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PEDIATRIC ANESTHESIA

Circulatory Responses to Fiberoptic Intubation in Anesthetized Children: A Comparison of Oral and Nasal Routes

From the Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China.

Address correspondence and reprint requests to F.S. Xue, MD, Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Ba-Da-Chu Rd., Shi-Jing-Shan District, Beijing, People's Republic of China 100041. Address e-mail to fruitxue{at}yahoo.com.cn.

	Abstract

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BACKGROUND: Previous studies have demonstrated a significant difference in the circulatory responses in adults to fiberoptic nasotracheal intubation (FNI) and fiberoptic orotracheal intubation (FOI). But, it is unknown whether there is a clinically relevant difference in the circulatory responses in children to these two intubation methods.

METHODS: In this randomized clinical study, we compared the arterial blood pressure and heart rate changes during FNI and FOI in 66 children, ASA physical status I-II, aged 3–9 yr scheduled for elective plastic surgery. After anesthesia induction with fentanyl-propofol and vecuronium, fiberoptic intubation was performed. Noninvasive arterial blood pressure and heart rate were recorded before (baseline values) and after anesthesia induction (postinduction values), at intubation, and every minute for the first 5 min after intubation. The maximum values of arterial blood pressure and heart rate during the observation were also recorded.

RESULTS: The total intubation time was significantly longer in the FNI group than in the FOI group. Both FOI and FNI caused significant increases in arterial blood pressure and heart rate compared with the baseline and postinduction values. Arterial blood pressure and heart rate at intubation and after intubation, and their maximum values during the observed periods were significantly lower in the FNI group compared with the FOI group. The times required to reach the maximum values of systolic blood pressure and heart rate were significantly longer in the FNI group than in the FOI group, but the times required for recovery of systolic blood pressure and heart rate to postinduction values were significantly shorter in the FNI group than in the FOI group. After the intubation, the times required to reach the peak levels of systolic blood pressure and heart rate were not significantly different between the two groups.

CONCLUSIONS: Both FOI and FNI can cause significant circulatory responses in healthy anesthetized children, and the circulatory responses to FNI are fewer and of a shorter duration than those to FOI.

	Introduction

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With the development of a thin fiberoptic bronchoscope (FOB), fiberoptic intubation can be easily performed in pediatric patients, and has been found to be a safe and useful device in the management of the pediatric difficult airway (1–9). Yoshihiro and Shuji (10) have demonstrated that there is a significant difference in the circulatory responses to airway stimulation at different sites. In adult studies, simple nasopharyngeal intubation and insertion of a nasopharyngeal airway produce a significant hypertensive response (11,12). In addition, the circulatory responses to fiberoptic nasotracheal intubation (FNI) are more pronounced compared with fiberoptic orotracheal intubation (FOI) (13). To the best of our knowledge, no previous study has compared differences in the circulatory responses to FNI and FOI in children. This randomized clinical study was designed, therefore, to determine whether there is a clinically relevant difference between the circulatory responses to FOI and FNI in children.

	METHODS

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After institutional ethics committee approval and written informed consent from the parents were obtained, 66 children (ASA physical status I-II) scheduled for elective plastic surgery under general anesthesia requiring tracheal intubation were included in this study. Exclusion criteria were a history of reactive airway disease, gastroesophageal reflux, morbid obesity, hypertension, and use of medications and nutraceuticals known to affect arterial blood pressure (BP) and heart rate (HR). Children were randomly allocated to either the FOI group (n = 33) or the FNI group (n = 33) according to a computer-randomized table.

