Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 7  |  Issue : 2  |  Page : 121-128

Role of intubating laryngeal mask airway for endotracheal intubation in the intensive care unit: an observational trial


Department of Anesthesiology and Intensive Care, Faculty of Medicine, Ain Shams University, Cairo, Egypt

Date of Submission27-Sep-2013
Date of Acceptance20-Nov-2013
Date of Web Publication31-May-2014

Correspondence Address:
Sherif S Wahba
Department of Anesthesiology and Intensive Care, Faculty of Medicine, Ain Shams University, Cairo 11566
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-7934.133342

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  Abstract 

Purpose
Avoidance of further worsening of hypoxemia is a prime objective during intubation of patients with acute respiratory failure. The aim of this study was to compare conventional laryngoscopy with intubating laryngeal mask airway (ILMA) with the aid of flexible fiberoptic bronchoscopes (FOBs) for intubation of class III/IV Coramck-Leahne patients in the intensive care unit.
Materials and methods
After failure of an initial attempt at intubation using conventional direct laryngoscopy, 112 Cormack-Lehane class III/IV patients were subjected to repeated attempts of intubation using either a Macintosh-type laryngoscope (ML, n = 59) or an ILMA with FOB (n = 53). After failure of two further trials using either technique, intubation would be attempted using the GlideScope video laryngoscope. The primary outcome was the incidence of severe hypoxemia (defined as arterial saturation <80%). Secondary outcomes were intubating time, number of attempts, and incidence of other complications.
Results
Twenty-five patients (42.2%) in the ML group suffered from severe hypoxemia, compared with eight (15.1%) patients in ILMA group (P = 0.002). The median (interquartile range) intubating time was 39 s (32.3-87.8 s) in the ML group versus 102 s (73.8-123 s) in the ILMA group (P < 0.001). Multiple logistic regression showed that the intubating technique was the only intubation-related predictor of severe hypoxemia (odds ratio, 4.08; 95% confidence interval, 1.63-10.18; P = 0.003). Both groups were comparable as regards the incidence of other intubation-related complications and postintubation course in the intensive care unit (P > 0.05).
Conclusion
In Cormack-Lehane class III/IV patients who failed to be intubated in the first attempt, retrying intubation using the ILMA with the aid of a flexible FOB was associated with a lower incidence of severe hypoxemia.

Keywords: Endotracheal intubation, hypoxemia, laryngeal mask airway, laryngoscopy, respiratory failure


How to cite this article:
Wahba SS, Hakim SM. Role of intubating laryngeal mask airway for endotracheal intubation in the intensive care unit: an observational trial. Ain-Shams J Anaesthesiol 2014;7:121-8

How to cite this URL:
Wahba SS, Hakim SM. Role of intubating laryngeal mask airway for endotracheal intubation in the intensive care unit: an observational trial. Ain-Shams J Anaesthesiol [serial online] 2014 [cited 2021 Dec 8];7:121-8. Available from: http://www.asja.eg.net/text.asp?2014/7/2/121/133342


  Introduction Top


Airway management in patients with acute respiratory failure is a challenging task because of decompensated physiological reserve and susceptibility to significant life-threatening complications, especially hypoxemia. Nearly 30% of patients admitted to the intensive care unit (ICU) will need mechanical ventilation, which is mostly facilitated through endotracheal intubation [1]. The practical conduct of endotracheal intubation is normally determined by the clinical context in which intubation is actually carried out. Besides preparedness and skill of the practitioner conducting the intubation, the choice of the intubating technique may affect the outcome. For instance, most of the intubations performed in the operating room are carried out on an elective basis by skilled anesthesiologists and carry a substantially low rate of complications. In contrast, endotracheal intubation in a critically ill patient is usually urgent [2],[3]. This entails that intensivists be especially skilled at airway management in patients with poor cardiorespiratory reserves, should serious complications such as hypoxemia, pulmonary aspiration, cardiac arrest, or death be reduced [4],[5],[6],[7].

Several trials have scrutinized the outcomes of emergency tracheal intubation in the ICU [8],[9],[10],[11]. However, the relation between the choice of the intubating aid and the outcome in this setting remains unclear. Recently, there have been reports on the use of the intubating laryngeal mask airway (ILMA) for emergency intubation in patients with difficult airways [12],[13] However, there is currently no adequate information on the feasibility of using the ILMA for tracheal intubation in patients having difficult-to-manage airways who present with acute respiratory failure.

