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Anesth Analg 2007;104:1352-1355 © 2007 International Anesthesia Research Society doi: 10.1213/01.ane.0000262041.46833.21
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Abstract |
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 Top Abstract IntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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BACKGROUND: Airway obstruction occurs in anesthetized children with obstructive sleep apnea syndrome (OSAS). The inspiratory attempts against the occluded airway lead to an increased sympathetic activity. Heart rate variability (HRV) analysis provides information about the autonomic nervous system. The low-frequency component/high-frequency component ratio of HRV is considered to be an index of sympatho-parasympathetic balance.
METHODS: We investigated the effects of general anesthesia, the neutral neck position, and jaw thrust in the supine and lateral positions on HRV in 20 children (aged 3–9 yr), with OSAS. HRV was recorded before and after anesthesia induction, at the neutral neck position and with jaw thrust maneuver in the supine and lateral positions with the patients breathing 5% sevoflurane.
RESULTS: General anesthesia with the patient in the neutral neck position increased airway obstruction. The patients’ stridor scores improved with the airway maneuver of jaw thrust and lateral position. The low-frequency component/high-frequency component ratio and heart rate increased at the postinduction measurement and reached the highest value with the patient in the neutral neck position. The values significantly decreased with the jaw thrust maneuver and with the patient in the supine and lateral positions. Ultra-short-term entropy of HRV decreased after anesthetic induction and reached the lowest value with the patient in the neutral neck position. The values increased during jaw thrust and with patients in the supine and lateral positions.
CONCLUSIONS: Changes of HRV induced by inhaled anesthesia, jaw thrust, and lateral positioning procedures corresponded to changes in the stridor score of children with OSAS.
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Introduction |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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Upper airway obstruction can occur in anesthetized children, especially in those with obstructive sleep apnea syndrome (OSAS) (1,2). Airway obstruction results in the increased respiratory effort which leads to an increase in the negative intrathoracic pressure and in the afferent inputs from the lung and the chest wall, thus affecting autonomic function (3,4). Our previous studies showed that the lateral position combined with airway maneuvers dramatically improved airway patency and alleviated airway obstruction in children with OSAS (5,6).
Heart rate variability (HRV) analysis is a noninvasive technique used to provide information about the autonomic nervous system. HRV analysis provides important information about the effects of anesthetics and surgical procedure on the autonomic and central nervous systems because variation of the heart rate (HR) is mediated by central and peripheral neural mechanisms (7). The low-frequency (LF) component (LF, 0.05–0.15 Hz) is influenced by sympathetic and parasympathetic activities, and the high frequency (HF) component (HF, 0.15–0.5 Hz) originates from parasympathetic activity. Thus, the LF/HF ratio is considered to be an index of sympatho-parasympathetic balance (8,9). Entropy, as it applies to signals like R–R intervals (RRI), quantifies the repetition of patterns of these signals and is expressed from 0% (regular interval pulse series, no variability) to 100% (maximal randomness, e.g., noise) (10). Entropy has a higher value for normal subjects in whom HR is more random (11). In addition, entropy reflects the parasympathetic modulation of HR.
We hypothesized that upper airway obstruction induced by general anesthesia would produce an increase in negative intrathoracic pressure affecting the afferent input from the lung, and that the airway maneuver and lateral position could alleviate upper airway obstruction, thereby reducing autonomic nervous activity. In the present study, we investigated the effects of general anesthesia, jaw thrust, and the lateral position on HRV in children with OSAS.
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METHODS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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After obtaining the approval of our IRB and written informed consent from the patient’s parents, we studied 20 children (aged 3–9 yr), with OSAS, scheduled for elective adenotonsillectomy. Children with craniofacial abnormalities, deformities of the chest or spine, or myopathies were excluded.
No premedication was given. After arrival in the operation room, the child had standard monitoring in place [noninvasive arterial blood pressure, electrocardiogram (ECG), pulse oximetry, end-tidal CO2, and anesthetic concentrations]. ECG electrodes were attached for HRV analysis and the ECG signals were obtained from a conventional anesthesia monitor (Hewlett Packard, Model 66s). The data were transferred to an online computer loaded with HRV analysis software (TARAWA/WIN; Suwa Trust, Tokyo, Japan). For real-time analysis, RRI were obtained in the accuracy of 1 ms and analyzed with the "MemCalc" computer program (10). The two series of power of the RRI (ms2), LF (0.04–0.15 Hz), and HF (0.15–0.5 Hz), were calculated. MemCalc also calculated ultra-short-term entropy (UstEn) from a pulse time series of eight R–R intervals. HR, LF/HF ratio, and UstEn were recorded.
