19.2 Systematic Pediatric Respiratory Assessment & Multimodal Diagnostic Integration

Developmental Airway and Bedside Examination

Observe respiratory rate, effort, chest movement, color and interaction before upsetting the child when possible. Infants have a relatively large occiput and tongue, a small airway and a compliant chest wall. Supine positioning can flex the neck. Reposition gently toward a neutral airway, using a shoulder roll when needed and preserving spinal alignment if injury is suspected. Young infants tend to breathe through the nose, so nasal obstruction can affect feeding and breathing. Small reserve and high oxygen demand relative to size contribute to rapid desaturation with apnea. Laryngeal measurements vary by level and method. The cricoid is a complete cartilaginous ring, and in vivo imaging can show a smaller transverse opening at the glottis. Pediatric laryngeal MRI study · Pediatric airway measurements · AHA/AAP pediatric advanced life support

Worked example: For steady laminar flow in a rigid circular tube, resistance varies as $1/r^4$ at fixed tube length and gas viscosity. If the starting diameter is 4 mm, the radius is 2 mm. A 1 mm layer of swelling around the wall leaves a radius of 1 mm and a diameter of 2 mm. The remaining area is $(1/2)^2=1/4$ of the original, a 75% decrease. Modeled resistance increases by $(2/1)^4=16$. This illustrates sensitivity to narrowing. Real airways are dynamic, and turbulent or variable flow cannot be quantified with this formula.

Compare the respiratory rate with age and context. Fever, crying and pain can increase it. Flaring, retractions, head bobbing, grunting or thoracoabdominal asynchrony indicate increased effort. Falling respiratory effort accompanied by poor air movement, altered alertness, apnea or gasping can indicate ventilatory failure. Begin support when needed while identifying the cause.

Pulsus paradoxus is an inspiratory systolic pressure fall greater than 10 mmHg. It can occur in severe asthma or other conditions, including tamponade. Use it in context with air entry, mental status and perfusion. It is not an isolated marker of impending arrest. GINA strategy report · ESC pericardial guideline

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Oxygenation, Ventilation and Blood Gas Selection

Standard two-wavelength pulse oximetry estimates arterial oxyhemoglobin saturation. Check signal quality and trend, including motion, probe fit and perfusion. Pulse oximetry can overestimate saturation in some children with darker skin pigmentation. Severe anemia can reduce oxygen content despite preserved saturation. If the result conflicts with the bedside assessment, verify the reading and obtain direct measurements when they will guide treatment. FDA pulse oximetry information · Pediatric skin-tone validation study

• Carbon monoxide: A reassuring conventional pulse oximeter value can coexist with substantial carboxyhemoglobin. Give oxygen promptly when clinically suspected and use arterial or venous blood co-oximetry to measure carboxyhemoglobin. Consider time since exposure and treatment, because levels can fall on oxygen. Evaluate associated smoke-inhalation injuries and other toxic exposures as indicated. CDC clinical guidance
• Methemoglobinemia: A standard pulse oximeter may trend toward the mid-80s at substantial levels. Cyanosis with a relatively preserved arterial oxygen tension suggests a dyshemoglobin when the exposure fits. Arterial oxygen tension reflects dissolved oxygen and can be normal or high. Use blood co-oximetry to measure methemoglobin. Oximetry study · Infant cases
• Blood gases: An arterial gas measures arterial oxygen tension and helps quantify ventilation and acid–base status. A venous or adequately perfused capillary sample can inform pH and carbon dioxide trends in selected children. Use arterial sampling if accurate arterial oxygen tension is needed, if perfusion makes the alternative sample unreliable, or if the result would change immediate management. For example, arterial pH 7.26, $PaCO_2$ 60 mmHg and bicarbonate 26 mmol/L fit acute respiratory acidosis in a child with deteriorating ventilation. Interpret the trend with treatment, breathing and clinical context. AARC pediatric blood gas guideline

Comparing oxygenation on respiratory support

Use $FiO_2$ as a fraction. On a stable setting, $PaO_2/FiO_2$ compares arterial oxygen tension with inspired oxygen. For invasively ventilated children with suspected pediatric ARDS, PALICC-2 uses the oxygenation index (OI), or the oxygen saturation index (OSI) when arterial tension is unavailable. These incorporate the mean airway pressure in cm H₂O. Use the pulse saturation as a percentage number in OSI, with a reliable steady-state reading at or below 97%.

