Ventilator in Critical Care

Mechanical Ventilation - Modes, Uses, indications, Complications

1. Ventilator in critical care Presenter : Dr. Dhileeban Maharajan Moderator : Prof. Lk . Sharatchandra

2. Contents History Types of Ventilators Modes of Mechanical Ventilation Indications Complications Ventilator setting in Specific diseases Weaning Newer methods

3. Introduction Mechanical Ventilation - Common life saving intervention Required for assisting and replacing spontaneous breathing Poor ventilatory management can inflict serious pulmonary and extra-pulmonary damage Optimizing ventilatory parameters reduces overall duration of mechanical ventilation and organ failure U psurge in utilization of non-invasive ventilation has permitted many patients to avoid the risks and complications

4. History 5 th century – Hippocrates (Treatise on air) 1530 – Paracelus – Pump air into patients mouth 1653 – Andreas Vesalius – Tracheostomy in dog 1744 – John Fothergill – Mouth to mouth breathing 1880 – First endotracheal intubation tried 1929 – Drinker and Shaw – Negative pressure ventilation 1963 – Positive pressure ventilation 1971 – Gregory et al – CPAP

5. Iron lung Cuirass Body suit Negative Pressure V entilation Negative pressure outside thorax Expansion of thoracic cage Fall in pleural pressure Air enter into the lungs Examples:

6. Positive Pressure V entilation Airway pressure is applied at the patient's airway through an endotracheal or tracheostomy tube. The positive nature of the pressure causes the gas to flow into the lungs until the ventilator breath is terminated. As the airway pressure drops to zero, elastic recoil of the chest accomplishes passive exhalation by pushing the tidal volume out. Polio epidemic in Scandinavia – 1950 Manual positive pressure ventilation Mortality reduced 80 to 25%

7. Positive Pressure Ventilation - Cont Mode: (Flow, Pressure, Time) Manner in which ventilator breaths are triggered, cycled and limited Trigger: (Flow, Pressure) Either an inspiratory effort or time based signal, defines what the ventilator senses to initiate an assisted breath Cycle: (Volume, Flow, Pressure, Time) Factors that determine the end of inspiration Limiting factors: Operator specified values such as airway pressure, to prevent injury to lungs

8. Types of support Control mode Delivers preset tidal volume once it triggered regardless of patient effort Support mode Provides inspiratory assistance (Requires adequate respiratory drive)

9. Methods of ventilatory support Continuous mandatory ventilation (CMV) Assist – Control ventilation (A/C) Intermittent mandatory ventilation (IMV) Synchronous intermittent mandatory ventilation (SIMV) Pressure support ventilation (PSV) Noninvasive ventilation CPAP BIPAP

10. Continuous Mandatory V entilation (CMV) Preset interval breath regardless of patients effort Patients should be sedated and paralysed (NM blockers) Used for patients fights the ventilator during initial stages , tetanus, seizures, complete rest for 24 hours, crushed chest injury.

11. Assist C ontrol V entilation (A/C) Preset breath in coordination with respiratory effort Delivers full assisted tidal volume Spontaneous breathing not allowed If patient had appropriate ventilator drive, allows patient to control frequency and minute volume to normalize PaCO2 To provide full ventilatory support for patients (full work of breathing) Used for patients having stable respiratory drive ( at least 10 /min )

12. Intermittent M andatory V entilation (IMV) Breaths at preset interval Spontaneous breath allowed Allow patients breath in addition to ventilator delivered breaths. Breath stacking – increased risk of barotrauma

13. Synchronous Intermittent M andatory V entilation (SIMV) Preset breaths in coordination with respiratory effort Spontaneous breathing allowed T ime interval just prior to time triggering in which ventilator is responsive to patients spontaneous inspiratory efforts is called as synchronization window mostly 0.5 sec (manufacturer set) SIMV maintains respiratory muscle strength, reduces V/Q mismatch, decreases mean airway pressure, facilitates weaning

14. Pressure support ventilation For spontaneously breathing patient To limit barotrauma and work of breathing Pressure support according to inspiratory flow when the patient triggers ,pressure supported breath is delivered by demand valves which generates high flow to increase airway pressure to pressure limit and maintains pressure plateau (demand and servo valves) for the duration of patients spontaneous inspiratory efforts . PSV used with SIMV to facilitate weaning

15. Noninvasive ventilation (NPPV) Ventilatory support through mask Decreases the intubation by 20% CPAP and BiPAP Used in COPD acute exacerbation Cardiogenic pulmonary edema Post- extubation respiratory failure in hypercapnic patients Pneumonia in immunocompromised patients Contraindications : Cardiac or Respiratory arrest Severe encephalopathy Hemodynamic instability Facial trauma or surgery Upper airway obstruction High risk aspiration Inability to clear secretions

