Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. 
Part 2 – practical use, including problems, and their use with paediatric patients

Abstract

SummaryHeat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways. The first part of this review considered the history, principles of operation and efficiency of these devices. The aim of this part of the review is to summarise recent guidelines on the use of these devices and outline the problems that can occur. In particular, the effect of these devices on gas analysis, dead space, resistance to gas flow and blockage of the breathing system is considered. In children, it is important to consider the addition of dead space and resistance to gas flow. A body weight of 2.5 kg is probably the lower weight limit for use with heat and moisture exchangers, and 3 kg for filters. The resistance to gas flow of a heat-and moisture-exchanging filter added to a Mapleson F breathing system can cause a delay in the induction of anaesthesia.

In Vitro Evaluation of Heat and Moisture Exchangers Designed for Spontaneously Breathing Tracheostomized Patients

“…Heat and moisture exchangers (HMEs) conserve a portion of the heat and humidity from the exhaled gas, conditioning the subsequently inspired gas. [8][9][10] The use of HMEs in chronically tracheostomized spontaneously breathing patients can reduce retained secretions and improve quality of life. 11,12 HMEs can also provide supplemental oxygen (O 2 ) flow through a direct connection to an O 2 delivery system.…”

Impact of Humidification and Nebulization During Expiratory Limb Protection: An Experimental Bench Study

“…[1][2][3] Such a problem has already been identified with the administration of ribavirin during mechanical ventilation back in the 1980s, for pediatric patients with bronchiolitis due to respiratory syncytial virus. 4 vances in humidifier design and efficiency, and the arsenal of aerosolized drugs and indications has expanded, this topic is relevant to intensive care and mechanical ventilation today.…”

“…[5][6][7][8][9] Few recommendations exist to help clinicians choose the filtering device in such cases. 3,8,9 Moreover, manufacturers usually recommend a daily replacement of the device, thus leading to potential healthcare worker exposure to aero-contaminants and inducing recurrent depressurization of the circuit and alveolar derecruitment. Problems related to the use of filters with nebulized drugs are another part of the problem.…”

“…Problems related to the use of filters with nebulized drugs are another part of the problem. 3,10 The performance of filters depends not only on the type, and bacterial or viral filtration efficiency may be inadequate or highly misleading. 1,9 Nebulization and humidification tend to be similar processes in that both are methods to convert liquid (medication or water) into mist or vapor for humidification and particles that remain suspended within a gas for a period of time for nebulization, and both can be inhaled into the lower respiratory tract.…”

Failed ventilation due to heat and moisture exchanger filters malfunction

“…[1] There have been concerns regarding the malfunctioning of HMEF when the patient stays on mechanical ventilation for a long duration. [2] We report the case of complete respiratory obstruction due to a manufacturing defect in the HMEF in a 38-year-old woman, scheduled for laparoscopic cholecystectomy.…”