Variability of RRate: breathing and quality data

Background: Respiratory rate is difficult to measure, especially in
neonates who have an irregular breathing pattern. The World Health
Organisation recommends a one minute count, but there is limited data to
support this length of observation. We sought to evaluate agreement
between the respiratory rate (RR) derived from capnography in neonates,
over 15 seconds, 30 seconds, 120 seconds and 300 seconds, against the
recommended 60 seconds rate. Methods: Neonates at two hospitals in Nairobi
were recruited and had capnograph waveforms recorded using the Masimo Rad
97. A single high quality 5 minute epoch was randomly chosen from each
subject. For each selected epoch, the mean RR was calculated using a
breath-detection algorithm applied to the waveform. The RR in the first 60
seconds was compared to the mean RR measured over the first 15 seconds, 30
seconds, 120 seconds, full 300 seconds, and last 60 seconds. We calculated
bias and limits of agreement for each comparison and used Bland-Altman
plots for visual comparisons. Results: A total of 306 capnographs were
analysed from individual subjects. The subjects had a median gestation age
of 39 weeks with slightly more females (52.3%) than males (47.7%). The
majority of the population were term neonates (70.1%) with 39 (12.8%)
having a primary respiratory pathology. There was poor agreement between
all the comparisons based on the limits of agreement [confidence
interval], ranging between 11.9 [-6.79 to 6.23] breaths per minute in the
one versus two minutes comparison, and 34.7 [-17.59 to 20.53] breaths per
minute in the first versus last minute comparison. Worsening agreement was
observed in plots with higher RRs. Conclusions: Neonates have high
variability of RR, even over a short period of time. A slight degradation
in the agreement is noted over periods shorter than one minute. However,
this is smaller than observations done 3 minutes apart in the same
subject. Longer periods of observation also reduce agreement. For device
developers, precise synchronization is needed when comparing devices to
reduce the impact of RR variation. For clinicians, where possible,
continuous or repeated monitoring of neonates would be preferable to one
time RR measurements.