A randomized controlled study investigated the effects of single-dose dexmedetomidine on emergence delirium (ED) in children who were under anesthesia induced with sevoflurane. A total of 2,500 patients age 2-7 who were scheduled for tonsillectomy were enrolled in the study; 80% were randomized to receive dexmedetomidine 0.5 μg/kg or volume-matched normal saline over 10 minutes after induction of anesthesia. The primary outcome was the incidence of ED within 30 minutes after extubating. The results show an incidence of ED of 300 cases per 1,000 patients for dexmedetomidine and 500 cases per 1,000 patients for saline. Which of the following is the best estimate of the absolute risk reduction for ED following dexmedetomidine compared to saline?
Common measures of therapeutic efficacy | ||
Term | Definition | Calculation |
Absolute risk reduction (ARR) | Percentage indicating the actual difference in event rate between control & treatment groups | ARR = control rate – treatment rate |
Relative risk reduction (RRR) | Percentage indicating relative reduction in the treatment event rate compared to the control group | RRR = ARR / control rate |
Relative risk (RR) | Ratio of the probability of an event occurring in the treatment group compared to the control group | RR = treatment rate / control rate |
Number needed to treat (NNT) | Number of individuals who need to be treated to prevent a negative outcome in 1 patient | NNT = 1 / ARR |
This randomized controlled study compared the incidence of emergence delirium (ED) in children who underwent tonsillectomy while under anesthesia induced with sevoflurane. Participants were randomized to receive dexmedetomidine 0.5 μg/kg (ie, treatment group) or volume-matched normal saline (ie, control group) over 10 minutes after induction of anesthesia. A total of 2,500 patients were enrolled in the study, but only 2,000 (= 0.80 × 2,500) were randomized into treatments (Choice A). The incidence of ED was as follows:
These results indicate that the absolute risk reduction (ARR) (ie, control rate − treatment rate) in ED between groups is (500 / 1,000) − (300 / 1,000) = 0.20. ARR = 0.20 indicates that 20% of patients did not develop ED as a result of having received dexmedetomidine rather than saline.
(Choice C) The calculation (300 / 1,000) / (500 / 1,000) = 0.60 provides the relative risk (RR) (ie, treatment rate / control rate). RR = 0.60 indicates that the risk of ED in the dexmedetomidine group is 0.60 the risk of ED in the saline group.
(Choice D) The calculation 1 / [(500 / 1,000) − (300 / 1,000)] = 5 provides the number needed to treat (NNT) (ie, 1 / ARR). NNT = 5 indicates that 5 of the patients undergoing tonsillectomy had to be given dexmedetomidine 0.5 μg/kg over 10 minutes after induction of anesthesia with sevoflurane to avoid 1 case of ED (compared to saline).
(Choice E) The calculation [(500 / 1,000) − (300 / 1,000)] / (500 / 1,000) = 0.40 provides the relative risk reduction (RRR) (ie, ARR / control rate). RRR = 0.40 indicates that dexmedetomidine offers a 40% reduction in ED compared to saline.
Educational objective:
Absolute risk reduction (ARR) is the difference in event rate between a control group and a treatment group (ie, the percentage of patients improved by treatment). It is calculated as:
ARR = control rate − treatment rate