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Original Article

Disposable laryngoscope blades do not interfere with ease of intubation in scheduled general anaesthesia patients

Galinski, M.*; Adnet, F.*; Tran, D.; Karyo, Z.; Quintard, H.; Delettre, D.; Lebail, E.; Guignard, B.; Lebrault, C.; Chauvin, M.

Author Information
European Journal of Anaesthesiology: September 2003 - Volume 20 - Issue 9 - p 731-735

Abstract

Anaesthesia providers must take appropriate precautions to reduce the potential transmission of infectious agents to patients under their care. Cross contamination during anaesthesia has rarely been proved but there is, probably, an underestimation of this risk [1-6]. In 1997, a new variant of Creutzfeld-Jakob disease was discovered after a biopsy of the tonsil [7]. Chemical decontamination is fraught with problems; duration (not <50 min), device corrosion, need for trained sterilization personnel, environmental pollution and incomplete effectiveness. For all these reasons, disposable devices have been made available for anaesthesia. Disposable sheaths have been assessed and it has been shown that 16% of the patients experienced difficulties in intubating the trachea [8]. On the other hand, the Vital View® laryngoscope (Vital Signs Inc, Totowa, NJ, USA) with disposable blades produced a brighter field than a metal laryngoscope with no difference in the view of the glottis or the success rate of tracheal intubation [9]. The purpose of this observational study was to assess intubation quality with the use of this new disposable equipment under usual intubating conditions.

Methods

We performed a prospective observational survey. During a 2-month period, anaesthetists were asked to complete daily questionnaires regarding the difficulty of endotracheal intubation experienced using Vital View® disposable laryngoscope blades (Fig. 1). At the start of the study, anaesthesiologists and nurse anaesthetists had used the disposable blades for the previous 18 months. Disposable blades was made from glazed nylon and the fibreoptic bundle was a mixture of acrylic and Plexiglas® (Vital Signs Inc, Totowa, NJ, USA). In our hospital, it is normal practice to use a disposable blade for anaesthesia but these disposable laryngoscope blades were available in only two of the four operating rooms due to a paucity of the product-specific handles. The choice of type of blade (conventional metal 'Macintosh' blade or disposable 'Macintosh' blade) for the first attempt at intubation depended only on the operating room assignment. In the case of difficult intubation, the operator had the option to switch from a disposable to a conventional blade. Anaesthesia teams were made up of nine anaesthesiologists and eight nurse anaesthetists, three resident anaesthesiologists and two nurse anaesthetist students. Everybody rotated between the four operating rooms. After intubation, the anaesthetist completed the questionnaire. The view of the glottis during laryngoscopy was assessed by the modified Cormack and Lehane classification [10] without external laryngeal manipulation, during the first attempt. This classification involves four grades of glottic visualization; Grade 1 corresponds to complete visualization of the vocal cords, Grade 2 to visualization of the inferior portion of the glottis, Grade 3 to visualization of only the epiglottis and Grade 4 to a non-visualized epiglottis. Difficult laryngoscopy was defined as a Cormack and Lehane Grade 3 or 4 [10]. The difficulty of intubation was assessed using the intubation difficulty scale (IDS) score [11]. This scale is based on the determination of seven parameters: N1, the number of supplementary intu-bation attempts; N2, the number of supplementary operators; N3, the number of alternative intubation techniques used; N4, the glottis exposure defined by the Cormack and Lehane Grade (Grade 1: N4 = 0, Grade 2: N4 = 1, Grade 3: N4 = 2 and Grade 4: N4 = 3); N5, the lifting force applied during laryngoscopy (N5 = 0 if little force was necessary and N5 = 1 if subjective increased lifting force was used); N6, the necessity of applied external laryngeal pressure for improved glottic exposure (N6 = 0 if no external pressure was applied and N6 = 1 if external laryngeal pressure was necessary) and N7, the position of vocal cords at intubation (N7 = 0 if the vocal cords were in abduction or if they were not seen and N7 = 1 if the vocal cords were adducted blocking the passage of the tube). The IDS score is the sum of N1 through N7. A score of 0 represents an ideal intubation; one performed by the first operator on the first attempt, with use of the first technique and with full visualization of the glottis and little effort. An IDS score between 1 and 5 represents slight difficulty and an IDS score >5 represents moderate to major difficulty. If intubation is impossible, the IDS score is the value attained before abandonment of intubation attempts.

Figure 1
Figure 1:
Daily questionnaires regarding the difficulty of endotracheal intubation experienced using Vital View® disposable laryngoscope blades.

Other parameters obtained from the anaesthetic record were size of used blade, physical status (height, weight, age, ASA Grade) and airway assessment factors (mouth opening, thyromental distance modified Mallampati classification and amplitude of neck and head movement). Pathological conditions associated with difficulty in laryngoscopy (such as malformation of the face, cervical spondylosis, tumour of the airway, long-standing diabetes mellitus, sleep apnoea syndrome and any loose teeth) were also recorded. We distinguished two kinds of operators according to experience of intubation (number of yr): juniors (<1 yr) and seniors (>1 yr).

Statistical analysis

The χ2 and Fisher's exact test were used for comparison of qualitative variables. Assuming a percentage of laryngoscopy with Cormack and Lehane Grade 3 or 4 of around 10%, we calculated the appropriate sample size using an α of 0.05 and a power of 0.80 with the Casagrande and Pike formula [12]. A minimum of 97 intubations for each group should be included to see an increase of 15% in Cormack and Lehane Grade 3 or 4 difficult intubations. Statistical analysis was made using Statview Software (Stat View® v. 4.1; Abacus Concepts, SAS Institute, Berkeley, CA, USA). P < 0.05 was considered significant.

