DESCRIPTION

• Nitrogen oxides are components of air pollution and may be present in some occupational settings.
• Nitrogen dioxide is a reddish-brown gas, heavier than air.
• Nitric oxide is colorless and is the major nitrogen oxide in smog.
• See also SECTION IV, Nitrous Oxide chapter.

FORMS AND USES

Nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO₂), dinitrogen trioxide (N₂O₃), nitrogen pentoxide (N₂O₅), nitrogen peroxide, dinitrogen trioxide, dinitrogen tetroxide, dinitrogen pentoxide, and nitrous anhydride.

Occupational exposures include:

• Fire fighting, arc welding, and work at missile sites
• Manufacturing of explosives, jet fuels, dyes, lacquers, and celluloid
• Ice rink resurfacing
• Grain silos, which release nitrogen dioxide within the first few weeks after filling
• Farm workers are at risk for silo-fillers' disease

Environmental sources include decaying organic matter, volcanic emissions, atmospheric lightning, fires, and burning of fossil fuels.

PATHOPHYSIOLOGY

• Nitrogen dioxide reacts with water within the airway and on the respiratory mucosa to form nitrous and nitric acids.
• Localized caustic mucosal injury and inflammation develop.
• Because the gas is of intermediate water solubility, inhalation causes both upper airway and lower airway injury.

EPIDEMIOLOGY

• Poisoning is uncommon.
• Most significant nitrogen dioxide exposures involve inhalation.
• Toxic effects following exposure are typically mild to moderate, with death following prolonged high-concentration inhalation exposure.
• Most serious toxicity is occupationally related.

DRUG AND DISEASE INTERACTIONS

• Children may be more severely affected because they have higher minute ventilation and because they absorb more by being closer to the ground (nitrogen dioxide is heavier than air).
• Geriatric patients with underlying pulmonary dysfunction may be at increased risk for toxicity.

CAUSES

Poisoning is usually an accidental occupational incident.

WORKPLACE STANDARDS

Nitrogen Dioxide

• ACGIH. TLV TWA is 3 ppm; STEL is 5ppm.
• NIOSH. REL TWA is 1 ppm; IDLH level is 20 ppm.

Nitric Oxide

• ACGIH. TLV TWA is 25 ppm.
• OSHA. PEL TWA is 25 ppm.
• NIOSH. IDLH level is 100 ppm.

Section Outline:

• DESCRIPTION
• FORMS AND USES
• PATHOPHYSIOLOGY
• EPIDEMIOLOGY
• DRUG AND DISEASE INTERACTIONS
• CAUSES
• WORKPLACE STANDARDS
  • Nitrogen Dioxide
  • Nitric Oxide

DIFFERENTIAL DIAGNOSIS

Toxic causes of airway irritation include acrolein, ammonia, chlorine, formaldehyde, mercury vapor, metal fume fever, methyl bromide, natural gas, nickel carbonyl, phosgene, smoke inhalation, sulfur dioxide, zinc chloride fumes and others.

SIGNS AND SYMPTOMS

Acute Phase

• Symptoms of mucous membrane irritation as well as upper and lower airway irritation appear.
• Mild cases resolve over a few hours, but severe cases may progress to pulmonary edema (delayed 3 to 30 hours).

Delayed Phase

Noncardiogenic pulmonary edema, bronchitis, and interstitial lung disease occur days to weeks following an acute exposure.

Vital Signs

• Tachycardia and tachypnea are common following inhalation.
• Hypotension can be caused by either nitrate-induced vasodilatation or hypovolemia.

HEENT

• Conjunctivitis, rhinorrhea, blepharospasm, and sore throat may occur, but are more common following high-concentration exposure.
• Acute upper airway obstruction has occurred following inhalation exposures at high concentrations.
• Corneal burns may follow high-level exposures but are rare.

Pulmonary

• Cough, chest pain or tightness, dyspnea, and bronchospasm are common following either low- or high-concentration exposures.
• Wheezing, hemoptysis, rhonchi, and rales have all been reported.
• Noncardiogenic pulmonary edema has been reported following high-concentration prolonged exposure and may be delayed for hours to days.
• Bacterial superinfection and pneumonia may develop.
• Interstitial lung disease, pulmonary fibrosis, bronchiolitis obliterans, and reactive airway disease have occurred after either severe acute or chronic exposures.

Cardiovascular

• Tachycardia is common.
• Hypotension can be caused by either nitrate-induced vasodilatation or hypovolemia.
• Myocardial ischemia may occur.

Gastrointestinal

Nausea and vomiting are common.

Neurologic

• Headaches and lightheadedness are common following low-level exposure.
• Anxiety and agitation often reflect hypoxia.
• Syncope and loss of consciousness have been reported following high-level exposures but are rare.

Hematologic

Methemoglobinemia occurs rarely.

PROCEDURES AND LABORATORY TESTS

Essential Tests

No tests may be required following minimal exposure.

Recommended Tests

• Arterial blood gases to evaluate acid-base status and pulmonary gas exchange in patients with pulmonary symptoms
• Serum electrolytes, lactate, BUN, creatinine in serious cases
• Methemoglobin levels in patients who present with cyanosis that does not correct following the delivery of 100% oxygen
• ECG for all symptomatic patients at risk for myocardial ischemia
• Chest radiography if symptoms develop or oxygenation is abnormal (a normal radiograph obtained shortly after exposure does not preclude the development of delayed pulmonary effects)
• Serial performance of pulmonary function testing to assess course of injury
• Pulmonary scans including xenon lung scans to aid in determining the extent of injury following severe exposure

Not Recommended Tests

Levels are not clinically useful.

