The respiratory rate is a key part of our assessment of illness and underpins many a paediatric early warning score. It’s time for me to go back to the basics again.
I’ve looked at a few things now:
- How accurate are we at taking a temperature?
- How good are we at determining dehydration?
- How good are we at estimating weights?
- How reliable is capillary refill?
Now, I am going to take a look at how good we are at measuring respiratory rate. Respiratory rate/effort is one of the sides of the Paediatric Assessment Triangle, so we should be good at it. Respiratory rate, along with the presence of intercostal recession, is one of the clinical parameters suggested by the World Health Organisation to determine whether a patient might have pneumonia and require antibiotics. They suggest that a respiratory rate of 60 or more in infants under two months of age, 50 or more in 2- to 11-month-olds, and 40 or more in those greater than 12 months old is required to make a diagnosis of a lower respiratory tract infection.
Let’s start with a seemingly straightforward question. What are you actually counting? It’s probably not one of those things you have ever thought of. You just do it – or put down some sort of random number that seems about right.
Jensen et al., when they were looking at the interobserver reliability of respiratory rate measurement in premature infants, used ten different methods – visual and auscultatory – to determine the rate. If you are wracking your brain to come up with ten, here they are…
Visual
- Full view of infant
- Close-up view of chest and abdomen
- Cross table lateral view of chest and abdomen
- Close-up view of the neck and upper chest
- Close-up view of head and face
Auscultatory
- Stethoscope held over mouth and nose
- A stethoscope held over the trachea
- Anterior lung fields bilaterally
- Lateral lung fields bilaterally
- Posterior lung fields bilaterally
Rather niftily, they video-recorded this 3-minute examination and then played it to a bunch of observers. When the examiners reviewed their recordings a couple of weeks later, there was an excellent agreement between what they thought they saw at the time and what they saw on the tape (intraclass correlation coefficient (ICC) 0.84 CI 0.71-0.96). Unfortunately, the ICC for the external observers ranged from a poor (0.22) to a fair (0.73) agreement. Visual cues, such as subcostal or suprasternal retractions or head bobbing, nasal flaring or thoracoabdominal dyssynchrony, were more useful than the auditory cues.
This study used 12-second samples for each area examined. Isn’t it better to actually count for a whole minute? The WHO certainly think so. Because of the natural variability of respiratory rate, young infants can have a baseline rate of over 50 despite being perfectly normal if it is only measured on one occasion. As with all vital sign measurements, it is the trend over time that is important. Is the rate going up, coming down, or staying constant? A one-off reading every 4 hours cannot give you that information.
What determines respiratory rate?
Here is a great video from Armando Hasudungan to refresh your basic physiology…
So what is normal?
Most of the charts that we use are based on PALS data, but according to Fleming et al., they are based on two textbooks that don’t even cite their sources. In these modern times of evidence-based medicine, is that accurate enough for you? It wasn’t for them, so they ran a systematic review and only found 20 studies looking at respiratory rate, totalling 3881 children. You can see the centile charts reproduced below.
It’s quite clear that the rate really drops off after the first couple of years from a median of 44 breaths/minute to 26 breaths/minute.
O’Leary et al. went a little further, though, than Flemings’ systematic review and looked at individual patient data for 111,696 encounters. Although this was a single-centre study, the number of data points is much greater by two orders of magnitude. They show that children under the age of three have a lower centile range than previously thought and that as a child gets older, the centiles are higher than those suggested by the Fleming data set.
It is worth taking a look at where your hospital gets its ‘normal observations’ from. The DFTB normal vital signs are based on standard APLS values, which are probably the least accurate with low provenance. The RCH normal physiological values are derived from the Bonafide data, though they do recognise that differing datasets do exist. Unfortunately, they then state that they have chosen these values because they are more representative of unwell children.
When you take a look at the studies, you can see that the rate also depends on where the measurement is taken – in the emergency department, on the ward, or in the school classroom.
A number of psychological factors can also influence respiratory rate, including fear, pain and apprehension.
The rise of the machines?
Instead of relying on a human observer, we could use technology to capture and record respiratory rates. There are a number of proprietary devices that can be attached to measure respiratory rate, such as nasal ETCO2 monitors or nasal thermocouples. There is evidence, however, that having such a device fixed to your face might artificially elevate the respiratory rate.
