Abstract
Objective
To evaluate the extraction force generated at different extubation angles using a manikin simulation and a randomized clinical trial.
Methods
Simulations were performed on a manikin to assess the force generated at extubation angles of 0°, 30°, 45°, 60°, 90° and 120° relative to the ground. The trial compared extraction force and changes in vital signs in patients undergoing general anaesthesia with tracheal intubation followed by extubation at 60° or 90°.
Results
The simulation study found that the extubation force was significantly lower at 45° and 60° than at all other extraction angles. In the trial, extubation at 60° resulted in significantly lower extraction force and systolic blood pressure elevation (n = 23) than extubation at 90° (n = 23).
Conclusion
Findings in a manikin simulation were confirmed by those of a randomized clinical trial, where extubation at 60° required less force than 90°, and was accompanied by less SBP elevation. Extubation at 60° is less invasive than extubation at 90°.
Introduction
Emergence from anaesthesia is a critical period for recovery of consciousness, neuromuscular conduction and airway protective reflexes. Although various anaesthesia procedures exist, recovery is always challenging, particularly at the moment of tracheal extubation.1–3 From the perspective of airway management, a failure to extubate is associated with various conditions, such as hypoxia, hypercapnia, vomiting, aspiration, inadequate ventilatory drive and laryngospasm. Such conditions may progress rapidly, thereby leading to potentially serious complications. In addition to respiratory events, emergence from general anaesthesia can occasionally result in undesirable side-effects such as agitation, abnormal hypertension or tachycardia, and arrhythmia; such side-effects may cause bleeding from the surgical wound site and an increase in intracranial and intraocular pressure.4–6 Noninvasive tracheal extubation with minimal force is therefore important for avoiding circulatory and airway collapse.
The angle of extraction of the tracheal tube may influence extubation force, but this has only been evaluated in a single simulation study. 7 We hypothesized that extraction force would be lower when the tracheal tube is extracted at a smaller angle relative to the ground than a vertical extubation at 90°. The aim of the present study was to evaluate the extraction force generated by different extubation angles using a manikin simulation and randomized clinical trial.
Patients and methods
Manikin-based simulation
The Airway Management Trainer® manikin (Laerdal, Stavanger, Norway), which is designed to represent the adult male anatomy, was used for tracheal tube intubation and extubation simulations. A tracheal tube with 8.5 mm internal diameter (Portex® Soft Seal®, Smiths Medical, Ashford, UK) was placed at the centre of the submandibular area, 24 cm from the incisors.
8
No lubricant was used. Extraction force was assessed at extubation angles of 0°, 30°, 45°, 60°, 90°, and 120° (relative to the ground) using a force-measuring device (Digital Force Gauge®, Shimpo Co. Ltd., Tokyo, Japan) tied tightly to the cuff of the tracheal tube. Extubation angles were confirmed as shown in Figure 1. The head of the manikin was fixed in neutral position with cohesive tape. The tracheal tube was removed 10 times at each angle, with the same individual performing all extubations (R.M.).
Equipment used for evaluating extubation force in a simulation using a manikin. (a) Angle guide; (b) extubation angle guide in place; (c) force measuring device (Digital Force Gauge®, Shimpo Co. Ltd., Tokyo, Japan) tied to the cuff of the tracheal tube. The colour version of this figure is available at: http://imr.sagepub.com
Randomized clinical trial
Study population
The study recruited patients scheduled for general anaesthesia with tracheal intubation at Osaka Medical College, Takatsuki, Japan, between November 2014 and December 2014. Based on results obtained from the simulation study, patients were assigned at random via an envelope method to undergo extubation at either 60° or 90° relative to the ground (Figure 2). Exclusion criteria were: contraindications to rapid induction (e.g., full stomach, gastro-oesophageal reflux); anticipated difficulty with airway (e.g., difficult head tilting or mouth opening); ischaemic heart disease; tooth instability.
