Effect of ultrasound-guided thyroid cartilage plane block on postoperative sore throat in patients undergoing vocal cord polypectomy under suspension laryngoscopy: a randomized controlled trial

Abstract

Objective

To evaluate the efficacy of ultrasound-guided thyroid cartilage plane block (TCPB) on postoperative sore throat (POST) in patients undergoing suspension laryngoscopy vocal cord polypectomy (SLVCP).

Methods

Ninety patients scheduled for elective SLVCP were randomized to either the TCPB group (general anesthesia + ultrasound-guided TCPB) or the C group (conventional GA), with 45 patients in each. The primary outcome was the incidence of POST at 2 h after extubation. Secondary outcomes included the incidence and severity of POST at 0.5, 2, 6, 12, and 24 h after extubation; the incidence and severity of hoarseness at 0.5, 2, 6, 12, and 24 h after extubation; and cough response during emergence.

Results

The incidence of POST was significantly higher in the C group compared to the TCPB group at 0.5 h (93% vs. 67%, RR = 0.20, 95% CI [0.06–0.64]; P = 0.003), 2 h (78% vs. 47%, RR = 0.42, 95% CI [0.23–0.77]; P = 0.004), and 6 h (64% vs. 27%, RR = 0.49, 95% CI [0.32–0.77]; P = 0.001) after extubation. No significant difference in the incidence and severity of hoarseness between the groups at any time point. During extubation, the incidence of cough response in the C group was 60%, significantly higher than the 20% in the TCPB group (RR = 0.50, 95% CI [0.34–0.74]; P = 0.001).

Conclusion

Ultrasound-guided TCPB significantly reduces the incidence and severity of POST and cough response in SLVCP patients.

Trial registration

This trial was registered in the Chinese Clinical Trial Registry (ChiCTR2500100227) on April 7, 2025 (https://www.chictr.org.cn/).

Key points

Question: Previous drug therapies for relieving postoperative sore throat (POST) after suspension laryngoscopy vocal cord polypectomy (SLVCP) remain controversial, while the superior laryngeal nerve block (SLNB) is technically challenging and yields inconsistent efficacy.

Findings: Compared with conventional general anesthesia, the combination of thyroid cartilage plane block (TCPB) and general anesthesia reduces the incidence of POST at 2 hours post-extubation by 31% and decreases the cough response during extubation by 40%.

Meaning: TCPB not only avoids drug-related adverse effects but is also simpler and safer to perform than SLNB, providing a standardized and reproducible clinical protocol for postoperative analgesia in SLVCP.

Introduction

Suspension laryngoscopy vocal cord polypectomy (SLVCP) is a common surgical procedure for vocal cord lesions, offering the advantages of a clear surgical field and precise operation [1]. However, laryngoscope insertion and suspension frequently cause postoperative sore throat (POST) in 40%-70% of cases [2, 3]. POST not only increases the consumption of perioperative analgesics but may also impair the quality of postoperative recovery. Furthermore, the larynx is a highly sensitive reflexogenic area. When subjected to mechanical stimulation (such as laryngoscope insertion and suspension), it can strongly stimulate the sympathetic or vagus nerves, triggering a series of cardiovascular responses, including hypertension, tachycardia, bradycardia, arrhythmias, or even cardiac arrest [4–7].

Previous studies have indicated that oral clonidine or metoprolol [8, 9], intravenous dexmedetomidine or esketamine [10, 11], or topical lidocaine spray applied to the larynx before or after suspension laryngoscope insertion [12, 13] can effectively attenuate the intraoperative stress response and alleviate POST and cough response after extubation in patients undergoing SLVCP, although the efficacy remains debated. Superior Laryngeal Nerve Block (SLNB) has been demonstrated to effectively suppress the hemodynamic fluctuations induced by sympathetic or vagal nerve activation during SLVCP [14, 15], significantly reducing the incidence and severity of POST, cough response, and hoarseness after extubation [16–18]. Additionally, this technique can reduce perioperative opioid consumption and improve the quality of recovery [19]. However, this technique is limited by the high rate of anatomical variations in the superior laryngeal nerve. Precisely localizing the superior laryngeal nerve (SLN), superior laryngeal artery, and thyrohyoid membrane using ultrasound remains challenging, and the procedure is associated with a long learning curve [20].

The ultrasound-guided Thyroid Cartilage Plane Block (TCPB) technique, introduced by Shan et al., offers a novel approach to SLNB [21]. This technique involves injecting local anesthetic onto the surface of the thyroid cartilage, allowing the drug to diffuse above the thyrohyoid membrane to achieve a superior laryngeal nerve block. This method effectively inhibits the sensory nerves of the pharynx, epiglottis, and laryngeal mucosa above the glottic fissure. Its advantages include being performed away from critical neurovascular structures, thereby enhancing safety. Concurrently, the thyroid cartilage is easily identifiable under ultrasound, simplifying the procedure. Based on this, we hypothesize that this new technique can effectively block the SLN, thereby reducing the intraoperative stress response during SLVCP, alleviating POST and cough during emergence after extubation, and consequently improving the quality of postoperative recovery.

