This study examined the performances of McGRATH™ MAC size 2 and size 1 blades in infants and compared the time required for tracheal intubation between the two. The McGRATH™ MAC size 1 blade shortened the time required for tracheal intubation with similar success rates.
To our knowledge, this is the first report examining McGRATH™ MAC blade size in infants. Previous reports comparing video and direct laryngoscopes for infants have demonstrated increased intubation success rates with the use of video laryngoscopes [5]. However, more time for intubation was required for the use of video laryngoscopes because more time is required for the tube to pass through the glottis [6, 7]. Reports comparing video laryngoscope models have not discovered a video laryngoscope model evidently advantageous for use in children [11–13]. Few studies have used McGRATH™ MAC on infants, especially since blade size 1, which is considered an appropriate size for infants, recently became available.
In this study, the glottis visualization time showed the main reduction in the intubation time, with no difference in the tube guidance time. The difference between blade size 2 from size 1 is the presence of a slightly thinner thickness and shorter distance from the camera to the tip. We speculate that the shorter glottis viewing time may be attributed to the smaller blade size, which results in the need for a smaller opening to insert the blade into the oral cavity, and reduced loss of orientation owing to the deep insertion of the blade. In Glidescope, Ji-Hye Kwony et al. reported that the time to guide the tube to the glottis was prolonged with the use of size 1 blade compared to that using size 2 blade owing to less adequate field of view [10]. In the present study, the closer distance between the camera and tip did not affect the tube guidance time. Differences in the blade shape and other factors may have played a role in the intubation time; however, further studies are warranted. When the McGrath size 1 blade became available, the functionality of the McGRATH™ MAC itself was upgraded to provide sharper images and more intense light; however, we believe these to be minor differences that do not influence the success rate or time required for intubation.
The strengths of this study are that it did not exclude patients with intubation difficulty factors and that the time required for intubation was measured later using video recordings, which allowed for more accurate time measurement. Most interventional studies exclude patients with anticipated intubation difficulties owing to safety concerns; however, because this was an observational study, we were able to include patients with chromosomal abnormalities and limited mouth opening in the study. In addition, anesthesiologists in the field usually prioritize patient safety, making it difficult to consider them as ideal candidates for performing the measurements and measure without an error of a few seconds; nevertheless, time measurement was observed to be more accurate by measuring from the recorded data in this study.
The tracheal intubation time measured in this study was comparable to that reported in other studies. Gupta et al. [12] reported a median intubation time of 27 s for the McGRATH™ MAC size 1 blade. This study defined intubation time as the time until end-expiratory CO2 detection. Since it is considered reasonable to take 3–4 s from the time the laryngoscope is removed from the oral cavity to the time the end-tidal CO2 is measured [14], 23.5 s could be considered the mean time required for intubation in the MAC1 group, which was externally valid.
However, in our study, the median difference in the intubation time required was approximately 3.5 s. Despite similar tracheal intubation success rates, we believe that shorter tracheal intubation time reduces the risk of exposure to hypoxia and improves patient safety. The apneic time for an adequately preoxygenated child of approximately 10 kg to drop below 90% SpO2 is approximately 3.5 minutes [2], while the time to drop to half below 90% SpO2 after positive pressure ventilation is interrupted is approximately 15 s in premature infants < 37 weeks [15]. Furthermore, the time allowed for apnea is shorter than when 100% oxygen is administered in patients who need to avoid high concentrations of oxygen due to cardiac disease or other factors. Therefore, the ability to complete tracheal intubation in a shorter time is of great clinical significance. In the current study, cases with a desaturation of ≥ 10% between the start of intubation and 1 minute after intubation did not differ statistically, which may be largely attributed to restriction of the administered oxygen levels in the patients of the study population due to their primary diseases. Further studies are warranted to examine hypoxemia during intubation.
Limitations
This single-center retrospective observational study was limited by the lack of a priori sample size estimation. The participants were patients who weighed ≥ 3 kg and underwent cardiac surgery; thus, the results may not be applicable to other populations. Adjustments were made for possible confounding factors (patient weight, career of intubation provider, and risk of difficult tracheal intubation). However, other confounding factors may also be present. In addition, improvements in the intubation performance over time may have been affected by the before-and-after comparisons.