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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 6  |  Issue : 3  |  Page : 355-361

Predictive value of cuff leak test, laryngeal ultrasound, and fiberoptic laryngoscopy for postextubation stridor after prolonged intubation


Department of Anesthesia and Surgical Intensive Care, Zagazig University, Zagazig, Egypt

Date of Submission23-Sep-2018
Date of Acceptance03-Dec-2018
Date of Web Publication29-Aug-2019

Correspondence Address:
MD Farahat I Ahmed
41 Elssehabah Street, Hadayek Alkobbah, Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/roaic.roaic_76_18

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  Abstract 

Background Endotracheal intubation is frequently complicated by laryngeal edema, which may present as postextubation stridor (PES) or respiratory difficulty or both. Multiple tests were used to predict the PES. The present study aimed at description and evaluation of the predictive values of the cuff leak test (CLT), laryngeal ultrasound (LUS), and indirect flexible fiberoptic laryngoscopy (FOL) to predict PES in ICU patients after prolonged intubation.
Patients and methods This prospective study was conducted on 60 intubated patients who were admitted into the surgical intensive care unit. After successful 30-min spontaneous breathing trial and within 6 h before the planned extubation, CLT, LUS, and FOL were performed for all patients. After extubation, the patients were observed and classified into two groups according to the presence of PES within 48 h.
Results Two patients were excluded owing to self-extubation, and 58 patient’s data were analyzed. There was no significant difference in CLT volume and the leak fraction between the patients with PES (PES group) and those without PES (non-PES group). However, statistically, air column width with balloon inflated or deflated was significantly lesser in the PES group than the corresponding values in the non-PES group (P=0.04 and 0.009, respectively). Moreover, there was a high significant difference in the air column width difference between both groups (P<0.001). Moreover, the incidence and severity of laryngeal injuries as per FOL grading scale and the rate of reintubation were statistically higher in the stridor than non-stridor patients group (P<0.001).
Conclusion For the noninvasive methods, the CLT has a low predictive value with high possibility of false results, but the data from LUS can be used for approximate evaluation of the laryngeal lumen narrowing; however, the interpretations of the ultrasound data are not conclusive. On the contrary, the FOL is the best accurate diagnostic tool but it is invasive.

Keywords: air column width, cuff leak test, fiberoptic laryngoscopy, laryngeal ultrasound, postextubation stridor, prolonged intubation


How to cite this article:
Hasan AM, Ahmed FI. Predictive value of cuff leak test, laryngeal ultrasound, and fiberoptic laryngoscopy for postextubation stridor after prolonged intubation. Res Opin Anesth Intensive Care 2019;6:355-61

How to cite this URL:
Hasan AM, Ahmed FI. Predictive value of cuff leak test, laryngeal ultrasound, and fiberoptic laryngoscopy for postextubation stridor after prolonged intubation. Res Opin Anesth Intensive Care [serial online] 2019 [cited 2019 Nov 21];6:355-61. Available from: http://www.roaic.eg.net/text.asp?2019/6/3/355/265729


  Introduction Top


Laryngeal edema owing to prolonged intubation is an important factor that may contribute to postextubation stridor (PES) or respiratory distress (or both) after extubation with subsequent need for reintubation. Extubation failure, as distinct from weaning failure, can be attributed to upper airway obstruction that might be recognized only after the Endotracheal tube (ETT) has been removed. Endotracheal intubation can result in laryngotracheal trauma, inflammation, granuloma formation, ulceration, and edema, which lead to glottic and subglottic narrowing. Prediction of PES and diagnosis of the ETT-related laryngeal injuries are valuable for correct management of the problem and to decrease the incidence of extubation failure and reintubation [1],[2].

Multiple factors may predispose to increase the risk of laryngeal injuries in patients with prolonged intubation, including traumatic intubation, emergency unplanned intubation, inappropriate large-sized ETT, and high ETT cuff pressure. In addition, nasogastric tube with ETT leads to nasogastric tube syndrome by prolonged external compression on the posterior cricoarytenoid muscle that may rarely induce ischemia and ulceration of this muscular structure, resulting in vocal cords paralysis in adduction [3]. Moreover, gastroesophageal reflux is a contributing factor of laryngeal edema [4].

