A randomized controlled study to evaluate and compare Truview blade with Macintosh blade for laryngoscopy and intubation under general anesthesia.

BACKGROUND: The Truview EVO2™ laryngoscope is a recently introduced device with a unique blade that provides a magnified laryngeal view at 42° anterior reflected view. It facilitates visualization of the glottis without alignment of oral, pharyngeal, and tracheal axes. We compared the view obtained at laryngoscopy, intubating conditions and hemodynamic parameters of Truview with Macintosh blade.
MATERIALS AND METHODS: In prospective, randomized and controlled manner, 200 patients of ASA I and II of either sex (20-50 years), presenting for surgery requiring tracheal intubation, were assigned to undergo intubation using a Truview or Macintosh laryngoscope. Visualization of the vocal cord, ease of intubation, time taken for intubation, number of attempts, and hemodynamic parameters were evaluated.
RESULTS: Truview provided better results for the laryngeal view using Cormack and Lehane grading, particularly in patients with higher airway Mallampati grading (P < 0.05). The time taken for intubation (33.06±5.6 vs. 23.11±57 seconds) was more with Truview than with Macintosh blade (P < 0.01). The Percentage of Glottic Opening (POGO) score was significantly higher (97.26±8) in Truview as that observed with Macintosh blade (83.70±21.5). Hemodynamic parameters increased after tracheal intubation from pre-intubation value (P < 0.05) in both the groups, but they were comparable amongst the groups. No postoperative adverse events were noted.
CONCLUSION: Tracheal intubation using Truview blade provided consistently improved laryngeal view as compared to Macintosh blade without the need to align the oral, pharyngeal and tracheal axes, with equal attempts for successful intubation and similar changes in hemodynamics. However, the time taken for intubation was more with Truview.

RCT Entities:   Population Interventions Outcomes

Introduction

Securing the airway with a cuffed endotracheal tube (ETT) in the trachea is still one of the most important skills in anesthesia. Complications arising from difficult or failed intubation remain a leading cause of anesthesia related morbidity and mortality.[1-3] Despite a number of factors and combinations of factors identified to predict difficult intubation preoperatively, none is capable of predicting all difficult intubation[4] Consequently, many potential difficult intubations remain unrecognized until the induction of anesthesia.

The above issue has stimulated research to develop novel laryngoscopes, which aim to reduce the difficulty of laryngeal visualization, particularly in the setting of both anticipated and unanticipated difficult airway. The main feature of the new devices, unlike the gold standard Macintosh laryngoscope, is to facilitate visualization of glottis without the need to align the oral, pharyngeal, and tracheal axes.

Truview EVO2 laryngoscope (Truphatek International Ltd. Netanya, Israel) is a recently introduced device with an integrated optical lens system and unique blade tip angulation that provides optimal sight of vision, allowing a view of larynx via the lens. The optical lens apparatus provides a 42° angled deflection view through a 15 mm eyepiece.[5] In addition, the Truview blade has an integrated oxygen port which prevents misting and provides continuous oxygen insufflations during laryngoscopy [Figure 1]. Considering the unique features Truview blade may be more advantageous than Macintosh blade during intubation, which has been assessed recently.[67]

Figure 1

(a) Parts of the Truview laryngoscope; (b) line diagram of Truview blade tip

The aim of study was to evaluate and compare the Truview with the Macintosh blade for ease of laryngoscopic intubation, time taken for intubation, number of attempts for successful intubation and hemodynamic parameters.

Materials and Methods

After obtaining approval from the Institutional Ethics Committee, the study was conducted with 200 adult patients of either sex in the age group of 20–50 years, of physical status ASA I and II, who were scheduled to undergo elective surgery under general anesthesia with endotracheal intubation and gave their informed, written consent to participate in this study.

Exclusion criteria included the following: ASA physical status ≥III, body mass index (BMI) > 35 kg/m2, coagulopathy or history of anticoagulant use, cervical spine injury, raised intracranial pressure risk factors for pulmonary aspiration of gastric contents i.e. full stomach, emergency surgery and pregnant patients, surgery involving oral cavity, larynx, pharynx or neck where postoperative pain and sore throat may occur from surgical factors.

