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Anesth Analg 2001;92:517-522
© 2001 International Anesthesia Research Society

GENERAL ARTICLES

Validation of a Simple Algorithm for Tracheal Intubation: Daily Practice Is the Key to Success in Emergencies— An Analysis of 13,248 Intubations

Thomas Heidegger, MD, Hans J. Gerig, MD, Brigitte Ulrich, MD, and Georg Kreienbühl, MD

Department of Anesthesiology, St. Gallen Cantonal Hospital, St. Gallen, Switzerland.

Address correspondence and reprint requests to Thomas Heidegger, Department of Anesthesiology, St. Gallen Cantonal Hospital, 9007 St. Gallen, Switzerland. Address e-mail to thomas.heidegger{at}kssg.ch


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
A fundamental skill of the anesthesiologist is airway management. We validated a simple endotracheal intubation algorithm with a large proportion of fiberoptic tracheal intubations used for years in daily practice. Over 2 yr, 13,248 intubations (>90% of all intubations, including obstetrics and ear, nose, and throat patients) in a heterogeneous patient population at our acute care hospital were evaluated prospectively. About 80 physician and nurse anesthetists were involved. Once the indication for intubation (oral or nasal) was established, the first step was to choose between the primary conventional technique (laryngoscope with Macintosh blades) and the primary fiberoptic technique. For the conventional technique, a well defined procedure had to be followed (maximum of two attempts at intubation; if unsuccessful, switch to secondary oral fiberoptic intubation). For the primary fiberoptic technique, the anesthesiologist had to decide between nasotracheal intubation in awake patients and oral intubation in anesthetized patients. Fiberoptics were used for 13.5% of the intubations. By following our algorithm, intubation failed in 6 out of 13,248 cases (0.045%; 95% confidence interval 0.02%–0.11%). We demonstrate that a simple algorithm for endotracheal intubation, basically limited to fiberoptics as the only aid, is successful in daily practice. Only methods that are practiced daily can be used successfully in emergencies.

Implications: The aim of this investigation was to validate a simple tracheal intubation algorithm used in daily practice for years as a quality control exercise. With the exception of the guidewire, the only airway management instrument used was the fiberoptic bronchoscope. Of 13,248 intubations evaluated (90.6% of all intubations), only six patients (0.045%) could not be intubated by following our algorithm. The high proportion of primary fiberoptic intubations (12.1% of all intubations) has resulted in a corresponding degree of practice and experience with this method, with the consequence that the number of unanticipated failed intubations is very small. Daily practice is the key to success in the emergency situation.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Airway management is often one of the greatest challenges for the anesthesiologist. Respiratory problems are the most frequent single cause of an adverse outcome (1). The incidence of difficult intubations lies between 1% and 4% (2) and that of failed intubations between 0.13% and 0.3%, depending, among other things, on the patient population under study (2–5). A wide range of airway management instruments, some used only very rarely (6), are described in guidelines for the difficult airway (7,8). In our hospital, we have been using a simple intubation algorithm for the past 10 yr that relies principally on fiberoptics as the only additional management instrument. This study was conducted as a quality control measure to validate this intubation algorithm.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
The study was conducted between 1 January 1997 and 31 December 1998 in St. Gallen Cantonal Hospital. This is an acute care hospital in eastern Switzerland with 650 beds (population in catchment area approximately 500,000). It covers many surgical disciplines, including an obstetrics department with more than 1000 births per year and an ear, nose, and throat (ENT) department with tumor surgery, bronchoscopy, and orthodontic surgery; however, it excludes cardiac and pediatric surgery. We documented all intubations prospectively, including those in the emergency room. Excluded were patients already intubated and those who had been intubated by the emergency services outside the hospital. The ethics committee gave consent for the study to be performed.

There are three decisions to be made after the preoperative evaluation on the day before surgery, as noted in Figure 1.



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  		Figure 1. Intubation algorithm. *BURP = backward-upward-rightward pressure (10). **Slit Guedel airway; Rüsch & Co, Kernen, Germany.

 
The standard approach was conventional intubation, i.e., planned primary intubation with a laryngoscope. If difficulty was anticipated with intubation for clinical reasons, primary nasal fiberoptic intubation in the awake patient was performed. Primary oral fiberoptic intubation in the anesthetized patient was chosen if difficulty with intubation was known from previous episodes of anesthesia. We have been recording the laryngoscopy grade according to Wilson et al. (9) for many years ( Table 1).


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  		Table 1. Laryngoscopy Grades
 
Primary fiberoptic intubations were performed only by fully trained anesthesiologists or residents in anesthesiology in the last year of training (20 physicians). Table 2 shows our indications for the primary nasal or oral fiberoptic approach.


