Anesth Analg 2006;103:1260-1263
© 2006 International Anesthesia Research Society
doi: 10.1213/01.ane.0000240872.08802.f0
GENERAL ARTICLES
The Twenty-Degree Reverse-Trendelenburg Position Decreases the Incidence and Severity of Postoperative Nausea and Vomiting After Thyroid Surgery
Kiyo Tominaga, MD, and
Toshiyuki Nakahara, MD
From the Department of Anesthesiology, Tokushima Municipal Hospital, Tokushima, Japan.
Address correspondence and reprint requests to Kiyo Tominaga, 2-34 Kitajosanjima-Cho, Tokushima 770-0812, Japan. Address e-mail to kiyokorin{at}yahoo.co.jp.
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Abstract
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BACKGROUND: In this randomized, single-blind, controlled study, we evaluated whether the 20° reverse-Trendelenburg position had an effect on postoperative nausea and vomiting in patients undergoing thyroid surgery.
METHODS: Patients (n = 224) were given a standardized propofol anesthetic. Intraoperatively, patients were randomly assigned into two groups according to the tilt of the table maintained during surgery: patients were positioned with the neck extended and the table tilted with 20° reverse-Trendelenburg or with the neck extended and the table positioned at a horizontal tilt. All episodes of postoperative nausea, vomiting, nausea severity score, frequency of vomiting, and the use of antiemetics were recorded during the first 24 h after anesthesia. We divided this time period into 0–3 h and 3–24 h.
RESULTS: During the 0–3 h postoperative period, all observed episodes were comparable between groups. However, during the 3–24 h and the overall postoperative period, the incidence of nausea and/or vomiting, the nausea severity score, and frequency of vomiting were significantly less in the 20° reverse-Trendelenburg position.
CONCLUSION: The 20° reverse-Trendelenburg position effectively ameliorates postoperative nausea and/or vomiting.
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Introduction
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The commonly identified risk factors that have consistently contributed to postoperative nausea and/or vomiting (PONV) are female gender, nonsmoking status, history of PONV or motion sickness, extended duration of anesthesia, postoperative opioid use, and age (1). In addition, other predictors may be of interest, such as the type and dosage of volatile anesthetics (2) and the types of surgery (3). As the number of risk factors increases, the chance of PONV also increases. The avoidance of risk factors during anesthesia can reduce the baseline risk of PONV (2,4,5). Thyroid surgery can cause neck and facial swelling from the neck dissection and temporary congestion of the craniocervical circulation. Elevating the head decreases intracranial pressure, mitigates craniocervical blood flow disturbances (6), and enhances venous and lymphatic drainage (7). Lovell et al. (6) reported that cerebral blood volume decreased and mean arterial blood pressure did not change in patients receiving propofol when positioning patients with an approximate 20° head-up tilt compared with a neutral position. The position used during the intraoperative period has the potential to be a practical strategy in the amelioration of PONV. We hypothesized that head elevation might reduce complications after thyroid surgery. The aim of the present study was to investigate the horizontal and 20° reverse-Trendelenburg positions in patients undergoing thyroid surgery and to compare the incidence and severity of PONV.
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METHODS
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After obtaining approval by the Hospital Ethics Committee, oral and written informed consent was obtained from all patients who agreed to participate. The sample size for this study was based on the observed incidence of PONV during a 3-mo preliminary study (45%). These data indicated that 112 patients in each group would provide an 80% power for detecting a 40% reduction in PONV (from 45% to 27%) with an 
-level of 0.05 (1).
All patients scheduled for elective thyroid surgery under general anesthesia were in a physiologically euthyroid state and were ASA physical status I–II adults. Patients who had neurologic, renal, or liver disease, or had received drugs with antiemetic properties, including corticosteroids, were excluded from participation. After enrollment, patients were randomized to two groups by sealed envelope: the 20° Trendelenburg position (group r–T) and the horizontal position (group H). We further stratified the patients by sex. The randomization process and the identity of the groups were blinded from the patients and the investigators who managed the postoperative aspects of the study and administered antiemetics. The anesthesiologists in charge were not blinded as to group assignment.
