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  Table of Contents 
Year : 2021  |  Volume : 25  |  Issue : 3  |  Page : 147-151

Quantitative assessment of nitrous oxide levels in room air of operation theaters and recovery area: An observational study

1 Post Graduate Institute Medical Education and Research, Chandigarh, India
2 Indian Institute of Science Education and Research, Mohali, Punjab, India

Date of Submission22-Jul-2019
Date of Decision09-Mar-2020
Date of Acceptance26-Apr-2020
Date of Web Publication9-Oct-2021

Correspondence Address:
Dr. Shyam C Meena
Assistant Professor, Anaesthesia and Intensive Care, PGIMER, Sector 12, 160012, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijoem.IJOEM_44_19

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Background: Nitrous oxide has been used during surgical anesthesia for many years. However, information about occupational exposure and related risks due to N2O exposure to the health care personnel in India are still poorly understood. Here, we measured the residual N2O levels during the working time of operation theatre room air in our tertiary care hospital. Material and Methods: The air samples were collected from different anesthesia exposure zones on different days for quantitative analysis of available N2O in the room air in respective areas. Nitrous oxide concentrations in the ambient air were also measured to compare outdoor and indoor levels. Observations and Results: Nitrous oxide mixing ratios were found to be 65.61 ± 0.05 ppm, 281.63 ± 0.43 ppm, and 165.42 ± 0.42 ppm in elective surgical theatres of the hospital on three different days whereas in emergency operation theatres of the same hospital levels of N2O were 166.75 ± 0.07 ppm, 510.19 ± 0.30 ppm and 2443.92 ± 0.64 ppm during same period. In elective pediatric surgical theatres levels of N2O were found to be 1132.55 ± 0.70 ppm and 362.21 ± 0.13 ppm on two days of reading respectively. Outdoor levels of N2O in contrast found 0.32 ± 0.01 ppm and was lower by a factor of 1000. Conclusion: We observed the very high ambient concentration of N2O in the surgical theatre's environment (up to 2443 ppm) and recovery areas (up to 50 ppm). It was 5 to 50 times higher ambient concentration of N2O than REL in OT area and 200-7000 times higher ambient concentration of N2O than outdoor ambient air in all surgical theaters other than CTVS OTs.

Keywords: Healthcare personnel, nitrous oxide pollution, occupational safety, quantitative air assessment, waste anesthetic gas

How to cite this article:
Puri G D, Meena SC, Sinha V, Hazarika A, Hakkim H, Sharma A, Kajal K, Dogra N. Quantitative assessment of nitrous oxide levels in room air of operation theaters and recovery area: An observational study. Indian J Occup Environ Med 2021;25:147-51

How to cite this URL:
Puri G D, Meena SC, Sinha V, Hazarika A, Hakkim H, Sharma A, Kajal K, Dogra N. Quantitative assessment of nitrous oxide levels in room air of operation theaters and recovery area: An observational study. Indian J Occup Environ Med [serial online] 2021 [cited 2023 Mar 28];25:147-51. Available from:

  Introduction Top

During surgical procedures, patients are exposed to relatively high concentrations of nitrous oxide (N2O) and other inhalational anesthetic gases (to make them anesthetized) but this happens once or rarely in their lives. Conversely, healthcare staff including anesthesiologists, surgeons, nurses, and Operation Theatre (OT) technicians may be exposed chronically to lower concentrations but at a much higher frequency (e.g., daily over their working life).

N2O is used worldwide as a carrier gas and analgesic-anesthetic agent for providing anesthesia during surgery. It reduces the induction time and the dosage of inhalational or intravenous inducing agents.[1] Concomitant use of N2O with volatile anesthetic agents reduces these agent usages proportional to its Minimum alveolar concentration (MAC) reduction as MAC is additive. These “MAC-sparing properties” of N2O on the side effects of the volatile anesthetics improved hemodynamic properties and decreased respiratory depression. Because of its short elimination half time regardless of its duration of use, lower lipid solubility aids wash out from the brain faster than other volatile agents and MAC awake value of 0.55–0.6 which is higher than other agents that translate into more rapid recovery.[2]

Despite many benefits, there are concerns in view of the occupational safety of N2O gas. Several observational studies have reported about the congenital malformations, increased risks of spontaneous abortion, and declined fertility upon chronic exposure to higher doses of N2O.[3],[4] Altered vitamin B12 status, diminishing of neuropsychological functions such as alertness, genotoxicity, and depression are also reported in many studies due to occupational exposure to N2O.[3],[4],[5],[6],[7],[8]

The recommended exposure limit (REL) of N2O in ambient air of surgical theaters is 25–100 ppm in most of the developed countries. Even when levels are below safety limits, chronic exposure of N2O in the OT environment and nonavailability of scavenging system, the risk of toxicity remains.

