Lithium (Li) absorption systems are equal to calcium (Ca) absorbers in their ability to scavenge nitrogen dioxide (NO2) when nitric oxide (NO) is administered via anesthesia systems in the cardiac lab or operating room, research suggests.
The anesthesia systems are “semiclosed” to conserve anesthetic agents and require carbon dioxide (CO2) absorption to allow recirculation. As a result, the recirculation and low fresh gas flow (FGF) rates typically used with anesthesia delivery systems lead to higher NO concentrations than prescribed, and could theoretically lead to an elevation in NO2 levels.
“Our anesthesia colleagues were trialing the Li absorber and asked us to do the study to determine if the Li absorber was at least equivalent to the Ca absorber when using NO, and if we needed to change our policy on the amount of fresh gas flow rate needed,” said Natalie Napolitano, MPH, a research clinical specialist in respiratory care services at Children’s Hospital of Philadelphia (CHOP), and the lead author of the study that was presented at the Society of Critical Care Medicine’s 2016 Critical Care Congress (abstract 717).
Li as Effective as Ca
The study found that Li absorbers eliminate NO2 with the same effectiveness as Ca absorbers and required the same FGF rate for safety, Ms. Napolitano said.
“This finding does have significance, particularly given the fact that anesthesiologists are taking care of pediatric patients who can present to us on nitric oxide in the operating room as well as other locations throughout the hospital,” said Cheryl K. Gooden, MD, pediatric anesthesiologist at Bronx-Lebanon Hospital Center in New York City.
“It is important to keep in mind that calcium absorbers have been used for many more years in anesthesia than lithium absorbers,” Dr. Gooden said, adding that Li absorbers have been used in many other industries with great success, most notably the space industry. “The use of lithium absorbers in anesthesia remains relatively new. So, it is quite useful information for the anesthesiologists to know that both absorbers are equivalent in their function to scavenge NO2.”
Richard Lin, MD, of CHOP’s Division of Anesthesia and Critical Care Medicine, and a co-author of the study, said lithium hydroxide–based absorbers hold an advantage over Ca-based absorbers in that they are recyclable and produce less compound A in reactions with volatile anesthetics. The lack of reactivity can result in cost savings since less volatile anesthetic is required, he said.
Dr. Gooden said the cost of a CO2 absorbent using a Li-containing catalyst (i.e., Litholyme, Allied Healthcare Products) is comparable to the traditional soda lime–based absorbents. The traditional CO2 absorbents use potassium or sodium catalysts and have a safety profile that is less appealing for use, particularly with low-flow anesthesia, she said. “When lithium is compared with these other absorbents, lithium offers safety advantages to our patients, especially with the use of low-flow systems, and at a lower cost.”
Dr. Gooden said, “This is the first study to compare the ability of lithium and Sodasorb [W.R. Grace] absorbents to scavenge NO2. The results of this small study are compelling, but also it should be noted that further research is needed in this area and with a larger patient group.”
The study found that both Ca and Li absorbers were able to scavenge NO2 with the highest measured concentration of 3.5 ppm (5 ppm is the recommended upper limit) at an NO dose of 40 ppm. When absorbers were in line, relative FGF at 1.0 times minute ventilation was sufficient to minimize NO2, with higher relative FGF of no benefit.
When absorbers were not in line, relative FGF at 3.0 times minute ventilation still caused decreases in NO2. A relative FGF of 1.5 times minute ventilation was sufficient to make the measured NO match the set dose. NO and NO2concentrations were slightly higher (by <2 ppm) measured near the patient “wye.”
Of note, NO concentrations at low relative FGF were higher with absorbers in line.
The researchers used a test lung configured to infants and toddlers connected to a Draeger Apollo delivery system with NO injector in the inspiratory limb at the Apollo to deliver 20 and 40 ppm of NO.
The ventilator setting was appropriate to each patient’s “condition” and was varied over a range of 0.5 to 3.0 times minute ventilation and was measured periodically.
Measu res were repeated with Ca and Li absorption systems, and under “toddler” conditions without an absorption canister for comparison.
“The recirculation and low FGF rates typically used with anesthesia delivery systems lead to higher NO concentrations than prescribed and could theoretically also lead to an elevation in nitrogen dioxide levels. We have shown that calcium absorption systems can scavenge NO2 and wanted to see if lithium systems could do the same,” the researchers said.