Overventilation Leading to Hypocarbia

In the time after birth, some infants may need help breathing through the use of machines. These machines must be set properly by a trained professional. If they are not, they will remove too much CO2 from the baby’s blood; this is called overventilation. Overventilation puts the baby at risk for brain damage, as CO2 levels that are too low prevent proper blood flow within the brain. Overventilation can cause tissue loss in the brain’s periventricular area, or periventricular leukomalacia (PVL). Overventilation can also cause lung tissue scarring or lung collapse.

Many newborns (especially preterm infants) require assisted ventilation at birth for conditions like apnea or respiratory failure (1). Despite its life-saving benefits, however, mechanical ventilation can cause serious damage if not managed properly. Brain damage, lung damage, and other complications may occur if the baby is over-oxygenated or over-ventilated. Throughout this page, our Michigan birth injury attorneys will discuss everything you need to know about birth injury as it relates to overventilation and hypocarbia.

Overventilation occurs when a baby is given breaths that are so large and/or fast, it causes the baby to get rid of too much carbon dioxide (i.e. they develop a condition called hypocarbia). When a baby has abnormally low levels of carbon dioxide, it may cause permanent damage to the brain due to a lack of perfusion (cerebral blood flow) to critical areas of the brain. Hypocarbia and subsequent lack of perfusion have been associated with periventricular leukomalacia (which involves the death of small areas of brain tissue around fluid-filled areas called ventricles; the damage forms “holes” in the brain), cerebral palsy, and hearing impairments (2).

Likewise, too much pressure from mechanical ventilation can cause lung problems such as a pneumothorax or worsen bronchopulmonary dysplasia (abnormal development of lung tissue in premature babies characterized by inflammation and scarring) (3, 4).

When the baby is getting help with some or all of their breathing, via one of the methods discussed below, overventilation can occur. Common methods of assisted ventilation (breathing) include:

• Mechanical ventilation. When a baby needs help with breathing, they might be placed on a breathing machine, called a ventilator, which will either assist with breathing or completely breathe for the baby. Even though these machines display the volume of air being delivered to the baby’s lungs, as well as the pressure in the baby’s lungs, sometimes the medical team fails to regulate the volume/pressure and lung damage occurs. The medical staff may set the volume of oxygen delivered to the baby high in order to decrease the carbon dioxide level in the baby’s blood. Oxygen volumes that are too high on the ventilator can cause lung damage that is similar to that from bagging (discussed below). In addition, large oxygen volumes can cause a baby’s carbon dioxide level in the blood to fall below normal. When a baby has a continuously low carbon dioxide level (for a few hours or more), it can cause decreased blood flow (decreased perfusion) to the brain, thereby leading to brain damage and other injuries (5, 6).
• Bagging. This is when either a flexible tube is inserted into the baby’s trachea (windpipe) or the baby is given an oxygen mask attached to a bag. The bag is squeezed to force air or oxygen into the baby’s lungs. This is also known as positive pressure ventilation (PPV), or “bagging.” Bagging is the method of breathing for a baby during an emergency situation, such as during CPR or while waiting to place the baby on a breathing machine (ventilator). Since bagging is done by hand, there really is no way to know how much air is being pushed into the baby’s delicate lungs. Lungs can be seriously injured when too much volume/pressure is forced into them (6, 7).

A pneumothorax occurs when the volumes of air administered during ventilation are too large and create too much pressure in the baby’s lungs. The alveoli (the tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place) become over-distended and rupture, causing the lung to blow out. This results in holes in the lungs which allow air to leak through into the surrounding spaces, forming a pneumothorax. This build-up of air prevents the lung from fully expanding. The longer this is left untreated, the more air there is that leaks into the space around the lung, which further restricts the ability of the lung to expand. This hinders the baby’s ability to breathe properly, which may cause oxygen levels to drop and carbon dioxide levels to increase in the long run. This decrease in the baby’s blood oxygen level can cause brain damage (4).

