What Is Continuous Positive Airway Pressure (CPAP)?

Learn About This Form of Mechanical Ventilation

A baby wearing a CPAP
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Continuous positive airway pressure, commonly called CPAP, is a type of respiratory support, or mechanical ventilation, used in adult and pediatric patients. In premature babies, CPAP is delivered through a set of nasal prongs or through a small mask that fits snugly over a baby’s nose.

Like nasal cannula, CPAP is used to deliver constant air pressure into a baby’s nose, which helps the air sacs in the lungs stay open and helps prevent apnea.

CPAP can deliver more pressure than nasal cannula, so is often used in babies who are breathing well enough on their own that they do not need mechanical ventilation, but who need more support than the cannula offers. CPAP can also be used to deliver higher concentrations of oxygen to premature babies who have trouble maintaining good oxygen levels in their blood.

How the CPAP Hooks up to the Nose

With infants, CPAP is applied using binasal cannula (nasal prongs), a single nasopharyngeal cannula, or a soft nasal mask. Of these methods, short binasal prongs are preferred by many clinicians. Most recently, researchers have been experimenting with using a helmet to administer CPAP.

CPAP Resistance Measures

CPAP can consist of the following resistance measures:

  • Underwater seal
  • Flow opposition with fluid flow reversal during expiration
  • Electronic feedback control

It's debatable which form of resistance makes breathing easier for an infant.

Variable Flow Systems and Continuous Flow Systems

Commercial CPAPs can be divided into two types: variable flow systems and continuous flow systems.

Variable Flow Systems

Variable flow systems set a CPAP level using rapid adjustments in flow rate. The pressure generated by variable flow systems is measured using a manometer hooked up to an alarm.

Continuous Flow Systems

Continuous flow systems adjust the CPAP level either by using a valve in the expiratory circuit to modulate resistance or by placing the expiratory tubing under water. Both these systems require high rates of constant flow to match the infant's peak inspiratory flow. 

Of note, simple high-flow systems have dubious efficacy and pressure variations using these simple systems is poorly controlled.

What Type of CPAP Is Best?

We have yet to exactly elucidate a "best" route of administration of CPAP. In other words, there's no weighty evidence favoring the use of a specific nasal interface or flow system. However, bubble systems (a type of continuous flow system) may be better than Infant Flow Systems (a type of variable flow system) when treating infants with respiratory distress syndrome (RDS). Specifically, some research suggests that babies with RDS placed on bubble systems needed less time on CPAP and were more likely to be extubated successfully. (Extubation is medical jargon meaning removal of a tube, in this case, removal of the CPAP tube and interface.) Other studies have also suggested that bubble systems result in better oxygenation.

When Is CPAP Used in Infants?

CPAP in infants is mainly used to treat respiratory distress syndrome (RDS). Respiratory distress syndrome results when a baby is born premature and her lungs have yet to fully develop. The lungs of these infants are deficient in surfactant, a slippery substance that reduces surface tension in the lungs and enables respiration. 

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