Positive end expiratory pressure

Positive end expiratory pressure (PEEP) is the amount of pressure that remains at the end of the expiratory phase which can be set in mechanically ventilated patients.

Benefits of PEEP

• Increased FRC
• Prevents closing of alveoli, thereby reducing airway opening pressure
• Increase Palv, making West's zone move more caudally, thereby reducing physiologic shunt from Zone 3

Consequences of PEEP

• Barotrauma/volutrauma: Increased peak airway pressure at high PEEP
• Decreased venous return from IVC due to increased thoracic pressure
• Decreased pulmonary blood flow
  • In patients with pulmonary hypertension, can worsen R heart strain
• Elevation in ICP from less venous return, leading to decrease in cerebral perfusion pressure
  • CPP = MAP - ICP

Indications for PEEP

Most patients benefit from a small amount of PEEP to improve lung compliance. Patients who are obese may benefit from higher PEEP due to relative restrictive lung disease. Patients in Trendelenburg position and/or abdominal insufflation (e.g. laparoscopy) also benefit from PEEP due to elevated diaphragmatic pressures.

Optimal PEEP

There is little concensus about optimal PEEP. Typical ranges of PEEP are 0 to 15 cm H2O, more commonly 5 to 10 cm H2O.

Surgeries where PEEP should be used cautiously

Increased PEEP reduces venous return from IVC, which can increase venous bleeding in certain surgical cases:

• Liver cases
  • Higher portal pressures and resulting in increased bleeding
• Open prostatectomy
  • Increased blood pooling in dorsal venous complex, resulting in increased bleeding
• Spine cases
  • Potential high risk complications with venous bleeding into spine

Increased PEEP resulting in elevation in ICP results in poor CPP, which should be considered with:

• Brain surgeries
  • Particularly when MAP is low