Lacking a standard algorithm for intubating critically ill patient, we hypothesized that the use of an intubating device with both ventilating and intubating properties, such as the ILMA, could reduce the incidence of intubation-related complications. Therefore, the aim of this study was to compare conventional direct laryngoscopy using the Macintosh laryngoscope (ML) with ILMA as regards the incidence of severe hypoxemia and other intubation-related complications, intubating time, and the number of intubating attempts in Cormack-Lehane class III/IV patients presenting with acute respiratory failure.


  Materials and methods Top


This prospective observational study was conducted at a 16-bed general ICU affiliated to Aljahra Hospital, Ministry of Health of Kuwait, during the period from January 2010 to September 2012. The study was approved by the local institutional review board and informed consent was obtained from the patients or their next of kin.

The study included 112 patients with acute respiratory failure who required endotracheal intubation and mechanical ventilation after failure of conservative management including noninvasive ventilation. All patients fulfilled one or more of the following clinical and arterial blood gas criteria: PaO 2 < 60 mmHg at FiO 2≥ 60%, PaCO 2 > 50 mmHg, respiratory rate >35 breaths/min, and severe respiratory acidosis (arterial blood pH < 7.2). Exclusion criteria were age lesser than 18 years, history of difficult intubation or gastroesophageal reflux, BMI greater than 35 kg/m², Mallampati class IV, interincisor distance less than 3 cm, and systolic blood pressure less than 90 mmHg. In all patients, intubation was initially attempted using a rapid sequence induction-intubation technique. Intravenous midazolam (0.05-0.1 mg/kg) was administered followed by 1-1.5 mg/kg succinylcholine and the cricoid pressure was maintained until the trachea was secured with a cuffed endotracheal tube. Rocuronium (0.6 mg/kg) was substituted for succinylcholine if the latter agent was contraindicated, for example, because of hyperkalemia. Intubation was attempted under direct laryngoscopy using a Macintosh-type blade of suitable size. Patients in whom the initial attempt at tracheal intubation failed were enrolled in the study if their laryngoscopic view was classified as Cormack-Lehane class III/IV [14]. According to our local institutional guidelines, it is advisable to conduct further attempts at tracheal intubation using the ILMA with the aid of flexible fiberoptic bronchoscopes (FOBs) should the initial attempt have failed and should the laryngoscopic view turn out to be Cormack-Lehane class III/IV. Consequently, following an initial unsuccessful attempt, intubation was retried using either an ML laryngoscope (ML group, n = 59) or an ILMA (ILMA group, n = 53). Patient allocation to either intubation technique was not at random. Rather, the choice of the intubating aid used for subsequent trials was left to the intubator's judgment as per institutional guidelines with no attempt at randomizing the patients to either technique.

All intubations were conducted by intensivists who had at least 3 years of experience following their postgraduate anesthesia or ICU qualification and who were experienced in the use of either intubation technique. Intensivists charged with intubating the patients were not involved in other aspects of the study such as assessment of outcomes, data collection, and data analysis.

Conventional cricothyrotomy kits were immediately available in case the airway was lost. During intubation, all patients underwent standard monitoring including three-lead electrocardiography, noninvasive arterial blood pressure measurement, pulse oximetry, and capnography. As per local hospital protocol, all candidates for tracheal intubation were connected to a noninvasive ventilation apparatus set to maintain a pressure support of 10-15 cmH 2 O and an FiO 2 of 1.0 before attempting elective intubation. During induction of hypnosis and between intubation attempts, ventilation was maintained by an assistant intensivist using an Ambu-bag and face-mask assembly connected to a source of 100% oxygen. If needed, a gum elastic bougie or an intubating stylet was used, and backward, upward, and rightward pressure was applied to the larynx to facilitate intubation during direct laryngoscopy. Endotracheal intubation was performed with the aid of a flexible FOB (Olympus Medical Systems Corp., Tokyo, Japan; 4.9 mm diameter through the ILMA according to after lubricating the bowl of a size 4 or 5 ILMA (Fastrach; LMA of North America Inc., San Diego, California, USA) with 2% lidocaine gel. Correct placement of the ILMA was verified by adequate chest movement on manual ventilation, by chest auscultation for breath sounds, and by inspection of the capnograph tracing. Assisted ventilation was maintained aiming at raising the SpO 2 to 90% or higher before reattempting endotracheal tube insertion. Correct placement of the endotracheal tube was confirmed by capnography, observation of the rise and fall of the chest with ventilation, and auscultation of breath sounds on both sides of the lung. If the endotracheal tube was misplaced, it was withdrawn, manual ventilation was provided through the ILMA, and intubation was reattempted upon improvement of the SpO 2 . A maximum of two further attempts were allowed in either group, after which intubation was completed using the GlideScope video laryngoscope (Saturn Biomedical Systems, Burnaby, British Columbia, Canada). The total number of attempts and the intervals from the start of the initial attempt at intubation (time the laryngoscope was introduced into the patient's mouth) to the start of the second attempt (introduction of the laryngoscope or ILMA) and from the start of the second attempt until the trachea was intubated successfully were recorded. The occurrence of the following events was noted: severe hypoxemia (SpO 2 < 80%), hypotension (systolic blood pressure <90 mmHg), and bradycardia (heart rate <60 bpm). The occurrence of pulmonary aspiration, as evidenced by retrieval of gastric contents through endotracheal suction and/or appearance of new infiltrates on the chest roentgenogram after 24 h, was also noted.

