When performing positive-pressure ventilation (PPV), you are pushing air into the lungs rather than relying on the body’s natural negative-pressure breathing mechanism. This reversal of normal physiology has immediate effects on the heart, lungs, and circulation that every rescuer needs to understand. Getting PPV right means choosing the correct equipment settings, positioning the airway properly, watching for signs that ventilation is working, and avoiding pressures that can injure the lungs or compromise blood flow.
How PPV Differs From Normal Breathing
During a normal breath, your diaphragm contracts and creates negative pressure inside the chest. That slight vacuum pulls air into the lungs and also draws blood back toward the heart. Positive-pressure ventilation does the opposite: it forces air in under pressure, raising the pressure inside the chest throughout the breathing cycle. Under normal conditions, the body only generates brief positive chest pressure during coughing or straining.
This pressure reversal has real consequences for the cardiovascular system. During spontaneous breathing, the pressure in the right atrium drops with each inhale, which acts like a suction force pulling blood from the large veins into the heart. With PPV, right atrial pressure increases instead, which means venous return (blood flowing back to the heart) is impaired regardless of where the heart is in its pumping cycle. Less blood returning to the heart translates directly into less blood pumped out.
Research comparing anesthetized patients breathing on their own versus receiving PPV found that cardiac output dropped by 10% with PPV alone, 18% when moderate positive end-expiratory pressure (PEEP) was added, and 36% with higher PEEP levels. The takeaway: higher airway pressures mean greater reductions in cardiac output, and patients who are already low on blood volume are especially vulnerable to this effect.
Airway Positioning Before You Start
PPV will not work if the airway is not open. The standard approach is the “sniffing position,” where the head is slightly extended and the neck is flexed forward, as if the person were leaning in to smell a flower. This alignment opens a straight path from the mouth through the throat and into the windpipe. Both the Difficult Airway Society guidelines and standard anesthesia references endorse it as the optimal position for ventilation and direct laryngoscopy.
For infants and young children, the anatomy is different. Their heads are proportionally larger, so a neutral or slightly extended position (without a pillow) often achieves the same alignment. Over-extending a baby’s neck can actually collapse the soft trachea and block airflow. A small rolled towel under the shoulders can help in newborns.
Recommended Pressures and Rates
The two key pressure settings in PPV are peak inspiratory pressure (PIP), the maximum pressure delivered with each breath, and positive end-expiratory pressure (PEEP), the baseline pressure maintained between breaths to keep the small air sacs in the lungs from collapsing.
For a term newborn, initial settings are typically a PIP of 20 to 25 cm of water pressure and a PEEP of 5 cm of water pressure, delivered at a rate of 40 to 60 breaths per minute. Preterm infants generally need lower pressures to avoid lung injury. Ventilation for newborns should start with room air (21% oxygen) for term infants, or 21 to 30% oxygen for preterm infants born at 35 weeks or earlier, then adjusted based on pulse oximetry readings.
For older children receiving CPR with an advanced airway or rescue breathing with a pulse, the 2020 American Heart Association guidelines recommend a respiratory rate of 20 to 30 breaths per minute. Adults in cardiac arrest generally receive ventilation at a slower rate. In all age groups, avoiding excessive ventilation is emphasized as a core component of high-quality resuscitation, because over-ventilation raises chest pressure unnecessarily, further reducing blood return to the heart.
Signs That Ventilation Is Working
The most immediate indicator of effective PPV is visible chest rise with each delivered breath. If the chest is not rising, the airway may be blocked, the seal between the mask and face may be inadequate, or the pressure may be too low. Beyond chest rise, several other signs confirm that ventilation is achieving its goals:
- Heart rate improvement: In newborns and children, a rising heart rate is one of the earliest and most reliable signs of successful ventilation. A persistently fast heart rate (tachycardia) that begins to slow toward normal suggests the body is getting the oxygen it needs.
- Oxygen saturation: Pulse oximetry should be used for continuous monitoring. A steady climb in oxygen saturation confirms gas exchange is happening.
- Decreased respiratory effort: If the patient has any spontaneous breathing, effective PPV should reduce their work of breathing. You will see less use of accessory muscles in the neck and abdomen, and the respiratory rate should come down.
- Improved color and consciousness: Resolution of cyanosis (bluish skin) and, in conscious patients, improved alertness are later signs that ventilation and oxygenation are adequate.
Clinical assessment should also include monitoring blood pressure and level of consciousness. If the patient is deteriorating despite ventilation, consider repositioning the airway, checking the mask seal, adjusting pressure settings, or evaluating for complications like pneumothorax.
Oxygen Delivery With a Bag-Valve-Mask
A bag-valve-mask (BVM) device connected to supplemental oxygen at a flow rate of at least 10 liters per minute can deliver close to 100% oxygen during active ventilation. Without supplemental oxygen, the BVM delivers only room air at 21%. The reservoir bag attached to the BVM is what makes high-concentration oxygen delivery possible; without it, oxygen concentration drops significantly even with a connected oxygen source.
Notably, the AHA’s 2020 guidelines found that for out-of-hospital cardiac arrest, bag-mask ventilation produces the same resuscitation outcomes as more advanced airway interventions like endotracheal intubation. This means that skillful BVM use, with a good seal, proper positioning, and appropriate rate, is genuinely effective and not just a temporary measure.
Risks of Excessive Pressure
Pushing too much air at too high a pressure causes ventilator-induced lung injury. Animal studies have demonstrated a clear pressure threshold: lungs ventilated at low pressures (around 14 cm of water) showed no injury after an hour, while pressures of 30 cm of water caused fluid accumulation in the tissue between air sacs (interstitial edema), and pressures of 45 cm of water caused both interstitial and alveolar edema, falling oxygen levels, decreased lung compliance, and death in some subjects.
PEEP, when used appropriately, actually helps protect the lungs. It keeps the small air sacs open between breaths, which improves gas exchange and allows you to use lower peak pressures without sacrificing the overall pressure needed to move oxygen. The ideal PEEP level varies by patient and should be set individually, balancing improved oxygenation against the cardiovascular effects of higher chest pressures.
Gastric inflation is another common risk during manual PPV, especially with a face mask. Excess pressure forces air into the stomach rather than the lungs, which can cause vomiting and aspiration. Delivering breaths slowly, using only enough volume to produce visible chest rise, reduces this risk.
Balancing Ventilation and Circulation
The central tension in PPV is that the lungs need pressure to exchange oxygen, but the heart needs that same pressure to be as low as possible to maintain blood flow. Every breath you deliver raises intrathoracic pressure, temporarily reducing blood return to the heart. The net effect on cardiac output is proportional to the mean airway pressure, so keeping pressures and ventilation rates at the minimum effective level protects the circulation.
During CPR, this balance becomes especially critical. Over-ventilating, whether by squeezing the bag too often or too forcefully, raises the average pressure in the chest and directly undermines the effectiveness of chest compressions. The principle is simple: deliver the lowest pressures and volumes needed to produce chest rise and improved oxygenation, and resist the instinct to ventilate more aggressively when a patient is not improving.