modes of ventilation
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Andreas Vesalius in 1555 suggested opening the trachea and inserting a tube to allow the lung to reinflate and strengthen the heart, representing one of the earliest descriptions of mechanical ventilation. Dr. Nikhil Yadav's document discusses various modes of mechanical ventilation including controlled modes like volume control and pressure control ventilation, assisted modes like assist-control and synchronized intermittent mandatory ventilation, and spontaneous breathing modes like pressure support ventilation and proportional assist ventilation. The summary provides a high-level overview of the key topics and historical context covered in the document.
modes of ventilation
- 1. “…an opening must be attempted in the trunk of the trachea, into which a tube of reed or cane should be put; you will blow into this, so that the lung may rise again… and the heart becomes strong…” Andreas Vesalius (1555) MODES OF MECHANICAL VENTILATION Dr. Nikhil Yadav
- 2. Introduction Mechanical ventilation forms a mainstay of critical care in patients with respiratory insufficiency. Ventilator must generate inspiratory flow to deliver tidal volume. Transairway pressure (PTA) = PAO – PALV PTA = 0, at the end of expiration and beginning of inspiration. Mechanical ventilator produce either negative or positive pressure gradient.
- 3. Negative pressure ventilation PTA gradient is created by decreasing PALV to below PAO e.g.- Iron lungs Disadvantages- poor patient access, bulky size, cost, dec. cardiac output (Tank shock). Chest cuirass or chest shell
- 4. Positive pressure ventilation Achieved by applying positive pressure at airway opening which produces PTA gradient that generates inspiratory flow. Inspiratory flow results in the delivery of tidal volume.
- 5. Modes of ventilation Ventilator mode is a set of operating characteristics that controls how the ventilator functions. An operating mode describes the way a ventilator is- • triggered into inspiration • cycled into exhalation • what variables are limited during inspiration • allowing mandatory or spontaneous breaths or both
- 6. Controlled Mode Ventilation Volume control The ventilator delivers a preset TV at a specific R/R and inspiratory flow rate. It is irrespective of patients’ respiratory efforts. In between the ventilator delivered breaths the inspiratory valve is closed so patient doesn’t take additional breaths. PIP developed depends on lung compliance and respiratory passage resistance.
- 8. Volume controlled CMV Indications- • In initial stage when patients “fighting” or “bucking” with the ventilator • Tetanus or other seizure activity • Crushed chest injury Disadvantages- • Asynchrony • Barotrauma d/t high PAW & dec. lung compliance • Haemodynamic disturbances • V/Q mismatch • Total dependence on ventilator
- 9. Pressure Controlled CMV Ventilator gives pressure limited, time cycled breaths thus preset inspiratory pressure is maintained. Decelerating flow pattern. Peak airway/alveolar pressure is controlled but TV, minute volume & alveolar volume depends on lung compliance, airway resistance, R/R & I:E ratio.
- 10. PC- CMV
- 11. PC-CMV Advantages- Less PAW, thus chances of barotrauma and hemodynamic disturbances are less. Even distribution of gases in alveoli In case of leakage, compensation for loss of ventilation is better as gaseous flow increases to maintain preset pressure. Disadvantages- Asynchrony TV dec. if there is dec. lung compliance or inc. airway resistance, thus causes hypoventilation and alveolar collapse. V/Q mismatch.
- 12. ASSIST-CONTROL MODE Ventilation (A-C Mode) Ventilator assists patient’s initiated breath, but if not triggered, it will deliver preset TV at a preset respiratory rate (control). Mandatory mechanical breaths may be either patient triggered (assist) or time triggered (control) If R/R > preset rate, ventilator will assist, otherwise it will control the ventilation.
- 14. A-C Mode Ventilation Advantages- Dec. patients work of breathing. Better patient ventilator synchrony. Less V/Q mismatch. Prevents disuse atrophy of diaphragmatic muscle. Disadvantages- Alveolar hyperventilation Development of high intrinsic PEEP in obstructed pts. Inc. mean airway pressure causes hemodynamic disturbances.
