|Year : 2019 | Volume
| Issue : 3 | Page : 294-299
The role of laryngeal ultrasound in predicting postextubation laryngeal edema
Tayseer Zytoun, Yasser Noeman, Mohamed A Abdelhady, Ahmed Waly
Department of Critical Care Medicine, Faculty of Medicine, Alexandria University, Alexandria, Egypt
|Date of Submission||04-Jun-2018|
|Date of Acceptance||04-Feb-2019|
|Date of Web Publication||29-Aug-2019|
PhD Mohamed A Abdelhady
160 Ahmed Shawky street, Alexandria, 21500
Source of Support: None, Conflict of Interest: None
Purpose The purpose of this study is to determine the accuracy of portable bedside ultrasound (US) in the ICU in predicting postextubation stridor (PES).
Patients and methods This prospective observational cohort study enrolled 80 patients who were admitted to Alexandria Main University Hospital, who were planned for extubation. The air-column width difference (ACWD) was measured before planned extubation using a portable US. The primary goal was to assess the diagnostic accuracy of ACWD to predict the presence of significant laryngeal edema (LE), enough to cause PES. Bronchoscopy was done to confirm the presence of PES, whenever possible.
Results The prevalence of LE was 25%. The data collected from patients, with and without PES showed no definite risk factors for PES. A cutoff point of 0.9 mm change in ACWD (ACWD at vocal cords) was identified (P<0.001), below which a high probability of developing PES was noticed. The sensitivity and specificity of ACWD below or equal to 0.9 mm were 80% and 90% in predicting PES, respectively, with a negative predictive value of 0.931 and a positive predictive value of 0.727. In selected cases, postextubation bronchoscopy showed good correlation with ACWD by confirming significant LE in six cases out of seven with PES, five of which had an ACWD of below 0.9 mm.
Conclusion Portable ICU US measuring ACWD between predeflation and postdeflation of endotracheal tube cuff balloon is a tool of a very good prospective in predicting PES.
Keywords: bronchoscopy, laryngeal ultrasound, postextubation stridor
|How to cite this article:|
Zytoun T, Noeman Y, Abdelhady MA, Waly A. The role of laryngeal ultrasound in predicting postextubation laryngeal edema. Res Opin Anesth Intensive Care 2019;6:294-9
|How to cite this URL:|
Zytoun T, Noeman Y, Abdelhady MA, Waly A. The role of laryngeal ultrasound in predicting postextubation laryngeal edema. Res Opin Anesth Intensive Care [serial online] 2019 [cited 2019 Nov 21];6:294-9. Available from: http://www.roaic.eg.net/text.asp?2019/6/3/294/265718
| Introduction|| |
Endotracheal intubation is a lifesaving procedure which is routinely performed in a critical care setting. The purpose of endotracheal intubation is to permit air to pass freely to and from the lungs in order to ventilate the lungs by using mechanical ventilation in critically ill patients who cannot oxygenate or ventilate well .
Laryngeal edema (LE) in intubated patients is common in ICU patients. The prevalence of LE ranges from 3 to 30% ,. This complication leads to reintubation that is associated with an increase in hospital mortality rate by 17.4% , and an increase in the rate of nosocomial pneumonia and duration of ICU stay .
The risk factors of LE in intubated patients have been studied. Some studies suggested that female sex , history of difficult intubation, self-extubation, and prolonged intubation periods  are associated with a higher incidence of LE. Studies such as de Bast et al.  and Chung et al.  have reported no specific risk factors to predict LE and/or stridor.
A reduced cuff-leak volume identifies increased risk for postextubation stridor (PES). Miller and Cole  reported that the cuff-leak test might be a useful index of clinically significant laryngeo-tracheal narrowing. Engoren  reported a high negative predictive value (NPV), but a low positive predictive value (PPV), for the cuff-leak test. Although safe and simple, the controversial results may cause the physicians to make difficult decisions regarding extubation if the cuff-leak test is positive .
Bronchoscopy allows the physicians to directly visualize edematous vocal cords (VCs), but is an invasive procedure. That is why it is used in selected patients to confirm clinical findings .
Ultrasound (US) imaging is a novel, simple, portable, and noninvasive helpful tool for airway assessment and management in the operation theater, ICU, and emergency department. Various applications of US imaging of the upper airway include identification of endotracheal tube (ETT) placement, guidance of percutaneous tracheostomy and cricothyroidotomy, detection of subglottic stenosis, prediction of difficult intubation and PES and prediction of pediatric ETT size ,.
