Respiratory gas conditioning with filters/ heat and moisture exchangers can increase the duration of hyperthermia in patients under mechanical ventilation.

Dear Editor,

Recommendations for mechanical ventilation include respiratory gas conditioning with filters/heat and moisture exchangers (HMEs) mounted at the Y-piece, or heated humidifier mounted within the inspiratory tubing.1 Filters/HMEs work by collecting heat and humidity from the expired gas.23 We assumed that filters/HMEs can reduce heat loss and increase the duration of the hyperthermia period in patients under mechanical ventilation.

The study was approved by the Ethics Committee of Izhevsk Medical Academy, Russia (approved No. 477) on April, 2016. Pilot prospective study included 12 adult Intensive Care Unit patients. Informed consents were obtained from the patients’ legal representatives. Inclusion criteria were the age of 18–65 years, mechanical ventilation of the lungs lasting up to 96 hours, sepsis, hyperthermia (> 38.5°C), level of consciousness of 14–15 points according to the Glasgow scale,4 and the absence of central nervous system diseases. Exclusion criteria were the body temperature of 38.4°C or less, low respiratory volume, and pulmonary bleeding. Patients were randomly divided into two equal groups. In the first group (n = 6), the respiratory gas conditioning was performed with the filters/HMEs (Covidien Ltd., Mansfield, MA, USA). In the second group (n = 6) it was performed with a heated humidifier (water vapor temperature was 37°C). Patients’ body temperature was controlled using an esophageal temperature sensor (model MR411, Mindray Bio-Medical Electronics Co., Ltd., Shenzhen, China). A single dose of 1000 mg of paracetamol (Perfalgan 10 mg/mL, solution for infusion, Bristol-Myers Squibb Pharmaceuticals Ltd., Rome, Italy) was administered to all patients intravenously as an antipyretic agent. We determined the time interval required to lower the patient’s body temperature to 37.5°C.

The mean age of patients in the first group was 54.0 ± 8.4 years, and in the second group it was 62.6 ± 7.2 years. The initial esophagus temperature in the patients in the first group was 38.9 ± 0.4°C, and in the second group it was 39.1 ± 0.2°C. After intravenous administration of 1000 mg of paracetamol, the body temperature of patients in the first group did not drop to 37.5°C for 4 hours, and the average temperature in this period reached 38.4 ± 0.2°C. In the second group, temperature of 37.5°C was recorded within 3 hours after paracetamol solution administration in all patients (n = 6).

Based on the results obtained, we can assume that the use of filters/HMEs in mechanically ventilated patients with hyperthermia reduces the effectiveness of antipyretic therapy by limiting heat transfer through the respiratory tract. This pilot research can lay the groundwork for further study addressing how respiratory gas conditioning methods affect effectiveness of antipyretic therapy in hyperthermia patients with different clinical diagnoses.