Newer modes of ventilation

newer and alternate modes of ventilation

1. Newer modes of Ventilation By : Dr. Rohit K. Saini Moderator – Dr. Gaurav

2. Conventional modes suffer many limitations. often fail to match the patient based requirements. settings appropriate for one point of time, may not be optimal with patient deterioration or improvement Deliver set parameters and take no feedback from patient. Thus, all the classical volume/pressure control modes are “Open Loop” (the feedback loop is absent)

3. Newer modes Newer modes make alterations with the changing lung mechanics and take feedback from patient parameters, thus completing the feedback loop and are “Closed loop” type . “Dual control” ventilation - The control, cycle, or the limit variables undergo self-adjustment but if threshold of one component is reached they shift to the other alternate set parameter . Branson RD, Davis K Jr. Respir Care Clin N Am 2001. Tehrani F, et al.. J Clin Monit Comput 2004

4. Classification

5. Newer/Alternative modes A lternative modes of ventilation developed to prevent ventilator induced lung injury, Patient ventilator asynchrony, promote better oxygenation, p romote faster weaning, easier to use

6. Ideal mode of ventilation Synchronizes with patient’s spontaneous respiratory effort Maintains adequate and consistent Vt and minute ventilation at low airway pressures Responds to rapid changes in pulmonary mechanics or patient demand Provides the lowest possible WOB

7. PRVC Closed loop ventilation Dual control ventilation mode clinician sets a target Vt and maximal pressure level achieved by v ariable decelerating flow pattern The breaths are pressure limited, time cycled A dvantage : constant Vt with automatic weaning of the pressure limit as patient's compliance improves

8. Test breath and hold manoeuvre

9. PRVC – initial settings Respiratory rate- physiological for age Target tidal volume Upper pressure limit Inspired oxygen concentration I: E ratio PEEP Rise time- 5% of inspiratory time usually satisfactory

10. PRVC - ARDS PRVC is one of the recommended modes in ALI/ARDS In two studies of patients with ARDS, survival is better when high ventilation pressures are avoided. compare PRVC and VCV, concluded significantly lower MAP required to improve oxygenation parameters in PRVC group. PRVC: statistically significant difference in PIP of 4 cmH2O vs VCV and alveolar ventilation was unchanged as indicated by the constant PaCO2. Sachdev A, et al. Ind J Crit Care Med 2005 Guldager H, et al. Crit Care. 1997

11. PRVC – Duration of MV SIMV vs PRVC: no differences in time to extubation or pulmonary outcomes IMV vs PRVC in neonates with RDS: no decrease in duration of MV or incidence of bronchopulmonary dysplasia D’Angio CT, et al. Arch Pediatr Adolesc Med. 2005 Piotrowski A, et al. Intensive Care Med 1997

12. PRVC First introduced on Servo 300 ventilator Now available on most modern ventilators : Autoflow ( Drager Evita ), Volume Guarantee ( DatexOhmeda , Drager Babylog ), Adaptive pressure ventilation (Hamilton Galileo), Variable pressure control ( Venturi ) Balke B, Ware RW. Basic principles of ventilator machinery. 2nd edition, Philadelphia, McGraw-Hill: 2006

13. Airway pressure release ventilation ( APRV) described in 1987 by Stock et al. It provides two levels of 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 Stock MC, et al. Respir Care Clin N Am. 1987

14. APRV CPAP with intermittent, regular and brief release of pressure release phase : alveolar ventilation and removal of CO2 The mode has dual functionality: In spontaneous breathing the patient can breathe in any phase of respiratory cycle with supported breaths. In absence of spontaneous breathing activity, the bi-level pressure acts as time cycled, pressure limited inverse ventilation. Yoshida T, et al. Anesth Analg 2009

15. APRV Oxygenation is better in APRV with spontaneous breathing than with MV alone d/t recruitment of collapsed lung tissue and increased aeration in dependant areas of lung Improve CO, renal blood flow, GFR and achieve high mean airway pressure with low peak airway pressure. CAUTION: Hypovolemia : increased intrathoracic pressure further lower venous return avoided in obstructive lung diseases as it can cause air trapping or rupture of bullae . Putensen C, et al. Am J Respir Crit Care Med 1999

16. APRV - initial settings P high: Initially kept same as Pplat measured on VC mode provided it is lower than 30 cm H2O P low: pressure release. T high: during which P high is maintained. Usually at 3-4 sec. T low: time where pressure is released. Should be short enough to avoid de-recruitment but still long enough to allow alveolar ventilation. usually set at 0.6 to 0.8 secs FiO2

