[Is the lithium chloride-coated heat and moisture exchanger a danger for patients?]

Such hygroscopic compounds as LiCl, CaCl2, and MgCl2 are used to improve water retention capacity and, as a consequence, the effectiveness of heat and moisture exchangers (HME). Resorption of these substances via the bronchopulmonary tract and a resulting systemic action cannot be excluded, especially if additional active moisturizing devices are used. The narrow therapeutic range of lithium is known, as are its unwanted side effects, such as nausea, vomiting, somnolence and even cardiac arrhythmia. These are symptoms that also frequently occur during anaesthesia and intensive care, so that differentiation against effects of lithium is nearly impossible. We investigated whether, in theory and in practice, LiCl-coated HME could result in effective Li plasma concentrations. We measured (1) total LiCl content of HMEs, (2) release of this content, simulating the worst-case situation with a breathing model, and (3) lithium plasma concentrations of adult patients being ventilated during anaesthesia with a rebreathing circuit and LiCl-coated HME, but with no additional active moisturizing system incorporated. RESULTS. The results show striking differences with LiCl content ranging from 3 to 251 mg varying not only between different types of HME but also within the same lots. After 20 min of ventilation more than 90% of the LiCl coating was rinsed into the test lung of the breathing model. In practical use, we observed an increase in lithium plasma concentration in 3 of 20 investigated patients. The plasma values of maximum 49.5 micrograms/l (= 0.007 mmol/l) do not amount to potentially toxic concentrations. Nevertheless, clinically relevant concentrations might occur in patients with small distribution volumes, e.g. newborns or infants with frequent exposition within short intervals such as in intensive care units. The differences in lithium content also indicate qualitative differences in water retention capacity. Because of the potential side effects of lithium, we prefer qualitatively equivalent HMEs, e.g., with MgCl2 or CaCl2 as hygroscopic substance.