This study aimed to investigate the effects of ultrasound-guided TCPB on the occurrence of POST in patients undergoing SLVCP to evaluate the efficacy and safety of this technique in SLVCP, thereby providing a reference for clinical practice.

Materials and methods

Study design and ethics statement

This study was approved by the Ethics Committee of the Bethune International Peace Hospital (Chairperson of the Ethics Committee: Tienian Zhu) on April 1, 2025 (Approval No.: 2025-KY-48). The clinical trial was registered before patient enrollment in the Chinese Clinical Trial Registry on April 7, 2025 (Registration No.: ChiCTR2500100227). The study was conducted in strict accordance with the Consolidated Standards of Reporting Trials (CONSORT) guidelines and the principles of the Declaration of Helsinki. Written informed consent was obtained from all enrolled patients prior to surgery.

Study participants

This study recruited patients scheduled for elective SLVCP at the Chinese People’s Liberation Army Bethune International Peace Hospital between April 8, 2025, and October 10, 2025.

Inclusion criteria included: age 18 to 70 years; ASA physical status I or II; and BMI < 30 kg/m².

Exclusion criteria included: patients with pre-existing cognitive impairment, psychiatric disorders, coagulation abnormalities, or contraindications to peripheral nerve blocks; patients requiring awake tracheal intubation due to a predicted difficult airway; patients with severe pre-existing cardiovascular or respiratory system diseases; patients with known allergies to any medications used in the study; and patients who declined to participate in the study.

Randomization and blinding

Patients were randomly assigned in a 1:1 ratio to either the TCPB group (GA + ultrasound-guided TCPB) or the C group (conventional GA). The random sequence was concealed using sequentially numbered, opaque, sealed envelopes, which were opened by the performing anesthesiologist just prior to the procedure. Following the intervention, the neck area was covered with a sterile dressing in all patients, which remained in place until the conclusion of the study observations. The anesthesiologist who performed the nerve block did not participate in subsequent intraoperative anesthetic management or data collection. All patients, the anesthesiologists responsible for induction and maintenance of anesthesia, and the outcome assessors were blinded to the group assignments.

The surgeries were performed by two otorhinolaryngologists with attending physician titles or higher, each possessing at least 10 years of successful experience in SLVCP. The anesthesiologist responsible for the block was required to have successfully performed at least 30 cases of ultrasound-guided TCPB.

Anesthetic management

Anesthesia followed a standardized protocol. Upon entering the OR, patients received standard monitoring, including ECG, invasive/non-invasive blood pressure, and pulse oximetry. The bispectral index was used for real-time monitoring of sedation depth.

Induction

Patients received IV remimazolam (0.2 mg/kg), with plasma target-controlled infusion concentrations of propofol and sufentanil set at 3–4 µg/mL and 3–8 ng/mL, respectively. After loss of consciousness, cisatracurium (0.1 mg/kg) and dexamethasone (10 mg) were administered. Tracheal intubation was performed using a video laryngoscope (ID 6.5 mm for males, 6.0 mm for females), with cuff pressure maintained at 20–30 cmH₂O.

Maintenance

TCI of propofol and remifentanil were adjusted to maintain BIS values between 40 and 60. Cisatracurium (0.05 mg/kg) was intermittently administered as needed. Prior to suspension laryngoscope insertion, IV atropine (0.05 mg/kg) was given, and the remifentanil target concentration was set to 8 ng/mL. If HR dropped below 50 bpm during insertion, the procedure was suspended. Persistent bradycardia was treated with bolus IV atropine (0.5 mg). Vasoactive drugs were administered if MAP or HR fluctuated by > 20%.

Five minutes before the end of surgery, IV oxycodone (0.05 mg/kg) was administered. After fulfilling extubation criteria (eye-opening to verbal commands and adequate spontaneous breathing), the tracheal tube was removed following gentle oral suctioning. Cough response and severity were assessed immediately post-extubation, followed by a 30-minute observation in the post-anesthetic care unit. In the ward, rescue analgesia (IM tramadol 100 mg) was provided if the NRS score was ≥ 4 or upon patient request.

Block procedure

TCPB group

After the completion of anesthesia induction, patients in the TCPB group immediately underwent ultrasound-guided bilateral TCPB performed by the designated anesthesiologist. A high-frequency linear array probe (5–12 MHz) of a portable ultrasound machine (TE7, Mindray Medical International Ltd., Shenzhen, China) was used, with the depth set to 3–4 cm. The patient was placed in the supine position with the neck fully extended. The probe was initially placed on the neck in an oblique sagittal plane to obtain an ultrasound image showing the hyoid bone cephalad and the thyroid cartilage caudally. The thyroid cartilage plate typically appears hyperechoic with a rocky surface texture in the ultrasound image. The probe was moved until the thyroid cartilage plate was identified, and its superior portion was centered on the ultrasound screen (Fig. 1A).

