Radiotherapy for carcinoma of the head and neck cause a wide variation in acute and late tissue reactions including oedema, soft tissue necrosis, laryngeal sclerosis and cervical fibrosis . These side-effects can potentially compromise the airway management. Fibreoptic endoscopy-aided tracheal intubation has been reported to be difficult in patients after cervical radiotherapy . However, we found neither reports documenting the incidence of difficulties during fibreoptic-guided intubation in this selected group of patients nor published data concerning predictive factors indicating possible difficulties during this procedure. Therefore, we undertook this study to ascertain prospectively the incidence of difficult fibreoptic-guided intubation in patients after radiotherapy of the head and neck. We also evaluated the usefulness of several bedside tests for airway assessment to predict difficult fibreoptic-guided intubation in these patients.
The study was approved by our hospital Ethics Committee and written consent was obtained from all patients. Eighty-six patients with previous radiotherapy of the neck scheduled for eye nose and throat (ENT) surgery who required tracheal intubation with general anaesthesia were prospectively included in the study. All patients had been treated with a standard irradiation dose (60-70 Gy) for carcinoma, in some cases combined with concomitant chemotherapy, either as primary therapy or after tumour resection. Preoperatively a detailed airway examination was performed in each patient. This included the following tests:
(a) modified Mallampati classification;
(b) thyromental distance;
(c) ratio of patient's height to thyromental distance;
(d) mouth opening (interincisor distance);
(e) protrusive ability of the mandible (protrusion of the lower incisors anterior to the upper incisors (categorized as 'possible', 'restricted' or 'severely restricted');
(f) range of head and neck movements (categorized as '>90°', '90°-70°' and '<70°');
(g) the possibility to laterally displace the thyroid cartilage with a two-finger grip (categorized as 'possible' or 'not possible');
(h) the assessment of laryngeal oedema investigated trans-orally with the aid of a magnifying 90° rigid endoscope.
The oedema was classified as 'no oedema', 'moderate' or 'severe' clinically corresponding to beginning breathing difficulties. Every patient was asked for a deep breathing manoeuvre and the result ('audible' stridor) recorded. Signs of hoarseness were also registered. The interval between last irradiation and current surgery as well as concomitant chemotherapy were documented. All patients underwent standard monitoring, including pulse oximetry (SPO2), electrocardiogram, non-invasive blood pressure and capnography after intubation.
Fibreoptic-guided intubation was performed with the patient breathing spontaneously with the nasal route preferred. Patients were normally positioned supine, however, those who could not lie flat were allowed to adopt a sitting position during the intubation procedure. Following an airflow test, cocaine 4% was applied by cotton pledget for topical anaesthesia into the more patent nostril. Then step-by-step cocaine 4% 1.5-2 mL was applied through the working channel of the fiberscope to obtain topical anaesthesia. After awaiting the clinical effect of topicalization, the tracheal tube was threaded over the scope into the trachea. Fibreoptic visualization of the vocal cords was classified as 'normal' (vocal cord localization with minimal to moderate manipulation) or 'difficult' (vocal cord localization only with the help of the patient by a deep breathing manoeuvre). Number of endoscopic attempts, adverse events like bleeding, laryngospasm and oxygen desaturation were recorded on a data sheet. After accomplishing intubation, anaesthesia was induced with thiopental, alfentanil (0.5-1.5 mg), and maintained with sevoflurane in oxygen/air. At the end of surgery just before extubation a cuff leak test was performed with the endotracheal tube occluded. In case of a positive result (air leak) the tube was removed.
For normally distributed variables, mean values are given with standard deviation (SD) and range. Relative frequencies of unpaired samples were compared using Fisher's exact test. The Mann-Whitney U-test was used for comparison of unpaired samples of continuous data. For univariate analysis of predictive ability of prognostic variables, the likelihood ratio (i.e. the ratio of post- and pre-test probability of difficult intubation) for each potential predictor was calculated. In case of having several classes the variable with the maximum predictive ability was selected by dichotomy. Confidence limits of likelihood ratios were calculated. Two-tailed P-values ≤0.05 were considered significant.
The study population consisted of 73 male and 13 female (ASA III-IV) with a mean ± SD age of 56 ± 10 yr (range: 18-75 yr), height of 170 ± 9 cm (146-200 cm) and weight of 65 ± 11 kg (41-92 kg). The mean interval between end of irradiation and intubation was 26 ± 40 months (1-173 months). Intubation was classified as difficult in five patients (6%). Difficulty of fibreoptic-guided intubation was significantly associated with the preoperative presence of laryngeal oedema, hoarseness and stridor. None of the 'classical' predictive bedside tests applied to identify difficult direct laryngoscopy reached significance in predicting difficulties during intubation in our study. Table 1 shows the likelihood ratios of significant predictors. In four patients tracheostomy was performed by surgeons at the end of surgery. All other patients could be extubated without problems after a positive cuff leak test. In two of the patients with difficult fibreoptic-guided intubation oxygen saturation dropped below 90% during the necessary second attempt.
We observed an overall rate of 6% of difficult fibreoptic-guided intubation in patients after cervical radiotherapy. This rate is higher than reported in previous studies with rates of 2-5% [3,4], however, in our series only patients after irradiation of the neck are included. In our investigation difficulty during fibreoptic-guided intubation was significantly associated with radiation-induced oedema. In this situation it was the decisive advantage to have the patient awake and co-operative because a deep active breathing manoeuvre enabled successful intubation even under difficult anatomical circumstances.
Our results clearly demonstrate that after cervical radiotherapy severe laryngeal oedema as well as hoarseness and stridor are strong predictors of difficult fibreoptic-guided intubation. Especially the presence of severe laryngeal oedema increases the likelihood of a difficult fibreoptic-guided intubation by a factor of 16. None of the 'classical' predictive bedside tests applied to identify difficult direct laryngoscopy was helpful in predicting difficulties in our study. Our results confirm the previous investigation demonstrating that most factors contributing to difficulties during direct laryngoscopy are different from those causing difficulties during fibreoptic-guided intubation .
In conclusion, in patients who had undergone radiotherapy of the head and neck we found a rate of 6% of difficult fibreoptic-guided intubation. Such difficulty was significantly associated with preoperative presence of larynx oedema, hoarseness and stridor.
H. J. Schmitt
Department of Anaesthesiology; Friedrich-Alexander University Erlangen-Nuremberg; Erlangen, Germany
Department of Otorhinolaryngology, Head and Neck-Surgery; Friedrich-Alexander University Erlangen-Nuremberg; Erlangen, Germany
Institute of Medical Informatics, Biometry and Epidemiology; Friedrich-Alexander University Erlangen-Nuremberg; Erlangen, Germany
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