Section Outline:

• DIFFERENTIAL DIAGNOSIS
• SIGNS AND SYMPTOMS
  • Acute Phase
  • Delayed Phase
  • Vital Signs
  • HEENT
  • Pulmonary
  • Cardiovascular
  • Gastrointestinal
  • Neurologic
  • Hematologic
• PROCEDURES AND LABORATORY TESTS
  • Essential Tests
  • Recommended Tests
  • Not Recommended Tests

• Treatment should focus on management of airway and on assuring oxygenation.
• The need for intubation should be evaluated.
• Wheezing should be treated symptomatically.
• Severe cases may develop life-threatening airway obstruction.

DIRECTING PATIENT COURSE

The health-care provider should call the poison control center when:

• Severe bronchospasm, upper airway obstruction, pulmonary edema, or other severe effects are present.
• Toxic effects are not consistent with nitrogen oxide poisoning.
• Coingestant, drug interaction, or underlying disease presents unusual problem.

The patient should be referred to a health-care professional when:

• Attempted suicide or homicide is possible.
• Patient or caregiver seems unreliable.
• History of significant exposure is obtained.
• Coingestant, drug interaction, or underlying disease presents unusual problems.

Admission Considerations

• Following most low-level inhalation exposures, asymptomatic patients rarely need to be evaluated in a health-care facility.
• Inpatient management is warranted for patients with persistent respiratory symptoms, upper airway edema, burns, pulmonary edema, or hypoxia.

DECONTAMINATION

Eye exposure. The eye should be irrigated with water for 15 minutes and evaluated for corneal burns.

Out of Hospital

The patient should be moved to fresh air and oxygen administered.

In Hospital

Oxygen should be administered to symptomatic patients.

ANTIDOTES

There is no specific antidote for exposure to oxides of nitrogen.

ADJUNCTIVE THERAPIES

Bronchospasm

• Oxygen is administered, followed by albuterol 0.15 mg/kg (maximum of 10 mg) in saline with humidified oxygen via nebulizer every 20 to 30 minutes. If the peak expiratory flow rate is greater than 90% of predicted after initial dose, additional doses may not be needed. Response should be continually monitored.
• Methylprednisolone is administered intravenously every 6 to 8 hours; adult dose is 60 to 125 mg (1.0-1.5 mg/kg); pediatric dose is 1 to 2 mg/kg; this may be decreased to a single daily dose and tapered.
• Initiation of prednisone, 2 mg/kg orally for several days, should be considered.
• Prophylactic antibiotic therapy is not recommended because it does not reduce morbidity or mortality.

Section Outline:

• DIRECTING PATIENT COURSE
  • Admission Considerations
• DECONTAMINATION
  • Out of Hospital
  • In Hospital
• ANTIDOTES
• ADJUNCTIVE THERAPIES
  • Bronchospasm

PATIENT MONITORING

Pulmonary and cardiac parameters should be monitored closely until the patient recovers.

EXPECTED COURSE AND PROGNOSIS

• Delayed pulmonary edema may develop within hours of a severe prolonged inhalation exposure.
• Patients suffering high-level inhalation exposure may have a protracted hospital course.
• Resolution of chest radiographic abnormalities usually occurs within 2 months. Persistent infiltrates are sometimes present and may be consistent with bronchiolitis fibrosa obliterans or focal interstitial fibrosis.

DISCHARGE CRITERIA/INSTRUCTIONS

• From the emergency department. Asymptomatic patients may be discharged following complete resolution of cough, dyspnea, and tachypnea during a 6-hour observation period.
• From the hospital. Patient may be discharged following resolution or stabilization of toxic effects.

Section Outline:

• PATIENT MONITORING
• EXPECTED COURSE AND PROGNOSIS
• DISCHARGE CRITERIA/INSTRUCTIONS

DIAGNOSIS

• Patients may develop life-threatening respiratory complications following a latent period of hours to days.
• Despite a normal chest radiograph result shortly after a high-level exposure, the patient may develop delayed pulmonary edema or radiographic abnormalities.

FOLLOW-UP

• Patients discharged following an acute exposure should be instructed to follow up with their primary care physician for a recheck within 24 hours.
• Patients should be told to return immediately for health-care evaluation if they develop difficulty breathing, shortness of breath, persistent cough, or chest pain.
• Patients should be followed closely for a few weeks following significant exposures.
• Pulmonary function testing is recommended in patients with persistent respiratory complaints.

Section Outline:

• DIAGNOSIS
• FOLLOW-UP

Toxic effect of other gases, fumes, or vapors: nitrogen oxides.

See Also: SECTION IV, Nitrous Oxide chapter.

RECOMMENDED READING

Kuffner EK. Athletes in Greenberg, MI. In: Hamilton RJ, Phillips SD, eds. Occupational, industrial and environmental toxicology. St. Louis: CV Mosby 1997:19-28.

Langley RL, Meggs WJ. Farmers and farm personnel in Greenberg, MI. In: Hamilton RJ, Phillips SD, eds. Occupational, industrial and environmental toxicology. St. Louis: CV Mosby, 1997:105-111.

Authors: Edwin K. Kuffner and Gerald F. O'Malley

Reviewer: Luke Yip