COMPARISON OF TWO METHODS OF FIBRESCOPE-GUIDED TRACHEAL INTUBATION

British Journal of Anaesthesia 1991; 66: 546-550

COMPARISON OF TWO METHODS OF FIBRESCOPEGUIDED TRACHEAL INTUBATION J. E. SMITH, A. A. MACKENZIE AND V. C. E. SCOTT-KNIGHT

We have compared intubation time and cardiovascular effects of fibrescope-guided orotracheal intubation aided by the Berman 11 Intubating Airway with those of the tongue traction method of fibreoptic intubation and with conventional Macintosh intubation. We studied 75 patients who received a standard genera/ anaesthetic which included non-depolarizing neuromuscular block; they were allocated randomly to one of the three groups immediately before intubation. The mean time required to effect Berman airway intubation (34.9 s) was similar to that required for tongue traction intubation (35.3 s) and significantly greater than that required for Macintosh intubation (11.7 s). The cardiovascular responses to both types of fibreoptic intubation were significantly greater and more prolonged than those of Macintosh intubation. There were no significant differences between the responses to the two fibreoptic techniques. Haemodynamic effects should be considered when performing fibrescope-guided trachea/ intubation under general anaesthesia and, when necessary, appropriate measures should be taken to minimize them.

KEY WORDS Intubation, trachea/: technique, complications. Equipment: fibreoptic laryngoscope.

The fibreoptic laryngoscope may permit tracheal intubation, often with ease, in awake or anaesthetized patients, when traditional methods have failed [1,2]. However, it has been shown that fibrescope-guided orotracheal intubation facilitated by anterior traction on the tongue under general anaesthesia requires a prolonged

intubation time and produces greater pressor and heart rate changes than intubation with the Macintosh laryngoscope [3]. Several types of pharyngeal guide and airway have been developed to facilitate fibreoptic laryngoscopy [4-8]. One of these devices, the Berman 11 Intubating Airway [9,10], is inexpensive and appears suitable for use as an aid to fibreoptic intubation, although it was introduced originally as an aid to blind intubation. It comprises a divided oropharyngeal airway through which the fibrescope can be passed co-axially and delivered close to the vocal cords. When the tip of the laryngoscope has been advanced a short distance into the trachea, the airway, which has a plastic hinge down the left side and a lateral opening down the right side, can be prized open and released from around the body of the laryngoscope. The tracheal tube may then be guided into the trachea over the laryngoscope. Use of this airway obviates the need for extrusion of the tongue and may reduce the amount of fibrescope manipulation required and the degree of fibrescope contact with pharyngeal mucosa. A decrease in pharyngeal stimulation might result in a decrease in reflex sympathetic activity and, if the airway enables fibreoptic intubation to be performed more rapidly, this may also minimize cardiovascular changes, since Stoelting has shown that increasing the duration of laryngoscopy increases the pressor response [11]. The object of this study was to compare the intubation time and cardiovascular responses of fibreoptic intubation aided by the Berman airway with those of fibreoptic intubation facilitated by This article is accompanied by Editorial II. J. E. SMITH, M.B., CH.B., F.C.ANAES.; A . A . M A C K E N Z I E , M.B., CH.B., F.C.ANAES.; V. C. E . SCOTT-KNIGHT, M.B., B.S.,

F.C.ANAES. ; Department of Anaesthesia, Selly Oak Hospital, Raddlebam Road, Selly Oak, Birmingham B29 6JD. Accepted for Publication: November 22, 1990.

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SUMMARY

FIBRESCOPE-GUIDED TRACHEAL INTUBATION

547

TABLE I. Age, weight and sex characteristics {mean (SEM) where applicable)

Control group (n = 25) Tongue traction group (n = 25) Bemoan airway group (n = 25)

Age (yr)

Weight (kg)

Sex (M/F)

33.0(1.5)

64.3 (2.4)

4/21

32.4 (1.6)

61.9(2.3)

6/19

32.3 (1.6)

65.0 (2.5)

