Anesth Analg 2004;98:870-871
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000106974.77869.9C
LETTERS TO THE EDITOR
Class Zero Airway and Laryngoscopy
Bingshuang Fang, MD, and
James Norris, MD
Department of Anesthesiology, University of Texas Medical Branch at Galveston, Galveston, TX
To the Editor:
The letters to the editor by Ezri et al. (1) and Grover et al. (2) were of interest to us. We recently encountered a class zero airway patient who presented us, like Grover et al. (2), with a difficult intubation following induction of general anesthesia. The patient was a 69-yr-old man, 5'7"in height, weighing 80 kg. He was otherwise healthy and was scheduled for left hip arthroplasty. The preoperative assessment demonstrated good visualization of the epiglottis with the patient’s mouth fully opened and tongue fully protruded without phonation. This was our first encounter with a class zero airway as defined by Ezri et al. (1). The anesthetic plan was for a standard IV induction of anesthesia followed by cisatracurium to facilitate orotracheal intubation. A colleague commented in the holding area that we "should be able to intubate this patient with a tongue blade."
The patient was placed in optimal sniffing position. General anesthesia was induced. To our surprise, attempts to prove the airway by bag-mask ventilation prior to administration of cisatracurium failed. An oral airway was placed with no improvement of ventilation. A nasal airway seemed to help minimally, but air movement was still poor. We opted to use succinylcholine instead of cisatracurium. Direct laryngoscopy was performed with a Macintosh No. 3 blade after succinylcholine took effect. The laryngoscopic view was grade III; only a big floppy epiglottis was seen, and we were unable to intubate. A Miller No. 2 blade was selected for the second direct laryngoscopy, and the patient was successfully intubated. The vital signs were stable throughout and there was no oxygen desaturation. Tracheal placement of the endotracheal tube was confirmed in the usual manner. The case continued uneventfully after that.
The study by Ezri et al. (3) found that all patients with class zero airways had grade I views during laryngoscopy. Grover et al. (2) reported an encounter of difficult laryngoscopy in a class zero airway due to a large obstructive epiglottis. A review of the previous studies and reports did not mention difficulty with bag-mask ventilation after induction of general anesthesia. We agree with Grover et al. (2) that the cause of difficult laryngoscopy in our patient was due to the large redundant epiglottis obstructing the glottis after the patient was anesthetized. It blocked the view of glottis. Even though our patient was older, he had excellent neck range of motion, more than adequate mouth aperture, and a thyromental distance greater than 7 cm. He had no obstructive neck adiposity or malocclusion of the teeth. The standard indicators would suggest that he should have been an easy intubation and we could not explain the difficulty by any other mechanism except the large epiglottis. The large epiglottis is both what qualifies him as a class zero airway, and the cause of difficult intubation. Our literature search revealed nine patients with class zero airways reported as easy intubations by Ezri et al. (1). However, Grover et al. (2) reported one patient with difficult laryngoscopy. Adding our case to the total, this makes 2 out of 11 total reported cases with class zero airway patients who were difficult laryngoscopies. Further studies of a larger patient population must be done before any conclusions about the class zero airway can be made. All nine patients in the Ezri et al. (1) study and the patient reported by Grover et al. (2) were young females. Our patient is the first reported class zero airway in an older male.
We conclude that class zero airway can be found in any gender or age group. It is not always a predictor for easy laryngoscopy. We would also like to emphasize the importance of demonstrating the ability to ventilate with a face mask before administering muscle relaxant. Finally, we should not be lulled into a false sense of security for an apparent promise of an "easy airway" and must always be prepared for difficult intubations at all times.
References
- Ezri T, Cohen I, Geva D, Szmuk P. Pharyngoscopy views [letter]. Anesth Analg 1998; 87: 748.
- Grover V, Mahajan R, Tomar M. Class zero airway and laryngoscopy [letter]. Anesth Analg 2003; 96: 911.[Free Full Text]
- Ezri T, Warters D, Szmuk P, et al. The incidence of class zero airway and the impact of Mallampati score, age, sex and body mass index on prediction of laryngoscopy grade. Anesth Analg 2001; 93: 1073–5.[Abstract/Free Full Text]
Response
V. K. Grover, MD MNAMS, and
Rajesh Mahajan, MD
Department of Anaesthesia and Intensive Care, Postgraduate Institute of Medical Education and Research, Chandigarh, India
In Response:
We read with interest the letter by Fang and Norris. They have reinforced our observation that a patient with class zero airway may not necessarily have an "easy intubation." Although we did not have any difficulty during bag-mask ventilation in our patient, they had difficulty in bag-mask ventilation as well. It is possible that a large redundant epiglottis may have acted as a flap and blocked the glottic opening, every time positive pressure was applied to ventilate the patient. Oropharyngeal airway may fail to help in this situation. Nasopharyngeal airway may be useful if it can be positioned posterior to epiglottis. Even laryngeal mask airway may be difficult to position in these patients.