Fig. 1.

Ultrasound image of the Thyroid Cartilage Plane Block. A Ultrasound image before the block. B Ultrasound image after the block. The white arrow indicates the ideal needle trajectory. The yellow solid-line area represents the spread of the local anesthetic. THM, Thyrohyoid Membrane; HB, Hyoid Bone; TC, Thyroid Cartilage; TM, Thyrohyoid Muscle; SM, Sternohyoid Muscle; LA, Local Anesthetic

Under aseptic conditions, a 22-gauge needle was inserted from the medial side of the probe using an out-of-plane approach, targeting the plane between the superior part of the thyroid cartilage plate and the pre-laryngeal muscles (specifically the sternohyoid and thyrohyoid muscles). Correct needle tip positioning within the fascial plane deep to the muscles was confirmed by injecting 0.5-1.0 ml of normal saline, observing hydrodissection of the plane between the pre-laryngeal muscles and the thyroid cartilage. After negative aspiration for blood, 3 mL of 2% ropivacaine was injected. The local anesthetic was observed spreading along the thyroid cartilage plate towards the thyrohyoid membrane plane (Fig. 1B).

Following the block, an anesthesiologist who was not involved in the procedure performed an ultrasound scan to verify the cephalad-caudal spread of the local anesthetic. The same procedure was then performed for the contralateral block. After successful bilateral blocks, the cervical area was covered with gauze until the end of the study observation to ensure blinding.

The time between covering the neck with gauze and insertion of the suspension laryngoscope is used for the surgeon to scrub, perform meticulous disinfection of the head and face area, and drape, as well as for the adjustment of the otorhinolaryngology microscope. Because the surgical team was consistent, this interval was stably controlled at approximately 25 min (this interval was not affected by the block, so it was the same for both the TCPB group and the C group) to allow the block to take full effect.

C Group

After anesthesia induction, no nerve block procedure was performed. To ensure successful blinding, the anesthesiologist responsible for the blocks covered the patient’s cervical area with gauze, which remained in place until the end of the study observation.

Outcome measures

Primary outcome

The incidence of POST at 2 h after tracheal extubation [17].

Secondary outcomes

(1) The severity of POST specifically at 2 h after extubation. (2) The incidence and severity of POST assessed at 0.5, 2, 6, 12, and 24 h after extubation. (3) The incidence and severity of hoarseness assessed before surgery and at 0.5, 2, 6, 12, and 24 h after extubation. (4) HR and MAP at the following time points: before induction (T0), at tracheal intubation (T1), before suspension laryngoscope insertion (T2), at laryngoscope insertion (T3), 5 min after laryngoscope insertion (T4), before tracheal extubation (T5), immediately after extubation (T6), and 5 min after extubation (T7), where the peak values at each time point were recorded. (5) The incidence and severity of cough response during emergence (at T6 and T7). (6) The Quality of Recovery-15 (QoR-15) score at 24 h postoperatively [13]. (7) The requirement for supplemental analgesic medication within the first 24 postoperative hours. (8) Block-related complications (including vascular puncture, local hematoma, or bleeding) and postoperative adverse events (such as dysphagia, dyspnea, aspiration, nausea, vomiting, and dizziness).

Explanation

POST was defined as throat pain or irritation occurring at rest or during swallowing at any time point after extubation. The severity of POST, hoarseness, and cough response during emergence were assessed using a 4-point scale [17, 22, 23]: POST (0, none; I, pain with swallowing; II, persistent pain that worsens with swallowing; III, pain interfering with eating and requiring analgesia); hoarseness (0, none; I, hoarseness perceived by the patient; II, hoarseness noticed by an observer; III, aphonia); cough response (0, none; I, single cough; II, multiple non-sustained coughs ≤5s; III, sustained cough >5s and/or head lift). The incidence of POST was defined as the number of patients with a POST grade of I or higher at each postoperative time point. Similarly, the incidence of hoarseness was defined as the number of patients with hoarseness grade ≥ I at each postoperative time point.

The QoR-15 score is a summary of 15 items assessing the domains of pain, physical comfort, physical independence, psychological support, and emotions. The total score ranges from 0 (very poor recovery) to 150 (excellent recovery).

