Magnesium sulfate therapy affects attention and working memory in patientsundergoing preterm labor

OBJECTIVE: Patients commonly consent to undergoing invasive procedures whil e receiving magnesium sulfate therapy. This study evaluated the effects of magnesium sulfate on attention, comprehension, and memory in patients under going preterm labor. STUDY DESIGN: Consenting patients were studied while receiving(study) and n ot receiving (control) intravenous magnesium sulfate tocolysis for preterm labor. Excluded were patients with possible preeclampsia, imminent delivery . sedative administration, or prior mental illness. Patient comprehension w as assessed with the Boston Diagnostic Aphasia Examination. Level of attent ion and working memory were evaluated with the Paced Auditory Serial Additi on Test. Verbal learning, short-term memory, and recognition were determine d with the Hopkins Verbal Learning Test. Gross mental-neurologic deficits w ere evaluated with the Mini-Mental Status Examination. The tests were admin istered by the same examiner. Control testing was performed >24 hours after intravenous magnesium sulfate was discontinued. Magnesium levels were obta ined at the time of testing. The primary outcome measure was the Paced Audi tory Serial Addition Test score because of its ability to elicit subtle dif ferences in attention capacity. Statistical analysis included the paired t test and the McNemar test. RESULTS: Fifteen patients completed the study. Paced Auditory Serial Additi on Test scores were significantly higher (ie, more errors were made) during magnesium sulfate therapy than periods without therapy (14 +/- 8 vs 7 +/- 7; P < .05). Comprehension (Boston Diagnostic Aphasia Examination score) wa s not different between the groups (P = .7). There was no difference in sho rt-term memory (Hopkins Verbal Learning Test) or gross mental-neurologic de ficits between the 2 groups (all P > .1). CONCLUSIONS: Magnesium sulfate therapy appears to have an effect on attenti on and working memory but not on long-term memory or comprehension. The sig nificant differences in Paced Auditory Serial Addition Test scores reveal d eficits in information-processing ability in patients on a regimen of magne sium sulfate therapy.