16. Noninvasive ventilation – Cont.. Place the patient in upright or sitting position Choose a proper fitting mask Attach the interface and circuit to ventilator Allow the patient to hold the mask Monitor oxygen saturation Secure the mask Titrate the pressure settings Check for any leaks Monitor RR, HR, Saturation, Minute ventilation, Exhaled Tt Obtain ABG within one hour (Protocol for initiating NIV)

17. Higher level consciousness Younger age Less severe abnormalities Minimal air leakage Intact dentition Synchronous breathing Absence of pneumonia Positive initial response Correction of pH Decreased respiratory rate Reduced PaCO2 Noninvasive ventilation – Cont.. Nasal bridge ulcer and necrosis Conjunctival irritation Gastric insufflation Ventilator asynchrony Claustrophobia Risk of aspiration Predictors of success Disadvantages

18. Indications for mechanical ventilation Bradypnoea or apnoea with respiratory arrest Acute lung injury and acute respiratory distress syndrome Tachypnoea (respiratory rate >30 breaths per minute) Vital capacity less than 15 mL/kg Minute ventilation greater than 10 L/min PaO2 with a supplemental FIO2 of less than 55 mm Hg Alveolar-arterial gradient of oxygen tension (A-a DO2) with 100% oxygenation of greater than 450 mm Hg

19. Indication – Cont… Clinical deterioration Respiratory muscle fatigue Obtundation or coma Hypotension Acute partial pressure of carbon dioxide (PaCO2) greater than 50 mm Hg with an arterial pH less than 7.25 Neuromuscular disease

20. Indications

21. Positive End Expiratory Pressure (PEEP) Positive end expiratory pressure (PEEP) refers to the application of a fixed amount of positive pressure during mechanical ventilation cycle Continuous positive airway pressure (CPAP) refers to the addition of a fixed amount of positive airway pressure to spontaneous respirations, in the presence or absence of an endotracheal tube. PEEP and CPAP are not separate modes of ventilation as they do not provide ventilation. Rather they are used together with other modes of ventilation or during spontaneous breathing to improve oxygenation, recruit alveoli , and / or decrease the work of breathing

22. PEEP - Advantages Ability to increase functional residual capacity ( FRC) and keep FRC above Closing Capacity The increase in FRC is accomplished by increasing alveolar volume and the recruitment of alveoli that would not otherwise contribute to gas exchange . Thus increasing oxygenation and lung compliance The potential ability of PEEP and CPAP to open closed lung units increases lung compliance and tends to make regional impedances to ventilation more homogenous.

23. Physiology of PEEP Reinflates collapsed alveoli and maintains alveolar inflation during exhalation PEEP Decreases alveolar distending pressure Increases FRC by alveolar recruitment Improves ventilation Increases V/Q, improves oxygenation, decreases work of breathing

24. Complications of Mechanical V entilation Laryngeal injury Pharyngeal laceration Infection of the retro pharyngeal space Mediastinitis Pneumothorax Tracheal rupture Nasal injury and epistaxis Dental trauma Cervical spine injury Esophageal intubation Right mainstem intubation Cardiac arrhythmia Aspiration Bronchospasm Peri - intubation complication

25. Endotracheal tube obstruction Endotracheal tube migration Self- extubation Cuff leak Barotrauma and Volutrauma Subpleural air cyst Pneumothorax Pneumomediastinum Pneumoperitoneum Subcutaneous emphysema Acute complications that can occur at any time during mechanical ventilation Biotrauma Hypotension Dynamic hyperinflation Atelectasis Alveolar hypoventilation or hyperventilation Gastric dilation Inadvertent disconnection from ventilator Machine failure

26. Peri -oral pressure sores Nasal necrosis Sinusitis Serous or purulent otitis media Pneumonia Tracheomalacia Tracheo -esophageal fistula Oxygen toxicity Mechanical Ventilation - Delayed complications

27. Ventilator induced lung injury (Barotrauma) Prevalence – 10% Large Tidal volume and elevated peak inspiratory and plateau pressure – Risk factors Barotrauma refers to rupture of the alveolus with subsequent entry of air into the pleural space (pneumothorax ) and/or the tracking or air along the vascular bundle to the mediastinum ( pneumomediastinum ) Decrease the inspiratory-to expiratory ratio is important to prevent barotrauma

28. local overdistention of normal alveoli lung-protective ventilation strategy is recommended Ventilator induced lung injury (Volutrauma)

29. Oxygen Toxicity Oxygen toxicity is due to the production of oxygen free radicals such as superoxide anion, hydroxyl radical, and hydrogen Peroxide R eported in patients given a maintenance FIO2 of 50% or greater Clinician should attempt to attain an FIO2 of 60% or less within the first 24 hours of mechanical ventilation PEEP should be considered a means to improve oxygenation while a safe FIO2 is maintained