5/20

PATIENTS AND METHODS

The study was approved by the Ethics Committee of the South Birmingham Health Authority and informed written consent was obtained from each patient. We studied 75 ASA class I or II patients aged 16-50 yr, undergoing elective gynaecological or general surgery requiring orotracheal intubation and mechanical ventilation of the lungs. Patients taking vasoactive drugs, the morbidly obese, those with a history of acid reflux or hiatus hernia and those in whom difficult intubation was expected were excluded from the study. Patients were premedicated 1 h before surgery with temazepam 20 mg orally. On arrival of the patient in the anaesthetic room, an appropriate vein was cannulated and the ECG monitored continuously. Arterial pressure and heart rate were measured at 1-min intervals using a recently calibrated Dinamap 1846 oscillotonometer and recorded with a Dinamap TR2000 printer. After a stabilization period of at least 5 min, baseline recordings were taken and anaesthesia was induced with a dose of thiopentone sufficient to obtund the eyelash reflex (usually 5 mg kg"1), followed by vecuronium 0.125 mg kg"1. The patient's lungs were ventilated with 1 % isoflurane and 50% nitrous oxide in oxygen using a Bain system and face mask with an initial fresh gas flow of 90 ml kg"1 min"1. A Datex Normocap capnometer sampling catheter was placed under the face mask and fresh gas flow rate and ventilation were adjusted to maintain the endexpired carbon dioxide concentration at 4.5-5 %. After 2 min of ventilation of the lungs, the patients were assigned on a random number basis (using sealed numbered envelopes) to the control group (intubation with the Macintosh laryngoscope), the tongue traction group (intubation with an

Olympus LF-1 fibreoptic laryngoscope with the aid of controlled tongue traction applied by an assistant) or to the Berman airway group (ribreoptic intubation using a Berman intubating airway). A Berman airway was then inserted into the pharynx in those patients assigned to the Berman group (medium size (90 mm) for males and small size (80 mm) for females) and a Guedel airway (size three for males and size two for females) was inserted into the pharynx of patients assigned to the other two groups. After a further 2-min period of ventilation, tracheal intubation was performed. The tongue traction fibreoptic intubations were carried out as described previously [2,3]. In the Berman fibreoptic intubations, the chin was elevated and the atlanto-occipital joint hyperextended by an assistant. The fibreoptic laryngoscope (onto which a tracheal tube had previously been threaded) was advanced through the airway, manipulated between the vocal cords, and advanced approximately 7.5 cm into the trachea. The Berman airway was then disengaged from the fibrescope, by means of the lateral opening, and withdrawn from the pharynx, and the tube was guided into the trachea by the fibrescope. Disposable, cuffed, Portex tracheal tubes (size 9 mm for males and size 8 mm for females), lubricated with KY jelly, catheter mount attached were used in all subjects. Successful intubation was confirmed by capnography. The intubation time was taken as the interval between removal of the face mask from the patient's face and reconnection of the Bain system to the catheter mount after intubation had been completed. If any intubation could not be completed within 60 s, the patient was withdrawn from the trial and the cardiovascular data obtained were not included in the results. Arterial pressure and heart rate measurements were continued for 5 min following successful tracheal intubation, after which surgery was allowed to proceed.

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anterior tongue traction and with conventional intubation using the Macintosh laryngoscope.

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548

Group

Time (s)

Control (n = 25) Tongue traction (n = 24) Berman airway (n = 24)

11.7 (0.7) [8-20] 35.3 (1.5) [25-54]* 34.9 (1.6) [25-55]*

Data were analysed using Student's paired t test (within groups) and analysis of variance (between groups). P < 0.05 was deemed significant. RESULTS

The three groups were similar in age, weight and sex (table I). The mean times for successful intubations in the tongue traction group (35.3 s) and in the Berman group (34.9 s) were significantly greater than in the Macintosh group (11.7 s). There was no significant difference between the intubation

TABLE I I I . Mean (SEM) systolic (SAP) and diastolic (DAP) arterial pressures in control, tongue traction and airway groups. *P < 0.05 compared with values before intubation

Time after intubation (min) Group Control (n = 25) SAP (mm Hg) DAP (mm Hg) Tongue traction (« = 24) SAP (mm Hg) DAP (mm Hg) Berman airway (n = 24) SAP (mm Hg) DAP (mm Hg)

Before induction

Before intubation

1

2

3

4

5

121 (3) 70(2)

116(3) 70(2)

141 (4)* 94(2)*

134 (4)* 79 (2)*

122(3) 73(2)

116(3)* 67 (2)*

113(2)* 64(2)*

116(2) 68(2)

115(4) 67(2)

141 (4)* 97 (3)*

153 (4)* 91 (3)*

138 (4)* 81 (3)*

128 (4)* 76 (3)*

122 (4)* 71(3)

120(3) 69(2)

121 (3) 72(2)

137 (4)* 90(3)*

153(3)* 89 (2)*

140 (4)* 79 (2)*

132(4)* 74 (2)*

122 (3) 67(2)

TABLE IV. Mean (SBM) values of heart rate (beat min'1) in control, tongue traction and airway groups. *P < 0.05 compared with values before intubation

