How Do I Use PEEP?

Dean R. Hess PhD RRT FAARC

Assistant Director of Respiratory Care

Massachusetts General Hospital

Associate Professor of Anesthesia

Harvard Medical School

Editor in Chief

Respiratory Care

Webb and Tierney, Am Rev Respir Dis 1974;110:556

14/0 45/10 45/0

Higher PEEPLower Tidal Volume

Normal Edema Consolidation Atelectasis

Over-Distention Opening/Closing

ALI/ARDS is Inhomogeneous

PEEP

ALVEOLI (Assessment of Low tidal Volume and

elevated End-expiratory volume to Obviate Lung Injury)

� 2 PEEP levels with VT 6 mL/kg PBW�Oxygenation and respiratory system compliance better with higher PEEP

� Stopped at 549 patients for futility: no mortality difference

N Engl J Med 2004;351:327

� Target tidal volume 6 mL/kg PBW

� Control (n=508): Pplat ≤ 30 cm H2O (VCV), lower PEEP

� Experimental (n=475): Pplat ≤ 40 cm H2O (PCV), recruitment maneuvers (40 s at 40 cm H2O), initial PEEP 20 cm H2O; higher PEEP

� No mortality difference, but improved secondary end points related to hypoxemia and use of rescue therapies

Meade, JAMA 2008;299:637

� Target tidal volume 6 mL/kg PBW� Control (n=382): low PEEP (5 - 9 cm H2O) minimal distension strategy

� Experimental (n=385): higher PEEP set to reach Pplat of 28 - 30 cm H2O (increased recruitment strategy); PEEP 16 ± 3 cm H2O on day 1

� No mortality difference, but improved lung function, reduced duration of mechanical ventilation and duration of organ failure

Mercat, JAMA 2008;299:646

Benefit of Higher PEEP Offset by Higher Pplat?

Lower PEEP

Higher PEEP

6 mL/kg

PPlat or PEEP (cm

H20) 6 mL/kg

Non-recruitable

6 mL/kg

Recruitable(↑Crs, ↓Vd)

Injury >

Benefit

Benefit >

Injury

N Engl J Med 2006;354:1775

N = 2299

ARR: 4%NNT: 25

Briel, JAM

A 2

010

;303:8

65

How to Set PEEP

� PEEP/FIO2 tables to per oxygenation

� Best Compliance (lowest Pplat – PEEP)

� Pressure-volume curve

� Lowest dead space

� Transpulmonary pressure (esophageal balloon)

� Stress index

� Incremental vs. decremental?

Optimal PEEP by Tidal Compliance

� 15 normovolemic patients requiring mechanical ventilation for ARF

� PEEP resulting in maximum oxygen transport and the lowest dead-space fraction resulted in highest compliance

� Optimal PEEP varied from 0 to 15 cm H2O

� Mixed venous PO2 increased from 0 PEEP to the PEEP resulting in maximum oxygen transport, but then decreased at higher PEEP

� Conclusion: compliance may be used to indicate the PEEP likely to result in optimum cardiopulmonary function

↑ PEEP

Suter, N Engl J Med 1975;292:284

Titrate PEEP to lowest Pplat – PEEP

0 10 20 30 40

0

0.4

0

.8

1.2

1

.6

normal

ARDS

airway pressure (cm H2O)

volu

me

abo

ve F

RC

(lit

ers)

lower inflectionpoint

upper inflectionpoint

0 10 20 30 40

0

0.4

0

.8

1.2

1

.6

normal

ARDS

airway pressure (cm H2O)

volu

me

abo

ve F

RC

(lit

ers)

lower inflectionpoint

upper inflectionpoint

Pressure-Volume Curve

Issues With PV Curves

�Requires sedation/paralysis

�Difficult to identify “inflection points” (Harris et al, AJRCCM 2000; 161:432)

�May require esophageal pressure to separate lung from chest wall effects (Mergoni, AJRCCM 1997; Ranieri, AJRCCM 1997; Owens, Crit Care Med 2008)

�Deflation limb may be more useful than inflation limb (Holzapfel et al, Crit Care Med 1983;11:561; Hickling, AJRCCM 2001;163:69)

� Pressure-volume curves of individual lung units not known (Hickling, AJRCCM 1998;158:194)

Role of PV curve for setting PEEP currently unknown

Stress Index

Grasso, AJRCCM 2007;176:761

tidal recruitment over-distention

PEEP= 18 cm H2OSI = 0.97Pplat = 28 cm H2OCrs = 34 mL/ cm H2O

PEEP = 8 cm H2OSI = 0.75Pplat = 20 cm H2OCrs = 28 mL/cm H2O

Pulmonary vs. Extrapulmonary ARDS

Gattinoni, Am J Respir Crit Care Med 1998;158:3

(consolidation) (atelectasis)

� Ccw

N Engl J Med 2008;359:2095

positive

transpulmonary

pressure

�PaO2??? mortality

Setting PEEP for ALI/ARDS

� 0 cm H2O: likely harmful

� 8 – 16 cm H2O: appropriate in most patients

� Higher PEEP for ARDS; lower PEEP for ALI

� >20 cm H2O: seldom necessary

� High PEEP should be reserved for cases where recruitment can be demonstrated

� PEEP should be selected in the context of prevention of ventilator-induced lung injury

� The benefit of “precise” PEEP is unproven

Positive End-Expiratory Pressure

� Maintain alveolar recruitment

� Prevent ventilator-associated pneumonia

� Counterbalance auto-PEEP

� Reduce preload and afterload

� Splint airway with tracheomalacia

� Improve speech with tracheostomy cuff deflated

Although we can debate how it is precisely set …. PEEP is good.