Iain Crossingham

Moderate agreement for cardiac output monitors: moderately good or moderately bad?

The past decade and a half has seen an explosion in the number of devices and techniques that monitor cardiac output. A frequent question for the anaesthesiologist and intensivist is therefore ‘what do the numbers from this new monitor tell me about my patient?’ One way we might answer this question is by comparison with data from established techniques. If a new and less invasive monitor reliably gives the same data as a familiar piece of equipment that has our trust, then it is easy for us to incorporate it into our practice.

Macrolide antibiotics for non-cystic fibrosis bronchiectasis

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows: To determine the impact of macrolide antibiotics in the treatment of adults and children with non-cystic fibrosis bronchiectasis.

Comparing cardiac output monitors and defining agreement: A systematic review and meta-analysis

Background Measuring cardiac output is common in critical care and perioperative medicine. Different monitoring systems are often judged against others in comparative studies. There is no agreed standard or definition on which to base the conclusions of such studies. Objectives To review comparative studies of cardiac output monitors using an agreement:tolerability index (ATI) as a measure of monitor precision. To compare the ATI of a monitor with the conclusions of authors regarding agreement and clinical utility. Design Systematic review of comparative studies of cardiac output monitoring systems. The precision of each monitor was standardised against an ATI using a tolerability interval based on the normal range for cardiac index. The conclusions of each study were described as positive, neutral or negative, depending on whether authors reported the monitor to be acceptably precise and/or clinically useful. Comparison was made between the precision of a monitor and the likelihood of it being favoured by authors. Data sources PubMed was searched up to March 2012. Eligibility criteria Studies published in English that compared two or more methods for measuring cardiac output in adult humans. Results A total of 213 papers documenting 409 separate comparisons of two methods of measuring cardiac output were included. ATIs for the different comparisons varied from 0.07 to 6.84 (where an ATI < 1 indicates acceptable agreement, 1–2 marginal and >2 unacceptable agreement). Thirty-one percent of authors defined their own terms for acceptable agreement. ATI was only moderately correlated with the conclusions of the authors (Spearman rho = 0.47, P < 0.0001). Conclusions Authors should define what constitutes acceptable agreement a priori when reporting comparative studies of cardiac output monitors. The ATI and the tolerability interval may be a useful basis for helping define acceptable precision.

In defence of ward-based non-invasive ventilation

The National Confidential Enquiry into Patient Outcome and Death (NCEPOD) have just published a report reviewing acute non-invasive ventilation (NIV) in the UK. Historically, NIV has had an unusual place on the fringe of critical care medicine. Acute mechanical ventilation is and has always been a standard intensive care therapy. However, with intensive care unit (ICU) beds scarce in the late 1990s, a number of respiratory physicians recognised that their chronic obstructive pulmonary disease (COPD) patients could not easily access such respiratory support. As a response they experimented with NIV outside of the ICUs. The ‘‘Yoniv’’ study published in 2000 showed that NIV could safely be delivered on general respiratory wards, albeit with carefully selected patients and under the care of enthusiasts in this technique. This encouraged other clinicians to set up ward-based NIV services, and over the next 15 years, such services and the demand for them grew explosively. By 2014, the vast majority of hospitals admitting patients with acute exacerbations of COPD had the ability to provide NIV outside of the critical care unit, most often on respiratory wards and/or medical assessment units. In many ways, ward-based NIV is a success, widening access to a potentially lifesaving treatment. It is however somewhat of a victim of its own success. Increasingly, COPD patients are surviving for longer with established type 2 respiratory failure as NIV allows them to survive acute episodes that would have previously been fatal. Judging by the pH, many patients currently treated with NIV are substantially sicker than was the norm in the Yoniv study. In my own organisation, of the patients treated with acute NIV, nearly 25% have one or more further episodes requiring NIV in the subsequent year (unpublished data). The complexity of the patients treated with ward NIV has increased over the years as services expand from ‘‘simple’’ COPD to obesity hypoventilation to neuromuscular disorders and kyphoscoliosis. No one in the critical care community would dispute that ventilation is a multifaceted therapy which requires specialist clinical knowledge and a decent working understanding of some of the finer points of respiratory physiology to do well. Medical cover out of hours for ward-based services is of necessity usually provided by juniorand middle-grade doctors from a variety of general medical backgrounds whose particular interests lie elsewhere. Without specialist gatekeeping, the risk is that NIV gets used inappropriately, for example in those with type 1 respiratory failure or metabolic acidosis or in patients who are unequivocally reaching the end of their lives and would be better served by palliation. An unexpected challenge for NCEPOD was that simply identifying NIV patients was less than straightforward. The procedure codes used nationally do not differentiate between NIV and Continuous Positive Airways Pressure (CPAP), clearly a different treatment used for different indications. It is reasonable to speculate that this coding issue is also hampering local audits and service reviews. NCEPOD found several problems with the delivery of NIV by teams on the ground. Overall, NCEPOD reviewers felt that there was room for improvement in the clinical management of patients in over half of cases. Over oxygenation, inadequate ventilator management (particularly insufficient inspiratory pressures) and poor patient selection were some of the emerging themes. Mortality was high, 25% in patients with COPD (compared to 10% in the treatment arm of Plant et al.) and up to 60% in those with ‘‘other’’ indications perhaps reflecting the inappropriateness of NIV for these ‘‘other’’ ‘‘indications’’. Forty percent of patients treated with NIV had evidence of consolidation on the chest X-ray. National NIV guidelines caution against the use of NIV in pneumonia. Whilst these guidelines were published just after the NCEPOD study period, it would appear that they represent a substantial change from what was contemporary practice. Whilst NIV is a poor choice in pure pneumonia without significant underlying lung disease, it is difficult sometimes to know the best primary label to give to the patient with severe COPD who exacerbates and presents febrile with minor pneumonic chest radiograph changes.