Saturation Oxygen Pressure Index for Assessment of Pulmonary Disease in Neonates on

research letter

Indian Pediatr 2015;52: 74-75

Saturation Oxygen Pressure Index for Assessment of Pulmonary Disease in Neonates on
Non-invasive Ventilation

*Srinivasa M Doreswamy, Aravanan A Chakkarapani and Prashanth Murthy

Department of Paediatrics, Division of Neonatology, McMaster University, Hamilton, Ontario, Canada.
Email: *[email protected]

This prospective observational study on 36 neonates aimed to estimate the correlation between the new Saturation Oxygen distending Pressure Index (SOPI) and Oxygenation index. SOPI had high correlation (r=0.94) with oxygenation index. SOPI of <2, 2, and 3.7 represented mild, moderate and severe pulmonary disease, respectively with high sensitivity and specificity.

Keywords: Acute lung disease, Newborn, Non-invasive ventilation, SOP index.

Neonates with respiratory distress need continuous distending pressure to achieve adequate functional residual capacity. Any change in the severity of pulmonary disease is reflected as a change in need for the distending pressure or fraction of inspired oxygen (FiO2) or both. A tool incorporating these parameters would potentially help in objectively assessing the severity of the pulmonary disease.

Current assessment of pulmonary disease is with blood gas, chest X-ray and Oxygenation index (OI). OI cannot be calculated for babies on Continuous Positive Airway Pressure (CPAP) and Non-invasive Positive Pressure Ventilation (NIPPV), and has resource implications. A non-invasive assessment tool would allow clinicians to use it more frequently. Non-invasive tools such as Oxygen saturation index and Respiratory severity score [1,2] cannot be used in babies on CPAP or non-invasive ventilation. Saturation (SPO₂), Oxygen (FiO₂) and distending Pressure (PEEP) index, or SOP index, attempts to objectively score respiratory disease with parameters available in babies on CPAP or non-invasive ventilation.

This was a single-centre prospective observational study undertaken in a Canadian tertiary care Neonatal intensive care unit (NICU). Our primary objective was to evaluate if the SOP index correlates with Oxygenation index in neonates. Secondary objective was to find the cut-off values of SOP index for mild, moderate and severe pulmonary disease. Both term and preterm neonates on conventional mechanical ventilation were enrolled. Babies with severe congenital anomalies and congenital heart disease and SPO2 above 98% were excluded from the study. Consent waiver for the study was provided by the McMaster Research Ethics Board.

SOP index was calculated by the formula, PEEP X FiO₂/ SpO₂. PEEP, FiO2 and SpO2 on the monitor was recorded prior to arterial blood gas sampling. SPO2 was recorded when there was a good waveform.

Thirty-six patients were recruited and total of 72 data sets were obtained. The first obtained value for each patient was separately tabulated. Pearson product moment correlation between SOP index and Oxygenation index was calculated. All the data sets combined were analyzed using linear mixed model effect with random intercept for predictive equation. We calculated sensitivity and specificity of SOP index corresponding to oxygenation index of <5, 5 -15 and >15 using ROC curve. We did not stratify the patients according to gestational age.

Pearson product moment correlation (r) of 0.94 (P=0.001) was noted between SOP index and Oxygenation index (Fig.1). The calculated predictive equation for SOP index was 0.28 X OI + 0.87. SOP indices corresponding to OI <5 (mild), 5-15 (moderate) and >15 (severe lung disease) are <2, 2 to 3.7 and >3.7, respectively. With 89% sensitivity and 94% specificity. The sensitivity and specificity of SOP index for mild, moderate and severe pulmonary disease was 89.5% and 94.1%, 89.5% and 94.1%, and 100% and 94.6%, respectively.

Fig. 1 Linear correlation between SOP index and Oxygenation index.

SOPI is calculated with PEEP. This makes it possible to use SOP index in babies who are on CPAP or NIPPV, where only PEEP is reliable. Lung injury assessment with PaO2:FiO2 [3] and Oxygenation index, which has been successfully used in neonates [4], can only be measured by an arterial puncture or indwelling catheter.

SOP index has very good correlation with oxygen index. SOPI of <2, 2 to 3.7 and greater than 3.7 indicates pulmonary disease with high sensitivity and specificity. SOP index has potential to be used for assessment of the severity of acute pulmonary disease in babies on CPAP and NIPPV.

Acknowledgement: Respiratory therapists at McMaster University NICU for their help in collecting the required data.

Contributors: SMD: conceived and designed the study. He analysed the data and prepared the manuscript; and will act as the guarantor. AAC: study design and collection of the data. He has revised and approved the manuscript. PM: helped in designing the study and data analysis. He has revised the manuscript and approved for submission.

Funding: None; Competing interests; None stated.

References

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