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Tachypnea in a Neonate and Diagnostic Conundrums

Udoka Asoh, Hilary Klonin
Department of Neonatology, Hull University Teaching Hospitals NHS Trust, Hull, United Kingdom

Address for Correspondence: Udoka Asoh, 3 Buxworth Close, Hull, United Kingdom HU35DZ. Email: ziduka@yahoo.com

Keywords: Lung Hyperinflation, Tachypnea

Clinical Problem:
A term male infant was born by normal vaginal delivery following an uncomplicated pregnancy. He was admitted to the neonatal intensive care unit (NICU) at 33 hours of age with tachypnea [respiratory rate 105 breaths/min (bpm)]. Examination was otherwise normal including preductal oxygen saturation of 97% and post-ductal oxygen saturation of 96%. Full blood count showed hemoglobin 15.1 gm/dL, white cell count 15.8 x10⁹ cells/cumm, platelets 317 x10⁹ cells/cumm) and C-reactive protein (CRP) was 40 mg/l. Chest x-ray was interpreted as a possible right upper lobe pneumonia in the presence of a degree of rotational artefact (Figure 1). Intravenous (IV) benzylpenicillin and gentamicin was commenced and given for 5 days. Cerebrospinal fluid (CSF) and blood cultures did not grow any organism. The presumptive diagnosis therefore was congenital pneumonia. He was commenced on 0.1L/min of low flow nasal cannula oxygen shortly after admission following a drop in his oxygen saturation to 93% and then escalated to high flow nasal cannula oxygen support (HFNC) within 3 hours due to worsening respiratory distress. (Figure 2 – run chart showing respiratory rate pattern vs time during admission). Capillary blood gas performed on 6L/min of high flow on 21% oxygen showed a pH 7.39, pCO2 5.6, bicarbonate (HCO3) 24.6. He remained on HFNC in air with stable blood gases with a significant drop in his respiratory rate (figure 2) from 105 bpm to 65 bpm. HFNC was stopped between day 2 and 3 and the respiratory rate was seen to rebound to 85 bpm (figure 2). A grade 3/6 systolic heart murmur was heard around 80 hours of life and an echocardiography revealed a small outlet muscular ventricular septal defect (VSD) not thought to be a contributing factor to his tachypnea. The cardiovascular examination remained otherwise normal. Nasogastric tube feeding was commenced a few hours after admission but interrupted by vomiting spells, however this was subsequently well tolerated without incidence after a brief pause. At one week of age, the tachypnea persisted, and respiratory rate remained between 65 bpm and 80 bpm on HFNC oxygen with increased work of breathing. At this stage the oxygen requirement then increased by up to 50% with worsening respiratory acidosis on capillary blood gas (pH 7.24, pCO2 9.3, HCO3 24.5). He was intubated and ventilated and thereafter investigated and treated for sepsis a second time. The post intubation x-ray showed a right upper lobe collapse with an overinflated left lung and displacement of the left main bronchus (Figure 3). HRCT chest is depicted as Figure 4. A trial of dexamethasone 75 mcg/kg/dose was started on day 10 and subsequently increased to 200 mcg/kg/dose after 48 hours without improvement in oxygen requirement. In view of the failure to respond to medical treatment he was referred for surgery.

Figure 1. Chest x-ray done shortly after admission on low flow oxygen. Image appears slightly rotated with possible right upper lobe collapse/consolidation and mild right sided mediastinal shift.

Figure 2. Run chart showing the respiratory rate pattern during admission.

Figure 3. Post intubation x-ray showing overinflated left hemithorax with significant right sided mediastinal shift.

Figure 4. Lung CT showed partial or complete segmental collapse bilaterally with relative hyperinflation of the left upper lobe. The left main bronchus is partially narrowed as it passes between the aorta and heart.