I’ve written before about the idea of using video reflectance photoplethysmography. It is certainly within the boundaries of current technology to detect respiratory rates based on video footage and computer algorithms. Once this technology becomes more robust, I can foresee a future when we might have a more accurate means of collecting patient physiologic data.
Electronic health records also have something going for them. They allow us to gather large volumes of data related to vital signs. Sepanski et al. interrogated a large multi-centre database of records for 16 hospitals over a 4-year period. With over 1.2 million patient encounters, they were able to create centile curves for respiratory rate by age and compare them with the traditionally used charts. They found that whilst the 50th centile data was similar to the O’Leary and PALS data, the 95th centile RR was 7-11 breaths higher than that from O’Leary. If your facility uses a paediatric early warning system, it is worth considering exactly where the normal range data comes from.
So, what should you do?
Continue to include respiratory rate in your basic assessment of all children but be aware that it changes with time and circumstances.
Record the actual respiratory rate rather than guessing.
Try to measure over a minute if you can, rather than just 10 seconds.
If you are tracking rate over time (and you should), it should be performed by the same person to reduce inter-observer error.
Selected References
Bonafide CP, Brady PW, Keren R, Conway PH, Marsolo K, Daymont C. Development of heart and respiratory rate percentile curves for hospitalized children. Pediatrics. 2013 Apr 1;131(4):e1150-7.
Cretikos MA, Bellomo R, Hillman K, Chen J, Finfer S, Flabouris A. Respiratory rate: the neglected vital sign. Medical Journal of Australia. 2008 Jun 2;188(11):657.
Davies P, Maconochie I. The relationship between body temperature, heart rate and respiratory rate in children. Emergency Medicine Journal. 2009 Sep 1;26(9):641-3.
Jensen EA, Panitch H, Feng R, Moore PE, Schmidt B. Interobserver Reliability of the Respiratory Physical Examination in Premature Infants: A Multicenter Study. The Journal of pediatrics. 2016 Nov 1;178:87-92.
Morley CJ, Thornton AJ, Fowler MA, Cole TJ, Hewson PH. Respiratory rate and severity of illness in babies under 6 months old. Archives of disease in childhood. 1990 Aug 1;65(8):834-7.
O’Leary F, Hayen A, Lockie F, Peat J. Defining normal ranges and centiles for heart and respiratory rates in infants and children: a cross-sectional study of patients attending an Australian tertiary hospital paediatric emergency department. Archives of disease in childhood. 2015 Apr 8:archdischild-2014.
Rusconi F, Castagneto M, Porta N, Gagliardi L, Leo G, Pellegatta A, Razon S, Braga M. Reference values for respiratory rate in the first 3 years of life. Pediatrics. 1994 Sep 1;94(3):350-5.
Sepanski RJ, Godambe SA, Zaritsky AL. Pediatric Vital Sign Distribution Derived From a Multi-Centered Emergency Department Database. Frontiers in Pediatrics. 2018 Mar 23;6:66.
Simoes EA, Roark R, Berman S, Esler LL, Murphy J. Respiratory rate: measurement of variability over time and accuracy at different counting periods. Archives of disease in childhood. 1991 Oct 1;66(10):1199-203.
Tarassenko L, Villarroel M, Guazzi A, Jorge J, Clifton DA, Pugh C. Non-contact video-based vital sign monitoring using ambient light and auto-regressive models. Physiological measurement. 2014 Mar 28;35(5):807.
Thompson M, Mayon-White R, Harnden A, Perera R, McLeod D, Mant D. Using vital signs to assess children with acute infections: a survey of current practice. Br J Gen Pract. 2008 Apr 1;58(549):236-41.
Valman HB, Wright BM, Lawrence C. Measurement of respiratory rate in the newborn. British Medical Journal (Clinical Research ed.). 1983 Jun 4;286(6380):1783.
Wallis LA, Healy M, Undy MB, Maconochie I. Age-related reference ranges for respiration rate and heart rate from 4 to 16 years. Archives of disease in childhood. 2005 Nov 1;90(11):1117-21.
World Health Organization. Technical bases for the WHO recommendations on the management of pneumonia in children at first-level health facilities.