In simple words, N2O emitted into the air due to leakages and other reasons remains undetected by human senses even in fairly high concentrations and ultimately due to chronic exposure by breathing these toxic concentrations of N2O can lead to significant health hazards to health-care staff of OT area as simple agitation, irritability, depression, lack of concentration, dizziness, chronic headache, excessive sweating, anemia, fatigue, nausea, vomiting, ringing or buzzing in the ears, brain, and nerve damage.[7],[9] The carcinogenicity and mutagenicity of N2O has also been reported.[9]

In this observational study, we quantified the ambient N2O in working OTs and postsurgery recovery environment of our premier health and research institute to assess prevalent N2O exposure concentrations and its exceedance in comparison to outdoor air and normal exposure limits in OTs and recovery areas.

  Materials and Methods Top

After approval from the institutional ethical committee (IEC, PGIMER, Chandigarh dated on 25/11/2017) and CTRI registration (CTRI/2018/07/014745), we took multiple air samples from different working places of our tertiary care hospital in different time intervals of active working hours.

Sample collection

The whole air samples from different zones of hospital were collected in commercially available 6 L passivated silicon air sampling steel canisters (Restek, USA) by using a Teflon VOC pump with a flow rate of 5500 sccm (Model – N 86 KT.45.18; KNF pump).[10]

These canisters are known to preserve sample integrity for trace gases such as N2O. Fifteen whole air samples were collected randomly from six different zones during working hours (between 9 AM and 11 AM), with time intervals of approximately 1 month in between two sample collected from the same zone to minimize any temporal bias.

In OTs, 10 cm from the common gas outlet of anesthesia workstation was considered as measuring spots for air sampling for quantification of the room air N2O, whereas in the recovery area 10 cm from patient's airway was considered as measuring spots for air sampling. Outdoor levels were measured outside the hospital on the roof top.

Measurement of nitrous oxide

N2O levels were determined in all these air samples by environmental research scientists and analyzers were kept completely blind about the air sampling sites. N2O in the air samples was measured using a high-precision cavity ring-down spectroscopy (CRDS) analyzer (Model G2508, Picarro, Santa Clara, California). A more detailed description of the instrument is available in the literature.[10],[11] Within this instrument, the light from a tunable semiconductor diode is passed through a high-precision wavelength monitor to a finesse optical cavity using high reflectivity (>99.995%) mirrors. The light circulates in the cavity traversing path lengths of ≥20 km. The ring-down time of the cavity with and without absorption due to N2O was calculated and compared continuously to obtain the concentration of the N2O gas. The temperature and pressure of the cavity were regulated at 45°C and 140 Torr (with minimal variations of less than 20 mK and 0.1 Torr, respectively), resulting in highly stable spectroscopic features. The canisters were analyzed for ~5 min with the CRDS instrument (suction flow of instrument ~230 mL/min). The measurements were performed at a frequency of 1 Hz. Calibrations for N2O were performed by dynamic dilution of a gas standard mixture (Phoenix Gases Ltd., Navi Mumbai, India). The overall uncertainty of measurements was always <4%.

  Observation and Results Top

Existing basic characteristics of surgical theaters, nature and type of surgery and anesthesia

Every surgical theater is made up of 150 m3 and having two doors in every theater. The surgical theater usually remains closed but their frequency of opening is quite variable and it ranges between 4 and 5 times in an hour. The fresh air (100%) was maintained from a central air conditioning plant to the OT environment. Relative humidity and temperature inside OT were maintained in a range of 50%–60% and 22°–24°, respectively. Fresh air flow is maintained in laminar pattern and approximately 2.5 m3/s by central air conditional plant team. The service of air conditioning done once in 2 months in our operative areas and the efficacy is checked daily.