Unless contraindicated (e.g. acute pulmonary edema), hypotension was treated with a 250-ml bolus of lactated ringer solution. If not corrected, vasopressor infusion (norepinephrine 1-4 μg/kg/min) was initiated. Atropine (0.5 mg intravenous bolus) was administered for bradycardia, which could be repeated if needed.

The primary outcome measure was the incidence of severe hypoxemia. Secondary outcome measures were intubation time, number of attempts, and incidence of intubation-related complications.

Statistical analysis

The required sample size was calculated using G *Power version 3.1.3 (Heinrich Heine Universitδt, Institut für ExperimentellePsychologie, Düsseldorf, Germany).

It was estimated that a sample of 50 patients in each group would achieve a power of 85% to detect a medium effect size (w) of 0.3 as regards the primary outcome measure. The test statistic used was the two-sided c2 -test with one degree of freedom, and the type I error was set at 0.05.

Statistical analysis was carried out on a personal computer using MedCalc© version 12.5 (MedCalc© Software, Ostend, Belgium). The D'Agostino-Pearson test was performed to examine the normality of numerical data distribution. Normally distributed numerical data were presented as mean and SD, and intergroup differences were compared using the unpaired Student t-test. Non-normally distributed numerical data were presented as median and interquartile range, and between-group differences were compared nonparametrically using the Mann-Whitney U-test. Qualitative data were presented as ratio or number and percentage, and differences between groups were compared using the Pearson c2 -test or the c2 -test for linear-by-linear association for nominal or ordinal data, respectively. Fisher's exact test was used in place of the c2 -test if greater than 20% of cells in any contingency table had an expected count of less than five.

Multiple logistic regression analysis was used to determine independent predictors of severe hypoxemia during intubation. Besides the intubation technique, other predictors expected to influence the outcome of interest were adjusted for. These included the hypoxic index (PaO 2 /FiO 2 ), the Cormack-Lehane class, and the operator's experience. The 'enter' (simultaneous) method was used to force all candidate predictors into the regression model. A receiver-operating characteristic (ROC) curve was plotted using the probability index derived from the regression model and the area under the curve was estimated.

All P-values are two-tailed. A P-value less than 0.05 is considered statistically significant.


  Results Top


During the study period, 2756 patients were admitted to ICU, 1121 (40.7%) of whom had acute respiratory failure. Of those with acute respiratory failure, 153 (13.6%) were ineligible for the study and consent could not be obtained from another 66 (5.9%) patients. Consent was obtained for 902 (80.5%) eligible patients, 157 (17.4%) of whom were managed conservatively and did not need tracheal intubation. Tracheal intubation was performed in 745 (82.6%) patients, 633 (85%) of whom were intubated in the first attempt. One hundred and twelve (15%) patients failed to be intubated in the first trial (Cormack-Lehane class III/IV) and were enrolled in the study [Figure 1].
Figure 1:

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[Table 1] shows patient characteristics and preintubation data. There was no statistically significant difference between the two study groups as regards any of these variables (P > 0.05), except for hypoxic index; this was found to have an insignificant effect as a predictor of hypoxia as shown in the multiple logistic regression model.
Table 1: Patient characteristics and preintubation data

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The details of the conduct of tracheal intubation are shown in [Table 2]. Following an initial failed trial of intubation using direct laryngoscopy, 41 (69.5%) patients were intubated at the next attempt in the ML group compared with 24 (45.3%) patients in the ILMA group. Eighteen (30.5%) patients in the ML group underwent two attempts following the initial failed trial compared with 29 (54.7%) patients in the ILMA group. These differences were statistically significant (P, 0.01).
Table 2: Conduct of intubation

