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Anesth Analg 2002;95:656-660
© 2002 International Anesthesia Research Society

TECHNOLOGY, COMPUTING, AND SIMULATION

The Use of a Uniquely Designed Anesthetic Scavenging Hood to Reduce Operating Room Anesthetic Gas Contamination During General Anesthesia

Moeen K. Panni, MD PhD*, and Stephen B. Corn, MD*{dagger}

*Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, and {dagger}Department of Anesthesiology, Children’s Hospital, Harvard Medical School, Boston, Massachusetts

Address correspondence and reprint requests to Stephen B. Corn, MD, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, 75 Francis St., Boston, MA 02115. Address e-mail to corn{at}zeus.bwh.harvard.edu


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Numerous studies have suggested that chronic exposure to trace levels of anesthetic gas is harmful to operating room (OR) personnel. In the delivery of pediatric general anesthesia, an uncuffed endotracheal tube (ETT) is normally used which can result in considerable volatile anesthetic and nitrous oxide contamination of the OR. In this report, we present a method to reduce exposure to these anesthetic gases by means of an anesthetic scavenging hood (ASH). The ASH was used on six pediatric patients undergoing general endotracheal anesthesia via an uncuffed ETT. Measurements of all ambient gas levels were made 6 in. horizontally from the patient’s ear and 6 in. from the table surface. The application of the vacuum source to the ASH resulted in a very significant (P < 0.01, paired t-test) decrease in levels of ambient anesthetic gas, with no measurable change in ventilatory variables or changes in body temperature (P > 0.05, paired t-test). Discontinuation of the vacuum force to the ASH resulted in a marked increase in ambient levels of anesthetic gas. We conclude that the ASH is extremely effective in reducing waste anesthetic gas associated with anesthesia administered via an uncuffed ETT. The ASH may be a valuable and cost-effective addition in the OR for both reducing ambient anesthetic waste gas levels and conserving patient heat.

IMPLICATIONS: Chronic exposure to trace levels of anesthetic gas is harmful to operating room personnel, especially in the delivery of pediatric general anesthesia via an uncuffed endotracheal tube. The anesthetic scavenging hood is a cost-effective and efficient method to reduce these waste anesthetic gases, and it offers patient heat conservation.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
There is much debate regarding the health risks associated with occupational exposure to inhaled anesthetics. The operating room (OR) exposure value of nitrous oxide (N2O) recommended by the National Institute for Occupational Safety and Health (NIOSH) is 25 ppm, over an 8-h period, primarily to prevent "decrements in performance, cognition, audiovisual ability and dexterity" (1). The Occupational Safety and Health administration has not adopted these NIOSH recommendations with the result that in many ORs throughout the United States, N2O is virtually unregulated (2). Numerous studies have suggested that chronic exposure to trace levels of anesthetic gas is harmful to OR personnel (3–5). Epidemiologic studies of dental and OR personnel exposed to N2O and volatile anesthetics reveal a particular risk for reproductive toxicity (2,6). A recent study (7) addressed the effects of inhaled anesthetic exposure on genotoxicity as assessed by the formation of micronucleated lymphocytes, which is an established cytogenetic procedure to assess chromosome damage in persons exposed to potentially genotoxic drugs (8). Interestingly, they found that the members of the group with high-level occupational exposure had an increased incidence of chromosomal damage, but not for those who were in the low-level exposure group (within NIOSH guidelines) (7). This study suggests that the NIOSH guidelines may provide an appropriate level of safety against chromosomal damage.

Investigators have used a variety of means to measure the N2O concentration present in ORs. "Averaging" systems using absorbent materials fixed on the person have been used as well as "direct reading" gas analyzers that sample from a fixed location in the OR. In two studies, a two- to fivefold reduction in N2O concentration was reported by use of hygienic measures in the OR venting system (9,10). Reiz et al. (11) were the first to report the use of a double mask technique to decrease the ambient levels of N2O. This method reduced the ambient N2O levels from an average exposure of 145 parts per million (ppm) to 15 ppm in the vicinity of anesthesiologists, during inhaled anesthesia. In other cases of mask anesthesia, Sik et al. (12) reported the use of a scavenging device for use in pediatric anesthesia with a reduction in N2O levels by 82% to 100 ppm.

