This study was performed to determine the effects of a humidifier with heated wire circuits on the incidence and severity of postoperative sore throat (POST) and cough after thyroidectomy.
A total of 61 patients scheduled for elective thyroid surgery under general anesthesia were included in this prospective study. We randomized the patients in to two groups, "without active warming and humidification" (Group C) and "using a heated humidifier" (Group H). The patients were interviewed to obtain the POST and cough scores at 1, 6, 24 and 48 hours after thyroidectomy.
The incidence of POST was significantly lower in Group H compared to Group C at 6 hours (57% vs 84%, P = 0.041), 24 hours (37% vs 65%, P = 0.045), and 48 hours (10% vs 52%, P = 0.001). Also the incidence of cough was significantly lower in Group H at 6 hours (27% vs 71%, P = 0.001), 24 hours (13% vs 45%, P = 0.015), and 48 hours (7% vs 32%, P = 0.028). The severity of POST was significantly lower in Group H at all times. In addition, the severity of cough was lower in Group H at other times except at 1 hour.
This result suggests that an active humidification of inspired gases may have the appreciable effect on reducing the incidence and severity of sore throat and cough after thyroid surgery using the endotracheal tube.
Postoperative sore throat (POST) is one of the common symptoms that occurs following surgery under general anesthesia, and is a feeling of discomfort that develops during the postoperative recovery period. It causes physical stress and can affect operation satisfaction and rate of recovery. POST may manifest in various forms following surgery, and it has been reported that POST may cause hoarse voice, swallowing difficulty, laryngitis, bronchitis and respiratory distress [
The incidence of POST varies according to different reports, with a range between 14.4% and 80%. POST is reported to be higher in patients that have undergone thyroid surgery as compared to other surgeries [
General anesthesia using the cool and dry anesthetic gas can also be one of the major causes of POST, hoarse voice and cough. The cool and dry anesthetic gas directly reaches the lower respiratory tract during mechanical ventilation after endotracheal intubation. It causes a decrease in heat and humidity, induces inflammation and irritates the tissue within the respiratory tract, and impairs the functions of cells lining the respiratory mucosa [
Therefore, we attempted to assess the effectiveness of a heated humidifier on the pattern of POST and cough occurrence following thyroidectomy.
From patients scheduled for an elective thyroidectomy under general anesthesia, 64 adults aged between 20 and 60 years old and corresponded to the American Society of Anesthesiologists (ASA) physical status Class 1 or 2 were randomly selected and enrolled in our study. This study was approved by the Institutional Review Board (IRB) at our hospital and patients were recommended to submit a written informed consent following oral explanation. Of these patients, those who had throat pain preoperatively, presented with the symptoms of upper respiratory infection within the recent two weeks, had smoking history or a past history of taking treatments for chronic respiratory symptoms, had abnormalities on the chest radiography, experienced hyperthyroidism or hypothyroidism, in whom endotracheal intubation was attempted more than twice, or more than 15 seconds elapsed for the endotracheal intubation, as well as those in whom the operation time was shorter than two hours, were excluded from this study.
The sample size was calculated from the assumption that the incidence of POST was set at 80% based on the report by Kadri et al. [
All patients were not pre-medicated. After monitoring with 3 lead EKG, noninvasive arterial blood pressure, and pulse oxymetry on arrival at the operation room, patients were given an intravascular injection of midazolam 0.05 mg/kg. Patients were also recommended to perform spontaneous breathing using 100% oxygen. In addition, propofol and remifentanil were connected to a specialized device for target controlled infusion (TCI) (Base Primea Ochestra®, Fresenius Vial, France). Thus, the effective concentrations were set at 3.0 µg/ml and 4.0 ng/ml, respectively, and the anesthesia was induced accordingly. Following the confirmation of loss of consciousness with the use of manual bagging using 100% oxygen 4 L/min, vecuronium 0.1 mg/kg was administered. After 3 minutes later, with the use of an anode tube with an internal diameter of 7.5 mm in men and 7.0 mm in women, the endotracheal intubation was performed for less than 15 seconds. The tube cuff pressure was adjusted from 15 to 20 cm H2O with the use of a barometer (Mallinckroft Medical, Athlone, Ireland). The cuff pressure was re-adjusted at 10-minute intervals Anesthesia was maintained such that the tidal volume (TV), respiratory rates, oxygen and medical air were set at 8 ml/kg, 10 breaths/min, 2 L/min and 2 L/min, respectively. In addition, the end-tidal partial pressure of carbon dioxide was maintained at 35-40 mmHg. Twenty minutes prior to the completion of the surgical procedure, all patients were intravenously given ramosetron 0.3 mg for the prevention of nausea and vomiting and ketolorac 30 mg for postoperative pain control. After surgery, patients were intravenously given pyridostigmine 0.2 mg/kg and glycopyrrolate 0.008 mg/kg. Also, the airway reflex recovered and extubation was performed.