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  		Table 2. Indications for Primary Nasal or Oral Fiberoptic Intubation
 
The primary conventional approach involved both the oral and the nasal technique. About 80 physicians and nurse anesthetists with all levels of training and experience were involved in performing the primary conventional approach. If a trainee was unable to perform intubation following the first two steps of our plan, the help of an experienced anesthesiologist had to be sought. The anesthesiologist then performed the intubation orally by using the fiberoptic technique (secondary oral fiberoptic intubation) via a slit Guedel airway. If conventional nasal intubation failed at the second attempt, the patient had to undergo primary oral intubation, and a fully trained anesthesiologist decided on further procedures. Patients with a full stomach were either intubated orally with the conventional approach (with cricoid pressure) or awake nasally.

The laryngoscopy grade according to Wilson et al. was documented for the primary conventional approach. Grades 4 and 5 had to be confirmed by an experienced anesthesiologist. The practitioners were required to document whether they had adhered to the algorithm. If they had not, or if the patients were in laryngoscopy Grades 4 or 5, these details had to be given on specially designed forms. The laryngoscopy grade according to Wilson et al. was not documented for any of the primary fiberoptic intubations. All records were reviewed within a few days by the authors and, if necessary, were completed after discussions with the anesthesiologist concerned.

In selecting intubation management instruments, we made a conscious decision to limit ourselves to the use of a laryngoscope with size 2, 3, or 4 Macintosh blades, a guidewire, Magill forceps, and a flexible bronchoscope. The fiberoptic intubation equipment was available for use at any time. For conventional oral intubation, 8.0-mm-internal-diameter (ID) tubes for men and 7.0-mm-ID tubes for women (Mallinckrodt®; Hazelwood, MO) were used. Fiberoptic intubation (primary and secondary) was performed with armored tracheal tubes with an ID of 6.5 mm (Rüschelit® tracheal tube). All anesthesiologists and residents in anesthesiology were practiced in the use of the equipment. The level of training was also regularly reviewed by two senior anesthesiologists with special responsibility for this.

At the time the study was conducted (1997–1998), the laryngeal mask was not in routine use in our hospital for management of the difficult airway.

All findings were entered into a FileMaker Pro® 3.0 database (FileMaker, Santa Clara, CA) (with plausibility checks) that we developed. The data were expressed in terms of the mean (SD) or median (range). We calculated the 95% confidence interval (CI). The evaluation was performed with the Systat® 7.0 for Windows program (SPSS, Chicago, IL).

All data were also simultaneously entered into our ANITA hospital database, which is used to document services provided.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
A total of 14,360 intubations were performed in the 2-yr period of observation (data from the ANITA database), of which 13,248 (90.6%) were available for use and evaluation in our study. The median age (range) was 48 yr (2 mo–97 yr).

The mean body mass index (SD) was 24.6 (6.0). The male/female ratio was 6854:6394 (51.7%:48.3%). Of the 13,248 intubations evaluated, 10,266 (77.5%) were done for elective surgery.

Tables 3 and 4 show details of the conventional and fiberoptic intubations and the distribution of the intubations across the surgical disciplines. The distribution of the laryngoscopy grades according to Wilson et al. for the primary conventional approach are given in Table 5. Laryngoscopy was not conducted in the patients who underwent primary fiberoptic intubation.


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  		Table 3. Type of Intubation
 

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  		Table 5. Distribution of Laryngoscopy Gradesa for the Primary Conventional Approach
 

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  		Table 4. Distribution of Intubations Across Surgical Disciplines
 
Among the 175 secondary fiberoptic intubations, two were in laryngoscopy Grade 1, one in Grade 2, 20 in Grade 3, 138 in Grade 4, and 14 in Grade 5.

Problems were encountered in 9 (see below) of our 13,248 intubations. In 6 of these, intubation ultimately failed (0.045%; 95% CI 0.02%–0.11%), or 1:2208 intubations (95% CI 1:909–1:5000). Table 6 shows details of these nine cases (intubation problem, anticipated or unanticipated difficulty with intubation, laryngoscopy grade, and whether the algorithm was adhered to).


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  		Table 6. Details of Problem Cases
 
Case 1
Case 1 involved hemostasis after bleeding carcinoma of the base of the tongue in a 77-yr-old patient. After agreement, the anesthesiologist administered etomidate and succinylcholine in the presence of an experienced specialist from the ENT clinic. The patient was bleeding continuously from the base of the tongue, coughing, and continually vomiting blood. Neither of the specialists was able to penetrate the glottis, partly for anatomical reasons and partly because of the continuous bleeding into the trachea. Fiberoptic intubation was not considered because of the severe bleeding (impaired view). They quickly decided to perform cricothyrotomy under local anesthesia. The cannula was introduced at the second attempt, and the patient was satisfactorily stabilized for a short period.

