic fibrosis – Patients not candidates for intubation
  16. 16. Initiation of NPPV • Do not delay intubation if needed. • Ensure appropriate mask or helmet size. • Assess patients’ tolerance of the mask by applying it by hands before securing the harness. • Explain the procedure to the patients • Initial ventilation settings– – – – – Mode: spontaneous Trigger: maximum sensitivity EPAP : 4-5 cm H2O IPAP : 10-15 cm H2O Rate: 6/min
  17. 17. Cont… • Adjust difference between EPAP & IPAP to achieve effective tidal vol. & CO2 clearance. • EPAP increments of 2 cm H2O /step to improve oxygenation by alveolar recruitment. • In assist control ventilation begin with VT 6-8 ml/kg. • Titrate pressure, vol & FiO2 to achieve appropriate PaO2 & PaCO2 levels. • Ventilator changes can be made every 15-30 mins.
  18. 18. Invasive mechanical ventilation
  19. 19. Intubation
  20. 20. Bare Essentials for Intubation ALSOBLEED Airway: oral Guedel airway to lift tongue off posterior pharynx to facilitate mask ventilation during pre-intubation phase. 2 Liquids: stop feed and aspirate ng tube. 3 Suction: extremely important to avoid pulmonary aspiration. 4 Oxygen: preoxygenate patient and ensure a source of O2 with a delivery mechanism (ambu-bag and mask) is available
  21. 21. Bare Essentials for Intubation ALSOBLEED 5 Bougie: to facilitate tube insertion in more difficult airway. 6 Laryngoscope: have a long and short blade available. 7 Endotracheal tube: for average adult, cuffed oral endotracheal tube 7.0 for women and 8.0 for men. 8 End tidal CO2: to confirm correct position of tube. 9 Drugs: an induction agent, muscle relaxant, sedative are usually required.
  22. 22. Principles of Mechanical Ventilation
  23. 23. Principles of Mechanical Ventilation • Positive pressure ventilation involves delivering a mechanically generated ‘breath’ to get O2 in and CO2 out. • Gas is pumped in during inspiration (Ti) and the patient passively expires during expiration (Te). • The sum of Ti and Te is the respiratory cycle or ‘breath’.
  24. 24. Basic mechanics Each mechanical ventilatory cycle can be divided into 2 phases: • Inspiration is the point at which exhalation valve closes and fresh gas enters the chest. • The amount of gas delivered during inspiration is limited by 3 parameters that can be set in the ventilator: • Volume • Pressure and/or • Flow
  25. 25. • Cycling : • Changeover from the end of inspiration to the second phase , expiration. • Cycling can occur in response to elapsed time , delivered volume or a decrease in flow rates. • Expiration begins when the gas flow from the ventilator is stopped and exhalation circuit is opened to allow gas to escape from the lungs.
  26. 26. • Triggering : • Changeover from expiration to inspiration. • All ventilators require some signal from the patient to determine when inspiration should begin. • Triggering signal results when patients inspiratory effort produces a drop in airway pressure or diversion of a constant gas flow in ventilator circuitry.
  28. 28. • In the absence of patients interaction with the ventilator, breaths are delivered based on elapsed time. • This is called UNASSISTED OR MANDATORY BREATH. • Based on this definitions two ventilator breath types are possible: • Mandatory/ UnAssisted breath • Assisted breath
  29. 29. Principles of Mechanical Ventilation • In the fully ventilated patient, positive pressure breaths are delivered either as preset volume or pressure continuous mandatory breaths (CMV) breaths. • The mechanical ventilator triggers the breath and switches from inspiration to expiration when the preset volume, pressure (or time) is achieved/delivered. • During CMV the patient takes no spontaneous breaths. • CMV is usually used in theatre and in very unwell ICU patients.
  30. 30. Types of ventilator breaths • A. volume cycled (control) breath • Ensures delivery of a preset tidal volume( unless the peak pressure limit is exceeded) • On some ventilators setting of peak inspiratory flow rate and choice of inspiratory flow waveform( sine, square, decelerating) determine length of inspiration. • with volume cycled breaths, worsening airway resistance or lung compliance results in increase in peak inspiratory pressure.
