1. The Art and Science of Intraoperative Ventilator Management
Ross Blank, MD
Assistant Professor
Division of Critical Care
Director, Thoracic Anesthesia

2. How Should We Ventilate Patients in the Operating Room?
What we have done
Pathophysiology of general anesthesia and mechanical ventilation
Recent clinical data on protective ventilation strategies

3. Older Anesthesia Machines
Ventilator had two modes:
Bag
Volume Control

4. Older Machines - Volume Control
CMV (Continuous Mandatory Ventilation)
No attempt to synchronize with patient effort
Constant flow rate
Ascending pressure
Set rate and I:E ratio determine inspiratory time
Flow x Inspiratory time = Tidal Volume
Tidal volume changed with fresh gas flow

5. Pressure vs. Volume Control
Pressure control
Volume control
(really flow control)
Tobin MJ. Principles and Practice of Mechanical Ventilation, 2nd Ed

6. Older PEEP

7. Newer Anesthesia Machines
Pressure dial
Flowmeters
No PEEP

8. What Tidal Volume Should We Use Under General Anesthesia?
Normal tidal volume in adult humans breathing spontaneously is approximately:
6 mL/kg predicted body weight
Should there be a different normal for mechanical ventilation?

9. Predicted Body Weight
Depends on height and gender only; as patients become more or less obese, their lungs stay the same size
Males: PBW (kg) =
x (height in inches – 60)
Females: PBW (kg) =
x (height in inches – 60)

10. Predicted Body Weight

11. Average Americans Male Female
Height: 5’9” PBW: 70.7 kg TV (6 mL/kg): 424 mL
Height: 5’4” PBW: 54.7 kg TV (6 mL/kg): 328 mL
The old default U of M tidal volume (600 mL) worked out to
8.5 mL/kg for males and 11 mL/kg for females; these are
supraphysiologic

12. Current/Recent Practice

13. Current/Recent Practice
Observational study of 2937 patients undergoing GA with MV in 49 hospitals in France over a 6-month period in 2006
Female sex and obesity independent risk factors for high tidal volumes per PBW
PEEP 4 cm H2O or less in 91% of patients
7.7 mL/kg
8.8 mL/kg PBW

14. Why do we use large tidal volumes in the OR?

15. “A Concept of Atelectasis”
Spontaneous breathing includes periodic deep breaths or sighs
Mechanical ventilation typically delivers constant tidal volumes
Over time, mechanical ventilation may lead to decreases in oxygenation and compliance due to alveolar collapse or atelectasis
Atelectasis may be reversible with periodic hyperinflations
Bendixen et al. NEJM 1963;269:

16. “A Concept of Atelectasis”
Declines in PaO2 and compliance reversible with hyperinflation maneuvers
No use of PEEP in this study
Bendixen et al. NEJM 1963;269:

17. “A Concept of Atelectasis”
Large TV
“Shallow” TV
No definition of magnitude of TVs
Bendixen et al. NEJM 1963;269:

18. “Perhaps the best course of action, during controlled ventilation, is
“Perhaps the best course of action, during controlled ventilation, is in providing reasonably large tidal volumes [and] periodic passive hyperinflation of the lungs.”
Bendixen et al. NEJM 1963;269:

19. Pathophysiology of General Anesthesia
Hedenstierna G. Acta Anaesthesiol Scand 2012;56:

20. Pathophysiology of General Anesthesia
Atelectasis occurs with anesthesia induction
Supine position
Loss of muscle tone
Decrease in FRC
Airway closure
Oxygen absorption
Lung compression
Surfactant deficiency
Shunting -> hypoxemia
Increased VD/VT -> wasted ventilation
May predispose to infection
Hedenstierna and Edmark. Best Pract Res Clin Anaesthesiol 2010;24:157-69

21. Atelectasis
Tusman and Bohm. Best Pract Res Clin Anaesthesiol 2010;24:

22. How to Reverse Atelectasis?
Large tidal volumes?
Recruitment maneuvers?
PEEP?
Alveolar Recruitment Strategy?
Inhaled Gas Composition?

23. Compliance Curve – The Lungs as a Single Balloon
Compliance low:
Overinflation
High VD/VT
Best Compliance
Compliance low:
Atelectasis, Shunt
Blanch et al. Curr Opin Crit Care 2007;13:

24. Ventilator-Induced Lung Injury
Slutsky and Ranieri. NEJM 2013;369:

25. Ventilator-Induced Lung Injury
Slutsky and Ranieri. NEJM 2013;369:

26. Open the Lungs . . . and Keep Them Open
Sequential CT scans, n = 13
Neumann et al. Acta Anaesthesiologica Scandinavica 1999;43:

27. Alveolar Recruitment Strategy
20/5
25/10
30/15
35/20
40/20
Tusman et al. Br J Anaesth 1999;82:8-13
Tusman and Bohm. Best Pract Res Clin Anaesthesiol 2010;24:

28. Compliance Curve – The Lungs as a Single Balloon
Tidal Volume
PEEP
Blanch et al. Curr Opin Crit Care 2007;13:

29. Possible Methods to Limit Atelectasis at Induction
Pre-oxygenation with < 100% FiO2
Pre-induction CPAP
Sitting position
Recruitment maneuver after induction
Hedenstierna G. Acta Anaesthesiol Scand 2012;56:

30. Pre-Oxygenation with < 100% FiO2?
No pre-induction CPAP
No RM after intubation
PEEP 3 cm H2O after intubation
Edmark et al. Acta Anaesthesiol Scand 2011;55:75-81