They then proceeded to perform regular conversion of the provisional cricothyrotomy into a permanent tracheotomy. It was suddenly no longer possible to ventilate the patient during the preparation of the trachea. It was presumed that the cricothyrotomy cannula had become dislodged, and the patient went into cardiac arrest as the bleeding worsened. In view of the advanced stage of disease and the limited possibilities for treatment, no further resuscitation measures were taken.

Case 2
Case 2 involved a 61-yr-old with cholecystectomy because of acute cholecystitis; the patient had poliomyelitis as child. At the preoperative evaluation, the anesthesiologist decided to perform primary conventional intubation. After repeated attempts, however, it was not possible to penetrate the glottis with either the laryngoscope or the fiberoptic bronchoscope. It was decided to end the anesthesia, and the patient regained consciousness.

With the agreement of the patient (a physician), the primary fiberoptic approach was then used. This also failed, and swelling and mild bleeding were now also impairing the view. It was also uncertain whether extubation would be complication free.

After considering all aspects, the patient was allowed to return to consciousness again, and he was offered the possibility of cholecystectomy under thoracic peridural anesthesia. The patient consented, and the surgery was successful.

Case 3
In Case 3, a 3-yr-old had a diagnostic eye inspection and stenosis of the lacrimal duct, as well as complex dysmorphic syndrome. The marked dysmorphia of the left side of the face with hypoplasia, hypoplasia of the pinna, and cleft lip and palate was obvious and was a warning signal that the approach had to be carefully considered. Because intubation anesthesia was felt to be necessary under the circumstances at that time for eye pressure measurement and rinsing the lacrimal duct (we had no experience with the laryngeal mask in such small children at that time), the anesthesiologist decided to use careful inhaled induction and then to attempt intubation. The glottis could not be visualized, even by a very experienced colleague who was immediately called in to assist. He finally advised insertion of a laryngeal mask, and this was achieved without problems.

Case 4
Case 4 involved a 2-mo-old with hyperplastic adenoid, middle ear effusion, and suspected Goldenhar syndrome. This patient also had marked dysmorphia with acromegaly, absence of mastication muscles, and an underdeveloped jaw. Because the indication for adenotomy was not urgent, the ENT specialist decided against it. This enabled the planned myringotomy to be conducted with the anesthetic mask. Careful attempts at intubation confirmed laryngoscopy Grade 5.

Two years later, the patient had to be intubated for orthodontic surgery. The patient was still in laryngoscopy Grade 5. However, it was now possible to perform intubation with the pediatric fiberoptic bronchoscope now available.

Case 5
Case 5 was a 65-yr-old with strumectomy because of a multinodular goiter. Although difficult intubation with this massive goiter was anticipated, the anesthesiologist responsible expected to be able to intubate the patient’s trachea by using the primary conventional approach. It was, however, not possible to intubate the patient successfully with conventional methods or by secondary fiberoptic procedure, and the patient was allowed to regain consciousness. The next day, the patient was intubated nasally without complications with the fiberoptic approach.

Case 6
Case 6 involved a 43-yr-old patient with wound revision after craniotomy for meningioma. A relatively inexperienced intern was unexpectedly confronted with this patient in laryngoscopy Grade 4. Contravening the study protocol, he attempted conventional intubation several times. The fully trained anesthesiologist, who was called too late in this case, was also unable to perform fiberoptic intubation (abundant secretions, glassy swollen mucosa, mild bleeding). The anesthesia was conducted with the laryngeal mask.

This patient had already been intubated 4 wk earlier, when laryngoscopy Grade 4 had also been documented, and oral fiberoptic intubation was without problems. This was unfortunately not taken into account on the second occasion.

Case 7
Case 7 involved a 58-yr-old patient with osteosynthesis caused by a fractured humerus. A rapid decrease in oxygen saturation occurred during a primary conventional procedure at Step 3 in our algorithm (first fiberoptic attempt). The anesthesiologist decided to let the patient regain consciousness and intubated the trachea nasally with the fiberoptic bronchoscope at the first attempt.

Case 8
The first attempt to intubate this patient (77 yr; ureterorenoscopy because of urolithiasis; laryngoscopy Grade 4) failed. The experienced anesthesiologist called in to assist decided to use a laryngeal mask. Fiberoptic intubation was not attempted; this did not comply with the study protocol.

