History
A 38 year-old woman was brought to the hospital directly from the airport because she complained of shortness of breath immediately after exiting the airplane. She had a history of depression and took amitriptyline and zolpidem and admitted to daily alcohol use. She also had a history of hypertension but did not recall the name of her medication. She reported that she was well prior to getting on the flight and only drank two beers about 6 hours apart. During the flight, she noted some abdominal and back pain, followed by difficulty breathing. She denied ingestions or suicidal ideations.
Physical Examination On arrival to the hospital she was noted to be severely short of breath with the following vital signs: blood pressure, 156/92 mm Hg; pulse, 140 beats/min; respiratory rate, 42 breaths/min; temperature, 98.2°F (36.8°C); oxygen saturation, 100% on a 100% non-rebreather mask. Her head was without signs of trauma, and her pupils were equally round and sluggishly reactive to light. Her neck was supple and her chest was clear. Her heart was tachycardic but regular, and without murmurs, rubs, thrills, or gallops. Her abdomen was soft with normal bowel sounds and no organomegally. She was slightly tender in all four quadrants, but without guarding or rebound. Her extremities were without clubbing, cyanosis, or edema, and a brief neurological examination was without deficit or focality.
Immediate Management The patient was immediately intubated, sedated with midazolam, and attached to a mechanical ventilator. A rapid bedside glucose was reported as 50 mg/dL, and she was given 25 g of D50W and 100 mg of thiamine intravenously. An arterial blood gas revealed a pH of 6.80, a PCO2 of 24 mm Hg, and a PO2 of 106 mm Hg on room air. A CT scan of the chest was negative for pulmonary embolus. Standard laboratories are shown in Table CS8–1.
What Is the Differential Diagnosis? The laboratory analysis shows a severe metabolic acidosis with elevated anion gap (40 mEq/L). Of the many mnemonics used to help recall the differential diagnosis, one of the most popular is MUDPILES (Methanol; Uremia; Diabetic and other ketoacidoses; Phenformin and metformin; Iron and isoniazid; Lactate; Ethylene glycol; Salicylates) (Chap. 19). It should be remembered that this is an imperfect mnemonic in that it is easy to forget cyanide, theophylline, and a number of other xenobiotics that are not directly noted.
What Clinical and Laboratory Analyses Can Help Identify the Etiology? A rapid clinical assessment will help to narrow the differential diagnosis. For example, iron poisoning is almost always associated with vomiting (Chap. 46), and isoniazid rapidly produces seizures (Chap. 58). Uremia can be excluded based on the BUN and creatinine. Likewise, the presentation glucose concentration helps diminish the probability of diabetic ketoacidosis.
At this point, additional rapid tests are useful. A urinalysis showing ketones would be helpful ...