Airway clearance techniques for the intubated adult: a scoping review

Introduction

The ACPRC editorial board is comprised of respiratory physiotherapy clinicians and academics who have volunteered through their ACPRC membership to be part of the editorial board. The purpose of the board is to lead scoping, commissioning, co-ordination and delivery of all new ACPRC guidance documents and resources, in order to facilitate knowledge sharing and drive improvements in the quality of care for respiratory patients.

The editorial board discussed potential areas for investigation which had been suggested by its membership and agreed that the area of airway clearance for the intubated adult should be prioritised. The lead author Gabriella Cork, as a member of the editorial board, was nominated to lead the scoping review and other ACPRC members who were practising respiratory physiotherapist clinicians volunteered to assist with the process.

Airway clearance for the intubated adult is an important responsibility for respiratory physiotherapists in the intensive care unit (ICU) (1) and involves the mobilisation and subsequent removal of respiratory secretions via the endotracheal or tracheostomy tube. Intubation and the associated mechanical ventilation, prolonged recumbency and sedation result in reduced cough efficacy, reduced mucociliary transport and atelectasis which can in turn lead to retained secretions and ventilator-associated pneumonia (2, 3, 4, 5). Physiotherapeutic techniques to assist with the removal of sputum from the intubated patient such as manual chest compression, hyperinflation and positioning are frequently used by physiotherapists (6, 7). However, evidence investigating the efficacy of such techniques has been deemed overall of poor quality with conflicting findings (8).

Recent Faculty of Intensive Care Medicine (FICM) guidelines recommend ‘targeted airway clearance interventions’ for invasively ventilated patients but do not stipulate which airway clearance interventions should be utilised (9). Furthermore, the same publication recommends that individual physiotherapy services should develop their own evidence-based guidelines for the use of airway clearance techniques. A major purpose of this scoping review was to determine whether there is sufficient evidence available on this topic to inform collaborative clinical guidelines.

A preliminary search of SCOPUS and the Cochrane Database of Systematic Reviews was conducted and whilst recent reviews in this area exist, they have focused on individual techniques such as manual therapy (10) or hyperinflation (11, 12), on specific populations such as those with community-acquired pneumonia (13) and traumatic brain injury (14), or on specific outcomes such as ventilation-associated pneumonia (VAP) rates (15). One systematic review (8) did have a wider focus and included a variety of physiotherapeutic techniques and outcomes relevant to airway clearance, however a number of new experimental studies have subsequently been published. These have not yet been captured by guidelines, recommendations or systematic review and may further contribute to the knowledge base in this topic.

The aim of this scoping review is to understand the extent and type of evidence in relation to airway clearance in the intubated adult in order to inform future recommendations for respiratory physiotherapy clinicians and researchers.

Review question

What is the extent of the current evidence-base in relation to airway clearance in the intubated adult?

Eligibility criteria

Participants

Adults who were intubated either via endotracheal or tracheostomy tube at the time of the investigation. Paediatric studies were excluded.

Concept

Airway clearance techniques that are performed by physiotherapists as summarised by Berry et al (16). Additional airway clearance techniques that are more commonly performed by medical staff such as bronchoscopy or that are pharmacological in nature were excluded. Techniques such as automated lateral bed rotation, humidification or endotracheal suctioning alone were excluded as these were deemed to be primarily routine, nurse-delivered interventions.

Context

Airway clearance techniques for the intubated adult are usually performed in the ICU, however studies were not excluded if they investigated intubated adults in other clinical settings such as weaning units or post-op recovery areas. This scoping review was planned and initial searches conducted prior to the global COVID-19 pandemic, therefore studies relating to the treatment of COVID-19 were excluded as they were deemed by the co-authors to be beyond the initial remit and purpose of the review.

Types of sources

This scoping review considered both experimental and quasi-experimental study designs including randomised controlled clinical trials, non-randomised controlled trials and before and after studies. In addition, analytical observational studies including prospective and retrospective cohort studies, case-control studies and analytical cross-sectional studies were considered for inclusion. This review also included descriptive observational study designs including case series, individual case reports and descriptive cross-sectional studies as well as animal and bench studies. Qualitative studies on this topic were additionally summarised alongside systematic reviews and meta-analyses that met the inclusion criteria.