N2O and other anesthetic gas contaminations are of particular significance in the delivery of pediatric anesthesia via an uncuffed endotracheal tube (ETT). This method of anesthesia delivery results in considerable volatile anesthetic and N2O contamination of the OR via a gas leak around the ETT. In this report, we present a method and apparatus to scavenge waste anesthetic gas by means of an anesthetic scavenging hood (ASH)1(13,14). The device also serves as a potential means to conserve heat and/or actively warm patients undergoing surgery. The scavenging hood consists of a bonnet (multiple sizes) that is used to fit over the head of the patient, with an opening for the ETT or a laryngeal mask airway. An adapter is present, which fits standard suction tubing, to enable low-suction continuous scavenging of waste anesthetic gases. This device should serve the purpose of reducing exposure of OR personnel to anesthetic gases as well as conserving heat for the patient.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Hood Design
The device is in the form of a gas-impermeable flexible fabric bag of sufficient size to enclose the patient’s head. The bottom portion of the hood can be selectively fastened around a patient in such a way as to close the hood without jeopardizing the safety of the patient. The ASH has one exhaust port, which engages a length of suction tubing that extends into and protrudes from the hood. An external protruding portion of the tubing mates to a section of suction hose, which in turn is connected to the vacuum source. In single section, the inner portion of the suction tubing terminates approximately adjacent to the patient’s face and includes an area of multiple perforations that are adjacent to the terminal end through which gas to be exhausted may enter. The suction hose connects to a standard wall-mounted suction source, which is present in most ORs and can be adapted to vent the gas out of the OR and/or the building. Alternatively, the suction hose can communicate with a portable suction unit that likewise is adapted to create a suction force and convey exhaust gases out of the OR. The magnitude of the suction force can be regulated directly by means of a roller-clamp that restricts flow within the hose. There is also an opening port within the ASH to allow the ETT to exit from the hood. Figures 1 and 2 outline schematic representations of the ASH. In terms of safety, the ASH functions by entraining room air. It is engineered not to create an air- tight seal. In fact, the flaps on the device are manufactured so that they cannot be tied around the patient’s neck. The flaps just tuck under the patient, making the ASH extremely safe for anyone to use, even those who have never used the device before.



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  		Figure 1. A schematic view illustrating the anesthetic scavenging hood (see Fig. 2 legend for explanation of numbers).

 


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  		Figure 2. The anesthetic scavenging hood (ASH) (10) is shown with a top portion (12) and bottom portion (14). A suction tube (16) enters the hood through the top portion. The bottom portion of the hood is located adjacent to the patient’s mouth and includes a slit or opening to accommodate and seal the endotracheal tube (32). In addition, the bottom portion of the hood includes flaps (28) or release tape (26) which enable a loose but effective closure whereas allowing entrainment of room—in the area of the patient’s neck. The suction tube (16) includes an external portion (20) and an internal portion (18). The suction tube (16) enters the ASH through a port (24) on the top portion of the ASH. The interior portion (18) of tube (16) has a distal opening end with a multitude of perforations (22) adjacent to its distal end, which facilitate evacuation of gases from within the hood. The external portion (20) of tube (16) includes a roller clamp (26), which can be used to control the magnitude of the vacuum force by restricting flow within the tube.

 
Hood Evaluation
After IRB approval and informed consent, six pediatric patients undergoing general endotracheal anesthesia with an uncuffed ETT were selected at random from the OR schedule at Children’s Hospital, Boston. The patients were anesthetized by their anesthesia team in the usual manner without any special instructions regarding induction. All customary (American Society of Anesthesiologists) monitors and devices were then placed (e.g., oral gastric tube, temperature probe). The disposable, single-patient-use ASH was then placed over the patient’s head (Figs. 1 and 2). Each patient in this study served as his or her own control. The only anesthetic requirements imposed on the anesthesiologist were to maintain the N2O and volatile anesthetic concentration constant during the study period. This involved keeping the delivery rate, tidal volume, and respiratory rate constant during the study period. Measurement of the OR gas levels was made with a MiranTM 1B2 portable ambient air analyzer (Foxboro Co., Foxboro, MA) at a level 6 in. horizontally from the patient’s ear and 6 in. from the table surface. After these conditions were met, a steady-state level of gas being studied was achieved, after which the vacuum was applied to the scavenging hood adapter. The vacuum was maintained between 5 and 15 mm Hg by means of a roller clamp.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
The application of the vacuum source resulted in a very significant (P < 0.01, paired t-test) decrease in ambient levels of anesthetic gas at the measured site in all patients (Table 1), with no measurable change in tidal volume, peak inspiratory pressure, or respiratory rate (Table 2). Discontinuation of the vacuum force (without disconnecting the vacuum tube) resulted in a marked increase in ambient levels of anesthetic gas at the measured site in most of the patients studied (Table 1). In addition, there were no significant changes (P > 0.05, paired t-test) in the patients’ body temperature from start to completion of the study period as measured by axillary temperature probe (Table 3), with a change in mean temperature from 36.1°C (±0.699°) to 35.9°C (±0.720°). No complaints or adverse effects were noted or reported by patients, their parents, surgeons, or nurses related to this study.


