Clinical overview
The first breath is the most dramatic physiological event of a human life. In utero the fetal lungs are not respiratory organs at all — they are fluid-filled, secretory, and bypassed by a circulation designed around the placenta. Within seconds to minutes of birth the newborn must clear that lung fluid, aerate hundreds of millions of alveoli for the first time, establish a functional residual capacity, drop pulmonary vascular resistance, and switch the entire circulation from a parallel (placental) to a series (pulmonary) arrangement. Most babies accomplish this themselves, driven by a tightly choreographed set of mechanical, chemical, thermal and sensory stimuli. The registrar's job is to understand which factors normally drive that transition, so that when a baby fails to breathe you can reason about why and intervene logically rather than by rote.
This is a high-yield, frequently-examined topic precisely because it underpins neonatal resuscitation. Roughly 5–10% of newborns need some help to start breathing and around 3–6% need positive-pressure ventilation; a much smaller fraction need chest compressions or adrenaline (standard teaching, ILCOR). Establishing aeration of the lungs is the single most important step in newborn resuscitation — and you cannot prioritise it correctly unless you know the normal physiology it is trying to recapitulate. This chapter lists and explains those factors; the practical sequence is developed in neonatal-transition and the formal drill in neonatal-resuscitation.
Core knowledge
The intrauterine baseline
Before birth the alveoli are filled with lung liquid actively secreted by the pulmonary epithelium (chloride-driven, ~20–30 mL/kg). Fetal breathing movements occur episodically — they are essential for lung growth and for conditioning the diaphragm and respiratory muscles — but they do not exchange gas; oxygenation is entirely placental (see contractions-fetal-oxygenation). Pulmonary blood flow is minimal because pulmonary vascular resistance (PVR) is very high in the hypoxic, fluid-filled, unexpanded lung, so most right-ventricular output is diverted across the ductus arteriosus to the systemic circulation, and oxygenated placental blood is shunted right-to-left across the foramen ovale.
For air breathing to begin, four things must happen, broadly in parallel: lung liquid must be cleared, the lungs must be inflated and a functional residual capacity (FRC) established, PVR must fall so pulmonary blood flow rises, and respiratory drive must switch from episodic to continuous.
Factors that trigger and sustain the first breaths
Figure L2.1 — Chemical, thermal, tactile, mechanical and cord-related stimuli acting on the substrates that let fluid-filled fetal lungs establish FRC and continuous breathing.
A useful way to "list the factors" for the exam is to group them into chemical, thermal, mechanical/tactile, and clamping-related stimuli, then add the structural/biochemical prerequisites that make breathing possible.
- Chemical (the dominant central drivers). The transient asphyxia of normal birth — interruption of placental gas exchange during labour and at cord clamping — produces a rise in PaCO₂ (hypercapnia), a fall in PaO₂ (hypoxia/relative hypoxaemia) and a fall in pH (acidaemia). These stimulate central and peripheral chemoreceptors and are classically regarded as the principal stimulus to the first breath. Importantly, profound hypoxia does the opposite — it depresses the respiratory centre (primary then secondary/terminal apnoea), which is why a severely asphyxiated baby is floppy and apnoeic rather than gasping.
- Thermal. The abrupt fall in ambient temperature on delivery (from ~37 °C to a much cooler delivery room) stimulates skin thermoreceptors, particularly on the face, providing a powerful afferent stimulus to breathe. This is one reason newborns gasp on exposure — and a reason hypothermia and overheating both blunt the response.
- Tactile and sensory. Handling, drying and the general somatosensory bombardment of being born (touch, light, sound, gravity, proprioception) stimulate breathing. Drying and gentle stimulation of the trunk/back/soles is the deliberate clinical use of this factor in resuscitation.
- Mechanical — chest recoil and the establishment of FRC. As the chest is delivered, recoil of the thorax after passage through the birth canal (and the elastic recoil after the first breaths) helps draw air in and expel some liquid. The first active inspirations generate large transpulmonary pressures (transiently very high, of the order of tens of cmH₂O) to overcome surface tension and the viscosity of residual liquid; subsequent breaths need far less pressure once an FRC is established.