17. APRV Advantages High MAP with low PIP Allow inverse ratio ventilation, increases oxygen delivery Reduces need for sedation/ paralysis Improve patient ventilatory synchrony with spontaneous respiration Improve CO, renal blood flow, GFR. Disadvantages Pressure targeted mode, variable tidal volume delivery Increase in airway resistance hampers CO2 elimination – auto PEEP Limited experience

18. Volume support ventilation Patient triggers every breath. Patient determines RR and Ti. automatically adjusts lowest possible inspiratory pressure to deliver the preset Vt. Vt used as feedback control to adjust pressure support level If apnea: automatic back-up with PRVC mode Inspiratory pressure is maintained constant during inspiration. Inspiratory flow is decelerating (flow cycled - peak flow drops to 5-15% of initial flow ).

19. Volume support ventilation modification of pressure support mode where the support pressure is automatically adjusted to meet set Vt. INDICATONS: post-op recovering from anaesthesia , spontaneous breathing who requires minimumVt , who are asynchronous with the ventilator, and weaning mode esp patient with neuromuscular weakness Sottiaux TM. Respir Care 2001. McGough EK, Chest 1990.

20. Proportional assist ventilation In 1992, Younes and colleagues developed PAV. commercially available in Europe in 1999 approved in US in 2006, (Puritan Bennett 840 ventilator) PAV has also been used for noninvasive ventilation. Other name: Proportional Pressure Support ( Drager Medical) ventilator generates pressure in proportion to the patient’s effort . Intrabreath variation

21. Proportional assist ventilation patient controls timing and size of breath no preset press., flow or vol. goals, but safety limits on vol. and press. delivered can be set. pressure applied is a function of patient effort: the greater the inspiratory effort, the greater is applied pressure. operator sets the % of support to be delivered by ventilator ventilator intermittently measures compliance & resistance of patient’s respiratory system and patient-generated flow and volume, and it delivers a proportional amount of inspiratory pressure accordingly. Ambrosino N, Rossi A. Thorax 2002

22. PAV

23. PAV – initial settings Airway type (ETT, TT) Airway size (inner diameter) Percentage of work supported (assist range 5%–95%) Vt and pressure limit Expiratory sensitivity (flow dependent). Disadvantage: if patient worsens or improves, the proportion of assistance may needed to be reset. newer modification of “PAV+” mode: capable of sensing patient lung mechanical properties and adjusting accordingly. Xirouchaki N, et al. Intensive Care Med 2008

24. PAV - Advantages reduce the work of breathing, improve synchrony, automatically adapt to changing patient lung mechanics and effort, decrease need for ventilator intervention and manipulation, decrease need for sedation, and improve sleep No trial has reported the effect of PAV on deaths. N Ambrosino , A Rossi. Proportional assist ventilation (PAV): a significant advance or a futile struggle between logic and practice? Thorax 2002

25. PAV not recommended for use in neonates or patients weighing less than 20 kg because of potential inaccuracies of flow measurements: ETT size (6.0 mm or lesser), leaks around ETT, and the ability of sensors to measure changing mechanics in this population Kacmarek RM. Respir Care. 2011 Schmidt M, et al. Crit Care. 2015

26. Volume assured pressure support Intra-breath variation - character of breath changes within same breath from press. to vol. control if minimum Vt not achieved. ventilator uses both (Pressure & Volume limited) within the same breath to achieve target minimum Vt. Type of breath will depend on adequacy of patient’s effort. Amato MB, et al. CHEST 1992;102:1225-34.

27. VAPS – initial settings mechanical parameters are as in conventional pressure: Pressure limit, ventilator rate, positive end-expiratory pressure (PEEP), FiO2, desired minimum tidal volume Oscroft NS, Smith IE. Respirology 2010 Okuda M, et al. J Med Case Rep 2012

28. Adaptive support ventilation ASV: form of mandatory minute ventilation implemented with adaptive press. control or press. support. automatically selects appropriate Vt and frequency for mandatory breaths and appropriate Vt for spontaneous breaths on the basis of respiratory system mechanics and target minute alveolar ventilation every breath is synchronized with patient effort if such an effort exists and otherwise, full MV is provided. Brunner JX. Adaptive Support Ventilation. Minerva Anestesiol 2002

