Introduction
Stereotactic headframes are often indicated in neurosurgical procedure requiring precise localization of target tissue such as deep brain stimulation, stereotactic radiosurgery, stereotactic electroencephalography (SEEG), and laser interstitial thermal therapy (LITT). However, airway management of patients with stereotactic headframes in situ poses a major challenge for the anesthesiologists. The stereotactic frame often obscures access to the mouth making bag mask ventilation impossible. In addition, head and neck manipulation is restricted making placement of a supraglottic airway, laryngoscopy, and intubation difficult. Currently, the literature on crisis airway management in stereotactic frames remains limited with no guidelines or consensus.
A previous mannequin study using a Leksell frame with a curved anterior bar demonstrated that intubation with both direct laryngoscopy (DL) and videolaryngoscopy (VL) as well as insertion of a laryngeal mask airway (LMA) is possible with stereotactic headframe in situ. Reference Brockerville, Unger, Rowland, Sammartino, Manninen and Venkatraghavan1 However, previous case reports have reported potential problems associated with airway management including failed insertion of intubating laryngeal mask airway (iLMA) and esophageal perforation following multiple intubation attempts. Reference York, Wharen and Bloomfield2,Reference Kurnutala, Kinthala and Padmaja3 Therefore, it has always been suggested to keep an Allen wrench with the patient to remove the frame in emergency situations where intubation or LMA insertion is not successful. Reference Kurnutala, Kinthala and Padmaja3
Recently, newer procedures such as SEEG and magnetic resonance imaging-guided laser interstitial thermal therapy (MRIgLITT) may require special configurations of the standard stereotactic frame (Leksell G series frame, Elekta, Stolkhom, Sweden). In such applications, a straight front bar may be required, which further restricts the access to the airway and makes airway management even more difficult (Figure 1). An additional concern is that many of these procedures require transfer of patients between different imaging and procedure locations where access to extra equipment and personnel may be a challenge. Bag mask ventilation would not be possible over the straight front bar; therefore, securing access in an airway emergency where LMA insertion or intubation has failed would require the removal of the frame. Removing the entire headframe may be time consuming and potentially complicated leading to catastrophic hypoxia and hypoventilation in patients with intracranial pathology during an airway crisis.
Figure 1: Frame removal techniques. (A) In the front bar removal technique, the front bar screws are completely released (steps 1 and 2). One of the frontal pins is then unscrewed until it does not make contact with the skin (step 3) and the front bar is pulled (step 4). If the front bar cannot be removed at this stage because of persistent tension in the frame, the second frontal pin can be loosened (step 5, optional) as the front bar is being pulled, until it is released. (B) In the full frame removal technique, both frontal (steps 1 and 2) and posterior (steps 3 and 4) pins are completely loosened. The frame is then removed superiorly (step 5).
The objectives of this study are (1) to assess the difficulty of intubation with or without the front bar of a Leksell frame and (2) to determine the time taken for the removal of the front bar versus the whole frame.
Methods
Study Design – Prospective Observational Mannequin Study
The study was approved by the institutional research ethics board (20-6052) and informed consent was obtained from all participants. Participation was open to all members of the anesthesia staff within the department of anesthesia. The study also included members of the functional neurosurgical service at our institution, including fellows and consultants. Eighteen anesthesia personnel and four neurosurgeons participated in the study. Of the anesthesia participants, there were 3 residents, 11 fellows, and 4 consultants. The neurosurgical participants included three functional neurosurgical fellows and one consultant neurosurgeon.
Setup
The study was conducted in the functional neurosurgery operating room (OR). A Leksell model G frame was assembled by the functional neurosurgery fellow using two short posterior poles, two long anterior poles, and the straight front bar. The frame was installed on a mannequin using 42.5 mm screws posteriorly and 45 mm screws anteriorly, all torqued to 60 cNm. The frame was positioned parallel to the cantomeatal plane with the front bar inferior to the nose. The framed mannequin was then placed at the head of the OR bed in the standard position.
Interventions
Intubation with or without the front bar
Standard intubation equipment including a size 7.5 endotracheal tube (ETT), stylet, and CMAC® videolaryngoscope (Karl Storz Products, Tuttlingen, Germany) with a size #3 blade was placed on a Mayo stand next to the mannequin. Participants were allowed to adjust the height of the bed as well as the positioning of the CMAC® screen prior to data collection; however, no other modifications to the mannequin were permitted.
Participants were first asked to intubate the mannequin with the headframe in situ and front bar on a total of three times. They repeated this again with the front bar completely removed. Successful insertion was confirmed by visualizing the ETT pass through the mannequin’s vocal cords and bilateral inflation of the lungs. If the participant was unable to intubate after three attempts, then it was considered unsuccessful.
Removal of the front bar versus removal of the whole frame
Neurosurgeons were timed removing just the front bar versus the entire headframe in the same setup. Removal of the front bar was achieved by removing both screws retaining the front bar and then completely removing one of the frontal pins and pulling on the front bar (Figure 1A). This decreased frame expansion allowed the front bar to be released. If the front bar could not be released at this stage, the second frontal pin was slowly unscrewed while the front bar was being pulled, until the front bar could be released. The other pins and frame were left in place. For the complete frame removal protocol, all four pins were completely unscrewed, and then the frame was pulled up to completely expose the head (Figure 1B). Both conditions were trialed three times.