Before surgery, all children fasted overnight and were restricted from oral intake of clear fluid for 2–3 h. One hour before the child arriving in the operating room (OR) a eutectic mixture of local anesthetic (EMLA®) was applied to the dorsum of a hand as surface anesthesia to facilitate placement of the IV catheter, and 30 min before arriving in the OR all children received two sprays of mixture solution of 2% lidocaine-0.5% ephedrine (total volume of 1 mL) to each nostril. After the child entered the OR, noninvasive BP and HR were measured with a multifunction monitor (Datex. Ohmeda F-CU8, Datex Instrumentarium, Helsinki, Finland). After a stabilization period of 10 min, baseline values of systolic BP (SBP), diastolic BP, mean arterial BP and HR were obtained from the average of the three measurements obtained 2 min apart. Then a 22-guage IV catheter was inserted into the veins on the dorsum of a hand.

Before anesthesia induction, a gas sampling tube was connected to sampling port of the right-angle connector, and the work mode of the multifunction monitor for BP determination was changed to the continuous mode with a response time of about 20–30 s. After routine administration of oxygen, anesthesia was induced with fentanyl 2 µg/kg and propofol 2.5 mg/kg IV over 15–20 s. Neuromuscular block was produced with vecuronium 0.1 mg/kg IV. When a response to verbal command was absent, the lungs were ventilated via a facemask with isoflurane and 100% oxygen. The inspired concentration of isoflurane was gradually increased to 1%, with an increment of 0.2% every 4 breaths. If any difficulty was encountered in performing facemask ventilation, the child was withdrawn from the study. Tracheal intubation was started 2 min after vecuronium injection. In the FNI group, a relatively clear nasal passage was selected for the intubation and a silicone-based lubricant was applied in this nasal cavity. In this study, the Portex cuffed latex nasal tube (Portex Limited Hythe, Kent, England) and the Murphy-type cuffed polyvinyl chloride oral tube (Hudson Respiratory Care, Temecula, CA) were used. The suitable size of tracheal tube for a child was determined by the following formula (14): ID (mm) = age/3 + 3.5. Before intubation, the tracheal tube was adequately lubricated with the lidocaine gel and was threaded over the FOB, which had an outer diameter of 3.1 mm (Olympus LF-DP, Tokyo, Japan).

During the intubation, the patient's head was placed in the sniffing position, and a jaw thrust was performed by one of two experienced assistants (CWL and KPL) by placing the fingers behind the posterior ramus of the mandible, with the thrust directed upward and the thumbs opening the mouth. After the glottis was exposed, the FOB was passed between the vocal cords and downward into the middle of the trachea. Care was taken to ensure that the tip of the FOB was not advanced too deep into the trachea, usually no more than 4 cm below the glottis, to avoid stimulation of the carina. A tracheal tube was then advanced over the FOB and rotated counterclockwise as the bevel of the tube negotiated the larynx (15). After the tracheal tube was inserted into the trachea, the jaw thrust maneuver was stopped. The FOB was then removed after confirmation of the correct tracheal tube placement. All fiberoptic intubations were performed by two anesthesiologists (FSX and HTS) who were experienced in both methods. Both anesthesiologists were similarly trained and each performed the FOI and FNI in more than 150 patients, including at least 40 children, before this study.

After the tracheal intubation was successfully accomplished, the tracheal tube was connected to the circle breathing system of an anesthesia machine. The lungs were then ventilated with intermittent positive pressure ventilation. Anesthesia was maintained with isoflurane and 60% nitrous oxide in oxygen. During the observation, a fresh gas flow of 1.5 L/min was used, and the ventilator settings and isoflurane concentration were adjusted to maintain end-expired carbon dioxide and isoflurane levels of 35–40 mm Hg and 1%, respectively. Inspired and end-tidal concentrations of isoflurane, oxygen, nitrous oxide and carbon dioxide were measured and displayed digitally with a multifunction monitor (Datex.Ohmeda F-CU8).

