Introduction and objectives Factors predicting the likelihood of failure of NIV, i.e. requirement of intubation or death, have been well documented with low pH shown to be the most important factor. Factors affecting the duration of NIV required in those patients who receive ward base treatment without the need for intubation have not been established. This study aimed to identify factors which influence the duration of NIV required in acute hypercapnic respiratory failure.

Methods A retrospective analysis of 123 consecutive episodes of acute hypercapnic respiratory failure requiring NIV between June 2013 and June 2014 was carried out. Correlation between duration of NIV treatment and a number of variables, namely admission creatinine, pH, worst arterial carbon dioxide level (CO₂) and presence and severity of chronic kidney disease (CKD) was assessed by simple linear regression.

Results There was a statistically significant regression coefficient between worst observed CO₂ and the duration of NIV (fitted equation: NIV Duration = 4.281 + 14.357 × Worst CO₂, p = 0.019). The plotted linear relationship showed an increase in duration of NIV treatment of 14.35 h for every 1 kPa increase in CO₂ above 6 kPa. The admission creatinine and severity of CKD did not significantly alter the duration of NIV required. The presence of acute kidney injury was also not significant. The pH value did not significantly alter the duration of NIV treatment.

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Abstract P42 Figure 1

NIV duration plotted against worst CO₂. Linear regression fitted equation shown (duration NIV (hours) = 4.281 + 14.357 x Worst CO₂)

Conclusion This survey shows that the level of CO₂ influences the duration of acute NIV required, in that for every 1 kPa rise in CO₂, the duration of acute NIV treatment rises by 14.35 h. The other studied variables do not correlate with treatment duration.