Abstract
Study Design
Prospective randomized controlled trial.
Objectives
Adjustment of endotracheal tube cuff pressure (ETCP) in anterior cervical discectomy and fusion (ACDF) may influence the incidence of complications such as recurrent laryngeal nerve palsy (RLNP), hoarseness, and dysphagia.
Methods
The prospective randomized controlled trial was designed to investigate the influence of ETCP on the incidence of postoperative complications. All eligible patients underwent vocal cord examination before and after ACDF and were randomized into a control group (CG) and intervention group (IG). Endotracheal tube cuff pressure was passively monitored in CG, and in IG, it was maintained at 20 mmHg. Outcomes were evaluated during hospitalization and during follow-up.
Results
A total of 98 patients were randomized, each group consisted of 49 patients. Statistical analysis showed that gender and age did not influence the incidence of complications. In CG, duration of retractor placement and extent of approach significantly impacted the occurrence of complications. The incidence of postoperative RLNP was 8.2% in IG and 12.2% in CG, hoarseness and dysphonia were present in 18.4% in IG and in 37.5% in CG, and dysphagia in 20.8% in IG and in 22.5% in CG. Hoarseness was significantly present more in CG (P = .018). Only one patient from CG presented with RLNP after 1 year, the remaining nine patients spontaneously recovered.
Conclusions
Unregulated ETCP can lead to a significantly higher incidence of hoarseness; however, its improvement rate is 100%. The early postoperative complication rate was higher in CG, and after one year, 1 patient had RLNP and 1 patient had dysphagia.
Keywords: anterior cervical discectomy and fusion, endotracheal cuff pressure, recurrent laryngeal nerve palsy, dysphagia, hoarseness, risk factors, prospective randomized controlled trial
Introduction
Recurrent laryngeal nerve palsy (RLNP) with subsequent vocal cord paralysis is a relatively common postoperative complication after anterior cervical spine surgery (ACDF), with a reported incidence from 0.6 to 13.3%.1-4 Besides RLNP, dysphagia or hoarseness can occur after the ACDF. According to the meta-analysis of Shriver et al. the total incidence of dysphagia after ACDF is 8.5%, of which 0.9% is transient and 7.6% is permanent. 5 Hoarseness occurs in up to 8% of cases. 6
The etiology of perioperative recurrent laryngeal nerve lesions is multifactorial. Possible causes are continuous pressure caused by retractor placement on medial anatomical structures of the neck, which contain the recurrent laryngeal nerve, stretching of the recurrent laryngeal nerve with impeded blood flow of the vasa nervorum causing an ischemic injury, increased surgery duration, an extensive approach, postoperative edema or hematoma, or trauma during intubation or the surgery itself.7-10
Previous studies demonstrated a relationship between retractor placement and increased endotracheal tube cuff pressure (ETCP). Maintaining ETCP between 15 and 25 mmHg could lower the complication rate after intubation.11,12 Our hypothesis is based on the assumption that maintaining a set ETCP during ACDF could lead to a lower complication rate.
Methods
The study methodology was approved by ethics committee of the Masaryk Hospital, Usti nad Labem, Czech Republic, reference number 251/46. All patients signed informed written consent with their clinical inclusion in the study. This clinical single-centered study was designed as double blinded (observer and patient blinded), prospective randomized controlled trial to investigate the influence of the ETCP on the incidence of the postoperative complications such as dysphagia, hoarseness (defined as subjective voice change), or RLNP.
Between September 2018 and August 2020, all patients between 18 and 90 years of age admitted to the Neurosurgical Department of the Masaryk Hospital, Usti nad Labem, Czech Republic for primary ACDF could be included in the study after signing written consent. Patients were excluded in presence of former known RLNP, previous ACDF, cervical spine trauma, cervical spine infection such as spondylitis or empyema, or mental disability. Included patients underwent vocal cord examination at the Department of Otorhinolaryngology, Head and Neck Surgery prior to and after the surgical procedure.
Eligible patients were randomized using an online randomization program (www.randomization.com) into a control and intervention group. Results of the randomization process were only known by the anesthesiologist, who administered general anesthesia to the patient. The patients and investigators were blinded during the surgery, hospitalization, and follow-up period.