- 15. Intermittent Mandatory Ventilation (IMV) Ventilator delivers preset number of time cycled mandatory breaths & allows patient to breath spontaneously at any tidal volume in between. Advantages- Lesser sedation Lesser V/Q mismatch Lesser hemodynamic disturbances Disadvantage- Breath stacking- lung volume and pressure could increase significantly, causing barotrauma.
- 16. IMV
- 17. Synchronized Intermittent Mandatory Ventilation (SIMV) Ventilator delivers either assisted breaths to the patient at the beginning of a spontaneous breath or time triggered mandatory breaths. Synchronization window- time interval just prior to time triggering. Breath stacking is avoided as mandatory breaths are synchronized with spontaneous breaths. In between mandatory breaths patient is allowed to take spontaneous breath at any TV.
- 18. SIMV
- 19. SIMV
- 20. SIMV It provides partial ventilatory support Advantages- Maintain respiratory muscle strength and avoid atrophy. Reduce V/Q mismatch d/t spontaneous ventilation. Decreases mean airway pressure d/t lower PIP & inspiratory time Facilitates weaning.
- 21. SIMV Disadvantages- Desire to wean too rapidly results in high work of spontaneous breathing & muscle fatigue & thus weaning failure.
- 22. Positive End Expiratory Pressure (PEEP) An airway pressure strategy in ventilation that increases the end expiratory or baseline airway pressure greater than atmospheric pressure. Used to treat refractory hypoxemia caused by intrapulmonary shunting. Not a stand-alone mode, used in conjugation with other modes. Indications- Refractory hypoxemia d/t intrapulmonary shunting. Decreased FRC and lung compliance
- 23. Physiology of PEEP PEEP reinflates collapsed alveoli & maintain alveolar inflation during exhalation. PEEP Increases alveolar distending pressure Increases FRC by alveolar recruitment Improves ventilation Increases V/Q Improves oxygenation Decreases work of breathing
- 24. PEEP
- 25. PEEP Complications Dec. venous return and cardiac output. Barotrauma Inc. ICP d/t impedance of venous return from head. Alteration of renal function & water imbalance.
- 26. Continuous Positive Airway Pressure (CPAP) PEEP applied to airway of patient breathing spontaneously Indications are similar to PEEP, to ensure patient must have adequate lung functions that can sustain eucapnic ventilation.
- 27. Mandatory Minute Ventilation (MMV) Similar to IMV mode except that minimum minute volume is set rather than R/R. Ventilator measures spontaneous minute volume, if found less than preset mandatory minute volume, the difference b/w two is delivered as mandatory breaths by ventilator at preset flow & TV. Suited for patients with variable respiratory drive Disadvantage- Hypoventilation as either minute volume recorded is not necessary alveolar ventilation.
- 28. Pressure Support Ventilation (PSV) Supports spontaneous breathing of the patients. Each inspiratory effort is augmented by ventilator at a preset level of inspiratory pressure. Patient triggered, flow cycled and pressure controlled mode. Decelerating flow pattern. Applies pressure plateau to patient airway during spontaneus br. Can be used in conjugation with spontaneous breathing in any ventilator mode.
- 29. PSV Commonly applied to SIMV mode during spontaneous ventilation to facilitate weaning With SIMV, PS- Inc. patient’s spontaneous tidal volume. Dec. spontaneous respiratory rate. Decreases work of breathing. Addition of extrinsic PEEP to PS increases its efficacy.
- 30. SIMV (VC) -PS
- 31. PSV Disadvantages- Not suitable for patients with central apnea. (hypoventilation) Development of high airway pressure. (hemodynamic distubances) Hypoventilation, if inspiratory time is short.
- 32. Adaptive Support Ventilation (ASV) Available on Galileo ventilator. Patient body weight (deadspace) & percent minute volume are feed in ventilator. Ventilator has pre determined setting of 100ml/kg/min. Test breath measures compliance, airway resistance & i. PEEP. Ventilator selects and provide the frequency, inspiratory time, I:E & sets high pressure limit for mandatory and spontaneous breaths. May be either time triggered or patient triggered.
