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Hypokalaemia, hypophosphataemia, hypomagnesaemia 5. Cardiac failure DO AUTOMATED WEANING MODES HAVE ANY ADVANTAGE OVER CONVENTIONAL APPROACHES? Automated weaning modes such as adaptive support ventilation, Smart Care/PS, proportional assist ventilation, mandatory minute ventilation, and volume support have come onto the market with a promise of faster weaning. However, the exact role of these modes in weaning is still unclear, though there is considerable enthusiasm in using advanced closed loop systems in weaning. For example, Schadler et al found no overall ventilation time difference between weaning using automatic control of PSV and ¨ weaning based on a standardized written protocol among an unselected surgical patient population.9 As of June 2014, the Cochrane database declared that whilst automated modes might reduce the duration of weaning, particularly in mixed ICU populations, the evidence is limited to only 2 types (adaptive support ventilation and Smart Care) and no conclusions can therefore be drawn about automated modes in general. They recommend further research and technological development.10 IS THERE A ROLE FOR NONINVASIVE VENTILATION (NIV) IN WEANING? In a randomised controlled trial, Nava et al compared continuing mechanical ventilation against extubation and noninvasive PSV in patients with COPD who had failed a T-piece SBT 48 hours after intubation for hypercapnic respiratory failure. They showed that the duration of ICU stay, nosocomial pneumonia, and 60-day mortality were lower in the patients weaned via NIV versus those weaned via invasive pressure support.11 The mean duration of mechanical ventilation was 16.6 6 11.8 days and 10.2 6 6.8 days for the invasive and NIV groups, respectively (p¼.021). Survival rate at 60 days was 92% and 72% for patients who received NIV and invasive ventilation, respectively (p ¼ .009). Seven patients weaned without the use of NIV developed nosocomial pneumonia, whereas none from the NIV group did. A small randomised controlled trial by Girault et al looked at patients with acute or chronic respiratory failure and compared planned extubation and conversion to NIV against continuing invasive PSV. However, they showed no difference in overall weaning success with NIV when compared to PSV and no difference in ICU or hospital stay or 3-month mortality, although the total duration of invasive mechanical ventilation was significantly shorter in the NIV group (4.56 6 1.85 days) than in the PSV group (7.69 6 3.79 days) (p ¼ .004). They concluded that NIV may be of help and that it did not increase the risk of weaning failure.12 The Cochrane database has also reported evidence for a beneficial effect on decreasing mortality and ventilator-associated pneumonia without increasing the risk of weaning failure or reintubation among patients with acute hypercapnic respiratory failure weaned with the help of NIV—most notably those patients with COPD.13 The data are less convincing in more heterogeneous populations; only trials looking at COPD or cardiogenic pulmonary oedema have really demonstrated benefits. HOW CARDIAC DYSFUNCTION AFFECTS WEANING The transition from positive-pressure ventilation to spontaneous breathing may precipitate or worsen pre-existing heart failure. Strategies to circumvent this problem include achieving significant negative fluid balance before extubation or transitioning from Subscribe to ATOTW tutorials by visiting www.wfsahq.org/resources/anaesthesia-tutorial-of-the-week ATOTW 372 — Evidence-Based Practice of Weaning from Ventilator: A Review (6 February 2018) Page 3 of 6 low pressure support ventilation to NIV (in order to maintain some positive end-expiratory pressure). Failure to wean should prompt consideration of an echocardiographic evaluation for cardiac dysfunction, including diastolic heart failure. A prospective observational study compared plasma levels of N-terminal pro–brain natriuretic peptide before and after a spontaneous breathing trial and demonstrated rises in patients who either failed the SBT or failed extubation, compared with a fall in levels in those