Department of Anaesthesiology and General Intensive Care, University of Vienna, Waehringer Guertel 1820, A-1090 Vienna, Austria*Corresponding author
Accepted for publication: August 21, 2000
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Br J Anaesth 2001; 86: 1246
Keywords: anaesthetics volatile, trace concentrations; anaesthetics gases, trace concentrations; equipment, tracheal tube
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
During general anaesthesia, more contamination occurs when unsealed airway devices and/or high concentrations of inhalational anaesthetics are used.25 In particular the laryngeal mask airway (LMA) or the oesophagealtracheal CombitubeTM (ETC) could increase contamination when used for ventilatory support during surgical procedures commonly associated with elevated airway pressures being increased (e.g. laparoscopic surgery with peritoneal carbon dioxide inflation and steep Trendelenburg position). The ETC has only been used infrequently during elective surgery,6 because the standard ETC model (41Fr) is a rather large and potentially traumatic device. Therefore, the small adult (SA) model (Combitube (37Fr) SATM; Kendall; Gosport, Hampshire, UK) has been introduced in clinical practice7 and is a valuable alternative airway for mechanical ventilation during routine surgery in our hospital.
Because there is a lack of data about the environmental safety of the new airway device, we planned a randomized controlled study to measure operating room air contamination by waste anaesthetic gases during Combitube SATM ventilation for gynaecological laparoscopy, compared with a second group of patients managed by conventional tracheal intubation.
![]() |
Methods and results |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Using a computer generated random list, treatment assignments (ETC, n=20 or endotracheal tube (ETT), n=20) were contained in sequentially ordered sealed envelopes, which were opened just before anaesthesia induction. Induction, maintenance, and emergence from anaesthesia were performed in the operating room. Anaesthesia was induced with propofol 1.53.0 mg kg1, neuromuscular block obtained with vecuronium 0.1 mg kg1, and anaesthesia was maintained with i.v. fentanyl, SEV, and 65% nitrous oxide in oxygen with a fresh gas flow of 3 litre min1. All tubes were connected without using swivels to the anaesthesia machine (Cicero, Draeger AG, Germany). The waste gas outlet of this machine was connected to a scavenging system which in turn was connected to the hospital vacuum system at aspiration rates of 45 litre min1. Inspiratory and end-expiratory SEV and nitrous oxide concentrations and ventilatory variables were recorded using the anaesthesia machines build-in monitoring system.
Intermittent positive pressure ventilation (IPPV) with the administration of SEV and nitrous oxide was started after insertion of either the Combitube SATM or tracheal tube. Using direct laryngoscopy, a Combitube SATM (37Fr) was oesophageally inserted by the same anaesthetist in all group ETC patients. After oesophageal placement of the ETC, the oropharyngeal balloon was inflated with air volumes according to the formula: balloon volume (ml)=height (cm)100.6 Thereafter, the distal oesophageal cuff was inflated with 8 ml of air and supraglottic ventilation was started via the longer blue lumen of the ETC. In group ETT, conventional endotracheal tubes (Portex, Vienna, Austria) with an internal diameter of 7.0 mm were used. Cuff pressure was kept within the range of 2030 cm H2O using an Endotest (Ruesch, Germany) manometer.
The study was conducted in a room that had 20-air exchanges h1, with all ventilation being fresh air. Ambient gas was continuously sampled from two different locations using a Teflon® tube (Merck, Vienna, Austria). One sampling probe was fixed 23 cm above the patients mouth and a second one fixed at the shoulder of the anaesthetist (breathing zone). Operating room anaesthetic vapour concentrations of SEV, and nitrous oxide samples were assessed at 1 min intervals using a Brüel and Kjaer (Naerum, Denmark) spectrometer connected to a multipoint sampler. Before starting the study, the system was calibrated for each gas, for example with 20.8 p.p.m. SEV in pure nitrogen (Kaiser, Vienna, Austria) to provide an accuracy of ±2% over the entire relevant range. During the calibration process, the system software compensated for potential confounding effects of humidity, air pressure and temperature, SEV, nitrous oxide, isopropanol, water and carbon dioxide.
