Magnesium sulfate therapy affects attention and working memory in patients undergoing preterm labor

OBJECTIVE: Patients commonly consent to undergoing invasive procedures while receiving magnesium sulfate therapy. This study evaluated the effects of magnesium sulfate on attention, comprehension, and memory in patients undergoing preterm labor. STUDY DESIGN: Consenting patients were studied while receiving(study) and not 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 was assessed with the Boston Diagnostic Aphasia Examination. Level of attention and working memory were evaluated with the Paced Auditory Serial Addition Test. Verbal learning, short-term memory, and recognition were determined with the Hopkins Verbal Learning Test. Gross mental-neurologic deficits were evaluated with the Mini-Mental Status Examination. The tests were administered by the same examiner. Control testing was performed >24 hours after intravenous magnesium sulfate was discontinued. Magnesium levels were obtained at the time of testing. The primary outcome measure was the Paced Auditory Serial Addition Test score because of its ability to elicit subtle differences in attention capacity. Statistical analysis included the paired t test and the McNemar test. RESULTS: Fifteen patients completed the study. Paced Auditory Serial Addition 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) was not different between the groups (P = .7). There was no difference in short-term memory (Hopkins Verbal Learning Test) or gross mental-neurologic deficits between the 2 groups (all P > .1). CONCLUSIONS: Magnesium sulfate therapy appears to have an effect on attention and working memory but not on long-term memory or comprehension. The significant differences in Paced Auditory Serial Addition Test scores reveal deficits in information-processing ability in patients on a regimen of magnesium sulfate therapy.