Multiple recent studies were done to evaluate the airway patency before extubation including the cuff leak test (CLT), the laryngeal ultrasound (LUS), and the flexible fiberoptic laryngoscopy (FOL). The CLT depends on the measurement of air leak volume around the ETT with the balloon deflated.

The real-time LUS depends on the measurement of the width of the air column between the vocal cords while the balloon inflated (ACWBI) and deflated (ACWBD) with the difference between both (ACWD). The ACW was decreased by the laryngeal edema.

Although both CLT and LUS are noninvasive, the FOL is an invasive method and enables for visualization of the laryngeal and upper tracheal lumen.


  Aim Top


The aim was to describe and evaluate the predictive value of both CLT and LUS as a noninvasive methods and the FOL examination as an invasive method to predict the probability of PES and extubation failure in ICU patients after prolonged intubation.

Sample size

The same size was based on two previous studies that evaluated the CLT and LUS as a predictors of PES. The ACWD is the primary predictor parameter with CI two sided 95 and 80% power. So, the calculated total sample size was either 31 or 77. An average sample size was 54 patients, but 60 patients were selected for possible dropouts.


  Patients and methods Top


This prospective study was conducted on 60 patients who were admitted into the surgical ICU. The study was carried out in Zagazig University Hospitals over a 10-month period after approval from the Institutional Review Board (IRB), and consents from all patients or their relatives were obtained.

Inclusion criteria

The following were the inclusion criteria:
  1. Age group from 18 to 60 years old of both males and females.
  2. American Society of Anaesthesiologist (ASA) status II and III.
  3. All patients intubated for acute respiratory failure or other different causes as for airway protection.
  4. ETT is a polyvinyl chloride cuffed tube with high-volume, low-pressure cuff with an ID of 6.5–8 mm for at least 72 h.
  5. ETT cuff pressure must be monitored thrice daily to maintain the balloon pressure of 20–25 cm H2O.
  6. All patients had fulfilled the criteria of weaning from the MV and passed successfully for a minimum period of 30 min spontaneous breathing trial and also sit comfortably in a semisitting position.
  7. All of the patients under the study must be awake and cooperative.


Within 6 h before the planned extubation, the ETT deflated CLT, the real-time LUS, and flexible FOL were performed for all patients before the planned extubation. During performing the test, light sedation was given to some patients to suppress coughing, ventilator fighting, or active expiration to avoid the possible artifacts of the test results. Sedation was carried out by intravenous increments of 25–50 mg of propofol to achieve the desired clinical effect.

Exclusion criteria

The following were the exclusion criteria:
  1. Age less than 18 years old.
  2. Inability to obtain an informed consent.
  3. Intubation owing to upper airway obstruction or vocal cord paralysis.
  4. Intubation outside the hospital.
  5. Self-extubation.
  6. Tracheostomy.
  7. History of previous laryngeal surgery, trauma, or neck exposure to radiotherapy.
  8. Disturbed conscious level.
  9. Failure of extubation after data collection.


ETT deflated cuff leak test

  1. The test was performed as described by MILLER and COLE [5]. Before performing the test, the patient must be awake with completely patent ETT by gentle suction of the oropharyngel and ETT secretion.
  2. The patient was reconnected to the mechanical ventilator with the following adjusted settings:
    1. The mode was changed into assist-control mode with 5 cm H2O of PEEP.
    2. Tidal volume (VT) was increased until the peak inspiratory pressure (PIP) reached up to 30 cm H2O.
    3. Inspiratory time of 1–1.5 s to create a stable plateau pressure.
    4. Mandatory rate that suppresses spontaneous breathing efforts.
    5. Peak flow rate of 1 l/kg±10 l/min
  3. The endotracheal tube cuff was deflated.
  4. The set inspiratory tidal volume (VT), peak inspiratory pressure (PIP), and the six consecutive exhaled volumes were recorded. The average of lowest three values was recorded.
  5. ETTBD leak volume was calculated by the difference between the inspiratory VT and the average of the three lowest exhaled volumes.
  6. The leak volume fraction ratio (LVFR) is the ratio of the average leak volume to the inspiratory VT.


After performing the test, the endotracheal tube cuff was reinflated, and the ventilator settings were readjusted again to the previously used settings.

