Anesth Analg 2005;101:382-384
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000150943.87520.6D
ANESTHETIC PHARMACOLOGY
Does Yawning Represent a Transient Arousal-Shift During Intravenous Induction of General Anesthesia?
Yoshiko Kasuya, MD*,
Tatsuo Murakami, MD*,
Tsutomu Oshima, MD
, and
Shuji Dohi, MD
*Division of Anesthesia, Gifu Red Cross Hospital; and Department of Anesthesiology, Gifu University Graduate School of Medicine, Gifu-City, Japan
Address correspondence and reprint requests to Tsutomu Oshima, MD, Department of Anesthesiology and Pain Medicine, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu City, Gifu 501-1194, Japan. Address e-mail to oshimat{at}cc.gifu-u.ac.jp.
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Abstract
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Although yawning occurs frequently during the IV induction of general anesthesia, the significance of this response remains unknown. In this study, we induced 30 surgical patients with 4 mg/kg thiopental IV, and 30 patients with 2 mg/kg propofol IV. Thereafter, the occurrence of yawning was continuously assessed, as the only clinical end-point, for 1 min. The electroencephalographic bispectral index was monitored throughout the observation period. The criterion for an arousal response was a transient increase during a continuing decrease in the bispectral index value. On the basis of this criterion, the sensitivity and specificity of the yawning response as an arousal sign were 77% and 80%, respectively. If a patient exhibited a yawning response, the chance of arousal was 84% (positive predictive value). With no yawning response, the chance of nonarousal was 71% (negative predictive value). According to simple logistic regression, the yawning response was predictive of a transient arousal-shift with an odds ratio of 13.5 (95% confidence interval: 3.8–48; P < 0.001). The occurrence of a yawning response during IV induction may be a clinical indicator of a transient arousal-shift during progressive loss of consciousness.
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Introduction
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One of the most frequently encountered clinical situations during which yawning occurs is the IV induction of general anesthesia (1). A typical yawn is characterized by a single large inspiration with simultaneous mouth opening and stretching of the trunk (2–4). Yawning can also be accompanied by changes in autonomic function, such as lacrimation and penile erection (5–7). Furthermore, yawning has been established as a phenomenon that subserves arousal (8). Although a transient arousal-shift during the yawning behavior has been demonstrated in awake humans as measured by skin conductance (9), sympathetic nerve activity (10), and behavior (11), we thought it important to know whether this phenomenon also applies to humans during IV induction, a clinical situation in which relevant information is still lacking.
We hypothesized that a yawning response during IV induction is associated with a transient arousal-shift during continuing loss of consciousness in humans. To examine this hypothesis, we recorded the electroencephalographic (EEG) bispectral index (BIS) during IV induction achieved using a single bolus induction dose of thiopental or propofol.
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Methods
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Sixty adult patients, each of ASA physical status I–II, who were scheduled for elective surgery under general anesthesia participated in this IRB-approved study at Gifu Red Cross Hospital. All gave prior written informed consent. The exclusion criteria were as follows: (a) renal, hepatic, or neurologic dysfunction, (b) use of benzodiazepines, anticonvulsants, alcohol, opioids, or other psychotropic drugs (chronically or within 24 h before the induction of anesthesia), and (c) any patient in whom a rapid sequence induction was indicated. Each patient received atropine sulfate 0.5 mg and hydroxyzine hydrochloride 25 mg IM 30 min before entry into the operating room. Routine monitors consisted of an automated blood-pressure cuff, electrocardiogram, pulse oximeter, and an EEG BIS monitor (model A-2000, version 3; Aspect Medical Systems Inc., Natick, MA) connected to a laptop computer (MN-390-X26; Sharp, Japan). We adopted 15 s from the 2 choices of smoothing rates over which the BIS value is averaged: 15 s provides increased responsiveness to state changes, such as induction or awakening and 30 s provides a smoother trend with decreased variability and sensitivity to artifact. After obtaining baseline values and oxygenation through the mask, an IV injection of either 4 mg/kg thiopental or 2 mg/kg propofol was administered by the investigator over a 5-s period. As the only clinical end-point, three observers who were blinded regarding the BIS value continuously assessed the occurrence of the yawning response (characterized by mouth-opening) after the start of the anesthetic infusion. The 1-min observation period was followed by the termination of this study. Then, vecuronium (0.16 mg/kg) was administered IV, and mask-assisted ventilation with 100% oxygen was applied. All data on the BIS monitor were stored for further off-line retrospective analysis. The criterion for the occurrence of transient arousal was a transient increase (
1 compared with the prevalue, 5 s in duration) during the continuing decrease in the BIS value that followed administration of the anesthetic.
