5.1 ARDS & Acute Respiratory Failure

ARDS & Acute Respiratory Failure in the PICU

Acute respiratory failure is the inability of the pediatric respiratory system to maintain adequate gas exchange. In the PICU you will see two classic patterns—and frequently both at once. Hypoxemic (Type I) failure is characterized by low PaO2 (or low SpO2) with a normal or low PaCO2 early on; the problem is oxygen transfer across injured or fluid-filled alveoli, V/Q mismatch, diffusion limitation, or true shunt. Hypercapnic (Type II) failure is characterized by rising PaCO2 and respiratory acidosis from inadequate alveolar ventilation—airway obstruction, neuromuscular weakness, central hypoventilation, or muscle fatigue after prolonged high work of breathing. Mixed failure is common in bronchiolitis, pneumonia, status asthmaticus, and evolving pediatric ARDS (PARDS).

Unlike the adult Berlin definition alone, pediatric ARDS is framed by the Pediatric Acute Lung Injury Consensus Conference (PALICC) criteria. Timing is onset of hypoxemia and new radiographic findings within 7 days of a known clinical insult. Imaging shows new infiltrate(s) consistent with acute pulmonary parenchymal disease. Edema is not fully explained by cardiac failure or fluid overload. Oxygenation impairment is graded with the oxygen index (OI) when an arterial blood gas is available, or the oxygen saturation index (OSI) when SpO2 is used under carefully defined conditions. OI = (FiO2 × mean airway pressure × 100) ÷ PaO2. Higher OI means worse disease. Severity bands (commonly mild, moderate, severe) guide intensity of support and candidacy for adjuncts such as prone positioning or ECMO referral pathways used by your center.

Escalation: HFNC → NIV → Intubation

Support is escalated by physiology and trajectory, not by a single SpO2 number. Start by treating reversible contributors: fever, secretions, pneumothorax, pulmonary hypertension crisis, and inadequate analgesia that worsens splinting. High-flow nasal cannula (HFNC) delivers heated, humidified oxygen at age- and weight-appropriate flows, washes nasopharyngeal dead space, and provides a modest continuous positive airway pressure effect. Titrate flow for comfort and work of breathing; titrate FiO2 to target SpO2 ranges ordered for that child (often avoiding prolonged SpO2 100% on high FiO2 once stable).

If tachypnea, retractions, or hypoxemia persist despite optimized HFNC, move to noninvasive ventilation (NIV)—CPAP or bilevel support—when the child can protect the airway, cooperate (or be safely managed), and has no contraindication such as untreated pneumothorax, copious vomiting risk, or facial trauma. NIV reduces work of breathing and recruits alveoli; nursing focuses on mask fit, skin integrity, gastric decompression as ordered, and continuous assessment for failure. Intubate for progressive hypoxemia or hypercapnia, apnea or near-apnea, loss of airway protective reflexes, refractory shock needing controlled ventilation, or clear NIV failure. Pre-oxygenate, have difficult-airway equipment ready, and anticipate hemodynamic changes with positive pressure in hypovolemic or pulmonary hypertensive children.

Lung-Protective Ventilation Nursing

Once intubated for PARDS or severe lung injury, the nursing mandate is protect the baby lung. Use tidal volumes in a lung-protective range (commonly about 5–8 mL/kg of ideal/predicted body weight—follow unit protocol), keep plateau pressure ideally ≤28–30 cmH2O, and apply PEEP sufficient to prevent cyclic collapse without causing overdistension or impaired venous return. Accept permissive hypercapnia when intracranial pressure and pulmonary hypertension status allow, prioritizing pH stability over a normal PaCO2. Minimize unnecessary disconnections that derecruit lung; use inline suction when appropriate; coordinate sedation so the child synchronizes without fighting the ventilator.

Daily nursing surveillance includes SpO2/EtCO2 trends, ABG correlation, peak/plateau pressures, auto-PEEP in obstructive disease, bilateral breath sounds, and signs of air leak (subcutaneous emphysema, sudden compliance drop, asymmetric chest). Prone positioning, when ordered for moderate-to-severe PARDS, requires a rehearsed team turn, secure lines and the endotracheal tube, eye and pressure-point protection, and planned duration (often prolonged daily sessions per protocol). Fluid stewardship matters: avoid indiscriminate volume loading that worsens pulmonary edema once shock is addressed. Throughout, treat the trigger—sepsis source control, aspiration prevention, and cardiac evaluation when left atrial hypertension could mimic or coexist with PARDS.

Nursing documentation should capture FiO2, MAP or PEEP/PIP, SpO2/EtCO2 trends, work-of-breathing scores, and any prone or recruitment maneuvers so the next handoff can see trajectory, not a single snapshot. When oxygenation fails despite optimized lung-protective settings, communicate early about adjuncts used in your center—inhaled pulmonary vasodilators for selected physiology, neuromuscular blockade for severe asynchrony, or ECMO consultation—while continuing to treat sepsis, aspiration, or other triggers. Remember that OSI (using SpO2) is a pragmatic alternative when arterial access is limited, but saturations must sit in the validated range used by PALICC guidance so the index remains interpretable.

The CCRN Pediatric exam expects you to distinguish hypoxemic from hypercapnic failure, apply pediatric ARDS concepts (OI/OSI and timing), escalate support logically, and operationalize lung-protective principles at the bedside—not merely recite adult Berlin cutoffs.