Study design
This was an observational, randomized, cross-over simulation study. The study protocol was approved by the Institutional Review Board (IRB) of the Polish Society of Disaster Medicine (Approval no: 21.11.2017.IRB), and registered in www.clinicaltrials.gov (identifier: NCT03733158).
Study participants
Following IRB approval and written informed consent, 32 experienced anesthesiologists with at least 2 years of clinical experience participated in this study. No anesthesiologist had any prior experience with the new flexible tip bougie, but each was experienced with the standard bougie and all had performed a minimum of 500 endotracheal intubations using the Macintosh laryngoscope.
Intubation devices
All intubation procedures were performed using a Macintosh blade size 3 (Heine Optotechnik, Herrsching, Germany) and one out of two bougies:
- 1.
The standard bougie for difficult intubation (Sumi, Sulejówek, Poland);
- 2.
The new flexible tip bougie (FMDSS Construct Medical, Hawthorn, Austria, Fig. 1).
Tracheal tubes (Portex, St. Paul, MN, USA) with an internal diameter of 7.5 mm were used for all intubations. Before each intubation attempt, the endotracheal tube and the manikin’s airway were thoroughly lubricated using an airway lubricant for training manikins (Laerdal, Stavanger, Norway). A regular 20 cc syringe (B. Braun Melsungen AG, Hessen, Germany) was used for cuff inflation.
Study protocol
Each anesthesiologist participated a standardized 5 min lasting practical demonstration of the flexible tip bougie and the standard bougie by one of the investigators. Once completed, each anesthesiologist performed tracheal intubation with both devices in a Laerdal Airway Management Trainer (Laerdal, Stavanger, Norway) in 2 scenarios:
- 1.
normal airway in the supine position
- 2.
normal airway with the neck immobilized using a hard-cervical collar.
Afterwards, anesthesiologists performed tracheal intubation in a SimMan 3G simulator (Laerdal, Stavanger, Norway) in 6 different airway scenarios:
- A)
Normal airway;
- B)
Tongue edema;
- C)
Pharyngeal obstruction;
- D)
Manual cervical inline stabilization;
- E)
Cervical collar stabilization;
- F)
Cervical collar stabilization and pharyngeal obstruction.
Once anesthesiologists completed all intubations in all eight scenarios, they were asked to perform another endotracheal intubations on the Laerdal Airway Management Trainer with a normal airway using both devices. The intubation procedure was closely monitored by one of the investigators, to certify, that intubations using both devices were performed in an adequate manner. If needed, endotracheal intubations were repeated until both the anesthesiologist and the investigator were satisfied.
For the study, the SimMan 3G simulator (Laerdal, Stavanger, Norway) was placed on a hard, flat table to simulate an “in the bed” scenario. Anesthesiologists were instructed to intubate the manikin with one of the two devices, insufflate the cuff of the tube, attach a bag valve mask, and provide one breath to ventilate the lungs of the simulator for an overall of six different airway scenarios:
Normal airway;
Tongue edema;
Pharyngeal obstruction;
Manual cervical inline stabilization;
Cervical collar stabilization;
Cervical collar stabilization and pharyngeal obstruction.
Both, the sequence of the intubation devices and the six airway scenarios were randomized using the research randomizer (randomizer.org).
Measurements
The primary endpoint was the rate of successful placement of the tracheal tube in the trachea with a maximum of three intubation attempts. A failed intubation attempt was defined as an attempt in which the trachea was not intubated, or lasted longer than 120 s [15]..
The secondary endpoint was time required for successful tracheal intubation. The time for successful intubation, was defined as the time between insertion of the blade between the teeth until the manikin was successfully ventilated, confirmed by lung insufflation during bas-mask ventilation [15].
Number of intubation attempts, and number of optimization maneuvers required (re-adjustment of manikin’s head position, and BURP -backward, upward, and rightward pressure to the larynx- maneuver performed by a researcher), served as additional secondary endpoints. All outcomes were assessed by one of the researchers. A researcher further scored the severity of dental compressions, which was assessed by the number of audible teeth clicks (0; 1; ≥2) with the Laerdal airway trainer, and by a grading of pressure of the teeth (none = 0; mild = 1; moderate/serve ≥2) on the SimMan 3G simulator. At the end of each scenario, each participant scored the ease of use of each intubation device on a visual analogue scale ranging from 0 (extremely easy) to 100 (extremely difficult).
Sample size
The sample size was calculated with the G*Power 3.1 software, and the two-tailed t test was applied (Cohen’s d, 0.8; alpha error, 0.05; power, 0.95). We calculated that at least 28 participants would be required (paired, 2-sided). To minimalize the impact of potentially data loss, we planned to enroll up to 32 anesthesiologists into this study.
Statistics
All statistical analyses were performed with statistical package STATISTICA 13.3EN (TIBCO Inc., Tulsa, OK, USA). The normal distribution of data was tested using the Kolmogorov-Smirnov test. Results obtained from each trial were compared using two-way repeated-measurements analysis of variance for intubation time. Fisher’s exact test was used for the success rate. The participants’ subjective opinions were compared with the use of the Stuart-Maxwell test. Data were presented as medians and interquartile range (IQR) or number and percentage (%). The α-error level for all analyses was set as P < .05.