Additionally, we recorded patient demographics and clinical data, including gender, age, height, weight, duration of surgery (defined as the time from the suspension laryngoscope contacting the teeth until it is completely withdrawn from the oral cavity), ASA physical status, history of hypertension, and smoking history. During the tracheal intubation process, the following were documented: the modified Cormack-Lehane grade, tracheal tube size, number of intubation attempts, tracheal intubation time (defined as the time from the video laryngoscope touching the teeth until complete inflation of the tracheal tube cuff), and tracheal extubation time (defined as the time from the end of surgery until the removal of the tracheal tube). The duration of suspension laryngoscope insertion (defined as the time from the initiation of suspension laryngoscope insertion until successful glottic exposure) was also recorded.

Sample size calculation

According to previous literature, the incidence of POST at 2 h after extubation in patients undergoing SLVCP is 80% [17]. Our pilot study results indicated that ultrasound-guided TCPB could reduce this incidence by 30%. The sample size was calculated using PASS software; with a power of 0.8 and a type I error rate < 0.05, a minimum of 36 patients per group (72 in total) was required. Accounting for a potential 20% dropout rate, the final sample size was set at 90 patients, with 45 patients enrolled in each group.

Statistical analysis

Statistical analysis was performed using SPSS version 26.0 (IBM Corp, Armonk, New York, USA). Categorical data are presented as numbers (percentages). Continuous variables are expressed as mean ± standard deviation or median [interquartile range], depending on the results of the normality test (Shapiro-Wilk test). Independent samples t-test was used for normally distributed continuous data, while the Mann-Whitney U test was applied for non-normally distributed data. Categorical variables were analyzed using the Chi-square test or Fisher’s exact test. The median differences between groups and their 95% confidence intervals (CIs) were calculated using the Hodges-Lehmann method. The primary outcome, the incidence of POST at 2 h after extubation, was compared between groups using the Chi-square test, with the risk ratio (RR) and 95% CI calculated. For repeated measures data, generalized estimating equations (GEE) were employed to analyze the robustness of group effects across different time points. All reported P-values are two-sided, and a P-value < 0.05 was considered statistically significant.

Results

This study was conducted between April 8, 2025, and October 10, 2025. A total of 103 patients were assessed for eligibility, of whom 13 were excluded. Reasons for exclusion included: BMI > 30 kg/m² (n = 3), coagulation disorders (n = 2), refusal to participate (n = 6), and surgical cancellation (n = 2). Consequently, 90 patients were randomized. Due to clearly defined admission plans and hospital stays lasting at least 24 h for all patients, no data were missing due to early discharge (Fig. 2). There were no statistically significant differences between the two groups in terms of baseline characteristics, including age, sex, height, weight, BMI, ASA physical status, duration of surgery, smoking history, and history of hypertension (Table 1). Tracheal intubation was successfully completed on the first attempt in all patients. No significant differences were observed between the two groups regarding intubation-related metrics, including Cormack-Lehane grade, endotracheal tube size, time to complete intubation, duration of suspension laryngoscopy, and time to extubation (Table 2).

Fig. 2.

CONSORT Flow Diagram. CONSORT stands for Consolidated Standards of Reporting Trials

Table 1.

Comparison of baseline characteristics between the two groups

Characteristic	C group (n = 45)	TCPB group (n = 45)	P value
Sex (Male/Female)	27/18	24/21	0.526
Age (years)	48 (34, 65)	46 (33, 63)	0.968
Height (cm)	167.7 ± 7.1	166.5 ± 8.1	0.444
Weight (kg)	71.7 ± 8.0	68.9 ± 9.5	0.129
BMI (kg/m²)	25.4 ± 2.2	24.7 ± 2.1	0.126
ASA (I/II)	14/31	15/30	0.823
Surgery time (min)	25 (20, 30)	22 (18, 28)	0.117
Smoking history (Yes/No)	16/29	18/27	0.664
Hypertension (Yes/No)	37/8	35/10	0.598

Data are presented as mean ± SD, median (IQR), or n (%)

ASA American Society of Anesthesiologists Grade, BMI Body mass index

Table 2.

Tracheal intubation-related indicators

Cormack-Lehane grade (1/2)	C group (n = 45)	TCPB group (n = 45)	P value
	43/2	42/3	0.647
Tracheal tube size (6.0/6.5)	27/18	24/21	0.526
Intubation attempts (n)	1	1	-
Intubation completion time (s)	28 (25, 31)	28 (23, 31)	0.138
Laryngoscope insertion time (s)	106 (100, 116)	108 (100, 118)	0.1
Tracheal extubation time (s)	317 (188, 582)	308 (180, 488)	0.793

