Dyspnea in prone position

Specialty: Respiratory.

• prone intolerance
• dyspnea face down

Why it occurs

• Bilateral diaphragmatic paralysis (in the prone position, gravity moves the abdominal contents towards the thoracic cavity, severely limiting the residual lung volume as there is no active diaphragmatic contraction to oppose it)
• Severe morbid obesity (compression of the abdomen against the mattress surface mechanically restricts the movement of the diaphragm and lower rib cage, increasing ventilatory work)
• Severe deformity of the spine such as marked kyphoscoliosis or severe pectus excavatum
• Congestive heart failure with poor left ventricular functional reserve (due to flow redistribution and increased venous return that overloads the heart)
• Massive diaphragmatic hernia with passage of abdominal viscera into the thorax (visceral displacement that worsens when prone due to pressure gradient).

Initial workup

Respiratory function tests (spirometry with measurement of forced vital capacity in sitting and supine positions, observing a drop of more than 25% in case of diaphragmatic paralysis); Dynamic diaphragmatic fluoroscopy (Sniff test); Diaphragmatic ultrasound to measure the percentage of inspiratory thickening; Polysomnography if associated with sleep disorders while lying down.

Standard management

• Avoid the prone position unless specifically indicated under mechanical ventilation with positive pressure — as in severe ARDS
• There are no specific drugs for diaphragmatic paralysis; Non-invasive supportive ventilation (BiPAP) is prescribed at night or day.
• Salbutamol (inhaled, to mitigate reactive bronchospasm if present).