Preanesthetic medication and prophylactic antiemetics were not administered. Monitoring before anesthetic induction consisted of automated noninvasive arterial blood pressure (oscillometric blood pressure), continuous electrocardiogram, and pulse oximetry. Anesthesia was induced with 2–2.5 mg/kg propofol and 2–3.5 µg/kg fentanyl. Neuromuscular block was established with 0.1 mg/kg vecuronium bromide. The trachea was sprayed with lidocaine (2 mg/kg) and intubated. After induction, the patient's head was placed at 30° straight extension on the table tilted with 20° reverse-Trendelenburg (group r–T) or on the neutral horizontal tilt (group H). The position was maintained until the patient awoke at the end of surgery. Anesthesia was maintained with an infusion of propofol (4–8 mg kg–1 h–1) and fentanyl (1.5–2 µg kg–1 h–1). Muscle relaxation was maintained with IV vecuronium bromide (0.04 mg kg–1 h–1). The baseline systolic arterial blood pressure was obtained on admission to the operating room. Additional doses of propofol (20–30 mg) were given when the heart rate or the systolic arterial blood pressure increased more than 20% compared with a baseline value recorded during anesthesia. If the heart rate or systolic arterial blood pressure did not return to baseline 3 min after a propofol bolus, 50–100 µg fentanyl IV was injected. After induction of anesthesia, end-tidal carbon dioxide and N2O concentration were monitored using a dedicated mass-spectrometer (COLIN BP-508, Komaki, Japan) that was calibrated before the study. Controlled ventilation with 33% oxygen in N2O was applied at an inspiratory peak pressure of <20 cm H2O. A Foley catheter was placed in the bladder, and urinary bladder temperature was continuously monitored. Temperature was maintained higher than 36°C by regulating ambient temperature and using warming blankets. During the first hour of anesthesia, 10 mL/kg Ringer's acetate solution was administered followed by 5 mg kg–1 h–1. All patients were fitted with intermittent pneumatic compression systems to prevent stasis and deep vein thrombosis. At the end of the operation, IV atropine (0.5 mg) and neostigmine (1.0 mg) were administered to reverse residual paralysis, and the trachea was extubated. All patients were administered naloxion hydrochloride (0.2 mg) as a respiratory stimulant. During postanesthetic recovery, all patients were kept in the supine position with the bed head at 10°. Ringer's acetate solution was administered at 2 mL kg–1 h–1 for 24 h postoperatively.
Morphometric and demographic characteristics of each group were recorded. The individual risk for PONV was calculated using the simplified risk assessment developed by Apfel et al. (1,8). The incidence and severity of PONV were determined by blinded observers at intervals over a 24-h period starting at arrival in the postoperative care unit. Nausea and vomiting were evaluated from 0 to 3 h and from 3 to 24 h postoperatively. If the patient had nausea, the severity of the episode was recorded during each assessment period using the following scale: no nausea, mild nausea, moderate nausea, and severe nausea. A vomiting episode was defined as vomiting events that occurred in a rapid sequence with <1 min between events. If vomiting events were separated by >1 min, they were considered separate episodes. Retching was classed as postoperative vomiting. Rescue antiemetics (IV metoclopramide 10 mg) were given in each blinded observer's judgment or by patient request. Postoperative pain was assessed with a 10-cm visual analog scale (0 = no pain to 10 = the worst pain imaginable) score. When patients complained of pain and requested analgesia, a diclofenac suppository of 25 or 50 mg was given. No opioid was administered during the postoperative period. Rescue antiemetics and pain relief treatments were repeated if necessary.
Demographic and baseline characteristics were compared between groups using a Student's t-test for continuous variables and a 
2 test for categorical variables. The incidence of PONV and the number of subjects who used antiemetics were compared by 2 analyses. Nausea severity score, vomiting episodes, and the number of times antiemetics were used were compared by Mann–Whitney's U tests. For PONV analysis, any score for nausea or vomiting exceeding "none" was considered positive. P < 0.05 was considered statistically significant.