$OI = \frac{100 \times FiO_2 \times \text{mean airway pressure}}{PaO_2}$

$OSI = \frac{100 \times FiO_2 \times \text{mean airway pressure}}{SpO_2}$

With $FiO_2=0.40$, mean airway pressure 12 cm H₂O and $PaO_2=80$ mmHg, the P/F ratio is 200 and OI is 6.0. If no arterial gas is available and a reliable saturation on those settings is 96%, OSI is 5.0. Use the appropriate index with the rest of the PARDS definition and timing. The calculation alone cannot establish the diagnosis. PALICC-2

Capnography

During CPR, an abrupt rise in end-tidal CO₂ can prompt assessment for return of spontaneous circulation. Trend the value with perfusion, ventilation and other measures of CPR quality. A single cutoff cannot determine when to end pediatric resuscitation. AHA/AAP PALS · PALICC-2

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Imaging and Airway Procedures

Chest radiograph: Assess projection, rotation and inspiration before interpreting the cardiothymic silhouette, lungs and pleura. An AP image can magnify the silhouette. A normal thymus can produce a sail sign, and mediastinal air can elevate the thymic lobes. Consolidation can have air bronchograms or obscure an adjacent heart border or diaphragm. A pleural line without peripheral markings suggests pneumothorax. Pleural fluid can blunt the costophrenic angle on an upright image. Supine positioning can change the appearance of both air and fluid. Normal thymic appearance · Neonatal pneumomediastinum image

Endotracheal tube: For an older child an age-based cuffed size estimate is age in years divided by four plus 3.5 mm. An uncuffed estimate adds 4 mm instead. An initial oral depth estimate in centimeters is three times the internal diameter in millimeters. For example, at age six the cuffed size estimate is 5.0 mm and the estimated oral depth is 15 cm. Use an appropriate length-based aid or local protocol where applicable, prepare adjacent sizes, and confirm tracheal placement with sustained waveform capnography in a perfusing child. Use radiography to check the depth in the trachea. In a neutral position aim for a tip clear of the carina with room for movement. Neck flexion tends to advance the tip and extension withdraws it. Reassess after moving the patient. ANZCOR pediatric tube size estimates · Pediatric tube-depth study · Prospective neck-position study · AHA/AAP PALS

Point-of-care lung ultrasound

For children older than 3 months with a moderate or large parapneumonic effusion on radiography, 2026 IDSA/PIDS suggests ultrasound over CT or MRI to characterize the collection. A small effusion with minimal symptoms usually needs no additional imaging. Contrast CT may be appropriate for a suspected abscess or another unresolved structural complication. Use a pediatric dose protocol and select CT pulmonary angiography when evaluation supports suspected pulmonary embolism. ESPNIC pediatric POCUS guideline · IDSA/PIDS 2026 pediatric CAP · ACR pediatric pneumonia imaging · ACR pediatric pulmonary embolism imaging

Flexible bronchoscopy can assess dynamic collapse, unexplained airway obstruction or persistent lobar collapse. Bronchoalveolar lavage can help identify infection in selected immunocompromised patients. Rigid bronchoscopy provides airway control and is commonly used for foreign body extraction. A specialist may use a flexible approach in selected cases with rigid backup. ATS pediatric endoscopy standards · ERS interventional bronchoscopy statement

Spirometry when the child is stable

Use technically acceptable efforts and appropriate reference values. Many school-age children can perform reproducible maneuvers, and some younger children can with suitable coaching. An $FEV_1/FVC$ below the age-appropriate lower limit of normal supports obstruction. A low FVC with a preserved ratio suggests possible restriction. Confirm restriction with total lung capacity below its lower limit of normal.

The ERS/ATS technical standard describes a significant bronchodilator response as an increase in $FEV_1$ or FVC greater than 10% of its predicted value. In the GINA asthma diagnostic framework, a child aged 6–17 can meet the spirometric bronchodilator criterion with an $FEV_1$ increase of at least 12% of predicted. For an increase from 1.20 to 1.40 L and a predicted $FEV_1$ of 1.80 L, the change is $0.20/1.80 \approx 11.1\%$ of predicted. It meets the ERS/ATS $FEV_1$ criterion and falls below the GINA threshold. Other evidence can establish variable airflow limitation in a child with asthma.

Reproducible inspiratory flattening can suggest variable extrathoracic obstruction, expiratory flattening variable intrathoracic obstruction, and flattening of both limbs a fixed central obstruction. Check effort and confirm the suspected lesion by appropriate airway evaluation. ERS/ATS interpretive standard · GINA 2026 diagnostic criteria