A pneumothorax also can compress the veins that bring blood to the heart. As a result, less blood fills the chambers of the heart, the output of the heart decreases, and the baby’s blood pressure decreases. This also can lead to serious problems and can cause a lack of blood flow to the brain, thereby increasing the chances of brain damage (4).

If only a small portion of the baby’s lung is collapsed, the physician may simply monitor the condition of the pneumothorax with a series of chest X-rays until the air is completely absorbed and the lung has re-expanded. A larger area of collapse may require that a needle or chest tube be inserted to remove the air. Surgery is the next option if a chest tube is unsuccessful (4).

Complications from a pneumothorax can cause serious damage and death, especially if the pneumothorax goes unnoticed. Signs and symptoms of a pneumothorax include (4):

• Bluish color of the skin
• Rapid heart rate
• Diminished breath sounds on the affected side of the lung
• Decreased blood pressure
• Windpipe shifting away from the affected lung
• Sudden deterioration in the condition of the baby

Bronchopulmonary dysplasia (BPD) is a common defect of the lungs among premature babies. It is characterized by scarring of the lungs, primarily from the immaturity of the lung tissue. BPD can be caused by the lungs taking in too much oxygen, which is common if supplemental oxygen administration is mismanaged. Many infants with BPD will improve gradually with proper care, but others go on to suffer from pulmonary hypertension, prolonged reliance on ventilation, and other complications (5).

When a baby is on a ventilator and is over-ventilated because the machine is giving breaths that are too large (and perhaps too fast), the carbon dioxide level in the blood may decrease below normal. When there is an abnormally low carbon dioxide level in the blood for too long (5 or 6 hours or more), blood flow to the brain is decreased (decreased perfusion) and permanent brain damage can occur as a result (2).

A baby that is receiving mechanical ventilation will likely have an umbilical artery catheter (UAC), which makes it easy to draw blood and monitor the oxygen and carbon dioxide levels in the blood. A sign of overventilation is a carbon dioxide level that is below normal. A low carbon dioxide level that is due to overventilation can be corrected by decreasing the volume of air given to the baby, as well as by decreasing the number of breaths the baby is given by the ventilator (2).

This is the death of the white matter of the brain due to softening of brain tissue. It is a risk in

This is the death of the white matter of the brain due to softening of brain tissue. It is a risk in premature babies and is caused by a lack of oxygen or blood flow to the periventricular area of the brain, which results in the death or loss of brain tissue (8).

The periventricular area is the area around the spaces in the brain called ventricles. These are critical areas, as they contain nerve fibers that carry messages from the brain to the muscles. Babies with PVL are at risk for motor disorders, delayed mental development, coordination problems, and vision and hearing impairments. PVL may be accompanied by a hemorrhage or bleeding in the periventricular-intraventricular area (the area around and inside the ventricles) and can lead to cerebral palsy. The disorder is diagnosed by an ultrasound of the head (8).

All babies that need help breathing are at risk for overventilation injuries. Babies with the following problems are more likely to need breathing assistance at birth (9):

• Asphyxia: This is when a baby’s brain and other organs do not get enough oxygen before, during, or just after birth.
• Meconium aspiration syndrome: This is when a baby has problems caused by inhaling meconium, which comes from the baby’s first stool.
• Respiratory distress syndrome
• Premature birth

Babies who have lung damage prior to being over-ventilated, or whose lungs are not fully developed, are the most susceptible to overventilation lung injury.

Signs of brain damage include the following (10):

• Bluish skin
• Muscle tone is poor or reflexes are weak
• Low heart rate
• Evidence of neurological problems, including coma and seizure
• Multi-system organ dysfunction

Tests used to diagnose brain damage:

• CT (computed tomography) scan
• MRI (magnetic resonance imaging) scan
• EKG (electrocardiogram)
• Blood glucose levels
• EEG (electroencephalogram)
• Ultrasound
• Evoked potential test
• Echocardiogram