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Acute disorders of the respiratory tract
Published in Janet M Rennie, Giles S Kendall, A Manual of Neonatal Intensive Care, 2013
Janet M Rennie, Giles S Kendall
A right-to-left shunt occurs when blood returns to the left side of the heart without being oxygenated. There are four shunt sites in the newborn: Cardiac veins draining into the left side of the heart and anastomoses between the bronchial and pulmonary circulations.The foramen ovale and ductus arteriosus during postnatal circulatory adaptation.Intrapulmonary shunting owing to pulmonary arterial blood going through the lung without passing a ventilated alveolus – this is a true intrapulmonary shunt with a VA/QC of 0.Intrapulmonary shunting owing to partially ventilated alveoli having a lower PaO2 than elsewhere in the lungs. These cause VA/QC ratios less than normal, but greater than 0. This component of the shunt can be eliminated by breathing pure oxygen for 15–20 minutes, which eventually washes all the nitrogen out of even poorly ventilated alveoli and equalizes the P aO2 throughout the lung. This procedure is known as the hyperoxia test. If the P O2 does not exceed 20 kPa (150 mmHg) in 100% oxygen there is a right-to-left shunt due to congenital heart disease (CHD) (Chapter 22), very severe respiratory disease, or persistent pulmonary hypertension of the newborn (PPHN) (p. 162).
Pulmonary Functionsl in Children with Interstitial Lung Disease
Published in Lourdes R. Laraya-Cuasay, Walter T. Hughes, Interstitial Lung Diseases in Children, 2019
Testing of pulmonary functions even in adults with ILD has its inconveniences, costs, and is dependent on a well-equipped and professionally staffed laboratory. In children the technical problems are greater and patient cooperation more difficult to obtain. In youngsters less than 6 years of age, hardly anything more than blood gases can be measured. Luckily, these can provide substantial information about ILD at any age. In addition to values obtained while breathing room air at rest, which provide general information about the degree of basic respiratory insufficiency, testing under special conditions can offer more. Raising the inhaled O2 concentration to 100% (hyperoxia test) exaggerates the effect of the extremely underventilated areas and allows to estimate the shunt-like situation in the lung. The calculated DA-a PO2 gradient will reflect the magnitude of the shunt. An only small increase of inhaled O2 concentration (e.g., to 24%) eliminates much of the true diffusion defect without influencing the effect of substantially. Also, when briefly lowering the O2 concentration to about 12 to 14% causes an inordinately large drop in arterial oxygenation, because now the artificially lowered alveolar-capillary PO2 gradient is hardly able to overcome the increased barrier. These tests, then, can give some idea, but never a precise measure of the relative contributions of diffusion and distribution defects to the overall insufficiency of the system. An increase of arterial PCO2 above normal levels is an ominous sign, since, as explained before, until the disease reaches an advanced stage, the usual finding is a moderate hypocapnia.
Posture Dependent Hypoxia Following Lobectomy: The Achilles Tendon of the Lung Surgeon?
Published in Journal of Investigative Surgery, 2022
Athanassios Krassas, Aikaterini Tzifa, Stavroula Boulia, Kosmas Iliadis
Given the fact that the presentation of the POS can be subtle, it requires a high degree of clinical suspicion. Firstly, it is useful to perform a hyperoxia test with 100% FiO2 both in sitting and supine position. A diagnosis of POS can be considered if a drop of the SATO2 of >5% is found in the sitting position, that improves in recumbency. When a large right-to-left shunt is established, the improvement of the hypoxemia may not be important even when the patient receives 100% oxygen. Marini [6] reported that 43% of his patients had a measured PaO2-while breathing 100% oxygen-that were compatible with the presence of a right-to-left shunt. Dyspnea after major pulmonary resections is mainly due to pain or to the extent of the resection. POS therefore is not the first diagnosis that comes to mind. The majority of patients underwent either CTPA or perfusion scan of the lungs in order to exclude pulmonary embolism. When a perfusion scan (early years) was performed, the findings were suggestive of a right-to-left shunt if the radioactive product was found in extrapulmonary sites (brain, kidney, spleen) [20, 21].
Heart Disease Screening and False Hypoxemia in the Neonate
Published in Fetal and Pediatric Pathology, 2023
David Rabiço-Costa, Laura Leite-Almeida, Sara Geraldes Paulino, Nuno Santos, Ana Cristina Gomes, Gustavo Rocha
The infectious work up revealed an elevation of C-reactive protein of 54.8 mg/L and anemia (11.2 g/L). He was started on ampicillin plus gentamicin. The blood cultures were negative and the SpO2 remained low (86%). The hyperoxia test had no response, the chest radiograph and the 2D-ecocardiogram were normal. ABG analysis revealed normal PaO2 and SaO2.