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Introduction NIV is utilised to manage acute hypercapnic respiratory failure, improving patient outcomes with decreased mortality, length of stay (LOS) and re-admission. Early reversal of acidosis is associated with survival and a critical treatment goal. 1 The British Thoracic Society (BTS) NIV guidelines provide general recommendations but do not specify target tidal volumes (TV). Trust NIV guidelines recommend TV’s of 7–10 ml/kg of Ideal Body Weight (IBW) but little evidence supports this. We aimed to review adherence to trust guidelines and whether TV-IBW influenced clinical outcomes.Method A retrospective, observational study was completed at a large UK NHS Hospital between October 2022-March 2024. Using electronic health records; patient demographics and NIV characteristics were collected. This included TV at 15-minute intervals (following initiation), inspiratory/expiratory positive airway pressures, treatment duration and time to reversal, defined as a pH level >7.35, categorised as: <1hour/1–3 hours/4–24 hours/>24 hours.Results Data was available for N=95 patients ( table 1). No significant association was seen between demographics and TV-IBW (P>0.2). Most patients had COPD (79%) or OSA/OHS (17%) with median NIV duration being 6 days. Median TV was 598 ml (IQR:458–763), correlating to 10.7 ml/kg-IBW (IQR:8.7–13.5), Only N=32 (34%) patients TV-IBW were trust guideline compliant, 58% (N=55) had values above this range.Reversal was achieved in <1 hour in N=39 (41%). Increasing TV-IBW was associated with significantly shorter reversal times (rho:-0.225,p=0.028) with 51% of patients >10.0 ml/kg-IBW reversing in <1hour. Additionally, a significantly lower on-NIV mortality rate, with the single death in the patient with the lowest TV-IBW value in the cohort.Abstract S79 Table 1Associations between cohort characteristics and TV-IBWConclusion This is the first study to review TV-IBW targets during NIV initiation and possible correlations to clinical outcomes. Only 34% of patients were compliant with trust guidelines, with the majority being above the TV-IBW target. Increasing TV-IBW was associated with progressively improved clinical outcomes, including shorter acidosis reversal times and lower on-NIV mortality. A review of local NIV guidelines would be warranted. Further research could compare current BTS guidelines vs efficacy of targeting >10 ml/kg-IBW.Reference Osadnik CR, et al. Non-invasive ventilation for the management of acute hypercapnic respiratory failure due to exacerbation of chronic obstructive pulmonary disease. Cochrane Library 2017(7). https://doi.org/10.1002/14651858.cd004104.pub4