A new assessment tool, the air-column width (ACW), had been shown to accurately measure the VCs using intensive care US. The current study aims to detect whether VCs ACW before and after deflation of the ETT cuff would be useful in this clinical setting to detect LE in patients with planned extubation in terms of sensitivity, specificity, PPV, and NPV .
| Patients and methods|| |
A total of 80 intubated patients were enrolled from different critical care units in Alexandria Main University Hospital. The inclusion criteria for the patients were admission to the ICU and intubation for various causes, for example acute respiratory failure or for airway protection. All of the patients were intubated with a cuffed ETT. The patients were older than 18 years and had no anatomical abnormality hindering laryngeal sonography. The patients were sedated on assist-control ventilatory support to ensure passive inspiration and expiration during the laryngeal US. The approval of the medical ethics committee was obtained and an informed consent was obtained from all patients or their next of kin before enrollment in the study.
The current study was a prospective observational cohort study:
- Within 24 h prior to the planned extubation, decided by the treating physicians, laryngeal US and bronchoscopy,whenever possible, were performed while the patient is on assisted-control mode of ventilation, PEEP of 5 cmH2O, and tidal volume of about 8 ml/kg.
- The laryngeal US was performed with a portable intensive care US (using a Mindry DP-20 made in China with a linear propbe) as follows:
- The patients were in supine position, with the neck hyperextended and the patients’ endotracheal and oral secretions were gently suctioned.
- The probe was placed on the cricothyroid membrane with a transverse view of the larynx.
- To avoid the examiner’s bias and artifacts standard scanning plane was predetermined: containing several landmarks, the VC, thyroid cartilage, and arytenoid cartilage.
- The laryngeal US was performed with the balloon-cuff inflated and repeated with the balloon-cuff deflated.
- The VCs, the surrounding soft tissues, and the air passing through the VCs was observed (the laryngeal ACW is defined as the width of air passed through the VC as determined by the US) , and the shape of the air column observed.
- The air-column difference was defined as the width difference between balloon-cuff inflation and balloon-cuff deflation while the change of the air column was observed by widening of the air column base with balloon-cuff deflation due to refraction when the air passes between ETT and VC.
- The physician recorded the ACW during balloon-cuff deflation and balloon-cuff inflation over three respiratory cycles, and then the average values were recorded.
- In selected patients bronchoscopic images was taken before extubation for direct visualization of the VCs with the ETT in place for correlation between US and bronchoscopic images.
- After extubation, bronchoscopy when possible was done to assess VC volume and movement changes especially in patients with stridor or required reintubation.
- Stridor was defined as the presence of a high-pitched inspiratory wheeze localized to the trachea or the larynx and was associated with respiratory distress, usually requiring medical intervention ,.
- All of the assessments for stridor, respiratory distress, and the need for reintubation was made by the ICU physicians who were blinded to the measurements of the air-column width difference (ACWD).
- The management of stridor was done according to local protocols.
- Reintubation due to PES was defined as the patient, after extubation, presenting with stridor, impending respiratory failure, and symptoms of respiratory distress, all of which were relieved after intubation.
| Results|| |
The demographic characteristics of these patients are shown in [Table 1].
Ultrasonographical features of the vocal cords and the larynx
The VCs were demonstrated, in the transverse plane, through the anterior neck at the cricothyroid membrane and the air column was clearly established. The air column was square shaped and the ACW could easily be measured. The arytenoid cartilage was clearly shown with the cuff balloon inflated. The air column became trapezoidal in shape and masked the arytenoid cartilage when the balloon cuff was deflated. The width of the top of the trapezoidal air column was measured. Hence, the ACWD could easily be measured. These changes are demonstrated in [Figure 1].
|Figure 1 The shape of the air column (a) predeflation, showing the square-shaped air-column and the arytenoid cartilage clearly visualized, (b) postdeflation, the air-column became trapezoidal in shape and masked the arytenoid cartilage.|
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Air-column width during balloon-cuff deflation accurately predicted the occurrence of postextubation stridor
Twenty (25%) patients had PES, the other 60 (75%) had no signs of PES. Fifty-five (68.8%) patients were true negative as they had an ACWD equal to or more than 0.9 mm and no PES, 16 (20.0 %) cases were true positive as they had an ACWD of less than 0.9 mm and PES, where four patients were false negative as they had an ACWD equal to or more than 0.9 mm and still manifested PES and finally five patients were false positive; these patients showed no PES although having an ACWD of less than 0.9 mm.