Laryngeal ultrasonography

  1. The LUS was performed with the US machine [Logiq 4 general Electric, Logiq 100 pro (Wipro GE Healthcare private Ltd., No. 4, Kadugodi industrial area, Bangalore, Karnataka, India)], using a linear probe (6–12 MHz).
  2. The patient was put in a supine position with hyperextended neck.
  3. The probe was placed on the cricothyroid membrane with a transverse view of the larynx.
  4. A standard scanning plane was followed in all patients where the US probe was put in a transverse plane on the cricothyroid membrane for visualization of the true vocal cords (VC), false cords, thyroid cartilage, and arytenoids cartilage ([Figure 1]).
    Figure 1 A diagrammatic representation of US images of the larynx demonstrates (a) laryngeal air column during balloon-cuff inflation. Square-shaped air column. True cords are over both sides of the air-column. Arytenoid cartilages are behind the true vocal cords and beside the air column. (b) Air column during balloon-cuff deflation. The air column became trapezoid in shape and the air column width increased. The arytenoid cartilage and part of the true cords were masked by the acoustic shadow. A, arytenoids cartilage; AC, laryngeal air column; T, thyroid cartilage; VC, true vocal cords. Arrow shows air column width.

    Click here to view
  5. US measurement of the laryngeal air column width with both the ETT BI (balloon inflated) ([Figure 1]a) and BD (balloon deflated) ([Figure 1]b) over the respiratory cycle for three consecutive times. An average value was recorded for both.
  6. The surrounding soft tissues was evaluated.
  7. The laryngeal ACW was the width of air passed through the VC ([Figure 1]).
  8. The ACWD was the difference between the top of air column with the ETT cuff inflated and deflated.
  9. The ratio of the external ETT size to laryngeal AP diameter was calculated by the regression equation developed by Higenbottam and Payne for estimating the laryngeal anterioposterior (A-P) diameter: A-P diameter (mm)=[33.9−height (m))–33.7] [6].


Fiberoptic laryngeal examination

  1. It was performed after performing both CLT and LUS and immediately before extubation in all patients.
  2. A flexible fiberoptic bronchoscope (Storz size 3.2 mm) was inserted nasally under local anesthesia and light sedation.
  3. The FOL view was planned to evaluate the posterior pharyngeal area, the arytenoid cartilage, the vocal cords, and their relationship with the endotracheal tube.
  4. ETT was immediately removed, and the FOL examination was completed to see the footprints of the ETT on the VC, the glottis, and subglottic areas.
  5. Any edema, ulceration, granuloma, obstruction, and abnormal VC mobility were recorded.
  6. A laryngeal lesion grading scale was utilized from 0 to 4 ([Table 1]) ([Figure 2]) [4],[7],[8].
    Table 1 Fiberoptic postextubation laryngeal lesions scale

    Click here to view
    Figure 2 Fiberoptic laryngeal view. (a) Normal, (b) mild edema, (c) moderate edema, (d) severe edema, and (e) very severe laryngeal edema.

    Click here to view


After extubation, all patients were monitored and clinically assessed for 48 h by the intensivists who were blinded for the test results for the presence of PES and signs and symptoms of respiratory distress.

Stridor: it 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. The management of stridor included the following
  1. Humidified O2 therapy with racemic epinephrine aerosol inhalation.
  2. Either inhalation or intravenous steroids.
  3. Noninvasive ventilation support.
  4. Heliox inhalation therapy if it was available.


Reintubation was done if the previous measurements failed and the patient had symptoms of respiratory distress with impending respiratory failure as tachypnea (RR >30), hypoxemia (SpO2<90 with 60% FiO2), sweating, and tachycardia that was immediately relieved after intubation. Extubation failure was defined as the need to reintubate the patient within 48 h following extubation, whatever the cause. Reintubation was considered early if was done within the first 6 h after extubation and late if performed in the time interval from 6 h until 48 h after extubation.

