Newer modes of Ventilation.ppt
- 1. Newer Modes of Ventilation Dr.AjayRakeshVarma MBBS,MD (Anaesthesia),M.Med(Family Medicine), CCEBDM,
- 2. Why? • Hemodynamic compromise as ventilatory pressures are transmitted to the heart and cause cardiac embarrassment. • Barotrauma (interstitial emphysema, pneumothorax and pneumomediastinum) as high airway pressures and levels of PEEP are used causing alveolar rupture. • Epithelial leaks from increased shear forces can lead to increased microvascular permeability and alveolar edema • Oxygen Toxicity (substernal distress, absorption atelectasis and pulmonary edema, also cns toxicity-seizures-divers) and V/Q mismatch • Need for sedation/neuro-muscular blockers because patients are dyssynchronous with the ventilator. • Lung injury with surfactant deficiency.
- 3. • The classical volume/pressure control modes are “Open Loop” (the feedback loop is absent). • The newer modes target to make alterations with the changing lung and take feedback from patient parameters, thus completing the feedback loop and are “Closed loop” type.
- 4. • Dual control within a breath-The control variable can change its nature (from pressure to volume or vice versa) within a single breath if the desired ventilation requirements are not met. • VAPS is an entirely controlled mode
- 5. Volume-assured pressure support (VAPS) • This is a modification into pressure control mode. It makes the ventilator to switch from pressure control mode to volume control if a minimum set tidal volume is not achieved. • In patients where the lung compliance decreases this mode provides safety against increasing blood CO2 levels by maintaining minimal minute ventilation.
- 7. • Dual control in subsequent breaths-The ventilator takes feedback from output parameters of initial breaths and makes automatic adjustments to set targets in the subsequent breaths. • Pressure limited flow cycled ventilation ( volume support) • Volume support is a spontaneous patient initiated mode.
- 8. • It is a modification of pressure support mode where the support pressure is automatically adjusted by the ventilator to meet the minimal set tidal volume. • The ventilator in initial breaths measures the delivered tidal volume and if the minimal volume set is higher than this, it automatically steps up the pressure support in the next breaths. • This mode achieves the advantages of pressure support assuring an adequate tidal volume despite changes in lung compliance.
- 10. • Respiratory rate, minimal tidal volume and PEEP are preset. • Volume support is a useful mode for weaning as once the patient begins to achieve a desired tidal volume it automatically decreases the pressure support, thus gradually loading the respiratory muscles to take on work of breathing.
- 11. • Like the pressure support mode patient controls the I:E and the total inspiratory time, this improves the ventilator-patient synchrony. • The basic caution prior to use of this mode is that patient must have spontaneous breathing activity else the ventilator will automatically shift to backup mode.
- 12. • If the set tidal volume is too large, the ventilator will raise the pressure support to achieve it and lead to problems like barotrauma, hemodynamic compromise, and intrinsic PEEP. • If the set volume is too low, it may lead to inadequate pressure support and thus increased respiratory rate leading to increased work of breathing
- 13. Adaptive support ventilation • Unique mode that sets minimal work of breathing as its end point to achieve desired minute ventilation. The control variable is “pressure” and is capable of delivering both pressure control or pressure support breaths. • The operating principle is based on pressure controlled synchronized intermittent mandatory ventilation with automatic adjustments to set pressure level and respiratory rate on the basis of measured lung mechanics in the previous breaths.
- 14. Adaptive Pressure Control • APC delivers pressure-controlled breaths with an adaptive targeting scheme – adjusting inspiratory pressure to deliver a set minimum tidal volume • Flow of gas varies to maintain constant to maintain constant airway pressure. • Allows a patient who generates an inspiratory effort to receive flow as demanded, which is more comfortable (as opposed to volume controlled, in which flow is fixed, and if the patient‟s effort is big enough flow asynchrony in which the patient doesn‟t get the flow they asked for) • If patient effort is large enough, the Tv will increase in spite of ↓respiratory pressure. Not appropriate for patients who have an inappropriate increased respiratory drive (eg metabolic acidosis) since the inspiratory pressure will ↓ to maintain the targeted average tidal volume, shifting the work of breathing onto the patient
- 16. • The set parameters are the ideal body weight, minimum minute ventilation, PEEP, and trigger sensitivity. • The target ventilation (tidal volume and respiratory rate) corresponds to the best combination from energy standpoint estimated by automatic measurements of lung compliance and resistance.
- 17. • The ventilator continuously optimizes I:E ratio to avoid any auto-PEEP.This mode can be used as partial to full support mode Acute respiratory distress syndrome (ARDS), asthma, and weaning. • The major limitation if this mode is inability to recognize dead space ventilation or shunts to make adjustments to ventilation. • In clinical conditions where lung physical parameters remain unchanged (pulmonary embolism), the mode fails to adapt to patients requirements. • Auto-PEEP may become problem in chronic obstructive pulmonary disease (COPD) patients needing longer expiratory times
- 18. Proportional assist ventilation (PAV) • It is a form of synchronized partial ventilator assistance with a unique feature that ventilator assists in proportion to patients instantaneous effort. • PAV unloads respiratory muscles and unaltered respiratory pattern allows synchrony between ventilator and patient's neural ventilator drive.
