Immediate effects of thyroid surgery on pulmonary dynamics of upper airway: A preoperative and postoperative comparison using flow volume loop and spirometry

Introduction

The thyroid, an endocrine gland is anatomically located in the neck. There are various indications of thyroid surgery, including but not limited to the diagnosis of thyroid nodules, relief of compressive symptoms caused by an enlarged thyroid, treatment of thyroid cancers, their recurrence, and prophylactic removal in case of genetic mutations predisposing to thyroid cancer.^1,2 Over the past century, thyroid surgeries have developed significantly to be rendered safe due to improved anesthesia, infection prophylaxis, modern hemostatic methods, and technological improvements.¹ The most common complication after thyroid surgery is hypocalcemia, followed by seroma and recurrent laryngeal nerve palsy.³

The thyroid gland lies close to the cricoid cartilage and tracheal rings, wrapping around these and being attached to the trachea via lateral suspensory ligament. These upper airways and the nerves supplying them (i-e, recurrent laryngeal, and superior laryngeal nerves) are at potential risk for injury during thyroid surgery due to close abutment with the gland.² It has been reported that thyroid surgery leads to a slight improvement of pulmonary airflow on the 10^th postoperative day followed by a significant improvement by six to twelve weeks after surgery.^4–6 However, the literature still lacks information regarding the impact of such surgeries on the upper airways in the immediate postoperative period. Preoperatively, only 61% of patients are informed regarding the risk of post-surgery dyspnea by their surgeons.⁷ Furthermore, the Goiter Symptoms (e.g., sensation of fullness in the neck, visible swelling in the front of the neck, sensation of a lump in the throat, etc.) persist for a week after the surgery before showing any significant improvement.⁸

The current study assesses the immediate effect of thyroid surgery on the airways by comparing pre-operative pulmonary dynamics with those on postoperative day 1.

Methods

This study was conducted prospectively at the ENT Department of Khyber Teaching Hospital, Peshawar, Pakistan from January 2023 to December 2023. It was conducted in accordance with ethical standards of institutional review board of Khyber Teaching Hospital, Peshawar, Pakistan (approval number 850/DME/KMC issued on 24/11/2022). Using non-probability convenience sampling, 40 adult patients undergoing thyroid surgery for benign euthyroid goiter were included in the study. All those patients who had any chronic respiratory disease or neck surgery in the past were excluded. Moreover, those patients who refused to participate, were not able to perform acceptable trials in spirometry, or had postoperative tracheomalacia were also dropped off.

Biodata and history of the patients including name, gender, age, and history of respiratory diseases were obtained through a questionnaire. The patient’s BMI was calculated. Preoperatively, forced vital capacity (FVC), forced expiratory volume in one second (FEV1), the FEV1/FVC ratio, and the peak expiratory flow (PEF), were measured along with a flow-volume loop (FVL) 24 hours before the surgery. MIR Spirolab spirometer with flowmeter was used, calibrated as directed by the manufacturer. All the surgical procedures were performed under general anesthesia followed by adequate postoperative analgesia. 24 hours after the surgery, the patients were assessed for pain using a visual analogue scale. At a score <3, postoperative day 1 spirometry with a flow-volume loop was done. A spirometry was considered valid if it had at least 3 acceptable trials and both the FVC and FEV1 were repeatable [i.e., the two highest values from acceptable maneuvers are within 0.15 L (150 ml)].⁹ The mean of acceptable trials was calculated. FVLs were visually interpreted by a pulmonologist as depicting upper airway obstruction (UAO) pattern or any other pattern. Empey’s and expiratory disproportionate indexes (EDI) were calculated through respective formulae. The size of the gland removed were obtained through the histopathological report.

SPSS v23.0 was used for analysis. Quantitative and qualitative variables were expressed as mean ± standard deviation and percentages, respectively. Paired sample t-test was applied to measure statistical significance between means of pre-operative and post-operative measurements. Chi-square test was used to compare categorical variables. A p-value of less than 0.05 was considered as statistically significant.

Results

A cohort of forty adult patients undergoing thyroid surgery was included in the study. The descriptive details of the sample population are given in table 1.