Time after intubation (min) Group Control (n = 25) Tongue traction (n = 24) Berman airway (n = 24)

Before induction

Before intubation

80(2)

88(2)

102(2)

98 (2)*

95 (2)*

91 (2)

88 (2)

76(2)

84(3)

102(3)

102 (2)*

101 (3)*

98 (3)*

96 (4)*

77(3)

88(3)

99(4)

105(4)*

102(3)*

100(4)*

94(3)*

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times of the two fibreoptic groups (table II). Intubation of the trachea in one patient in the tongue traction group could not be completed within the 60 s allowed because of inadequate clearance between the base of tongue and posterior pharyngeal wall. There was also one failure in the Berman group when the tip of the airway entered the left pyriform fossa. As the airway was withdrawn slightly to correct this, obstruction by the tongue became a problem which could not be surmounted within the time allocated. In these two patients, tracheal intubation was performed uneventfully using the Macintosh laryngoscope. Details of the changes in mean arterial pressures and heart rates within the three groups are summarized in tables III and IV. Analysis of variance showed no significant differences between the three groups before tracheal intubation. Intubation resulted in significant differences between the control group and tongue traction and Berman groups with respect to systolic pressure (P= 1.3E-7), diastolic pressure (P = 6.8£-7)

TABLE II. Time to achieve successful intubation (mean (SEM) [range]). *P < 0.05 compared with control values

FIBRESCOPE-GUIDED TRACHEAL INTUBATION and heart rate (P = 3.6E—3). There were no significant differences between the tongue traction and Berman airway groups at any stage. DISCUSSION

This investigation has demonstrated that both the controlled tongue traction and the Berman airway methods of fibreoptic intubation caused a

significantly greater and more sustained increase in arterial pressure and heart rate than Macintosh intubation. The pressor effects may be related to the extended period of airway intervention which characterizes both these methods of intubation, as Stoelting [11] has demonstrated that increasing the duration of Macintosh laryngoscopy caused a progressive increase in mean arterial pressure. However, it is possible that other mechanisms may also be involved. When examining the effects of laryngoscopy with and without tracheal intubation, Shribman, Smith and Achola [14] observed that Macintosh laryngoscopy alone generated a significant increase in arterial pressure and plasma concentrations of catecholamine, and that tracheal intubation caused little additional response. They suggested, therefore, that tissue tension in the supraglottic region produced by the rigid laryngoscope blade was the major cause of the pressor response. However, this investigation has shown that fibreoptic laryngoscopy and intubation produced a greater pressor response, even though the tongue traction method is associated with little, and the Berman airway with no, increase in supraglottic tissue tension. It is possible, therefore, that superficial stimulation of the pharyngeal mucosa and glottic and tracheal stimulation contribute to the pressor response associated with fibreoptic intubation, particularly as they are applied for an extended period. Shribman, Smith and Achola [14] reported also that significant increases in heart rate did not occur during Macintosh laryngoscopy alone, but became evident only after intubation of the trachea. This is consistent with earlier work by King and colleagues [15], and implies that glottic and tracheal stimulation may be more important determinants of chronotrophic effects than supraglottic stimulation. This may explain why fibreoptic intubation elicited a greater tachycardia than Macintosh intubation, as insertion of the fibrescope itself into the trachea, in addition to the tracheal tube, may represent a more noxious stimulus. This explanation would also be compatible with the findings of Smith and colleagues [16], who studied the differences between Macintosh and fibreoptic nasotracheal intubation. In this study, the mean fibreoptic intubation time was only 25% greater than mean Macintosh intubation time and the arterial pressure responses were broadly similar, whereas the tachycardia was significantly greater and more sustained in the fibreoptic group.

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This study has confirmed a previous report that orotracheal fibreoptic intubation facilitated by direct tongue traction under general anaesthesia takes three times longer to perform than Macintosh intubation [3], even by experienced personnel. While the technical limitations of current instruments and the presence of airway secretions may account for some of this delay, perhaps the most intractable problem is that the base of tongue and epiglottis fall backwards and tend to obstruct the pharyngeal lumen [12,13]. Anterior displacement of the tongue is therefore a vital factor for successful endoscopy in anaesthetized patients. One way of achieving this is by extrusion of the tongue, but an alternative approach is to advance the fibrescope through a modified pharyngeal airway, which not only retracts the tongue anteriorly but also directs the fibrescope towards the larynx. Several types of pharyngeal guide and airway have been described and recommended as useful adjuncts to fibreoptic laryngoscopy [4-8], although there have been no controlled trials to support these claims. We found that, when the Berman airway was used, many of the laryngoscopies were indeed easy. The vocal cords were presented directly ahead of the distal end of the airway and it was simple to advance the laryngoscope into the trachea. However, time was lost in extricating the airway from the pharynx and removing it from around the fibrescope before the intubation could be completed. In a minority of cases, the airway did not come to lie in such a favourable position and either failed to control the tongue and epiglottis satisfactorily or entered one of the pyriform fossae, and on these occasions considerable delay and difficulty were experienced. We therefore conclude that, although the airway may be useful in some fibreoptic intubations, it does not reliably expedite the procedure, as indicated by the rinding that the mean intubation time was similar to that required for the tongue traction method and substantially in excess of that of Macintosh intubation.