  31. 31. B.Time cycled breath • Often called pressure cycled( controlled) breath, applies a constant pressure over preset time. • Produces a decelerating inspiratory flow waveform as the pressure gradient between the ventilator( constant pressure) patient( pressure rises as lung fills) falls. • In this setting , changes in the airway resistance or lung compliance will alter the tidal volume.
  32. 32. C. Flow cycled breath • usually pressure support breath. • Similar to a time cycled breath. • However, pressure support is terminated when the flow rate decreases to a predetermined percentage of initial flow rate e.g 25%.
  33. 33. Principles of Mechanical Ventilation Volume cycled/ Control Breath Flow Pressure Pressure cycled/Control Breath Ti Te Ti Te
  34. 34. Why is the peak airway pressure (PAP) important? • Ventilator Induced Lung Injury (VILI). • Mechanical ventilation is injurious to the lung. • Aim PAP< 35 cm H20.( platue pressure < 30 cm water) • HIGH PAP may cause barotruma(pneumothorax), • Volutruma( lung parenchymal injury) Don’t forget that the peak airway pressure will also include the PEEP that is added
  35. 35. Principles of Mechanical Ventilation Volume Breath Pressure Breath Flow Pressure 35 cm H20 Ti Te Ti Te
  36. 36. Pneumothorax- Example of ventilator induced barotruma
  38. 38. Overview of topics 1. Settings 2. Modes 3. Advantages and disadvantages between modes 4. Guidelines in the initiation of mechanical ventilation 5. Common trouble shooting examples with mechanical ventilation
  39. 39. Settings 1. 2. 3. 4. 5. 6. 7. Trigger mode and sensitivity Respiratory rate Tidal Volume Positive end-expiratory pressure (PEEP) Flow rate Inspiratory time Fraction of inspired oxygen
  40. 40. Trigger  There are two ways to initiate a ventilator-delivered breath: pressure triggering or flow-by triggering  When pressure triggering is used, a ventilatordelivered breath is initiated if the demand valve senses a negative airway pressure deflection (generated by the patient trying to initiate a breath) greater than the trigger sensitivity.  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
  41. 41. Tidal Volume • The tidal 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.
  42. 42. Respiratory Rate • An optimal 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
  43. 43. Positive End-Expiratory Pressure (PEEP) • Mechanically ventilated patients usually receive positive end-expiratory pressure (PEEP), to overcome the loss of physiological PEEP provided by the larynx and vocal cords. • Applied PEEP is generally added to mitigate end-expiratory alveolar collapse.
  44. 44. PEEP • PEEP is delivered throughout the respiratory cycle and is synonymous to CPAP, but in the intubated patient. A typical initial applied PEEP is 5 cmH2O. However, up to 20 cmH2O may be used in patients undergoing low tidal volume ventilation for acute respiratory distress syndrome (ARDS)
  45. 45. Flow Rate • The peak 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
  46. 46. Inspiratory Time: Expiratory Time Relationship (I:E Ratio) • During spontaneous breathing, the normal I:E ratio is 1:2, indicating that for normal patients the exhalation time is about twice as long as inhalation time. • If exhalation time is too short “breath stacking” occurs resulting in an increase in end-expiratory pressure also called auto-PEEP. • Depending on the disease process, such as in ARDS, the I:E ratio can be changed to improve ventilation
  47. 47. Fraction of Inspired Oxygen • The lowest possible fraction of inspired oxygen (FiO2) necessary to meet oxygenation goals should be used. • This will decrease the likelihood that adverse consequences of supplemental oxygen will develop, such as absorption atelectasis, accentuation of hypercapnia, airway injury, and parenchymal injury
  48. 48. Modes of Ventilation: The Basics • • • • Assist-Control Ventilation :Volume Control Assist-Control Ventilation: Pressure Control Pressure Support Ventilation Synchronized Intermittent Mandatory Ventilation :Volume Control • Synchronized Intermittent Mandatory Ventilation :Pressure Control
  49. 49. Assist Control Ventilation • A set tidal volume (if set to volume control) or a set pressure and time (if set to pressure control) is delivered at a minimum rate • Additional ventilator breaths are given if triggered by the patient.