Data are presented as median (IQR) or n

Incidence and severity of POST

In the comparison of POST incidence between the two groups at different time points, no sore throat was observed in either group preoperatively. For the C group and TCPB group, the incidence rates of POST at 0.5 h after extubation were 93% (42/45) and 67% (30/45), respectively; at 2 h after extubation, they were 78% (35/45) and 47% (21/45), respectively; at 6 h after extubation, they were 64% (29/45) and 27% (12/45), respectively; at 12 h after extubation, they were 40% (18/45) and 27% (12/45), respectively; and at 24 h after extubation, they were 29% (13/45) and 13% (6/45), respectively. The incidence of POST was significantly higher in the C group compared to the TCPB group at 0.5 h (RR = 0.20, 95%CI [0.06–0.64];P = 0.003), 2 h (RR = 0.42, 95%CI [0.23–0.77]༛P = 0.004), and 6 h (RR = 0.49, 95%CI [0.32–0.77]༛P = 0.001) after extubation. However, the data at 12 h (RR = 0.82, 95%CI [0.61–1.10]༛P = 0.263) and 24 h (RR = 0.82, 95%CI [0.66–1.02]༛P = 0.120) postoperatively showed no statistically significant differences in POST incidence between the groups (Table 3).

Table 3.

Incidence and severity of POST, hoarseness, and cough response

Outcome / Time point		C group (n = 45)	TCPB group (n = 45)			Risk Ratio (95% CI)	P value
POST (None/I/II/III)
Preoperative		45/0/0/0	45/0/0/0			-	-
0.5 h post-extubation		3/7/32/3	15/29/1/0			0.20 (0.06–0.64)	0.003
2 h post-extubation		10/18/17/0	24/21/0/0			0.42 (0.23–0.77)	0.004
6 h post-extubation		16/27/2/0	33/12/0/0			0.49 (0.32–0.77)	0.001
12 h post-extubation		27/18/0/0	33/12/0/0			0.82 (0.61–1.10)	0.263
24 h post-extubation		32/13/0/0	39/6/0/0			0.82 (0.66–1.02)	0.120
Outcome / Time point		C group (n = 45)	TCPB group (n = 45)			Risk Ratio (95% CI)	P value
Hoarseness (None/I/II/III)
Preoperative		3/30/12/0	4/30/11/0			0.75 (0.18–3.16)	0.703
0.5 h post-extubation		0/18/27/0	0/25/20/0			-	0.205
2 h post-extubation		0/19/26/0	0/25/20/0			-	0.292
6 h post-extubation		1/21/23/0	2/27/16/0			0.50 (0.05–5.32)	0.310
12 h post-extubation		3/30/12/0	3/31/11/0			1.00 (0.21–4.69)	0.971
24 h post-extubation		3/30/12/0	4/30/11/0			0.75 (0.18–3.16)	0.911
Outcome / Time point	C group (n = 45)			TCPB group (n = 45)	Risk Ratio (95% CI)			P value
Cough Response (None/I/II/III)
At extubation		18/14/10/3	36/9/0/0			0.50 (0.34–0.74)	0.001
5 min post-extubation		38/7/0/0	41/4/0/0			0.93 (0.79–1.08)	0.522

In the GEE analysis, superscript letters are used to indicate significant differences between time points after multiple comparison correction. Shared letters indicate no statistically significant difference, while different letters indicate a statistically significant difference between time points

POST Postoperative sore throat, CI Confidence Interval

During follow-up, moderate-to-severe POST (Grade II or III) cases were observed at 0.5, 2, and 6 h after extubation, but no moderate-to-severe POST cases were observed at 12–24 h in either group. The proportion of patients with moderate-to-severe POST was significantly higher in the C group compared to the TCPB group at 0.5 h (35/45 vs. 1/45; χ²=53.52; P = 0.000) and 2 h (17/45 vs. 0/45; χ²=20.96; P = 0.000) after extubation. However, no statistically significant difference in POST severity was found between the two groups at the 6-hour time point (2/45 vs. 0/45; χ²=2.05; P = 0.153) (Table 4; Fig. 3).

Table 4.

Comparison of intergroup POST severity at different time points after extubation

	0.5 h		2 h		6 h		12 h		24 h
	C	TCPB	C	TCPB	C	TCPB	C	TCPB	C	TCPB
0 + I	10	44	28	45	43	45	45	45	45	45
II + III	35	1	17	0	2	0	0	0	0	0
χ²	53.52		20.96		2.05		/		/
P value	0.00		0.00		0.15		/		/

Fig. 3.

Severity of postoperative sore throat at different time points after extubation: (A) 0.5 h, (B) 2 h, (C) 6 h, (D) 12 h, (E) 24 h

GEE analysis demonstrated that, compared with C group, the TCPB group had a significantly lower incidence of POST at 0.5, 2, 6, and 12 h after extubation (P < 0.05); however, no statistically significant differences were observed between these specific time points. The incidence of POST showed a progressive decline over time (Table 3).

Cough response and hoarseness during emergence

The incidence of cough response during extubation in C group was 60% (27/45), which was significantly higher than the 20% (9/45) observed in the TCPB group (RR = 0.50, 95% CI [0.34–0.74]; P = 0.001). At 5 min after extubation, no statistically significant difference in the incidence of cough response was found between the two groups. GEE analysis indicated a significant difference in the incidence of cough response between 5 min post-extubation and the time of extubation. No statistically significant differences were observed between the two groups in the incidence or severity of hoarseness at any time point (Table 3).

