Volume 189 - Issue 9
Respiratory rate: the neglected vital sign
Authors: Simon C Gandevia and David K McKenzie
Med J Aust 2008; 189 (9): 531-532. || doi: 10.5694/j.1326-5377.2008.tb02165.x
Published online: 3 November 2008
Published online: 3 November 2008
To the Editor: The concept that respiratory rate (RR) is a key vital sign is hardly new,1 but it is being re-emphasised.2,3 The recent article by Cretikos et al3 highlights the diagnostic relevance of a raised RR for serious adverse events. The authors make sensible recommendations regarding the need to educate hospital staff about the importance of measuring patients’ RR.
However, they do not specify how this rate should be measured. Indeed, most textbooks of general medicine, and even respiratory medicine, fail to provide guidance on this or to define an abnormal rate. A widely used book on clinical examination4 suggests measuring RR while feeling the pulse, and quotes a normal (adult) resting range of 16–25 breaths/min, but no source for this information is provided.
There are few reports of true normal resting RR measurements obtained by covert observation. Respiratory physiologists have long known that RR commonly increases and becomes more regular as soon as a subject becomes aware of the measurement. This is especially so if a mouthpiece is in place. Rates as low as 8 breaths/min may be seen at rest, and the normal adult range quoted by physiologists is 11–14 breaths/min.5 Bradypnoea is usually defined as a rate less than 8 breaths/min and tachypnoea as a rate greater than 18–20 breaths/min.
There is no gold standard method for accurate measurement of RR in clinical practice. Of course, when patients are being monitored, particularly with a nasal cannula, it should be easy to obtain the rate. Oximetry is not a surrogate measure of RR, although it is often easier to record. Inductance bands around the chest provide a simple non-invasive way to measure RR. In addition to the absolute rate, an irregular and erratic rate is of concern.
In settings in which formal monitoring is not being conducted, RR is the one “vital” sign that must be assessed when the patient is resting quietly, unaware of its measurement, and not conversing with staff. Duplicate measurements should be made over an interval of at least 1 minute. An RR of over 20 breaths/min, particularly if irregular, is noteworthy. Tachypnoea is intimately linked with the sensation of breathlessness, and hence the patient’s respiratory sensations should be assessed. In some patients with a normal RR at rest, marked tachypnoea may be precipitated by mild exertion, such as walking a few paces.
References
- Lenfant C. Time-dependent variations of pulmonary gas exchange in normal man at rest. J Appl Physiol 1967; 22: 675-684.
- Cullinane M, Findlay G, Hargraves C, et al. An acute problem? London: National Confidential Enquiry into Patient Outcomes and Death, 2005. http://www.ncepod.org.uk/2005aap.htm (accessed Aug 2008). 0_i1091840
- Cretikos MA, Bellomo R, Hillman K, et al. Respiratory rate: the neglected vital sign. Med J Aust 2008; 188: 657-659. 0_i1091842
- Talley NJ, O’Connor S. Clinical examination: a systematic guide to physical diagnosis. 5th ed. Sydney: Churchill Livingstone, 2006. 0_i1091844
- Comroe JH, Forster RE, Dubois AB, et al, editors. The lung: clinical physiology and pulmonary function tests. 2nd ed. Chicago: Year Book Medical Publishers, 1962. 0_i1091846