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  		Table 1. Table 1. Nitrous Oxide and Isoflurane (Forane) Anesthetic Levels Measured at the Fixed Reference Point During Anesthesia of the Six Study Patients
 

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  		Table 2. Table 2. Tidal Volume, Respiratory Rate, Peak Inspiratory Pressure at the Start of (Prior) and During Maximal Suction Application (Max) During the Study Period, and Leak and Mean Airway Pressures in the Six Patients Studied
 

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  		Table 3. Table 3. Axillary Body Temperature at the Start and Close of the Study Period in the Six Patients Studied
 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
During the 1970s, OR gas-scavenging systems were introduced to decrease the exposure to waste anesthetic gases. The use of low-flow anesthesia systems, in combination with activated charcoal filters, also reduced anesthetic exposure to health care providers (15,16). The NIOSH reported that approximately 400,000 dental personnel are exposed to N2O and >50,000 OR personnel are exposed to waste anesthetic gases annually. The principal health concerns for workers exposed to anesthetics are cancer, reproductive abnormalities, interference of N2O with vitamin B12 metabolism, and hepatic and renal toxicity. Several neurobehavioral deficits have also been demonstrated after exposure to N2O, including impaired perception, decreased reaction time, headaches, drowsiness, and irritability (17). Chronic high-level exposure to N2O causes neurologic diseases indistinguishable from that caused by vitamin B12 deficiency, in which N2O oxidizes the cobalt atom in vitamin B12, interfering with its metabolism (18), which further emphasizes the importance of reducing these anesthetic gas contaminants in the OR. Application of the vacuum force to the port of the ASH resulted in a dramatic reduction of the levels of ambient anesthetic gas levels in the OR immediately. Even with markedly increased levels of ambient waste gas (>2000 ppm), the ASH decreased the levels to well within NIOSH recommended levels. With discontinuation of the vacuum force to the ASH, ambient gas levels immediately began to increase. Of note, the postsuction levels increased, but did not return to the presuction levels. This is probably attributable to a diminishing leak around the ETT with time. Even though postsuction levels were not as high as presuction levels, all postsuction levels were more than NIOSH recommended levels.

Thermoregulatory vasoconstriction or shivering helps prevent individuals from becoming hypothermic. In contrast, core hypothermia does develop rapidly in the hour immediately after the induction of general anesthesia (19,20). Cooling produced by ventilation with dry, cold gases (21), surgical skin preparation (22), and cutaneous heat loss (19)contribute to patient heat loss. General anesthesia does reduce metabolic heat production (22,23). However, these decreases in body heat balance do not seem to be sufficient to explain the observed initial decrease in core temperature, suggesting that redistribution of heat from core to peripheral tissues is a major cause of core hypothermia (19,24). Matsukawa et al. (25) demonstrated that core hypothermia decreased during the first hour after induction general anesthesia as a result, almost exclusively from redistribution of body heat, and this redistribution remained the most important cause even after three hours of anesthesia (25). The potential for heat conservation and maintenance of body temperature by the ASH cannot be accurately made without a full analysis of the OR temperature gradients involved; however, our data show no significant decrease in body temperature from start to completion of the study during a time frame in which one would expect a substantial decrease in body temperature, as shown in the studies mentioned above.

The ASH described in this report dramatically reduced the levels of anesthetic contamination in the OR to well within NIOSH recommended standards. The data also suggest that the ASH offers patient heat conservation, even with a vacuum source applied to its maximal level. We conclude that the ASH is extremely effective in reducing waste anesthetic gas associated with anesthesia administered via an uncuffed ETT. The ASH may be a valuable and cost-effective addition in the OR for both reducing ambient anesthetic waste gas levels and for conserving patient heat.


   Footnotes
 
SBC is the inventor of the ASH and has voluntarily assigned the technology to Children’s Medical Center Corp., Boston, MA.

