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Original Article

Fibre-optic intubation teaching in sedated patients with anticipated difficult intubation

Gueret, G.*; Billard, V.; Bourgain, J.-L.

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European Journal of Anaesthesiology (EJA): March 2007 - Volume 24 - Issue 3 - p 239-244
doi: 10.1017/S0265021506001475
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Abstract

Introduction

Fibre-optic tracheal intubation is included in most anaesthesia residents’ training programmes as a useful technique in the management of difficult airway. It is often initially taught in anaesthetized patients without anticipated difficult intubation which does not prepare students for the difficulties encountered during real difficult airway management (e.g. airway obstruction, anatomical changes).

Teaching fibre-optic intubation in an awake patient with anticipated difficult intubation may be tricky because the senior anaesthesiologist is not comfortable in giving advice if the patient is listening and the junior’s inexperience may worsen patient anxiety and agitation, and increase the difficulties of the procedure.

Propofol light general anaesthesia has been demonstrated to improve both operator’s and patient’s comfort during routine fibre-optic intubation but may worsen airway patency. It is unclear in the literature whether this type of anaesthesia could be safely used for teaching with regard to the clumsiness and slowness expected from residents in training.

The aim of this prospective study was to compare the efficacy and safety of fibre-optic intubation performed by trainees vs. a senior anaesthesiologist on patients with anticipated difficult intubation, anaesthetized by propofol.

Patients and methods

After informed consent, patients with upper airway cancer scheduled for surgery under general anaesthesia with intubation were prospectively included if they had at least two among the following criteria of anticipated difficult intubation:

  1. Previous difficult intubation.
  2. Systemic diseases usually associated with difficult intubation.
  3. Clinical symptoms of airway impairment.
  4. Inter-incisor gap <50 mm and impossible mandibular luxation.
  5. Short thick neck.
  6. Thyro-mental distance <65 mm.
  7. Head and neck movement <90°.

Patients with a preoperative upper airway major obstruction or with a large laryngeal tumour were excluded because general anaesthesia may induce complete airway obstruction.

The operator was not randomized: residents usually performed all scheduled fibre-optic tracheal intubation (LF3 Olympus with video remote display) under the supervision of a senior anaesthesiologist, whatever the expected difficulty of the case. All of them had previously performed less than 10 fibre-optic intubations, but had participated in a workshop on manikins. When no resident was present in the operating room, as the day after a night call or during theoretical course sessions, a senior anaesthesiologist with more experience (more than 100 fibre-optic intubations) performed intubation. In both groups, all intubations were performed during working hours.

Patients did not receive any preoperative sedative drugs and were fasting for at least 8 h. Perioperative monitoring included a three-lead electrocardiogram, pulse oximetry (SPO2), non-invasive blood pressure (BP) and capnograph after tracheal intubation.

In case of nasal intubation, 0.5% lidocaine with naphazoline was applied to the nasal cavities 10 min before anaesthesia. The ‘spray as you go’ method was chosen to apply local anaesthetic on airway mucosa.

After 3 min of pre-oxygenation, induction was performed using a loading dose of propofol (1.5 mg kg−1) administered over 2 min followed by a continuous infusion of 10 mg kg−1 h−1, which was assumed to maintain a predicted plasma concentration of around 3.5 μg mL−1 [1] and to produce loss of verbal response while maintaining spontaneous ventilation. No other drug was given. In case of light anaesthesia (cough or movement), a bolus of propofol (0.5 mg kg−1) was injected and the infusion rate increased by 5 mg kg−1 h−1 (i.e. predicted concentration increased by 50%). When systolic arterial pressure decreased below 80 mmHg or if apnoea developed, the propofol infusion rate was decreased to 6 mg kg−1 h−1. During the whole procedure, pharyngeal oxygen was administered at 10 L min−1. Before tracheal passage of the fibre-optic bronchoscope, 3 mL of 2% lidocaine were injected above the vocal cords.

In case of upper airway obstruction that could not be reversed with simple manoeuvres, a transtracheal jet ventilation machine was ready to be used and the surgeon was ready to perform an emergency tracheotomy.

Preoperative assessment included patient characteristics parameters (age, height, weight, sex), difficult intubation criteria as listed above, calculation of the Arne score [2], as well as specific criteria related to ear, nose and throat (ENT) tumour: tongue mobility, cervical radiotherapy, cervical sclerosis, tumour location (laryngeal or hypopharyngeal) and previous ENT surgery.

