Learning objectives

• Describe the differences in anatomy and physiology between pediatric patients and adults
• Understand how these differences impact anesthesia practice in pediatric patients

Background

• Pediatric patients include the following groups
  • Neonates: A baby within 44 weeks of age from the date of conception
  • Infants: Up to 12 months of age
  • Children: 1-12 years
  • Adolescents: 13-16 years
• The differences between pediatric and adult anesthetic practice are reduced as patients become older

Anatomy and physiology

Airway and respiratory system

• Large head, short neck, and prominent occiput
• The tongue is relatively large
• The larynx is high and anterior (C3-C4 level)
• Epiglottis is long, stiff, and U-shaped → flops anteriorly → head needs to be in the neutral position to visualize it
• Neonates breathe through their nose → narrow nasal passages are easily blocked by secretions and may be damaged by a nasogastric tube or nasally placed endotracheal tube (ETT) 
• 50% of airway resistance comes from the nasal passages
• The airway is funnel-shaped and narrowest at the level of the cricoid cartilage
  • Trauma to the airway results in edema
  • 1 mm of edema can narrow a baby’s airway by 60% 
  • Presence of a leak around the ETT to prevent trauma resulting in subglottic edema and subsequent post-extubation stridor
• ETT must be inserted to the correct length to sit at least 1 cm above the tracheal carina and taped securely to prevent tube dislodgement with head movement
• Neonates and infants have a limited respiratory reserve
• Horizontal ribs prevent the “bucket handle” action seen in adult breathing and limit an increase in tidal volume (TV)
  • Ventilation is primarily diaphragmatic
  • Bulky abdominal organs or a stomach filled with gases from poor bag-mask ventilation can impinge on the contents of the chest and splint the diaphragm, reducing the ability to ventilate adequately
• The chest wall is more compliant → functional residual capacity (FRC) is relatively low
  • FRC decreases with apnea and anesthesia, causing lung collapse
• Minute ventilation is rate-dependent as there are little means to increase TV
• Closing volume is larger than FRC until 6-8 years → increased tendency for airway closure at end-expiration → neonates and infants need intermittent positive-pressure ventilation (IPPV) during anesthesia and benefit from a higher respiratory rate (RR) and use of PEEP
• Continuous positive airway pressure (CPAP) during spontaneous ventilation improves oxygenation and decreases the work of breathing
• Work of respiration may be 15% of oxygen consumption
• Muscles of ventilation are easily subject to fatigue due to the low percentage of type I muscle fibers in the diaphragm → number increases to the adult level over the first year of life
• Alveoli are thick-walled at birth → only 10% of the total number of alveoli found in adults → alveoli clusters develop over the first 8 years of life
• Apnea is common postoperatively in premature infants → associated with desaturation and bradycardia
• RR = 24 – age/2
• Spontaneous ventilation TV = 6-8 mL/kg; IPPV TV = 7-10 mL/kg
• Physiological dead space = 30% and increased by anesthetic equipment

Cardiovascular system

• The myocardium is less contractile in neonates, causing the ventricles to be less compliant and less able to generate tension during contraction → limits the size of the stroke volume → cardiac output is rate-dependent
• The infant behaves with a fixed cardiac output state
• The vagal parasympathetic tone is predominant, making neonates and infants more prone to bradycardia
• Bradycardia is associated with reduced cardiac output
• Treat bradycardia associated with hypoxia with oxygen and ventilation
• External cardiac compression is required in neonates with a heart rate of ≤60 bpm or 60-80 bpm with adequate ventilation
• Cardiac output = 300-400 mL/kg/min at birth; 200 mL/kg/min within a few months
• Sinus arrhythmia is common in children, all other irregular rhythms are abnormal
• The patent ductus contracts in the first few days of life and will fibrose within 2-4 weeks
• Closure of the foramen ovale is pressure-dependent and closes in the first day of life but it may reopen within the next 5 years

Normal heart rates (beats/min) and systolic blood pressure (mmHg)

Normal blood volumes

Renal system

• Renal blood flow and glomerular filtration are low in the first 2 years of life due to high renal vascular resistance
• The tubular function is immature until 8 months → infants are unable to excrete a large sodium load
• Dehydration is poorly tolerated
• Urine output = 1-2 mL/kg/h

Hepatic system

• Immature liver function with decreased function of hepatic enzymes
• E.g., barbiturates and opioids have a longer duration of action due to the slower metabolism

Glucose metabolism

• Hypoglycemia is common in the stressed neonate
  • Monitor glucose levels regularly
  • Neurological damage may result from hypoglycemia → infusion of 10% glucose to prevent this
  • Infants and older children maintain blood glucose better and rarely need glucose infusions
• Hyperglycemia is usually iatrogenic

Hematology

• 70-90% of hemoglobin molecules are fetal hemoglobin (HbF)
• Within 3 months, the levels of HbF drop to 5%, and adult hemoglobin (HbA) predominates
• Vitamin K-dependent clotting factors (II, VII, IX, X) and platelet function are deficient in the first months → administer vitamin K at birth to prevent hemorrhagic disease
• Transfusion is recommended when 15% of the circulating blood volume has been lost

