Factors affecting the use of neurally adjusted ventilatory assist in the adult critical care unit: a clinician survey

Background

Neurally adjusted ventilatory assist (NAVA) uses the electrical activity of the diaphragm (Edi), obtained via a specialised nasogastric feeding catheter (Getinge, Solna, Sweden), as a measure of neural respiratory drive to control the delivery of inspiratory support by a mechanical ventilator (MV).1 In 12 years of clinical use, numerous clinical studies have suggested important physiological benefits2 3 with recent trials suggesting reduced weaning time4 and increased ventilator-free days.5 6 Despite this, no trial has yet definitively demonstrated improved patient outcomes and NAVA has not been widely adopted into clinical care.

The implementation of any new technology-based healthcare treatment is complex. Evidence from clinical trials is important, but the success of trials and the subsequent implementation into practice is dependent on a number of other factors. In the case of NAVA, such factors potentially include contextual issues (eg, prevalent culture, cost and access to the technology), human issues (eg, user skill level, training requirements, beliefs and attitudes) and technological issues (eg, performance and limitations of the technology). Feasibility studies are recommended to investigate such factors prior to the conduct of large, resource intensive randomised controlled rials (RCTs), to optimise efficiency and chances of success.7

In a recently published trial, we demonstrated the feasibility of evaluating NAVA in an RCT compared with PSV for patients at risk of prolonged ventilation support, with adequate compliance to the assigned ventilatory mode over prolonged durations.5 Despite satisfactory mode compliance, some non-adoption and mode cross-over from NAVA to PSV were still observed. To improve our understanding of these cross-over events and wider factors affecting the use of NAVA, we developed and conducted a survey aimed at exploring clinician attitudes, beliefs, perceived barriers and other factors that potentially affect the implementation of NAVA in critically ill adult patients. These data are critical to the design and interpretation of subsequent trials and may help to explain the slow progress towards efficacy and effectiveness trials and clinical adoption of NAVA worldwide.

Methods

An anonymous, self-administered cross-sectional survey of nurses, doctors and physiotherapists was undertaken in four ICUs (surgical, general medical, neuro/trauma and liver) totalling 75 beds at a university affiliated hospital in London, UK. The survey was conducted alongside a randomised controlled feasibility trial (NCT01826890) comparing NAVA to PSV in adults at risk of prolonged ventilation. The purpose of the study, assurance of anonymity and voluntary nature of the survey was outlined in the participant information sheet. Informed consent was assumed on completion of the questionnaire.

Results

Of the 466 questionnaires distributed, 301 (64.6%) were returned including responses from 236 nurses (78.4%), 53 doctors (17.6%) and 12 physiotherapists (4.0%). The response rate expressed as a proportion of the eligible staff was 64.7% for nurses, 59.6% for doctors and 100.0% for physiotherapists. Responses were obtained across all levels of seniority; most participants were junior grade (72.7%), aged 25–34 years (56.0%), and with less than 3 years of ICU experience (60.8%) (table 1), which reflected the general profile of ICU staff.

Of all participants, 157/295 (53.2%) had received NAVA training, 207/294 (70.4%) reported clinical exposure to NAVA (at least one patient treated where NAVA was used), 163/291 (56.0%) indicated that they were familiar (slightly, moderately, very or extremely) with evidence supporting NAVA use in weaning, 269/292 (92.1%) with evidence supporting PSV in weaning, and 289/294 (98.3%) with risk factors for prolonged MV (table 1 and online supplemental figure S1). Of those reporting clinical exposure to NAVA, 125/193 (64.8%) indicated use of Edi monitoring (online supplemental figure S2) and 110/180 (61.1%) had participated in the concurrent clinical trial. Of those who had received NAVA training, the majority (140/157, 89.2%) received individual bedside training from local staff. Doctors were more likely than nurses or physiotherapists to have used NAVA clinically, in greater than five patients and recently (within the month prior to the survey), perhaps reflecting their role in medical management of multiple patients compared with nursing management of individual patients (table 1). Doctors were also more likely to indicate familiarity with NAVA evidence compared with nurses or physiotherapists (p=0.006). Overall, very few staff had used NAVA in the week (5/185, 2.6%) or month (16/185, 8.3%) prior to the survey, but most had used NAVA within the past 6 months (113/185, 61.1%) (table 1).

Only those reporting clinical exposure to NAVA (as opposed to training experience) were asked to proceed to subsequent questions.

