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Does isolation technique have any impact on inhalational exposure of neuroanaesthetists to sevoflurane during craniotomies?

Szelei, Emil; Molnár, Csilla; Büdi, Timea; Tankó, Béla; Mikos, Borbála; Novák, László; Fülesdi, Béla

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European Journal of Anaesthesiology: November 2010 - Volume 27 - Issue 11 - p 994-996
doi: 10.1097/EJA.0b013e32833cad40

Editor,

Volatile anaesthetics may pose both short-term and long-term risks to the operating theatre staff.1 Despite the clinical and experimental observations, acceptable exposure levels for the to date administered anaesthetic gases are either not defined in many countries or the regular screening of the occupational exposure in the operating room is missing.2–4

A recent study reporting on occupational exposure to sevoflurane during craniotomies has shown that sevoflurane levels measured at the anaesthetist's breathing zone were significantly higher than those measured at the neurosurgeon's breathing zone and at the farthest corner of the operating room. It has also been postulated that the source of this higher evaporation is the patient's mouth.5

In neurosurgical anaesthesia, there have been traditionally two methods of patient isolation. In some centres, the anaesthesia staff, along with the equipment, is located on the side of the patient. The other possible isolation technique is positioning the anaesthesia staff at the feet of the patient. We wanted to test the hypothesis that different isolation techniques during intracranial surgeries pose different exposure levels to sevoflurane.

Twenty-two patients undergoing craniotomy for removal of intracerebral tumours were included in our study. For induction of anaesthesia, we used propofol (1–2.5 mg/kg body weight), whereas for maintenance of anaesthesia, we used the combination of fentanyl-rocuronium-sevoflurane. Low-flow anaesthetic technique was applied at a sevoflurane concentration ranging from 0.6 to 2.1 vol.% as required for maintenance of adequate anaesthesia. All endotracheal tube cuffs were inflated slightly above 30 mmHg. Surgeries were performed in operating rooms equipped with modern ventilation, air conditioning and a scavenging system compliant with international standards. A continuous air circulation along with air changing and refill at a rate of 50 m3/min was ensured in the operating theatres.

Sample collection and quantification technique

To detect anaesthetics, we used a set-up that consisted of an air sampling pump (224-51TX Air Sampling Pump SKC, Dorset, England), an integrated tube system and an absorber ampule embedded in the tube system. The suction pump attached to the sample collector ensured that air samples flowed through the absorber that collected sevoflurane for quantification occurring later as described previously elsewhere in detail.5 As our intention was to assess the impact of isolation technique on occupational exposure of the anaesthetists, sample collection was restricted to the period between placing the isolation drape on the patient and the closure of the dura.

During the present study, the distal parts of the absorbers were placed in two locations: one sampling tube was placed in close proximity of the tracheal tube in the angle of the patient's mouth and the other one in the anaesthetist's breathing zone.

Isolation of the patients occurred by single-use operation drapes that were fixed to the patient's forehead as was necessary for the craniotomy. Two locations of the anaesthetists along with the anaesthesia equipment were assessed during the study. In the first set-up, the anaesthesia team was placed on the right side of the patient and accessing of the patient was ensured from the side, whereas in the second group of patients, the anaesthesia team was located at the feet of the patient.

Ethics

Ethical approval for this study (Ethical Committee NAC 207) was provided by the Ethical Committee of University of Debrecen, Hungary (president Professor J. Szentmiklósi) on 18 May 2006 (DEOEC RKET/IKET 2483-2006).

Statistical methods

Means and standard deviations are reported for all values. Because normality tests indicated nonnormal distribution of the samples, comparative statistics were performed by nonparametric tests. Differences were considered statistically significant if P was less than 0.05.

A series of 22 patients (13 women and nine men, average age: 52.1 ± 6.2 years) undergoing craniotomies were included in the study. The surgeries included eight meningiomas, seven glioblastomas, four metastatic brain tumours, one medullaoblastoma and two astrocytomas. The average duration of anaesthesia was 218.3 ± 24 min and the average duration of surgery was 157.7 ± 14 min. In the first step of the analysis, we compared the amounts of sevoflurane that escaped at the patient's mouth in the two groups (e.g. isolation to the side and to the feet). No significant difference was found between the amounts of anaesthetic gas evaporated at the patient's mouth in the two groups (side: 5.02 ± 3.5 ppm vs. feet: 6.5 ± 9.2 ppm; P = 0.33). When comparing the exposure of the anaesthetists at different locations depending on the isolation technique, we found that there was a significant difference among the two groups: the exposure of the anaesthetists to sevoflurane is lower if the anaesthesia team is located at the patient's feet (0.19 ± 0.15 ppm) compared to exposure at the bedside (1.34 ± 1.09 ppm). The results are depicted in Fig. 1.

Fig. 1
Fig. 1

In neurosurgical centres throughout Europe, different isolation strategies and consequently different locations of the anaesthesia team exist during craniotomies. We found that despite the modern ventilatory and scavenging system of the operating room, if the anaesthesia team are situated at the side of the patient, the anaesthetist's exposure to sevoflurane is higher than that at the feet of the patient.

In neurosurgical anaesthesia, there is a debate about whether intravenous or inhalational anaesthesia is preferable for craniotomies when taking the patient's outcome into account.6 In terms of the other side, for example, the environmental exposure of the operating room staff during craniotomies, it is clear from previous observations that the operating neurosurgeon's exposure is not higher than the average pollution measured in the farthest corner of the operating theatre and the neuroanaesthetist's relative exposure is higher.5 In the present study, we have demonstrated that the location of the team does influence the amount of sevoflurane measured at the anaesthetist's breathing zone. In all fairness, the average exposure of the anaesthetist with the team positioned at the side (1.34 ± 1.08 ppm) is still below the accepted threshold levels for sevoflurane (e.g. 2 ppm). It has to be noted, however, that these threshold levels were arbitrarily defined on the basis of animal experiments. No clear-cut evidence exists between levels of exposure or short-term and long-term consequences of exposure for humans. Therefore, the much lower exposure of the anaesthesia team to sevoflurane during craniotomies performed with the team positioned at the feet (0.29 ± 0.15) may be of importance for occupational safety of the anaesthesia staff. Further, prospective studies are encouraged to prove whether this difference between the exposure levels results in short-term and/or long-term side-effects on the anaesthesia team.

References

1 Zacny JP, Yajnik S, Lichtor JL, et al. The acute and residual effects of subanaesthetic concentrations of isoflurane/nitrous oxide combinations on cognitive and psychomotor performance in healthy volunteers. Anesth Analg 1996; 82:153–157.
2 Burm AGL. Occupational hazard of inhalational anesthetics. Best Pract Res Clin Anesthesiol 2003; 17:147–161.
3 Nilsson R, Björdal C, Andersson M, et al. Health risks and occupational exposure to volatile anaesthetics: a review with a systemic approach. J Clin Nurs 2005; 14:173–186.
4 Halsey MJ. Occupational exposure to inhalational anaesthetics. Anaesthesia Rounds, Zeneca. The Medicine Group (Education) Ltd.; 2005.
5 Tankó B, Molnár C, Bűdi T, et al. The relative exposure of the operating room staff to sevoflurane during intracerebral surgery. Anesth Analg 2009; 109:1187–1192.
6 Engelhard K, Werner C. Inhalational or intravenous anaesthetics for craniotomies? Pro-inhalational. Curr Opin Anaesthesiol 2006; 19:504–508.
© 2010 European Society of Anaesthesiology