  50. 50. • Once stabilised on CMV, the level of ventilatory support may be reduced (weaning). • This can be done by providing a mixture of synchronised intermittent mandatory breaths (SIMV) and spontaneously triggered pressure supported breaths (PSV).
  51. 51. Synchronized Intermittent Mandatory Ventilation  Breaths are given are given at a set minimal rate, however if the patient chooses to breath over the set rate no additional support is given  One advantage of SIMV is that it allows patients to assume a portion of their ventilatory drive  SIMV is usually associated with greater work of breathing than AC ventilation and therefore is less frequently used as the initial ventilator mode  Like AC, SIMV can deliver set tidal volumes (volume control) or a set pressure and time (pressure control)  Negative inspiratory pressure generated by spontaneous breathing leads to increased venous return, which theoretically may help cardiac output and function
  52. 52. SIMV and Pressure Support Ventilation • In SIMV mode the ventilator allows two kinds of breath. • The first is delivered according to the preset waveform and is the “mandatory breath”. The timing of the start of this breath may be triggered by the patient’s respiratory effort but, if the patient is not making sufficient respiratory effort, is determined by the ventilator. The second is a spontaneous breath. If SIMV is combined with pressure support then the ventilator facilitates this second breath by providing pressure support. This second type of breath is entirely dependent on patient effort. • The graphs illustrate the changes in pressure and flow that occur with first a mandatory breath and then a pressure-supported breath
  53. 53. SIMV and Pressure Support Ventilation Ventilator Patient
  54. 54. SIMV and Pressure Support Ventilation • Ventilator assisted breaths are synchronized with the patient’s breathing to prevent the possibility of a mechanical breath on top of a spontaneous breath. • However, the patient’s attempt at a breath would not be enough to generate an adequate tidal volume on its own, hence the term ‘pressure support’.
  55. 55. Pressure Support Ventilation • The patient controls the respiratory rate and exerts a major influence on the duration of inspiration, inspiratory flow rate and tidal volume • The model provides pressure support to overcome the increased work of breathing imposed by the disease process, the endotracheal tube, the inspiratory valves and other mechanical aspects of ventilatory support.
  56. 56. PSV • As patients improve, mandatory breaths are withdrawn and receive pressure-supported breaths alone. • Finally, as tidal volumes improve, the level of pressure support is reduced and then withdrawn so patients breathe spontaneously with PEEP alone. • Extubation can now be contemplated. • Spontaneous modes of breathing should always be encouraged as respiratory muscle function is maintained
  57. 57. Pressure Support Ventilation Patient Patient
  58. 58. • PSV augments the patients own respiratory effort and best adjusted by observing changes in patients resp rate, vt and comfort. • Pressure support is only delivered during inspiration and the patient’s attempt at breathing triggers the breath rather than the ventilator. • A standard level of pressure support delivered in inspiration is 20 cm H20
  59. 59. Airway pressure & flow tracings for commonly used modes of mechanical ventilation
  60. 60. Advantages of Each Mode Mode Advantages Assist Control Ventilation (AC) Reduced work of breathing compared to spontaneous breathing AC Volume Ventilation Guarantees delivery of set tidal volume AC Pressure Control Ventilation Allows limitation of peak inspiratory pressures Pressure Support Ventilation (PSV) Patient comfort, improved patient ventilator interaction Synchronized Intermittent Mandatory Ventilation (SIMV) Less interference with normal cardiovascular function
  61. 61. Disadvantages of Each Mode Mode Disadvantages Assist Control Ventilation (AC) Potential adverse hemodynamic effects, may lead to inappropriate hyperventilation AC Volume Ventilation May lead to excessive inspiratory pressures AC Pressure Control Ventilation Potential hyper- or hypoventilation with lung resistance/compliance changes Pressure Support Ventilation (PSV) Apnea alarm is only back-up, variable patient tolerance Synchronized Intermittent Mandatory Ventilation (SIMV) Increased work of breathing compared to AC
  62. 62. Successful Weaning and Extubation • To succeed, the initiating cause of respiratory failure, sepsis, fluid and electrolyte imbalance and nutritional status should all be treated or optimised. • Failure to wean is associated with: • Ongoing high V02. • Muscle fatigue. • Inadequate drive. • Inadequate cardiac reserve.