Adequacy of spontaneous ventilation during fibroscopy was expressed by:

  1. The incidence of hypoxaemia based on continuous SPO2 monitoring (SPO2 < 90%).
  2. Clinical upper airway obstruction.
  3. Laryngospasm identified during fibroscopy.
  4. Apnoea.
  5. Post intubation ETCO2 in mmHg.

Intubation conditions assessment included the following parameters:

  1. Duration of intubation (nasal or oral) defined as the time elapsed between starting fibroscopy (patient unconscious) and the first respiratory cycle observed on the capnograph after intubation.
  2. Propofol total dose and number of propofol boluses.
  3. Bleeding which impaired glottis visualization.
  4. Intubation was deemed a failure and aborted if intubation time exceeded 900 s or if the number of attempts was higher than three or oxygen saturation decreased below 85%.

Heart rate (HR) and non-invasive BP were recorded every 2 min. Cardiovascular instability was defined as hypertension (systolic BP higher than 160 mmHg), hypotension (systolic BP lower than 80 mmHg), tachycardia (HR higher than 120 bpm) or bradycardia (HR lower than 60 bpm).

Results are presented as mean ± standard deviation (SD) or number of patients. t-test was used to compare continuous variables. For discrete variables, Fisher’s exact test was used when there were two groups to be compared, and X2-test was used when there were more than two groups to be compared. P < 0.05 was considered as significant.

Results

Forty-six patients were included, 26 in the resident group and 20 in the senior group. Preoperative assessment variables (Table 1) and intubation conditions (Table 2) were similar in both groups.

Table 1
Table 1:
Relevant factors of preoperative assessment in both groups.
Table 2
Table 2:
Anaesthesia/intubation description (number of patients or mean ± SD).

The incidence of intubation events was similar in both groups (Table 3). The senior managed without difficulty the four patients who could not be intubated by the junior. In one case, oesophageal intubation was recognized by capnography but was responsible for an episode of low oxygen saturation; the patient was successfully intubated at the second fibre-optic attempt by the senior anaesthesiologist. In the senior group, fibre-optic intubation failed in one patient because a pharyngeal delta-pectoral flap hid the glottis and emergency tracheotomy was required after transtracheal ventilation.

Table 3
Table 3:
Intubation events (number of patients).

Apnoea (n = 6) occurred in all cases just after the loading dose of propofol and was reversed by patient stimulation. Laryngospasm (n = 3) was successfully treated by stopping airway stimulation and giving a propofol bolus. Upper airway obstruction (n = 3) was controlled by adjusting the neck position and by lifting the jaws. Cardiovascular event rate was similar in both groups (Table 3). No bradycardia was observed.

Discussion

Our data showed that non-experienced anaesthesiologists could perform fibre-optic intubation under propofol light anaesthesia with reasonable safety, as far as they are supervised by a senior and have a rescue oxygenation technique immediately available.

First reported in 1967, fibre-optic tracheal intubation is indicated in the management of anticipated difficult airway [3] and should be included in all anaesthesia training. Several training programmes have been proposed: manikin [4], animal model [5], awake or anaesthetized patients without difficult intubation [6].

Teaching fibre-optic intubation in patients without anticipated difficult intubation raises several problems. Fibre-optic intubation is usually significantly longer than laryngoscopy (56 ± 24 s vs. 34 ± 10 s according to Cole and colleagues [7]) and may sometimes reach very long duration (18 min from starting light general anaesthesia to starting controlled ventilation [8]). It does not prepare students for the difficulties encountered during difficult airway management. Also, the costs of fibre-optic intubation are higher than those of laryngoscopic intubation including cost of the fibre-optic bronchoscope, time of cleaning and decontamination. The patient may also have a recall of the procedure [9].

The main concern in avoiding fibre-optic intubation in patients without anticipated difficult intubation is the risk of cross-contamination related to fibre-optic procedures [10]. In Europe, it has led to defined decontamination protocols and the necessity to record both bronchoscope and patient identification at each use. The potential for transmission of infection between patients and other nosocomial infections may be minimized [10]. Nevertheless, the risk of cross-contamination through a bronchoscope remains clinically relevant and makes it unacceptable to recommend this procedure in a patient without anticipated difficult intubation.

Fibre-optic intubation may be performed in a patient awake [11] or anaesthetized. Hoarseness and stridor are risk factors of difficult fibre-optic intubation [12]. In these cases, anaesthesia has to be avoided when performing fibrescope intubation [3].

