Anesth Analg 2001;93:973-974
© 2001 International Anesthesia Research Society
TECHNOLOGY, COMPUTING, AND SIMULATION
Hypercapnia Related to a Faulty Adult Co-Axial Breathing Circuit
W. Scott Jellish, MD PhD,
Tom Nolan, CRNA, and
Bruce Kleinman, MD
Department of Anesthesiology, Loyola University Medical Center, Maywood, Illinois
Address correspondence and reprint requests to Bruce Kleinman, MD, Department of Anesthesiology, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153. Address e-mail to bkleinm{at}luc.edu
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Abstract
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IMPLICATIONS: This report describes the appearance of CO2 on the capnograph during inspiration, which was linked to disconnection of the inner tube of a coaxial circuit extension piece. The increased use of coaxial breathing systems for adults makes inner tubes disconnections an important consideration when the CO2 appears during inspiration.
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Introduction
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The Bain circuit has been used in the practice of pediatric anesthesia for decades (1). In recent years its co-axial design has been adapted for circle absorbers where the afferent limb is contained within the outer efferent portion of the circuit. We report a case where an unrecognized disconnection of the inner tube of an adult co-axial breathing circuit led to a sudden appearance of carbon dioxide on the inspiratory baseline of the capnograph.
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Case Report
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A 50-yr-old man, who had suffered a closed head injury in 1996 that left him in a persistent vegetative state, had intractable aspiration of gastric contents despite a previous tracheostomy and placement of a feeding jejunostomy tube. His persistent problems with chronic aspiration and his deteriorating pulmonary status necessitated an esophagoscopy, laryngoscopy, and total laryngectomy. After anesthetic induction and tracheal cannulation using a 7.5 armored endotracheal tube (ETT), bilateral breath sounds were confirmed, and the tube was secured to the skin using two silk sutures. Immediately thereafter, the surgical bed was turned 180° requiring the addition of a co-axial circuit extender (XF60 Universal F2 Anesthesia Breathing Circuit, King Systems Corporation, Noblesville, IN) to the end of the normal co-axial breathing circuit (D345–80XP Universal F2 Anesthesia Breathing Circuit, King Systems Corporation). The capnograph aspiration port was positioned immediately after the 90° elbow that connects to the ETT. Anesthesia was maintained with 1.1% isoflurane and 50% nitrous oxide. Ninety minutes after incision, carbon dioxide was noted on the inspiratory baseline of the capnograph and end-tidal carbon dioxide increased from 39 to 73 mm Hg. PaCO2 was 74 mm Hg with a pHa of 7.19. The patient’s temperature was unchanged. Inspection of the inspiratory and expiratory valves of the anesthesia machine was unremarkable. The soda lime absorbent was cool to the touch and nondiscolored but was changed to fresh absorbent. This did not change the findings on the capnograph. The minute ventilation was increased from 6 L/min to 14 L/min and the inspiratory to expiratory ratio adjusted to 1:1. This decreased the PaCO2 to 53 mm Hg, but carbon dioxide was still present on the inspiratory baseline of the capnograph (Fig. 1). Surgery continued and the patient subsequently underwent an uneventful intraoperative course. After the procedure, the anesthesia machine was examined with specific attention given to the inspiratory and expiratory valves. Both were intact and worked as designed. The original breathing circuit had been discarded, but an identical co-axial circuit and the co-axial circuit extension were examined. We found that a slight lateral movement of the co-axial circuit extension’s outer tube could displace the central inner tube from its seating (Fig. 2). Displacement of this nature might be slight and undetectable during visual observation. A similar extension system was placed in another patient and the inner tube was displaced from its seating, reproducing the capnographic finding observed in our patient.
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Figure 1. Capnograph showing carbon dioxide on the inspiratory baseline at differing I to E (inspiratory to expiratory) ratios. All ventilatory adjustments done at 14 L minute ventilation. 1–2 = inspiratory phase; 2–3 = expiratory phase begins; 3–4 = alveolar or expiratory plateau.
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Figure 2. Slight flexion of the circuit causes a disconnection of the central inner tube from its proper position.
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Discussion
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This case demonstrates concerns about the integrity of the central inner tube of the Bain circuit relevant to today’s contemporary adult co-axial breathing circuits (2–3). In addition to a defective expiratory valve, exhausted carbon dioxide absorbent, or excessive gas channeling through the absorbent, we must now also consider a disconnection of the central inner tube of a co-axial breathing circuit as a factor that could cause the rebreathing of carbon dioxide during anesthesia.
Historically, there has always been a concern about the integrity of the central inner tube of the Bain circuit. An unrecognized disconnect could lead to rebreathing of expiratory gases leading to hypercarbia and hypoxemia (3). Various tests of central inner tube integrity for co-axial circuits were proposed, all of which relied on pressurization of the circuit or creating of a Venturi (4). Because the circuit used in this case was originally aligned and intact, the problem that we experienced would not have been detected before surgery using any of the proposed tests for central tube integrity. We speculate that a slight lateral movement or stretching of the co-axial extension tube caused displacement of the central inner tube from its seated position leading to rebreathing of expiratory gases.
We suggest several options to solve the problem. The first option is for the manufacturer to redesign the co-axial circuit extension to prevent disconnection of the inner tube from its seat. The second option is to avoid the use of co-axial circuit extensions. The final option would require the use of appropriate low-pressure alarms that would sense this type of disconnection. However, this particular solution is problematic because the flow resistance of some co-axial breathing systems can be high enough to defeat low-pressure alarms (5).
We offer this case report as a warning and a reminder that the integrity of the coaxial circuit must always be checked visually before initiation of general anesthesia. The manufacturer in question was contacted and determined that the extension sets were misassembled by an operator who believed they were Universal F circuits. The manufacturer will counsel the assembly inspectors and supervisors for both Production and Quality Assurance and retraining has been scheduled to secure the inner tube to prevent disconnections in the future.
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References
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Spoerel WE. A streamlined anaesthetic system. Can Anaesth Soc J 1972; 19: 426–35.[Web of Science][Medline]
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Mansell WH. Bain circuit: the hazard of the hidden tube [letter]. Can Anaesth J 1976; 23: 227.
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Hannallah R, Rosales JK. A hazard connected with re-use of the Bain’s circuit: a case report. Can Anaesth Soc J 1974; 21: 511–3.[Web of Science][Medline]
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Heath PJ, Marks LF. Modified occlusion tests for the Bain breathing system. Anesthesia 1991; 46: 213–6.[Web of Science][Medline]
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Sinclair A, Van Bergan J. Flow resistance of coaxial breathing systems: investigation of a circuit disconnect. Can J Anaesth 1992; 39: 90–4.[Web of Science][Medline]
Accepted for publication May 15, 2001.
This article has been cited by other articles:
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B. Ghai, J. K. Makkar, and A. Bhatia
Hypercarbia and arrhythmias resulting from faulty bain circuit: a report of two cases.
Anesth. Analg.,
June 1, 2006;
102(6):
1903 - 1904.
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Abstract
Introduction
