Accelerating demand from ICUs has been driving the use of mechanical ventilation (MV). This is due to demographic changes triggering growth in elderly patient numbers, as well as advances in the ability to delay or prevent mortality. Nevertheless, there are also significant differences in the management of ventilated patients, and no necessary correlation in outcomes. Given the relatively high costs of mechanical ventilation, experts are seeking ways to develop and share best practices.
Growth in ICU drives demand
The Society for Critical Care Medicine (SCCM) estimates 20-30% of patients admitted to an intensive care unit (ICU) require MV. The scale of the challenge is underlined by the fact that about one-fifth of all acute care admissions in the US and 58% of emergency department admissions are made to an ICU.
The above facts are somewhat ironical. The mechanical ventilator is one of the most powerful symbols of modern medical technology and progress in intensive care technologies has allowed more patients to survive acute critical illness than ever before. However, the very same advances have created what one study describes as ‘a large and growing population of patients with prolonged dependence on mechanical ventilation and other intensive care therapies.’
The roots of such developments go back decades. In 1985, two North American clinicians coined the term chronically critically ill’ in an article about the ICU titled ‘To Save or Let Die’? It is estimated that between 5 and 10% of patients who require mechanical ventilation for acute conditions develop chronic critical illness. Many of these result in death.
Other sources endorse these findings. In 2004, a study on patients with tracheostomy for respiratory failure found that the mortality of ventilator-dependent patients was as high as 57%.
Europe and the US
The situation is challenging in Europe, too, in spite of differences vis-a-vis the US. For instance, although the UK has a seven-fold lower level of ICU beds per capita than the US, 68% of UK patients are mechanically ventilated within 24 hours after ICU admission, well over twice the 20-30% level estimated by the SCCM in the US. In spite of this, there are no differences in mortality for mechanically ventilated patients admitted from the ER.
The impact of these spill over into other areas. Although strictly comparable figures are not available, differences in the ICU environment between one European country and another would clearly have an impact. The per capita density of adult ICU beds varies seven-fold from 3.3/100,000 population in the United Kingdom to 24.0/100,000 in Germany.
Prolonged mechanical ventilation
One of the most pressing challenges, with respect to divergent practices, is the duration of ventilation.
Prolonged mechanical ventilation (PMV) is now generally accepted to be ventilation that lasts for 21 or more days. There are few studies of PMV incidence, and even these are accompanied by variations in definitions.
Nevertheless, a Canadian workshop cites two studies , to estimate that on an international’ basis, patients requiring PMV account for up to 10% of all mechanically ventilated patients, 40% of ICU bed days, and 50% of ICU costs. These figures may be slightly over-estimated. One US study, for example, finds PMV accounting for 7.7% of ventilated ICU admissions.
In Europe, the proportion of PMV is clearly lower than 10% of ventilated patients. In Scotland, for example, the University of Edinburgh’s Old Medical School reports the incidence of PMV to be 4.4% of ICU admissions and 6.3% of ventilated ICU admissions.
The challenges of PMV growth
The rate of PMV has been growing, rapidly, both due to an ageing population and technological advances which allow delaying or preventing mortality in the ICU. In the US, data show patients requiring prolonged mechanical ventilation to be steadily rising. One study covering the period 1993 to 2002 found the incidence of tracheostomy for prolonged mechanical ventilation growing by about 200%, and surpassing changes in the overall incidence of respiratory failure by a factor of three.
The resource load on PMV patients is clearly higher. Up to 40% of ICU resources may be spent on them, even though they represent only 10-15% of the ICU population. The University of Edinburgh study mentioned above found that PMV patients used 29.1% of all ICU bed days. In spite of this, the majority of PMV patients die within six months.
The costs of ventilation
Overall, the sharp growth in demand for mechanical ventilation and the frequent lack of correlation with outcomes is a major strain on financial and human resources, making it necessary to optimize ventilator use by developing best practices.
The cost of mechanical ventilation has been estimated at 1,522 US dollars per day (about 1,345 euros) in the US, and 2,110 euros per day in a recent European evaluation. The US figures are adjusted for patient and hospital characteristics, while the European figures are unadjusted. Nevertheless, it appears that intensive care unit costs are highest during the first two days of admission, stabilizing at a lower level thereafter. Still, the burden of PMV is clearly enormous. In the US, estimated costs per one-year survivor are as high as 423,596 US dollars (371,500 euros).
Costs are also non-financial. These include long-term physical and psychological consequences which impact upon quality of life and often impose substantial symptom burden. One study of 23 hospitals in the US pointed to the risks of ‘prolonged ventilator dependence, reduced mobility, as well as anxiety and depression.’ The study also called for an interdisciplinary, rehabilitative approach in the ICU. This trend correlates with wider lessons acquired over half-a-century of ICU care.
