The Art and Science of
Intraoperative Ventilator
Management
Ross Blank, MD
Assistant Professor
Division of Critical Care
Director, Thoracic Anesthesia
rossblan@med.umich.edu
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
Older Anesthesia Machines
Ventilator had two
modes:
1. Bag
2. Volume Control
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
Pressure vs. Volume Control
Pressure control
Volume control
(really flow control)
Tobin MJ. Principles and Practice of Mechanical Ventilation, 2nd Ed. 2006.
Older PEEP
Newer Anesthesia Machines
Pressure dial
Flowmeters
No PEEP
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?
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) =
50.0 + 2.3 x (height in inches – 60)
• Females: PBW (kg) =
45.5 + 2.3 x (height in inches – 60)
http://www.ardsnet.org/node/77460
Predicted Body Weight
http://www.ardsnet.org/system/files/pbwtables_2005-02-02_0.pdf
Average Americans
Male
Female
Height: 5’9”
Height: 5’4”
PBW: 70.7 kg
PBW: 54.7 kg
TV (6 mL/kg): 424 mL
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
Current/Recent Practice
Current/Recent Practice
•
•
Observational study of 2937
patients undergoing GA
with MV in 49 hospitals in
France over a 6-month
period in 2006
7.7 mL/kg
Female sex and obesity
independent risk factors for
high tidal volumes per PBW
8.8 mL/kg PBW
•
PEEP 4 cm H2O or less in
91% of patients
Why do we use large tidal volumes
in the OR?
“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;269:991-996
“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;269:991-996
“A Concept of Atelectasis”
Large TV
Bendixen et al. NEJM 1963;269:991-996
“Shallow” TV
“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;269:991-996
Pathophysiology of General
Anesthesia
Hedenstierna G. Acta Anaesthesiol Scand 2012;56:675-685
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
Atelectasis
Tusman and Bohm. Best Pract Res Clin Anaesthesiol 2010;24:183-197
How to Reverse Atelectasis?
• Large tidal volumes?
• Recruitment maneuvers?
• PEEP?
• Alveolar Recruitment Strategy?
• Inhaled Gas Composition?
Compliance Curve –
The Lungs as a Single Balloon
Best Compliance
Compliance low:
Atelectasis, Shunt
Blanch et al. Curr Opin Crit Care 2007;13:332-337
Compliance low:
Overinflation
High VD/VT
Ventilator-Induced Lung Injury
Slutsky and Ranieri. NEJM 2013;369:2126-2136
Ventilator-Induced Lung Injury
Slutsky and Ranieri. NEJM 2013;369:2126-2136
Open the Lungs . . .
and Keep Them Open
Neumann et al. Acta Anaesthesiologica Scandinavica 1999;43:295-301
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;24:183-197
Tidal Volume
Compliance Curve –
The Lungs as a Single Balloon
PEEP
Blanch et al. Curr Opin Crit Care 2007;13:332-337
Possible Methods to Limit
Atelectasis at Induction
1. Pre-oxygenation with < 100% FiO2
2. Pre-induction CPAP
3. Sitting position
4. Recruitment maneuver after induction
Hedenstierna G. Acta Anaesthesiol Scand 2012;56:675-685
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
Emergence with < 100% FiO2?
Benoit et al. Anesth Analg 2002;95:1777-1781
•
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
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;293:589-595
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.”
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;113:1338-1350
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;144:596-608
Postoperative ALI/ARDS
• > 50,000 low-risk surgical admissions
• 0.2% incidence of ALI/ARDS
Blum et al. Anesthesiology 2013;118:19-29
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
1.
Acute onset, bilateral
infiltrates on CXR
2.
PCWP ≤ 18 mmHg or no
clinical evidence of left
atrial hypertension
3.
PaO2/FiO2 (P/F) Ratio
≤ 300 for ALI
≤ 200 for ARDS
Ashbaugh DG et al. Lancet 1967;290:319-323
Bernard GR et al. AJRCCM 1994;149:818-824
Postoperative ALI/ARDS
• 4,366 high-risk operations
• 2.6% incidence of ALI/ARDS
Kor et al. Anesthesiology 2011;115:117-128
Surgical Lung Injury Prediction
Kor et al. Anesthesiology 2011;115:117-128
Small Prospective Trials of Lung
Protective Ventilation in the OR
Author
Population
LPVS
Control
Outcome
Mascia
Organ
donors
• TV 6-8 mL/kg
• PEEP 8-10
• CPAP
for apnea testing
• Closed circuit
for suctioning
• TV 10-12 mL/kg
• PEEP 3-5
• Vent disconnect
for apnea testing
• Open circuit
for suctioning
Increased # of
eligible and
harvested lungs
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
Elective
cardiac
surgery
•
TV 6 mL/kg
•
TV 10 mL/kg
Lower rate of
mechanical ventilation
at 6h and lower
reintubation rate
(JAMA 2010;
304:2620-7)
Yang
(Chest 2011;
139:530-537)
Sundar
(Anes 2011;
114:1102-10)
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;118:1307-1321
Severgnini RCT
Protective
TV = 7 mL/kg PBW
Standard
TV = 9 mL/kg PBW
PEEP = 10 cm H2O
PEEP = 0 cm H2O
Prescribed RMs after
induction, after any circuit
disconnection, and before
emergence
No prescribed RMs
Severgnini et al. Anesthesiology 2013;118:1307-1321
Severgnini Results
Severgnini et al. Anesthesiology 2013;118:1307-1321
Severgnini Results
Pulmonary infection score
includes points for
temperature, white blood cell
count, secretions, P/F ratio, and
CXR
Severgnini et al. Anesthesiology 2013;118:1307-1321
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;369:428-437
The IMPROVE Trial
Lung-Protective
TV = 6-8 mL/kg PBW
Nonprotective
TV = 10-12 mL/kg PBW
PEEP = 6-8 cm H2O
PEEP = 0 cm H2O
Prescribed RMs after
induction and every 30
minutes
No prescribed RMs
Futier et al. NEJM 2013;369:428-437
Las Vegas
• 10,000 patients in 142 centers
• Enrollment closed in 3/2013
Conclusions
The common practice of using
supraphysiologic tidal volumes without
PEEP will support oxygenation and not
cause overt harm in the majority of patients.
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.
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.
rossblan@med.umich.edu