What is assisted ventilation of the newborn?
Assisted ventilation of the newborn is a procedure to assist and stabilize a newborn’s breathing until the baby’s respiratory system starts working normally. A mechanical ventilator provides oxygen to the lungs at the required pressure and frequency.
Why would a newborn need a ventilator?
The fetus gets its oxygen supply from the mother’s blood. The fetal lungs are nonfunctional, and the blood circulation mostly bypasses the lungs through shunts in the cardiac system, which usually close within a short period after birth. The lungs start functioning spontaneously at birth in normal babies and respiration usually stabilizes within a day or two.
Some babies, typically premature or ill babies, may not start breathing spontaneously, or have trouble breathing. Respiratory distress or failure may be the result of underdeveloped lungs or a congenital condition which compromises lung function.
The mechanical ventilator provides oxygen to the baby and stimulates the respiratory system until the baby can breathe adequately on their own. Assisted ventilation has greatly improved the survival rate of preterm babies.
Respiratory distress or failure may occur in newborns for several reasons which include the following:
- Birth depression: The period immediately after birth when the baby transitions from non-breathing intrauterine life to breathing with their own lungs.
- Neonatal encephalopathy: Depressed brain function because of lack of oxygen during birth.
- Neonatal apnea: Pause in breathing for 20 seconds at a time or more.
- Shock of birth: Shock due to acute blood loss or defective heart functioning.
- Pulmonary disease: Pulmonary diseases such as respiratory distress syndrome occur due to underdevelopment of the lungs in preterm babies.
How does assisted ventilation help respiration?
Respiration is a combination of precise functioning of respiratory muscles and molecular exchange of oxygen for carbon dioxide in the lungs, with the brain regulating the entire activity. Impairment in any part of this respiratory system can cause respiratory distress or failure in infants.
Assisted ventilation delivers oxygen at the required rate and frequency to the lungs, which gradually stimulates the lung, brain and the respiratory muscles to start functioning normally.
What are the factors that influence assisted ventilation?
Following are the important aspects of respiration which influence the choice of the right kind of assisted ventilation, depending on the respiratory distress cause.
Lungs are made of millions of tiny air sacs known as alveoli. With each inhalation, the alveoli fill with air, the oxygen from which travels into the blood. An equivalent volume of carbon dioxide is released by the blood for exhalation. The chemical process of gas exchange is driven by the positive and negative air pressure inside the lungs, which changes with each breath during the course of healthy breathing.
- Low functional residual capacity (FRC), which is the residual volume of air in the lungs after normal exhalation
- Reduced lung compliance (elasticity of the lung)
- Increased resistance to airflow in the airway
- Ventilation/perfusion (V/Q) mismatch, which occurs when air flow and blood flow do not synchronize in the alveoli, which is essential for proper gas exchange to take place
Newborns also have the potential risk for persistence of certain fetal cardiac circulatory systems such as:
- Patent foramen ovale: A small hole in the wall (septum) between the two upper chambers (atria) of the heart which normally closes within a year after birth.
- Patent ductus arteriosus: A connection between the aorta and the pulmonary artery that closes within two or three days after birth. It may take longer in premature babies.
Impaired gas exchange leads to:
- Hypercapnia: Elevated carbon dioxide level in the blood, lowering the pH and making the blood acidic (respiratory acidosis).
- Hypoxemia: Low level of oxygen in the blood leading to inadequate oxygen supply to the tissues.
A newborn baby’s lungs are fragile and can be easily injured. The mechanical properties of the baby’s respiratory system are an important consideration for selecting the safest and most effective ventilation strategy. The factors that influence ventilation include the following:
- Pressure gradient: Presence of a pressure gradient between the airway opening and the alveoli is necessary to drive the flow of gases during inspiration and expiration.
- Compliance: Compliance is the elasticity of the respiratory structures such as the alveoli and chest wall, in inflating and deflating.
- Resistance: Resistance is the inherent opposition to airflow in the airway or the endotracheal tube, due to friction.
- Time constant: Time constant is the amount of time taken by an alveolus to fill during inhalation (inspiratory time constant) and empty during exhalation (expiratory time constant) at a stable pressure.
- Gas trapping: Gas trapping is abnormal retention of air in the lungs when inspiratory time is too long, expiratory time is too short, or the tidal volume is excessive.
- Tidal volume is the volume of air that flows in or out of the lungs in a respiratory cycle.
- Chest wall motion: Chest wall motion is the movement of the chest wall that allows expansion and contraction of the lungs. Assessing chest wall motion with ECG leads helps in delivering appropriate ventilation.
Physiologic control of breathing
- Chemoreceptors: Two types of chemoreceptors send feedback to the brain for regulation of respiration:
- Central chemoreceptors: Sensors located in the brainstem region which sense increase in carbon dioxide pressure and decrease in the pH level in blood.
- Peripheral chemoreceptors: Sensors found in certain structures on the carotid artery and aorta, known as carotid bodies and aortic bodies, sense decrease in oxygen pressure in the blood.
- Mechanoreceptors: Mechanoreceptors sensors present in the respiratory tract, lungs and the pulmonary vessels sense airway stretch and air pressure in the lungs and produce a multitude of reflex responses. Mechanical ventilation results in stimulation of chemoreceptors and mechanoreceptors, which facilitates respiration.