Neonatal Ventilation: “The Bivent”

1. Neonatal Ventilation: “The Bivent” Paul Kingma, MD PhD

2. Ventilation Basics: Goals • Oxygenation • FiO2 • Mean airway pressure • Ventilation • Respiratory rate • Tidal volume

3. Conventional Pressure Ventilation Itime PIP Pressure PS PEEP Time

4. Conventional Pressure Ventilation How do you improve oxygenation? Itime PIP Pressure PS PEEP Time

5. Conventional Pressure Ventilation How do you improve oxygenation? Itime PIP Pressure PS PEEP Time

6. Conventional Pressure Ventilation How do you improve ventilation? Itime PIP Pressure PS PEEP Time

7. What do you do? • If a 2700g intubated baby has oxygen sats 70% and pCO2 80 and… • 30%FiO2 and ventilator settings of 16/5 and rate of 20? • 100%FiO2 and ventilator settings of 28/7 and rate of 60?

8. Risk of Lung Injury

9. Conventional Pressure Ventilation How do you improve oxygenation? Itime PIP Pressure PS PEEP Time

10. Conventional Pressure Ventilation How do you improve oxygenation? LONG I time Itime PIP Pressure PS PEEP Etime Time

11. Reynolds and Strang: 1970’s • Inverse I:E ratio • Improve oxygenation in neonates

12. Inverse I:E in infants = Air Leak • Factors associated with pulmonary air leak in premature infants receiving mechanical ventilation. Jpeds 1983 R.A. Primhak • Compare infants with pneumothorax vs ventilated controls • “No significant difference was found between the groups in any clinical factor, nor in any maximum ventilator setting other than a longer maximum inspiratory time in the study group.”

13. Conventional Pressure Ventilation How do you improve oxygenation? LONG I time Problem: Inverse I:E…Breath Stacking…Pneumothorax PIP Pressure PS PEEP Time

14. Is there a better way to increase Itime?

15. Another Option: Airway Pressure Release Ventilation (APRV) • Think of it as sustained high CPAP with timed “releases” to encourage ventilation • High and low CPAP settings: P high and P low • Baseline is at P high with pressure released periodically to allow ventilation • Release time is short to prevent collapse • Spontaneous exhalation allowed during ALL phases of respiratory cycle. • Therefore no breath stacking and no pneumothorax

17. Potential Advantages: Adults • Uses lower PIP to maintain oxygenation and ventilation without compromising the patient’s hemodynamics(Syndow AJRCCM 1994, Kaplan, CC, 2001) • Longer I-time means higher mean airway pressure with lower peak pressures • Shown to improved V/Q matching(Putensen, AJRCCM, 159, 1999) • Decreases dead space ventilation • Longer I-time allows diffusion of gases • Spontaneous respiration may • reduce need for sedation and avoid large changes in CO2 (Ratheberger, 1997; Putensen 2001) • improved ventilation in dependent lung regions • Better cardiac filling when compared to HFOV • Reduces time at extremes of pressure volume curve • decreased atelectasis • decreased barotrauma

18. What about Pediatrics? • Very little data

19. What about Pediatrics? • Schultz, et al Crit Care Med 2001 • Cross over study from SIMV to APRV or reverse in 15 patients with mild to moderate lung disease • Findings • Comparable oxygenation and ventilation with significantly lower peak pressures (33 vs 19 cm H2O) • No change in hemodynamic variables

20. What about Pediatrics? • Krishnan, et al Ped Pulmonol, 2007 • Case series of 7 pts (age 1 – 16 years) • Findings • Oxygenation (decrease in OI) improved with APRV over time • No problems with ventilation • No change in sedation requirements but No patients required neuromuscular blockade • No change in hemodynamic stability • Easier pt care than with HFOV

21. What about Pediatrics? • Dermirkol, et al Indian J Pediatr 2010 • Case series of 3 patients (3.5-11 mo old) changed from PC to APRV • Findings • FiO2 decreased from 0.97 to 0.68 • Mean Airway pressure increased from 17.9 to 27 cm H2O • Tidal volume increased from 8.3 ml/kg to 13.2 ml/kg

22. What about Pediatrics? • Kamath et al. Ped Pulmonol 2010 • Retrospective study of 11 pts on APRV for 12 hours due to failed conventional vent. • Findings after 10 hrs on APRV • FiO2 decreased from 0.83 to 0.67 • Mean airway pressure increased from 16.1 to 21.1 cm H2O • No change in HR, CVP, BP, UOP, IVF

23. What about Neonates? • No Data • Neonatal Sheep. Martin et al, 1991 Crit Care Med • Compared with PPV, APRV provided similar ventilation and oxygenation with lower peak pressures and without compromising cardiovascular performance.