Case 9
This 33-yr-old woman weighing 88 kg (body mass index 33) had to undergo emergency intubation for cesarean delivery because of preeclampsia. The first attempt to intubate her trachea (laryngoscopy Grade 3) failed. The anesthesiologist present decided to let the patient regain consciousness, and the surgery was conducted under spinal anesthesia.


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
This survey showed that the difficult airway can be managed with a simple algorithm limited to a small number of airway management instruments and that the method can be used safely and reliably in everyday practice. It was demonstrated that this can also be achieved in a major teaching hospital where both experienced anesthesiologists and nurse anesthetists, as well as physicians and nurses under training, perform intubation. Guidelines and recommendations for the management of the difficult airway already exist (7,8). All agree that it is extremely important to gain adequate practice with the necessary airway management instruments.

We made a conscious decision to limit ourselves to the use of fiberoptic equipment (in addition to the use of backward-upward-rightward pressure and a guidewire) (10). In addition to the classic indications, such as the anticipated difficulty with intubation in the presence of tumors in the neck region or morbid obesity, we use the fiberoptic bronchoscope daily for training purposes. Of the 13,248 intubations, 1787 (13.5%) were performed with the fiberoptic approach (46.2% of them for training purposes). We are therefore in a position to guarantee structured training for our trainee anesthesiologists and continuous training in fiberoptic intubation for our experienced anesthesiologists. In their survey of American anesthesiologists, Rosenblatt et al. (6) showed that most of them preferred fiberoptic-assisted intubation. A French working group [Avarguès et al. (11)] reported that 64% of respondents felt that they needed additional training in the technique of fiberoptic intubation.

Six of our 13,248 intubations failed finally (Cases 1–4, 8, and 9). This failed intubation rate of 0.045% (95% CI 0.02%–0.11%) was markedly less than that reported by Rose and Cohen (4) (0.3%), who, unlike us, did not include intubations in obstetric patients in their sample. It is generally recognized that the failed intubation rate is more frequent in obstetrics (5,12). The small intubation frequency in our study (<1%) in this area is because cesarean deliveries are increasingly being performed under regional anesthesia (80% in our hospital).

By strictly adhering to the algorithm, intubation was finally successful in three of nine problem cases (Cases 5–7). Difficulties with intubation were anticipated in five of the nine patients (Cases 1–5) because the problems were obvious. In the remaining four cases (Cases 6–9), the difficulties with the airway were not anticipated. Two of these cases (Cases 6 and 7) were finally successfully intubated. In relation to the total sample, therefore, the rate of failed and unanticipated difficult intubations was very small, particularly considering that the algorithm was not fully applied in Cases 8 and 9.

The "cannot intubate, cannot ventilate" rate of 1:13,248 was similar to the rate in the literature (1:5000–1:1,000,000) (13). We deliberately did not document predictors in our study because several authors have found these to be unreliable (4,14–16). We agree with Rose and Cohen (4), who state that careful and reliable recording of data is a prerequisite for valid conclusions on process quality. However, in contrast to Rose and Cohen, who had missing documentation in 24.8% of cases, only 9.4% of all intubations in our period of observation were not available for evaluation.

We demonstrated that our algorithm, centered around frequent use of the fiberoptic approach, was able to be used successfully in daily practice. The proportion of patients who could not be intubated amounted to 0.045%, which means that we are using a valid method that is also successful when used in emergency situations. For patients who cannot be tracheally intubated and ventilated, we use a transtracheal catheter with the possibility of jet ventilation (17,18). In addition to the fiberoptic approach as an indispensable aid to intubation, we are currently making more frequent use of the laryngeal mask in cases in which intubation is not absolutely indicated (in 1999, 1291 of 9621 general anesthetics were performed with a laryngeal mask). But here too, the same principle applies: what has to work in an emergency situation has to be practiced every day.

In conclusion, our findings show that an algorithm for tracheal intubation confined to only two methods—namely, conventional or fiberoptic intubation—is reliable, successful, and easy to learn. The more difficult, urgent, and dangerous the situation, the more important it is to keep the methods simple and safe and to practice them every day.


   Acknowledgments
 
We would like to thank all colleagues in our hospital for the assiduous completion of the intubation records and our team of administrative assistants for the data entry. Professor Harald J. Sparr, Department of Anesthesia and Intensive Care Medicine, Leopold Franzens University of Innsbruck, Austria, was kind enough to review the manuscript.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Accepted for publication October 3, 2000.




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Lippincott, Williams & Wilkins 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 HighWire Press