The Noninvasive Ventilation Outcomes (NIVO) score: prediction of in-hospital mortality in exacerbations of COPD requiring assisted ventilation

Abstract

Introduction: Acute exacerbations of COPD (AECOPD) complicated by acute (acidaemic) hypercapnic respiratory failure (AHRF) requiring ventilation are common. When applied appropriately, ventilation substantially reduces mortality. Despite this, there is evidence of poor practice and prognostic pessimism. A clinical prediction tool could improve decision making regarding ventilation, but none is routinely used.

Methods: Consecutive patients admitted with AECOPD and AHRF treated with assisted ventilation (principally noninvasive ventilation) were identified in two hospitals serving differing populations. Known and potential prognostic indices were identified a priori. A prediction tool for in-hospital death was derived using multivariable regression analysis. Prospective, external validation was performed in a temporally separate, geographically diverse 10-centre study. The trial methodology adhered to TRIPOD (Transparent Reporting of a Multivariable Prediction Model for Individual Prognosis or Diagnosis) recommendations.

Results: Derivation cohort: n=489, in-hospital mortality 25.4%; validation cohort: n=733, in-hospital mortality 20.1%. Using six simple categorised variables (extended Medical Research Council Dyspnoea score 1-4/5a/5b, time from admission to acidaemia >12 h, pH <7.25, presence of atrial fibrillation, Glasgow coma scale ≤14 and chest radiograph consolidation), a simple scoring system with strong prediction of in-hospital mortality is achieved. The resultant Noninvasive Ventilation Outcomes (NIVO) score had area under the receiver operating curve of 0.79 and offers good calibration and discrimination across stratified risk groups in its validation cohort.

Discussion: The NIVO score outperformed pre-specified comparator scores. It is validated in a generalisable cohort and works despite the heterogeneity inherent to both this patient group and this intervention. Potential applications include informing discussions with patients and their families, aiding treatment escalation decisions, challenging pessimism and comparing risk-adjusted outcomes across centres.

Conflict of interest statement

Conflict of interest: T. Hartley reports grants from Philips Respironics and Pfizer OpenAir during the conduct of the study. Conflict of interest: N.D. Lane reports non-financial support for meeting attendance from Chiesi, grants from Bright Northumbria and The ResMed Foundation, outside the submitted work. Conflict of interest: J. Steer reports grants from Chiesi Ltd, outside the submitted work. Conflict of interest: M.W. Elliott reports personal fees for lectures from Philips, personal fees for consultancy and lectures from Resmed, outside the submitted work. Conflict of interest: M.P. Sovani reports grants from Radiometer, other (support for courses) from Resmed and Philips Respironic, personal fees for lectures from Chiesi, AstraZeneca and Boehringer Ingelheim, outside the submitted work. Conflict of interest: H.J. Curtis has nothing to disclose. Conflict of interest: E.R. Fuller has nothing to disclose. Conflict of interest: P.B. Murphy reports grants and personal fees from Philips, ResMed, F&P and B&D Electromedical, personal fees from Santhera and Chiesi, grants from GSK, outside the submitted work. Conflict of interest: D. Shrikrishna has nothing to disclose. Conflict of interest: K.E. Lewis reports other (medical director) from Respiratory Innovation Wales, outside the submitted work. Conflict of interest: N.R. Ward has nothing to disclose. Conflict of interest: C.D. Turnbull reports personal fees for consultancy from Bayer, outside the submitted work. Conflict of interest: N. Hart reports unrestricted grants from Philips and Resmed outside the area of work commented on here with the funds held and managed by Guy's & St Thomas' NHS Foundation Trust; financial support from Philips for development of the MYOTRACE technology that has patent approved in Europe and US outside the area of work commented on here; personal fees for lecturing from Philips-Respironics, Philips, Resmed and Fisher-Paykel outside the area of work commented on here; N. Hart is part of the pulmonary research advisory board for Philips, outside the area of work commented on here, with the funds for this role held by Guy's & St Thomas' NHS Foundation Trust. Conflict of interest: S.C. Bourke reports grants from Philips Respironics and Pfizer OpenAir during the conduct of the study; grants from GSK and ResMed, personal fees from AstraZeneca, Chiesi, Novartis, Pfizer and ResMed, and non-financial support from AstraZeneca, Boehringer Ingelheim, Chiesi and GSK, outside the submitted work.

Copyright ©The authors 2021.

Figures

FIGURE 1

The Noninvasive Ventilation Outcomes (NIVO) score. Maximum score of 9, as cannot score for both extended Medical Research Council dyspnoea scale (eMRCD) 5a and 5b. Atrial fibrillation (AF) should be positively scored if: persistent AF, new AF or paroxysmal AF (even if in sinus rhythm at initiation of ventilation). Time to acidaemia >12 h should be positively scored if: >12 h have elapsed between arrival at hospital and index episode of acidaemia.

FIGURE 2

Area under the receiver operating characteristic curve (95% CI) for the Noninvasive Ventilation Outcomes (NIVO) score and comparison scores within validation cohort. All scores in 24 h pre-ventilation. DECAF: Dyspnoea, Eosinopenia, Consolidation, Acidaemia and atrial Fibrillation; APACHE: Acute Physiology and Chronic Health Evaluation; CAPS: COPD and Asthma Physiology Score; CURB-65: confusion of new onset, blood urea nitrogen >7 mmol·L−1 (19 mg·dL−1), respiratory ⩾30 breaths·min−1; blood pressure <90 mmHg systolic or ≤60 mmHg diastolic, age ⩾65 years; HACOR: heart rate, acidosis, consciousness, oxygenation and respiratory rate.