CO poisoning seems to spare memory

Carbon monoxide (CO) poisoning seems not to harm memory in the short term, according to a controlled preliminary study that has used objective psychometric testing for the fist time.

Functional memory and attention and memory one month after intoxication in a highly selected group of 32 patients with no other risk factors for impaired memory were similar to those of matched controls. Some aspects—verbal significance, recall, quality learning (committing to memory), and reaction time—were significantly better. The patients were also significantly better at quality learning, immediate visual memory, and constancy of effort if their initial blood CO concentration was high, though this may be attributed merely to better effort and should be tested in other studies, the authors say.

Patients and controls had a median age of 27.5; 20 were women. Median initial CO concentration was 2.08 (range 1.00–8.58) mmol/l, and 24 had been treated with hyperbaric oxygen. The patients studied were selected from 944 consecutive patients over four years treated for acute CO poisoning by standard normobaric or hyperbaric oxygen therapy. The selection criteria were age 18–60 years, no risk factors for impaired memory, and a minimum CO concentration ≥1.0 mmol/l in the first blood sample. They were tested one month after their poisoning for various aspects of memory, attention, and divided attention by psychometric tests.

Subtle neuropsychological effects have been described shortly after acute CO poisoning, but these have been based on subjective testing or without controls for comparison, or both.