BP and HR were recorded immediately after anesthesia induction (postinduction values), at intubation and every minute for the first 5 min after intubation. The maximum and minimum values of BP and HR measured by the multifunction monitor during the observation period, from the beginning of anesthesia induction to 5 min after intubation, were also recorded. During the observation, a third person acted as the time keeper using a digital stopwatch, time zero was (zero seconds) when the facemask was removed from the patient. The time keeper recorded four further times using the "lap" function on the stopwatch, when the jaw thrust maneuver was stopped (duration of jaw thrust), when ventilation was restarted through the tracheal tube and carbon dioxide was detected by capnography (total intubation time), when the maximum values of SBP and HR occurred (times required to reach the maximum values of SBP and HR during the observation), and when SBP and HR recovered to within 10% of the postinduction values. If SBP and HR did not recover to within 10% of the postinduction values after 5 min following intubation, BP and HR were observed until the target values were achieved. The watch was stopped when SBP and HR recovered to the postinduction values.

Hypertension and hypotension were arbitrarily defined as a SBP more than 130% and <70% of a child's baseline value, respectively. Tachycardia and bradycardia were arbitrarily defined as a HR more than 120 and <65 bpm, respectively. A dysrhythmia was defined as any ventricular or supraventricular premature beat or any sustained rhythm other than sinus. The incidences of hypertension, hypotension, tachycardia, bradycardia, and dysrhythmia were recorded throughout the observation and compared between the two groups.

During the observation, no manipulation (including movement of head, tube fixation, and skin preparation of operating field) on any child was performed. The intubation manipulation was stopped if bradycardia occurred, or if the Spo₂ decreased to 95% or less. IV atropine (5–10 µg/kg) was administered to treat bradycardia and facemask ventilation with 100% oxygen was applied to correct arterial desaturation or hypoxemia. Children requiring more than one attempt to achieve successful intubation were excluded from statistical analysis of the data. The statistical analysis of data was performed with SPSS (Version 11.5 SPSS, Chicago, IL) and a POMS (Version 5.0, Shanghai Scientific and Technical Publishers, Shanghai, China) statistical software. The comparisons of gender distribution and incidence of hypertension, hypotension, tachycardia, bradycardia, and dysrhythmia between groups were done using a ² test. Demographic and clinical data from the two groups were compared using the two-tailed t-tests. The intragroup differences among the circulatory variables recorded over time were analyzed using the Friedman's repeated measures analysis of variance on ranks, with multiple comparisons versus baseline and postinduction values using the Dunnett's method. Intergroup differences among the circulatory variables recorded over time were analyzed by using the two-way repeated measure analysis of variance, with group as the independent sample factor and time as the repeated measurement factor. A significant group by time interaction was followed by tests of significance using the Tukey's method to compare the two groups at various points in time. The hypothesis of this study was that there would be a clinically meaningful difference in the hemodynamic responses to two fiberoptic intubation methods. Power analysis indicated that if the minimal clinically important difference in SBP was deemed to be 20 mm Hg and the expected standard deviation of residuals was 12.5 mm Hg, then a sample size of 26 children each group would be required when is 0.05 and ß is 0.2. To detect a 30% difference in the incidence of hypertension and tachycardia during the intubation, 33 children in each group would be required when is 0.05 and ß is 0.2. The quantitative data were expressed as mean ± sd. A P value of <0.05 was considered statistically significant for all tests.

	RESULTS

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Fiberoptic intubation was successfully completed with one attempt in all children. Twenty-one FNI and 23 FOI were completed by FSX, and the remaining intubations were performed by HTS. The proportions of the fiberoptic intubations completed by the two anesthesiologists were not significantly different between the two groups (P > 0.05). The times required to complete tracheal intubation by FSX and HTS were 39.9 ± 12.8 and 42.4 ± 13.3 s in the FNI group, respectively, 35.1 ± 13.1 and 33.8 ± 13.7 s in the FOI group. There was no significant difference in the times required to complete each fiberoptic intubation between the two anesthesiologists (P > 0.05). Both duration of jaw thrust and mean total intubation time were significantly longer in the FNI group, 35.2 ± 8.2 and 41.2 ± 11.1 s, than in the FOI group (28.3 ± 7.4 s and 34.4 ± 11.8 s). The two groups were similar with respect to demographic data and baseline values of BP and HR (Tables 1 and 2).