Anesthesia was induced by increasing the inhaled concentration of sevoflurane by 0.5% every three breaths up to 6% via a facemask with 100% oxygen from a circle system. After the induction of anesthesia with the patient spontaneously breathing 5% inspired sevoflurane, the patient’s chin was softly lifted for 5 min (5,6,12) and HRV measurements were made. The child was then placed into the neutral neck position, with the chin unsupported, and HRV measurements were made. After these measurements, a jaw thrust was applied with both hands, displacing the jaw upwards and anteriorly with the patient’s mouth open (Esmarch maneuver). After the measurements in the supine position, the child was placed in the left lateral decubitus position (right side up) with the head supported by an additional pillow so that the trunk and head were aligned. A jaw thrust maneuver (as described above) was done with the patient in the lateral position. Airway patency was assessed clinically during the measurement of HRV by an observer, blinded to the value of HRV (5,6) and the assessment were as follows: stridor score 1 = normal breathing sounds detected by auscultation over the trachea; 2 = stridor over the trachea detected by stethoscope; 3 = stridor detected without auscultation (audible); 4 = no airway sound detectable over the trachea. Pre- and postinduction measurements, measurements during the neutral neck position in the supine, and the jaw thrust in the supine and lateral positions were made for 1 min, respectively.
Data were expressed as median (interquartile range). Data were analyzed by means of the nonparametric Friedman’s test for repeated-measure analysis followed by Student–Newman–Keuls method, using Sigmastat software, version 3.0 (Systat Software, Point Richmond, CA). P < 0.05 was considered statistically significant.
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RESULTS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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Twelve boys and eight girls with OSAS were included in the present study. The median (interquartile range) age was 5 yr (4–6), height was 110 (102–114) cm, and weight was 17.5 (15.5–19.5) kg. The children demonstrated a significant increase in the LF/HF ratio and a significant decrease in the UstEn of HRV in line with upper airway obstruction (stridor score) (Figs. 1–4). During the postinduction period, although they were breathing spontaneously with the chin softly lifted, the median stridor score changed from 1 to 3, with the median LF/HF ratio: 2.75 to 16 and the median UstEn: 56 to 23.5. With the patient in the neutral neck position and the chin unsupported, the stridor score increased to 4, the LF/HF ratio of HRV increased to 23, and the UstEn decreased to 7. After jaw thrust in the supine and lateral positioning, the stridor score decreased to 1 and the LF/HF ratio significantly decreased to 3.5 and 3, respectively, whereas the UstEn increased to 38.5 and 39, respectively.
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DISCUSSION |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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The present study showed that the stridor scores in the children with OSAS reflected HRV either when inhaled anesthesia occluded the airway, or when the occlusion was relieved by jaw thrust and lateral positioning procedures.
Adenotonsillar hypertrophy is the most common cause of OSAS in children. During anesthesia, inspiratory collapse of the upper airway occurs. OSAS is now thought to be caused by a dynamic process resulting from a contribution of anatomical upper airway narrowing and abnormal upper airway neuromotor tone (13,14). As in our previous studies (5,6), we showed in the present study that jaw thrust improved airway patency and the lateral position significantly enhanced the effect of the airway maneuver in children with OSAS.
Respiration per se strongly influences RRI or HR fluctuation, and ventilation also affects both vagal activity and sympathetic nerve traffic (15–17). Moreover, apnea/hypopnea events significantly increased sympathetic activity (3,4,18,19). The inspiratory attempts against the occluded airway lead to an increase in respiratory effort, thereby inducing an increase of negative intrathoracic pressure (3,4) and an increased sympathetic activity. Thus, changes in respiration may alter spectral oscillations of RRI.
The LF of HRV is influenced by sympathetic and parasympathetic activity, and the HF originates from parasympathetic activity. Thus, the LF/HF ratio is considered to be an index of sympatho-parasympathetic balance. Entropy quantifies the repetition of patterns of the RRI signals of HRV (10) and entropy values of HRV decrease in line with the decrease of the heart activity or function (11,20).
The present HRV data showed that an occluded airway in children with OSAS increased sympathetic activity with a significant decrease in cardiac function, but relief from the occluded airway by jaw thrust and lateral positioning returned HRV to preanesthetic levels. We thus postulated that although upper airway occlusion induced by anesthesia might have increased negative intrathoracic pressure and respiratory effort, resulting in an excitation of the sympathetic nervous system, jaw thrust, and lateral positioning alleviated airway occlusion and might have decreased respiratory effort, thereby reducing the excited sympathetic nerve activity.
A limitation of the present study was the failure to randomize the chronological order of the patient’s position to test the lateral position last. Because our previous studies demonstrated that the measurements of airway patency were made twice, and the stridor scores obtained first and second were the same (5,6), we made the measurements once in the present study.
In conclusion, inhaled anesthesia worsened the occluded airway and significantly increased the stridor score and the LF/HF ratio of HRV in the neutral neck position. Jaw thrust and lateral positioning procedures relieved the occlusion and decreased the LF/HF ratio.
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Footnotes |
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Accepted for publication February 21, 2007.
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