Based on a specific standardized test combining a swallowing test and a clinical evaluation of the cranial nerves involved in swallowing, we found that 25% of patients mechanically ventilated for 7 days or more exhibited clinical evidence of SD. Surprisingly, SD were considered persistent in only 10% of them based on the second test performed 48 h after the first one. Presence of persistent SD was associated with longer duration of ICU stay after extubation and longer time of enteral feeding. SD were not associated with an increased risk of pneumonia and reintubation in the present study.
Incidence of swallowing disorders
During the last decade, there has been an increasing interest in the literature regarding the long-term outcomes of ICU stay in terms of physical or psychological effects [1]. Among these effects, swallowing dysfunction is considered as a complication of MV that may favor aspiration of oral secretion, with an associated risk of pneumonia, a higher rate of reintubation, malnutrition or dehydration [3, 6,7,8]. Nevertheless, the incidence of SD among mechanically ventilated patients is difficult to assess and the methodology used in numerous studies is heterogeneous, sometimes non-specific, frequently enrolling specific subgroups of patients. Thereby in a systematic review of 14 highly heterogeneous studies (regarding population enrollment diagnosis strategy), SD incidence ranged from 3 to 62% [3].
Diagnostic strategy for SD detection
Reliable detection of SD is necessary to decide the optimal time to resume safe oral administration of foods, liquids or oral medications. In addition, erroneous diagnosis of SD may lead caregivers to wrongly postpone oral feeding since the fear of regurgitation is widespread. The screening procedure to systematically detect SD in routine practice must be reliable and easy to perform. Our results from the ICUs of two university hospitals suggest that a pragmatic clinical bedside assessment performed by an experienced caregiver following a systematic process could be implemented in routine practice. Macht et al. published in 2011 a retrospective observational study, using a bedside swallow evaluation [9]. In their large cohort of critically ill patients, they showed that swallowing disorders diagnosed by this clinical method were associated with a composite outcome of pneumonia, reintubation and death. Furthermore, in this study MV for more than seven days was significantly associated with moderate or severe dysphagia. Padovani also described a clinical method of SD diagnosis for critically ill patients, usable by health professionals as a first-line, with steps very similar to ours [10]. More recently, Schefold et al. in a prospective observational trial observed that systematic dysphagia screening performed by trained ICU nurses was positive for 12.4% of patients after extubation [11]. The same authors, in a review published in 2019, highlighted the need for studies assessing a clinical approach to this problem [12].
Complications and factors associated with swallowing disorders
In our study, patients with persistent SD were older, thinner at admission and received less often neuromuscular blocking agents (36% vs 66%) during the first days of MV compared to patients without or with only transient SD. In their study [13], Macht et al. found in univariate analysis an association between duration of MV and post-extubation dysphagia, but not with age or weight. Although several risk factors have been identified, the underlying mechanisms contributing to dysphagia in ICU patients remain incompletely understood. Most studies report conflicting results that could be explained by selection bias and the small number of patients enrolled [14]. The effect of neuromuscular blocking agents has been poorly analyzed in previous studies. However, we believe that these agents help to prevent laryngeal injury, which is frequently found in patients with prolonged intubation [15] and which may contribute to the onset of SD.
In our study, patients with persistent SD had significantly more frequently injury of XII cranial nerve at extubation. This original finding may be explained as a local injury due to the use of endotracheal tube, or as a complication due to an ICU acquired weakness [16, 17]. In parallel, we observed lower scores of MRC Scale for Muscle Strength at extubation for patients with persistent SD, without reaching significance. It should be noted that the MRC was measured on extubation while the persistent SD was diagnosed on average 72 h later. This could explain that the difference is not significant. Our objective was to determine an association between critical illness polyneuromyopathy and SD, as suggested in recent publications [16,17,18].
Patient outcomes
In a non-adjusted analysis, we highlighted, significant differences in duration of ICU stay after extubation and delay to oral feeding between patients with persistent SD and patients without SD or only transient SD. Macht et al. found that the presence of severe post-extubation dysphagia was significantly associated with poor patient outcomes, including pneumonia, reintubation, in-hospital mortality, hospital length of stay, discharge status and surgical placement of feeding tubes. In multivariate analysis, authors found that the presence of moderate or severe dysphagia was independently associated with the composite outcome of pneumonia, reintubation and death [9].
We arbitrarily selected a period of 7 days of invasive MV to keep only prolonged ventilation. Interestingly, Macht et al. [9] showed after multivariate analysis, that mechanical ventilation for more than 7 days was significantly associated with moderate or severe dysphagia. These results corroborate a posteriori our criteria for duration of MV.
The design of our study allowed us to discriminate between transient and persistent SD. In our series, the persistence of SD in only 14 among 35 patients with post-extubation SD indirectly suggests that oral feeding could have been resumed earlier in almost 60% of patients who were wrongly identified as at risk for aspiration pneumonia. This hypothesis warrants further more powerful studies to assess the clinical impact of such a strategy.