The study design was prospective, randomized and controlled. Randomization was done by picking up a chit randomly from a box containing 200 chits. The patients were distributed into two groups of 100 (N = 100) each, and the grouping was as follows: Laryngoscope equipped with Truview blade was used for group 1 patients and the one equipped with Macintosh blade was used for group 2 patients.

The patients were evaluated preoperatively for their fitness of proposed surgical procedure under general anesthesia and kept fasting after midnight. They were premedicated with alprazolam 0.25 mg and ranitidine 150 mg PO the night before and during the morning of surgery. Preoperative airway assessment was performed by anesthetists who were unaware of the patient's group allocation. Airway assessment included the following: Opening of the mouth (normal ≥ 3cm or restricted), thyromental distance (normal ≥ 6.5 cm or abnormal if shorter), protruded teeth (yes/no), condition of teeth (normal, loose or denture), temporomandibular joint mobility (normal or restricted), neck movement (normal or restricted), mandibular size (normal or micrognathia or retrognathia or prognathia) and modified Mallampati grading (MPG).[8] The anesthetist had to give a YES/NO answer to whether the intubation could be difficult. It was a subjective, unguided decision, based on the patient's airway anatomy and the anesthetist's own experience.

On arrival in the operating room, all the patients were monitored for continuous ECG, heart rate (HR), noninvasive blood pressure (NIBP), SpO2 and EtCO2 (AS5, Datex Ohmeda, Finland) and intravenous access was established. A standard anesthesia technique was used for all the patients. After preoxygenation for 3 minutes, anesthesia was induced with intravenous morphine 0.1 mg/kg and propofol 2-2.5mg/kg. Vecuronium bromide 0.1 mg/kg body weight was administered to facilitate tracheal intubation. All the patients in group 2 were kept in “sniffing position” with their head on a pillow. No head and neck manipulation was done in group 1 patients; they were kept in neutral position.

Laryngoscopy was performed with different blades according to group allocation of the patient: Large or medium-sized Truview blade was used in group 1 patients and blade size of 3 or 4 of the Macintosh was used in group 2 patients, in accordance with the preference of the anesthesiologist. Endotracheal intubations were performed using size 7.0 or 7.5mm ETT in females and 8.0 or 8.5 mm ETT in males by the same anesthesiologist who had undertaken at least 50intubations with each laryngoscope in manikins and at least 20 intubations in the clinical setting with each laryngoscope before the conduct of this study. The view of the glottis at laryngoscopy was scored according to the Cormack and Lehane[9] (CL) grading criteria (grade 1, most of the glottis is visible; grade 2, only the posterior extremity of the glottis is visible; grade 3, no part of the glottis and only the epiglottis is visible; and grade 4, not even the epiglottis can be seen), and Percentage of Glottic Opening[10] (POGO) score (0% when glottis is not seen and 100% when the entire glottis is seen). No laryngeal manipulation was done to improve the laryngoscopic view or improve the score.

The time to intubation (TTI) was measured from time of insertion of the laryngoscope into the patient's mouth until the placement of ETT in the trachea and confirmed by capnography. If more than one attempt was required the patient was ventilated with bag and mask between the attempts and the anesthetist was allowed to change the blade, patient position or apply external laryngeal pressure. The number of attempts needed to correctly place the tube was recorded. Failure to intubate trachea after two attempts was considered as failure to intubation. In such a case, alternate techniques to maintain airway were employed. After successful intubation, the patients were mechanically ventilated for the surgical procedure and anesthesia was maintained with isoflurane 1.0-1.5% in a mixture of nitrous oxide and oxygen in a 2:1 ratio. No other medication was given or procedure was performed during the data collection period after tracheal intubation. During the tracheal intubation, continuous ECG, HR, NIBP and SpO2 were monitored and recorded every 1 min during induction and intubation, and thereafter every 5 min for 15 min during the post-intubation period. Subsequent management of anesthesia was left to the anesthetist providing care for the patient.

Postoperatively, the patient was evaluated for the symptoms of sore throat, broken teeth, soft tissue edema, bleeding from gums or lips, stridor or hoarseness and any other complication. Ease of intubation was assessed depending on TTI, number of attempts with or without laryngeal manipulation, glottic view and occurrence of complications. Ease of intubation was correlated with difficulty of airway anticipated on preoperative airway evaluation.