Opinion papers (including editorials) as well as conference abstracts were excluded.

Methods

The scoping review was conducted in accordance with the JBI methodology for scoping reviews (17).

Search strategy

An initial limited search of SCOPUS was undertaken to identify articles on the topic. The text words contained in the titles and abstracts of relevant articles, the index terms used to describe the articles, and a collaborative, iterative process by the co-authors were used to develop a full search strategy (see Appendix 1 for full SCOPUS search strategy). The search strategy, including all identified keywords and index terms, was adapted for each of the included databases. The reference lists of all review papers were subsequently screened for additional studies.

Studies published in any language where a full English version was available were included. Studies published from 2011 onwards were included as the most comprehensive systematic review was published in 2013, and the vast majority of its 85 included papers were published pre-2011 (8).

The databases searched were SCOPUS, PubMed, CINAHL Plus, and PEDro. Google Scholar search engine was additionally employed using the same search terms, limited to the initial 500 papers due to default sort by relevance. The Clinical Trials Registry was also searched for unpublished studies that were completed within the previous three years which might reasonably be in the process of being published at the time of the review. The final search was completed in December 2021.

Source of evidence selection

Following the search, titles and abstracts were screened by co-authors (Clare Wade, Alison Gordon, Anna Vaughan-France, Amelia Palmer, Katy Walker and Una Jones) for assessment against the inclusion criteria. Potentially relevant sources were retrieved in full and uploaded into EndNote X9, 2018 (Clarivate Analytics, P.A., U.S.A.) and duplicates removed. The full text of selected citations was assessed in detail against the inclusion criteria by the lead author (Gabriella Cork) and cross-checked independently by Clare Wade. Reasons for the exclusion of evidence following full text review were recorded and reported (Figure 1).

Data extraction and synthesis

Data regarding study design, population, intervention, comparator and outcome (PICO) was extracted from papers included in the scoping review by the co-authors using a data extraction tool developed by Una Jones. The data extracted included key findings relevant to the review question. Themes were identified during the data extraction process and the papers grouped both by type of evidence and sub-themes within the overall airway clearance topic. For papers which included more than one type of airway clearance, the intervention was classified as ‘multi-modal chest physiotherapy’. Key outcome measures were also identified. Due to the breadth of the scoping review, quality assessment of the experimental papers was not undertaken beyond classifying them according to their study design.

Results

The scoping review retrieved 138 relevant papers (see Figure 1). Of these, 11 were systematic reviews (summarised in Appendix 1) and 39 were randomised clinical trials (summarised in Appendix 2), see Figure 2 for full break-down of papers by evidence-type and Appendices 3–8 for summaries of all other included papers.

The most common reported intervention was multi-modal chest physiotherapy with 45 publications exploring this topic. Common airway clearance techniques such as hyperinflation and manual chest compressions were also extensively studied. Figure 3 gives a full break-down of the papers included in the scoping review according to their theme.

The key interventions, outcome measures and findings from comparative studies included in this scoping review are summarised in Table 1. The most commonly reported outcome measures were sputum yield and oxygenation.

See Figure 1: PRISMA flow chart for the scoping review process.

See Figure 2: Summary of included sources according to evidence type.

See Figure 3: Summary of included sources according to theme and evidence type.

MHI = manual hyperinflation; VHI = ventilator hyperinflation; MI:E = mechanical in-exsufflation.

Table 1: Summary of key interventions and outcome measures.

= Denotes no significant difference between intervention and control/comparison.

+ Denotes significant finding in favour of the intervention compared with control/comparison.

- Denotes significant finding in favour of the control/comparison compared with the intervention.

RCT = randomised clinical trial; MHI = manual hyperinflation; VHI = ventilator hyperinflation.

A summary of the non-experimental research included in this scoping review is provided in Table 2.

Table 2: Summary of non-experimental research.