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The median (interquartile range) time from the start of the initial attempt at intubation to the start of the second attempt was comparable in both ML and ILMA groups [101 s (108-119 s) versus 108 s (101-117 s), respectively; P, 0.7]. In contrast, the median (interquartile range) time from the start of the second attempt until successful intubation of the trachea was significantly shorter in the ML group compared with the ILMA group [98 s (89-245 s) versus 239 s (128-384 s), respectively; P < 0.001]. The median (interquartile range) total intubating time was 212 s (198-338 s) in the ML group compared with 396 s (235-496 s) in the ILMA group (P < 0.001). One (1.7%) patient in the ML group and three (5.7%) patients in the ILMA group failed to be intubated using direct laryngoscopy or the ILMA (P, 0.343). All four patients could be intubated successfully with the aid of the GlideScope video laryngoscope [Table 2].

[Table 3] shows the incidence of intubation-related complications. Twenty-five (42.2%) patients in the ML group suffered from severe hypoxemia compared with eight (15%) patients in the ILMA group (P, 0.002). Otherwise, the incidence of other complications related to the conduct of intubation was comparable in both groups (P > 0.05). Likewise, there were no statistically significant differences between the two groups as regards postintubation course in the ICU (P > 0.05; [Table 4]).
Table 3: Incidence of intubation-related complications

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Table 4: Postintubation course in the intensive care unit

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The results of multiple logistic regression are shown in [Table 5]. Of the included variables, only the intubating technique was an independent predictor of severe hypoxemia [odds ratio (OR), 4.08; 95% confidence interval (CI), 1.63-10.18; P, 0.003]. The model had adequate fit (−2log likelihood, 135.8; c2 , 11.23; P, 0.024) and could classify 71.43% of patients correctly. The ROC curve derived from the regression model is shown in [Figure 2]. The ROC curve had an area under the curve of 0.7 (95% CI, 0.61-0.78; P, 0.0004). The best cut-off criterion was a predicted probability of greater than 0.393. This had a sensitivity of 66.7% (95% CI, 48.2-82%) and a specificity of 72.2% (95% CI, 60.9-81.7%).
Figure 2:

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Table 5: Multiple logistic regression model for predictors of severe hypoxemia during intubation

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  Discussion Top


The current study showed that in Cormack-Lehane class III/IV patients who required urgent tracheal intubation for acute respiratory failure, the incidence of severe hypoxemia was less frequent following a failed initial trial of intubation if subsequent trials were aided with FOB through ILMA compared with conventional direct laryngoscopy. Although using the ILMA was associated with a significantly longer time to complete tracheal intubation successfully, the incidence of failed intubation was comparable using either technique, as was the incidence of other intubation-related complications.

Hypoxemia is the most commonly encountered complication related to airway management, especially during rapid sequence intubation [15]. Although there is currently no clear definition for severe hypoxemia, an arterial saturation of less than 80% is most commonly cited as representative of clinically significant desaturation [11]. Patients with acute respiratory failure have pre-existing low oxygen saturation and are at a particularly higher risk for severe hypoxemia during intubation [7]. Further deterioration in oxygenation during intubation of a hypoxemic patient, such as those with acute respiratory failure, may be deleterious as derangement of arterial oxygen saturation to levels below 70% has been shown to be a risk factor for cardiac arrest, hypoxic cerebral insult, and death [5],[16].

The incidence of difficult intubation in critically ill patients is almost twice the rate expected in surgical patients with an apparently normal airway [4],[6],[17],[18]. Although guidelines and algorithms have been introduced for the management of difficult airways and/or failed intubation in surgical patients [19], there are currently no clear guidelines on the best method for the management of difficult airways in patients with acute respiratory failure undergoing urgent intubation. In this regard, the ILMA has stood its ground as an intubating aid for patients with a difficult-to-manage airway in the operating room [20]. However, data on the role of the ILMA in the ICU setting are scarce [12].

Recently there have been reports on the successful use of the ILMA in emergency prehospital intubation [13]. At our institute, of late we have adopted the recommendation to encourage the early use of ILMA in the management of ICU patients in whom endotracheal intubation could not be readily accomplished with direct laryngoscopy. The primary aim of the present trial was, therefore, to assess the feasibility and safety of using the ILMA with the aid of FOB for subsequent attempts at intubation, should the initial trial using conventional laryngoscopy turn out to be a failure in Cormack-Lehane class III/IV patients who present a real challenge to intensivists striving to secure the airway and provide adequate oxygenation to such high-risk patients.

