Background and importance
Critically-ill adults and children who need assistance from machines (ventilators) to help them breathe may have difficulty coughing and clearing secretions. This can reduce their chances of successful removal of the breathing tube (extubation) and being able to breathe without the machine. Their respiratory muscles may be weak; they may have neuromuscular disorders, spinal cord injury, or restrictive lung disease, or be experiencing delirium, cognitive impairment or additive effects of sedation. Techniques such as building up the volume of air in the lungs over a number of breaths (breathstacking), manually- and mechanically-assisted cough with an insufflation-exsufflation (MI-E) device can be used to encourage people to cough. The potential for these techniques to help critically-ill adults and children to come off and stay off the ventilator is unclear.
Do techniques that promote cough in mechanically-ventilated, critically-ill adults and children in a high-intensity care setting improve rates of successful extubation and weaning?
To look at controlled studies of techniques to promote cough in critically-ill adults and children, to see if these techniques are useful for helping them come off and stay off the ventilator, and to determine if there are any associated harms. The complications we looked for included decreased or increased blood pressure, irregular heart rhythm, leakage of air from the lungs to the chest cavity, coughing up blood, and mucus plugging requiring a new breathing tube.
We found two randomized controlled trials (95 adult participants) and one non-randomized controlled study (17 children aged at least four weeks) conducted in Portugal, Canada, and the United States. We rated the two randomized trials as being of unclear quality and the non-randomized study as being low quality. The largest randomized trial (75 participants) found a 83% success rate for extubation with mechanically- and manually-assisted cough used in combination, compared with 53% in the control group (extubation success over 1½ times more likely) (very low-quality evidence). The time spent on a ventilator was six days less in people using mechanically- and manually-assisted cough (very low-quality evidence). No participants died in this trial.
Complications were reported by the two randomized trials. One person receiving mechanically-assisted cough experienced a prolonged drop in blood pressure; another person receiving breathstacking and suctioning in addition to manually-assisted cough experienced a prolonged rise in blood pressure. In one trial, following removal of the breathing tube, more people in the group not receiving mechanically-assisted cough experienced secretion retention, a drop in oxygen levels, and needed the breathing tube to be reinserted (nine people compared with two, very low-quality evidence).
The non-randomized study reported that the breathing tube could be removed in all of the six children in the group receiving interventions to assist with coughing. In this non-randomized study, death was only reported for children receiving a cough-promoting technique. One child died, but this was not thought to be related to the cough technique. This study did not report adverse events associated with assisted coughing. No included study evaluated a single cough-promoting technique in isolation. The two randomized trials combined manually-assisted cough with either mechanical assistance (MI-E) or breathstacking, and the non-randomized study used all three methods.
Very low-quality evidence from single trial findings suggests that cough-promoting techniques might increase successful removal of the breathing tube and decrease the time spent on mechanical ventilation, while not causing harm. The limited participant numbers made it difficult to determine the likelihood of harms.
The overall quality of evidence on the efficacy of cough augmentation techniques for critically-ill people is very low. Cough augmentation techniques when used in mechanically-ventilated critically-ill people appear to result in few adverse events.
There are various reasons why weaning and extubation failure occur, but ineffective cough and secretion retention can play a significant role. Cough augmentation techniques, such as lung volume recruitment or manually- and mechanically-assisted cough, are used to prevent and manage respiratory complications associated with chronic conditions, particularly neuromuscular disease, and may improve short- and long-term outcomes for people with acute respiratory failure. However, the role of cough augmentation to facilitate extubation and prevent post-extubation respiratory failure is unclear.
Our primary objective was to determine extubation success using cough augmentation techniques compared to no cough augmentation for critically-ill adults and children with acute respiratory failure admitted to a high-intensity care setting capable of managing mechanically-ventilated people (such as an intensive care unit, specialized weaning centre, respiratory intermediate care unit, or high-dependency unit).
Secondary objectives were to determine the effect of cough augmentation techniques on reintubation, weaning success, mechanical ventilation and weaning duration, length of stay (high-intensity care setting and hospital), pneumonia, tracheostomy placement and tracheostomy decannulation, and mortality (high-intensity care setting, hospital, and after hospital discharge). We evaluated harms associated with use of cough augmentation techniques when applied via an artificial airway (or non-invasive mask once extubated/decannulated), including haemodynamic compromise, arrhythmias, pneumothorax, haemoptysis, and mucus plugging requiring airway change and the type of person (such as those with neuromuscular disorders or weakness and spinal cord injury) for whom these techniques may be efficacious.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL; Issue 4, 2016), MEDLINE (OvidSP) (1946 to April 2016), Embase (OvidSP) (1980 to April 2016), CINAHL (EBSCOhost) (1982 to April 2016), and ISI Web of Science and Conference Proceedings. We searched the PROSPERO and Joanna Briggs Institute databases, websites of relevant professional societies, and conference abstracts from five professional society annual congresses (2011 to 2015). We did not impose language or other restrictions. We performed a citation search using PubMed and examined reference lists of relevant studies and reviews. We contacted corresponding authors for details of additional published or unpublished work. We searched for unpublished studies and ongoing trials on the International Clinical Trials Registry Platform (apps.who.int/trialsearch) (April 2016).
We included randomized and quasi-randomized controlled trials that evaluated cough augmentation compared to a control group without this intervention. We included non-randomized studies for assessment of harms. We included studies of adults and of children aged four weeks or older, receiving invasive mechanical ventilation in a high-intensity care setting.
Two review authors independently screened titles and abstracts identified by our search methods. Two review authors independently evaluated full-text versions, independently extracted data and assessed risks of bias.
We screened 2686 citations and included two trials enrolling 95 participants and one cohort study enrolling 17 participants. We assessed one randomized controlled trial as being at unclear risk of bias, and the other at high risk of bias; we assessed the non-randomized study as being at high risk of bias. We were unable to pool data due to the small number of studies meeting our inclusion criteria and therefore present narrative results rather than meta-analyses. One trial of 75 participants reported that extubation success (defined as no need for reintubation within 48 hours) was higher in the mechanical insufflation-exsufflation (MI-E) group (82.9% versus 52.5%, P < 0.05) (risk ratio (RR) 1.58, 95% confidence interval (CI) 1.13 to 2.20, very low-quality evidence). No study reported weaning success or reintubation as distinct from extubation success. One trial reported a statistically significant reduction in mechanical ventilation duration favouring MI-E (mean difference -6.1 days, 95% CI -8.4 to -3.8, very low-quality evidence). One trial reported mortality, with no participant dying in either study group. Adverse events (reported by two trials) included one participant receiving the MI-E protocol experiencing haemodynamic compromise. Nine (22.5%) of the control group compared to two (6%) MI-E participants experienced secretion encumbrance with severe hypoxaemia requiring reintubation (RR 0.25, 95% CI 0.06 to 1.10). In the lung volume recruitment trial, one participant experienced an elevated blood pressure for more than 30 minutes. No participant experienced new-onset arrhythmias, heart rate increased by more than 25%, or a pneumothorax.
For outcomes assessed using GRADE, we based our downgrading decisions on unclear risk of bias, inability to assess consistency or publication bias, and uncertainty about the estimate of effect due to the limited number of studies contributing outcome data.