Comparing intubation techniques of Klippel–Feil syndrome patients in the last 10 years: a systematic review

Methods

This study is a systematic review of all case reports on PubMed utilizing the keywords “Klippel–Feil Syndrome.” Case reports were the sole source of data extraction due to lack of research in the study of KFS and the field of anesthesiology. The initial search was conducted on September 1, 2023, and researchers found 1,234 articles, 657 of which were case reports, and 157 were published in the previous 10 years. Articles were searched for the keywords “anesthesia” and/or “intubation,” and 56 were observed. Case reports were selected if they contained relevant information regarding the intubation of KFS patients – 27 case reports covering 30 cases were selected. Cases not meeting these criteria were excluded from this study. A total of 29 case reports were excluded for: not enough clinically related information (n=16), nonintubation anesthetic method (n=7), no procedure performed (n=3), duplicate (n=1), or the patient was a nonhuman subject (n=2). Any articles written in foreign languages were translated utilizing online software. A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram is shown in Figure 1, depicting the selection process. Any discrepancies related to article inclusion or exclusion were assessed by the researchers utilizing Joanna Briggs Institute (JBI) critical appraisal guidelines, and final decisions were made by the lead researchers (MF, AS).

Figure 1:

A PRISMA diagram demonstrating the article selection criteria.

Examiners reviewed the remaining cases for information regarding the vertebral abnormalities presented and the relevance to the success rate of the chosen intubation technique. The articles detailed fiberoptic, direct, laryngeal mask airway (LMA), and video-guided intubation techniques with varied levels of success. For a more standardized statistical analysis, the authors chose to analyze the first-attempt success rates of the initial intubation technique selected for each case. The researchers also wanted to focus on the location of the cervical vertebral fusion, the number of total fusions, and the Mallampati score that was reported to see if there was a correlation that could benefit the field of anesthesia. Examiners stratified this data with the first-attempt success rates accordingly. For the purposes of the study, the cervical vertebral fusions were divided into three relatively similar-sized sections, including: superior (AO-C3), middle (C3-C5), and inferior (C5-C7) cervical regions. A mixed category was also included in cases in which there were multiple fusions in different regions. As an example, a C2-C3 fusion would be described as a superior fusion, whereas a C3-C4 fusion would be described as a middle fusion. Any fusions that contained multiple sections were categorized into the mixed grouping.

Results

Of the 27 articles and 30 total cases included in the study, the average age was 25.4 ± 21.6, and 73.3 % were female. Direct (n=10), fiberoptic (n=12), video-guided (n=6), and LMA (n=2) were the four chosen first-time intubation maneuvers. Limited cervical range of motion (70 %), and short neck (57 %) were the most frequent reasons listed for difficulty during intubation. The number and anatomical location of cervical vertebral fusions varied from patient to patient and were recorded. Depicted in Table 1 are the 30 case reports with information related to cervical vertebral fusions and the intubation-related difficulties.

This information was analyzed first by comparing the differences in first-attempt success rates of intubations based on the method utilized. Figure 2 depicts this information.

Figure 2:

The first-attempt success rates by intubation technique utilized. The most successful first-time intubations were among the video-guided and fiberoptic techniques.

Fiberoptic and video-guided intubation were the most successful techniques utilized among KFS patients with a first attempt success rate of 83 %, while direct and LMA techniques showed 50 % first-time success rates. Researchers were unable to perform a chi-square test of independence due to the lack of case reports available; however, a Fisher’s exact test was calculated in its place. The Fisher’s exact test of independence was utilized in the six possible comparisons: direct vs. fiberoptic, direct vs. video-guided, direct vs. LMA, fiberoptic vs. video-guided, fiberoptic vs. LMA, and video-guided vs. LMA. These six comparisons utilizing the Fisher’s exact independence test revealed: p=0.027, p=0.124, p=0.433, p=0.092, p=0.193, and p=1.000, respectively. The only p value with statistical significance was the comparison between Fiberoptic and Direct laryngoscopy. This analysis shows that the fiberoptic technique appears to be a more successful maneuver to utilize when compared to the traditional direct method. More data would be needed to prove this and to accurately compare the other groups. Table 2 stratifies the analysis of the intubation success rates by the number of cervical fusions, the location of the cervical fusions, and the reported Mallampati score.

Analysis of the cervical fusions showed a correlation between the quantity and success rates. First attempts were more likely to be successful, with fewer segment fusions when compared to the KFS patients who had 3 or more fusions. Data showed that the most successful category was 2 cervical segment fusions (70 %), compared to 1 fusion (67 %) and 3 fusions (33 %). The data collected also showed that inferior fusions had a 100 % success rate, whereas the least successful were the middle (33 %) and mixed categories (50 %).

