What’s new in reducing the impact of tracheostomy on communication and swallowing in the ICU

OWVs can be used safely in ventilated patients with no evidence of negative effects on ventilation [5]. However, serious adverse events (e.g. gas trapping, barotrauma, asphyxiation and death) can occur with misapplication of OWVs, particularly if used with a fully or partially inflated cuff, or where there is reduced airway patency. Airway patency assessment is typically a subjective clinical evaluation. Some guidance suggests a 40–50% reduction of tidal volume (V_t) is indicative of adequate patency for OWV use [5], but there has been a lack of evidence to support this. A recent study comparing four non-invasive measurements to assess upper airway patency, reported 86% of patients with a transtracheal pressure (TTP) of ≤ 9 cmH₂O and 93% of patients with a TTP of ≤ 5 cmH₂O were successful with a OWV trial [6]. There was no significant difference in the percentage reduction in V_t, but there was significantly higher loss of V_t in successful patients (268.5 ml ± 177.2 ml) compared with unsuccessful patients (88.6 ml ± 99.6 ml) [6].

As OWVs prevent air escape via the tracheostomy, subglottic pressure can be restored. It can also restore physiological positive end-expiratory pressure, cough, facilitate vocalisation, and improve airway protection. A recent randomised controlled trial (RCT) used videofluoroscopy, high-resolution manometry (HRM), and computed tomography and computational fluid dynamic simulation analysis to compare swallowing metrics in patients who had used OWV for 2 weeks with patients with an inflated cuff [7]. The OWV group had a mean subglottic pressure of 6.95 cmH₂O, comparable to normal subglottic pressures measured directly (5.5–9.5 cmH₂O), and improvements to velopharyngeal maximum pressure, upper oesophageal relaxation, and reduced aspiration and penetration. Another recent RCT highlighted the feasibility and safety of early use of OWVs with a reported shorter time to decannulation with early cuff deflation and OWV (as early as 12–24 h after insertion) compared with late use (48–60 h) [8].

There continues to be widespread use of ‘leak speech’ or ‘ventilator-adjusted leak speech’, where the cuff is deflated but a OWV is not used. Although similar speech function can be achieved with both leak speech and OWV [9], no studies have evaluated the impact of leak speech on subglottic pressures or swallowing function.

Above cuff vocalisation (ACV) (also known as ‘Talking Tracheostomy’ and ‘External Subglottic Air Flow’), involves application of an external airflow via the subglottic suction port. The only RCT reported improvements to quality-of-life, including speech score, and moderate patient independence and satisfaction [10]. However, there was increased ICU and hospital length of stay compared to the control group, 10 of whom proceeded to OWV trials [10]. The first systematic review of ACV highlighted the limited and low-quality evidence available and variation in practice [11]. A recent survey of healthcare professionals (HCPs) (presented at the 33^rd European Society for Intensive Care Medicine Congress) found limited implementation in practice, but confirmed the variety of potential benefits for patients including improving communication, swallowing, sensation, cough and quality-of-life [12, 13]. Both the systematic review and survey have demonstrated the variability in application, implementation and practice, which has highlighted areas for further research [11, 12]. More recently, a qualitative study exploring HCPs’ experiences of ACV has reinforced these findings, showing that the subjectivities and uncertainties surrounding ACV are leading to variations in practice and the purpose for which ACV is used, which results in varying opinions regarding whether ACV is ‘worth a try or a last resort’ [Unpublished data presented at the 2022 Critical Care Canada Forum, 14].

There are a wide variety of minor complications, such as discomfort, strained vocal quality and stomal air escape. Serious adverse events include subcutaneous emphysema, air trapping, bleeding, and tracheal dilation secondary to misapplication of the airflow to the cuff [11, 12]. As with OWV, airway patency is essential for successful and safe use. However, the objective measures for airway patency described above could not be used for ACV without cuff deflation, and assessment currently relies on subjective clinical assessment.

Some of the variation in practice and opinions may be due to the different tracheostomy tube designs. For example, the subglottic port of the Portex^® tube has a 2 mm lumen with a single lateral exit, whereas the TRACOE^® tube has a 4 mm lumen with bilateral exits. Passing high airflows through a narrow lumen will increase the velocity of the air. It is unclear what forces and pressures are applied to the laryngo-tracheal mucosa, what intra-luminal pressures build-up during glottal closure with continuous airflow application, or how these vary with tube design. A recent study evaluated the pressures exerted by tracheostomy tubes and found when in position, 15 of 17 tubes applied pressure to the posterior tracheal wall above the threshold for mucosal injury (3.99 kPa) [15]. Similar research is needed to evaluate the impact of different airflows on laryngo-tracheal mucosa with different tubes.

Various proposals for the mechanism of action have been suggested including improvement in laryngo-pharyngeal sensation and subglottic pressures as laryngo-pharyngeal airflow improves [11]. The extent of the improvement to sensation and pressures is likely to depend on airflow delivery and rates.