A comparative study between Truview^PCD laryngoscope and Macintosh laryngoscope in viewing glottic opening and ease of intubation: A crossover study

Abstract

Background:

Truview^PCD laryngoscope is specially designed to aid positioning of the endotracheal tube as well as to record entry of the tube into glottis. Aim of the study is to compare the view of glottic opening and ease of intubation between Truview^PCD laryngoscope and Macintosh laryngoscope in patients undergoing general anesthesia (GA).

Methodology:

Two hundred patients undergoing elective surgery, under GA were randomized into two groups, Group TV and Group ML. In Group TV, Trueview^PCD laryngoscope was used initially to visualize the vocal cords for Cormack and Lehane grading (CLG) and to spray the vocal cords with 10% lignocaine. Then the patient was ventilated for 1 min and Macintosh laryngoscope was used to visualize the vocal cords for CLG and proceed with intubation. In Group ML, Macintosh laryngoscope was used initially and later Truview^PCD laryngoscope. Time to intubation, CLG, number of attempts and hemodynamic parameters were recorded.

Results:

Ninety-six and 89 patients had CLG1 visualization when Truview^PCD laryngoscope was used as 1^st and 2^nd device respectively compared to 41 and 68 with Macintosh laryngoscope (P = 0.00). Four patients had CLG 4 visualization with Macintosh laryngoscope that turned out to be grade II visualization with Truview^PCD laryngoscope (P = 0.00). Mean time taken for intubation with Truview^PCD and Macintosh laryngoscope was 21.10 ± 5.64 s and 15.79 ± 2.76 s respectively (P = 0.00).

Conclusion:

Better visualization with lesser CLG was found with Truview^PCD laryngoscope but it took longer time for intubation than Macintosh laryngoscope. The hemodynamic response to intubation was significantly less with the use of Truview^PCD laryngoscope when compared to that of Macintosh laryngoscope.

INTRODUCTION

In the day-to-day practice of anesthesiology, securing the airway using an endotracheal tube remains an on-going challenge for anesthesiologists in patients with unanticipated or anticipated difficult airway.[1] We encounter common problems like inadequate ventilation, esophageal intubation or difficult intubation which in turn increases the incidence of adverse respiratory events.[2] Endotracheal intubation with direct laryngoscopy requires positioning of the patient in sniffing position (extension at the atlanto-occipital joint, flexion at the lower cervical spine) for adequate exposure of the glottis. These manoeuvres are not possible and can aggravate or produce new injury to the spinal cord in patients with suspected cervical spine injury or cervical intervertebral disc prolapse.[3,4,5] In patients with cervical injury, manual in line stabilization is recommended because it produces less movement during scopy but it worsened the laryngoscopic view,[6,7,8,9] due to improper alignment of oral, pharyngeal and laryngeal axes.[10] Difficulty to visualize the laryngeal inlet is one of the major causes for an increase in the incidence of difficult intubation.[11] Different designs of laryngoscopes have been developed in an effort to address all these problems. Among these, Truview^PCD laryngoscope is a device with a unique blade that provides an optical view “around the corner,” allowing a view of the glottis via the prismatic lens without having to align oral, pharyngeal and tracheal axes. The device is specially designed to confirm positioning of the endotracheal tube as well as to record entry of the tube into glottis for research and archiving. Therefore, we compared laryngoscopic view and the ease of intubation of the Truview^PCD laryngoscope with the conventional Macintosh laryngoscope in patients undergoing general anesthesia (GA).

METHODOLOGY

After getting approval from the Institutional Ethics Committee and informed consent from 200 patients between the ages of 12 and 80 years, belonging to American Society of Anesthesiologists (ASA) physical status I and II, who were scheduled for elective surgery under GA and requiring elective endotracheal intubation were enrolled for the study. Sample size calculations were based on pilot data in 50 patients. It was estimated that with the power of 90%, 168 patients would be required. To allow for dropout, 200 patients were recruited. Patients with compromised cardiovascular and respiratory function, emergency cases, those requiring rapid sequence induction and patient with head and neck pathology were excluded from the study. All patients were premedicated with oral diazepam 10 mg and oral ranitidine 150 mg in the previous night and on the morning of the surgery.