The pattern of POST and cough were assessed at a recovery room after 1 hour. On postoperative 6, 24 and 48 hours, the study subjects were evaluated at a ward. The assessment of POST was done by scores according to the direct questionnaire survey proposed by Harding et al. [
All the data was expressed as mean ± standard deviation. Statistical analysis was performed using SPSS 12.0 (SPSS Inc., Chicago, IL, USA). Between group differences in the age, height, weight, operation time and anesthetic time were made with the use of a t-test. Also, a comparison of the incidence of throat pain and cough was made with the use of a Chi-square test. In addition, the severity of POST and cough was performed using the Mann Whitney-u-test. A P value of < 0.05 was considered statistically significant.
The number of patients that were assigned to Group C and H were 31 and 30, respectively. Of a total of 64 subjects, 1 patient from Group C and 2 patients from Group H had an operation time of less than 2 hours. These patients were excluded from the current analysis. There were no significant differences in the demographic variables such as sex, age, weight and height between the two groups. Also, there were no significant differences in the anesthetic time between the two groups (
On postoperative 1 hour, there was no significant difference in the incidence of POST between the two groups. However, on postoperative 6 hours (57% vs 84%, P = 0.041), 24 hours (37% vs 65%, P = 0.045) and 48 hours (10% vs 52%, P = 0.001), the incidence of POST was significantly lower in Group H (
In addition, on postoperative 1 hour, there was no significant difference in the incidence of cough between the two groups. However, on postoperative 6 hours (27% vs 71%, P = 0.001), 24 hours (13% vs 45%, P = 0.015) and 48 hours (7% vs 32%, P = 0.028), the incidence of cough was significantly lower in Group H (
In our study, we evaluated the effectiveness of the active warming and humidification of inhaled gas in patients that underwent thyroid surgery that lasted over 2 hours of operation time. This showed that the incidence of POST and the severity of cough were significantly lower in Group H, which implied that the warming and humidification of inhaled gas during the operation were effective.
Christensen et al. [
Kadri et al. [
It is possible that the variability of POST incidence arises from differences in the kinds of anesthesia, the technical expertise of anesthesiologist, the definition about sore throat and interviews with patients.
Firstly, it can be predicted that the subjectivity about sore throat and the methods of inquiry and interview may further increase the discrepancy in POST incidence. In our study, questionnaires were generated based on a previous report by Harding et al. [
In addition, It has been reported that POST can be perceived as symptoms such as continuous neck pain, hoarse voice, swallowing difficulty, dry mouth, a feeling of discomfort in specific parts of the body (laryngitis and bronchitis) and cough [
According to Ayoub et al. [
In addition, following a comparison between throat pain and cough symptoms, the incidence of throat pain was higher than that of cough on postoperative 1 hour. In our study of a comparison between throat pain and cough, the incidence of POST was relatively higher than cough. These results were identical to previous studies [
However, Herlevsen et al. [
POST is one of the most common outcomes following general anesthesia. According to Higgins et al. [
The effects of active warming and humidifying associated with POST were first identified by Kim et al. [
Accordingly, by using the endotracheal intubation in patients who underwent the thyroidectomy for more than 2 hours, we evaluated the effects of using the warming and humidifying circuit as the non-pharmacological treatment method in reducing the incidence of POST. In general, studies about the warming and humidifying circuit have determined the effects on protection of the structure and functions of mucociliary cells lining the bronchus. The criteria for recommending warming and humidification in low-flow anesthesia were established by Branson et al. [
For warming and humidifying the inhaled gas, in addition to the methods for using the heated humidifier circuit, there were the low-flow anesthesia or closed circuit methods, as well as the heat and humidity exchanger. Further studies are needed to compare the clinical effects of these additional methods [
In conclusion, based on the results that the incidence and severity of POST and cough following the thyroidectomy with using the endotracheal intubation over 2 hours, we suggest that the use of a heated humidifier may be an effective modality that can prevent the occurrence of POST and cough.
Scoring System for Sore Throat and Cough
Demographic Data, Surgical and Anesthesia Data
Values are as mean ± SD or the number of patients (%). Group C: control group, Group H: heated circuit group.
Incidence of Postoperative Sore Throat and Cough
Values are number of patients and %. Group C: control group, Group H: heated circuit group.
Severity of Postoperative Sore Throat and Cough
Data are the actual numbers in each grade. Sore throat was graded as: 0, absent; 1, minimal; 2, moderate; 3, severe. Cough was graded as: 0, absent; 1, minimal; 2, moderate; 3, severe. Group C: control group, Group H: used a heated circuit kit. *Denotes P < 0.05 during inter-group between Group C vs. Group H. †Denotes P < 0.01 during inter-group between Group C vs. GroupH.