Data recorded

  1. Patient’s demographic data including age, sex, weight, ASA physical status, and the indication of intubation.
  2. Duration of intubation.
  3. ETT cuff pressure.
  4. CLT parameters: ETTBD leak volume and the LVFR as mentioned before.
  5. LUS measurements:
    1. Air column width with ETT balloon inflated (ACWBI) and deflated (ACWBD) and the difference between both (ACWD).
    2. Calculated laryngeal A-P diameter (mm) and the ratio between ETT external diameter/A-P laryngeal diameter.
  6. FOL grading scale: the degree of the laryngeal lesion as per the FOL scale as mentioned before ([Table 1]).
  7. PES is the stridor within the first 48 h following extubation.
  8. Reintubation rate and timing.


Statistical analysis

For continuous variables, comparisons were performed with Student’s t-test. For categorical variables, comparisons were performed with χ2-test and Fisher’s exact test when appropriate. P value less than 0.05 was considered statistically significant, and P less than 0.01 was considered highly significant.


  Results Top


The study was conducted on 60 patients but 58 cases were included in the final analysis. Two patients were excluded from the study because of self-extubation. In [Table 2], according to the occurrence of post-PES, the patients were divided into two groups, seven (12%) patients had PES and 51 (88%) patients had no PES.
Table 2 Patients demographic data, indication and duration of intubation, cuff pressure, test variables, and the reintubation rate

Click here to view


There were no statistical significant differences between both groups regarding the age, sex, predicted body weight, and ASA physical status. Moreover, there were no statistical significant differences between PES and non-PES groups regarding the reason of intubation, duration of intubation, and the cuff pressure (P=0.67, 0.16, 0.72, respectively) ([Table 2]).

The cuff leak volume (ETTBD leak volume) and the LVFR were statistically comparable in both group (P=0.15 and 0.07, respectively) ([Table 2]).

Statistically, the laryngeal real-time ultrasound (LUS) measurements values within 6 h before planned extubation showed that the ACWBI (with the ETT balloon inflated), ACWBD (with ETT balloon deflated), and the ACWD in the PES group were significantly lesser than the corresponding values in the non-PES group (P=0.04, <0.009, and <0.001, respectively) ([Table 2]).

The calculated A-P diameter of the larynx and the ratio of the ETT external diameter to the calculated laryngeal A-P diameter have statistically no significant differences between the PES and non-PES groups (P=0.21, and 0.45, respectively).

On the contrary, the flexible FOL grading scale showed high significant correlation between the incidence of PES and the severity of the laryngeal lesions. The FOL laryngeal lesion grading scale showed that the airway lesions were moderate to very severe (2–4 grading scale) in PES group, but the lesions were mild to moderate (0–2 grading scale) in the non-PES group (P<0.001) ([Table 2]).

The incidence of reintubation was significantly higher in the PES group than in the non-PES group (P<0.001). In the PES group, reintubation was done early (within 6 h postextubation) in four patients (57%) and was done late (within 6–48 h) in one (14%) patient after failure of conservative measurements with 71% total incidence of reintubation. However, in the non-PES group, one (2%) patient required late reintubation after extubation ([Table 2]).


  Discussion Top


In clinical practice, an intensivist can easily evaluate the weaning from mechanical ventilation in intubated patients, but it is difficult to predict the failure of extubation owing to upper airway obstruction. Pre-extubation evaluation of these patients can hardly be achieved because the ETT blocks direct visualization of the larynx, trachea, and VC [9],[10],[11]. In his recent review study, Pluijms et al. [12] demonstrated a wide variation of reported incidence of postintubation laryngeal injuries ranging from 5 to 54.4% with a wide range of estimated incidence of PES from 1.5 to 26.3% according to previous research studies.

In the present study, statistical analysis of both PES and non-PES groups revealed that the age, sex, duration of intubation, and cuff pressure have no statistical significance. These results are similar to the studies by Mikaeili et al. [13] and Ding et al. [14]. However, other studies showed that the female sex, prolonged duration of intubation, high cuff pressure, and high patient height/ETT ratio increased the risk of PES [4].

The overall incidence of PES was 12%, and the reintubation rate was 10.3% in all patients who were included in the present study. These results are nearly similar to previous reports [11],[15]. On the contrary, after failure of conservative treatment of PES, reintubation was done in five (71.4%) patients in the PES group. Multiple previous studies showed a wide range of reintubation from 10 to 100% in patients with PES as per the review study by Pluijms et al. [12].

