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LETTER TO THE EDITOR

Hypercarbia and Arrhythmias Resulting From Faulty Bain Circuit: A Report of Two Cases

Department of Anaesthesia and Intensive Care; Post Graduate Institute of Medical Education & Research; Chandigarh, India; jeet1516{at}gmail.com

To the Editor:

We wish to report two cases, one in which a faulty Bain circuit manufactured by Intersurgical Limited (Workingham, Berkshire, UK) led to hypercarbia during surgery and another in which we were able to correct a faulty Bain circuit during surgery in which arrhythmias occurred. We recommend redesign of the circuit.

The first case was that of a 46-yr-old, 70-kg female who presented for clipping of a ruptured right middle cerebral artery aneurysm. All equipment was routinely checked in accordance with the association guidelines (1). After induction, anesthesia was maintained with O₂:N₂O (33%:67%) and propofol infusion. The lungs were ventilated via a Bain circuit. The anesthesia machine was then moved towards the foot of the bed to provide space for the surgeon.

One hour after incision, the patient's heart rate increased from 80 to 130 bpm, and her arterial blood pressure increased from 146/78 mm Hg to 210/106 mm Hg. The surgeon observed bulging of the brain. Arterial blood gas analysis, performed immediately, showed a pH of 6.97, a Pao₂ of 80 mm Hg, and a Paco₂ of 107 mm Hg. Her airway pressure was normal, and breath sounds were equal bilaterally, excluding pneumothorax. The patient's temperature remained unchanged. Fresh gas flows were increased from 6 to 12 L/min.

We replaced the Bain circuit. The patient's heart rate decreased to 100 bpm, and her invasive arterial blood pressure decreased to 160/90 mm Hg. After 10 min, the arterial blood gas analysis showed a pH of 7.2, a Pao₂ of 110 mm Hg, and a Paco₂ of 67 mm Hg. Subsequently, the patient underwent an uneventful intraoperative course.

Close examination of the original Bain circuit revealed that the inner tubing of the coaxial circuit had disconnected from its seat at the machine end of the circuit (Fig. 1). The disconnection was visually undetectable because the outer tubing was opaque, rather than transparent.

View larger version (93K): [in this window] [in a new window]   Figure 1. Displaced inner tubing of the coaxial circuit from its seating.

We could have prevented this patient's hypercarbia if we had an ETco₂ monitor. However, this was not available to us, as is the case in many developing countries.

The second case was that of a 15-yr-old, 30-kg female with a perforating eye injury who was scheduled for primary repair. The anesthesia machine and Bain circuit were checked before anesthetic induction. After anesthetizing the patient, we moved the anesthesia machine to provide space for the surgeon. Twenty minutes into the surgery, ventricular ectopic beats, followed by bigeminy, were noticed on the electrocardiogram monitor. We then administered lidocaine 2 mg/kg. The arrhythmias subsided but reappeared in a few minutes. Because of our previous experience, we checked the Bain circuit, discovered a disconnected inner tube, and reseated it (Fig. 2). The arrhythmias subsided, and the surgery was completed uneventfully.

View larger version (87K): [in this window] [in a new window]   Figure 2. Similar disconnection detected on closer inspection in second case.

The literature has reported concerns about the integrity of the Bain circuit's central inner tube (2,3); various tests have been proposed and performed (4). The circuits we used met the test criteria ("aligned" and "intact"). Nevertheless, the circuits failed, causing the patients to rebreathe expired gases. We speculate that failure occurred when the machine was moved: the circuit flexed at the machine end, disconnecting the central inner tubing from its seat. Continuous wear and tear of the circuit from repeated use probably had already loosened the connection. To avoid this failure in the future, we recommend that Intersurgical Limited redesign this coaxial circuit, so that the hidden inner tube connection at the machine end can be inspected. A low-pressure alarm could also be used to sense this type of disconnection. However, the high flow resistance of some coaxial breathing systems can defeat low-pressure alarms (5).

References

1. AAGBI. Checklist for anesthesia apparatus. London: Association of Anaesthetists of Great Britain and Ireland, 2004.
2. Jellish WS, Nolan T, Kleinman B. Hypercapnia related to faulty adult coaxial breathing circuit. Anesth Analg 2001;93:973–4.[Abstract/Free Full Text]
3. Gooch C, Peutrell J. A faulty Bain circuit. Anaesthesia 2004;59:618.[Medline]
4. Heath PJ, Marks LF. Modified occlusion tests for the Bain breathing system. Anesthesia 1991;46:213–6.
5. 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]

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