24. APRV in Neonates When we know NOTHINGit is easy to be an expert! This is where I come in 

25. APRV Terminology • AKA: Bivent (Servo), APRV (Drager and Hamilton), Bilevel (Puritan-Bennett) • P High - the upper CPAP level. • P Low - the lower CPAP setting. • T High - is the inspiratory time phase for the P High. • T Low - is the release time allowing gas exchange and CO2 elimination

27. Bi-Vent Ventilation P High T low T High

29. How do you pick the settings?

30. Two Approaches • Similar to Pressure Targeted Ventilation • Select Phigh and Plow based on expected upper and lower inflection points of pressure volume curve • 1-3:1 inverse Thigh to Tlow ratio • Tlow long enough to allow minimal trapping of exhaled gas

31. Two Approaches • “Habashi method” • Phigh set to plateau pressure in conv vent • Plow set to zero! • Thigh adjusted to determine desired “release rate” • Tlow adjusted to stop exhalation at 50-70% of peak-expiratory flow

32. What do we do in NICU?Initial Settings • Newly intubated • P high—set at desired plateau pressure (typically 13–24 cm H2O in NICU) to achieve oxygenation and chest rise • Absolute value (NOT relative to P Low) • Bivent requires lower peak pressures than SIMV because of longer I-time • P low—0-5 cm H2O (mostly 3 cm H2O) • “Set” value but often actual PEEP is higher because of limited exhalation time • T high—1–3 secs (1/0.2 = release rate of 50, 3/0.2 = release rate of 19) • Used to control release rate • Time in Bivent is an absolute value not a relative value • T low—0.2–0.4 • Used to control alveolar recruiting, “actual” PEEP, and tidal volumes • More on this in a bit

33. In the NICU: Initial Settings • Transition from conventional ventilation • Phigh—peak airway pressure in pressure-cycled mode minus 2-4 • PEEP—0-5 cm H2O • T high—1–3 secs (usually target similar rate) • T PEEP—0.2–0.4 sec • Transition from HFOV • Phigh—target mPaw equal to HFOV plus 0–2 cm H2O • PEEP—0-5 cm H2O • T high—1–3 secs (use judgment to determine rate) • T PEEP—0.2–0.4

34. Adjusting Settings: Increase Oxygenation • Increase FiO2 • MAP • Increase P high (1-2 cm per change) • Increase T high (will impact rate also) • Increase Pressure support • Unlike SIMV or AC • Plow in Bivent has minimal impact on oxygenation • Tlow does not impact oxygenation directly (may impact recruitment)

35. Adjusting Settings: Oxygenation • T high • Increasing T high will improve oxygenation by increasing time at P High and subsequently increasing mean airway pressure • Increasing T high will also worsen ventilation by decreasing the number of releases per minute • Therefore, when adjusting T high, make small changes ~10% to avoid dramatic shifts in both oxygenation and ventilation

36. Adjusting Settings: Increasing Ventilation • Increase P high to raise the tidal volume • Decrease T high to raise the number of releases per minute (may need to increase Phigh to produce same mean airway pressure • Increase PS • Decrease Plow – more later • Increase Tlow – more later

37. Plow • Recommend set Plow at 0 cm H2O. • This provides a rapid drop in pressure, and a maximum pressure gradient for unimpeded expiratory gas flow during pressure release. • However, may lead to lung collapse if left unchecked….

38. Plow Reality Check • Adult literature (Habashi) recommends setting Plow at 0 cm H2O, but to avoid potential risk of severe collapse if Tlow is too long, I usually set Plow no lower than 2-3 cm in neonates. • This provides a rapid drop in pressure and a maximum pressure gradient for unimpeded expiratory gas flow during pressure release. • BUT if you are brave and need absolute maximum exhalation rate, then set Plow to 0 cm H20 but monitor very closely for changes in lung compliance and quickly make appropriate changes in Tlow • HOW do you adjust Tlow?

39. RT Comfort Zone Tlow

40. Expiratory Flow Goal: Maximum ventilation without risk of atelectasis De-recruitment Recruitment From Habashi, et al 2005

41. Tlow • To avoid collapse • Set Tlow so that expiratory flow from patient ends at about 50 to 75% of peak expiratory flow • In practice, this is difficult with neonates • Can also look at “actual” PEEP on vent to determine how low of pressure patients lungs are actually seeing • Target “normal” actual PEEPS of 5 cm H2O • Tlow • Too little results in not enough tidal volume • Too much results in atelectasis • Will change as compliance changes

42. Bivent Weaning • With SIMV we wean by lowering PIP and increase time during expiratory phase of cycle. • If you do this in BIVENT, patient will develop collapse from too long of Tlow. • Therefore DO NOT WEAN RATE IN BIVENT BY INCREASING Tlow • With BIVENT you lower pressure and increase time during inspiratory phase of cycle. • Gradually lower Phigh to decrease mean airway pressure • Gradually increase T High to lower number of releases per minute (this will increase your mean airway pressure so you may need to decrease Phigh even more) • Eventually patient will wean to equivalent of CPAP PS • As settings decrease remember may need to adjust PS to help with increased respiratory work load

43. Bivent Weaning: Drop and Stretch

44. Things to keep in mind • Bivent is a pressure mode of ventilation and will not change in response to changes in lung compliance • Tlow must be monitored frequently for changes in expiratory flow • Airway plugging can significantly impact expiratory flow • Technically, without spontaneous breaths, Bivent is the same as AC with a long I time BUT… • Since patient initiated inhalation/exhalation can occur at P High, “breath stacking” should not occur and the risk of pneumothorax should be minimal • Limited data in pediatrics and no data in neonates

45. What is our experience so far?

46. The End Questions?