What is the physiology of a newborn's first breath?

From the Guidelines

The first breath of a newborn is a complex physiological process that involves the transition from fetal to extrauterine life, requiring significant effort to generate negative pressure and overcome surface tension in the lungs. The process begins when the infant exits the birth canal, experiencing a sudden drop in temperature and mechanical stimulation that triggers the respiratory center in the brain 1. The newborn must generate substantial negative pressure (about -40 to -100 cmH2O) to overcome surface tension and open the collapsed alveoli. Surfactant, produced by type II pneumocytes in the lungs during late gestation, is crucial in this process as it reduces surface tension and prevents alveolar collapse. As the lungs expand with air, pulmonary vascular resistance decreases dramatically, increasing blood flow to the lungs. Simultaneously, the ductus arteriosus begins to close, completing the transition from fetal to neonatal circulation. Oxygen levels rise in the blood, triggering further physiological changes. This entire process occurs within seconds to minutes after birth, establishing regular breathing patterns. Premature infants may struggle with this transition due to insufficient surfactant production, potentially leading to respiratory distress syndrome requiring medical intervention with exogenous surfactant therapy. According to the American Heart Association guidelines, approximately 10% of newborns require some assistance to begin breathing at birth, and less than 1% require extensive resuscitation measures, such as cardiac compressions and medications 1. The guidelines also emphasize the importance of avoiding unnecessary delay in initiation of ventilation, as this is the most important step for successful resuscitation of the newly born who has not responded to the initial steps 1. In terms of ventilation, an initial inflation pressure of 20 to 25 cmH2O is adequate for most preterm infants, and positive end-expiratory pressure (PEEP) is likely to be beneficial during initial stabilization of apneic preterm infants who require positive-pressure ventilation 2. However, the most recent and highest quality study, which is the 2015 American Heart Association guidelines, should be prioritized when making decisions about neonatal resuscitation 1. Key factors to consider when assessing the need for resuscitation include term gestation, good tone, and breathing or crying, and if the answer to any of these assessment questions is “no,” the infant should be moved to a radiant warmer to receive stabilization and potential ventilation 1. The most sensitive indicator of a successful response to each step is an increase in heart rate, and assessment should consist of simultaneous evaluation of heart rate, respirations, and oxygen saturation, as determined by pulse oximetry 1. Overall, the physiology of a newborn's first breath is a complex and critical process that requires careful attention and potential intervention to ensure a successful transition to extrauterine life.

From the Research

Physiology of a Newborn's First Breath

The physiology of a newborn's first breath is a complex process involving multiple factors and mechanisms.

• The transition to lung gas exchange begins within seconds of birth with the newborn's first breath and is largely complete by 30 minutes of age 3.
• Sensory stimulation caused by cutaneous cooling or sciatic nerve stimulation can result in the initiation of breathing within seconds 3.
• The increase in pulmonary blood flow facilitates the onset of pulmonary gas exchange and allows pulmonary venous return to take over the role of providing preload for the left ventricle 4.
• Lung aeration involves three mechanisms: Na+ reabsorption and fetal postural changes during labor, and pressure gradients generated by inspiration after birth 4.
• The newborn's first breath is also influenced by the regulation of breathing, which is controlled by various factors, including sensory stimulation, arterial PCO2, and pH levels 3.

Factors Influencing the Newborn's First Breath

Several factors can affect the newborn's first breath, including:

• The level of sensory stimulation, which can initiate breathing within seconds 3.
• The presence of liquid in the airways, which can adversely affect postnatal respiratory function 4.
• The increase in pulmonary blood flow, which facilitates the onset of pulmonary gas exchange 4.
• The use of positive pressure ventilation, which can improve lung recruitment and oxygenation 5, 6.

Clinical Implications

Understanding the physiology of a newborn's first breath has important clinical implications, including:

• The use of lung protective ventilation strategies to minimize lung injury and improve outcomes 5.
• The importance of proper positive pressure ventilation technique to ensure effective lung recruitment and oxygenation 6.
• The potential benefits of physiological based cord clamping to avoid the loss of preload and reduction in cardiac output 4.