- Cord clamping / loss of placental circulation. Removing the low-resistance placenta and the interruption of umbilical venous return raise systemic vascular resistance and contribute to the chemical stimulus (rising CO₂). The timing of clamping matters for the smoothness of the cardiovascular transition (see Management).
The prerequisites that make a first breath effective
Listing trigger factors is incomplete without the substrate they act on:
- Surfactant. Type II pneumocytes secrete pulmonary surfactant (phospholipid, chiefly dipalmitoylphosphatidylcholine, with surfactant proteins). Surfactant lowers alveolar surface tension, prevents end-expiratory collapse, and allows an FRC to be maintained after the first breaths. Surfactant production rises through the third trimester; classically the lecithin:sphingomyelin (L:S) ratio rises and mature surfactant is generally present by ~34–35 weeks (standard teaching). Antenatal corticosteroids accelerate surfactant maturation (RCOG GTG 74).
- Lung liquid clearance. Two complementary mechanisms: (1) labour and the catecholamine surge of birth switch the pulmonary epithelium from chloride/fluid secretion to sodium absorption (epithelial sodium channels, ENaC), and (2) the mechanical forces of vaginal delivery plus the pressure gradients of the first breaths drive liquid from the air spaces into the interstitium and pulmonary lymphatics/capillaries. Elective caesarean before labour bypasses much of this priming — hence the increased risk of transient tachypnoea of the newborn ("retained lung liquid").
- A patent, developed airway and adequate chest-wall/diaphragm function — structurally normal lungs (no pulmonary hypoplasia, e.g. from prolonged oligohydramnios — see liquor-volume-abnormalities), a patent upper airway, an intact diaphragm and a competent respiratory centre.
The coupled circulatory switch
Figure L2.2 — How liquid clearance and first-breath aeration lower PVR, increase pulmonary flow and functionally close the fetal shunts.
Aeration is not just about gas exchange — lung inflation and the rise in alveolar oxygen cause pulmonary arterioles to dilate, so PVR falls and pulmonary blood flow rises sharply. This raises left-atrial pressure (more pulmonary venous return) above right-atrial pressure (less, once the cord is clamped), functionally closing the foramen ovale. Rising arterial oxygen and falling prostaglandins (the placenta was a prostaglandin source) cause the ductus arteriosus to constrict functionally over the first hours to days. Thus the same stimuli that start breathing also drive the circulation from fetal parallel shunting to the mature series circuit. Failure of PVR to fall is persistent pulmonary hypertension of the newborn (PPHN), with ongoing right-to-left shunting and profound hypoxaemia.
Assessment
The "assessment" here is the immediate evaluation of whether the newborn has successfully initiated effective respiration — the foundation of every delivery-room decision.
At the moment of birth — the three questions
ILCOR/NRP teaching frames the initial rapid assessment around: term gestation? good tone? breathing or crying? A vigorous term baby who is breathing or crying with good tone needs only warmth, drying, stimulation and (ideally delayed) cord clamping, and can stay with the mother. Any "no" prompts the structured response in neonatal-resuscitation.
Ongoing assessment of effective respiration
- Respiratory effort: crying and regular breathing vs gasping (a sign of severe hypoxia/secondary apnoea) vs apnoea. Gasping and apnoea are both indications for positive-pressure ventilation.
- Heart rate is the most important single indicator of a successful transition. A rising heart rate is the best early sign that ventilation is effective; persistent bradycardia (< 100/min) almost always reflects inadequate lung aeration. Assess by auscultation (or ECG, where available) rather than relying on palpation, which underestimates.
- Tone and colour: central cyanosis at birth is normal and resolves over minutes as SpO₂ climbs; persistent central cyanosis or pallor is abnormal.
