Prone Ventilation (Prone Positioning) 


The landmark:PROSEVA Trial

 Demonstrated significant mortality reduction in severe ARDS when:

  • Used early
  • Used for prolonged periods
  • Combined with lung-protective ventilation

Since then, prone positioning became standard care for severe ARDS.


Physiological Basis

Why Supine Position Is Harmful in ARDS?

In ARDS:

  • Lungs become heavy due to:
    • Edema
    • Inflammation
    • Atelectasis

In supine position: Dorsal (posterior) lung regions

Become compressed by:

  • Heart—Mediastinum—Edematous lungs—Abdominal pressure

Result:

  • Collapse of dependent alveoli
  • Atelectasis
  • Shunt formation

Ventral (anterior) regions

Remain relatively aerated and may become overdistended.

Thus:

Ventilation → Anterior lung

Perfusion → Posterior lung

Result:

Severe V/Q mismatch


Physiological Effects of Prone Positioning

1. Improved Ventilation-Perfusion Matching

Most pulmonary blood flow remains:

  • Dorsal—Posterior Even after proning.

However proning: Reopens dorsal alveoli AND Improves ventilation to well-perfused regions


2. Recruitment of Collapsed Alveoli

Proning:

  • Relieves compression
  • Recruits posterior lung units

Result:

  • Increased functional lung volume
  • Improved gas exchange


3. More Homogeneous Transpulmonary Pressure Distribution

Supine:Large ventral-dorsal pleural pressure gradient.

Prone:Pressure gradient becomes more uniform.

Result:

  • More even inflation
  • Less regional stress


4. Reduction of Ventilator-Induced Lung Injury (VILI)

  • Volutrauma-Less overdistension
  • Atelectrauma-Less cyclic opening and closing.
  • Biotrauma-Reduced inflammatory mediator release.


5. Improved Right Ventricular Function

ARDS causes:

  • Hypoxic pulmonary vasoconstriction
  • Pulmonary hypertension

Proning:

  • Improves oxygenation
  • Reduces pulmonary vascular resistance

Result:

  • Reduced RV afterload
  • Improved RV function

Particularly useful in:

  • Cor pulmonale
  • Severe ARDS with RV dysfunction


6. Improved Secretion Drainage

Facilitates:

  • Airway drainage
  • Mucus clearance

Especially useful in:

  • Pneumonia
  • Aspiration


Indications

Strong Evidence-Based Indication-Moderate to Severe ARDS

Berlin Definition:

Severity

PaO₂/FiO₂

Mild

200–300

Moderate

100–200

Severe

<100

Prone positioning recommended when:

PaO₂/FiO₂ <150 mmHg

Despite:

  • Lung protective ventilation
  • Adequate PEEP
  • FiO₂ optimization


Common Practical Trigger

PaO₂/FiO₂ <150

with:

  • FiO₂ ≥0.6
  • PEEP ≥5–10 cmH₂O


Guideline Recommendations

European Society of Intensive Care Medicine

Strong recommendation:

  • Moderate-severe ARDS
  • ≥16 hours/day

Society of Critical Care Medicine

Strong recommendation for severe ARDS.

American Thoracic Society

Recommends early prone positioning for severe ARDS.


Contraindications

Absolute Contraindications

Relative Contraindications

Unstable spinal injury (especially cervical spine instability)

Raised intracranial pressure (risk-benefit assessment required)

Open chest (e.g., recent unstable sternotomy)

Recent neurosurgery

Open abdomen without protective closure

Massive hemoptysis

Massive facial trauma when airway cannot be safely secured

Unstable pelvic fracture

—

Late pregnancy

—

Recent tracheal surgery

—

Hemodynamic instability*

*Hemodynamic instability is not an absolute contraindication. Many patients can still be safely proned while receiving vasopressor support, provided close monitoring is available.


When Should Proning Be Started?

Current evidence:

Early initiation Within:24–48 hours of ARDS diagnosis Produces greatest mortality benefit.

Avoid waiting until:

  • FiO₂ 100%
  • Severe refractory hypoxemia


Preparation Before Proning

Nutrition

Pause feeds briefly before turning.

Aspirate stomach if necessary.


Sedation

Deep sedation usually required.

Examples:

  • Propofol
  • Midazolam


Neuromuscular Blockade

Often used initially.

Examples:

  • Cisatracurium
  • Rocuronium

Particularly during:

  • Severe ARDS
  • First proning sessions


Proning Procedure

Step 1

Preoxygenate.


Step 2

Secure:

  • ETT
  • Lines
  • Tubes


Step 3

Protect pressure points.

Padding under:Forehead—Chest—Pelvis—Knees


Step 4

Turn patient:Supine → Lateral → Prone

Using coordinated maneuver.


Step 5

Confirm:ETT depth—Breath sounds—Hemodynamics


Step 6

  • Reposition arms
  • Swimmer Position-One arm up.One arm down.
  • Alternate every:2–4 hours.


Ventilator Management During Proning

  • Continue:Lung Protective Ventilation
  • Plateau Pressure—<30 cmH₂O
  • Driving Pressure—<15 cmH₂O preferred
  • Driving Pressure=Pplat −PEEP


Permissive Hypercapnia

Accept if pH acceptable.


Duration of Proning

At least 16 hours/session

Common:16–20 hours/day


Criteria for Discontinuation of Daily Proning

When:PaO₂/FiO₂ >150–200 AND PEEP ≤10 AND FiO₂ ≤0.6

Maintained after returning supine.


Monitoring During Proning

Skin

Inspect:Face—Nose—Chin—Chest—Knees

Eyes

Prevent:

  • Corneal abrasion
  • Increased ocular pressure

Lubricate eyes.Tape eyelids closed.


Complications

Complication Category

Details

Airway Complications

Accidental extubation (most feared complication), ETT obstruction (kinking, secretions), endobronchial intubation

Pressure Injuries

Most common overall complication; commonly affects forehead, nose, chin, cheeks, chest, iliac crests, knees, and toes

Facial Edema

Frequently occurs after prolonged proning; usually resolves after return to supine position

Ocular Complications

Corneal abrasion, increased intraocular pressure, ischemic optic neuropathy (rare)

Nerve Injuries

Brachial plexus injury, ulnar neuropathy, peroneal nerve injury; risk reduced by regular repositioning and alternating arm positions

Hemodynamic Complications

Reduced venous return, increased intrathoracic pressure, transient hypotension, increased vasopressor requirement

Gastrointestinal Complications

Feed intolerance, vomiting, aspiration (risk lower than previously believed); enteral feeding can often be continued during proning with appropriate precautions


Proning and Enteral Nutrition

Current ICU practice:

  • Gastric feeding can continue
  • Head elevated 10–25°
  • Monitor residuals

Routine cessation not required.


Proning and ECMO

Proning remains beneficial even during:

VV-ECMO

Potential benefits:

  • Better recruitment
  • Improved oxygenation
  • Reduced VILI

Increasingly used in expert centers.


Awake Proning

Prone positioning without intubation.

Commonly used in:

  • Hypoxemic respiratory failure
  • Viral pneumonia

Including:COVID-19

Benefits:

  • Improved oxygenation
  • May reduce intubation rate

Mortality benefit less certain.