Efficacy of prone position in acute respiratory distress syndrome patients: A pathophysiology-based review

Table 1 The Berlin definition of the acute respiratory distress syndrome

Timing	Within 1 wk of a known clinical insult or new or worsening respiratory symptoms
Chest imaging1	Bilateral opacities - not fully explained by effusions, lobar/lung collage, or nodules
Origin of edema	Respiratory failure not fully explained by cardiac failure of fluid overload. Need objective assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk factor present
Oxygenation2
Mild	200 mmHg < PaO2/FiO2 ≤ 300 mmHg with PEEP or
	CPAP ≥ 5 cmH2O3
Moderate	100 mmHg < PaO2/FiO2 ≤ 200 mmHg with PEEP or
	CPAP ≥ 5 cmH2O
Severe	PaO2/FiO2 ≤ 100 mmHg with PEEP or CPAP ≥ 5 cmH2O

¹Chest radiograph or computed tomography scan;

²If attitude is higher than 1000 m, the correction factor should be calculated as follows: [PaO₂/FiO₂× (barometric pressure/760)].

³This may be delivered noninvasively in the mild acute respiratory distress syndrome group. CPAP: Continuous positive airway pressure; FiO₂: Fraction of inspired oxygen; PaO₂: Partial pressure of arterial oxygen; PEEP: Positive-end expiratory pressure.

Table 2 Meta-analyses on prone position in acute respiratory distress syndrome patients

Meta-analysis	No. of studies included	Total number of patients	Main findings
Sud et al[138]	10	1867	Prone ventilation reduces mortality in patients with severe hypoxemia
Gattinoni et al[136]	4	1573	The individual patient meta-analysis of the four major clinical trials available clearly shows that with prone positioning, the absolute mortality of severely hypoxemic ARDS patients may be reduced by approximately 10%
Lee et al[137]	11	2246	Ventilation in the prone position significantly reduced overall mortality in patients with severe acute respiratory distress syndrome. Sufficient duration of prone positioning was statistically significant in associated with a reduction in overall mortality
Beitler et al[134]	7	2119	Prone positioning was associated with a significant decrease in RR of death only among studies with low baseline tidal volume
Tonelli et al[133]	159	20671	Limited supportive evidence that specific interventions can decrease mortality in ARDS, while low tidal volumes and prone positioning in severe ARDS seem effective
	(93 with overall mortality reported)
	(44 trials reported mortality as a primary outcome)
Park et al[139]	8	2141	Prone positioning tends to reduce the mortality rates in ARDS patients, especially when used in conjunction with a lung protective strategy and longer prone position durations. Prone positioning for ARDS patients should be prioritized over other invasive procedures because related life-threatening complications are rare
Bloomfield et al[140]	9	2165	No convincing evidence of benefit nor harm from universal application of prone positioning in adults with hypoxaemia mechanically ventilated in intensive care units Three subgroups (early implementation of prone positioning, prolonged adoption of prone positioning and severe hypoxaemia at study entry) suggested that prone positioning may confer a statistically significant mortality advantage

ARDS: Acute respiratory distress syndrome.

Table 3 Absolute and relative contraindications to prone positioning

Absolute

Unmonitored or significantly increased intracranial pressure

Unstable vertebral fractures

Relative

Difficult airway management

Tracheal surgery or sternotomy during the previous 15 d

New tracheostomy (less than 24 h)

Single anterior chest tube with air leaks

Serious facial trauma or facial surgery during the previous 15 d

Increased intraocular pressure

Hemodynamic instability or recent cardiopulmonary arrest

Cardiac pacemaker inserted in the last 2 d

Ventricular assist device

Intra-aortic balloon pump

Deep venous thrombosis treated for less than 2 d

Massive hemoptysis requiring an immediate surgical or interventional radiology procedure

Continuous dialysis

Severe chest wall lesions ± rib fractures

Recent cardiothoracic surgery/unstable mediastinum or open chest

Multiple trauma with unstabilized fractures

Femur, or pelvic fractures ± external pelvic fixation

Pregnant women

Recent abdominal surgery or stoma formation

Kyphoscoliosis

Advanced osteoarthritis or rheumatoid arthritis

Body weight greater than 135 kg

Table 4 Potential complications of prone positioning

Edema (facial, airway, limbs, thorax)

Pressure sores

Conjunctival hemorrhage

Compression of nerves and retinal vessels

Endotracheal tube dislocation (main stem intubation or non-scheduled extubation), obstruction or kinking

Airway suctioning difficulty

Transient hypotension or oxygen desaturation

Worsening gas exchange

Pneumothorax

Thoracic drain kinking or obstruction

Cardiac events

Inadvertent dislodging of Swan-Ganz catheter

Vascular catheter kinking or removal

Vascular catheter malfunction during continuous veno-venous hemofiltration

Deep venous thrombosis

Urinary bladder catheter or nasogastric feeding tube displacement

Enteral nutrition intolerance; vomiting; feeding complications

Need for increased sedation or muscle paralysis

Difficulty in instituting cardiopulmonary resuscitation