We have come across one more patient of class zero airway, after we reported the one earlier. This patient was a 48-yr-old male patient who had laryngoscopy grade I and hence an easy intubation. Ezri et al.(1) have reported a 1.18% incidence of class zero airway in an age group ranged between 19–38 yr, however our patients were 54 and 48 yr old. We are studying the incidence of class zero airway at our institute and will correlate the same with age, sex, body mass index, and other factors. This will take some more time before it is available for publication.
At present, we reaffirm that all the patients with class zero airway may not be as young as reported by Ezri et al. (1) and can belong to any age group. Since we have seen one male patient and one has been reported by Fang and Norris, they may not always be females. These patients with class zero airway should be subjected to indirect laryngoscopy to check whether the epiglottis hinders the laryngoscopic view. Finally, the ability to ventilate such patients with a face mask must be confirmed before administering muscle relaxant. Until such time before definite conclusions are drawn, we agree with Fang and Norris that patients with class zero airway should not be taken as "easy intubation" and one must be prepared for "difficult intubation drill."
Reference
- Ezri T, Warters D, Szmuk P, et al. The incidence of class zero airway and the impact of Mallampati score, age, sex and body mass index on prediction of laryngoscopy grade. Anesth Analg 2001; 93: 1073–5.
Response
Tiberiu Ezri, MD,
Peter Szmuk, MD,
Yitzhak Cohen, MD, and
Robert D. Warters, MD
Department of Anesthesia, Wolfson Medical Center, Holon, Tel Aviv School of Medicine, Israel, Visiting Professor of Anesthesiology, The University of Texas Medical School at Houston, Texas
Department of Anesthesiology, Director, PACU, Hermann Hospital, The University of Texas Medical School at Houston, Texas
Department of Anesthesia, Sourasky Medical Center, Tel Aviv School of Medicine, Israel
Department of Anesthesiology, Director, OR, Hermann Hospital, The University of Texas Medical School at Houston, Texas
In Response:
We read with interest the letter by Fang and Norris and we learned from their case presentation that a large, floppy epiglottis may not only cause a poor laryngoscopy view, but, even worse, it may render mask ventilation difficult or even impossible, presumably by impaction of the floppy epiglottis into the glottic aperture. Unfortunately, few of such cases can be diagnosed before induction of anesthesia. In this regard, having a class zero airway may actually confer the advantage of diagnosing a floppy, large epiglottis in an awake patient, by simply examining the back of the patient’s mouth and subsequently tailoring the anesthetic technique accordingly. In our opinion, a patient who is difficult to ventilate after the induction of anesthesia should not receive any muscle relaxant (not even succinylcholine). Rather, ventilation should be assisted until the resumption of spontaneous breathing, and then a trial should be taken to intubate the patient under spontaneous ventilation. Alternatively, the patient may be awakened and the case managed in a different way (i.e., awake fiberoptic intubation, postponing surgery, etc.). This case of difficult intubation presented by Fang and Norris, encountered with a class zero pharyngoscopic view reinforces the clinical observation (1–3) that the pharyngoscopic view alone ("Mallampati" plus class zero) is not a reliable predictor of laryngoscopy grade. Evidently, the positive predictive value of the pharyngoscopic view is improved, if combinations with other tests (i.e., thyromental distance, neck extension, mouth opening, etc.) are used (4).
References
- Karkouti K, Rose DK, Ferris LE, et al. Inter-observer reliability of ten tests used for predicting difficult tracheal intubation. Can J Anaesth 1996; 43: 554–9.[Web of Science][Medline]
- Khan ZH, Kashfi A, Ebrahimkhani E. A comparison of the upper lip bite test (a simple new technique) with modified Mallampati classification in predicting difficulty in endotracheal intubation: a prospective blinded study. Anesth Analg 2003; 96: 595–9.[Abstract/Free Full Text]
- Ezri T, Weisenberg M, Khazin V, et al. Difficult laryngoscopy: incidence and predictors in patients undergoing coronary artery bypass surgery versus general surgery patients. J Cardiothorac Vasc Anesth 2003; 17: 321–4.[Web of Science][Medline]
- Randell T. Prediction of difficult intubation. Acta Anaesthesiol Scand 1996; 40: 1016–23.[Web of Science][Medline]
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