10.1 PALICC-2 Diagnosis & Severity

10.1 PALICC-2 Diagnosis & Severity

PALICC-2 uses pediatric physiology and available monitoring rather than importing the adult Berlin definition. Apply the definition to patients younger than 18 years without active perinatal lung disease, then reassess severity after initial stabilization. Identify and treat the precipitating insult while ruling out hydrostatic edema as the main explanation.

Diagnostic Framework

PARDS begins within seven days of a known clinical insult. Chest imaging shows new unilateral or bilateral opacities consistent with acute pulmonary parenchymal disease; atelectasis or pleural effusion alone does not satisfy the imaging element. Respiratory failure must not be fully explained by cardiac failure or fluid overload, although cardiac disease can coexist. Echocardiography and hemodynamic assessment help when the origin of edema is uncertain.

For an invasively ventilated patient, OI or OSI is preferred:

• OI = (mean airway pressure x FiO2 x 100) / PaO2
• OSI = (mean airway pressure x FiO2 x 100) / SpO2

Use OSI only when saturation is in a range where it can track changes in oxygenation; obtain arterial oxygen tension when the classification or treatment decision requires it.

Invasive PARDS Thresholds

An invasively ventilated patient meets the oxygenation criterion at OI 4 or higher or OSI 5 or higher. Grade severity at least four hours after the initial diagnosis so the result reflects response to stabilization rather than one transient value.

PALICC-2 does not divide invasive disease into separate mild OI 4-8 and moderate OI 8-16 bands. A computed OI of 16.1 is severe. Record the inputs and verify that FiO2 is entered as a decimal; multiplying by 100 is already part of the equation.

Calculation Discipline and Reclassification

Compute OI from measurements obtained close together. If MAP is 14 cm H2O, FiO2 is 0.60, and PaO2 is 70 mmHg, OI is (14 x 0.60 x 100) / 70 = 12, which is mild/moderate invasive PARDS. If PaO2 falls to 50 with the other inputs unchanged, OI becomes 16.8 and meets severe criteria. That change should prompt confirmation of tube position, circuit function, hemodynamics, secretion burden, pneumothorax, and disease progression before attributing it only to PARDS.

OSI is most useful when arterial sampling is unavailable and the saturation signal is reliable. Dyshemoglobinemia, motion, poor perfusion, a weak plethysmographic waveform, or saturation on the flat upper portion of the oxyhemoglobin curve can distort interpretation. Do not mix PaO2 from one time with MAP and FiO2 from another.

Differential diagnosis

Cardiogenic edema, fluid overload, diffuse atelectasis, pleural disease, pulmonary hemorrhage, and chronic lung disease can resemble PARDS. PALICC-2 allows cardiac dysfunction to coexist, but acute lung disease must not be fully explained by the heart or volume status. Use echocardiography, fluid balance, examination, imaging, and response to therapy together.

Timing Example

A child may meet PARDS criteria at noon yet have an OI inflated by a brief derecruitment event. Stabilize the airway, ventilator, PEEP, and circulation, then assign severity after at least four hours. Record whether the score represents the worst value or a protocol-specified assessment. A later improvement from OI 18 to 11 changes the severity band but does not erase the diagnosis; continue trending and treating the underlying pneumonia, sepsis, aspiration, trauma, or other insult.

Cyanotic heart disease

Children with cyanotic congenital heart disease can still develop PARDS. Compare current oxygenation with the patient's baseline and determine whether the acute deterioration is explained by the cardiac lesion alone. OI, OSI, P/F, and S/F may be difficult to interpret at low baseline saturations, so combine the trend with imaging, ventricular and shunt assessment, perfusion, and the precipitating insult. The diagnosis requires an acute pulmonary process beyond the expected cardiac physiology.

When a value sits at a category boundary, repeat the measurement after checking signal quality, arterial sampling, ventilator data, and patient stability. Classification is a communication tool; it never replaces urgent treatment of a displaced tube, tension pneumothorax, shock, or another immediately reversible emergency.

Reassessment Rule

Record which oxygenation metric was used, when it was measured, and whether signal quality and airway pressure were reliable. Reclassify after stabilization; an improving or worsening trend can matter more than a single boundary value.