	DISCUSSION

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The primary goal of this investigation was to determine whether there is a clinically relevant difference between the circulatory responses to FOI and FNI in healthy anesthetized children. Using strict exclusion criteria, we controlled for factors known to interfere with BP and HR changes during intubation. There were no significant differences between groups in the distribution of gender, age, height, and weight. BP and HR were measured using the same monitor in both groups. Ventilation was controlled to normocapnia throughout the study period. To minimize bias, all fiberoptic intubation and jaw thrust maneuvers were performed by the same anesthesiologists experienced in the two procedures. To lessen the effect of rapidly changing inhaled anesthetic concentrations on circulatory variables (16), the inspired concentration of isoflurane was gradually increased to 1% during anesthesia induction and maintenance. In addition, preadministration of a small-dose fentanyl also helped to attenuate the circulatory responses to inhaled isoflurane (17).

It is well known that the stimuli to airway structures are the main causes of circulatory responses to tracheal intubation (16). FNI is a more time-consuming and more invasive airway procedure than FOI because both the tracheal tube and FOB have to be inserted through the nasal passage. As a result, nasotracheal intubation can cause stronger circulatory responses than orotracheal intubation (12,18–20). Previous work has suggested that the increase in BP after laryngoscopic nasotracheal intubation is significantly greater than that after laryngoscopic orotracheal intubation under the same condition (19,20). In addition, Shibata et al. (13) demonstrated that, in adults receiving neuroleptic analgesia and topical anesthesia, the circulatory responses to FNI were more severe than those to FOI. In contrast, our results showed that, in children undergoing general anesthesia, FNI resulted in milder and shorter circulatory responses than FOI. These contrasting results might be attributable to differences in study methods (sample size) and techniques of anesthesia and intubation. Differences between our study and that of Shibata et al. include topical application of 1:5000 epinephrine to the nasal mucosa, use of a rigid spiral tracheal tube during nasotracheal intubation, the inclusion of hypertensive patients (3/8), and prolonged airway manipulation because of airway topical anesthesia.

In addition, the nasal tube used in our study was made of soft-textured latex and was adequately lubricated before intubation. This may have alleviated the mechanical stimuli to the nasal cavity (nasopharynx), larynx, and trachea applied by the nasal tube itself. However, the oral tube used in our study was made of polyvinyl chloride with a stiffer texture, which could have resulted in a greater stimulus on passage through the airway. Also, the nasal spray of 2% lidocaine in our study could have produced topical nasal anesthesia, blocked the mechanical stimuli, and attenuated the circulatory responses to FNI. Previous studies (11–18,21) have demonstrated that nasotracheal intubation can cause a nasocardiac reflex, which is a vagal reflex and contributes to the significant bradycardiac response to the stimuli on nasal mucosa (22). This might be the main reason why the tachycardic response was less and of shorter duration in the FNI group than in the FOI group. Finally, the anatomy of the upper airway in children is characterized by an anterior larynx (large tongue), more anteriorly angulated glottis, and short neck (23). The passage of a FOB and tracheal tube through the nasal cavity tends to be more aligned with the laryngeal and tracheal axes than when introduced through the mouth (24); therefore, it is possible that FNI results in less friction and stimuli to the epiglottis, glottis, and trachea compared with the FOI.

Hirabayashi et al. (25) demonstrated that, in anesthetized adults receiving lightwand-guided tracheal intubation, the magnitude of stimulus from the jaw thrust maneuver was sufficient to cause circulatory responses similar to those observed in laryngoscopic intubation. Thus, one might argue that the differences in nociceptive stimulation from the jaw thrust maneuver cause the differences in the circulatory responses between the two fiberoptic intubation methods. But, it should be noted that in the study of Hirabayashi et al., the jaw was grasped and lifted upward using the thumb and index finger of the intubator's hand. However, Tong et al. (26) found that the mechanical stimulus of lingual traction plus jaw thrust performed by experienced anesthesiologists evoked less pressor response than that of Macintosh laryngoscopy when these interventions were followed by fiberoptic intubation. These results suggest that the airway clearance maneuver performed by experienced anesthesiologists possibly results in less nociceptive stimulation.