Urgent intubation in the ICU is usually performed using rapid sequence induction preceded by a brief period of preoxygenation [21]. However, doubling the period of preoxygenation from 4 to 8 min was not shown to influence the incidence of severe hypoxemia in critically ill patients [22]. To counteract this increased risk, Baillard et al. [23] recommended the use of noninvasive ventilation before intubating hypoxemic patients.

Practice guidelines have been established for the management of difficult airways in the operating room [19]. Although similar guidelines have been proposed for the ICU setting [24], they have not been widely adopted by critical-care practitioners. In the absence of consensus on the optimal management of difficult airways in a particular setting, clinicians often resort to expert opinion. For instance, the best approach for dealing with a difficult airway caused by a huge retrosternal goiter has not been established. Nonetheless, a group of experts have proposed a wide range of options for this scenario [25]. Unfortunately, to the authors' knowledge, no similar expert opinion is available for managing patients with acute respiratory failure and a difficult airway who are potential candidates for artificial ventilation. In this respect, the ILMA may serve as a helpful tool in managing such patients.

The optimal approach to airway management should be goal-directed, with the ultimate aim being the maintenance of adequate oxygenation during the conduct of intubation rather than merely securing the trachea with an endotracheal tube in as short a time as feasible. To achieve this goal, the ideal algorithm used for airway management should be context-sensitive to fit the clinical scenario encountered. Obviously, the time factor and success rate directly influence both the incidence and severity of hypoxemia. In accord with a previous study [26], the time needed to introduce the endotracheal tube in the current study was significantly longer on using the ILMA and FOB compared with conventional direct laryngoscopy. However, the incidence of severe hypoxemia was significantly lower when using the former technique, a finding that may be assumed to be prompted by the more efficient ventilation provided by the ILMA in between the intubation attempts compared with the face mask.

Pulmonary aspiration is always a potential risk that is associated with the use of supraglottic airway devices such as the LMA. In a multicenter trial involving cardiopulmonary resuscitation, the incidence of aspiration associated with use of the ILMA was less than 1% [27]. Moreover, another study reported that ILMA could be protective against aspiration [28]. In the current study, the incidence of pulmonary aspiration was comparable on using both intubating techniques.

Hemodynamic instability is common during or immediately after tracheal intubation and institution of intermittent positive pressure ventilation [7]. In a prospective study on 136 critically ill patients, severe hypotension (systolic blood pressure <70 mmHg) was reported in 9.6% of patients during intubation [11]. In the current study, the overall incidence of hypotension (systolic blood pressure <90 mm Hg) and bradycardia (heart rate <60 bpm) was 31.4 and 26.5%, respectively. None of the patients in the current study suffered from major cardiovascular collapse or cardiac arrest in relation to intubation. At our institute, a policy has been adopted to lessen the incidence of complications related to tracheal intubation in critically ill patients. This policy is based on the rational application of a 10-component bundle tailored to each individual's needs. This comprises preoxygenation using noninvasive positive pressure ventilation if feasible, presence of two operators conducting the intubation, rapid sequence induction with application of cricoid pressure, utilization of capnography to ensure proper placement of the tracheal tube, administration of fluid bolus and vasopressors if needed, and use of sedation to facilitate intubation and ventilation [10].

There are several limitations to the current study. First, the study was nonrandomized, which could be a potential source of bias. However, in view of obvious logistic and ethical constraints, it would not have been feasible to carry out a proper randomization in the setting of emergency intubation for patients with decompensated acute respiratory failure. Second, the choice of the intubating aid was left to the operator's judgment, which could be another source of bias. Although our local institutional guidelines do recommend the early use of the ILMA for intubating Cormack-Lehane class III/IV patients after a failed initial attempt at intubation, this recommendation has not been formulated into a standard policy yet. Hence, the current trial may be considered as a planned appraisal for this recommendation. Third, although operators involved in airway management did not participate in outcome assessment, data collection, or data analysis, clinicians charged with outcome assessment could not be blinded as to the intubation technique. This could also have confounded the results of the current study.

In Cormack-Lehane class III/IV patients who required urgent tracheal intubation for acute respiratory failure, the incidence of severe hypoxemia was less frequent following a failed initial trial at intubation if subsequent trials were aided with FOB through the ILMA compared with conventional direct laryngoscopy. These results need be validated by other randomized controlled trials.


  Acknowledgements Top


Support was provided solely from institutional and departmental sources.

Conflicts of interest

There are no conflicts of interest.

 
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