30. Ventilator Associated Pneumonia (VAP) Incidence 1 to 4 cases per 1000 ventilator days R ate of 3% per day for the first 5 days, 2% per day for next 5 days VAP is defined as a new infection of the lung parenchyma that develops within 48 hours after intubation F ever , leukocytosis , and purulent tracheobronchial secretions. Qualitative and quantitative cultures of protected brush and bronchoalveolar lavage specimens may help First 48 hours after intubation - Flora of the upper airway, including Haemophilus influenza and Streptococcus pneumonia

31. VAP – cont.. After this early period , gram-negative bacilli such as Pseudomonas aeruginosa , Escherichia coli, Acinetobacter , Proteus, and Klebsiella species predominate Staphylococcus aureus , especially methicillin-resistant S aureus (MRSA), typically becomes a major infective agent after 7 days I nitial therapy - with broad-spectrum antibiotics and change the antibiotic after the culture sensitivity report

32. Intrinsic PEEP M ost frequently occurs in patients with COPD or asthma who require prolonged expiratory phase of respiration T his problem occurs, a portion of each subsequent tidal volume may be retained in the patient's lungs, a phenomenon sometimes referred to as breath stacking R esults in barotrauma, volutrauma The normal inspiratory to expiratory ratio (I:E ratio) is 1:2. In patients with obstructive airway disease, the target I:E ratio should be 1:3 to 1:4 .

33. Breath stacking

34. Ventilator Setup Assist – Control mode Tidal volume depending upon the lung status Normal - 12mL/kg; COPD – 10mL/kg; ARDS – 6-8mL/kg Rate of 10 – 12 breaths/min FIO 2 of 100% PEEP only as indicated

35. Ventilator setting in COPD and asthma Permissive hypercapnia Reduce the expiratory rate Low set tidal volume Increase the expiratory flow time NPPV reduced the endotracheal intubation by 59% High airway pressure Breath stacking Intrinsic PEEP Barotrauma

36. Compliance reduced and dead space increased Lung protective ventilation Low tidal volume ( Close to 6ml/kg BW) Prevent plateau pressure exceeding 30cmH2O Lowest possible FIo2 to keep the Spo2 at >90% Adjust the PEEP to maintain alveolar patency Early prone positioning Ventilator setting in ARDS

37. To decrease the work of breathing and oxygen demand of the respiratory muscles Arrhythmia common with hypocapnia In CHF - CPAP or BiPAP r educe p reload Potential effects of PEEP in LV dysfunction Reduce venous return and preload Increased FRC lead to increased pulmonary patency Compression may increase afterload Ventilator setting in Heart Disease

38. Prevent aspiration Hyperventilation  Reduce the intracranial pressure Maintain PaCO2 between 30 to 39mmHg Recent studies suggest poor outcome Ventilator setting in Traumatic Brain I njury

39. Weaning Unsupported spontaneous breathing trials(SBT) The machine support is withdrawn T-Piece (or CPAP) circuit can be attached Intermittent mandatory ventilation (IMV) weaning The ventilator delivers a pre-set minimum minute volume Synchronized (SIMV) to the patient's own respiratory efforts Pressure support weaning Patient initiates all breaths and these are 'boosted' by the ventilator. Gradually reducing the level of pressure support, Once the level of pressure support is low (5-10 cmH 2 O above PEEP), a trial of T-Piece or CPAP weaning should be started

40. Weaning- Cont… Lung injury is stable or resolving Gas exchange adequate L ow PEEP (<8cmH2O) Low FIO2 (<0.5) Stable hemodynamic variables Able to initiate spontaneous breath Absence of infection or fever Indications Failed SBT Resp. Rate >35 for >5min Heart Rate >140/min SPO2 <90% for >30sec Systolic BP >180 or <90 Sustained increased WOB Cardiac dysrhythmia pH <7.32 10 to 15% patient require reintubation

41. Newer Modes Dual modes Pressure regulated volume control(PRVC) ventilation Volume support ventilation (VSV) Variable pressure control mode Volume assured pressure support ventilation Proportional assist ventilation Inverse ratio ventilation High frequency jet ventilation Neurally adjusted ventilatory assist ventilation (NAV) Extracorporeal membrane oxygenation (ECMO)

42. Summary Technological advances added new methods in MV NPPV is an important treatment modality prevents the need for endotracheal intubation Recent guidelines suggest that the use of low tidal volume in ARDS associated with favorable outcome Weaning guidelines have shown improved outcome Although MV is life saving, it is fraught with a plethora of complications

43. Thank you REFERENCE Pittsburgh critical care medicine – Mechanical Ventilation; Second Edition Ashfaq Hasan – Understanding mechanical ventilation; Harrison’s Principles of internal medicine; 20 th Edition API Textbook of Medicine; 11 th Edition Medicine Update 2019; Volume 29