Volume 189 - Issue 9
Respiratory rate: the neglected vital sign
Authors: Olivier Steichen, Gilles Grateau and Eric Bouvard
Med J Aust 2008; 189 (9): 531-532. || doi: 10.5694/j.1326-5377.2008.tb02164.x
Published online: 3 November 2008
Published online: 3 November 2008
To the Editor: Cretikos et al make a strong case for routinely recording patients’ respiratory rate (RR) in acute wards.1
In a prospective study designed to evaluate the prognostic value of RR in acutely hospitalised patients aged over 75 years, we analysed data from all admissions to a single 14-bed acute-care geriatric unit between 15 May and 15 November 2007. Clinical data were recorded on admission and blood tests were performed the next morning. The Charlson score was used to assess comorbidity.2
Features of the 195 admissions during the study period (13 patients were admitted twice) are reported in the Box. The main reasons for admission were falls (15%), left ventricular failure (11%), pneumonia (11%), cancer complications (9%), pyelonephritis (7%) and stroke (5%). Twenty-nine patients died in hospital, including six from cancer complications, five from pneumonia, four from pyelonephritis and four from left ventricular failure.
Based on univariate logistic regression analysis at the 0.05 significance level, the following variables were predictive of death during hospitalisation: being male (odds ratio [OR], 2.42, Wald test P = 0.03); increased Charlson score (OR, 1.50 for each additional point between 3 and 13; P < 0.001); decreased systolic blood pressure (OR, 6.71 for systolic blood pressure < 100 mmHg; P =0.004); abnormal heart rate (< 60 beats/min or > 100 beats/min) (OR, 3.63; P = 0.003); increased RR (OR, 1.81 for each additional 5 breaths/min between 14 and 44; P < 0.001); abnormal blood sodium level (< 137 mmol/L or > 143 mmol/L) (OR, 2.82; P = 0.01) and raised C-reactive protein level (OR, 2.67 for C-reactive protein level > 45 mg/L; P = 0.02).
After multivariate logistic regression analysis with stepwise backward elimination, the only remaining factors that were significant predictors of death during hospitalisation were Charlson score (OR, 1.53 for each additional point between 3 and 13; P < 0.001) and RR (OR, 1.83 for each additional 5 breaths/min between 14 and 44 breaths/min; P < 0.001).
RR on admission was associated with an area under the ROC (receiver operating characteristic) curve of 0.73 (95% CI, 0.64–0.82) for the prediction of death during hospitalisation. An RR of ≥ 20 breaths/min had a sensitivity of 97% (95% CI, 80%–100%), a specificity of 28% (95% CI, 21%–35%) and a negative likelihood ratio of 0.12 (95% CI, 0.02–0.82) for prediction of death during hospitalisation. Only one patient (admitted for stroke) with an RR of < 20 breaths/min at admission died in hospital. Higher RR cut-off values increased specificity but reduced sensitivity. For instance, an RR of ≥ 30 breaths/min had a specificity of 90% (95% CI, 84%–94%), but a sensitivity of 38% (95% CI, 21%–58%), leading to a positive likelihood ratio of 3.68 (95% CI, 1.93–7.04) for prediction of death during hospitalisation.
In conclusion, besides comorbidity (Charlson score), RR was the most useful predictor of death in acutely hospitalised patients aged over 75 years. Our results extend the evidence base promoting regular documentation of RR in acute-care departments.1
References
- Cretikos MA, Bellomo R, Hillman K, et al. Respiratory rate: the neglected vital sign. Med J Aust 2008; 188: 657-659.
- Charlson M, Szatrowski TP, Peterson J, Gold J. Validation of a combined comorbidity index. J Clin Epidemiol 1994; 47: 1245-1251. 0_i1091834