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A normal capnogram despite esophageal intubation

¹ Boston, Massachusetts

To the Editor:

The authors reported normal capnograms despite esophageal intubation in a spontaneously breathing patient, who had a difficult intubation.¹ Given the sequence of events, experience suggests that a different scenario is more likely.

When the authors attempted a blind intubation, the tip of the tube could have been at or over the glottis, thereby producing normal CO₂ waveforms as well as normal end-tidal PCO₂ values during spontaneous ventilation. An armoured endotracheal tube can coil in the pharynx easily. On inflation of the endotracheal tube cuff, however, the tip of the tube dislodged out of the area above the glottis into the esophagus. This is consistent with the dramatic reduction in the end-tidal PCO₂ to values below 10 mmHg from the initial values of 38–40 mmHg. Furthermore, passing even the smallest fibreoptic bronchoscope through a 6.0-mm endotracheal tube requires considerable force which could have uncoiled the endotracheal tube, thereby, pushing the distal tip further along into the esophagus.

In absence of the following confirmatory tests, the hypothesis that the esophageal intubation produces normal CO₂ waveforms may not be valid. The initial position of the endotracheal tube tip, before inflation of the cuff when CO₂ waveforms were normal in shape and values, should have been confirmed via fibreoptic bronchoscope. Second, reproducing normal CO₂ waveforms with normal end-tidal PCO₂ values each time the cuff was deflated following inflation would strengthen the author's hypothesis that the endotracheal tube was indeed all along in the esophagus.

Reference

1 Asai T, Shingu K. Case report: a normal capnogram despite esophageal intubation. Can J Anesth 2001; 48: 1025–8.[Abstract/Free Full Text]

² Osaka, Japan

I am aware of the possibility of an endotracheal tube being coiled in the pharynx (as cited such a report¹ in my article),² but would like to refute Drs. Shankar and Posner's claims.

They claim that passing even the smallest fibrescope through a 6.0 mm endotracheal tube requires considerable force. I^3,4 (as well as others)⁵ have used a fibrescope (diameter: 3.5 or 4.0 mm) and a reinforced endotracheal tube (internal diameter: 6.0 mm) in several studies and have never experienced such a difficulty.

They also suggest that insertion of a fibrescope could have uncoiled the endotracheal tube and pushed the tube tip further along into the esophagus. In the case presented,² I could clearly see the distal aperture of the endotracheal tube even when the tip of the fibrescope was 5–6 cm proximal to the tube tip. Therefore, neither was the tube coiled nor did the fibrescope uncoil the tube during insertion.

My hypothesis was that expired gas entered the esophagus during inspiration and forced gas out through the tube during expiration. Therefore, inflation of the cuff prevented gas entering the esophagus and made carbon dioxide waveforms to disappear, and re-deflation of the cuff made waveforms reappear. A likely reason for a low end-tidal carbon dioxide concentration after re-inflation of the tube cuff was that pooled gas in the esophagus had been reduced during cuff inflation.

Therefore, I maintain my claim that, under exceptional circumstances, when a patient is breathing spontaneously, apparently normal carbon dioxide waveforms could appear despite accidental esophageal intubation.

References

1 Deluty S, Turndorf H. The failure of capnography to properly assess endotracheal tube location. Anesthesiology 1993; 78: 783–4.[Medline]

2 Asai T, Shingu K. Case report: a normal capnogram despite esophageal intubation. Can J Anesth 2001; 48: 1025–8.

3 Asai T, Murao K, Shingu K. Cricoid pressure applied after placement of the laryngeal mask impedes subsequent fibreoptic intubation through mask. Br J Anaesth 2000; 85: 256–61.[Abstract/Free Full Text]

4 Koga K, Asai T, Latto IP, Vaughan RS. Effect of the size of a tracheal tube and the efficacy of the use of the laryngeal mask for fibrescope-aided tracheal intubation. Anaesthesia 1997; 52: 131–5.[Medline]

5 Silk JM, Hill HM, Calder I. The distance between the grille of the laryngeal mask airway and the vocal cords. Anaesthesia 1994; 49: 170–1.[Medline]

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