2025 – PAGE 213 – EMERGENCY MEDICINE & TOXICOLOGY
METHEMOGLOBINEMIA
Methemoglobinemia is an enzyme deficiency (NADH methemoglobin reductase) that results in increased methemoglobin levels (thus reducing O2-carrying capacity). Symptoms include BLUE or CYANOTIC SKIN without evidence of respiratory distress, hypotension/shock, and tachycardia. The blood becomes CHOCOLATE-COLORED (with less oxygen). Certain exposures increase the methemoglobinemia (this is associated with sulfa drugs and well water being used with formula). Treat with methylene blue, oxygen, and removal of the offending agent.
PEARL: In methemoglobinemia, the pulse oximeter reading will be low. It may show a saturation level of around 85% even if the TRUE hemoglobin oxygen saturation is higher. When the PaO2 is measured, it may be normal. The pulse oximeter will not improve with hyperoxia. Measure the methemoglobin level to get the diagnosis.
MNEMONIC: To remember the discrepancy between pulse oximetry and the ABG, think of the pulse oximeter as a “quick and dirty” tool that cannot tell the difference between regular hemoglobin and methemoglobin. It scans all of the hemoglobin, but only sees O2 bound to 85%. The “fancy” ABG is TOO specific. It can ONLY see regular hemoglobin. Since there’s plenty of oxygen around, what little regular hemoglobin is available is carrying plenty of O2. So, the ABG gives a normal PaO2 value. Giving more oxygen (hyperoxia) doesn’t change much because the extra O2 simply floats around without the ability to bind to any new hemoglobin sites until the “met” falls off (or is forced off with medication).
MNEMONIC: “METH HEMOGLOBINEMIA” is treated with METHylene BLUE for the kid who looks BLUE. Or, imagine a PALE BLUE teen who abuses METH.
ACID OR BASE INGESTION
NEVER do a gastric lavage for an acid or base ingestion. These are CAUSTIC/CORROSIVE substances, and lavage can lead to emesis and subsequent aspiration. Symptoms may include drooling, chest pain, dysphagia, odynophagia, oral ulcers, or tachycardia. If an acid or base ingestion is suspected, you MUST ORDER AN UPPER ENDOSCOPY (AKA EGD) to look for esophageal burns.
PEARL: ACIDS are sour and may leave esophageal and stomach burns. They are not neutralized.
PEARL: BASES are bitter (e.g., baking soda) and cause “liquefaction necrosis” and injury of the esophagus. They are neutralized in the stomach. Drain cleaners often contain sodium hydroxide (quick, often associated with oral lesions and may cause airway obstruction due to edema).
CYANIDE POISONING
Cyanide poisoning is a mitochondrial toxin and it also helps to form cyanohemoglobin. Cells become incapable of utilizing ATP, they switch to anaerobic respiration, the person becomes acidotic (elevated lactate), and because of the cyanohemoglobin, giving additional oxygen does not help. Death comes rapidly unless treated with a small inhaled dose of amyl nitrite, followed by IV sodium nitrite, and finally IV sodium thiosulfate.
FOREIGN BODY INGESTION
Coins are most common in cases of foreign body ingestion.
- Coin in PROXIMAL esophagus: REMOVE IT.
- Other coin in DISTAL ESOPHAGUS: LEAVE IT and reimage 24 hours later. If it still has NOT REACHED THE STOMACH AFTER 24 HOURS, REMOVE IT. If it is in the stomach, leave it because it will usually pass within about five days.
- BUTTON BATTERY: When lodged in the esophagus, this is a medical emergency, so REMOVE IT. Immediately give honey (if > 1 year old) or sucralfate to reduce esophageal injury. In an asymptomatic child, if the battery is < 20 mm and it has passed beyond the esophagus, observation is appropriate. However, if the battery is >20 mm or there is evidence of injury (e.g., symptoms or endoscopic findings), remove the battery, even if it is in the stomach.