Adverse events and quality of recovery

At T3, T6, and T7, both HR and MAP in C group were significantly higher than those in the TCPB group (P < 0.05). No statistically significant differences were observed at other time points (Fig. 4). In C group, three patients experienced an increase in MAP exceeding 20% of baseline during suspension laryngoscope insertion, requiring intervention with vasoactive drugs. Due to vagal reflexes during surgery, two patients in C group and three in the TCPB group received intravenous atropine (0.05 mg).

Fig. 4.

Perioperative Hemodynamic Parameters A Heart rate trends at various perioperative time points and intergroup differences B Mean arterial pressure trends at various perioperative time points and intergroup differences. Time points marked with an asterisk (*) indicate statistically significant differences in hemodynamic parameters between the TCPB group and the C group (P < 0.05). T0: Before induction; T1: At tracheal intubation; T2: Before suspension laryngoscope insertion; T3: At suspension laryngoscope insertion; T4: 5 min after suspension laryngoscope insertion; T5: Before tracheal extubation; T6: Immediately after extubation; T7: 5 min after extubation

Within 24 h postoperatively, one patient in C group required rescue analgesia, and three experienced nausea; no other adverse events were reported in the remaining patients. At 24 h postoperatively, the total QoR-15 score in the TCPB group (median 142, interquartile range [141–144]) was significantly higher than that in C group (median 140, interquartile range [139–141]) (P = 0.000). This significant difference was primarily attributed to substantial improvements in pain and physical symptoms (Table 5).

Table 5.

Postoperative adverse reactions and recovery quality

Outcome	C group (n = 45)	TCPB group (n = 45)	P value
MAP elevation requiring vasoactive agent intervention	3 (6.7%)	0	0.242
Heart rate reduction requiring atropine intervention	2 (4.4%)	3 (6.7%)	1.000
Dyspnea	0	0	-
Choking on water	0	0	-
Aspiration	0	0	-
Nausea	3 (6.7%)	0	0.242
Vomiting	0	0	-
Dizziness	0	0	-
QoR-15 Score	140 (139–141)	142 (141–144)	0
Pain	16 (14–20)	18 (16–20)	0
Physical comfort	28 (26–30)	30 (28–30)	0
Psychological state	29 (26–30)	29 (26–30)	0.131
Physical independence	19 (18–20)	19 (18–20)	0.303
Support & comfort	48 (46–50)	48 (46–50)	0.451

Data are presented as n (%) or median (IQR). QoR-15: Quality of Recovery-15

Discussion

This study demonstrated that, compared with conventional GA, ultrasound-guided TCPB significantly reduced the incidence and severity of POST during the early post-extubation period (0.5–6 h) in SLVCP patients. TCPB also decreased cough response during emergence and improved hemodynamic stability during laryngoscope insertion and extubation, collectively enhancing recovery quality.

According to Shan et al. [24], the average time required for experienced physicians to complete bilateral TCPB is approximately 86 s. In our actual practice, the time needed for the complete block can be controlled to within 2 min, demonstrating practical feasibility and reproducibility. To ensure that TCPB has achieved full onset by the time of the primary noxious stimulus, we referred to the study by Chen et al. [22] on SLNB for reducing postoperative sore throat, and controlled the time interval between completion of the block and insertion of the suspension laryngoscope to approximately 25 min. Although a 25-minute interval may appear relatively long, in our actual study process, this period was utilized for the surgeon to scrub, perform meticulous disinfection of the head and face area, and drape, as well as for the adjustment of the otorhinolaryngology microscope, allowing the interval to be appropriately controlled to around 25 min. However, we did not precisely measure the TCPB-to-suspension laryngoscope interval for each patient. Future studies could further investigate the impact of this interval on the efficacy of TCPB and perioperative outcomes. This approach ensures complete onset of TCPB on the one hand, and allows the early hemodynamic benefits to be reasonably attributed to the clinical effects of TCPB on the other.

POST is highly prevalent after suspension laryngoscopy, primarily due to mucosal trauma and edema [5, 25]. While ultrasound-guided SLNB is effective, its technical complexity and variable anatomy limit widespread use [20, 21, 26, 27]. Our study evaluates the simpler TCPB technique as an alternative analgesic approach. In this study, the incidence of POST in C group at 2 h post-extubation was 78%, consistent with previous reports [17]. TCPB reduced this incidence by 31%, which is achieved by blocking the SLN to provide local anesthesia for the base of the tongue, epiglottis, and the laryngeal mucosa above the glottis. Furthermore, this technique may inhibit sympathetic nerves, thereby promoting local vasodilation, reducing tissue edema, and effectively alleviating pain symptoms [21, 28].