Induction to anesthesia consisted of propofol, sufentanil, and myorelaxants and was continued with sevoflurane and a reversal agent if necessary. The process was identical in both groups of patients. The anterior cervical spine approach was performed to access the disc with placement of Caspar cervical retractors followed by discectomy and fusion. Endotracheal tube cuff pressure was measured and adjusted to 20 mmHg in each patient after general anesthesia was initiated using a manometer. Endotracheal tube cuff pressure measurements using manometer were performed before and after retractor placement and after refractor removal. In the control group, ETCP was recorded throughout the surgery and was not modified in any way. In the intervention group, ETCP was maintained at 20 mmHg throughout the procedure by withdrawing air when the ETT cuff pressure exceeded 20 mmHg.
Recorded parameters were ETCP throughout surgery, duration of the surgery, time of retractor placement, extent of the surgical approach, and demographic information of the patient such as age, gender, or smoking habits.
The incidence of clinical complications was checked 24 hours after surgery, on the day of discharge, and throughout the follow-up period via the outpatient clinic at 6 weeks, 3 months, and 6 months intervals. On the first postoperative day, standard laryngoscopy was performed to examine vocal fold mobility. In cases where laryngoscopy revealed postoperative RLNP, two follow-up examinations were planned, 1 week after the initial laryngoscopy and shortly before each patient’s first check-up in the outpatient clinic.
The sample size in each group is based on the hypothesis that the incidence of complications in the intervention group is 10% and in the control group 30%. Assuming a power of 70%, 49 patients needed to be included in each group. Patients were randomized into two groups in a ratio of 1:1. Results of both groups and their relationships were independently statistically analyzed by an external statistician using descriptive methods by categorical data, and both groups were compared using the Pearson’s chi-squared test, Fisher’s exact test, or Mann–Whitney test. Continuous variables between the intervention and control group were compared using the test of significance between two relative means. A P value < 0.05 was considered statistically significant in all analyses.
Results
Between September 2018 and August 2020, 275 patients were admitted for primary ACDF. Forty-six patients were admitted with cervical spine trauma, 8 patients had infectious disorders such as discitis or empyema of the cervical spine, and 9 patients underwent surgery for adjacent segment disease. All of these patients were excluded from the study. From 212 patients with degenerative cervical spine disorders, data from 114 patients were not included for various reasons: incorrectly executed study procedures, rapid transfer to the operation theatre without the possibility of performing the study protocol, patients who could not undergo the vocal fold examination due to irritability, and patients who declined the postoperative examination because of discomfort. The study was suspended during COVID-19 restrictions. In addition, 4 patients without early postoperative complications after 24 hours were lost to follow-up.
Table 1 shows characteristics of patients in the control and intervention group. A total of 98 patients were included and randomized, 49 patients in the control group and 49 in the intervention group. A total of 72.4% of patients were under 60 years of age, of which 79.6% were in the control and 65.3% in the intervention group. The percentual representation of women was higher in both groups, 53.1% in the control group and 65.3% in the intervention group. Fifty patients from 92, whose information was known, were smokers. In the control group, smokers made up 66.0% of patients, which was higher than in the intervention group (42.2%). Body mass index values were similar in both groups. None of the patients presented with silent RLNP before surgery.
Table 1.
Demographic and Perioperative Parameters.
| Control group | Intervention group | P value | |
|---|---|---|---|
| Demographic parameters | |||
| Patients, n | 49 | 49 | |
| Sex, female/male, n (%) | 26/23 (53.1/46.9) | 32/17 (65.3/434.7) | 0.22 |
| Age, years ± SD | 51.9 ± 9.8 | 54.8 ± 11.0 | 0.11 |
| Age <60 years, % | 79.6 | 65.3 | |
| BMI, kg/m2 ± SD | 27.7 ± 4.8 | 28.1 ± 4.2 | 0.94 |
| Smoking, n (%) | 31 (66) | 19 (42) | 0.02 |
| Perioperative parameters | |||
| Incision site, right/left, n | 49/0 | 49/0 | |
| Retractor time, >90 minutes, % | 40.8 | 30.6 | 0.29 |
| ETCP after retractor placement, mmHg ± SD | 41.7 ± 15.3 | 20.0 | 0.00 |
| Levels | 0.20 | ||
| one, % | 71.4 | 59.2 | |
| C3/4, n | 2 | 4 | |
| C4/5, n | 6 | 3 | |
| C5/6, n | 17 | 12 | |
| C6/7, n | 9 | 11 | |
| C7/Th1, n | 1 | 0 | |
| two, % | 28.6 | 38.8 | |
| C3–5, n | 1 | 1 | |
| C4–6, n | 6 | 5 | |
| C5–7, n | 5 | 13 | |
| C3/4, C5/6, n | 1 | 0 | |
| three, % | 2.0 | 0 | |
| C3–6, n | 1 | 0 | |
Abbreviations: BMI, body mass index; ETCP, endotracheal cuff pressure. Boldfaced P values denote statistical significance.
