Case Reports

diagnostic pitfall: carbon monoxide poisoning mimicking hyperventilation syndrome

Jiann-Ruey Ong MD^a, Sheng-Wen Hou MD^a, Hsien-Tsung Shu MD^a,

Huei-Tsair Chen MD^a, Chee-Fah Chong MS, MD^a,b,*

^aEmergency Department, Shin-Kong Wu Ho-Su Memorial Hospital, Taipei 11101, Taiwan, ROC

^bSchool of Medicine, Fu Jen Catholic University, Taipei 24205, Taiwan, ROC

Received 15 July 2005; accepted 16 July 2005

Carbon monoxide is a great imitator. It is colorless, odorless, and ubiquitous in our environment. In large concentrations, it is known to be a stealthy killer. In lower concentrations, patients with carbon monoxide toxicity often are unaware of having had carbon monoxide exposure and may simply complain of vague and varied flu-like symptoms (headache, dizziness, nausea, vomiting, diarrhea, weakness, or general malaise) [1]. We report a case of a young female with carbon monoxide poisoning, who initially presented with delirium, breathlessness, carpopedal spasms, and numbness of the hands and around the mouth. She was therefore initially misdiagnosed as having hyperventilation syndrome. This Unusual presentation of carbon monoxide intoxication delayed correct diagnosis and therefore specific treatment in this patient. We were able to find only 1 previous report of a similar case of carbon monoxide poisoning presenting as hyperventilation syn- drome in literature [2].

A 23-year-old female with symptoms of shortness of breath and confusion was brought by ambulance to our ED. Her roommate had contacted police after entering the house when she noticed that the patient was delirious and sitting naked on the floor outside the bathroom. The police officers

T Corresponding author. School of Medicine, Fu Jen Catholic University, Hsin-Chuang Hsih, Taipei Hsien, Taipei 24205, Taiwan, ROC. Tel.: +886 2 29053490; fax: +886 2 29052096.

E-mail address: [email protected] (C.-F. Chong).

found that the patient was frightened, tachypneic, and unable to talk when they arrived. On their way to the hospital, the roommate was told to hold a paper bag tightly around the patient’s mouth for several minutes.

On arrival in the ED (about 30 minutes later), the patient was still hyperventilating but was able to talk. She denied taking illicit drugs or alcohol but recalled seeing a ghost while taking bath. Her vital signs were blood pressure of 105/70 mm Hg; pulse rate, 126 beats per minute (regular); respiratory rate, 36 breaths per minute; and temperature,

36.28C (97.28F). Auscultation of the chest gave normal results. She had numbness in both hands and around the mouth. She also had cramps over her hands and feet. However, no focal neurologic signs were elicited. arterial blood gases revealed pH 7.51; Paco₂, 22 mm Hg; and Pao₂, 96 mm Hg (room air). The presumptive diagnosis was panic disorder with hyperventilation syndrome. She was instructed to breathe intermittently into a paper bag. The toxicological screen was negative, and a psychiatrist was consulted to evaluate her Visual hallucinations. During her interview with the psychiatrist, the patient volunteered that she had a new gas water heater installed indoor and she had closed all the external doors and windows of the house while bathing. Without delay, she was given 100% oxygen using a tight- fitting face mask with a reservoir bag because carbon monoxide poisoning was suspected. The diagnosis was then confirmed by measuring her Blood carboxyhemoglobin level, which turned out to be 28.8% (about 100 minutes

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904 J.-R. Ong et al.

after removal from scene). She made a Full recovery after

22 hours of normobaric oxygen therapy in the ED. No delayed neurologic sequela was found during her scheduled visit to the neurology clinic 4 weeks after the event.

Exposure to fires in closed spaces, vehicle exhaust fumes, combustion fumes, and vapors of paint removers containing methylene chloride can all lead to carbon monoxide poisoning. The clinical presentation of carbon monoxide poisoning is extremely variable. Common symp- toms of exposure to low concentrations of carbon monoxide include headache, fatigue, confusion, dizziness, paresthe- sias, chest pain, palpitations, Visual disturbances, and Gastrointestinal symptoms [3].

The diagnosis of carbon monoxide exposure requires careful History taking, astute physical examination, and in particular, a high index of suspicion [4]. The diagnosis is confirmed by measurement of blood carboxyhemoglobin. Carbon monoxide alters the dissociation properties of hemoglobin and reduces oxygen delivery to tissues, leading to central hyperventilation and respiratory alkalosis. As a result, characteristic symptoms of hyperventilation syn- drome such as shortness of breath, lightheadedness, fatigue, numbness, carpopedal spasms, and fainting spells can also be found in patients with carbon monoxide poisoning.

The cornerstone of treatment of carbon monoxide poisoning is supplemental oxygen, which hastens the dissociation of carbon monoxide from hemoproteins in direct relation to the partial pressure of oxygen. The outcomes of previous studies comparing Hyperbaric oxygen (HBO) and normobaric oxygen therapy have been incon- clusive because of methodologic difficulties. Although most reported nonrandomized studies have suggested benefit from HBO, results of published randomized studies remain controversial [5-8] Finally, it must be emphasized that neither HBO nor any other therapy can be expected to prevent cognitive deficits due to cell death sustained during

the episode of poisoning. [9] Therefore, prevention of carbon monoxide exposure remains the most important means to reduce the morbidity and mortality associated with carbon monoxide exposure.

In conclusion, this case has brought to our attention that carbon monoxide poisoning can be misidentified by health personnel as psychogenic hyperventilatory attacks. We hope that a heightened awareness of this situation by emergency physicians, especially in winter months, will improve the diagnosis and management of this life-threatening condition.

References

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