All air samples were collected during working time, when the surgeries were going inside operative theaters and general anesthesia were being administered to majority of patients in approximately 60% concentration of N2O with 40% oxygen plus volatile agent (e.g., isoflurane, sevoflurane, desflurane) at the rate of 2–3 L/min of total gas flow. All of anesthesia delivery system and anesthesia machine were having minimal leakage (<150 mL/min) and checked on every day prior to starting of any anesthesia.

Carcinoma of larynx surgery, thyroid surgery, and middle ear surgery (average duration of such surgeries is 3–4 h) was conducted, respectively, three different time in “elective General surgical theater.” In “pediatric elective OTs,” abdominal surgeries were conducted both time of air sampling and airway was secured with appropriately sized endotracheal tubes. However, in “emergency surgical theater” exploratory laparotomy surgery for intestinal obstruction was conducted all three times of observations. In “elective cardiothoracic and vascular surgical theaters” (CTVS), heart valve repair surgery was conducted during air sampling.

Observed environmental/ambient Nitrous oxide concentration in different working places

We found the high ambient concentration of N2O 65.61 ± 0.05 ppm, 281.63 ± 0.43 ppm, and 165.42 ± 0.42 ppm, respectively, in three different points of observations in elective general surgical theaters. We also observed the high ambient concentration of N2O 166.75 ± 0.07 ppm, 510.19 ± 0.30 ppm, and 2443.92 ± 0.64 ppm in three different time of sampling from emergency surgical theaters, whereas the high ambient concentrations of N2O were 1132.55 ± 0.70 ppm and 362.21 ± 0.13 ppm in two different time of sampling from pediatric surgical theaters, respectively [Table 1].
Table 1: Ambient nitrous oxide concentrations in different working places of tertiary care hospital

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In the same period, we found lesser concentration (1.25 ± 0.09 and 0.64 ± 0.02 ppm) in elective cardiac surgical theater as compared to other OTs, where we are not using N2O since more than 10 years.

We also found the higher concentration of N2O (50.79 ± 0.04 ppm and 21.90 ± 0.024 ppm, respectively, in two different time) in recovery rooms because of the patient's exhalation of residual N2O to the recovery room air after their awakening from anesthesia. We also observed little high residual concentration of N2O in nonanesthesia zone of hospital like general medical ward (1.39 ± 0.01 ppm, 0.73 ± 0.01 ppm, and 0.57 ± 0.01 ppm in three different time of sampling) as compared to green area. In the green area of the same city (approximately 5 km from the hospital), a value of 0.32 ± 0.01 ppm of N2O was measured.

The mixing ratios in ambient air outdoors are globally only 320 ppb, showing elevated concentration exposure up to 100–1000 times more (1000 ppb is 1 ppm) for personnel working in the room air environment, and suggesting a significant occupational health risk exposure.

  Discussion Top

Anesthesiologists, surgeons, and other operating room personnel such as nurses, technicians of all ages, and pregnant and/or nonpregnant staff spend significant time in the OTs. Occupational health and the safety of these OT personnel should be of utmost importance to any health-care system. We recently surveyed and asked them about side effects of chronic exposures of N2O and other inhalational agents. Majority of staff were having very less information and were casual toward their side effects on long-term exposures. To the best of our knowledge, this is the first effort to measure the residual concentration of N2O in ambient air of OTs and recovery areas during working time in a premier tertiary health-care center and research institute of India.