Extubation force evaluation in a clinical setting using an angle guide and force measuring device (Digital Force Gauge®, Shimpo Co. Ltd., Tokyo, Japan) tied to the cuff of the tracheal tube. The colour version of this figure is available at: http://imr.sagepub.com
This study was approved by the institutional review board of Osaka Medical College, Takatsuki, Japan (clinical trial registry no. UMIN000015656), and written informed consent was obtained from each patient prior to enrolment.
Anaesthesia and intubation
No premedication was used. Percutaneous oxygen saturation, invasive blood pressure, heart rate, electrocardiography and end-tidal carbon dioxide tension were monitored for each patient using standard techniques. Anaesthesia was induced with 1–2 mg/kg propofol bolus or continuous target-controlled infusion and 0.3–0.5 µg/kg per min remifentanil. Rocuronium 0.8–1.0 mg per kg was used as muscle relaxant. A size 3 or 4 laryngoscope blade was used, according to the anaesthetist’s preference.
The size of the tracheal tube (Portex Soft Seal®) was determined by the staff anaesthetist using the formula: patient height/20 mm. The number of intubation trials was recorded and Cormack’s classification was assessed. The tip of the tracheal tube was placed ∼2 cm into the trachea with the indicator on the tracheal tube, then fixed at the right side of the mouth using cohesive tape. Anaesthesia was maintained by continuous administration of desflurane or sevoflurane, remifentanil and rocuronium (using standard procedures). The decision to use epidural block, peripheral nerve blockade, continuous fentanyl administration or intravenous acetaminophen for postoperative analgesia was made by the anaesthetist.
Extubation
At the end of surgery, the continuous infusion of sedatives and analgesics was stopped, and muscle relaxation was reversed with a sufficient dose of sugammadex, as recommended by the manufacturer (Merck & Co., Kenilworth, NJ, USA). While the patient was supine with the head at a neutral position, the fixation tape was removed, the tracheal tube was moved to the centre of the submandibular area, and the force-measuring device was tied tightly to the cuff of the tracheal tube. Mechanical ventilation continued until the patient regained consciousness and breathed spontaneously (with care taken to not exceed 40 mmHg end-tidal carbon dioxide), at which point the patient was instructed to open his/her mouth widely and extubation was performed. The extubation angle was guided by the same indicator as used in the simulation study (Figure 1c). Force measurement was performed by two anaesthetists each with >8 years’ experience (R.M., N.K.). Systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate were monitored before extubation (at tracheal tube cuff deflation) and after extubation (maximum values during 60 s after extubation). Postoperative hoarseness and pharyngeal pain were assessed after extubation and arousal (by R.M. or N.K).
Statistical analyses
Sample size was calculated based on a preliminary study of the force required to extubate at 90° or 60° relative to the ground in eight patients. The mean ± SD force was 9.9 ± 3.2 N at 90° and 5.4 ± 2.5 N at 60°. With an α-error of 0.05 and β-error of 0.2, it was determined that 20 patients per group would be adequate. We aimed to recruit 23 patients per group to adjust for missing data.
Data were presented as mean ± SD or median (interquartile range [IQR]). Kruskal Wallis test followed by Scheffe’s multiple comparison was used to compare differences in tracheal tube extraction force in the simulation study. Patient demographic and clinical characteristics were compared using χ2-test and unpaired Mann–Whitney U-test. χ2-test was used to assess postoperative hoarseness and pharyngeal pain. Mann–Whitney U-test was used to compare extubation force and vital signs (blood pressure and heart rate) in the randomized clinical trial. Statistical analyses were performed with JMP® 11 software (SAS Institute Inc., Cary, NC, USA). P-values < 0.05 were considered statistically significant.
Results
Manikin-based simulation
Median extraction force was significantly lower at 45° (7.5 ± 0.5 N) and 60° (7.2 ± 0.5 N) than at all other extubation angles tested (P < 0.001 for each comparison; 0°, 14.1 [0.7] N; 30°, 10.5 [0.6] N; 60°, 7.2 [0.5] N; 90°, 8.5 [0.4] N; 120°, 8.6 [0.4] N;). There was no significant difference in extraction force between 45° and 60°. Based on these findings, extubation angles of 60° and 90° were chosen for the randomized clinical trial.