  63. 63. Successful Weaning and Extubation • Weaning screens exist to help select patients for extubation. • In the unsupported patient, if f/Vt is >100, extubation is likely to be unsuccessful. • There is some evidence to support extubation to NIV, particularly in patients with COPD.
  64. 64. Guidelines in the Initiation of Mechanical Ventilation • Primary goals of mechanical ventilation are adequate oxygenation/ventilation, reduced work of breathing, synchrony of vent and patient, and avoidance of high peak pressures • Set initial FIO2 on the high side, you can always titrate down • Initial tidal volumes should be 8-10ml/kg, depending on patient’s body habitus. If patient is in ARDS consider tidal volumes between 5-8ml/kg with increase in PEEP
  65. 65. Guidelines in the Initiation of Mechanical Ventilation • Use PEEP in diffuse lung injury and ARDS to support oxygenation and reduce FIO2 • Avoid choosing ventilator settings that limit expiratory time and cause or worsen auto PEEP(espl in obstructive airway disease) • When facing poor oxygenation, inadequate ventilation, or high peak pressures due to intolerance of ventilator settings consider sedation, analgesia or neuromuscular blockage
  67. 67. Trouble Shooting the Vent • If we have a patient with history of COPD/asthma with worsening oxygen saturation and increasing hypercapnia differential includes: – Given the nature of the disease process, patients have difficultly with expiration (blowing off all the tidal volume) – Must be concern with breath stacking or autoPEEP – Management options include: Decrease respiratory rate Decrease tidal volume Adjust flow rate for quicker inspiratory rate Increase sedation Adjust I:E ratio
  68. 68. Trouble Shooting the Vent • Increase in patient agitation and dis-synchrony on the ventilator: – Could be secondary to overall discomfort • Increase sedation – Could be secondary to feelings of air hunger – Options include increasing tidal volume, increasing flow rate, adjusting I:E ratio, increasing sedation
  69. 69. Trouble shooting the vent • If you are concern for acute respiratory distress syndrome (ARDS) – Correlate clinically and radiologic findings of diffuse patchy infiltrate on CXR – Obtain a PaO2/FiO2 ratio (if < 200 likely ARDS) – Begin ARDS net protocol: • Low tidal volumes • Increase PEEP rather than FiO2 • Consider increasing sedation to promote synchrony with ventilator
  70. 70. ARDS Protocol • Start with a PEEP of 5 and uptitrate..optimal PEEP is usually 8-15 cm H2O. • Start with a Vt of 8 ml/kg then gradually decrease till Vt of 6 ml/kg is reached. • P plat should be < 30. • Ph> 7.15 is acceptable.
  71. 71. CM V PSV PEE P S IM V PSV M a n d a to ry O v erla p S p o n ta n eo u s
  72. 72. Standard Ventilator Settings MORITE Mode O2 CMV, Volume Control 0.5 (50% 02) Respiratory Rate 12/minute Inspiratory Action Set Vt at 500 mls Inspiratory Time Set I:E ratio 1:2 Expiratory Action Set PEEP at 5 cm H20 Be Aware PAP ≤35 cm H2O
  74. 74. TAKE HOME MESSAGE • 1) Goals of NIV and IPPV are to suppport ventilation and oxygenation, reduce work of breathing and patient comfort. • 2)NPPV is best utilized in C/A/C patients whose resp condition is expected to improve in 48-72 hrs. • 3)Guidelines for initiating mechanical ventilation should be carefully followed. • 4)Inspiratory plateue pressures should be maintained <30 cm H2o.
  75. 75. TAKE HOME MESSAGE • 5) During mech ventilation, patient must be carefully monitored using vent alarm systems, rintermittant ABG analysis, pulse oximetry , physical assessment, and chest radiograph as needed. • 6) Hypotension in ventilated pt should be prompt evaluated for pneumothorax, auto PEEP, AMI. • 7)The primary determinants of oxygenation are Fi02 and Mean airway pressure whereas alveolar ventilation affects CO2 exchange. • 8) THE Complex interaction of inspiratory pressures, I:E Ratio, Fio2, and PEEP must be evaluated.