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NIV: the acute and domiciliary settings
S70 Non-invasive ventilation (NIV) in Chronic Obstructive Pulmonary Disease (COPD) exacerbations with acute hypercapnic respiratory failure (AHRF) with pH
  1. A Thomas1,
  2. B Beauchamp1,
  3. B Chakraborty2,
  4. E Gallagher1,
  5. A Ali1,
  6. R Mukherjee1,
  7. D Banerjee1
  1. 1Heart of England NHS Foundation Trust, Birmingham, UK
  2. 2School of Mathematics, University of Birmingham, Birmingham, UK

Abstract

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.

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