ICU = intensive care unit; VHI = ventilator hyperinflation; IMV = invasive mechanical ventilation; NMD = neuromuscular disease; SCI = spinal cord injury; NIV = non-invasive ventilation.

Discussion

The papers retrieved by this deliberately wide-ranging scoping review were diverse and as well as clinical efficacy papers, included assessment of the requirements for airway clearance techniques (ACTs), physiological effects of ACTs, opinions of caregivers, service delivery and clinical recommendations.

Non-experimental research

Clinician opinion regarding airway clearance techniques using surveys of current practice has been the subject of a number of recent studies (18, 19, 20, 21, 22, 23, 24). These surveys have highlighted that a number of varying airway clearance and cough augmentation techniques are used by critical care clinicians. Studies reported heterogeneity of intensity and combination of ACTs in addition to variation in clinical practice. Rationale for commencing airway clearance techniques is similar across studies, including to aid in sputum clearance and promotion of improved alveolar recruitment and ventilation. Some studies highlight that lack of knowledge, training, and expertise may contribute to reduced adoption of techniques such as mechanical in-exsufflation (22) and ventilator hyperinflation (23). Such studies recognise the lack of clinical guidance in this area.

Qualitative studies with physiotherapists and wider critical care clinicians highlight the importance of teamwork, clinical reasoning, clinical experience and communication as key in the selection and effective implementation of airway clearance interventions for mechanically ventilated adults (6, 25).

A recent focus of non-experimental research has been the production of clinical guidelines using a Delphi technique to achieve expert consensus, specifically to identify core clinical competencies for practitioners implementing airway clearance techniques (1, 26) and best practice for the treatment of community-acquired pneumonia (21). Expert consensus panels recognise that physiotherapy competence in airway clearance interventions such as hyperinflation techniques, manual chest wall techniques, positioning, normal saline instillation and suction are a minimum standard of practice for physiotherapists working in ICU in their respective countries (1, 26). This scoping review did not retrieve any recent clinical guidelines to aid in the selection, implementation or evaluation of airway clearance techniques for non-specific intubated adults.

Experimental research: short-term outcomes

Papers focusing on clinical efficacy investigated interventions that enhanced inspiratory volume and/or expiratory flow. The effects of such airway clearance techniques were primarily reported on short-term outcomes such as oxygenation, sputum yield, respiratory mechanics (for example, dynamic compliance) and peak expiratory flow (PEF; either absolute PEF or peak inspiratory-expiratory flow (PIF:PEF) ratio). Although sputum yield is the most direct outcome measure for the efficacy of airway clearance techniques, oxygenation and respiratory mechanics are reported frequently. Techniques which appear to enhance sputum yield include adjuncts such as high-frequency chest wall oscillation (HFCWO) and oscillatory positive expiratory pressure (OPEP) devices (27, 28, 29, 30), head down positioning (31), and multi-modal chest physiotherapy (13, 32). The evidence for the effect of hyperinflation, manual techniques and cough augmentation on sputum yield is mixed, with contradictory findings. Several studies have reported no difference in effect between manual hyperinflation and ventilator hyperinflation regarding sputum yield, including a systematic review (11).

The most effective interventions to improve oxygenation in the short-term appear to be manual and ventilator hyperinflation with multiple studies reporting statistically significant if not necessarily clinically significant findings in favour of this intervention (12, 33, 34, 35, 36, 37, 38, 39). Improvements in respiratory mechanics such as static and dynamic lung compliance were reported with multi-modal chest physiotherapy by multiple systematic reviews (8, 13, 40). Several experimental studies reported a similar effect with airway clearance adjuncts (27, 41, 42) which seems to be an emerging area of research that warrants further attention.

Animal studies have investigated the effect of airway clearance techniques on PEF, particularly to determine whether the threshold for mucous movement can be achieved by head down positioning and manual techniques (43, 44). A number of clinical studies have also explored this outcome measure with adjuncts (27) and manual techniques (45, 46) being shown to improve PEF.