In this investigation, all jaw thrust procedures were performed by experienced anesthesiologists who received the same training for this airway maneuver. Despite the duration of jaw thrust being about 7 s longer in the FNI group than in the FOI group, FNI did not cause greater circulatory responses than FOI. The maximum circulatory responses also occurred at 13–30 s after completion of intubation, rather than during the jaw thrust maneuver. Our results correspond with those of previous studies (15,26,27). The jaw thrust maneuver requires less force and is easier in children (28), when compared with that in adults, which possibly results in less mechanical stimuli to the airway. Furthermore, it is also conceivable that the jaw thrust maneuver is a more gentle airway stimulus than the insertion of a FOB and tracheal tube.

Our study also showed that the times required to reach the maximum values of SBP and HR during the observation were significantly longer in the FNI group than in the FOI group. This may have resulted from a longer intubation time in the FNI group compared with the FOI group. But, the times from completion of intubation to reach the peak levels of SBP and HR were not significantly different between groups. It is suggested that the circulatory changes observed in this study were mainly attributed to the fiberoptic intubation procedures themselves. Therefore, we consider that the differences in mechanical nociception to the airway related to route of intubation account for the differences in the circulatory responses of the two fiberoptic intubation methods.

One problem of this study is that changing anesthetic concentrations may have been a cause for the observed circulatory changes. Adachi et al. (29) reported that fentanyl 2 µg/kg administered IV immediately before anesthesia induction with propofol 2 mg/kg (propofol was infused at 250 µg·kg^–1·min^–1 for 8 min) could completely abolish the circulatory responses to FOI in adults. But, our results showed that hypertension and tachycardia occurred in 18.2%–54.6% of children during the observation. In addition, in the FOI group, maximum increases in BP and HR during observation were also more than 20% of baseline values. It suggested that, in children, fentanyl 2 µg/kg administered IV 2 min before intubation failed to effectively blunt the circulatory responses to fiberoptic intubation. This different result may have contributed to the differences in times of fentanyl administered IV and study subjects between our studies and that of Adachi et al.

It is generally believed that administration of fentanyl at the optimal time may reduce the dose required to blunt circulatory responses during intubation. This is very important for children, because the reduced fentanyl dose also minimizes the risk of side effects such as hypotension, bradycardia and delayed recovery (30). But, the optimal time of administration and adequate dose of fentanyl blunting the circulatory responses to fiberoptic intubation in children has not been documented. It has been shown that in children aged 1–8 yr, fentanyl 3 µg/kg administered IV 5 min before anesthesia induction could provide adequate laryngoscopic orotracheal intubation conditions without significant circulatory changes (31). Our previous study (32) confirmed that, in anesthetized children, orotracheal intubation using a FOB and a direct laryngoscope caused similar circulatory responses. Based on the results of this study and previous studies (30–32), we consider that the effective dose of fentanyl blunting the circulatory response to FOI may be 3 µg/kg in healthy children, and that fentanyl should be administered IV 5 min before intubation. These problems deserve further study.

On the basis of the results of this study, we conclude that both FOI and FNI can cause significant circulatory responses in anesthetized healthy children, and the circulatory responses to FNI are fewer and of a shorter duration than those to FOI.

	Footnotes

 
Accepted for publication October 19, 2006.

This paper was presented as a Poster Discussion at the SPA/AAP Pediatric Anesthesiology 2006, February 16–19, 2006, Fort Myers, Florida.

	REFERENCES

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999