- 20. • Percent of assistance is preset, Parameters like I:E ratio and inspiratory time are completely patient controlled and further add to successful patient synchronization. • The potential disadvantage noted is that if the patient worsens or improves, the proportion of assistance may needed to be reset according to newer clinical situation.
- 21. • Newer modification of “PAV+” mode, which is capable of sensing patient lung mechanical properties and adjusting accordingly. • Other advantages of PAV include low airway pressures, optimal weaning, and decreased work of breathing • A technical important aspect of PAV is that there should be minimal air leak in the system this would cause the ventilator to overassist or cause auto cycling(a positive back pressure wont build up during inspiration and ventilator would presume inspiration is going on). • PAV has been used in early/late ARDS, hypercapnic respiratory failure, and weaning.
- 22. Mandatory minute ventilation (MMV) • It is a modification of pressure support ventilation. The ventilator takes feedback to alter both respiratory rate and the level of pressure support to achieve set minimum minute ventilation. • The operator sets minimum minute ventilation required adjudging the present patient clinical state. These values often fall in 70%-90% of current minute volume.
- 23. • If the patient fails to achieve the set value, the ventilator provides the deficit. • MMV forms a reliable weaning mode,as the set value can be gradually decreased loading the respiratory muscles. • In patients with apneic episodes or central drive pathologies, MMV sets safety by providing a set value ventilation as mandatory ventilation
- 24. • The ventilatory setting of MMV need extreme caution, if the set value is significantly lower than current minute ventilation, this may lead to increased work of breathing by the patient and in reverse situation this can lead to complete unloading of respiratory muscles causing possibility of muscle atrophy. • A maximal respiratory rate set too high can cause significant increase in ventilator frequency during ventilator automatic adjustment leading to “rapid shallow” breathing.
- 26. Airway pressure release ventilation (APRV) • APRV is a bi-level mode representing another open-lung ventilation strategy. It provides two levels of continuous positive airway pressure (CPAP) with an inverse I:E ratio of 2:1 or more. • The rationale of using prolonged high-pressure phase is to prevent alveolar collapse and maintain recruitment. • The release phase (expiratory phase) brings down mean airway pressure and plays significant role in maintaining normocarbia.
- 27. • The mode has dual functionality in presence of spontaneous breathing the patient can breathe in any phase of respiratory cycle with supported breaths thus bringing down needs of sedation. • In absence of spontaneous breathing activity, the bi-level pressure acts as time-cycled inverse ratio ventilation. • The tidal volume generated mainly depends upon respiratory compliance and difference between the two CPAP levels.
- 28. • The set Phigh,(high pressure in CPAP) Plow,(low pressure in CPAP) Thigh(time for Phigh)and Tlow (Time for Plow). • Initial Phigh should be set to plateau pressure or the upper inflection point and Plow should be set at lower inflection point on volume-pressure curve. • APRV should be used with caution in hypovolemic as increased intrathoracic pressure further lower venous return. APRV should be avoided in patients with obstructive lung diseases as it can cause air trapping or rupture of bullae in COPD. APRV has been shown to improve oxygenation in patients with ARDS simultaneously decreasing need of sedation or paralysis.
- 30. Neurally adjusted ventilatory assist (NAVA) • NAVA is a closed loop mode that delivers breath proportional to patient's inspiratory effort. • Unlike all other modes available that use pressure, flow or volume sensing to initiate a breath, NAVA uses diaphragmatic electromyogram to detect inspiratory effort of patient. • An esophageal catheter with electrodes placed at the level of diaphragm is used to record time of initiation and strength of contraction.
- 31. • This mode over scores all other modes in synchronization of patients efforts to ventilator by having least possible delay among the two. • Like PAV, NAVA assists in accordance to measured strength of diaphragmatic contractions and most of parameters like inspiratory time, I:E ratio are patient controlled. • Leaks in the circuit can cause false initiation of breaths in conventional modes leading to severe ventilator asynchrony
- 32. • NAVA is completely unaffected by this phenomena as breath initiation is completely independent of physical properties of the circuit. • In other modes auto-PEEP increases work of ventilator initiation in COPD and asthma, this does not effect ventilatory cycle in NAVA and thus overall work of breathing decreases in these patients. • Setting up a NAVA ventilator is straightforward and gain over diaphragmatic electrographic potential is the only single input required. A practical limitation with NAVA is placement of esophageal catheter with electrodes and its validity of longer duration of ventilation.
- 34. NeoGanesh (Smartcare) • It is closed loop modification of pressure support ventilation with integrated artificial intelligence. • The system mimics clinical approach of adjusting ventilator assistance depending on patient's respiratory pattern and literature based weaning protocols. • This mode is based on three fundamental principles: • 1. Adapt pressure support to patient's current clinical situation, • 2. In case of stability the ventilator tends to wean of pressure support, • 3. Initiate spontaneous breathing trials as per prerecorded clinical guidelines.
- 35. • Ventilator takes feedback from monitored respiratory rate, tidal volume, and end-tidal CO2. • Once the patient remains stable on a setting, it tries to gradually wean off to maintain optimal respiratory variables, which are predefined as “Patient comfort zone.” • Trials have shown that it not only reduces weaning failures but also significantly hastens weaning duration.