29. ASV – Otis equation ASV uses the Otis Equation to calculate the optimal frequency that corresponds with the lowest work of breathing Chen et al., 2008 Otis et al., 1950

30. ASV – initial settings Gender and height (for ideal body weight) Percent of normal predicted minute ventilation goal. It can be set from 20% to 200% FiO2 and PEEP High-pressure alarm Advantages: provides decelerating flow waveform to improve gas distribution with guaranteed Vt. decreases work of breathing. automatic weaning is possible with disease reversal

31. Mandatory minute ventilation MMV was first described by Hewlett et al in 1977 MMV is the first closed loop mode (changes its output based on measured input variables) allows patient to breathe spontaneously with guaranteed minimum minute ventilation accomplished by the use of increasing levels of pressure support or by delivery of mandatory breaths (time triggered, volume controlled).

32. Neurally adjusted ventilatory assist unique mode: based on neural respiratory output breath is controlled by the respiratory center, which decides the characteristics of each breath, timing and size electrical activity of the diaphragm is captured, fed to the ventilator and used to assist the patient's breathing in synchrony with and in proportion to the patients own efforts. Sinderby C, Beck J. Clin Chest Med 2008. Navalesi P, Costa R. Curr Opin Crit Care 2003.

33. NAVA Unlike all other modes available that use pressure, flow or volume sensing to initiate a breath, NAVA uses diaphragmatic electromyogram to detect inspiratory effort. An esophageal catheter with electrodes placed at the level of diaphragm is used to record time of initiation and strength of contraction effort of patient.

34. NAVA PAV and NAVA perform similar functions: both support patients in proportion to their needs. NAVA uses diaphragm activity rather than a sensor on the ventilator circuit to trigger. So, NAVA is not prone to issues a/w air leaks and intrinsic PEEP that may reduce responsiveness of the ventilator to patient efforts. Further, NAVA can be used in neonatal and pediatric patients Schmidt M, et al. Neurally adjusted ventilatory assist and proportional assist ventilation both improve patient-ventilator interaction. Crit Care. 2015

35. NeoGanesh ( Smartcare ) closed loop modification of pressure support ventilation with integrated artificial intelligence based on three fundamental principles: Adapt pressure support to patient’s current clinical situation, In case of stability, tends to wean of pressure support, Initiate spontaneous breathing trials as per prerecorded clinical guidelines. Lellouche F, Brochard L. Best Pract Res Clin Anaesthesiol 2009

36. NeoGanesh ( Smartcare ) Ventilator takes feedback from monitored respiratory rate, tidal volume, and end-tidal CO2. 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. Lellouche F, Brochard L. Best Pract Res Clin Anaesthesiol 2009

37. High frequency oscillatory ventilation HFOV is a form of pressure controlled IMV. HFOV superimposes very small mandatory breaths (oscillations) on top of spontaneous breaths. delivers a constant flow while a valve creates resistance to maintain constant airway pressure, on top of which a piston pump oscillates at frequencies of 3 to 15 Hz

38. High frequency oscillatory ventilation unique ability to provide adequate gas exchange using Vt below dead-space volume in the setting of continuous alveolar recruitment Oxygenation is achieved by lung recruitment with high MAP and ventilation is achieved with an oscillating piston that creates cycles of pressure above and below MAP at a Supraphysiologic RR (180–900/min), resulting in small Vt (1 - 2.5mL/kg) Exhalation is an active process.

39. HFOV – initial settings control of oxygenation and ventilation are independent MAP is adjusted to achieve SaO2> 90% while CO2 elimination is increased by adjusting the amplitude and decreasing frequency on machine.

40. HFOV - weaning Decrease FiO2, MAP, and amplitude Switch to conventional ventilation when: Reversal of disease process Adequate gas exchange & improving oxygenation indices MAP < 15 (12-18 cm H2O) FiO2< 0.5 (0.4-0.6) Different studies has found no differences in survival or duration of MV while comparing conventional and HFOV. Bollen CW, et al.. Crit Care 2005

41. Key learning points Dual modes of ventilation are more patient friendly than conventional modes even in difficult ventilation or at time of weaning. Newer modes reduced the need of ventilation and decreased ventilator induced lung injury. These modes have favourable effects on cardiopulmonary interactions. Further clinical trials are needed to make a recommendation for various modes of ventilation according to disease and patient status.

42. At last No ventilator can replace clinician judgement , thus a smart brain can work better with an old fashioned machine rather than a latest machine alone

43. Thank you