Using Measurements of Shunt and Ventilation-to-Perfusion Ratio to Quantify the Severity of Bronchopulmonary Dysplasia

Abstract

Background: Classifying the severity of bronchopulmonary dysplasia (BPD) by continuous numerical variables would facilitate follow-up of disease progression and quantified analysis of disease determinants. Objectives: To non-invasively measure oxygenation impairment in BPD by the degree of right-to-left shunt, right shift of the oxyhaemoglobin dissociation curve and ventilation/perfusion (V_A/Q) inequality and to explore their relation with clinical parameters. Methods: Prospective cohort study of 24 infants with a median (interquartile range, IQR) gestation of 25 weeks (24-27) and a birth weight of 0.70 kg (0.63-0.93), studied at 36 days (30-66), at a postmenstrual age (PMA) of 33 weeks (29-36). Inspired oxygen (F_IO₂) was varied to obtain three to five transcutaneous oxygen saturation (SpO₂) values between 85 and 96%. Values of shunt, shift and V_A/Q were obtained by plotting the paired data of SpO₂ against F_IO₂ for each infant using a unique program. Right-to-left shunt, right shift of the oxyhaemoglobin dissociation curve and V_A/Q were measured in infants born <32 weeks PMA receiving oxygen at 28 days. Results: The median (IQR) shunt was 8% (0.3-16.5), shift 14.5 kPa (10.9-19.4) and V_A/Q 0.40 (0.30-0.48). Shunt, shift and V_A/Q were significantly related to gestational age (GA) at birth, PMA at study, weight at study and weight gain per week. Conclusions: Severity of pulmonary oxygenation impairment in BPD can be quantified at the cot-side by non-invasive measurement of shunt, shift and V_A/Q. Low GA at birth, low weight at birth and at the time of study and impaired weight gain are significantly associated with the severity of oxygen-exchange impairment in infants with BPD.

Physiology and Predictors of Impaired Gas Exchange in Infants with Bronchopulmonary Dysplasia

“…Strengths of our study include the large cohort size and the use of sub-atmospheric oxygen concentrations to obtain outcome measures across the no BPD to severe BPD spectrum (2). These features distinguish this study from previous smaller (≤ 32 infants), and underpowered investigations (9,11,12), and facilitated identification of physiological thresholds for shift, VA/Q and shunt that align with the NIH classification of BPD severity (2).…”

“…Previous studies in preterm infants are limited by the small cohort size (≤32 infants) (9-12), a focus on infants with moderate to severe BPD, (9)(10)(11) and compensation for adult rather than fetal hemoglobin. (9)(10)(11)(12). Full utility and application of the SpO2 vs PIO2 approach requires application of the methodology across the full range of severity of BPD.…”

Predictors of outcome of prematurely born infants with pulmonary interstitial emphysema

“…The P A‐a O 2 was derived from the following equation: where P I O 2 is the partial pressure of inspired oxygen and R the expiratory exchange ratio assumed to be 0.85. Using two paired values of F I O 2 and SpO 2 corresponding to the highest and lowest value of SpO 2 six hours before the radiograph and using the foetal curve as a reference, we calculated for each infant the ventilation‐perfusion ratio (V A /Q), the right shift of the oxyhaemoglobin dissociation curve and the percentage of right to left shunt .…”

Influence of pulmonary factors on pulse oximeter saturation in preterm infants

“…All of the infants in this report had BPD where the dominant gas exchange abnormality is a reduced V A /Q 7 12 13 19. Earlier in the clinical course, when the alveoli are more unstable and there is more intrapulmonary shunting, the same method could be applied but the slopes would be predicted to be flatter.…”