Waste gas exposure to sevoflurane and nitrous oxide during anaesthesia using the oesophageal–tracheal Combitube small adultTM

K. H. Hoerauf, T. Hartmann, S. Acimovic, A. Kopp, G. Wiesner, B. Gustorff, H. Jellinek and P. Krafft

Department of Anaesthesiology and General Intensive Care, University of Vienna, Waehringer Guertel 18–20, A-1090 Vienna, Austria*Corresponding author

Accepted for publication: August 21, 2000


    Abstract
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Exposure to sevoflurane (SEV) and nitrous oxide during ventilation using a Combitube (37Fr) small adult (SA)TM was compared with waste gas exposure using conventional endotracheal tubes. Trace concentrations of SEV and nitrous oxide were assessed using a direct reading spectrometer during 40 gynaecological laparoscopic procedures under general anaesthesia. Measurements were made at the patients’ mouth and in the anaesthetists’ breathing zone. Mean (SD) concentrations of SEV and nitrous oxide measured at the patients’ mouth were comparable in the Combitube SATM (SEV 0.6 (0.2) p.p.m.; nitrous oxide 9.7 (8.5) p.p.m.) and endotracheal tube group (SEV 1.2 (0.8) p.p.m.; nitrous oxide 17.2 (10.6) p.p.m.). These values caused comparable contamination of the anaesthetists’ breathing zone (SEV 0.6 (0.2) p.p.m. and nitrous oxide 4.3 (3.7) p.p.m. for the Combitube SATM group, compared with SEV 0.5 (0.2) p.p.m. and nitrous oxide 4.1 (1.8) p.p.m. for the endotracheal tube group). We conclude that the use of the Combitube SATM during positive pressure ventilation is not necessarily associated with increased waste gas exposure, especially when air conditioning and scavenging devices are available.

Br J Anaesth 2001; 86: 124–6

Keywords: anaesthetics volatile, trace concentrations; anaesthetics gases, trace concentrations; equipment, tracheal tube


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Because the health consequences of environmental exposure to anaesthetic vapour1 are controversial, US and European health authorities recommend limits ranging between 2 and 75 p.p.m. for volatile anaesthetic exposure and between 25 and 100 p.p.m. for nitrous oxide to minimize health hazards.2 The European community has yet to establish exposure limits for sevoflurane (SEV), but the likely level is expected to be similar to that of isoflurane or enflurane ranging between 10 and 20 p.p.m.

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 oesophageal–tracheal 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
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
After approval by the Institutional Ethics Committee and obtaining patients written informed consent, 40 otherwise healthy patients (ASA physical status I–II) scheduled for elective laparoscopic gynaecological procedures were recruited.

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 1.5–3.0 mg kg–1, neuromuscular block obtained with vecuronium 0.1 mg kg–1, and anaesthesia was maintained with i.v. fentanyl, SEV, and 65% nitrous oxide in oxygen with a fresh gas flow of 3 litre min–1. 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 min–1. Inspiratory and end-expiratory SEV and nitrous oxide concentrations and ventilatory variables were recorded using the anaesthesia machine’s 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 20–30 cm H2O using an Endotest (Ruesch, Germany) manometer.

The study was conducted in a room that had 20-air exchanges h–1, 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 2–3 cm above the patient’s 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 (Mann–Whitney 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 h–1 in group ETC vs. 1.0 (0.2) vol% or 0.5 (0.2) MAC h–1 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.



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Fig 1 Distribution of average SEV and nitrous oxide concentrations for each group and patient at each measurement point (median ––, 10th, 25th, 75th and 90th percentile). AnSev represents the location anaesthesist’s breathing zone and measured substance SEV, AnN2O nitrous oxide at the location anaesthesist’s breathing zone, PatSev and PatN2O SEV and nitrous oxide, respectively, at the location patient’s mouth.

 
During anaesthesia and ventilatory support using tracheal intubation, 1.2 (0.8) p.p.m. SEV and 17.2 (10.6) p.p.m. nitrous oxide were found at the patients’ mouth giving an exposure of the anaesthetist of 0.5 (0.2) p.p.m. SEV and 4.1 (1.8) p.p.m. nitrous oxide over the time of anaesthesia.

No significant differences between ETC and ETT were recorded for both substances measured at the patient’s mouth, and at the breathing zone of the anaesthetist.


    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
We found that the Combitube SATM gave a patent airway with an adequate seal during controlled mechanical ventilation for gynaecological laparoscopy. Although the ETC provides only supraglottic ventilation and does not seal the trachea directly, the waste gas exposure was comparable with tracheal intubation. Gynaecological laparoscopic procedures were chosen for the environmental measurements, because these procedures represent a special challenge for airway management and ventilatory support6 with an increased risk of gas leakage because of the elevated intra-abdominal and airway pressures. Because the ETC does not seal the trachea directly, we expected leakage and significant environmental waste anaesthetic gas contamination, especially at the patients’ mouth.

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
 
The study was supported in part by the Hochschuljubila«umsstiftung, Vienna.


    References
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Boivin J. Risk of spontaneous abortion in women occupationally exposed to anaesthetic gases: a meta-analysis. Occup Environ Med 1997; 54: 541–8[Abstract]

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: 925–9[Abstract/Free Full Text]

3 Hoerauf K, Funk W, Harth M, Hobbhahn J. Occupational exposure to sevoflurane, halothane and nitrous oxide during paediatric anaesthesia. Anaesthesia 1997; 52: 215–9[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: 189–93[Abstract/Free Full Text]

5 Hall J, Henderson K, Oldham T, Pugh S, Harmer M. Environmental monitoring during gaseous induction with sevoflurane. Br J Anaesth 1997; 79: 342–5[Abstract/Free Full Text]

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: 670–5[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: 764–6[Abstract/Free Full Text]





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