Injection glycopyrrolate 0.004 mg/kg intravenous was given 15 min before expected start of anesthesia. In the operating room, standard monitors (SpO₂, NIBP, end-tidal carbon dioxide [EtCO₂], and ECG) were connected on all the patients. Patients were placed in the “sniffing” position. All the patients were preoxygenated for 3 min with 100% oxygen before induction of GA. The anesthesia was induced with, injection propofol 2.5 mg/kg, and neuromuscular blockade was achieved using injection vecuronium 0.1 mg/kg. Patients were ventilated with oxygen, N₂O and isoflurane 1.5%. Neuromuscular blockade was monitored with neuromuscular blockade monitor (TOF-Watch SX Organon (Ireland)). Laryngoscopy was performed on 90% suppression of single twitch response. The patients were randomized by close envelope technique to either one of the groups, Group TV or Group ML (100 each). In Group TV, Trueview^PCD laryngoscope was used initially to visualize the vocal cords for Cormack and Lehane grading (CLG) (1-visualization of entire glottis, 2-visualization of posterior laryngeal aperture but not anterior portion, 3-visualization of epiglottis but not any part of larynx, 4-visualization of soft palate but not epiglottis) and to spray the vocal cords with 10% lignocaine. Then the patient was ventilated with 100% oxygen for 1 min and Macintosh laryngoscope was used to visualize the vocal cords for CLG and proceed with intubation. In Group ML, Macintosh laryngoscope was used initially to visualize the vocal cords for CLG and to spray the vocal cords with 10% lignocaine. Then the patient was ventilated for 1 min with 100% oxygen and Truview^PCD laryngoscope was used to visualize the vocal cords for CLG and proceed with intubation. No laryngeal manipulation was used to improve the laryngoscopic view to improve this score. The time to intubation (TTI) was measured from the time endotracheal tube entered the patient's mouth until EtCO₂ waveform detection on the monitor. Numbers of intubation attempts were also noted. All complications related to intubation were recorded if any. Blood pressure (systolic blood pressure [SBP], diastolic blood pressure [DBP], and mean arterial pressure [MAP]), heart rate (HR), and SpO₂ were measured at baseline, before 1^st device, after 1^st device, before 2^nd device, after 2^nd device and after intubation. The anesthesiologists who performed all the laryngoscopies and intubations had experience of minimum 20 intubations with the Truview^PCD before the study was commenced. Anesthesia was maintained with isoflurane, N₂O in oxygen during the study and analgesics agents were administered according to patient's requirements. Parametric data were analyzed with unpaired t-test and nonparametric data analyzed with Mann–Whitney test.

RESULTS

Demographic data age, sex, weight and ASA physical status and Mallampatti classification were comparable among the two groups [Table 1].

Table 1.

Demographic data

Cormack and Lehane grade attained using Truview^PCD laryngoscope as first device or second device were superior to Macintosh laryngoscope (P = 0.00). Ninety-six and 89 patients had CLG 1 visualization when Truview^PCD laryngoscope was used as 1^st and 2^nd device respectively compared to 41 and 68 with Macintosh laryngoscope (P = 0.00). Four patients in Group ML where Macintosh laryngoscope used as the first device had CLG of 4 but when Truview^PCD laryngoscope used as a second device on those same patients they had improved score of CLG 2 for three patient and CLG 3 for one patient [Table 2]. All patients could be intubated with the designed laryngoscopes in both the groups.

Table 2.

CLG between Group TV and Group ML

The mean time taken to intubate with Truview^PCD laryngoscope was 21.10 s whereas with Macintosh laryngoscope the time was 15.79 s. The difference was statistically significant (P = 0.00). However, there was no difference in a number of attempts taken for endotracheal intubation between the two groups. There was no incidence of any trauma as evidenced by blood smeared on the laryngoscope blade or the endotracheal tube or injury to teeth between the two groups.

Hemodynamic variation were analyzed separately to look at the difference when each of the device was used as a first and second device. Macintosh laryngoscope produced increased hemodynamic response compared to that of Truview^PCD laryngoscope. There were no significant changes in hemodynamic response when Macintosh laryngoscope or Truview^PCD laryngoscope was used as a second device [Figure 1].

Figure 1.

Hemodynamic response

DISCUSSION

We observed that Truview^PCD laryngoscope was associated with better glottic exposure when compared to Macintosh laryngoscope (P = 0.00). One hundred and eighty five out of 200 patients had CLG 1 visualization with Truview^PCD laryngoscope whereas with Macintosh laryngoscope 109 out 200 patients had grade I visualization. Four patients in Group ML where Macintosh laryngoscope was used as the first device had CLG of 4 but when Truview laryngoscope used as a second device on same patients, they had an improved score of CLG 2 for three patients and CLG 3 for one patient. This can be attributed to the 46° anterior refraction provided by the optical lens in Truview^PCD laryngoscope. In a study done by Riveros et al., they observed that among 130 patients 14% patients showed CLG 1 views with Glidescope as compared to 82% patients with Truview^PCD.[12] Li et al. observed that among the 200 patients 105 patients (87.5%) showed an improved glottic visualization with the Truview EVO2 laryngoscope (P < 0.001) than Macintosh laryngoscope and in all the patients with a CLG 3 or 4 there was an improved view with the Truview EVO2 laryngoscope. This was due to design of the Truview EVO2 laryngoscope, as it offers an optical view “around the corner,” allowing a view of the glottis via the prismatic lens without having to align oral, pharyngeal and tracheal axes.[13]