The analysis of success rates of the Mallampati scores showed that even though a Mallampati score of a 4 typically would correlate with a more difficult intubation, the success rate was the highest (100 %). All of the Mallampati class 4 intubations were performed with fiberoptic intubation.

Discussion

KFS is a rare congenital disorder with varying systematic abnormalities that cause difficult and high-risk airway management among patients [2]. When providing care for a patient with KFS, it is important to be aware of the technique and level of caution required for specific presenting symptoms. The authors suggest that utilizing more advanced techniques when difficult airways are anticipated may prove to minimize the surgical complications. Although analysis showed that fiberoptic and video-guided intubation are the preferred methods for success, randomized controlled trials are needed to establish the best practices for intubation techniques in patients with difficult airways.

This study is crucial to the field of anesthesiology because multiple failed intubations can lead to laryngeal edema and necessitate postsurgical tracheostomies [18]. The laryngeal edema makes it difficult to extubate the patient without complications and can close off the airway [18]. Failed intubations can also lead to extended postsurgical hospital stays. In certain procedures with KFS patients, extubation has been successfully performed with the patient awake to avoid some of the aforementioned complications [10]. Considering that fiberoptic intubation is the gold standard with KFS patients, physician education on the subject could lead to more successful intubations and less complications [3], 5].

An increased quantity of cervical vertebral fusions showed worse success rates when compared to less fusions. This intuitively makes sense because more vertebral fusions would cause more restricted neck range of motion, which is a major listed cause of difficult intubations. The study also showed that patients with inferior fusions had better success rates. This may be due to the location of the adult glottis approximately at the level of C4-C5 [30]. The limited cervical range of motion at this level can narrow the glottis, making it difficult to intubate. Inferior fusions are below the C4-C5 level, making this a likely reason why the inferior cervical fusions appear to have less of an effect on intubation difficulty.

It was also unexpected to see Mallampati class 4 intubations with the highest success rates compared to lower Mallampati scores. After the data were stratified according to the intubation technique, it showed that the class 4 intubations were all performed with the fiberoptic technique. It is unclear whether the perceived difficulty of the case led to the anesthesiologists utilizing the fiberoptic method. Another potential reason for the difficulty in Mallampati score comparison is the clinical bias that may be present. Although anatomical classification though Mallampati scores are utilized frequently by anesthesiologists, they may report lower or higher scores based on varying personal experience. Anesthesiologists may inadvertently report a higher Mallampati score when the intubation is anticipated to be more difficult, and scoring lower when the intubation difficulty is minimal.

The authors suggest that a more thorough osteopathic structural examination of the cervical region may prove useful in screening for restricted cervical range of motion when clinical presentation and examination may not suggest it. This literature review also supports the need for specialized training in advanced intubation method selection, especially in patients with anatomical abnormalities. Future research in this area could potentially lead to new screening methods for patients with vertebral fusions, not just those with KFS.

This review faced some limitations due primarily to the number of cases available that met the selection criteria. Many reports did not discuss in depth the intubation process or did not provide enough information to be included in the study. Another limitation was the consistency of information reported about the number and location of cervical fusions and Mallampati score. Other limitations to this review include the spectrum of airway diameters ranging from infants to adults. This may have impacted the decisions and intubation success. Intubation-related pharmacology was also not included in the analysis due to the focus on anatomical presentation and its effect on intubation success. Further research on the drugs involved in anesthesia may show correlations to success. As more case reports become available, another review should take place to add insight into the care of KFS patients. Future studies on KFS patients and anesthesia techniques should focus on the precise cervical fusion so that more data may someday show a significant correlation between the location and number of vertebral fusions and its effect on intubation success rates. Further research should also be done to assess if the Mallampati score is predictive of successful intubation and/or complication rates postsurgery for KFS patients.

Conclusions

Thirty total case reports were found on PubMed in the last 10 years of KFS patients that were related to anesthesiology intubations. There were several interesting findings, although future research would be needed to prove correlations. KFS patients are more difficult to intubate due to the limited neck range of motion and cervical instability. More cervical fusions and various fusions correlated with increased difficulty in first-time intubation attempts. Difficult airway intubation in patients with a known cervical anatomic abnormality or well-described syndrome should have their airways initially secured via advanced laryngoscopy technique modalities such as a fiberoptic or videoscope-guided approach. Doing so will ensure maximal success rates on the first attempt and reduce postoperative complications. This systematic review presents data not previously reported that is important for this subset of patients.