Introduction Recent British guidelines on NIV suggest patients with AHRF and pH <7.26 on arterial blood gases (ABG) should be managed by critical care (ITU) depending upon local circumstances with a low threshold for intubation, unless NIV is deemed to be the ceiling of treatment. The 7.26 pH cut-off was derived from subgroup analysis of in-hospital mortality assessment from the study by Plant et al (Lancet 2000; 355:1931–5). The use of NIV as an alternative to endotracheal intubation in more severely acidotic COPD patients (pH<7.26) has been controversial but there is increasing evidence that the outcomes in such patients may not be any worse if treated with NIV.
Methods Analysis of initial ABG (pre-commencement of NIV) for AHRF secondary to COPD between 1 August 2004 and 31 December 2009 was performed. NIV was undertaken in a dedicated unit on a respiratory ward. The admission episodes were stratified by initial pH ranges (predictor variable) and in-hospital mortality was recorded (outcome variable).
Results Out of 728 (505 unique patients) admissions with COPD requiring NIV for AHRF, 282 admissions had a pH <7.26. Of these, 224 admissions survived to discharge (mortality 20.6%). Stratifying the admissions by pH categories of 0.05, there is no significant difference in the mortality with pH ranges 7.2–7.25 and 7.25–7.30 (p value=0.845). If all COPD admissions requiring NIV (n=728) are stratified into two groups above and below 7.2, the ratio of odds of survival below pH 7.2 drops sharply (p=0.000000088): Abstract S70 Table 1.
Conclusion Mortality in the group with pH 7.20–7.25 was similar to the group with pH 7.26–7.30, suggesting that NIV on a dedicated respiratory ward can manage COPD patients with AHRF and pH <7.26. Our findings suggest that it is probably justified to recommend that the initial pH cut-off is modified from pH >7.26 to pH >7.20 for ward-based NIV in COPD exacerbations with AHRF. This has important resource implications, given that more patients could be managed in a ward-based dedicated NIV unit rather than the utilising ITU beds in the UK National Health Service.