- Oximetry targets. Preductal SpO₂ (right hand/wrist) rises gradually after birth; ILCOR/NRP provide a minute-by-minute target range (roughly the low-60s% at ~1 min rising to ~80–85%+ by ~5–10 min — standard teaching; use the published target table). Do not expect a pink, fully saturated baby in the first minute.
- Apgar score at 1 and 5 minutes documents the transition but is a descriptor, not a trigger — never wait for the 1-minute Apgar before acting on a baby who is not breathing.
Anticipating the baby who won't breathe
Good assessment is largely antenatal and intrapartum anticipation. Risk factors for a failed or delayed transition include prematurity (surfactant deficiency), elective caesarean before labour (retained lung liquid), intrapartum hypoxia/abnormal CTG (see ctg-interpretation), meconium-stained liquor, maternal opioids or general anaesthesia (respiratory-centre depression), oligohydramnios with pulmonary hypoplasia, sepsis, and congenital anomalies. Every such delivery should have a person skilled in newborn resuscitation present with equipment checked.
Management
Figure L2.3 — The Golden Minute approach: assess quickly, support normal triggers, open the lungs with PPV when needed, and use rising heart rate as the response marker.
Management is the deliberate clinical reproduction of the normal initiating factors when they are insufficient on their own. The detailed algorithm is in neonatal-resuscitation; what follows is how the physiology maps to the intervention.
Support the normal triggers
- Thermal care: dry the term baby immediately, remove wet linen, place skin-to-skin or under a radiant warmer; for the preterm < ~32 weeks use a polyethylene wrap/bag without drying and a hat. Maintain normothermia (36.5–37.5 °C) — hypothermia is both a failed-transition risk and an independent predictor of mortality, and is a particular hazard in cool, under-resourced South African delivery rooms.
- Tactile stimulation: drying itself stimulates; if still not breathing, briefly rub the back/trunk or flick the soles. Do not waste time on prolonged stimulation if the baby is apnoeic or gasping — move to ventilation.
- Position the airway: "neutral"/slightly extended (sniffing) position; suction only if the airway is obstructed by secretions (do not perform routine deep suction, which can cause reflex bradycardia and apnoea).
Establishing aeration — the key intervention
If the baby is apnoeic, gasping, or has a heart rate < 100/min after initial steps, the priority is lung aeration with positive-pressure ventilation (PPV) — inflation breaths to establish FRC. ILCOR/ERC/NRP emphasise that aerating the lung is the single most effective action in neonatal resuscitation; a rising heart rate confirms it is working. Use:
- Air for term babies (start in 21% O₂) and a low oxygen concentration for preterm, titrated to preductal SpO₂ targets — avoiding both hypoxia and hyperoxia (ILCOR 2025 / ERC Newborn Life Support / NRP 8th ed).
- A mask and T-piece or self-inflating bag with a controlled peak inspiratory pressure; CPAP/PEEP helps maintain the newly established FRC, especially in the preterm.
- If the heart rate stays < 60/min despite effective ventilation, add chest compressions at 3:1 with ventilation — but always optimise ventilation first, because in the newborn the problem is almost always the lungs, not the heart.
Cord clamping and the transition
ILCOR/NRP and the SA National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) support delayed cord clamping (commonly ≥ 60 seconds) in the vigorous newborn — it smooths the cardiovascular transition, improves haemodynamic stability and iron stores, and lets the lung aerate before the placental circulation is removed. A baby needing resuscitation should be moved to where effective ventilation can be given without dangerous delay; where feasible, providing initial respiratory support with the cord intact (or a short delay) is increasingly favoured.
South African context
- The SA Maternity Guideline (NDoH, 2024) and the widely-taught Helping Babies Breathe (HBB) programme structure delivery-room care around the "Golden Minute" — drying, stimulating, and where needed establishing bag-mask ventilation within the first 60 seconds.