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RESULTS
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Two-hundred-forty-one patients were assessed for eligibility. Five were excluded by the inclusion criteria; two had cerebral infarction, one had craniotomy for brain tumor, one had ischemic heart disease, and one had chronic renal failure. One declined the invitation to participate. A total of 235 patients were enrolled. Eleven were eliminated from the study after enrollment: six underwent a second surgical operation for hematoma within the first 24 h, five underwent reconstruction of the trachea and were given artificial ventilation for 24 h postoperatively.
The data obtained from the remaining 224 patients were analyzed. The patients' characteristics, such as age, weight, height, and the risk score for PONV, as well as duration of surgery and anesthesia, type of thyroid surgery, total doses of perioperative propofol, fentanyl, and vecuronium bromide, intravascular fluid volume, and temperature were comparable between groups (Table 1). Blood loss volume was significantly less in group r–T (Table 1). There was no difference between groups in mean visual analog scale at 3 and 24 h after surgery (Table 1).
Table 2 shows the incidence and severity of PONV. In the first 3 h of the postoperative period, the incidence of nausea, vomiting, and PONV, nausea severity score, and the use of rescue antiemetics were comparable between groups. The incidence of nausea, vomiting, and PONV were significantly less in group r–T than in group H from 3 to 24 h and in the overall 24-h period. The nausea severity score and frequency of vomiting were also significantly less in group r–T than in group H from 3 to 24 h and in the overall 24-h period. The use of antiemetics was comparable between groups.
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DISCUSSION
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The results of this study indicate that the 20° reverse-Trendelenburg position during thyroid surgery reduces the incidence and severity of PONV. This result is surprising because there is no established mechanism by which the position during thyroid surgery influences nausea and vomiting many hours after the operation. Our results showed that the position has the possibility of influencing PONV.
Our results showed that the 20° reverse-Trendelenburg position during thyroid surgery provided a 40% reduction in PONV, and reduced vomiting by more than 50%. As all patients were in the same position postoperatively, our data suggest that the intraoperative position is more important than the postoperative position in reducing PONV.
The incidence of PONV in group H (43%) was in accord with other clinical studies evaluating postoperative complications and propofol anesthesia after thyroid surgery (9,10). The frequency of antiemetic use was 13%–35% after thyroid surgery when prophylactic antiemetics were not administered (11), similar to the 18% use in group H. Although there was reduced PONV in Group r–T, it did not reach statistical significance. The lack of a significant effect may have been due to the effects of propofol for maintenance of anesthesia (2,12).
The neck extended position required for thyroid surgery decreases the diameter of internal jugular veins (7) and reduces extrajugular pathways of cerebral blood drainage (8,13). The reduction of PONV from using the 20° reverse-Trendelenburg position may result from the reduction in craniocervical venous congestion. Furthermore, the lower central venous pressure and/or cervical venous congestion caused by the 20° reverse-Trendelenburg position may reduce blood loss during thyroid surgery (14).
Our study has a few limitations. We did not measure intracranial pressure, central venous pressure, cerebral blood volume, or cerebral blood flow, as these measurements are invasive, and we felt it would not be ethically justified to make them without knowing whether the study would find a reduction in PONV. The second limitation is that there was a significant difference in blood loss volume between groups. Three patients in group H and one in group r–T hemorrhaged beyond 3 sd of the mean blood loss. Of these four patients, only the two in group H had PONV. Intravascular volume deficits may be a factor in PONV, and thus part of the effect may have been either the difference in blood loss, or the difference in crystalloid fluid used to replace shed blood. While IV fluid administration reduces gut mucosal hypoperfusion and ameliorates PONV (15,16), we do not know what the effect is with thyroid surgery.
In summary, the 20° reverse-Trendelenburg position decreased blood loss and reduced the incidence and severity of PONV in thyroid surgery. Reverse Trendelenburg position provides a practical strategy to decrease the risk of PONV after thyroid surgery.
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ACKNOWLEDGMENTS
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The authors thank their colleagues from the Department of surgery and postoperative anesthetic care unit nurses for their assistance with this study.
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Footnotes
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Accepted for publication August 2, 2006.
This work has not been funded by any sources of financial support.
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REFERENCES
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Abstract
Introduction