Sample size calculation was based on a pilot study on 50patients, with laryngeal view as the primary outcome. It was estimated that with a power of 90% at 5% significance, 168patients would be required. To allow the potential dropout, we decided to recruit a total of 200 patients in the present study. Paired t test was used to compare demographic data, hemodynamic parameters heart rate, systolic and diastolic blood pressure (SBP and DBP) airway parameters and total time taken for intubation. Chi square test was used to compare laryngeal view, time taken for intubation and number of attempts. A value of P < 0.05 was taken as statistically significant.

Results

ASA physical status, mean age, weight, height and sex ratio distribution of patients were nearly identical in both the groups (P > 0.05) [Table 1]. Preoperative airway assessment variables, mouth opening, thyromental distance, neck movement, teeth, TMJ movement, and mandibular size were within normal distribution.

Table 1

Patient characteristics (Mean ± SD)

MPG was related to the view of glottis assessed by CL grading for both laryngoscopes. Both the blades produced similar laryngeal view in patients with normal airway. There was improvement of glottic view with the Truview blade in higher MPG. Truview blade use was associated with better glottic view even in predicted difficult airway.

Except for two patients in group 1 in whom glottic view was <50%, in all other patients, a full glottic view was seen (mean POGO Score of 97.26±8%), despite the fact that 61 of the 100 patients (61%) in this group were MPG II or more. In contrast, mean POGO score in group 2 was 83.7±21.5% as compared to 97.26±8% in group 1, which was statistically a significant difference (P < 0.05). Time taken for intubation was more with Truview blade in comparison with Macintosh blade and was statistically significant (P < 0.05) [Table 2].

Table 2

Mallampati grading and observations during laryngoscopy and intubation

Heart rate and SBP were observed to rise significantly under the stimulus of laryngoscopy and intubation in both the groups (P < 0.05). They returned to near baseline values by 10 min in both the groups. The maximum rise in HR and SBP above pre-intubation value in group 1 was 13.9/min and 18.4 mmHg, respectively, as compared to 13.5/min and 22.2mmHg, respectively, in group 2. This peak rise in HR and SBP above the pre-intubation value was comparable in both the groups [Table 3 and Figure 2].

Table 3

Peri-operative hemodynamic changes (Mean ± SD)

Figure 2

Peri-operative HR/min and SBP mmHg in groups

Eight of the 100 patients in the Macintosh group gave a positive history of sore throat at the time of discharge from PACU as compared to 5 of 100 patients in the Truview group, but this difference was not statistically significant (P > 0.05). There was no case of failure to intubate, no teeth damage, soft tissue edema, bleeding from gums and lips, stridor and hoarseness in either group.

Discussion

The results of our study show the following: 1) Truview blade produced better laryngeal view in higher Mallampati airway classes than Macintosh blade; however, both the Truview and Macintosh produced similar laryngeal view in patients with normal airway. 2) The numbers of attempts for successful endotracheal intubation were comparable with both the laryngoscope blades. 3) Time taken for intubation was more with Truview blade in comparison with Macintosh blade. 4) There was increase in heart rate and blood pressure from the baseline values with both laryngoscopes, without any significant difference between the two groups.

Observing the glottis during intubation is a reliable method for correct placement of ETT. Direct vision avoids trauma while negotiating the tube into trachea. CL grades of laryngeal view were similar in both the groups irrespective of airway class. The number of patients with good laryngeal view CL grades I/II in patients with airway class MPG I/II was comparable in both the groups. Among patients with MPG III, use of Truview blade in 68.48% cases provided CL grade I; and with Macintosh blade 22.22% cases CL grade I was seen. In patients with MPG IV, no patient had CL grade III/IV with Truview blade, whereas 50% cases had CL grade III/IV with Macintosh blade. The results of the present study are similar to that of Li et al. who reported that MPG determined prior to laryngoscopy was significantly related to the view of the glottis during laryngoscopy for both the laryngoscopes. The view of the larynx was better with the Truview than with the Macintosh blade in patients with CL grade greater than one.[6]

