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Carbon-Dioxide-Induced Flashback in a Healthy Man with a History of Near-Drowning

about traumatic and major life events and did not rate any traumatic events on the Posttraumatic Diagnostic Scale [5] . A structured diagnostic interview (SCID) revealed no psychiatric disorders including no former or current posttraumatic stress disorder or other anxiety disorders. The Anxiety Sensitivity Index did not indicate a higher individual disposition towards fear-related sensations. He had no family history of anxiety disorders. Physical examination and laboratory workup showed no peculiarities. A urinary drug screen was negative. We used a mixture of 35% CO 2 and 65% oxygen. Vital capacity was evaluated by a respirometer connected to a face mask. He was informed that he would be inhaling a gas mixture of CO 2 and oxygen, and that he might experience anxiety. He inhaled a single breath of 1 80% of vital capacity. Before and after the inhalation he completed the Acute Panic Inventory, the Panic Symptom Scale and the Acute Dissociation Inventory. He indicated very low levels of anxiety and dissociation before the inhalation, but a strong anxiety, panic and prodissociative reaction to CO 2 ( fig. 1 ). Surprisingly, he felt as if near-drowning and reported life-like flashbacks and intrusions. Visual and auditory modalities were involved. He also experienced massive fear of suffocation and death. He fulfilled criteria for a panic attack in the Panic Symptom Scale. Anxiety and intrusions persisted over 3 min. These symptoms were related to a respective traumatic event at the age of 10 years, which he had not thought about for years. This case advises that a history of traumatic events, particularly suffocative events like near-drowning, could lead to panic and posttraumatic flashbacks in a subject without any former or current posttraumatic stress disorder symptoms or anxiety sympIncreased carbon dioxide reactivity has been linked to anxiety disorders, especially panic disorder [1, 2] . Recent research focused on the impact of adverse life events on carbon dioxide reactivity: higher anxiety and panic response in subjects pertaining to the general population was predicted by symptoms of childhood separation anxiety, childhood parental loss, common stressful events, major life events and suffocative events like near-drowning [3] . However, triggering of f lashbacks or intrusions in subjects with a history of suffocative events by the carbon dioxide challenge has not been described so far. Furthermore, patients with posttraumatic stress disorder do not seem to show increased carbon dioxide reactivity according to preliminary data [4] . We report an unexpectedly considerable dissociative and panic reaction to inhalation of 35% CO 2 in a healthy 31-year-old male student, who was recruited as a healthy comparison subject for a clinical study, approved by the local ethics committee. Initially, he did not mention any traumatic events in a clinical interview Received: April 7, 2010 Accepted after revision: June 7, 2010 Published online: November 18, 2010