2.4 Ventilation and Bag-Mask Basics

2.4 Ventilation and Bag-Mask Basics

Ventilation supplies oxygen and removes carbon dioxide, but during CPR it is secondary to compressions. The governing principle in the AHA Guidelines is just enough: deliver each breath over 1 second with only enough volume to make the chest visibly rise. Over-ventilating is actively harmful — it raises intrathoracic pressure, reduces venous return and cardiac output, and inflates the stomach (gastric inflation), which raises the risk of regurgitation and aspiration.

Ventilation rates: the numbers you must know

The most-tested distinction: without an advanced airway you pause compressions to give 2 breaths after every 30 compressions; once an advanced airway (endotracheal tube, supraglottic airway) is in place you do NOT pause — compressions run continuously and the breaths are timed independently at 1 every 6 seconds.

Airway positioning

Before ventilating, open the airway. Use the head tilt-chin lift for a patient without suspected trauma. If a cervical spine injury is suspected and you are trained, use the jaw thrust without head extension to protect the spine; if the jaw thrust fails to open the airway, a head tilt-chin lift takes priority because a patent airway is essential. Opening the airway lifts the tongue off the posterior pharynx, which is the most common cause of obstruction in an unresponsive patient.

Bag-mask (bag-valve-mask) technique

The bag-mask (also called bag-valve-mask, BVM) is the workhorse of BLS ventilation. The key to success is the seal. With one rescuer, use the E-C clamp: the thumb and index finger form a C pressing the mask onto the face, while the remaining three fingers form an E lifting the jaw up into the mask. Two-rescuer bag-mask is preferred whenever available — one rescuer uses both hands (a two-handed E-C clamp) to hold a tight seal and maintain head position, while the second squeezes the bag. This consistently delivers better tidal volume than a single rescuer juggling seal and squeeze.

Attach supplemental oxygen (10-15 L/min) and, when available, a reservoir so the bag delivers high-concentration oxygen. Squeeze the bag smoothly over 1 second and watch for chest rise; do not crank the bag fully or rapidly.

Troubleshooting no chest rise

When the chest does not rise, do not assume the lungs cannot be ventilated. The two most common, correctable causes are an inadequate mask seal and improper head position. Reposition the head (re-do the head tilt-chin lift or jaw thrust), reseat the mask, consider a two-rescuer seal, and check for an obstruction. Only after these steps is a true airway obstruction (foreign body) considered.

Avoiding hyperventilation

During cardiac arrest the lungs need far less ventilation than a person at rest because cardiac output (and therefore CO2 production) is very low. Squeezing too hard, too fast, or too often raises intrathoracic pressure between compressions and chokes off the venous return that recoil is trying to create. A cyanotic appearance tempts rescuers to over-bag — resist it. The fix for cyanosis is better compressions and correct (not excessive) ventilation, not faster bagging.

Common traps

• Hyperventilating because the patient looks blue.
• Pausing compressions far too long to place an airway.
• Squeezing the bag hard/fast instead of watching for gentle chest rise.
• Continuing 30:2 pauses after an advanced airway is in place (should switch to continuous compressions + 1 breath q6sec).

Airway adjuncts: OPA and NPA

Two simple adjuncts help maintain a patent airway during bag-mask ventilation. An oropharyngeal airway (OPA) is a rigid curved device inserted into the mouth to hold the tongue off the posterior pharynx; it is used only in unconscious patients with no gag reflex, because it can trigger gagging, vomiting, and aspiration in a responsive patient. Size it from the corner of the mouth to the angle of the jaw. A nasopharyngeal airway (NPA) is a soft tube inserted through a nostril; it is better tolerated in patients with an intact gag reflex but is avoided when severe facial or basilar skull trauma is suspected.

Neither device is an advanced airway and neither protects against aspiration the way an endotracheal tube does, but both improve mask ventilation by relieving tongue obstruction.

Compression-first ventilation and oxygenation targets

During the first minutes of a witnessed shockable arrest, oxygen stores in the blood are usually adequate, which is part of why compressions take priority over breaths. As the resuscitation continues, ventilation with supplemental oxygen becomes more important to keep the blood oxygenated for the perfusion that compressions provide. Once return of spontaneous circulation (ROSC) is achieved, the goal shifts: avoid both hypoxia and hyperoxia by titrating oxygen to a target SpO2 of 92-98 percent, and avoid hyperventilation, keeping ventilation in a normal range rather than over-bagging.

The recurring theme across this section is restraint: enough ventilation to oxygenate and clear CO2, never so much that it raises intrathoracic pressure and starves the heart of venous return.