An unusual foreign body in breathing circuit detected by capnography.

Sir,

It is a well-known fact that failure in properly checking equipment is the main factor in many critical incidents. Disastrous consequences are possible when an anesthetic breathing circuit is obstructed by a foreign body.[1] Proper preuse checking of equipment can help prevent equipment-related morbidity and mortality, educate anesthesiologist about equipment and improve maintenance. Unfortunately, failure to perform a proper check before use is common in practice.[2]

A 45-year-old, 55 kg, ASA physical status I male patients was scheduled for emergency exploratory laparotomy. After preoxygenation (target end-tidal oxygen >90%) with 100% oxygen, standard rapid sequence anesthesia was induced. Volume-controlled ventilation was started. Intraoperatively 5 leads ECG, heart rate, NIBP, oxygen saturation, end-tidal carbon dioxide (EtCO2), inspiratory and expiratory tidal volumes and airway pressures were monitored. After 45 minutes, during the course of an otherwise uneventful anesthesia, a sudden fall in the EtCO2 and final drop of the capnogram reading to zero was observed. There were no disconnections of the breathing circuit or capnography and no malfunctioning of ventilator was there. Hemodynamic parameters showed no significant variations. The peak inspiratory pressure and the plateau pressure remained unaltered. The tidal volume delivered to the patient was unchanged as indicated by movement of the bellows, peak inspiratory pressure and chest movement. Kinking or water banking in sample line tubing of capnography was also excluded. The inspection of the circuit adapter of capnograph showed a small plug of wet cotton stuck at the centre of the sampling port [Figure 1]. The problem was rectified immediately. The capnograph adapter and the tubing were replaced, following which the reading and waveform returned to normal. Subsequent anesthesia proceeded uneventfully.

Figure 1

Circuit adaptor showing wet cotton

Various types of foreign bodies have been reported in breathing circuits, having a great potential for serious outcomes.[13] Proper pre use checking of equipment and unusual changes in ventilator settings (airway pressures and volumes), capnography and patient vitals during the course of anesthesia can detect such foreign bodies. In our case, we discuss how the isolated changes in the capnography helped us detect an unusual foreign body in the breathing circuit. Above-mentioned findings in our case prompted us to look for kinking, water vapour or liquid water in the sample tube and water trap which can lead to gross inaccuracies in readings.[4] Contaminants may partially obstruct the sampling tubes of sidestream capnometers and increase resistance to flow thus affecting the response time and accuracy of the CO2 measurement. In more severe cases, the sampling tube may be occluded.[5]

Furthermore, thorough inspection of the circuit adapter showed a plug of wet cotton stuck at the sampling port placed in the centre of the circuit. This might have been missed during the routine inspection of the circuit due to the white colour of cotton. The initial normal capnography waveforms dampening to zero may be explained by the fact that on examination the cotton plug was wet, which might be due to the moisture of the expired gases of the patient. The wetting of cotton plug led to complete obstruction of the centrally placed sidestream sampling port. It has been reported that leaks and obstructions can occur at any of the numerous connection points and tubes within the sidestream sampling system, the resulting distorted waveforms and the end-tidal values can be significantly different from actual, may not be detectable by normal calibration procedures[6] and pose a potential hazard to the patient monitoring.

The exact cause of this unusual incident could not be concluded. One hypothesis is that nontechnical staff, while cleaning the nondisposable circuits and machine, might have left a piece of cotton in the adapter. Thorough inspection of the circuits and machine and proper training of nontechnical staff of operation theatre can prevent equipment related mortalities and morbidities.