Anaesthesia Circuits, Humidity Output, and Mucociliary Structure and Function

Abstract

We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method. Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15±1.4 vs 9±0.8 vs 5±0.4 mg H 2 O, P<0.01) after two hours. Mean cilia length (µm) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8±0.4 vs 8.6±1.1 vs 15.4±2.1, P<0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3±0.5 vs 3.2±1.1 vs 4.2±0.8, P <0.001). Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H 2 O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.

The effect of the humidifier on sore throat and cough after thyroidectomy

“…In general, studies about the warming and humidifying circuit have determined the effects on protection of the structure and functions of mucociliary cells lining the bronchus. The criteria for recommending warming and humidification in low-flow anesthesia were established by Branson et al [7]. It was shown that there were effects in maintaining the absolute humidity at least 12-15 mgH 2 O/L.…”

“…The cool and dry anesthetic gas directly reaches the lower respiratory tract during mechanical ventilation after endotracheal intubation. It causes a decrease in heat and humidity, induces inflammation and irritates the tissue within the respiratory tract, and impairs the functions of cells lining the respiratory mucosa [6,7]. Various types of pharmacological and non-pharmacological methods have been examined to reduce the occurrence of POST [1,8-11].…”

Klimatisierung von Narkosegasen bei Einsatz unterschiedlicher Patientenschlauchsysteme

“…Es werden absolute Feuchten der Inspirationsluft zwischen 15 und 30 mgH 2 O/l und Atemgastemperaturen zwischen 28 und 32°C angegeben [2,7,8,9]. Branson et al geben eine absolute Feuchte von 12-15 mgH 2 O/l als ausreichendes Minimum an [4]. In Analogie zur physiologischen Atemgasklimatisierung wird von Rathgeber hingegen erst eine Atemgastemperatur zwischen 30 und 37°C und eine absolute Feuchte der Narkosegase zwischen 30 und 35 mgH 2 O/l als ausreichend angesehen [13,14].…”

Low-flow anesthesia: Theory, practice, technical preconditions, advantages, and foreign gas accumulation

“…During anesthesia, the absolute humidity of the inspired gas should range between 17 and 30 mgH 2 O·l Ϫ1 , and its temperature between 28° and 32°C. After an initial period of 30-45 min in an actively heated compact breathing system, these values can be achieved only by the use of a low-flow technique [37][38][39][40][41].…”