The infection control Department at our hospital raised an alert for potential ICU patient cross-contamination via the CO2 sampling tubing in the operating rooms. My understanding is that this is almost impossible given the physics of constant negative pressure suction/aspiration in the CO2 sample line that is emptied into the evacuation system. I would expect that any ventilatory effort by the patient would always draw gas from the breathing circuit tubing, never from the gas sample line, because the gas analyzer continues to draw gas out of the breathing circuit throughout the entire respiratory cycle.
Throughout discussions with hospital administration they have maintained that they wish for us to change the CO2 sampling tubing after EVERY case. I would appreciate any insight that you could provide.
Evan Pivalizza, MD
After a recent tour of other surgery institutions I have noticed a difference in opinion regarding CO2 and gas sampling disposable lines. Most of the time on the anesthesia circuit I see the sampling line attached to a HME filter where there should be no cross contamination between patients when reusing a sampling line from case to case and patient to patient. But on occasion I have noticed an intubated patient on a t-piece, baby safe system, or other types, delivered to the PACU, and the sampling line is directly connected to a patient without an HME filter filter in the line. And then, later on in the day, I noticed it being utilized on another patient without a filter again. It was my understanding that the sampling line was being reused for quite some time, and unless there were known or suspected conditions of TB, influenza, and maybe pneumonia or other warranted conditions, there was no changing of the sampling line from patient to patient. I have contacted our manufacturer but their statement was very vague.
Eric J. Peterson, CRNA, MS, MBA, MHA
There is general agreement with your analysis concerning the negative pressure and constant flow path exiting into the scavenging system, and the minimal likelihood of airborne contamination. However, it is conceivable that contact contamination from the connector might result in low level initial colonization of the connector housing the sampling site, and possibly the endotracheal tube. Currently, there are no published data to support this theoretical concern.
Some recent machines, and perhaps some retrofitted conventional gas machines, have connectors that route effluent gas from the analyzer to the breathing circuit via the absorber. This could theoretically contaminate the breathing circuit, but one Committee on Technology (COT) member remarked that his department employed this effluent return for many years in over 600,000 cases without a recognized problem. Sending the effluent to the scavenging system, instead, would eliminate this theoretical concern.
Some very old gas analyzers had a reverse-purge function to clear the sample line, which would have also suggested a potential contamination problem, but to our knowledge, that has never been documented either.
Anecdotally, in the institution mentioned above that recycled the effluent, the sample line was only changed during scheduled maintenance every 6 months or when thought to be contaminated. The line was routed into an elbow connector with the port protruding approximately 5 mm into the lumen, which may have minimized the contamination risk. More recently, however, that institution changed to disposable sampling lines, and the dramatically increased incidence of loose or incorrect connections led to numerous clinical problems. Also, several COT clinicians from other institutions agreed that the "law of unintended consequences" had also occurred in their own locations. Following an inclusive literature search, performed by medical library staff, there are no reports of cross contamination of patients that were attributable to non-disposable sampling lines in the operating room. While it would be very difficult, and hugely expensive to design a study capable of definitively addressing this issue, anecdotal data from approximately a half million cases at a single institution suggest that cross contamination was probably not a significant patient care issue. However, a latent cross contamination problem might exist if someone is actually looking for it.
A suggested compromise for your particular situation may be to install a fresh sampling line prior to performing an anesthetic on cases likely to require long-term postoperative intubation, or after any case with a high likelihood of contaminating the tubing inlet with unusual pathogens. Another solution may be to purchase filters that connect between the gas sample line and sampling port on the elbow. This may be particularly useful to help protect the biomedical equipment technicians who service the equipment as well as those machines that effuse the gas into the breathing circuit. Above all, more plastic pieces and more connections may actually introduce the unintended complications of extra connections, including leaks, misconnections, cracked filters, and split tubing.
One last suggestion may be to use a traditional breathing circuit filter between the circuit Y-piece and the endotracheal tube, with the gas sampling port on the breathing circuit side of the filter. Care must be taken to continuously evaluate the proper operation of the filter.
The Committee on Technology, APSF
Numerous questions to the Committee on Technology are individually and quickly answered each quarter by knowledgeable committee members. Many of those responses would be of value to the general readership, but are not suitable for the Dear SIRS column. Therefore, we have created this simple column to address the needs of our readership.