Dear Editor,

I read with interest the paper of Baranwal et al. [1] on the use of a 24-h versus a 6-h pre-extubation (pretreatment) protocol of dexamethasone (24hPD vs. 6hPD) to prevent post-extubation airway obstruction (PEAO) in children in a resource-limited pediatric intensive care unit. The primary outcome of the study was the occurrence of clinically significant PEAO, as defined by a composite indicator comprised of a modified version of Westley’s croup score (mWCS) of ≥4, which required adrenaline nebulization treatment(s) and/or reintubation during the 48-h post-extubation period.

As I was evaluating the paper, I noticed that the relative risk (RR) for the primary outcome was incorrectly calculated. Based on the information provided in the paper, the 2 × 2 table is:

 

24hPD

6hPD

Total

+PEAO

43

48

91

−PEAO

23

10

33

Total

66

58

124

Event rate (%)

65

83

 

The RR for PEAO should be calculated as 0.79 [95 % confidence interval (CI) 0.63–0.97]:

$$ \frac{{{\text{Probability}}\;{\text{of}}\;{ + }\;{\text{PEAO}}\;{\text{in}}\; 2 4 {\text{hPD}}}}{{{\text{Probability}}\;{\text{of}}\;{ + }\;{\text{PEAO}}\;{\text{in}}\; 6 {\text{hPD}}}}{ = }\frac{{\left( { 4 3 / 6 6} \right)}}{{\left( { 4 8 / 5 8} \right)}}{ = 0} . 7 9. $$

However, the RR is reported in the paper as 2.02 (95 % CI 1.05–3.88), and it appears as if the authors calculated the RR as:

$$ \frac{{{\text{Probability}}\;{\text{of}}\;{ - }\;{\text{PEAO}}\;{\text{in}}\; 2 4 {\text{hPD}}}}{{{\text{Probability}}\;{\text{of}}\;{ - }\;{\text{PEAO}}\;{\text{in}}\; 6 {\text{hPD}}}}{ = }\frac{{\left( {23/66} \right)}}{{\left( {10/58} \right)}}{ = 2} . 0 2. $$

A similar error was made in calculating the RR for reintubation alone. The RR for reintubation should be calculated as 0.53 (95 % CI 0.19–1.49):

$$ \frac{{{\text{Probability}}\;{\text{of}}\;{ + }\;{\text{reintubated}}\;{\text{in}}\; 2 4 {\text{hPD}}}}{{{\text{Probability}}\;{\text{of}}\;{ + }\;{\text{reintubated}}\;{\text{in}}\; 6 {\text{hPD}}}}{ = }\frac{{\left( { 5 / 6 1} \right)}}{{\left( { 9 / 5 8} \right)}}{ = 0} . 5 3. $$

In contrast, the RR for reintubation in the paper is reported as 1.09 (95 % CI 0.96–1.25), and it appears as if the authors calculated the RR for reintubation as:

$$ \frac{{{\text{Probability}}\;{\text{of}}\;{ - }\;{\text{reintubation}}\;{\text{in}}\; 2 4 {\text{hPD}}}}{{{\text{Probability}}\;{\text{of}}\;{ - }\;{\text{reintubation}}\;{\text{in}}\; 6 {\text{hPD}}}}{ = }\frac{{\left( { 5 6 / 6 1} \right)}}{{\left( { 4 9 / 5 8} \right)}}{ = 1} . 0 9. $$

Finally, the RR for the secondary outcome, i.e., measuring the number of patients requiring epinephrine nebulization treatments, should be calculated as 0.76 (95 % CI 0.61–0.95):

$$ \frac{{{\text{Probability}}\;{\text{of}}\;{ + }\;{\text{adrenaline}}\;{\text{NEB}}\;{\text{in}}\; 2 4 {\text{hPD}}}}{{{\text{Probability}}\;{\text{of}}\;{ + }\;{\text{adrenaline}}\;{\text{NEB}}\;{\text{in}}\; 6 {\text{hPD}}}}{ = }\frac{{\left( { 3 9 / 6 1} \right)}}{{\left( { 4 1 / 4 9} \right)}}{ = 0} . 7 6. $$

The authors calculated the RR as 2.21 (95 % CI 1.2–7.3), and it appears that the RR for the secondary outcome was calculated as:

$$ \frac{{{\text{Probability}}\;{\text{of}}\;{ - }\;{\text{adrenaline}}\;{\text{NEB}}\;{\text{in}}\; 2 4 {\text{hPD}}}}{{{\text{Probability}}\;{\text{of}}\;{ - }\;{\text{adrenaline}}\;{\text{NEB}}\;{\text{in}}\; 6 {\text{hPD}}}}{ = }\frac{{\left( { 2 2 / 6 1} \right)}}{{\left( { 8 / 4 9} \right)}}{ = 2} . 2 1. $$

In addition, I noticed that in the RR calculation for the reintubation rate there seems to be five children missing from the 24hPD analysis group, making the total n reported 119 patients rather than the 124 patients included in the per protocol analysis in the study. There is no explanation as to why these five children in the treatment group are missing from the analysis.