31. Methods to Limit Atelectasis during Maintenance and Emergence
PEEP + Periodic recruitment maneuvers
Limit FiO2 to decrease absorption atelectasis
At emergence, maintain PEEP/CPAP, minimize disconnections/suctioning, avoid 100% FiO2
Hedenstierna G. Acta Anaesthesiol Scand 2012;56:

32. Emergence with < 100% FiO2?
Intervention 10 minutes before end of surgery; patients transported to CT scanner after extubation; supplemental O2 only prn
Least atelectasis and highest PACU PO2 observed with RM followed by 40% FiO2
Positive pressure not maintained after RM
Benoit et al. Anesth Analg 2002;95:

33. Role for CPAP after Extubation?
Multi-center RCT
209 patients with hypoxemia after elective open abdominal surgery
Mask O2 vs. O2 + CPAP 7.5 cm H2O
Stopped early after CPAP group showed lower rates of reintubation and pneumonia, and less ICU days
Squadrone et al. JAMA 2005;293:

34. Postoperative Pulmonary Complications
“The main outcome was the development of at least one of the following:
Respiratory infection, respiratory failure, bronchospasm, atelectasis, pleural
effusion, pneumothorax, or aspiration pneumonitis.”

35. ARISCAT
Population-based surgical cohort of 2464 patients were followed prospectively for development of postoperative pulmonary complications -> incidence of at least one PPC = 5.0%
Regression modeling identified seven independent risk factors
Canet et al. Anesthesiology 2010;113:

36. Postoperative Pulmonary Complications
What works:
Postoperative lung expansion modalities
Selective nasogastric decompression
Avoidance of long-acting neuromuscular blockers
Laparoscopic approaches when feasible
Lawrence et al. Ann Intern Med 2006;144:

37. Postoperative ALI/ARDS
> 50,000 low-risk surgical admissions
0.2% incidence of ALI/ARDS
Blum et al. Anesthesiology 2013;118:19-29

38. What is ALI/ARDS?
Acute Lung Injury/Acute Respiratory Distress Syndrome
First described by Ashbaugh et al. in 1967
Definition formalized in 1992 American European Consensus Conference
Acute onset, bilateral infiltrates on CXR
PCWP ≤ 18 mmHg or no clinical evidence of left atrial hypertension
PaO2/FiO2 (P/F) Ratio
≤ 300 for ALI
≤ 200 for ARDS
Ashbaugh DG et al. Lancet 1967;290:
Bernard GR et al. AJRCCM 1994;149:

39. Postoperative ALI/ARDS
4,366 high-risk operations
2.6% incidence of ALI/ARDS
Kor et al. Anesthesiology 2011;115:

40. Surgical Lung Injury Prediction
Kor et al. Anesthesiology 2011;115:

41. Small Prospective Trials of Lung Protective Ventilation in the OR
Author
Population
LPVS
Control
Outcome
Mascia
(JAMA 2010;
304:2620-7)
Organ
donors
TV 6-8 mL/kg
PEEP 8-10
CPAP
for apnea testing
Closed circuit
for suctioning
TV mL/kg
PEEP 3-5
Vent disconnect
Open circuit
Increased # of
eligible and
harvested lungs
Yang
(Chest 2011;
139: )
Lung
cancer
resection
TV 6 mL/kg
PEEP 5
FiO2 50%
PCV
TV 10 mL/kg
PEEP 0
FiO2 100%
VCV
Lower rate of
lung dysfunction
(hypoxemia, infiltrate,
atelectasis) within
72h of surgery
Sundar
(Anes 2011;
114: )
Elective
cardiac
surgery
mechanical ventilation
at 6h and lower
reintubation rate

42. What about more routine cases?
56 open abdominal operations randomized to protective vs. standard ventilation strategies
Outcomes = CXR, oxygenation, postoperative pulmonary infection score, and PFTs
Severgnini et al. Anesthesiology 2013;118:

43. Severgnini RCT Protective Standard
TV = 7 mL/kg PBW PEEP = 10 cm H2O Prescribed RMs after induction, after any circuit disconnection, and before emergence
TV = 9 mL/kg PBW PEEP = 0 cm H2O No prescribed RMs
Severgnini et al. Anesthesiology 2013;118:

44. Severgnini Results
Severgnini et al. Anesthesiology 2013;118:

45. Severgnini Results
Pulmonary infection score includes points for temperature, white blood cell count, secretions, P/F ratio, and CXR
Severgnini et al. Anesthesiology 2013;118:

46. The IMPROVE Trial
400 major abdominal surgeries (open and laparoscopic) Primary Outcome = composite of major pulmonary (pneumonia, respiratory failure) and extrapulmonary (sepsis, death) complications
Futier et al. NEJM 2013;369:

47. The IMPROVE Trial Lung-Protective Nonprotective
TV = 6-8 mL/kg PBW PEEP = 6-8 cm H2O Prescribed RMs after induction and every 30 minutes
TV = mL/kg PBW PEEP = 0 cm H2O No prescribed RMs
Futier et al. NEJM 2013;369:

49. Las Vegas
10,000 patients in 142 centers
Enrollment closed in 3/2013

50. Conclusions
The common practice of using supraphysiologic tidal volumes without PEEP will support oxygenation and not cause overt harm in the majority of patients.

51. Conclusions
Atelectasis develops quickly and reliably after induction of anesthesia and can be minimized with RMs after induction and circuit disconnections, application of PEEP after RMs, minimization of FiO2 when possible, and continuation of lung expansion modalities into the recovery room and postoperative ward.

52. Conclusions
A comprehensive strategy of lung-protective ventilation aims to minimize both atelectasis and ventilator-induced lung injury and is increasingly being shown to be beneficial in varied surgical populations. There is no evidence that such strategies confer harm.