Data are mean (±sd), and P < 0.05 was considered statistically significant. The demographic data of the patients in the thiopental and propofol groups were compared using Fisher’s exact probability test or a Student’s t-test, as appropriate. Two-by-two frequency tables were constructed, cross-tabulating the occurrence rate of the yawning response against that of the transient arousal-shift on the BIS record. Positive and negative predictive values were determined. Furthermore, simple logistic regression was used to determine the validity of the yawning response as a potential clinical indicator of a transient arousal-shift during progressive loss of consciousness.
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Results
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Eighteen and 14 patients exhibited a yawning response in the thiopental and propofol groups, respectively. There was no statistical difference between both groups in any of the demographic variables (age, weight, height, ASA physical status, or sex). With regard to the percentage of patients exhibiting a yawning response or a transient arousal-shift, there was no statistically significant difference between the two groups (Table 1).
Figure 1 presents a representative BIS trend against time for one yawning and one nonyawning patient, each from the thiopental group. Unlike the nonyawning patient, the yawning patient exhibited a transient increase during the continuing decrease in the BIS value after IV administration of thiopental. Among the patients in this study (both groups), a transient increase in the BIS value (mean ± sd: 3.7 ± 2.4) was consistently observed 15–20 s after the occurrence of a yawning response. Using the criterion defined by a transient increase (1 compared with the prevalue, 5 s in duration) during the continuing decrease in the BIS value that followed administration of the anesthetic, the sensitivity and specificity of the yawning response as an arousal-related sign in all patients were 77% and 80%, respectively (Table 2). If a given patient exhibited a yawning response, the chance of arousal was 84% (positive predictive value; Table 2). Without the yawning response, the chance of nonarousal was 71% (negative predictive value; Table 2). According to simple logistic regression, the yawning response was predictive of a transient arousal-shift on the BIS record (odds ratio = 13.5, 95% confidence interval: 3.8–48; P < 0.001).
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Figure 1. A, A representative electroencephalographic bispectral index (BIS) trend against time for a patient who exhibited a yawning response. A transient increase during the thiopental-induced decrease in the BIS value was observed 15–20 s after the yawn. B, A representative BIS trend against time for a patient who did not exhibit a yawning response. Throughout the steady decrease in the BIS value caused by IV administration of thiopental, no transient increase in the BIS value was observed.
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Discussion
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The principle finding in this study was that, in humans, a yawning response was related to a transient increase during the continuing decrease in the BIS value seen after IV administration of thiopental or propofol. This phenomenon, observed using BIS monitoring, may reflect a transient arousal-shift during the progressive loss of consciousness caused by IV induction. We therefore focus the following discussion on the arousal-shift that seems to be related to the yawning response.
In our study, the yawning response elicited during IV induction had positive and negative predictive values of 84% and 71%, respectively, for predicting a transient increase in the BIS value, with the sensitivity and specificity being 77% and 80%. Moreover, simple logistic regression indicated that the odds ratio of the yawning response as a prediction of a transient increase in the BIS value was 13.5 (95% confidence interval: 3.8–48; P < 0.001). These statistical values are all consistent with our hypothesis that the yawning response might represent a transient arousal-shift during continuing loss of consciousness and on the assumption that the BIS monitor is capable of detecting rapid changes in arousal or consciousness or whatever it actually measures.
On the BIS record, a transient increase during a continuing decrease was consistently observed 15–20 seconds after the occurrence of a yawning response. However, because the BIS value that actually correlates with a given event is the value recorded after a 20-second delay to compensate for the time delay in calculating the BIS value (1), the underlying phenomenon may occur either before or during the yawning response. This arousal effect may be of considerable significance because the data were obtained under general anesthesia. A few years ago, Sato-Suzuki et al. (12) recorded the electrocorticogram to evaluate arousal responses during yawning in anesthetized rats. During both spontaneous yawning and yawning responses evoked by chemical stimulation of the paraventricular nucleus, electrocorticogram arousal (represented by lower voltage and faster rhythms) occurred before the actual yawning behavior. However, Concu et al. (8) demonstrated that EEG arousal and yawning appeared concomitantly in cats. When taken together with these findings in animal experiments (8,12), the present data suggest that yawning-induced EEG arousal does not result from the stretching of the trunk. Although the BIS monitor is capable of rejecting the electromyographic artifacts, we cannot exclude the possibility that the transient increase in the BIS value may incorporate electromyographic activity which could have increased because of muscle activity during opening of the mouth. Further studies using a multichannel EEG with electrodes over the mandible are needed to solve this problem. Although the BIS monitor involves this limitation, this study is the first to indicate an arousal-shift associated with yawning during induction of general anesthesia in humans (9–11).
In conclusion, the yawning observed in patients during IV anesthetic induction with thiopental or propofol was related to a transient increase during continuing decrease in the BIS value. This type of yawning may be a clinical indicator of a transient arousal-shift during progressive loss of consciousness.
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Footnotes
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Accepted for publication November 1, 2004.
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References
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Abstract
Introduction