Variables associated with surgery such as retraction time, extent of surgery, and ETCP values in the control group are shown in Table 1. In 40.8% of cases, the time of retractor placement was longer than 90 minutes in the control group, compared to 30.6% in the intervention group. One level surgery was most frequent in both groups, 71.4% in the control and 59.2% in the intervention group, 1 patient underwent a three-level procedure. The mean ETCP after the retractor placement was 41.7 mmHg in the control group. A right-sided approach was performed in all cases.
The incidence of postoperative RLNP was 8.2% in the intervention group and 12.2% in the control group; early postoperative hoarseness and dysphonia (24 hours after surgery) were present in 18.4% of cases in the intervention group and in 37.5% in the control group; with early dysphagia present in 20.8% and 22.5% of cases in the intervention and control groups, respectively (Table 2). Eighteen patients had sore throats without RLNP. Two patients in the intervention group had persisting postoperative RLNP at 6 weeks; however, both cases resolved after 3 months. Only 1 patient from the control group presented with RLNP after 1 year of follow-up. One patient had minor dysphagia after 1 year. All patients with early postoperative hoarseness improved (Table 3).
Table 2.
Incidence of Complications.
| Complications | Control group | Intervention group | P value |
|---|---|---|---|
| RLNP, % (n) | 12.2 (6) | 8.2 (4) | 0.25 |
| Hoarseness, % (n) | 37.5 (18) | 18.4 (9) | 0.02 |
| Dysphagia, % (n) | 22.5 (11) | 20.8 (10) | 0.42 |
Abbreviations: RLNP, recurrent laryngeal nerve palsy. Boldfaced P values denote statistical significance.
Table 3.
Follow-up Visits and Complications.
| Follow-up | 1 day | 6 weeks | +3 months | +6 months | 1 year |
|---|---|---|---|---|---|
| Remaining recurrent laryngeal nerve palsy, n | |||||
| Control group | 6 | 3 | 3 | 2 | 1 |
| Intervention group | 4 | 1 | 0 | 0 | 0 |
| Remaining hoarseness, n | |||||
| Control group | 18 | 4 | 2 | 1 | 0 |
| Intervention group | 9 | 4 | 0 | 0 | 0 |
| Remaining dysphagia, n | |||||
| Control group | 11 | 5 | 2 | 2 | 0 |
| Intervention group | 10 | 6 | 4 | 1 | 1 |
Hoarseness was significantly more frequent in the control group (P = 0.02); however, no statistically significant differences were found in the incidence of RLNP (P = 0.25) and dysphagia (P = 0.42) between both groups. No statistically significant association was found between gender and age and the incidence of complications. Interestingly, 4 patients in the control group with postoperative RLNP were nonsmokers, whereas only 1 patient with RLNP was smoker (P = 0.04). The duration of retractor placement significantly impacted the occurrence of RLNP in the control group. Within this group, duration of retractor placement under 90 minutes was associated with a higher incidence of RLNP. In the control group, 1 level ACDF had a significantly lower incidence of postoperative dysphagia (P = 0.03) (Table 4).
Table 4.
Statistically Significant Connection Between Complications and Factors, P Values.
| RLNP | Hoarseness | Dysphagia | ||||
|---|---|---|---|---|---|---|
| CG | IG | CG | IG | CG | IG | |
| Age | 0.64 | 0.43 | 0.10 | 0.92 | 0.13 | 0.31 |
| Sex | 0.12 | 0.43 | 0.82 | 0.38 | 0.57 | 0.25 |
| Smoking | 0.04 | 0.10 | 0.49 | 0.25 | 0.85 | 0.16 |
| Retractor time | 0.03 | 0.36 | 0.49 | 0.32 | 0.08 | 0.40 |
| Level | 0.11 | 0.18 | 0.56 | 0.32 | 0.03 | 0.45 |
| Pressure | 0.91 | - | 0.35 | - | 0.12 | - |
Abbreviations: RLNP, recurrent laryngeal nerve palsy; CG, control group; IG, intervention group. Boldfaced P values denote statistical significance, interpretation in the text.
Discussion
The aim of this prospective randomized controlled study was to determine if monitoring and adjustment of the ETCP during ACDF could decrease the incidence of postoperative complications. In this study, postoperative hoarseness, dysphagia, and RLNP had a higher incidence in the control group. However, the statistical association between the incidence of dysphagia and RLNP and adjustment of the ETCP after retractor placement was not significant. Only hoarseness was statistically predominant complication in the control group.
