Residency · Residency · Medicine Pediatrics

Acute Respiratory Failure and Mechanical Ventilation Across Ages

Introduction

Acute respiratory failure is among the most common reasons for ICU admission in both pediatric and adult populations. The med-peds physician must understand the physiologic differences in respiratory mechanics across ages, recognize respiratory failure early, and be competent in initiating and managing mechanical ventilation in neonates, children, and adults.

Definitions

Type 1 (Hypoxemic): PaO2 <60 mmHg on room air; failure of oxygenation. Type 2 (Hypercapnic): PaCO2 >50 mmHg; failure of ventilation. Type 3 (Perioperative): Atelectasis-related. Type 4 (Shock-related): Hypoperfusion of respiratory muscles.

Age-Specific Respiratory Physiology

Neonates and Infants

Higher metabolic rate and oxygen consumption per kilogram; Smaller functional residual capacity (FRC) relative to closing capacity; Compliant chest wall with less elastic recoil; Obligate nasal breathers (neonates); Diaphragm-dependent breathing with fatigue-prone type II muscle fibers; Desaturate rapidly due to lower oxygen reserve.

Children

Transition to more adult-like physiology by school age. Smaller airways increase resistance (resistance proportional to 1/r^4) Lower airway disease (bronchiolitis, croup) is a frequent cause of respiratory failure.

Adults

Greater respiratory reserve and FRC. COPD, pneumonia, ARDS are leading causes. Comorbidities (obesity, heart failure) compound respiratory failure.

Common Etiologies by Age

Assessment and Recognition

Clinical Signs of Impending Respiratory Failure

Tachypnea (age-appropriate rates); Accessory muscle use: nasal flaring, intercostal/subcostal retractions, head bobbing (infants) Grunting (neonates and infants); Altered mental status (agitation progressing to lethargy); Cyanosis (late sign); Declining SpO2 despite supplemental oxygen.

Arterial Blood Gas Interpretation

Assess oxygenation (PaO2), ventilation (PaCO2), and acid-base status. Calculate P/F ratio (PaO2/FiO2): <300 = ALI; <200 = ARDS; <100 = severe ARDS. Oxygenation index (OI) used in pediatrics: (FiO2 x MAP x 100) / PaO2.

Non-Invasive Support

High-Flow Nasal Cannula (HFNC)

Provides heated, humidified oxygen at high flow rates. Generates modest positive pressure; washes out dead space. Increasingly used as first-line in bronchiolitis and adult hypoxemic failure. Pediatric flows: 1-2 L/kg/min; Adult flows: 30-60 L/min.

Non-Invasive Positive Pressure Ventilation (NIPPV)

CPAP: Continuous positive airway pressure; splints airways, improves FRC. BiPAP: Adds inspiratory pressure support for work of breathing. Effective in COPD exacerbation, cardiogenic pulmonary edema, and pediatric respiratory distress. Contraindicated in facial trauma, inability to protect airway, hemodynamic instability.

Invasive Mechanical Ventilation

Indications for Intubation

Failure of non-invasive support; Inability to protect airway (GCS 8 or less); Severe respiratory acidosis or refractory hypoxemia; Anticipated clinical course (e.g., burn airway, impending deterioration).

Endotracheal Tube Selection

Neonates/Infants: Uncuffed ETT traditionally used; cuffed tubes increasingly accepted. Tube size: (age/4) + 3.5 (uncuffed) or (age/4) + 3 (cuffed) Adults: Cuffed ETT; 7.0-7.5 mm for women, 7.5-8.0 mm for men.

Initial Ventilator Settings

Lung-Protective Ventilation

ARDS Management

Low tidal volume ventilation: 6 mL/kg ideal body weight (ARDSNet protocol) Plateau pressure <30 cmH2O. Driving pressure <15 cmH2O (Pplat - PEEP) PEEP titration: Use ARDSNet PEEP/FiO2 tables. Prone positioning: Improves oxygenation and mortality in moderate-severe ARDS (PROSEVA trial); also used in pediatric ARDS. Permissive hypercapnia: Accept elevated PaCO2 to avoid ventilator-induced lung injury.

Pediatric ARDS (PALICC Guidelines)

Similar lung-protective principles apply; OI used for severity stratification; Tidal volume 5-8 mL/kg; exhaled tidal volume monitoring critical in smaller patients. ECMO considered for refractory cases.

Weaning and Extubation

Readiness Assessment

Improvement or resolution of underlying cause; Adequate oxygenation on FiO2 40% or less and PEEP 8 or less; Hemodynamic stability without high-dose vasopressors; Intact cough and gag reflex.

Spontaneous Breathing Trial (SBT)

T-piece or pressure support (5-8 cmH2O) for 30-120 minutes. Monitor for tachypnea, tachycardia, desaturation, accessory muscle use. Cuff leak test in pediatrics to assess for post-extubation stridor.

Post-Extubation

Plan for potential reintubation. Consider dexamethasone pre-treatment to reduce laryngeal edema (especially in children) HFNC or NIPPV as bridge in high-risk patients.

Clinical Pearls

Infants and neonates desaturate faster than adults due to lower FRC and higher oxygen consumption; preoxygenation is critical before intubation. Low tidal volume ventilation (6 mL/kg IBW) is the standard of care for ALL ventilated patients with ARDS, regardless of age. Prone positioning reduces mortality in moderate-to-severe ARDS and should be initiated early. In pediatric patients, pressure-control modes may be preferred for better compensation of air leaks around uncuffed tubes. The med-peds physician managing ventilators on both pediatric and adult services must remember to adjust all parameters for ideal body weight and age-appropriate physiology.

References

1. Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and ARDS. N Engl J Med. 2000;342(18):1301-1308.
2. Guerin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome (PROSEVA). N Engl J Med. 2013;368(23):2159-2168.
3. Khemani RG, Smith LS, Zimmerman JJ, et al. Pediatric acute respiratory distress syndrome: Definition, incidence, and epidemiology (PALICC). Pediatr Crit Care Med. 2015;16(5 Suppl 1):S99-S117.
4. Rochwerg B, Brochard L, Elliott MW, et al. Official ERS/ATS clinical practice guidelines: Noninvasive ventilation for acute respiratory failure. Eur Respir J. 2017;50(2):1602426.

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