Preoperative FVC, FEV1, and PEF were reduced in the immediate postoperative period and the alterations were statistically significant ( Table 2, Figure 1). Conversely, Empey’s index and EDI increased, depicting obstructive effects of thyroid surgery on the upper airway. ( Table 2, Figure 2). Moreover, no significant association was found between postoperative Empey’s Index and gender, BMI, extent of surgery, or size of the gland removed.

Figure 1. Box plot showing the distribution of preoperative and postoperative parameters of spirometry.

Figure 2. Box plot showing the distribution of preoperative and postoperative Empey's Index.

Regarding the FVL, a significantly higher number of patients exhibited fixed upper airway obstruction patterns in the postoperative period ( Table 3).

Discussion

Modern thyroid surgery has been refined enough, rendering it a safe and reliable surgical procedure with relief of symptoms, lower rates of complications, good cosmetic, and excellent surgical outcomes.^2,10 However, it is noteworthy that the health-related quality of life (HRQoL) of the patients six months after thyroid surgery remains lower than the general population.¹¹ This lingering impact necessitates thorough postoperative care and the need to identify the risk factors causing HRQoL deficits.

It has been well reported in the literature that the UAO is quite prevalent among patients with goiter, often in the absence of any subjective respiratory symptom.^12,13 As per Poisseulle’s law (flow proportional to radius⁴), minor compression of the trachea due to goiter can cause a significant reduction in airflow. This overlooked UAO may lead to acute respiratory insufficiency after thyroidectomy.¹⁴ Six months after the surgery, substantial improvement in airflow is observed, resulting in gains in HRQoL.⁶ However, this surgical intervention can paradoxically lead to worsening of the airflow in the immediate postoperative period, which can be attributed to anesthesia, manipulation of airways and nerves, post-surgery inflammation, pain, and restricted neck movements.

In this study, none of the patients had any gross tracheal deviation. Regarding subjective pulmonary symptoms (dyspnea, choking, a feeling of fullness in the neck, a sensation of a lump in the throat, orthopnea, etc.), only two out of forty patients reported such symptoms preoperatively. However, 24 hours postoperatively, twenty-two subjects reported these complaints. Empey’s Index, calculated as the ratio between FEV1 (ml) and PEFR (L/min), has a high sensitivity and specificity for the detection of UAO.⁵ Preoperatively, 15 patients had Empey’s Index >8, while postoperatively, this number increased to 31.

Immediate postoperative derangements in pulmonary function tests after cardiac, thoracic, and abdominal surgeries have been studied extensively.^15,16,17,18 Interestingly, this area has not been explored in neck surgeries including thyroidectomy. Furthermore, various rehabilitation strategies, such as incentive spirometry, positive-pressure breathing techniques (i.e., bi-level positive airway pressure, continuous positive airway pressure, and intermittent positive pressure breathing), early mobilization, deep breathing exercises, and chest physiotherapies have been practiced after cardiac, thoracic and abdominal surgeries to mitigate these postoperative derangements in pulmonary dynamics.^19,20 Given the potential of overlooked preoperative UAO in goiter followed by alterations in pulmonary functions post-thyroidectomy, investigating rehabilitative measures in this context is a promising area for future research.

Conclusion

Thyroid surgery significantly affects pulmonary dynamics of the upper airway, leading to obstruction in the immediate postoperative period. This study highlights the importance of careful respiratory monitoring of patients undergoing thyroid surgery in the postoperative phase and its due management. Further research is required to explore the role of rehabilitative measures in mitigating these effects in post-thyroidectomy patients, thereby improving postoperative care and overall patient outcomes.

Reporting guidelines

STROBE checklist for ‘Immediate Effects of Thyroid Surgery on Pulmonary Dynamics of Upper Airway: A Preoperative and Postoperative Comparison Using Flow Volume Loop and Spirometry.’ https://doi.org/10.17605/OSF.IO/HS94A

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC0 1.0 Public domain dedication).

Declarations

Limitations of study

This study is limited in its scope by its small sample.