These results were calculated after statistical analysis of the documented data deducing the proposed cutoff point below which the probability of PES is significantly higher (0.9 mm); this had a sensitivity of 80%, specificity of 90%, PPV of 72.7%, and NPV of 93.1%. These results are shown in [Figure 2] and [Table 2].
|Figure 2 ROC curve for ACWD to diagnose positive stridor cases versus negative stridor cases. ACWD, air-column width difference; ROC, receiver operating characteristic.|
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|Table 2 Agreement (sensitivity, specificity, and accuracy) for air-column width difference to predict postextubation stridor|
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Confirming laryngeal edema with fibro-optic bronchoscopic images
Direct visualization of the VCs using bronchoscopy was possible in limited number of cases, so only 21 cases before extubation were examined to try assessing VCs with ETT in place; 18 cases postextubation were examined promptly after extubation to assess VCs from which seven cases had PES. Only two cases had evident VCs edema causing encroachment on the ETT and these two cases had PES correlating with US finding of limited ACWD. Most of the cases examined after extubation showed different degrees of VCs edema or trauma, but six of the cases with PES showed significant edema; five of these cases had limited ACWD before extubation demonstrating good relation between ACWD and bronchoscopic findings.
Assessing risk factors for postextubation stridor
Risk factors for PES were investigated in this study such as demographic data, duration of intubation (45 cases with over or equal to 5 days of intubation with a mean of 4.39±2.37 days), and repeated reintubation. No specific risk factor was found to be a good predictor for the occurrence of PES in this study.
Relation between duration of intubation and stridor
As shown in [Table 3], cases with duration of intubation less than 5 days were 36 cases (representing 60%) and cases with more than or equal to 5 days of intubation were 24 cases (representing 40%). In the 20 cases with PES, nine (45%) cases were intubated for less than 5 days and 11 (55%) cases were intubated for more than or equal to 5 days. This showed no statistical significance between the two groups in the PES group as regards the incidence of PES (P=0.242).
| Discussion|| |
Postextubation LE is a common cause of airway obstruction after extubation in critical care patients and is thought to arise from direct mechanical trauma to the larynx by the ETT ,. The severity of airway obstruction due to LE varies up to emergency reintubation ,,,,,,. Reintubation itself is associated with increased mechanical ventilation days and length of stay in the critical care unit, higher costs, morbidity, and mortality ,,,,.
Diagnosis of PES is of significant clinical importance as these patients can benefit from close monitoring and specific therapies. Nonetheless, there is no consensus on a method to identify patients at risk of PES. Cuff-leak test, illustrating a leak around the ETT with the cuff deflated, has been proposed as a simple method of predicting the occurrence of PES ,,. However, cutoff point of the cuff-leak volume substantially differs between previous studies and the controversial results may cause the physicians to make difficult decisions regarding extubation if the cuff-leak test is positive, so there is a substantial need for defining risk of PES development through other methods ,.
The main objective of the current study was to identify the role of bedside US in predicting PES.
Using US ACWD was calculated with observing the shape of the air column before and after cuff deflation. Twenty-five percent of the cases had PES representing 20 cases. The other 75% of the cases had no signs of PES. The measurements of ACWD were documented and statistical analysis of the data deduced a proposed cutoff point (0.9 mm) below which the probability of PES is significantly higher and had a sensitivity of 80%, specificity of 90%, PPV of 72.7%, and NPV of 93.1%.
Results from the study by Ding et al.  showed a significantly lower ACWD (0.35 vs. 1.5 mm; P<0.01) and lower ACW during cuff deflation (4.5 vs. 6.4 mm; P=0.01) in patients who developed a stridor compared with patients who did not, but did not identify a cutoff point for predicting PES. Owing to the small sample size (n=51), including only four patients with PES, results from this study should be interpreted with caution. In the study by Sutherasan et al. , similar results were found with decreased ACW after cuff deflation (5.97 vs. 6.87 mm; P<0.05) and ACWD (1.08 vs. 1.99 mm; P<0.001) in patients who developed PES and they have identified a proposed cutoff point value at 1.6 mm of ACWD and demonstrated the high predictability of the ACWD measured by bedside ICU US with a sensitivity of 70.6%, specificity of 70.2%, high NPV of 92.2%. Both of these studies reported similar changes in the shape of the air column after ETT cuff deflation. Unfortunately, these results could not be replicated in the study by Mikaeili et al. . They reported no significant difference regarding ACW before deflation (12 vs. 11.5 mm; P=0.48) or ACWD (0.1 vs. 1.0 mm; P=0.59) between patients with and without PES. This might be explained by the small sample size (n=41) and the subsequent small number of patients developing PES (n=4); in that study they reported a very low sensitivity and specificity of 50 and 57%, respectively, and PPV of 11% and NPV of 91% at a proposed ACWD of 0.85 mm, concluding that cuff-leak test is still a better predictor of PES than portable bedside ICU US.