- Every delivery in SA — district, regional or tertiary — must have at least one person able to initiate newborn ventilation and a checked, functioning self-inflating bag-valve-mask of the correct size, a heat source and a clock. Equipment failure (no functioning bag, no suction, cold room) is a recurring, preventable theme in perinatal mortality review (NCCEMD/Saving Mothers, perinatal arm). Antenatal corticosteroids for anticipated preterm birth (RCOG GTG 74) are a key upstream intervention that improves the newborn's ability to initiate effective respiration by maturing surfactant.
Red flags / pitfalls
Emergency drill — the baby who does not breathe. Apnoea or gasping, or a heart rate < 100/min after drying and stimulation, is a respiratory emergency. Call for help, start the clock, position the airway, and begin positive-pressure ventilation without delay. A rising heart rate is the sign ventilation is working. If the heart rate stays < 60/min despite effective ventilation, add chest compressions 3:1 and escalate. Do NOT wait for an Apgar score, do NOT prolong stimulation, and do NOT delay ventilation to suction a non-obstructed airway. Establish aeration first — that is the whole game.
- Mistaking gasping for breathing. Gasping is a sign of severe hypoxia (secondary apnoea) and mandates PPV, not reassurance or more stimulation.
- Confusing primary and secondary apnoea. In primary apnoea stimulation may restart breathing; in secondary (terminal) apnoea only ventilation will — and you cannot reliably tell them apart at the cot side, so treat apnoea as secondary and ventilate.
- Chasing the heart rate with compressions before the lungs are open. Newborn bradycardia is almost always hypoxic/ventilatory in origin. Compressions and adrenaline are useless if the lungs are not aerated; optimise ventilation (seal, position, airway, pressure) first.
- Hyperoxia. Resuscitating term babies in 100% oxygen is harmful; start in air and titrate to preductal SpO₂ targets.
- Routine deep suctioning, including of the non-vigorous meconium-stained baby — current ILCOR/NRP teaching does not recommend routine intubation-and-suction; prioritise ventilation. Deep pharyngeal suction can cause reflex bradycardia and apnoea.
- Cold delivery rooms and wet babies — hypothermia blunts the respiratory drive, worsens acidosis and surfactant function, and independently raises mortality. A common, fixable SA failure.
- Forgetting the substrate: a baby with pulmonary hypoplasia (prolonged oligohydramnios), surfactant deficiency (prematurity), or a congenital airway/diaphragm anomaly may not respond to standard steps — anticipate and escalate. Persistent profound cyanosis despite good ventilation suggests PPHN or congenital heart disease.
- Elective pre-labour caesarean babies are prone to retained lung liquid (transient tachypnoea) — counsel and anticipate, and avoid non-medically-indicated caesarean before 39 weeks.
Evidence anchors
- ILCOR 2025 CoSTR (Neonatal Life Support), ERC 2025 Newborn Life Support, and AAP Neonatal Resuscitation Program (NRP, 8th ed) — the international source of truth for delivery-room transition and resuscitation: initial rapid assessment, the priority of lung aeration/PPV, heart rate as the key indicator, start-in-air with titrated oxygen to preductal SpO₂ targets, 3:1 compression:ventilation, and delayed cord clamping.
- South African National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024), NDoH — the SA obstetric/perinatal source of truth, including delayed cord clamping and newborn care; and the Helping Babies Breathe (HBB) "Golden Minute" framework used in SA training.
- Saving Mothers / NCCEMD (perinatal arm) — recurring preventable factors (equipment, hypothermia, delayed/ineffective resuscitation) relevant to the SA delivery room.
- RCOG Green-top Guideline No. 74 — Antenatal corticosteroids — accelerates surfactant maturation and improves the preterm newborn's capacity to establish and maintain an FRC.
Note on hedged facts: the surfactant maturity threshold (~34–35 weeks / L:S ratio), the typical transpulmonary pressures of the first breaths, the proportion of newborns needing help, and the exact minute-by-minute SpO₂ target figures are standard physiology/teaching presented cautiously here; use the current published ILCOR/NRP target table for precise oximetry values rather than memorised numbers.