Furthermore, we observed that the improvement of POST by TCPB was relatively weak at 0.5 h post-extubation, with the incidence of POST in the TCPB group reducing by only 26% compared with C group. This may be due to residual anesthetic effects masking pain. The 2‑h time point was chosen as the primary outcome because general anesthesia effects have waned, acute inflammatory pain peaks (1–4 h), and patients typically begin drinking, allowing assessment of both resting and swallowing pain [26, 29–31]. At 0.5 h and 2 h post-extubation, the proportion of patients in C group with severe POST (Grade II or III) was significantly higher than that in the TCPB group, whereas no significant difference in POST severity was observed between the two groups at 6 h. This result can also be explained by the peak duration of POST: between 4 and 6 h post-extubation, the intensity of POST gradually diminishes, and the pain level in C group decreases significantly or even resolves, reaching a low level comparable to that of the TCPB group.

The 60% incidence of cough response during extubation in C group aligns with prior SLVCP studies [17]. To date, no similar studies have explored the application of the TCPB technique in managing cough responses during the emergence period. We observed that patients receiving ultrasound-guided TCPB experienced a significant 40% reduction in the incidence of cough response during extubation. This effect may also be attributed to the successful blockade of the superior laryngeal nerve by TCPB, which inhibits the reflex arcs triggered by pharyngeal and glottic stimulation. This finding is partially consistent with the results of Zhou et al. [32] and Sagdeo et al. [27], who demonstrated that SLNB effectively reduces cough responses during extubation in SLVCP patients. Therefore, TCPB may serve as an effective management strategy for cough responses during emergence.

In this study, no statistically significant differences were observed between the two groups regarding the incidence or severity of hoarseness at any time point post-extubation. This may because hoarseness relates more to operative trauma to the vocal cords and regions innervated by the recurrent laryngeal nerve, while being less influenced by the SLN [33]. It should be noted that early postoperative hoarseness was documented and assessed while patients actively communicated with others, and there were no ethical concerns that would interfere with patients’ voice rest or healing. However, the study by Zhou et al. [32] indicated that patients receiving ultrasound-guided SLNB experienced more severe hoarseness within 2 h after extubation compared with conventional GA. This discrepancy with our findings may stem from differences in block coverage resulting from distinct block strategies. Zhou et al. utilized a short-axis in-plane approach targeting the vicinity of the superior laryngeal nerve, with 5 ml of 0.375% ropivacaine injected on each side. Previous research has suggested that excessive injection volumes in a single block can easily lead to the simultaneous blockade of the external branch of the SLN, thereby paralyzing the cricothyroid muscle and causing changes in the patient’s vocal pitch [20].

The results of this study demonstrated that during periods of peak noxious stimulation, specifically during suspension laryngoscope insertion, tracheal extubation, and the immediate post-extubation period, patients in the TCPB group exhibited more stable changes in HR and MAP. This suggests that the TCPB technique not only blocks the transmission of noxious stimuli but also significantly attenuates the overactivation of the sympathetic nervous system induced by laryngeal manipulation, thereby achieving more stable perioperative hemodynamic management. This finding is consistent with the results of Bao et al. [34], which indicated that blocking the internal branch of the SLN can effectively mitigate perioperative hemodynamic fluctuations in patients undergoing SLVCP. In the C group, three patients experienced an increase in MAP exceeding 20% of the baseline during suspension laryngoscope insertion and required vasoactive intervention, whereas no such cases occurred in the TCPB group. Although this difference did not reach statistical significance, the trend is consistent with the theoretical expectation that TCPB can effectively suppress cardiovascular stress responses triggered by pharyngeal and laryngeal stimulation.

Our study indicated that the TCPB technique significantly increased the QoR-15 scores at 24 h postoperatively compared with the C group. Although this difference was statistically significant, it did not reach the threshold for clinical significance [35]. This improvement was primarily attributed to the significant enhancements in the “pain” and “physical symptoms” dimensions, the latter of which is a key component of modern enhanced perioperative care pathways [36].

The safety of ultrasound-guided TCPB is supported by prior studies on SLNB, which report minimal complications such as dyspnea, reflux, or aspiration [37–39]. Compared with SLNB, the main advantage of TCPB also lies in its safety profile. The traditional posterior approach to SLNB uses the thyrohyoid membrane as a landmark, with the needle inserted deep to it and local anesthetic injected near the superior laryngeal artery to allow drug diffusion around the SLN. In some patients, the superior laryngeal artery may be poorly visualized or exhibit anatomical variations, potentially leading to difficulties in needle localization and even an increased risk of vascular puncture [38, 40]. According to reports, the overall failure rate of this method is as high as 14% [41]. Another interfascial-based approach to SLNB involves injecting local anesthetic superficial to the thyrohyoid membrane, achieving SLNB through drug diffusion. However, this method may also result in unintentional puncture of the SLN or artery due to poor visualization of anatomical structures under ultrasound [21]. In contrast, TCPB targets the surface of the thyroid cartilage, with local anesthetic injected into the plane between the thyroid lamina and the pretracheal muscles, allowing drug diffusion to the region of the thyrohyoid membrane where the internal branch of the superior laryngeal nerve travels. The thyroid cartilage is easily identified, and the needle path avoids critical neurovascular structures, thereby enhancing procedural safety. To date, this technique has been successfully applied in awake endotracheal intubation, confirming its clinical safety and efficacy. Currently, no studies have compared the effectiveness of TCPB and SLNB on clinical outcomes such as POST. Future research could further investigate the clinical effects of these two techniques [21].

