What is the effect of PEEP (Positive End-Expiratory Pressure) on intracranial pressure?

Effects of PEEP on Intracranial Pressure: Evidence from 1990-2025

Elevated PEEP levels increase intracranial pressure (ICP), particularly in patients with severe lung injury or during the vasospasm period (around day 7) following subarachnoid hemorrhage. 1, 2

Physiological Mechanisms

The relationship between PEEP and ICP is mediated through several mechanisms:

• Venous return impairment: High PEEP decreases cerebral venous return and increases intracranial venous pressure, potentially raising ICP 2
• Cerebral blood flow changes: PEEP can indirectly affect cerebral perfusion by decreasing mean arterial pressure (MAP), especially in patients with disturbed cerebrovascular autoregulation 3
• Intracranial compliance: PEEP reduces intracranial compliance, making the brain more susceptible to ICP increases from expanding lesions 4

Key Research Findings

Effects on ICP in Different Patient Populations

• Subarachnoid hemorrhage (SAH) patients:

  • A prospective observational study found that patients with PEEP of 20 cmH₂O had significantly higher ICP on post-bleed day 7 (19.5 vs 11 mmHg) compared to those with PEEP of 5 cmH₂O 1
  • Day 7 is critical as it corresponds with maximal vasospasm, which can cause cerebral ischemia and edema 1

• Patients with severe neurologic injuries:

  • In patients with severe lung injury (PaO₂/FiO₂ <100), every 1 cmH₂O increase in PEEP was associated with a 0.31 mmHg increase in ICP and a 0.85 mmHg decrease in cerebral perfusion pressure (CPP) 1, 2
  • Patients with normal lung compliance showed no significant ICP changes with PEEP increases 1

• Brain-injured patients:

  • Early studies (1978-1981) demonstrated that ICP responses to PEEP depend on intracranial compliance 5, 6
  • Patients with normal volume-pressure response (VPR <2 torr) showed no significant ICP changes with PEEP therapy 5
  • Patients with abnormal VPR and normal lung compliance experienced significant ICP increases or CPP decreases with PEEP 5

Recruitment Maneuvers

• Continuous positive airway pressure recruitment maneuver (CRM):

  • Associated with higher ICP (20.50 ± 4.75 vs 13.13 ± 3.56 mmHg) and lower CPP compared to baseline 1
  • No significant improvement in PaO₂/FiO₂ ratio 1

• Pressure control recruitment maneuver (PCRM):

  • No significant effect on ICP but increased CPP 1
  • Clinically significant improvement in PaO₂/FiO₂ ratio (108.5 to 203.6) 1

Clinical Management Algorithm

1. Assess baseline risk factors:

   • Intracranial compliance status (if available)
   • Lung compliance
   • Timing post-hemorrhage (especially for SAH patients)
   • Severity of lung injury (PaO₂/FiO₂ ratio)

2. For patients requiring PEEP:

   • Low risk patients (normal intracranial compliance, early post-bleed period):

     • PEEP up to 15 cmH₂O may be safely applied 1, 7
     • Monitor for hemodynamic changes that could affect cerebral perfusion

   • High risk patients (abnormal intracranial compliance, day 7 post-SAH, severe lung injury):

     • Consider ICP monitoring before applying PEEP >5 cmH₂O 1, 2, 6
     • Use pressure control recruitment maneuver rather than continuous positive airway pressure recruitment 1
     • Maintain MAP to preserve cerebral perfusion pressure 3

3. Monitoring during PEEP therapy:

   • Continuous ICP monitoring in high-risk patients
   • Maintain CPP >60-70 mmHg by supporting MAP as needed 2
   • Consider CSF drainage capability if available 1

Pitfalls and Caveats

• Rapid PEEP withdrawal: Can cause significant ICP elevations in patients with abnormal intracranial compliance 5
• Overreliance on PEEP: Higher mortality has been associated with high PEEP ventilation compared to low PEEP ventilation in some studies 1
• Ignoring timing: The effect of PEEP on ICP may be more pronounced during the vasospasm period (around day 7 for SAH) 1
• Neglecting MAP: PEEP-induced decreases in MAP should be corrected to maintain cerebral perfusion, especially in patients with disturbed cerebrovascular autoregulation 3

The evidence suggests that PEEP should be carefully titrated in neurologically injured patients, with close monitoring of both pulmonary and cerebral parameters to balance adequate oxygenation with optimal cerebral perfusion.