S. L. Watkin’s research while affiliated with Staffordshire and Stoke-On-Trent Partnership NHS Trust and other places

Objective: The aim of this study was to compare the ability of NIRS and pulse oximetry to detect changes in cerebral oxygenation occurring in response to a pause in nasal airflow (PNA). Methods: Twenty-one recordings of cerebral oxygenation index by NIRS together with oxyhemoglobin saturation by pulse oximetry were measured on 17 preterm infants with a history of apnoea. Photoplethysmography was used to confirm the accuracy of the pulse oximetry data. PNA events were defined as pauses of greater than 4 seconds in a thermistor trace measuring nasal air flow. Results: Baseline variability in oxygenation index (Hbdiff) was found to be from -0.12 to +0.13 micromol 100 g brain(-1). A fall in Hbdiff or SpO2 was defined as a decrease of greater magnitude than 2 standard deviations from the baseline, i.e., -0.12 micromol 100 g brain(-1) and 3% respectively. In 68% of 468 PNA events a fall in oxyhemoglobin saturation (SpO2) was detected and in 56% a fall in Hbdiff was detected. In 20% of events there was no fall in cerebral oxygenation despite a fall in SpO2. In 8% of PNA episodes we recorded a fall in cerebral oxygenation but no fall in SpO2. When a fall in cerebral oxygenation was recorded, the fall was greater when the event was also associated with a fall in SpO2 (median (interquartile range (IQR)) 0.32 (0.21-0.69) vs. 0.25 (0.16-0.43) micromol 100 g brain(-1), p < 0.05). When all the PNA episodes were reviewed no close correlation was shown between the magnitude of change in cerebral oxygenation and the change in SpO2 for small changes in both indices. However, large falls (>1.5 micromol 100 g brain(-1)) in cerebral oxygenation were closely associated with large changes in SpO2. Conclusions: We conclude that both techniques are sensitive to changes in oxygenation during PNA. Small changes in cerebral Hbdiff and arterial SpO2 do not always correlate for physiological reasons. A change in Hbdiff of >0.3 micromol 100 g brain(-1) is likely to be physiologically significant and is associated with a change in SpO2 of 12%.

Physiological recordings were undertaken to study the temporal relationship between apnea, defined as pauses in nasal airflow (PNA), and desaturation in preterm infants. Seventeen infants with a history of apnea of prematurity were studied on 21 occasions. Median (range) birthweight was 1,180 g (575–2,475) and gestation was 30 weeks (26–33). Median age at time of study was 10 days (range, 2–52). Arterial beat to beat oxygen saturation (SaO2), photoplethysmographic waveform, electrocardiogram, abdominal and ribcage breathing movements, and nasal airflow were recorded. Falls in SaO2 ≥ 3% occurring during or after a PNA ≥ 4 seconds were recorded. Episodes of periodic breathing were excluded from this analysis. Four hundred and sixteen episodes of PNA and desaturation were analyzed. Application of a definition of “outliers” for non-parametric data suggested an association when the desaturation occurred up to 7.20 seconds after the end of the PNA for infants nursed in air. For infants on oxygen treatment, a temporal association was suggested when desaturation occurred up to 9.76 seconds after the end of PNA. Pediatr Pulmonol. 1996; 21:171–175.