Heated breathing tubes affect humidity output of circle absorber systems

J Clin Anesth. 1993 Nov-Dec;5(6):463-7. doi: 10.1016/0952-8180(93)90062-j.


Study objective: To verify whether the airway climate in circle systems can be improved with heated breathing tubes.

Design: Randomized, controlled, prospective clinical study.

Setting: Operating theater of the Department of Maxillofacial Surgery.

Patients: 26 adult patients undergoing prolonged anesthesia.

Interventions: A total of 26 prolonged anesthetics were conducted in adult patients using a minimal fresh gas flow rate (0.6 L/min) and silicon breathing tubes (16 mm internal diameter) containing a heated coil. Group 1 (n = 10 patients) was the control group; breathing tubes were unheated. In Group 2 (n = 10 patients), breathing tubes were heated to 30 degrees C. In Group 3 (n = 6 patients), breathing tubes were heated to 36 degrees C.

Measurements and main results: Humidity and temperature were measured at the Y-piece. Inspiratory temperature on Group 2 was significantly higher than in Group 1. In Group 3, both inspiratory temperature and absolute humidity were significantly higher than in Group 1. After 5 minutes of ventilation, water content and temperature of inspiratory gases were significantly higher in Group 3 than in Group 1.

Conclusion: Low-flow systems need at least 120 minutes to achieve a satisfactory airway climate. Heated breathing tubes effectively reduce this delay.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Absorption
  • Adult
  • Anesthesia, Closed-Circuit / instrumentation*
  • Anesthetics / administration & dosage
  • Electric Impedance
  • Electric Power Supplies
  • Equipment Design
  • Equipment Safety
  • Hot Temperature
  • Humans
  • Humidity
  • Intubation, Intratracheal / instrumentation*
  • Prospective Studies
  • Respiration, Artificial / instrumentation
  • Silicon
  • Temperature


  • Anesthetics
  • Silicon