Most participants agreed or strongly agreed that NAVA was safe (136/177, 76.8%), and clinically effective (99/176, 56.3%), that diaphragm monitoring was clinically effective (101/172, 58.7%), and that ventilator dysynchrony was a clinically significant issue (133/174, 60.3%) (table 2 and online supplemental figure S3). When asked about general feelings, 94/179 (52.5%) indicated ambivalence, 59/179 (33.0%) ‘liked’ (slightly, moderately or strongly) and 26/179 (14.5%) ‘disliked’ (slightly, moderately or strongly) NAVA, suggesting good equipoise for future randomised trials (online supplemental figure S4). In comparison to PSV, similar numbers of participants perceived better (slightly, moderately or significantly) (43/190, 22.6%), worse (slightly, moderately or significantly) (37/190, 19.5%), or equivalent (49/190, 25.8%) NAVA clinical performance, with 61/190 (32.1%) indicating ‘don’t know’, and with no significant differences between professional groups (online supplemental figure S5). More participants indicated a preference for PSV (93/171, 54.4%) compared with NAVA (29/171, 17.0%) for initiation of ventilatory weaning, although a large proportion (49/171, 27.1%) were ambivalent.

Overall most participants indicated that NAVA was more difficult than PSV (105/174, 60.3%) (table 2), and considered it was harder (much/moderately/slightly) rather than easier (much/moderately/slightly) in relation to ‘set up and start’ (85/116 (73.3%) vs 9/116 (7.8%)), ‘ventilation’ (49/121 (40.5%) vs 26/121 (21.5%)) and ‘reliability’ (55/110 (50.0%) vs 23/110 (20.9%)) (figure 1 and online supplemental figure S6). More participants indicated that NAVA was easier than PSV, rather than harder, in relation to ‘synchrony’ (79/131 (60.3%) vs 34/131 (26.0%)), ‘patient comfort’ (75/131 (57.3%) vs 22/131 (16.8%)) and ‘weaning’ (62/126 (49.2%) vs 32/126 (25.4%)). The most frequent response was ‘no difference’ between the two modes in relation to ‘lung protection’ (44/120, 36.7%) and ‘oxygenation’ (92/123, 74.8%). NAVA was not perceived to increase workload by 85/188 (45.2%) of participants, while 74/188 (39.4%) perceived either a slight, moderate, large or substantial workload increase, and with no differences between professional groups (table 2 and online supplemental figure S7).

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Participants reported low confidence in performing eight NAVA related tasks (median ranks range from 1 to 2 across all tasks); those with greater NAVA exposure in terms of patients treated, were more likely to indicate greater confidence (r=0.562, 95% CI 0.453 to 0.654) (figure 2 and online supplemental figure S8). Level of NAVA exposure was related to years of ICU experience; participants with more years ICU experience were more likely to have used NAVA in a greater number of patients (r=0.531, 95% CI 0.442 to 0.610). Doctors expressed greater confidence compared with nurses, who were consistently more likely to reply, ‘not at all confident’.

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When asked about the potential benefits of using NAVA and participants could select multiple options, the most common response (140/190, 73.7%) was ‘improved synchrony’ (figure 3 and online supplemental figure S9. The single most important benefit (single choice) was ‘reduced time in ventilation’ (57/183, 31.3%). The need to improve ventilator synchrony and weaning were also considered the most common clinical reasons for NAVA use (133/192 (69.3%) and 99/192 (51.6%), respectively). In regard to the disadvantages of NAVA (figure 3 and online supplemental figure S10), most selected ‘technical issues’ (129/189, 68.3%), with half (88/173, 50.9%) selecting this option as the most important single disadvantage. The next most commonly selected disadvantage was ‘difficult to adjust or regulate’, further suggesting the perception of difficulty and/or complexity with this mode. There were no significant differences between nurses and doctors in their perception of clinical advantages or disadvantages.

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The most commonly selected barrier to acceptance and implementation of NAVA, was ‘low experience, skills or confidence’ (172/183, 94.0%) (figure 3 and online supplemental figure S11), which was also selected as the single main barrier (132/171, 78.4%). Most participants believed that in their experience of NAVA, the mode was ‘often switched’ to PSV (56/182, 30.8%), with only very few (19/182, 10.4%) believing the mode was ‘switched rarely’ or ‘not at all’ (online supplemental figure S12). The reasons most often selected for switching were ‘lack of experience’ and ‘Edi signal problems’, which were also the most selected single main reasons for cross-over (57/168, 33.9% and 39/168, 23.2%, respectively) (figure 3 and online supplemental figure S13). When asked what single initiative would most help acceptance and use of NAVA, the majority (101/167, 60.5%) selected ‘improved training and sharing of the evidence base’ (online supplemental figure S14).

When asked about research aimed at investigating the use of NAVA in prolonged MV weaning, 161/180 (89.4%) of participants were supportive, 3/180 (1.7%) were not supportive, and 16/180 (8.9%) did not know. ‘Research evidence’ was considered to be less influential on clinicians’ views on NAVA (21/174, 12.1%) compared with ‘personal, clinical experience’ (93/174, 53.5%) and ‘colleague/peer recommendation’ (54/174, 31.0%).