Results

The anaesthetic staff recorded 219 intubations over 2 months. We distinguished two intubation groups, one using disposable blades (DB group) and the other using conventional blades (CB group). Fifty-four percent of first laryngoscopies were performed with disposable blades (n = 119) and 46% with conventional blades (n = 100). Table 1 describes patients and operator characteristics. There were no significant differences between the two groups in any of the variables tested. Table 2 shows the Cormack and Lehane grade distribution in the two groups. There were no significant differences between the two groups for Cormack and Lehane score of 3, for IDS score >5 and for IDS score of 0 (Table 3). There were 21 changes of operators, 10 in the disposable blades and 12 in the conventional blades. There were 12 blade changes before successful intubation. In 10 cases, a change from a disposable blade to a conventional Macintosh blade was undertaken and in two cases only a change in blade size was required. In five cases, there were changes from size 3 to 4, and in one case from size 4 to 3. There was no size change in one case. In five cases data were missing.

Table 1
Table 1:
Baseline characteristics of patients of DB and CB groups.
Table 2
Table 2:
Distribution of Cormack and Lehane grades between DB and CB groups.
Table 3
Table 3:
Difficulty of laryngoscopy, IDS score distributions among patients in DB and CB groups.

A short introducer was placed into the tube in nine cases, five times in the disposable blades (4%) and four times in the conventional blades (4%). There were blade changes in only one of these cases; from a conventional blade size 4 to size 3.

Discussion

Our study did not detect any significant differences between the DB and CB groups for ease of intubation. The Vital View® laryngoscope with disposable blades has been assessed by Asai and colleagues and their results were similar to ours, without significant difference in the view of the glottis or the success rate of tracheal intubation [9]. However, these authors did not assess the complexity of the intubation procedure in its entirety. The main predictive factor of intubation difficulty is the view of the larynx. On the other hand, Adnet and colleagues showed that 61.7% of intubations with Cormack and Lehane scores of 3 were completed at first attempts [11]. The improvement of our study is that we assessed both the intubation and laryngoscopic difficulties with the IDS, which comprises seven factors that have been identified as being associated with difficult endotracheal intubation. The incidence of difficult intubation varies markedly among studies, ranging from 0.05 to 18% [20]. One of the most frequently used criteria for diagnosis of difficult intubation is Cormack and Lehane's classification. The incidence of Cormack 3 or 4 Grade laryngoscopy found in the literature is 2-13% [13-15]. However, the quality of glottic exposure depends on the presence or absence of external laryngeal manipulation. Without such manipulation, the incidence is 8-13% [14,16]. Our results were similar to the latter (11%). The IDS score permitted identification of intubation without difficulty (IDS = 0) and intubation involving moderate to major difficulty (IDS > 5). In a prospective observational study in the operating room concerning 1171 patients, IDS was 0 in 55%, and >5 in 8% of the patients [15]. Our results were similar to the latter (50% and 8%, respectively). We neither assessed the incidence of difficult ventilation nor oxygen desaturation during intubation attempts. In our institution, we follow the French guidelines with respect to dealing with cases of difficult intubation; in most cases we use a fibreoptic technique [19].

The weakness of our survey was lack of randomization, whereas Asai and colleagues used a randomized crossover design. Nevertheless, Benson and Hartz demonstrated in a comparison of observational studies and randomized controlled trials, that in most cases results were similar [17]. We took advantage of the fact that these new laryngoscopes were only available in half of our operating rooms, allowing a comparison without altering existing anaesthetic practice.

It is time to replace conventional laryngoscope blades with disposable ones as most studies have demonstrated that a risk of cross contamination exists. Indeed, on the one hand occult blood and infectious agents have been found on laryngoscopes, and on the other hand decontamination procedures are not perfect [1-6]. The incidence of the presence of occult blood on blades and handles after washing and decontamination was 10.5-20% and 40-50%, respectively [1-3]. Two reports of iatrogenic infection related to the repeated use of laryngoscopes have been reported [4,5]. One study found that 42% of adult blades were contaminated with microbes after routine use [6]. In 1997, a new variant of Creutzfeld-Jakob disease was discovered after tonsillar biopsy [7].

Airway control devices are classified in accordance with contamination risk (defined by the Spaulding classification) [24]. Laryngoscopes belong to the high-risk category and sterilization is by autoclaving at 134°C for 18 min. Since 2001, according to the French guidelines, medical devices have to be disposable - if commercially available - if there is any risk of transmissible non-conventional agents and if quality of care and security are to be ensured. If there is no disposable device available, management depends on patient status (with risk of transmissible non-conventional agents or not) and on which tissue is in contact with the device [21-23]. In anaesthesia, laryngoscope blades are in contact with lymphoid tissues (tonsils). Autoclaving at 134°C for 18 min leads to a degradation in the reliability of the device, which becomes rapidly less usable [18]. The cost of disposable blades has decreased over the last several years. The current price is €3.45 per blade. For conventional metal blades, the cost per use is €2.29 per blade if sterilization, personnel time and stocking of devices are taken into account [25].

Conclusion

In routine use the Vital View® appears to be an efficient device because it does not modify the ease of endotracheal intubation in most cases. Nonetheless, it may be advisable to maintain conventional laryngoscopes in reserve in case of difficult intubation. Additional studies will be necessary to confirm these results.

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Keywords:

ANALYTICAL, DIAGNOSTIC AND THERAPEUTIC TECHNIQUES AND EQUIPMENT CATEGORY, equipment and supplies, disposable equipment; INTUBATION, INTRATRACHEAL

© 2003 European Academy of Anaesthesiology