Mechanical Ventilation in patients with COPD

Predicting Outcomes of Mechanical Ventilation in patients with COPD

An elderly man with an infective exacerbation of COPD deteriorated during his medical admission with type 2 respiratory failure. He was commenced on ward-based non-invasive ventilation while establishing further history. He was on home nebulisers, was awaiting assessment for home oxygen, and was limited to household mobility only. He could not climb stairs. He had secondary polycythaemia. After discussion with the patient and family, a ward-based ceiling of care was set. He remained on NIV for several days before being weaned off and discharged to a rehabilitation facility after a two week admission.

Can we predict outcomes for patients with respiratory failure and COPD who require invasive ventilation?Prad Shanmugasundaram

 

Exacerbations of COPD present a significant healthcare burden. Non-invasive ventilation is the mainstay of treatment for these patients. However, a significant issue for intensivists presents itself when NIV fails, or is contraindicated. Accurately identifying those patients who would benefit from invasive ventilation, or more importantly those for whom invasive ventilation would be futile is an ongoing challenge.

The CAOS trial investigators attempted to shed further light on this. In the first of a sequence of trials they compared clinician-predicted outcomes to actual 180 day survival of patients admitted to 92 intensive care units and three respiratory high dependency units in the UK. They confirmed the viewpoint that clinicians are overly pessimistic, predicting a 10% survival rate in those with the poorest prognosis whereas the actual 180 day survival rate was 40%. This prognostic nihilism is further reinforced by the fact that this study only included those patients that actually were admitted to ITU/HDU and not those that were denied admission. (1)

Their second study followed up the same patient cohort with a patient questionnaire, and found that 73% of the respondents considered their quality of life to be the same or better at 180 days after treatment. Most tellingly, 96% would have chosen similar treatment again. (2)

A recent systematic review and meta-analysis aimed to identify predictors of mortality in acute exacerbations of COPD. Their study considered 37 trials comprising over 189,000 patients. They identified 12 prognostic factors (age, male sex, low body mass index, cardiac failure, chronic renal failure, confusion, long-term oxygen therapy, lower limb edema, Global Initiative for Chronic Lung Disease criteria stage 4, cor pulmonale, acidemia, and elevated plasma troponin level) were significantly associated with increased short-term mortality. Nine prognostic factors (age, low body mass index, cardiac failure, diabetes mellitus, ischemic heart disease, malignancy, FEV1, long-term oxygen therapy, and PaO2 on admission) were significantly associated with long-term mortality. Three factors (age, low Glasgow Coma Scale score, and pH) were significantly associated with increased risk of mortality in ICU-admitted study subjects. (3)

Another recent review aimed to identify factors with prognostic value for patients with COPD exacerbations who have failed or unsuitable for NIV. This review identified that nutritional state, significant comorbidities, length of stay in hospital prior to ICU admission, cor pulmonale, multi-organ failure and sepsis were indicators of adverse in-hospital outcome. The degree of blood gas derangement, baseline FEV1, the need for long-term oxygen therapy did not predict outcome in the acute setting. Increasing age, home ventilation and chronic hypercapnia did not necessarily predict poor outcome. (4)

The third and final CAOS study attempted to aid clinicians by developing an outcome prediction model for patients with exacerbations of COPD which proved to be more discriminating than clinicians’ predictions. However, this model seems to have not yet received widespread uptake in UK clinical practice. (5)

NICE has recommended that functional status, body mass index, baseline oxygen requirement when well, previous hospital admissions, comorbidities, age and FEV1, should be considered during the decision making process for invasive ventilation. However, no formal recommendations have been made about who should be offered invasive ventilation in the event of failure of NIV by NICE, the British Thoracic Society, the Intensive Care Society or the Royal College of Physicians. (6)


References:
1. Implications of prognostic pessimism in patients with chronic obstructive pulmonary disease (COPD) or asthma admitted to intensive care in the UK within the COPD and asthma outcome study (CAOS): multicentre observational cohort study. Wildman MJ, Sanderson C, Groves J, Reeves BC, Ayres J, Harrison D, Young D, Rowan K. BMJ. 2007 Dec 1;335(7630):1132.

2. Survival and quality of life for patients with COPD or asthma admitted to intensive care in a UK multicentre cohort: the COPD and Asthma Outcome Study (CAOS). Wildman MJ, Sanderson CF, Groves J, Reeves BC, Ayres JG, Harrison D, Young D, Rowan K. Thorax. 2009 Feb;64(2):128-32

3. Singanayagam A, Schembri S, Chalmers JD. Predictors of mortality in hospitalised adults with acute exacerbations of chronic obstructive pulmonary disease. Ann Am Thorac Soc. 2013 Apr; 10(2):81-9

4. Invasive mechanical ventilation in acute exacerbation of COPD: prognostic indicators to support clinical decision making. Wakatsuki M, Sadler P. J Intensive Care Soc. 2012 Jul; 13: 238-243

5. Predicting mortality for patients with exacerbations of COPD and Asthma in the COPD and Asthma Outcome Study (CAOS). Wildman MJ, Sanderson C, Groves J, Reeves BC, Ayres J, Harrison D, Young D, Rowan K. QJM. 2009 Jun;102(6):389-99

6. Chronic obstructive pulmonary disease. National clinical guideline on management of chronic obstructive pulmonary disease in adults in primary and secondary care. Thorax 2004;59 Suppl 1:1-232

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