Anesthesiology APPLIED Exam › Pediatric and neonatal

Neonatal physiology and resuscitation

T1Pediatric and neonatal·1088 words · ~6 min read·v0.1✓ Sourced · 2DRAFT

Why examiners ask this

The neonate is where physiology stops being background and becomes the plan. The examiner uses this topic two ways: as the foundation under every neonatal surgical stem, and as a stand-alone inject when the obstetric stem delivers a limp baby and the pediatrician is not in the room. It tests application of knowledge (transitional circulation, oxygen consumption, temperature), organization (the Neonatal Resuscitation Program sequence) and judgment about when a neonate is too sick for the operating room.

The 60-second answer

I think of a neonate as a patient with twice the adult oxygen consumption, a quarter of the reserve, and a circulation that will revert to fetal pattern if I let the pH, oxygen or temperature fall. Oxygen consumption is 6–8 mL/kg/min with a closing capacity above functional residual capacity, so apnea desaturates in seconds; the heart depends on rate because the ventricle is stiff; the kidney cannot concentrate or excrete a sodium load; glycogen stores run out in hours; and heat loss is rapid, with cold driving hypoxemia through pulmonary vasoconstriction. In the delivery room I run the NRP algorithm: warm, dry, stimulate and position, then positive-pressure ventilation at 30–60 inflations per minute, started within 60 seconds of birth if the infant is apneic or the heart rate is below 100, compressions at 3:1 if it stays below 60 after 30 seconds of ventilation that moves the chest, and epinephrine 0.02 mg/kg IV through an umbilical venous catheter if it remains below 60.¹ Effective ventilation fixes almost every neonatal arrest.

Decision points and the "why"

Ventilation before everything — neonatal bradycardia is hypoxic until proven otherwise, so a rising heart rate is my marker of effective breaths. I correct the mask, reposition, suction, open the mouth and increase pressure before I touch the chest, and I place an endotracheal tube or a laryngeal mask if ventilation is ineffective or compressions begin.²
Oxygen concentration — I start at 21% at 35 weeks or more, 21–30% at 32–34 weeks and 30–100% below 32 weeks,¹ titrating to preductal saturation targets that rise from 65–70% at 2 minutes to 85–95% at 10 minutes.² Hyperoxia injures the preterm retina and lung, and 100% oxygen does not speed recovery; I go to 100% when compressions start and titrate back down once they stop.¹
Compressions at 3:1 — the ratio delivers 90 compressions and 30 inflations a minute, because the arrest is respiratory in origin; I use two thumbs with the hands encircling the chest, a third of the anteroposterior diameter, and reassess every 60 seconds.¹
Epinephrine and volume — intravenous epinephrine 0.01–0.03 mg/kg via the umbilical vein, the preferred route, every 3–5 minutes; the endotracheal route is a bridge at 0.05–0.1 mg/kg while access is obtained.¹ I give 10 mL/kg of saline or O-negative blood for suspected hemorrhage, such as an abruption or a cord accident.
Temperature — I keep the baby at 36.5–37.5 °C with a radiant warmer, plastic wrap and a cap for preterm infants, and warmed gases,¹ because hypothermia raises pulmonary vascular resistance, reopens the ductus and foramen, and converts a recovering baby into a cyanotic one. I use therapeutic hypothermia only as a deliberate neonatology decision for encephalopathy after 36 weeks.
Fitness for the operating room — a neonate who needs an operation also needs a glucose above 45 mg/dL, a corrected acidosis, an echocardiogram if there is any murmur or cyanosis, and warmed, dextrose-containing maintenance fluids. I delay a non-emergent case until these are met because the operating room amplifies every one of these vulnerabilities.

The complication they will inject

The baby is pink with ventilation, then turns cyanotic and bradycardic when the surgeon starts, or when I let the temperature drop in a cold operating room. This is persistent pulmonary hypertension with right-to-left shunting through the ductus and foramen ovale, and I confirm it with a preductal-postductal saturation gap. I treat the triggers: 100% oxygen, hyperventilation to a PaCO2 of 30–35 mmHg, correction of acidosis, warming, and deeper anesthesia or opioid to blunt the stress response. If it persists I ask for inhaled nitric oxide and I support the right ventricle with an inotrope rather than a pure vasoconstrictor. The alternative inject is hypoglycemia presenting as lethargy or a seizure after a long fast, treated with dextrose 10% at 2 mL/kg and a continuous infusion.

Pitfalls that cost points

Starting compressions or epinephrine before establishing effective ventilation.
Reaching for 100% oxygen as the first step in a preterm infant.
Reciting the NRP sequence with no heart-rate thresholds attached.
Describing neonatal physiology as a list without connecting each item to a management decision.
Forgetting glucose and temperature, the two numbers that quietly decide the outcome.

Rapid-why

Q: Why do neonates desaturate so fast? A: Oxygen consumption of 6–8 mL/kg/min against a small functional residual capacity that closing capacity encroaches on during tidal breathing.

Q: Why is cardiac output rate-dependent? A: The immature myocardium has fewer contractile elements and poor compliance, so stroke volume cannot rise; bradycardia is a direct fall in output.

Q: Why do neonates become hypothermic? A: A large surface-to-mass ratio, thin skin, little subcutaneous fat and no shivering; non-shivering thermogenesis burns brown fat and oxygen, which the sick neonate cannot spare.

Q: Why does the circulation revert? A: Hypoxia, acidosis and cold raise pulmonary vascular resistance above systemic, and the anatomically open ductus and foramen let blood bypass the lungs.

Numbers to know

Item	Value
PPV trigger	Heart rate <100/min or apnea after initial steps; 30–60 inflations/min¹
Compressions	Heart rate <60/min after 30 s of effective PPV; 3:1, 90 compressions + 30 inflations/min¹
Epinephrine	0.01–0.03 mg/kg IV (0.1 mg/mL) every 3–5 min; ET 0.05–0.1 mg/kg¹
Volume	10 mL/kg saline or O-negative blood
Preductal SpO2 targets	65–70% at 2 min, 80–85% at 5 min, 85–95% at 10 min²
Hypoglycemia treatment	D10 2 mL/kg, then 4–6 mg/kg/min infusion
Target temperature	36.5–37.5 °C¹

Sources

1.2025 American Heart Association and American Academy of Pediatrics Guidelines for CPR and ECC, Part 5: Neonatal Resuscitation · AHA/AAP, 2025 · cpr.heart.org
2.Neonatal Resuscitation Algorithm (2025) · AHA/AAP, 2025 · cpr.heart.orgSource of the preductal SpO2 target table (2 to 10 minutes); the 2025 table has no 1-minute row.

Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.