Data Collection and Analysis
The required sample size was calculated using data from a previous study by Brockerville et al. Reference Brockerville, Unger, Rowland, Sammartino, Manninen and Venkatraghavan1 which reported an average intubation time using VL of 55 versus 45 seconds with and without headframe, respectively. Using a power of 0.8, an alpha of 0.05 with an expected drop out rate of 10%, a sample size of 18 participants was needed. Data collected from anesthesia participants included level of training and time taken to secure the airway. Time zero started when the participant picked up the CMAC® handle and time completed once the ETT passed through the cords. We also compared the times for each group (residents, fellows, and staff). For the neurosurgical participants, timing started when they touched the frame until frame manipulation was completed. The time to remove the headframe versus the front bar was compared. All data are presented as mean SD and statistics were performed using unpaired t-tests where a p-value < 0.05 was considered to be significant.
Results
All participants successfully intubated the mannequin using the CMAC® 3 blade with the Leksell frame intact and again with the front bar removed. Results for the airway study are shown in Table 1. The mean time for intubation was 23.5 (17.4) seconds with the front bar in situ. The average time for intubating with the front bar removed was significantly less at 10.9 (4.1) seconds (p < 0.001). The time required for intubation with the front bar removed is effectively decreased by half in this study with the effect being more pronounced with junior anesthesia staff.
Table 1: Mean intubation times
The time taken to remove the front bar versus the entire frame by the neurosurgical participants is shown in Table 2. The mean time to remove the front bar was 35.4 (7.3) seconds compared to the time to remove the entire frame of 83.3 (18.6) seconds (p < 0.001).
Table 2: Time to remove the entire frame versus front bar removal
Discussion
With the development of more sophisticated MRI thermometry, Reference Missios, Bekelis and Barnett4 techniques such as LITT are becoming much more prevalent. LITT has notable uses in neuro-oncology with the ability to treat recurrent gliomas, tumors in eloquent areas, and in patients with multiple metastases. Reference Shah, Semonche and Eichberg5–Reference Barnett, Voigt and Alhuwalia8 LITT is also useful in treating refractory epilepsy, patients with deep-seated epileptogenic foci, mesial temporal lobe epilepsy, hypothalamic hamartomas, tuberous sclerosis, and focal cortical dysplasia. Reference Lee, Kalia and Hong9,Reference Salem, Kumar and Madewell10
Although very beneficial, this procedure also poses numerous difficulties for the anesthesiologist. As discussed previously, the use of the Leksell G series headframe with the straight bar provides unique challenges for airway manipulation. In addition, the LITT procedure in our institute involves several transfers out of the OR with the stereotactic headframe in situ. Although the majority of procedures are performed supine, LITT procedures may also require the lateral and prone positions increasing the inherent risk of losing the airway. Reference Jimenez-Ruiz, Arnold, Tatsui and Cata11 Although airway management with various other versions of the Leksell frame has been previously investigated using both an LMA or ETT, there has never been to our knowledge any investigations assessing airway management with G series frame where the straight front bar obscures oral access nor described this technique for rapidly removing the front bar on a Leksell headframe.
This study demonstrates that, contrary to a popular saying in the neurosurgical community, removal of the front bar without complete frame removal is possible if the tension in the frame is first decreased by the loosening of one pin (Figure 1). Removal of the front bar is a simple and faster procedure than removing the entire headframe and could be considered when improved access to airway is emergently required. Although this study demonstrates that intubating with the Leksell front bar in situ is possible with VL under ideal intubating conditions, most scenarios requiring emergency airway management in this headframe are unlikely to be under ideal intubating conditions as in our study, increasing the likelihood of failed intubation attempts. Therefore, statistically significant intubating times of 10 seconds faster with the front bar removed may translate into even greater clinical significance in a real airway crisis. In addition, the time taken to remove the front bar was 48 seconds faster on average than removing the entire frame. In addition, a simpler and more streamlined approach provides less opportunity for complications, errors, or injury to the patient or care provider. This study clearly demonstrates a rapid and simple method to improve intubating conditions by removing only the front bar.
Limitations
A major limitation of this study is that it was completed on a single mannequin with an uncomplicated airway, which does not replicate real life conditions. Although the headframe was placed by the functional neurosurgical fellow in the standard fashion, the positioning relative to the front bar may be slightly different on a person creating different intubating conditions. The difference in intubating times with the front bar removed is on average 10 seconds less than with the front bar in situ. The clinical significance of this can only be extrapolated in the context of an airway crisis with a rapidly deteriorating patient. In addition, the study did not specifically evaluate the time for insertion of an LMA or the difference in intubating times with DL versus with VL. We included participants with varying degrees of clinical experience especially in the context of neuroanesthesia. However, interestingly participants with the shortest time taken to intubate had the most clinical experience and may highlight the importance of training and experience when managing a difficult airway. We examined the stereotactic frame using only the straight bar setup as this likely proves the most challenging for securing a definitive airway; however, there are also a number of other configurations that were not specifically tested.
Conclusion
In conclusion, we have demonstrated that it is feasible and easier to remove only the frontal bar without removal of the entire frame to facilitate airway management. In addition, regardless of the level of experience, this method requires significantly less time compared to removing the entire frame. Therefore, removing only the front bar should be considered in an emergency situation to facilitate airway access using VL.
Statement of Authorship
TD contributed to experimental design, data acquisition, analysis, and manuscript. CIM contributed to the experimental design, data acquisition, analysis, and manuscript. SK contributed with experimental design and manuscript. LV contributed to manuscript and editing. MD contributed to experimental design, analysis, and manuscript.
Disclosures
The authors report no disclosures relevant to this manuscript.
