Nitrous Oxide in the Pre-hospital Setting
By: Gregory Cassidy M.D., PGY3
Nitrous oxide is a colorless, tasteless gas that is administered in combination with oxygen, often referred to as “laughing gas”. It is absorbed via the pulmonary vasculature following inhalation through a facemask. The patient may self-administer the gas by holding the facemask to their face until the desired effect is reached. Nitrous does not combine with hemoglobin or any other body tissues and is safe for use in both adult and pediatric patients. Once administered it has rapid onset as well as rapid elimination, less than 60 seconds.
Nitrous should be primarily thought of as a pain medication. Studies have shown that it has a similar analgesic effect as morphine 10 mg IM. Although primarily thought of as a pain medication, it also carries anxiolytic and sedative properties. It may be used along with other analgesic medications such as local anesthetic or non-opioid pain medications. It is important to note, however, that it should not be administered in combination with opioids or benzodiazepines. If a patient has received an IV opioid you should wait 30-45 minutes before using nitrous. This is done to avoid excessive sedation and possible airway complications.
Nitrous oxide has been used in EMS since the 1970s and is regaining popularity across the US in recent years as well as in France, Canada, Australia and the UK. It is an ideal agent for pre-hospital use for multiple reasons. First, as mentioned above, it is effective in treating both pain and anxiety, two conditions frequently encountered in the pre-hospital environment. Second, it has rapid onset and elimination, both attractive properties for treatment of acute illness. Nitrous oxide will reach its peak effect within 2-5 minutes of administration and will wear off within 60 seconds of discontinuation, giving the patient the ability to provide an appropriate history upon arrival to the ED. In addition, administration only requires pulse oximetry monitoring which can easily be performed with current equipment. Additionally, there is no requirement that the patient must be NPO prior to administration. Patients may drive after administration and do not even require an IV if one is not available.
Contraindications to use of nitrous oxide include severe COPD or asthma, pneumothorax, active otitis media (ear infection) or sinusitis, bowel obstruction, 1st and second trimester pregnancy, complex advanced active cardiac disease, or any altered level of consciousness including psychiatric disease, alcohol intoxication and head injury.
It may be used to treat a wide variety of painful conditions, including but not limited to, procedural pain such as pain experienced during reduction of a dislocation or splinting of a fracture, pain following trauma, pain as a result of burns and even chest pain.
The gas is administered with oxygen at a fixed ratio of 1:1 (50% nitrous oxide/50% oxygen. The gas is carried in a small nitrous oxide cylinder and is combined with either an in-rig oxygen supply or any portable oxygen cylinder. The gases are combined automatically by the unit prior to delivery via the facemask. The combination is administered with a unit called Nitronox, the most common delivery system found in use among EMS agencies in the United States. The facemask on the Nitronox unit delivers the gas based on demand via negative pressure. The patient will hold the mask to their face and once an airtight seal is established and the patient inhales, the medication will be administered. The patient should be instructed to take slow, deep breaths until the desired level of analgesia is reached. If the patient were to become drowsy the mask will naturally fall away from the face, the airtight seal will be lost and the patient will therefore not receive any additional medication. Under ideal circumstances, the medication should be administered in a well-ventilated area. All attempts should be made to ventilate the patient compartment when used during transport through means such as activating exhaust fans and opening windows when possible to avoid inadvertent exposure of providers to the medication.
Possible side effects to be mindful of with administration include a sensation of lightheadedness, dizziness, headache, confusion, nausea and vomiting as well as euphoria. Should these symptoms become concerning for the patient or interfere with patient care the treatment can easily be stopped and the symptoms treated accordingly. Side effects attributed to nitrous oxide typically resolve within minutes of discontinuation.
Data examining the use of nitrous oxide in the pre-hospital environment spans several decades and indicates that it can be used safely and effectively for treatment of painful conditions by EMS agencies. The use of nitrous oxide is included in the national scope of practice model for paramedics and offers an alternative to traditional opioid medications for the treatment of acute pain. Nitrous oxide is an ideal agent for pre-hospital use and should be considered for the treatment of pain due to its safety, efficacy and ease of use once it is available.
Nitronox Field Unit:
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