Out of 42 participants who made a qualitative comment, 10 (23.8%) were supportive of NAVA and/or NAVA research, 23 (54.8%) stated that more training was needed, and 18 (42.9%) highlighted a lack of clinical experience. The following statements are representative and support other data presented above:

1. Nurse: ‘I found that when I had more exposure to NAVA, I became more confident and could see the benefits. But I found the inconsistency made it difficult to use. Sometimes I found it worked really well and other times very difficult to use.’

2. Doctor: ‘In theory NAVA sounds great. I wish I had more experience with it.’

3. Nurse: ‘NAVA is a great idea, but more training needed for staff confidence and being able to troubleshoot.’

Discussion

This multidisciplinary survey of 301 critical care clinicians, conducted across four adult ICUs at one academic hospital with >8 years of NAVA experience, sought to describe attitudes, beliefs, barriers and other factors relating to NAVA use, both in usual clinical practice and within clinical trials. In summary, the results indicate: (1) supportive attitudes to NAVA and belief that NAVA is safe and clinically effective with broadly equivalent performance to PSV, indicating good equipoise for future research; (2) a perception of increased difficulty and/or complexity compared with PSV; (3) a perception of low experience, skills and confidence, despite reasonable numbers of participants having clinical exposure to NAVA, and a need for improved training and (4) broad support for future NAVA research. These results provide context and feasibility data that can benefit clinical implementation of NAVA and the design of future trials. Perceived increased difficulty of using NAVA, low confidence of clinical staff and technical issues, may help to understand the current disparity between NAVA studies suggesting clinical benefit to patients, and the slow progress towards adequately powered efficacy or effectiveness trials and potential clinical adoption worldwide.

Technical difficulties with the equipment and/or Edi signal acquisition was the most often selected clinical disadvantage and reason for mode cross-over from NAVA to PSV. Cross-over is potentially a significant issue in future trials; low compliance will impact on statistical power and interpretation of results in a definitive study.13 Similar issues were not reported in three recent clinical trials,3 6 14 however, Edi signal problems were a stated cause of cross-over in 10 out of 36 participants (27.8%) in the concurrent feasibility RCT,5 and Edi synchrony and/or signal issues were reported in seven out of 20 (35%) patients recruited to an RCT by Di Mussi et al.15 Reasons for the differences between these trials remain unclear. Issues may relate to one or a combination of component failures, usability issues, or user behaviour, and these factors may be further influenced by environmental factors, such as staff to patient ratios, admission rates, availability of hardware, and varying levels of clinical expertise across a large staff group. In the NAVA mode, the Edi triggers and controls the support during the respiratory cycle, therefore acquisition of a stable, reliable signal is essential. Although trials have tested the catheter positioning technique,16 17 and demonstrated the reliability of the signal in different clinical situations,1 18–22 these studies were small (n<20), using cross-over designs with observations of limited durations—usually around 30 min. The results of this survey suggest a need to explore catheter positioning, signal acquisition and signal stability over prolonged periods and in a variety of clinical situations where the neural respiratory drive may become unreliable.

Despite >70% of participants indicating clinical exposure to NAVA and despite >8 years of NAVA use at the study site, perceived low confidence and/or inexperience of clinicians when using NAVA is a central theme within the survey. This finding was also detected in the concurrent feasibility RCT, where clinical inexperience of the mode was considered the reason for cross-over to PSV for four (11%) of 36 participants randomised to NAVA.5 Infrequent application within the difficult-to-wean patient group may be relevant to these perceptions, but the results also suggest perceived difficulty and/or complexity of NAVA and technical difficulties in relation to the Edi signal, both likely to impact use and confidence with NAVA.

In the context of a clinical trial, these issues may reduce the fidelity of the NAVA intervention and threaten the internal validity of the results. They may also significantly impact clinical implementation; clinical staff are unlikely to choose a more complex, difficult and novel treatment where an easier existing option that is not perceived to cause harm is available. A comparison may be made to the exponential increase in use of nasal high flow internationally despite a lack of evidence of efficacy,23 which may be partially due to its ease of use.

Critically, these factors are potentially modifiable. Our results suggest a need for high quality algorithms, training and standard operating procedures to mitigate these risks. Such approaches would improve the potential of demonstrating a true effect in a clinical trial by ensuring the fidelity of the intervention.13 24 Given the limited influence of current NAVA evidence on clinician behaviour suggested here, combined with growing evidence of clinical benefit from NAVA in preliminary studies,4 5 a well-designed clinical trial to demonstrate efficacy and/or effectiveness is required and is necessary to prompt behavioural change and clinical implementation.

Conclusions

This study presents the experience and views of a large and diverse staff group, describing attitudes, beliefs, perceived barriers and other factors that potentially affect NAVA use in critically ill adult patients. The central perceptions of low confidence, increased difficulty and technical issues reported here, may partially explain slow progress towards clinical implementation and large trials. In this context, high-quality training, algorithms and evidence from large definitive trials are even more critical to clinician acceptance and the future success of NAVA.