The occupational exposure standards were calculated according to the UK Occupational Exposure Limits 1999.8 Data are separately presented for each measurement point as average exposure of each anaesthesia as medians with 10th, 25th, 75th, and 90th percentiles. Values were compared using non-parametric tests (MannWhitney U test) using SPSS 6.1 (Macintosh OS 8.5) and a P<0.05 was considered statistically significant.
Patients characteristics were comparable between the groups. All patients in both groups were either oesophageally or tracheally intubated at the first attempt, ventilatory support was sufficient and no differences in ventilatory and respiratory variables were observed between the groups. No respiratory or cardiopulmonary complications occurred in either group.
Average (mean (SD)) vaporizer settings of the anaesthesia machine were 1.1 (0.3) vol% in group ETC and 1.2 (0.2) vol% in group ETT. The resulting mean end-tidal SEV concentrations were 1.0 (0.2) vol% or 0.6 (0.3) MAC h1 in group ETC vs. 1.0 (0.2) vol% or 0.5 (0.2) MAC h1 in group ETT (P=n.s. between the groups).
The distributions of the average waste anaesthetic gas concentrations observed during each procedure are presented as box-plots (median 10th, 25th, 75th and 90th percentile) in Fig. 1. The mean (SD) trace gas concentrations at the patients mouth observed during anaesthesia were 0.6 (0.2) p.p.m. SEV and 9.7 (8.5) p.p.m. nitrous oxide using a ETC. This gave an exposure of the anaesthetist to 0.6 (0.2) p.p.m. SEV and 4.3 (3.7) p.p.m. nitrous oxide over a period of about 60 min lasting each anaesthesia.
|
No significant differences between ETC and ETT were recorded for both substances measured at the patients mouth, and at the breathing zone of the anaesthetist.
![]() |
Comment |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Most international health authorities set occupational standards ranging from low to relatively high levels, demonstrating their uncertainty about the risks of chronic exposure. Chromosomal damage can be detected even when exposure was well within the recommended standards, but no long-term outcome of these changes could be established. Although these studies investigated the effects of a combined exposure to isoflurane and nitrous oxide, the amount of waste anaesthetic gases during different operating room settings and anaesthetic procedures should be assessed.
We conclude that using the Combitube SATM in patients undergoing positive pressure ventilation is not necessarily associated with greater waste gas exposure, especially when air conditioning and scavenging devices are available.
![]() |
Acknowledgements |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
2 Hoerauf K, Wallner T, Akca O, Taslimi R, Sessler D. Exposure to sevoflurane and nitrous oxide during four different methods of anesthetic induction. Anesth Analg 1999; 88: 9259
3 Hoerauf K, Funk W, Harth M, Hobbhahn J. Occupational exposure to sevoflurane, halothane and nitrous oxide during paediatric anaesthesia. Anaesthesia 1997; 52: 2159[ISI][Medline]
4 Hoerauf K, Koller C, Jakob W, Taeger K, Hobbhahn J. Isoflurane waste gas exposure during general anaesthesia: the laryngeal mask compared with tracheal intubation. Br J Anaesth 1996; 77: 18993
5 Hall J, Henderson K, Oldham T, Pugh S, Harmer M. Environmental monitoring during gaseous induction with sevoflurane. Br J Anaesth 1997; 79: 3425
6 Hartmann T, Krenn C, Zoeggeler A, Hoerauf K, Benumof J, Krafft P. The oesophageal-tracheal Combitube small adultTM: an alternative airway for ventilatory support during gynaecological laparoscopy. Anaesthesia 2000; 55: 6705[ISI][Medline]
7 Krafft P, Nikolic A, Frass M. Esophageal rupture associated with the use of the Combitube. Anesth Analg 1998; 87: 1457
8 Health and Safety Executive. EH40/99 Occupational Exposure Limits 1999, Sudbury: HSE books, 1999
9 Hoerauf K, Wiesner G, Schroegendorfer K, Jobst B, Spacek A, Harth M, et al. Waste anaesthetic gases induce sister chromatid exchanges in lymphocytes of operating room personnel. Br J Anaesth 1999; 82: 7646