Case Continued
With respect to the elderly patient in this case with dementia and multiple potential causes for hypoactive delirium, the life-saving measure was the New York City (NYC) mandate that all 911 responding EMS workers wear ambient carbon monoxide (CO) detectors. Though the value of these detectors is controversial due to their low sensitivity, the emergency medical technicians (EMTs) detected an elevated CO level of 300 ppm when they arrived at the patient’s home.
Without this information, the patient’s age and clinical presentation would almost certainly have prompted an extensive evaluation to determine the etiology of her change in mental status and most likely would have missed the true cause of CO toxicity, which was confirmed by venous co-oximetry showing the patient to have a carboxyhemoglobin (HbCO) level of 19.5%.
Carbon Monoxide Toxicity
Carbon monoxide affects multiple cell types. It binds to myoglobin and in high concentrations depresses myocardial contractility. In platelets, CO displaces nitric oxide potentially resulting in vasodilation. Life-threatening CO poisoning causes hypotension, syncope, tachycardia, and an altered mental status. Delayed neuropsychiatric sequelae also may occur as the result of free radical injury to the brain.13
Symptoms
Patients with chronic CO poisoning who can adequately communicate may report nausea, headache, lightheadedness, and lethargy mimicking other seasonal illnesses. In debilitated or cognitively impaired patients who are unable to communicate, findings may include tachycardia, a mild change in mental status, and little else. Prolonged exposure and physiologic accumulation of CO may cause depressed mental status, coma, or death.
Although HbCO levels are confirmatory of exposure, venous levels do not necessarily reflect tissue concentrations or outcomes. Patients with a similar level to that of this patient (19.5%) may present with no symptoms, mild headache, or a deep coma depending on the duration of exposure to CO.
Definitive treatment is removal from the toxic environment and prompt administration of O2. In some cases, hyperbaric therapy may be beneficial.14
Diagnosis
Although CO exposure is the most common cause of poisoning death worldwide, its detection requires a high index of suspicion, especially in areas where public-health protection measures are absent.
Although CO exposure is the most common cause of poisoning death worldwide, its detection requires a high index of suspicion, especially in areas where public-health protection measures are absent.
It is rarely easy to diagnose the first case of an illness of which one is unfamiliar or not accustomed to treating. Likewise, it is very difficult to consider, diagnose and, as a result, effectively manage the first presentation of a known condition that is typically seasonal or linked to a different geographic location. Acute presentations of environmental exposures, illicit drug poisonings, and communicable infectious diseases are increasingly the purview of emergency medicine. Whether it is the first case of Ebola, of severe acute respiratory syndrome, the influenza virus, a new lethal street drug overdose, or CO poisoning prior to the onset of winter, maintaining a high index of suspicion for the “index case” is of paramount importance. The patient presented here, the first CO poisoning of the season at the authors’ institution, illustrates the responsibility the EP to consider, diagnose, and prevent a wide-range of deadly consequences—injury prevention as the result of vigilance. Moreover, the consequences of missing the diagnosis would have placed others at risk for continued poisoning and possibly death.
Portable and Ambient Carboxyhemoglobin Monitors
The NYC Department of Health (NYCDOH) requires that all EMTs and paramedics wear CO detectors and all residential housing contain CO monitors. The NYCDOH also mandates that all identified cases of CO poisoning be reported to the NYC Poison Control Center. This centralization of data on any and all patients exposed to CO can result in an investigation of the source of CO by the fire department and capture symptomatic patients who present for care outside of the 911 response system. The source of CO in this patient was ultimately traced to a faulty furnace that was repaired to prevent others in the building from becoming victims of CO poisoning.
It should be noted that portable noninvasive HbCO monitors may be inadequate to rule out CO poisoning as the sensitivity of such devices can be as low as 48%.15 Carbon monoxide poisoning can result from brief exposure to a high ambient concentration, such as a fire in which environmental concentrations may exceed 500 ppm or more insidiously, in a setting of a chronic exposure. Faulty furnaces—a common seasonal cause of CO poisoning—may continue to produce adequate heat and fail to prompt any concerns.
Since CO is colorless and odorless, ambient CO detectors stationed in the home are the best means of alerting one to exposure. In this case, though mandated by NYCDOH, a CO detector was not present in the patient’s home.