Direct visualization of the VCs using bronchoscopy was possible in limited number of cases, this was due to both availability and decision made with the treating physician according to the general condition of the patients. So only 21 cases before extubation were examined to assess VCs with ETT in place; 18 cases postextubation were examined to assess VCs from which seven cases had PES. Examined cases before extubation gave limited data due to ETT placement, only two cases had evident VCs edema causing encroachment on the ETT and these two cases had PES correlating with the US finding of limited ACWD. Most of the patients examined after extubation showed different degrees of VCs edema or trauma, but six of the cases with PES showed significant edema five of these cases were predicted by using bedside US before extubation. In the study conducted by Ding et al. , laryngeal US had a very good correlation with bronchoscopic images. Typical US and bronchoscopic images were documented. The landmarks seen by the laryngeal US, such as VC and false cords, could also be seen directly by bronchoscopy. In a patient with PES, necessitating reintubation, the bronchoscope examinations of the VC showed swelling, edematous change, and little changes of space between the VC, in this case the US of the VC also revealed increased VC width and no change in the ACW. In Newmark et al.  a case series included two patients with PES and one patient with LE secondary to extensive airway manipulation due to an unanticipated difficult airway of unknown cause. In these patients, it was shown that video laryngoscopy enables visualization of periglottic structures and pathology. Video laryngoscopy or flexible endoscopy might potentially enable identification of the cause of the laryngeal narrowing and thus guide treatment. However, further studies on the added value of video laryngoscopy or flexible endoscopy (or both) in the prediction of postextubation laryngeal edema (PLE) and PES as well as the diagnostic approach of laryngeal narrowing are needed before they can be implemented in clinical practice.
In the current study some suspected risk factors of PES were investigated such as different age groups, female sex, the duration of intubation, and reintubation times.
In different age groups, there was no statistical significance as regards the incidence of PES (P=0.365). This results were similar to the results reported in both Ding et al.  with age (years), mean±SD 72.24±17.71 in the PES group and 66.86±12.74 in the no PES group and which had no statistical significance (P=0.142) and Sutherasan et al.  with age (years), mean±SD 71±20 in the PES group and 67±10.5 in the no PES group and demonstrating no statistical significance (P=0.57).
Female sex, in the present study, showed no statistical significance as regards the incidence of PES. This was similar to the results of multiple studies as that of Francois et al. , Kriner et al. , and Chung et al. . On the other hand, other studies showed different findings and defined female sex as a risk factor for both LE and PES as that of Ho et al. , Darmon et al. , Cheng et al. , and Maury et al. .
Duration of intubation in the present study was not a predictor of PES, given that the present study had 45 cases with over or equal to 5 days of intubation with a mean±SD of 4.39±2.37 day and which may not be long enough to cause LE significant enough to be manifested as PES. This finding was similar to that in Sutherasan et al.  with a duration of intubation (days), mean±SD 6.45±8.93, Colice et al. . This was contradicted in the results reported by Esteller More et al.  and in the study conducted by Tadié et al.  the duration of intubation in patients with PES (mean±SD, 8.0±9.3) was significantly higher than in the group with no PES (mean±SD, 3.7±4.9) identifying prolonged intubation as a risk factor.
Reintubation events recorded according to data given by the attending physician with maximum times of reintubation being three events in only four cases, two events in 17 cases, single event in 11 cases, and 41 cases had no history of reintubations along their courses in the ICU. Reintubation events during the course of ICU stay did not have an effect on the incidence of PES in the current study even with recurrent reintubation events of up to three times. Jaber et al.  found that reintubation after self-extubation was a risk factor for developing PES.
In the present study, reintubation was the final decision in 23 of the extubated cases; seven of them had PES and stridor was the main cause of reintubation in three of them forming 13% of all reintubated cases confirming the threat posed by PES in the ICU and the need to continue searching for a predictive test to confirm or exclude the presence of significant LE before extubation.
Limitations of this study
Bronchoscopy was not feasible in all patients, ETT size could not be standardized in all examined cases, and the examination was only applied on a specific age group.
| Conclusion|| |
Portable ICU US measuring ACWD between predeflation and postdeflation of ETT cuff balloon is a very good tool for predicting PES.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]