1 Full text versions of the United States patents may be viewed at www.uspto.gov. Back


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. NIOSH. Criteria for a recommended standard-occupational exposure to waste anesthetic gases and vapors. Cincinnati, OH: National Institute for Occupational Safety and Health, 1977 (DHWE [NIOSH] no. 77–140).
  2. Cohen EN, Gift HC, Brown BW, et al. Occupational disease in dentistry and chronic exposure to trace anesthetic gases. J Am Dent Assoc 1980; 101: 21–31.[Abstract]
  3. Cohen EN, Brown BW, Bruce DL, et al. Occupational disease among operating room personnel: a national study. Anesthesiology 1974; 41: 321–40.[Web of Science][Medline]
  4. Buring JE, Hennekens CH. Health experiences of operating room personnel. Anesthesiology 1985; 62: 325–30.[Web of Science][Medline]
  5. Guirguis SS, Pelmear PL, Roy ML, Wong L. Health effects associated with exposure to anaesthetic gases in Ontario hospital personnel. Br J Ind Med 1990; 47: 490–7.[Web of Science][Medline]
  6. Rowland AS, Baird DD, Shore DL, et al. Nitrous oxide and spontaneous abortion in female dental assistants. Am J Epidemiol 1995; 141: 531–8.[Abstract/Free Full Text]
  7. Wiesner G, Hoerauf K, Schroegendorfer K, et al. High-level, but not low-level, occupational exposure to inhaled anesthetics is associated with genotoxicity in the micronucleus assay. Anesth Analg 2001; 92: 118–22.[Abstract/Free Full Text]
  8. Fenech M. The cytokinesis-block micronucleus technique: a detailed description of the method and its application to genotoxicity studies in human populations. Mutat Res 1993; 285: 35–44.[Web of Science][Medline]
  9. Borm PJ, Kant I, Houben G, et al. Monitoring of nitrous oxide in operating rooms: identification of sources and estimation of occupational exposure. J Occup Med 1990; 32: 1112–6.[Web of Science][Medline]
  10. Meier A, Jost M, Ruegger M, et al. Occupational exposure to anaesthetic gases during paediatric surgery. Anaesthetist 1995; 44: 154–62.[Web of Science][Medline]
  11. Reiz S, Gustavsson AS, Haggmark S, et al. The double mask: a new local scavenging system for anaesthetic gases and volatile agents. Acta Anaesthesiol Scand 1986; 30: 260–5.[Web of Science][Medline]
  12. Sik MJ, Lewis RB, Eveleigh DJ. Assessment of a scavenging device for use in pediatric anesthesia. Br J Anaesth 1990; 1: 117–23.
  13. Corn SB. Anesthetic scavenging hood. US Patent 5,370,110, Dec 6, 1994.
  14. Corn SB. Anesthetic scavenging hood. US Continuation Patent 6,076,524, June 20, 2000.
  15. Lewy R. Employees at risk: protecting the health of the health care worker. New York: Van Nostrand Reinhold, 1991.
  16. Suruda A. Health effects of anesthetic gases in the health care worker. In: McDiarmid M, Kessler E, eds. The health care worker state of the art reviews. Philadelphia: Hanley & Belfus, 1997.
  17. Udasin IG. Health care workers. Prim Care 2000; 27: 1079–102.[Web of Science][Medline]
  18. Lumb M, Perry J, Deacon R, Chanarin I. Recovery of tissue folates after inactivation of cobalamin by nitrous oxide: the significance of dietary folate. Am J Clin Nutr 1981; 34: 2418–22.[Abstract/Free Full Text]
  19. Sessler DI, McGuire J, Moayeri A, Hynson J. Isoflurane-induced vasodilation minimally increases cutaneous heat loss. Anesthesiology 1991; 74: 226–32.[Web of Science][Medline]
  20. Bickler P, Sessler DI. Efficiency of airway heat and moisture exchangers in anesthetized humans. Anesth Analg 1990; 71: 415–8.[Abstract/Free Full Text]
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  22. Stevens WC, Cromwell TH, Halsey MJ, et al. The cardiovascular effects of a new inhalation anesthetic, Forane, in human volunteers at constant arterial carbon dioxide tension. Anesthesiology 1971; 35: 8–16.[Web of Science][Medline]
  23. Viale JP, Annat G, Bertrand O, et al. Continuous measurement of pulmonary gas exchange during general anaesthesia in man. Acta Anaesthesiol Scand 1988; 32: 691–7.[Web of Science][Medline]
  24. Sessler DI. Perianesthetic thermoregulation and heat balance in humans. FASEB J 1993; 7: 638–44.[Abstract]
  25. Matsukawa T, Sessler DI, Sessler AM, et al. Heat flow and distribution during induction of general anesthesia. Anesthesiology 1995; 82: 662–73.[Web of Science][Medline]
Accepted for publication May 13, 2002.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins and Stanford University Libraries' HighWire Press®. Copyright 2002 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press