Understanding the possible risks of WAG in the OT environment has had a pivotal evolution. N2O, diethyl ether, and halothane may be liable for contrary reproductive and general systemic effects.[12] The similar effects on the reproductive system by N2O and added the risk of cancer, long-standing damage to the hepato-renal system and genetic mutation were also observed in another study.[13] The higher incidence of spontaneous abortions, inherited anomalies, and the risk of hepato-renal impairment were also observed in another study.[14]

As per the National Institute for Occupational Safety and Health (NIOSH) the REL for WAG is 25 parts per million (ppm), that measured as a time-weighted average (TWA) during the period of anesthetic administration for N2O when used as the sole inhaled anesthetic agent.[15] However, European countries such as Britain, Netherlands, Switzerland, France, and Germany have distinctive recommended standards and have REL for N2O and halogenated agents in the range of 25–100 and 10–50 ppm, respectively, measured as TWA for 8 h.[16],[17]

In this observational study, we obtained high ambient concentrations of N2O in emergency and pediatric surgical theaters possibly due to surgical theaters are running continuously in emergency, inhalational pediatric induction, leaving gas flow control valves open and vaporizers on after use, and ill-fitting face masks or inadequately inflated tracheal tube and laryngeal mask airway cuffs enhance to the escape of WAG into the OT atmosphere.

The source of the leakage of anesthetic gases may be from both the high-pressure and low-pressure systems of the anesthesia machine.[18] In addition, lack of good workplace practices such as leaving gas flow control valves open and vaporizers on after use, and ill-fitting face masks or inadequately inflated tracheal tube and laryngeal mask airway cuffs enhance to the escape of WAG into the OT atmosphere.

OT pollution and related unfavorable long-term outcomes due to N2O can be reduced by use of effective scavenging systems, installation of more effective ventilation systems, by making advance modular OTs, more use of advanced anesthesia techniques like very low flow anesthesia/TIVA practices and more attention to equipment maintenance and leak detection.[19] In recovery rooms also have a WAG from the exhaled gases of the recovering patients. It is worthwhile to place an exhaust in such an area so that WAGs are not restored in same. The most effective way of controlling the air level of N2O is the employment of a good scavenging system combined with effective air ventilation.[5]

The air conditioning and an efficient pressure/exhaust ventilation (above 12 air exchanges/h) together with efficient active scavenging systems are sufficient enough to sustain residual N2O concentration in operating rooms within the OEL value of 180 mg/m3.[20] Gilly et al. also assessed that in surgical suites without mechanical ventilation or scavenging systems (2 of 41), maximum occupational threshold limits (i.e., 100 ppm N2O; 5 ppm halothane) were exceeded uninterruptedly and to substantial degrees throughout the whole duration of anesthesia.[21] Koda et al. found that under efficient scavenged conditions, residual concentrations of N2O in ambient air were 70–190 ppm in anesthesiologist's areas and 70–90 ppm in surgeons and nurses' areas.[22] Barker et al. suggested that anesthetic vapors may escape into the OT environment primarily from the anesthetic breathing assembly during filling of vaporizers, inhalational induction, leakages around the patient's face mask, leakages from monitoring equipment, and loose-fitting equipment.[23]

We have laminar air flow, HEFA filters, adequately sized rooms, minimal or leak free anesthesia machine, better air conditioning system in our OTs complex but anesthesia waste gas scavenging system (AGSS) is not existing available in any OT. Government is stressing on establishment of AGSS in modular OTs for newer construction.

N2O is responsible for approximately 6% of the warming effect of greenhouse gases in the atmosphere which are contributing to climate change. N2O also provides a source of reactive nitrogen in stratosphere where it can photo-dissociate resulting in depletion of the protective stratospheric ozone layer.[24],[25] From the results obtained in this study, it appears that hospitals through the OT source can be significant sources of fugitive N2O. Being a greenhouse gas and source of reactive nitrogen in the stratosphere, this new source needs to be better quantified for impacts on outdoor atmospheric environments.

  Conclusion Top

We quantified the high ambient N2O in working OTs (up to 2443 ppm) and postsurgery recovery environment (up to 50 ppm). This points to enhanced exposure of healthcare personnel in OT environments due to waste anesthetic gas leaks and unavailability of proper anesthesia scavenging system in old-designed OTs of low resource countries which are 200–7000 times higher than normal outdoor air level of 0.32 ppm. As per NIOSH guideline for OT working area, the ambient N2O in our OT and recovery area was found 5 to 50 times higher. Better control measures during anesthesia, periodic training by effectual education curriculums and regular monitoring of trace levels of WAG are therefore important for hazard awareness, prevention, and control of exposure to WAG.

Financial support and sponsorship


Conflict of interest

There is no conflict of interest.

  References Top

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  [Table 1]


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