Cardiovascular and neurological stability have been investigated in a number of studies and whilst some statistically significant deteriorations have been reported during various airway clearance techniques, authors concluded that these were transient and non-clinically significant. This suggests that ACTs are safe for the intubated patient (47, 48).

Experimental research: longer-term outcomes

Longer-term outcome measures such as mortality, ICU length of stay, ventilator-acquired pneumonia (VAP) rates and extubation outcome were reported by some studies although far less frequently than short-term outcomes. Understandably, these longer-term outcome measures have been a focus of systematic reviews (8, 13, 15, 49). With the exception of mortality (49), systematic reviews included in this scoping review report no significant effect of airway clearance techniques on any of these longer-term outcome measures (8, 13, 15).

This scoping review retrieved a number of experimental studies reporting reduced VAP rates with airway clearance adjuncts (30, 50), head-down positioning (43), manual techniques (51) and multi-modal chest physiotherapy (34, 52). Similarly, an improved likelihood of extubation success has been reported in some studies with cough augmentation (53) and multi-modal chest physiotherapy (54). Whilst quality was not assessed as part of this scoping review, these findings suggest that the effect of airway clearance techniques on VAP rates and extubation outcome may warrant further investigation.

Limitations of this scoping review

This scoping review was intentionally limited to airway clearance techniques that are typically delivered by respiratory physiotherapists in the adult ICU. Due to this, some aspects of airway clearance such as routine suctioning, humidification, regular repositioning, bronchoscopy and pharmacological interventions were not included.

A major methodological limitation was the lack of quality assessment of the included papers. Due to the wide-ranging remit of the review and number of papers retrieved, this was beyond the scope of this review and was not deemed necessary in order to meet the aims and objectives set out in advance. Randomised clinical trials were carefully screened and if they failed to meet the criteria for randomisation as described by PEDro (55), they were classified as ‘other experimental’ studies.

Future research

Future experimental research is still required to determine the effectiveness of airway clearance techniques in the intubated adult. Existing randomised clinical trials have focused on short-term outcomes and therefore a reasonably comprehensive body of evidence is available for common interventions such as hyperinflation and manual techniques in this regard. There are emerging interventions with an increasing evidence-base such as cough augmentation and airway clearance adjuncts. As an outcome measure, PEF appears to be influenced by ACTs, however its relevance to other, more clinical outcomes would benefit from further experimental investigation. Another under-researched area is positioning for airway clearance, despite this being a routinely used intervention for intubated adults (20). A focus for future research should be the effect of airway clearance on longer-term outcomes, particularly VAP rate and extubation success as these appear to be outcomes that may be influenced by ACTs.

Future reviews should be carefully considered and rationalised. There would be merit in an updated systematic review investigating the effect of manual techniques as several recent studies have not yet been captured by such a review. Furthermore, airway clearance adjuncts for the intubated patient have not yet been investigated by systematic review and this may be an area that warrants the same. A plethora of narrative reviews on this topic are already available and therefore any future narrative reviews should have a clear and unique focus.

Conclusion

This scoping review was undertaken as an area of priority for the ACPRC editorial board. The extent of the available evidence regarding airway clearance for intubated adults has been summarised, thus achieving the aim of the scoping review. Included papers were diverse and wide-ranging in their findings. Overall, the evidence-base regarding the efficacy of airway clearance techniques for short-term clinical outcome measures is moderately large. Currently, there is limited evidence regarding their efficacy for longer-term outcome measures. There is a moderate body of evidence reporting that airway clearance techniques are safe for the intubated adult.

Future clinical research should focus on the effects of airway clearance techniques on longer-term outcome measures such as VAP rates and extubation outcome as well as investigating common but under-researched interventions such as positioning. As the quality of the studies was not assessed in this scoping review, future work is needed to develop clinical recommendations based on both short- and long-term efficacy of airway clearance techniques for adults who are intubated.

Acknowledgements

Association of Chartered Physiotherapists in Respiratory Care editorial board.

Gareth Cornell for review of the database search terms.

Funding

There was no funding provided for this scoping review. All participants gave their time voluntarily.

Conflicts of interest

There is no conflict of interest in this project.

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