Investigations
1st investigations to order
pulse oximetry
Test
A non-invasive method to measure oxyhaemoglobin saturation and detect hypoxaemia. It provides an assessment of acute disease severity, but data on its ability to predict clinical outcomes are inconsistent.[44][69]
Pulse oximetry is not recommended for outpatients with mild disease.[58]
In general, infants with viral bronchiolitis are more hypoxaemic than their chest x-ray findings would suggest.
Guideline statements differ in their recommended lowest acceptable oxyhaemoglobin saturation limits.[61]
The American Academy of Pediatrics recommends that infants who are hypoxaemic should be given supplemental oxygen to maintain an oxyhaemoglobin saturation (saturation of peripheral oxygen, SpO₂) of at least 90%, the point at which small decreases in arterial partial pressure of oxygen (PaO₂) are associated with large changes in SpO₂.[44]
In one study on infants with bronchiolitis, an oxygen saturation target of 90% or higher was found to be as safe and clinically effective as one of 94% or higher.[62]
No long-term neurodevelopmental studies have been performed to determine the safety of lower oxyhaemoglobin saturation targets, leading some guidelines to recommend oxygen supplementation if the oxyhaemoglobin saturation falls below 92%.[63]
In non-hypoxaemic inpatients, intermittent pulse oximetry did not affect rate of escalation of care or duration of oxygen therapy, compared with continuous pulse oximetry monitoring.[60] When the SpO₂ is 92% or greater, continuous monitoring is not required and intermittent monitoring is preferred.[63]
Result
hypoxaemia
Investigations to consider
enzyme-linked immunosorbent assay (ELISA) rapid antigen detection
Test
Commercial ELISAs are available for respiratory syncytial virus (RSV) and influenza but should be used only when the prevalence of disease is high in the community.
Positive rapid antigen tests are usually predictive of the viral agent of bronchiolitis, but a negative result does not rule out the presence of the virus. Rapid antigen testing, therefore, is not necessary for diagnosis of bronchiolitis. However, identifying the specific agent may be useful for infection control cohorting in the hospital setting, although there is some question as to whether testing adds any advantage over routine use of contact precautions.[56][63] A positive antigen test may also reduce the need for further investigations in a febrile infant and reduce the use of antibiotics.
Testing is recommended for infants receiving immunoprophylaxis with palivizumab or nirsevimab who experience a breakthrough episode of bronchiolitis. If RSV is detected, monthly immunoprophylaxis should be discontinued because of the low likelihood of a second RSV infection in the same year.[44] Such considerations are not necessary if nirsevimab is used for immunoprophylaxis. AAP: nirsevimab frequently asked questions Opens in new window
Testing can provide epidemiological data that could affect care beyond that of the individual patient.[59]
Result
positive detection of viral antigen
chest x-ray
Test
Not required for clinical diagnosis but it may be obtained when the diagnosis of bronchiolitis is unclear, in the setting of severe bronchiolitis or if infants with clinically diagnosed bronchiolitis are not improving at the expected rate.[61]
Radiographic abnormalities in bronchiolitis can resemble those seen in bacterial pneumonia, and chest x-rays should not be used as the sole criterion for the diagnosis of bacterial pneumonia.[44]
Result
hyperinflation, interstitial inflammation, atelectasis
reverse transcriptase polymerase chain reaction (RT-PCR)
Test
RT-PCR is more sensitive than ELISA.[1]
In addition, infants under 12 months can shed virus for prolonged periods.[65] Similarly, when using respiratory virus multiplex PCR, positive nucleic acid testing for non-RSV organisms may reflect prolonged viral shedding from an unrelated previous illness.
Result
positive detection of viral nucleic acid
Emerging tests
respiratory inductive plethysmography (RIP)
Test
Evaluates pulmonary ventilation by measuring the movement of the chest and abdominal wall. RIP is a non-invasive method to assess respiratory function without sedation.[70]
Result
degrees of thoraco-abdominal asynchrony as described by a phase angle or laboured breathing index correlate with degree of airway obstruction
electrical impedance tomography (EIT)
Test
EIT is a non-invasive method to assess distribution of ventilation without the need for ionising radiation or sedation.[71][72]
Result
changes in thoracic impedance in arbitrary units (AU) can reflect ventilation inhomogeneity, changes in end-expiratory lung volume, variation in tidal volume, and alterations in distribution of ventilation
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