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5. Patil V, Stehling LC, Zauder HL, Koch JP. Mechanical aids for fiberoptic endoscopy. Aneslhesiology 1982; 57: 69-70. 6. Rogers SN, Benumof JL. New and easy techniques for fiberoptic endoscopy-aided trachea] intubation. Aneslhesiology 1983; 59: 569-572. 7. Hogan K, Harpur MH, Pollard BJ. Use of a pharyngeal guide to aid intubation with the fibreoptic laryngoscope. Anaesthesia and Intensive Care; 12: 18—21. 8. Ovassapian A. A new fiberoptic intubaung airway. Anesthesia and Analgesia 1987; 66: S132. 9. Berman RA. A method for blind oral intubation the trachea or esophagus. Anesthesia and Analgesia 1977; 56: 866-867. 10. Latto IP. Management of difficult intubation. In: Latto IP, Rosen M, eds. Difficulties in Tracheal Intubation. Eastbourne: Bailhere Tindall, 1985; 131. 11. Stoelting RK. Circulatory changes during direct laryngoscopy and tracheal intubation: influence of duration of laryngoscopy with or without prior lidocaine. Anesthesiology 1977; 47: 381-384. ACKNOWLEDGEMENTS 12. Sia RL, Edcns ET. How to avoid problems when using the fibreoptic bronchoscope for difficult intubations. We thank the following companies who loaned the equipment Anaesthesia 1981; 36: 74-75. used in this study: KeyMed U.K. (Olympus LF-1 fibreoptic laryngoscope), Critikon U.K. (Dinamap 1846 monitor and 13. Boidin MP. Airway patency in the unconscious patient. British Journal of Anaesthesia 1985; 57: 306-310. TR2000 printer) and Vickers Medical (Datex Normocap). 14. Shribman AJ, Smith G, Achola KJ. Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation. British Journal of Anaesthesia 1987; REFERENCES 59: 295-299. 1. Raj PP, Forestner J, Watson TD, Morris RE, Jenkins 15. King BD, Harris LC, Greifenstein FE, Elder JD, Dripps MT. Technics for fiberoptic laryngoscopy in anesthesia. RD. Reflex circulatory responses to direct laryngoscopy Anesthesia and Analgesia 1974; 53: 708-714. and tracheal intubation performed during general anesthesia. Anesthesiology 1951; 12: 556-566. 2. Witton TH. An introduction to the fiberoptic laryngoscope. Canadian Anaesthetists Society Journal 1981; 28: 16. Smith JE, Mackenzie AA, Sanghera SS, Scott-Knight 465--168. VCE. Cardiovascular effects of fibrescope-guided nasotracheal intubation. Anaesthesia 1989; 44: 907-910. 3. Smith JE. Heart rate and arterial pressure changes during fibreoptic trachcal intubation under general anaesthesia. 17. Ovassapian A, Yelich SJ, Dykes MHM, Brunner EE. Anaesthesia 1988; 43: 629-632. Blood pressure and heart rate changes during awake fiberoptic naiotracheaJ intubation. Anesthesia and Anal4. Wang JF. Fiberoptic laryngoscope guide and protector. gesia 1983; 62: 951-954. Anesthesia and Analgesia 1977; 56: 126-127.

In conclusion, we observed that the Berman airway appeared to have no advantage over tongue traction with regard to the speed of intubation, and it was not an effective method of attenuating the pressor response to fibreoptic intubation. Anaesthetists should be aware that the cardiovascular disturbances produced by both types of fibreoptic intubation are of an order which may be hazardous in debilitated or frail patients. If fibreoptic techniques are indicated in such patients, awake intubation under local anaesthesia should be considered [17]. Alternatively, in the event of unexpected difficult intubation under general anaesthesia, pharmacological methods should be used to attenuate the pressor response.