The most common clinical complication was hoarseness, which occurred in 18.4% of cases in the intervention group and in 37.5% in the control group. It was the only complication that was dependent upon stable ETCP maintenance during surgery and was significantly more common in the control group. Recurrent laryngeal nerve palsy caused hoarseness in 8 of 26 cases. Although all patients eventually recovered, all of them mentioned that hoarseness significantly affected their comfort and activities of daily living. In the literature, postoperative dysphonia and hoarseness mostly resolve within 3 to 9 months after surgery; however, Yue et al recorded permanent postoperative dysphonia in 18% of cases on average of 7.2 years after ACDF.13-17 ACDF improves patients’ neurological state and has an unequivocally positive impact on their daily life; however, we should consider incorporating the ETCP measurement to clinical practice to increase our patients’ life quality even further. 18
Three randomized studies were conducted to analyze the impact of adjusting the ETCP after retractor placement on the development of postoperative dysphagia. In all of these studies, maintaining ETCP at 20 mmHg did not decrease the risk of postoperative dysphagia.7,19,20 Interpretation of these results is that ETCP in control groups did not reach the degree required to cause clinically relevant dysphagia. Development of this complication is most likely the result of multiple coinciding factors such as the duration or extent of surgery.
The majority of previously published studies focusing on ACDF complications were either retrospective or did not have an adequate follow-up, which makes our cohort, study methodology, and follow-up period a unique trial.
In previously published retrospective studies, lesions of recurrent laryngeal nerve were verified with a laryngoscope only in symptomatic patients, who postoperatively presented with hoarseness and dysphagia.21,22 Therefore, these studies underestimate the actual incidence of RLNP, as cases of silent RLNP are overlooked. 4 In our study, we did not ascertain silent RLNP before surgery.
In two prospective studies, Jung et al. describe that the laterality of approach and maintenance of the ETCP during surgery influenced the incidence of the RLNP in three patient groups.4,23 After a three-month follow-up period, the incidence of RLNP was 11.3% in patients operated from right side, 6.5% in patients operated from left side, and 1.3% in patients operated from left side and with reduced ETCP.
In the past, only one randomized controlled study focused on RLNP after ACDF. 24 Audu et al. analyzed 94 patients, randomized into 2 groups, where postoperative vocal fold immobility was present in 15.4% in the control group (no adjustment of the ETCP) and in 14.5% in the intervention group (ETCP maintained at 20 mmHg). Clearly, ETCP adjustment did not influence the incidence of RLNP; however, right-sided approaches led to a higher incidence of RLNP. In this study, from 11 patients operated from the right, 3 patients developed postoperative RLNP and none of the 83 patients operated from the left were affected. 24 However, no follow-up statistical analysis was performed.
Although the left-sided approach in ACDF successfully decreased the incidence of RLNP in previously mentioned studies, no long-term results were presented. Our trial demonstrates the importance of long-term patient follow-up. Despite a right-sided approach, 10 patients (3.1%) presented with RLNP at the three-month follow-up; however at the one-year follow-up, RLNP completely resolved in 9 of the 10 patients. Due to anatomical relations, the right recurrent laryngeal nerve is more susceptible to direct or stretch-induced injuries. However, our results after a right-sided approach are comparable with results presented by Jung et al. who utilized a left-sided approach and are also in agreement with the cohort of Beutler et al.23,25 In this respect, we question the assumption of previously published studies that a right-sided approach could lead to a significant long-term increase of complication incidence.
Conclusion
Endotracheal tube cuff pressure does not influence the incidence of the RLNP or dysphagia. However, unregulated ETCP leads to increased postoperative hoarseness compared to stable ETCP at 20 mmHg. And thus, if we aim to reduce the incidence of this complication, which influences our patient’s satisfaction after surgery, we should implement the measurement of ETCP as a standardized procedure.
Compared to results of previous studies, our study demonstrated that the right-sided approach does not impact the complication rate in long-term follow-up.
Acknowledgments
I would like to acknowledge Jan Lodin, MD for the proofreading of the article and language corrections.
Footnotes
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The Internal Grant Agency of the Krajská zdravotní, Czech Republic, provided financial support in the form of a grant (IGA-KZ-2018-1-4).
Ethical Approval: Ethics committee of the Krajská zdravotní, Masaryk Hospital, Czech Republic, reference number 251/46.
ORCID iD
Alena Sejkorová https://orcid.org/0000-0001-9987-1110
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