The mean time taken for intubation with Truview^PCD laryngoscope was 21.10 ± 5.64 s whereas with Macintosh laryngoscope it was 15.79 ± 2.76 s. This difference was statistically significant (P = 0.00). This finding was similar to the study done by Riveros et al., where they observed in 130 patients (neonate to 10 years of age) the median TTI were 39 s, 44 s and 23 s with Glidescope, Truview^PCD and direct laryngoscope respectively, with mean differences of 14 s between Glidescope and direct laryngoscope and 17 s between Truview^PCD and direct laryngoscope.[12] Timanaykar et al.[14] also observed that time taken to intubation was more with Truview EVO2 laryngoscope than Macintosh laryngoscope (33.06 ± 5.6 vs. 23.11 ± 57 s) (P < 0.01). Li et al.[13] and Nasim et al.[15] also had a similar observation. This could be due to Truview^PCD comes with its camera attachment on the top of the blade in order to magnify the view of vocal cords via the eyepiece. The glottic view was angulated which necessitates the use of preformed angulated stylet, during tracheal intubation, which comes with Truview^PCD laryngoscope. It was difficult to advance the tracheal tube toward the view with this stylet. This could be one of the reasons for increased duration of tracheal intubation. Secondly, Truview^PCD provides an indirect view of the glottis and vocal cords through an optical lens, while Macintosh laryngoscope allows direct view of the vocal cords. It required sufficient expertise and hand-eye coordination to master the technique of intubation with Truview^PCD laryngoscope. Thirdly, Truview^PCD laryngoscope needs a midline entrance and may lead to difficulties in manipulation of the tongue which prolongs and complicates the intubation process. Fourth reason could be familiarity of the anesthesiologist with the usage of Macintosh laryngoscope when compared to the Truview^PCD laryngoscope would have influenced the difference in time taken for intubation.

We looked at number of intubation attempts; we were able to successfully intubate 95% patients in first attempt in both the groups. There was no statistically significant difference between the two groups. Similar results were found in a study done by Malik et al. They compared the use of Macintosh, Truview, Glidescope and Airway scope laryngoscope in patients with cervical spine immobilization. In their study, there were no significant difference between group in the number of attempts required with each device.[16] Nasim et al. compared the Airtraq and Truview laryngoscopes to the Macintosh laryngoscope for use by advanced paramedics in easy and simulated difficult intubation in manikins. They also found similar results with no significant difference amongst the two groups in the normal airway scenario and in manikins with a hard collar.[15] Patients who had CLG 4 visualization with Macintosh were intubated only by using Truview^PCD laryngoscope, which showed improved CLG visualization. Those patients were not tried to intubate using Macintosh laryngoscope as by chance they fell on Group ML. This was one of the reasons. Secondly all other patients studied were with CLG 1 and 2.

We looked at the complication; there was no statistically significant difference in the trauma as evidenced by blood smeared on the laryngoscope blade or the endotracheal tube and injury to teeth with Truview^PCD blade. In contrast, a study done by Barak et al. showed a significant decrease in the incidence of trauma with Truview laryngoscope when compared to Macintosh blade.[17] In the manikin study done by Malik et al. reported no decrease for potential dental trauma with Truview blade when compared to Macintosh laryngoscope in a normal airway scenario and in the condition with cervical spine rigidity.[18] For optimal visualization of the glottis during direct laryngoscope, the anterior structures of the larynx are elevated. In a difficult airway, scenario this may lead to the application of undue pressure on gums, teeth and periglottic structures for maximal exposure of the vocal cords. The Truview blade is designed to enable indirect laryngoscopic view, therefore, the anesthesiologist applies les force on the anterior larynx, resulting in fewer patients with bleeding and soft tissue damage.[17] Most of the patients in our study were with better Glottic exposure with CLG 1 and 2, so there was no incidence of trauma during scopy with both the devices.

We also looked at the hemodynamic response between the groups. There was a significant increase in HR (P = 0.02) from the baseline with Macintosh laryngoscope than Truview^PCD laryngoscope when they used as the first device but not when they both were used as a second device P = 0.51 and P = 0.87 for HR and MAP respectively. These findings are similar to the study done by Khan et al. who studied the Truview and Macintosh laryngoscopes for cardiovascular response and percentage of glottic opening scoring. They found that the “anterior view” design of the Truview laryngoscope is associated with less lifting force at laryngoscopy and consequently an attenuated intubation response when compared to Macintosh laryngoscope. However, in their study there was no significant difference in the laryngoscopy time between two groups.[19]

In our study, there was no significant difference in HR, minimum alveolar concentration, SBP and DBP while both the laryngoscope used as a second device. This may be due to the spraying of vocal cord with 10% lignocaine after visualization of glottis opening with the first device in each group for CLG.

Limitations of our study are that we did not use simulated difficult airway scenario to find the ease of intubation. Second, the intubation difficulty score was not used, which would have been a better evaluation tool for the process of tracheal intubation.

CONCLUSION

Base on the result and methodology employed, we have concluded that the Truview^PCD laryngoscope gives better glottis visualization but prolong TTI than Macintosh laryngoscope. However, the hemodynamic response to intubation was significantly less with the use of Truview^PCD laryngoscope when compared to that of Macintosh laryngoscope.