Temperature control

• Babies and infants have a large surface area to weight ratio with minimal subcutaneous fat → poorly developed shivering, sweating, and vasoconstriction mechanisms
• Brown fat metabolism is required for non-shivering thermogenesis 
• The optimal ambient temperature to prevent heat loss is 34°C for the premature infant, 32°C for neonates, and 28°C for adolescents and adults
• Hypothermia causes respiratory depression, acidosis, decreased cardiac output, increased duration of action of drugs, decreased platelet function, and increased risk of infection

Central nervous system

• Pain is associated with increased heart rate, blood pressure, and neuroendocrine response
• Narcotics depress the ventilation response to a rise in PaCO2
• The blood-brain barrier (BBB) is poorly formed → barbiturates, opioids, antibiotics, and bilirubin cross the BBB easily, causing a prolonged duration of action
• Cerebral vessels in the preterm infant are thin-walled and fragile → prone to intraventricular hemorrhages → risk is increased with hypoxia, hypercarbia, hypernatremia, low hematocrit, awake airway manipulations, rapid bicarbonate administration, and fluctuations in blood pressure and cerebral blood flow
• Cerebral autoregulation is present and functional from birth

Psychology

• Infants <6 months are usually not upset by separation from their parents and will accept a stranger
• Children up to 4 years are upset by separation from their parents, and unfamiliar people and surroundings 
• School-age children are more upset by the surgical procedure and the possibility of pain
• Adolescents fear narcosis and pain, loss of control, and the possibility of not being able to cope with the illness 
• Parental anxiety is readily perceived and reacted to by the child

Anesthetic considerations

• Preoperative fasting
  • Solids and milk >12 months: 6 hours
  • Breast milk and formula feed <12 months: 4 hours
  • Unlimited clear fluids: 2 hours
  • Increased incidence of nausea and vomiting with long fasting periods
• Preoperative medical and anesthetic history
• • Previous problems with anesthetics, including family history
  • Allergies
  • Previous medical problems, including congenital anomalies
  • Recent respiratory illness
  • Current medications
  • Recent immunizations
  • Fasting times
  • Presence of loose teeth
• Weigh the child → all drug doses are related to body weight
• Physical examination of the airway and cardiorespiratory systems
• Further investigations that may be necessary
  • Hemoglobin: Large expected blood loss, premature infants, systemic disease, congenital heart disease
  • Electrolytes: Renal or metabolic disease, intravenous fluids, dehydration
  • Chest radiograph: Active respiratory disease, scoliosis, congenital heart disease
• Uncooperative patient
• Altered airway anatomy
• Increased risk of laryngospasm
• Inhalational induction: Halothane and sevoflurane
• Intravenous induction: Propofol, thiopentone, or ketamine
• Rapid desaturation on induction
• Increased vagal tone and potential for bradycardia
• Rate-dependent cardiac output
• Altered pharmacokinetics and -dynamics
  • Increased minimum alveolar concentration (MAC)
  • Immature liver and kidney function
  • Increased total body water

Suggested reading

• Macfarlane F. Paediatric anatomy and physiology and the basics of paediatric anaesthesia. December 16, 2005. Accessed February 2, 2023. https://resources.wfsahq.org/atotw/paediatric-anatomy-and-physiology-and-the-basics-of-paediatric-anaesthesia/ 

Clinical updates

Azimaraghi et al. (BJA, 2024) analyzed over 18,000 pediatric anesthetics and found that intraoperative dexmedetomidine use was associated with longer PACU stays, higher hospital costs, and increased odds of bradycardia and hypotension, without reducing emergence delirium. PACU delays were most pronounced in children ≤ 2 years and in short ambulatory cases, particularly with higher doses or late administration. These findings call into question routine dexmedetomidine use in pediatric anesthesia and support more selective, dose-conscious protocols.

• Read more about this study HERE.

McCormack et al. (BJA, 2025) analyzed 429,310 children undergoing noncardiac surgery and found that preoperative anemia (25.7%) and perioperative transfusion (10.4%) rates remained unchanged from 2012 to 2023, yet each was independently associated with higher 30-day mortality and postoperative complications. Children with both anemia and transfusion had the highest risk, with adjusted odds ratios of ~4 for mortality and 5–7 for major complications. These findings highlight a persistent implementation gap in pediatric patient blood management and support earlier anemia screening, iron therapy, and restrictive, physiology-guided transfusion strategies.

• Read more about this study HERE.
• Listen to NYSORA’s podcast discussing this HERE.

Reysner et al. (RAPM, 2025) report that adding preservative-free perineural dexamethasone to ropivacaine for ultrasound-guided popliteal sciatic nerve blocks in children aged 2–5 years significantly prolongs analgesia and reduces postoperative opioid consumption in a dose-dependent manner. A dose of 0.1 mg/kg nearly doubled the time to first rescue opioid compared with ropivacaine alone, without increasing blood glucose or inflammatory stress markers. 

• Read more about this study HERE.