Randomized clinical trial
The CONSORT flowchart for patient recruitment is shown in Figure 3. A total of 60 patients were assessed for eligibility; three refused and 11 were excluded. After obtaining written informed consent, 46 patients were included in the study (23 male/23 female; mean age 63.5 ± 13.2 years; age range 20–80 years). The final analysis included 23 patients in each group. There were no statistically significant between-group differences in any demographic or clinical characteristic Table 1.
CONSORT flowchart for patient recruitment in a randomized clinical trial to evaluate the extraction force generated at different extubation angles Baseline demographic and clinical characteristics of patients undergoing general anaesthesia with tracheal intubation included in a randomized controlled trial of the force required for extubation at an angle of 90° or 60° relative to the ground Data presented as mean ± SD or n of patients. No statistically significant between-group differences (χ2-test and unpaired Mann–Whitney U-test).
Extraction force was significantly lower at 60° than 90° (4.8 [2.0]N and 9.4 [2.5]N, respectively; P < 0.001).
Intra- and postoperative characteristics of patients undergoing general anaesthesia with tracheal intubation followed by extubation at an angle of 90° or 60° relative to the ground
Data presented as mean ± SD or n of patients.
BPM, beats per min
P = 0.004 versus 90° group; Mann–Whitney U-test.
Discussion
Careful airway and circulatory management during anaesthesia recovery is essential. 9 The timing of extubation is particularly important because its failure can be associated with severe complications. 10 Early extubation is associated with laryngospasm or airway obstruction by the tongue, and respiratory suppression via the action of analgesics and anaesthetics remaining in the system. Conversely, delayed extubation is associated with abnormal hypertension or tachycardia associated with cardiac and brain morbidity, and frequent bagging can lead to pneumothorax and chronic obstructive pulmonary disease. 11 Thus, smooth and noninvasive extubation has long been a goal for anaesthetists.12–15
Studies have reported gentle and smooth extubation techniques that rely on the administration of drugs or application of local anaesthetics to the pharyngeal or tracheal structure, or even into tracheal tube cuffs.16,17 Although several simulation and clinical studies have assessed extraction force with various fixation methods (aiming to avoid unintentional extubation),18,19 very little is known regarding extraction force during recovery from anaesthesia. To our knowledge, ours is the first clinical trial to evaluate extraction force by extubation angle without fixation. The current simulation study indicated that extubation at 45° or 60° relative to the ground required significantly less force than other angles. Based on these findings, we conducted a randomized clinical trial to compare extraction forces at 60° and 90°. Extubation at 60° required significantly less force than at 90°, consistent with data from the simulation study. Moreover, changes in SBP were larger when extubation was performed at 90° compared with 60°, suggesting that extubation at 60° is less invasive for patients than extubation at other angles.
This study has several limitations. First, the use of a manikin simulation meant that factors encountered in the clinical setting (such as saliva and sputum in the oropharynx) were not adequately reflected. 20 Secondly, only one type of tracheal tube was used. Several tracheal tubes with various stiffness and shapes exist, and evaluating differences based on the type of tube may be warranted. 21 Thirdly, although simulation analysis showed that an extubation angle of 45° resulted in lower extraction force than other angles (with the exception of 60°), the clinical evaluation was performed at 60° and 90° only. The 60° angle was selected because the median extraction force was slightly lower than at 45° in the simulation trial. Randomized clinical trials including 45° angles may help to optimize noninvasive extubation. Finally, the precision of the force-measuring device used in this study should be taken into consideration, as well as measurement uncertainties resulting from manual extubation. Further multicentre studies or meta-analyses would help to validate our findings.
In conclusion, data from the simulation study indicate that extubation at 45° or 60° requires less force than extubation at 90°. This was confirmed by the randomized clinical trial, where extubation at 60° required less force than 90°, and was accompanied by less SBP elevations. Extubation at 60° is less invasive than extubation at 90°.
Footnotes
Declaration of conflicting interest
The authors declare that there are no conflicts of interest.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.