- 33. Proportional Assist Ventilation (PAV) PAV is a spontaneous breathing mode that offers assistance to the patient in proportion to the patient’s effort. Inspiratory flow, volume & pressure are variable & pressure support changes according to elastance & airflow resistance & patients demand (volume or flow). PAV is set to overcome 80% of elastance & airflow resistance. PAV instantaneously measures the flow and volume being pulled in by the patient, and automatically calculates the compliance and resistance of the respiratory system to determine how much pressure to provide for each breath.
- 34. PAV Flow Assist (FA)- Pressure is provided to meet patient’s inspiratory flow demand. Dec. inspiratory effort to overcome airflow resistance. Volume Assist (VA)- Pressure is provided meet patient’s volume requirement. Dec. inspiratory efforts to overcome systemic elastance. Indications- Spontaneously breathing patient Intact respiratory drive Intact neuromuscular function Generally, a patient considered suitable for pressure support ventilation could be considered for PAV.
- 35. PAV Advantage- The patient ‘drives’ the ventilator Better patient ventilator synchrony as pressure vary to augment flow & demand. Disadvantage- Barotrauma- if elastance & resistance show sudden improvement.
- 36. Volume Assured Pressure Support (VAPS) Incorporates inspiratory pressure support ventilation & conventional volume assisted cycles to provide optimal inspiratory flow during assisted/controlled ventilation. Desired TV & pressure support level are preset. Once triggered desired PS level reaches asap & delivered volume is compared with preset TV. If volume delivered = 0r > preset volume, it is PS breath. If volume < preset volume, ventilator switches to volume limited, resulting in longer inspiratory time until preset TV is delivered
- 37. Pressure Regulated Volume Control (PRVC) Used to achieve volume support while keeping PIP to lowest level. Achieved by altering the peak flow & inspiratory time in response to changing airway or compliance characteristics. At constant flow PIP increases d/t inc. airflow resistance, so decreasing flow reduces the airflow resistance. To compensate for lower flow, inspiratory time is prolonged.
- 38. Airway Pressure Release Ventilation (APRV) Similar to CPAP as patient breathes spontaneously. Airway pressure is maintained at moderately high level (15-20 cmH2O) throughout most of respiratory cycle with brief periods of lower pressure to allow deflation of lungs. Inc. pressure ensures alveolar recruitment & oxygenation & brief deflation allows CO2 elimination without alveolar collapse. Indicated as an alternative to conventional volume cycled ventilation for patients with decreased lung compliance (ARDS), as chances of barotrauma is less d/t less PAW.
- 39. APRV
- 40. Inverse Ratio Ventilation (IRV) Used to promote oxygenation esp. in ARDS. Normal I:E ratio is 1:1.5 – 1:3, in IRV I:E is 2:1 – 4:1 Improves oxygenation by • Reducing intrapulmonary shunting. • Improving V/Q mismatch. • Decreasing deadspace ventilation. • Increasing mean airway pressure. • Presence of auto PEEP. Disadvantages- Barotrauma d/t inc. mPaw & auto PEEP. High rate of transvascular fluid flow. May worsen pulm. oedema
- 41. Tracheal Gas Insufflation (TGI) Adjuvant to mechanical ventilation in which O2 enriched gas is insufflated into trachea to ventilate anatomical dead space during expiration. Decreases PaCO2 at any level of inspiratory minute ventilation. Extra flow may cause inc. airway pressure and hyperinflation.
- 42. Independent Lung Ventilation (ILV) It is simultaneous separate ventilation of individual lung. Separation achieved by double lumen tube and two ventilators- synchronized or asynchronized. Indication- Severely diseased one lung which can not be treated with conventional ventilation. e.g.- unilateral pulmonary contusion, aspiration pneumonia, bronchopleural fistula, massive unilateral pulmonary embolism etc.
- 43. High frequency ventilation (HFV) For all high frequency techniques during which tidal volume equals or less than anatomical dead space volume and respiratory frequency between 60 to 3000 breaths / minutes. They are 3 types: HFPPV …..60 to 110 breaths/min HFJV…….110 to 600 breaths/min HFO……..600 to 3000 breaths/min Advantages- Low PAW, less V/Q mismatch, less barotrauma
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