Carbon monoxide poisoning is a protean disease characterized by hypoxic injury, metabolic poisoning of cells, reperfusion injury mediated by damage to the inside lining of blood vessels, brain lipid peroxidation, and other pathologic processes. Hyperbaric oxygen therapy is beneficial when delivered hyperacutely, but the dose is less certain when there is delay to treatment. Dr. Harch has presented information at the UHMS meeting showing the benefit of low-pressure HBOT and SPECT brain imaging in the treatment of chronic persistent or delayed neuropsychiatric sequelae of CO poisoning (26). In addition, he has successfully used SPECT brain imaging in acute CO poisoning to help track the patient's progress. Below is an example of such a case.

Case Presentation:

The patient is a 44 year old male who sustained a 4 hour exposure to propane and carbon monoxide while working in a closed space with a poorly tuned propane-powered forklift. He was taken to a nearby hospital where he was placed on high flow oxygen for 2 hours. Carboxyhemoglobin before discharge was 14%. Over the next 72 hours his headaches, lethargy, dizziness, and cognitive symptoms intensified, prompting referral for evaluation. The patient was treated on a course of HBOT through clinical plateau, but then presented 6 months after the poisoning with persistent neuropsychiatric sequelae. Figure 1 shows SPECT brain imaging on a dual-head scanner immediately prior to first retreatment HBOT. Note the diffuse patchy heterogenous pattern compared to the normals above. Maximum brain blood flow (pixel count) is 258. This is the amount of radioactivity in the smallest measured piece of brain tissue and is proportional to brain blood flow; the higher the pixel count, the higher the blood flow. Color scale is yellow, red, green, blue, purple, black from highest to lowest flow. Images proceed from the base of the brain in the left upper corner to the top of the brain in the lower right hand corner (opposite of the convention above). Figure 2 is a repeat SPECT scan five days after Figure 1 and four days after a single low pressure HBOT. Note the global smoothing (more normal pattern) and improvement in average blood flow (more yellow) while only showing a minimal increase in maximum pixel count (265). The patient underwent an additional course of low-pressure HBOT with improvement in symptomatology and psychometric testing that was reflected in improvement on SPECT at the completion of treatment, Figure 3. Again, note the global smoothing effect of HBOT and improvement in overall blood flow with maximum pixel count of 330. The lesser amount of yellow on Figure 3 is misleading and due to computer scaling. To more accurately compare scans 1 and 3, Figure 4 shows Figure 3 on the same maximum pixel scale, 258, as Figure 1. The dramatic improvement in overall brain blood flow is now very clearly demonstrated.

26. Harch PG, et al. HMPAO SPECT brain imaging of acute CO poisoning and delayed neuropsychological sequelae (DNSS). Undersea and Hyperbaric Medicine, 1994;21(Suppl):15.