BackgroundOf the more than 550,000 patients receiving maintenance hemodialysis (HD) in the United States, each has an average of 1.6 admissions annually (>880,000 inpatient HD sessions). Little is known about the temporal changes in laboratory values, ECGs, and intravascular and extravascular volume during inpatient HD sessions.MethodsIn this prospective cohort study of hospitalized HD patients, we assessed intradialytic laboratory values (metabolic panels, blood gases, ionized calcium levels), ECGs, and sonographic measures of volume status.ResultsAmong 30 participants undergoing HD (mean age 62 years; 53% men, 43% Black) laboratory values had the largest changes in the first hour of HD. There was no significant change in ionized calcium levels pre- to post-HD (change: –0.01±0.07, P=0.24); 12 of 30 and 17 of 30 patients had levels below the lower reference limit at the beginning and end of HD, respectively. The mean pH increased pre- to post-HD (change: 0.06±0.04, P<0.001); 21 of 30 had a pH above the upper reference limit post-HD. There was a trend toward longer median QTc duration from pre- to post-HD (change: 7.5 msec [–5 msec, 19 msec], P=0.07). The sum of B lines on lung ultrasound decreased from pre- to post-HD (median decrease: 3 [1, 7], P<0.01). The collapsibility index of the inferior vena cava increased pre- to post-HD (median increase: 4.8% [1.5%, 13.4%], P=0.01), whereas internal jugular vein diameter did not change (P=0.24).ConclusionsAmong hospitalized patients undergoing HD, we found dynamic changes in laboratory values, QTc duration, and volume status. Further research is required to assess whether HD prescriptions can be tailored to alter these variations to potentially improve patient outcomes.