The ability of Truview to produce better laryngeal view than Macintosh has been reported in a recent study. Truview improved laryngeal view in 92% cases by one or more CL grades, in patients who had CL grade II or above with Macintosh.[11] The POGO was better in Truview group particularly with predicted difficult intubation as compared to the Macintosh group. Although CL grading is the most common means of describing laryngeal view, it has been never validated. Ochroch et al. stated that POGO score was a simple and an easy way to categorize laryngeal view and it had better inter-physician reliability than CL grading.[17]

Multiple attempts to endotracheal intubation increase the morbidity related to airway management. Difficult airway and poor glottic view are associated with airway manipulations and several attempts at laryngoscopy. Addressing these two issues will prevent potential catastrophes in airway management. In our study, the numbers of attempts for successful tracheal intubations were comparable in both the groups. Higher airway classes (MPG III/IV) and CL grade III/IV were associated with multiple attempts; similar observations were also reported earlier by Barak et al.[7]

In the present study, the TTI was 33.62±5 seconds with Truview and 23.11±5 seconds with Macintosh blade. Studies comparing the Truview with the Macintosh blade have reported more time to intubate with Truview, irrespective of airway anatomy and grading of airway difficulty.[6-7] Time taken for intubation in our study was comparable to those reported by Barak et al.[7] Laryngoscopy and intubation is performed in an indirect manner with Truview, seeing the ETT through the lens. The anesthesiologist looks through the Truview lens and focuses on the vocal cords. Then, the tube needs to be advanced blindly until its tip enters the Truview visual field. Performing this maneuver requires good eye-hand coordination and some practice. We used Truview with its camera attachment on the top of the blade in order to magnify the view of vocal cords via eyepiece. However, the camera made the Truview quite cumbersome to use. Anesthetists experience considerable difficulty advancing the tracheal tube toward the view of the digital camera; this may be the reason why TTI was more with Truview laryngoscope, a finding also reported by other investigators.[7] Recent manikin studies did show reduced TTI by Truview in normal airway, but it was higher than with Macintosh blade. The authors stated that Truview demonstrated advantages over the Macintosh including a better view of glottis, greater success of tracheal intubation, and ease of device use.[13] Further, Truview was evaluated for tracheal intubation in patients with neck immobilization using manual inline axial cervical spine stabilization. TTI was 22.5 ± 7.5 sec with the Truview and 13.9 ± 9.2 sec with the Macintosh laryngoscope.[14]

HR and SBP increased from their pre-intubation values with both the blades without any significant difference between the two groups and returned to near pre-intubation values by 10 min in both the groups. Laryngoscopy and intubation are associated with increase in HR and blood pressure secondary to the sympathetic discharge. Several studies have shown a lesser increase in HR and blood pressure by the lightwand aided tracheal intubation, which has been attributed to the lack of stretching and distortion of pressure sensitive extraglottic structures by the lightwand as compared to the conventional laryngoscope.[1516] A laryngoscopy technique requiring lesser lifting force would proportionally reduce the sympathetic discharge and hence changes in hemodynamic parameters. Khan et al. reported that the force applied during laryngoscopy and intubation of the trachea is significantly reduced with Truview as compared to Macintosh blade with equal TTI, which is responsible for a lesser increase in HR and SBP.[17] In our study, the TTI was more with Truview laryngoscope. The rise in HR and blood pressure is associated with time required for laryngoscopy and intubation and it occurred about 14 sec after the start of laryngoscopy and became maximal after 30–45 sec. This could be the reason for similar hemodynamic changes in both the groups. We have recorded hemodynamic parameters at 1 min interval; the rise in HR and blood pressure might have occurred early with Macintosh blade and later with Truview blade. The incidence of postoperative sore throat was similar with both the laryngoscopes. There was no report of trauma caused by laryngoscopy in our study.

Conclusion

Using Truview blade consistently provided better laryngoscopic view than using Macintosh blade for tracheal intubation, without the need to align the oral, pharyngeal and tracheal axes, needed similar number of attempts for successful intubation and was associated with similar changes in hemodynamics. However, the time taken for intubation was slightly more with Truview blade.