Awake intubation may be technically difficult and needs local anaesthesia, which may induce a complete obstruction of the upper airways [13,14] and does not suppress pain associated with nasal intubation [15]. Coughing and straining during awake intubation may cause trauma and bleeding from a tumour, further worsening the conditions [16]. The senior anaesthesiologist may not feel free to make comments and give advice because the patient is listening, and the junior’s inexperience may increase patient anxiety, produce adverse patient recall or make the patient agitated and uncooperative, thus increasing the difficulties of the procedure.

Historically, sedation was first ensured by diazepam or midazolam. Patients were drowsy but still conscious and responsive. The rate of success was high, but 45–50% of the patients recalled the procedure [17]. Deep anaesthesia with apnoea, combining opioid, hypnotic and non-depolarizing neuromuscular blocking agent has been proposed for teaching in patients without predictive factors of difficult intubation [18–20].

General anaesthesia with spontaneous breathing has been demonstrated to improve the operator’s and patient’s comfort but may worsen airway patency. Propofol is attractive because its delivery is independent of airway management, and it provides unconsciousness, amnesia and upper airway muscle relaxation with doses between 1 and 2 mg kg−1 [21]. Followed by an infusion at rates similar to our study (10 mg kg−1 h−1), it ensured a high rate of success [22]. Propofol may induce respiratory depression or apnoea when combined with alfentanil [22] or given at excessive rates. In our study, this happened in six patients but was easily reversed by patient stimulation or decreasing propofol infusion rate. As a consequence, opioid drugs should be avoided and light general anaesthesia maintaining spontaneous ventilation should be preferred for teaching fibre-optic intubation. One would expect that target-controlled infusion titrated until loss of response to moderately painful stimulation would have reduced the incidence of apnoea [23,24].

Hypoventilation and desaturation were rare except when an opioid was given [25] and could be prevented by adequate preoxygenation [6] and pharyngeal oxygen supply. Therefore, preoxygenation should be especially careful and intubation duration should not exceed the time needed to consume the oxygen stored during preoxygenation. In case of hypoxaemia, a specific algorithm including facemask ventilation, laryngeal mask, transtracheal ventilation and tracheotomy [26] should be immediately executed. However, in patients having obstructing tumours, complete airway obstruction may occur at very light general anaesthesia level. That is the reason why those patients were excluded from our study, and had fully awake intubation [3].

In patients with anticipated difficult airway, fibre-optic intubation usually failed in about 8% [22] when performed by an experienced physician, and our results (1 patient/20 = 5%) are consistent with this estimation. Higher incidence of failure or adverse events and prolonged intubation duration were expected if a junior performs fibre-optic intubation.

The incidence of intubation failure in our study was higher in the group of patients managed by the resident (15%), but had no detrimental consequence for the patient since all patients could easily be intubated by the supervisor. This result suggests that a teacher should be permanently present in the operating room when a non-experienced physician performs fibre-optic intubation.

Surprisingly, intubation duration did not differ significantly between groups, all procedures being shorter than 20 min, despite a trend towards a longer duration for juniors (mean 9.3 vs. 7.5 min). This lack of statistical significance may be due to the fact that the intubation duration was expressed from starting propofol infusion to the tube placement inside the trachea. It may decrease the statistical power of the result, since all patients, in both groups, needed 2–4 min to achieve a level of light general anaesthesia before starting the fibroscopy. The ‘short’ intubation duration observed in both groups may also be due to the use of video remote display, which allowed the senior anaesthesiologist to advise his trainee colleague [27]. It may also be related to an optimized level of light general anaesthesia in both groups.

In summary, the non-experienced physician may learn fibre-optic intubation under propofol light general anaesthesia titrated in order to maintain adequate spontaneous ventilation and local anaesthesia sprayed through the fibre-optic bronchoscope. Even if maintaining spontaneous ventilation could be achieved in most of the cases, hypoventilation by anaesthesia underdosage or overdosage is possible, and alternative methods of oxygenation should be immediately ready for use. The presence of a supervisor is mandatory to help the trainee in case of difficulties.

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Keywords:

INTUBATION INTRATRACHEAL, fibre-optic; SEDATION CONSCIOUS; EDUCATION; ANAESTHESIOLOGY; AIRWAY OBSTRUCTION

© 2007 European Society of Anaesthesiology