Future innovations in ventilation are likely to be focused ‘on reducing the need for user input, automating multi-element protocols, and carefully monitoring the patient for progress and complications.’
Delivery models: the role of home ventilation
Differences between the US and Europe in delivery models also influence the development of best practices.
The preferred models of care in the US include ‘delivery of protocolized rehabilitation-based care either within the acute ICU or specialized post-ICU venues.’ Patients are generally transferred to respiratory units within an acute hospital or to a long-term acute care hospital, physically located within the former or set up as free-standing institutions.
One crucial factor in the US is the lack of home ventilation, due to current funding models. In Europe, home ventilation is generally present or attaining an increasing profile. Nevertheless, there is still significant variability in practices across countries. The prevalence of home ventilation per 100,000 population averages 6.6 in Europe, but ranges from 17 in France to 0.1 in Poland.
Divergence in care practices and cognitive bias
Heterogeneity of care is probably one of the strongest indicators of the need for best practices. In the context of MV, the need for the latter is underlined by a finding that ICU clinicians are prone to cognitive biases and this may lead to systematic and predictable errors.
The most prominent divergences in practice seem to lie in sedation management and weaning.
Sedation management has been the subject of interest for decades, but is still marked by a lack of consensus.
In 2000, The New England Journal of Medicine’ published results of a study by the University of Chicago study on the benefit of administering sedatives to MV patients by continuous infusion, against daily interruption which allowed patients to wake up’ and be assessed by clinicians. The latter practice was found to reduce the duration of mechanical ventilation as well as the length of stay in the ICU, and sedative dosage.
In 2008, a study in The Lancet’ by the Vanderbilt School of Medicine in the US proposed that a protocol pairing daily interruption of sedatives (spontaneous awakening) with daily spontaneous breathing resulted in better outcomes for MV patients and should become routine practice.
In 2010, a team at the Odense Hospital in Denmark compared interrupted sedation of MV patients versus patients who received no sedation at all. Their findings, also published in The Lancet’, indicated that patients receiving no sedation had significantly more days without ventilation and a shorter ICU stay, with no difference in accidental extubations, need for CT or MRI brain scans or ventilator-associated pneumonia. The researchers called for a study ‘to establish whether this effect can be reproduced in other facilities.’
One ambitious recent effort to study differences in sedation management involved a multicentre study of 40 ICUs in France and Switzerland. The researchers found that a quarter of the participating units did not even have a sedation-management protocol in place. This, they speculated, might be due to a lack of awareness about protocols, or because of limited resources. Another possibility was that physicians tend to resist cookbook recipes’ and limitations to their autonomy. In other words, they observed, the presence of a written procedure ‘does not mean that physicians will follow it.’ Even in ICUs with sedation management protocols, ‘approximately 20% of the physicians were unaware’ about their existence.
Another priority for protocols concerns weaning MV patients in the ICU. Studies have shown that 20% of MV patients fail to wean in the ICU and become dependent on mechanical ventilation.
In 2005, as a first step, an international consensus panel proposed classifying weaning into three types, based on difficulty and duration. These consisted of simple’ weaning (successful extubation on a first attempt), difficult’ weaning (patients who require up to three spontaneous breathing trials/SBT, or 7 days) and prolonged’ weaning (patients failing at least three SBT attempts or requiring over 7 days after the first attempt).
The classification was, however, the subject of a major attack in 2011 by Dean Hess, the Assistant Director of Respiratory Care at Massachusetts General Hospital and Neil MacIntyre, a Professor of Pulmonary Medicine at Duke University Medical Center. Writing in The American Journal of Respiratory and Critical Care Medicine’, the two took the international panel to task for using the term weaning’ interchangeably with discontinuation’ of mechanical ventilation. They also attacked the very concept of weaning, suggesting that little evidence supported a gradual reduction of respiratory support. They urged clinicians to focus on treatment of the underlying disease process rather than manipulating the ventilator settings.
Indeed, the linkage between sedation management and weaning, and the lack of hard data and conclusions on either, was highlighted in a 2014 commentary by Italian, French and German ICU clinicians titled Sedation and weaning from mechanical ventilation: time for best practice’ to catch up with new realities?’. The article, published in Multidisciplinary Respiratory Medicine’, argues that ‘delivery of sedation in anticipation of weaning of adult patients from prolonged mechanical ventilation is an arena of critical care medicine where opinion-based practice is currently hard to avoid because robust evidence is lacking.’