In this prospective study, the CLT has no value to predict PES. It relies on the principle that the leak detected around the ETT with a deflated cuff depends on the patent area around the ETT and thus will be inversely related to the degree of airway obstruction owing to laryngeal edema. Moreover, multiple factors such as respiratory mechanics, inspiratory flow, compliance of the chest wall and lung, and presence of secretion in the tracheobronchial tree, have been shown to influence the degree of leak around the ETT with deflated cuff, thus rendering the interpretation of the test difficult and unreliable [16].

According to a previous study, the results of the CLT were conflicting but may be reasonable to use the test if combined with the presence of risk factors to identify patients with increased risk for laryngeal edema [9]. Moreover, there was no definite cutoff value of CL volume or the percentage of leak volume that can be used to predict the PES after prolonged intubation. These studies used a wide variation of the CL volume that ranged from 110 to 310 ml leak and CL fraction that ranged from 12 to 24% [12],[17],[18].

Multiple previous studies used LUS for evaluation of airway patency [13],[14],[19]. A study by Lakhal et al. [20] showed a good correlation between magnetic resonance and US airway caliber. The ultrasound was used to measure the air column width (ACW), which is the width of the acoustic shadow at the level of the vocal cords. If this width was measured before and after ETT cuff deflation, then the ACWD was calculated. In the current study, the ACWBI, ACWBD, and ACWD were significantly lesser in the PES group than the corresponding values in non-PES group (P=0.04, 0.009, and <0.001, respectively). These results are similar to the results of previous two studies [14],[19].

In spite of the statistical significant differences of the LUS values between both PES and non-PES groups in the current study, other previous studies noticed that, the LUS has a low positive predictive value, low sensitivity, and low specificity for predicting PES or postextubation laryngeal injuries with nonsignificant difference of the ACW before deflation between patients with and without PES [13],[21]. According to the results of the previous studies, the finding of the LUS should be interpreted with caution because these studies were conducted on a small sample size with less number of patients who had PES. Moreover, there were no fixed cutoff values for ACW and ACWD to predict PES in all studies [12].

The advantage of FOL over the other tests is that it enables indirect visualization of the laryngeal lumen, vocal cord mobility, periglottic structures, and the subglottic area and also enable identification of the types and extent of the lesions and thus guides treatment [12]. Multiple previous studies have used different laryngeal FOL grading scale for the postintubation laryngeal injuries [4],[7],[8],[22],[23].

In this study, by flexible FOL examination, it was found that 72% of patients with PES have severe laryngeal lesion (grade 3) and 14% with total laryngeal edema (grade 4) with high significant difference compared with the non-PES group. From these results, it was demonstrated that patients with grades 3 and 4 laryngeal lesion scale were highly prone to have PES with subsequent high incidence for reintubation, where five (83.3%) patients from six patients with grade 3 and 4 were re-intubated in this study. These results are similar to the results of the previous studies [4],[7],[8]. From the current and previous studies, the FOL evaluation and grading for the degree of the laryngeal lesions in the patients with prolonged intubation is the most accurate diagnostic and predictive method for expectation of PES, but the test needs patient sedation, an expert clinician, a small-size flexible fiberoptic bronchoscope, and it is an invasive method.The question, if we have FOL grading scale 3–4, is it wise to proceed for extubation and manage the expected problem, to give steroid 48 h before extubation as per previous study [18] with controversial outcome, or to do tracheostomy for those patients until relief of the laryngeal lesions? These questions open the door for more researches.


  Conclusion Top


The value for diagnosis or expectation of the laryngeal injuries with subsequent PES after prolonged intubation is to treat the accurately diagnosed laryngeal injuries and select the proper timing for successful extubation to decrease the rate of extubation failure with subsequent reintubation. For the noninvasive methods, the CLT has no predictive value with high possibility of false results. The data from LUS can be used for evaluation of the degree of laryngeal lumen narrowing but the interpretations of the ultrasound measurements are not conclusive. On the contrary, the FOL is the best accurate diagnostic tool, but it is invasive and needs an expert physician.

Limitation of the study

The small number of patients and the need for ultrasound or flexible fiberoptic bronchoscope that may not be available in all ICU are some of the limitations.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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