The Use of Nitrous Oxide During COVID-19

Is nitrous oxide sedation an AGP?
Aerosol-generating procedures result in the production of airborne particles (aerosols) that create the potential for airborne transmission of infections that may otherwise only be transmissible primarily by the droplet route. 
 
During nitrous oxide sedation, the mixed gases are delivered via a nasal mask with a relatively low flow rate (approx. 6L/minute) using a closed breathing circuit, with the scavenging system attached to the dental suction (airflow rate of 40-45L/minutes) so as to remove exhaled gases.
 
Inhalation driven nitrous oxide delivery systems have lower aerosolisation compared to other forms of nitrous oxide sedation (e.g. during labour), and while the active scavenging system reduces exposure to a patient’s aerosol droplets, it doesn’t fully prevent or protect from aerosols as the nasal mask is not completely sealed.
 
 
How do I reduce any potential risks associated with nitrous oxide sedation during COVID-19?
During use, the RA tubing will become contaminated 
  • externally from splashes and droplets from aerosols generated by handpieces or ultrasonic instruments , as well as by direct contact with the contaminated gloved hands of the operator or dental assistant.
  • Internally as the patient’s respiratory system is in direct communication with the RA machine via the breathing circuit. The breathing circuits are long, and as they are often internally corrugated, are difficult to clean.
 
In most nitrous oxide delivery systems, the flowmeter has a non-rebreathing valve present between the reservoir bag and the patient breathing circuit. The non-rebreathing valve acts as a check valve, allowing forward gas flow only when a slight negative inspiratory force is applied or when the reservoir bag fills to capacity and overflows into the breathing circuit. Although labelled a ‘continuous flow’ device, flow is continuous to the reservoir bag but not always to the breathing circuit, and for this reason, it may be beneficial to consider placing a bacterial/viral filter between the tubing and the machine. Opinion regarding the benefit of these filters remains ambiguous and research has demonstrated that the viral filtration efficacy of most filters is usually less than that for bacterial filtration.
 
Nasal hoods commonly incorporate a one-way valve to separate the incoming gas mixture from the exhaled scavenged gases, however some do not, especially the low-profile nasal hoods.
 
Most componentry of relative analgesia equipment can be reprocessed, and manufacturers offer detailed instructions (cleaning, disinfection and sterilisation) for the reprocessing of all componentry including reusable scavenging circuits, reusable nasal hoods and RA hoses.
 
High level disinfectants are active against vegetative bacteria, viruses, fungi and mycobacteria, and typically require 10-45 minutes of contact time for disinfection depending on the temperature. After disinfection, items require thorough rinsing with sterile or filtered water to remove any residual chemical residues.
 
The spiral vacuum tubing and the exterior of the vacuum gauge are cleaned only with a mild detergent and warm water. Usually both manual and automated disinfection instructions are provided for the reusable scavenging circuits, reusable nasal hoods and connectors.   Automated disinfection processes are superior to manual processes, as washer-disinfectors can deliver high pressure hot water with highly alkaline detergents at high flow through the tubing.  The same level of disinfection cannot be achieved by manual cleaning.
 
The ADA Dental Service Restrictions were developed to ensure a proportionate, pre-planned response in the event of escalating community-based transmission of COVID-19, to mitigate infection risks for both patients and staff.  Taking into consideration the potential risks associated with the provision of RA during a pandemic, under
  • Level 1 restrictions  - either a low profile nasal hood or nasal hood incorporating a one-way valve may be used.  Reprocessing procedures are determined by manufacturer’s instructions, with manual disinfection (as a minimum), followed by steam sterilization
  • Level 2 restrictions -  only  a nasal hood incorporating a one-way valve can be used.  Reprocessing procedures are determined by manufacturer’s instructions with only automated disinfection using a washer-disinfector recommended, followed by steam sterilization
  • Level 3 restrictions – RA is not recommended, unless necessary for management of trauma in children. Reprocessing procedures are determined by manufacturer’s instructions with only automated disinfection using a washer-disinfector recommended, followed by steam sterilization
 
The provision of RA should only be provided if the general principles for infection control measures in the context of COVID-19 are followed, as outlined in the ADA COVID-19 Risk Management Guidance document.

Date of document: 23 September 2020

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