Recent cadaver-based studies on the efficacy and safety of TCPB have shown that in all necks where TCPB was performed, the internal branch of the SLN was adequately infiltrated and surrounded by the anesthetic solution, while the recurrent laryngeal nerve was well protected in all cases [24]. For sensory blockade targeting the internal branch of the SLN, attention must be paid to unintended spread of the anesthetic to the external branch of the superior laryngeal nerve above the thyrohyoid membrane, which can lead to reduced vocal cord tension and transient hoarseness. Overall, the incidence of hoarseness following TCPB is only 31%. This is because the injectate in TCPB remains consistently medial to the thyroid cartilage and deep to the thyrohyoid muscle, and is anatomically completely separated from the motor branch of the superior laryngeal nerve, which runs more laterally [24]. In comparison, the incidence of hoarseness following interfascial-based SLNB is 40%, and traditional posterior approach SLNB results in hoarseness in as high as 72%-100% of cases [42, 43]. Therefore, TCPB offers significantly higher safety and practicality.

There are several limitations to this study. First, although it was a prospective randomized controlled trial, the relatively small sample size and single-center design inevitably limit its external validity. Second, to ensure strict blinding of the group assignments, we did not perform sensory conduction testing to assess the block effect after TCPB. However, to ensure block efficacy, a secondary ultrasound scan was performed by an anesthesiologist not involved in the procedure to verify the post-injection spread of the local anesthetic. Third, this study did not include a sham-block control group (e.g., saline injection in the C group); therefore, we could not entirely exclude the potential influence of physical effects (such as hydrodissection) caused by the local diffusion of the anesthetic solution on the outcomes. Finally, as the follow-up was limited to 24 h postoperatively, we were unable to assess the impact of TCPB on longer-term outcomes, such as chronic sore throat or long-term vocal cord function. Future research could extend the follow-up period to several days postoperatively to evaluate its impact on chronic pain. Finally, we did not precisely measure the interval from the completion of TCPB to the insertion of the suspension laryngoscope in each patient. Future studies are needed to further investigate the impact of this interval on the efficacy of TCPB in improving POST and on perioperative hemodynamic parameters.

Conclusion

The ultrasound-guided Thyroid Cartilage Plane Block (TCPB) technique significantly reduces the incidence and severity of postoperative sore throat (POST) in patients undergoing suspension laryngoscopy vocal cord polypectomy (SLVCP). It also maintains intraoperative hemodynamic stability and reduces the incidence and severity of cough response during emergence, thereby significantly enhancing the quality of patient recovery.

Abbreviations

TCPB

Thyroid Cartilage Plane Block

POST

Postoperative Sore Throat

SLVCP

Suspension Laryngoscopy Vocal Cord Polypectomy

GA

General Anesthesia

QoR-15

Quality of Recovery-15

HR

Heart Rate

MAP

Mean Arterial Pressure

SLNB

Superior Laryngeal Nerve Block

CONSORT

Consolidated Standards of Reporting Trials

GEE

Generalized Estimating Equations

Authors’ contributions

FH: Writing - original draft, Conceptualization, Methodology, Data curation, Formal analysis. YZ: Writing - original draft, Methodology, Data curation. ZC: Data curation, Methodology. JW: Data curation, Conceptualization. SX: Data curation, Methodology. HL: Writing - review & editing, Funding acquisition. YW: Writing - review & editing, Conceptualization, Resources, Funding acquisition. All authors read and approved the final manuscript.

Funding

This work was supported by the Natural Science Foundation of Beijing Municipality [grant numbers 7252025, 7252029, 7254332]; Beijing Friendship Hospital Zhongzi Project [grant number YYZZ202332]; Municipal Education Commission’s New Teacher Support Program Project [grant number XJJS202548].

Data availability

The data of this study are available from the corresponding author, Yun Wang, upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of the Bethune International Peace Hospital (Chairperson of the Ethics Committee: Tienian Zhu) on April 1, 2025 (Approval No.: 2025-KY-48). This study adhered to the principles of the Declaration of Helsinki. Written informed consent was obtained from each patient before enrollment.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.