Post-AKI Mortality, Readmission With Blood Pressure, Time From Discharge

More than one-fourth of patients discharged from the hospital after AKI will die within the next year, with cardiovascular disease (CVD) being the leading cause. Among patients in the Veterans Health Administration (VHA) system, the prevalence of cardiovascular risk factors and existing CVD are higher than in the general population. Blood pressure control is critical for patients who have experienced AKI, yet optimal blood pressure targets and timing of blood pressure control for this population are not defined. 

Data on the association of blood pressure with post-AKI outcomes and the degree to which time from discharge is associated with risks and benefits is lacking. Researchers led by Benjamin R. Griffin, MD, wanted to determine the associations of systolic blood pressure (SBP) with mortality and hospital readmission, as well as whether time from hospital discharge affects these associations among those post-AKI. Their findings were published in JAMA Network Open. 

The retrospective cohort study was conducted between January 2013 and December 2018 and included 80,960 adults with AKI during hospitalization in VHA hospitals. Data analysis took place from May 2022 to February 2024.  

The study excluded patients with ≤1 year of data within the health system prior to admission, severe or end-stage liver disease, stage 4-5 chronic kidney disease, end-stage kidney disease, metastatic cancer, or no blood pressure values within 30 days of discharge. Of the total participants, 77,965 (96.3%) were male, 2,995 (3.7%) were female, and 57,242 (70.7%) were aged 65 years or older.  

Rates of diabetes were high and included 16,060 patients (20.0%). In addition, 22,516 patients (28.1%) had congestive heart failure and 27,682 (34.2%) had chronic lung disease. One-year mortality occurred in 12,876 patients (15.9%). 

SBP was treated as time-dependent and was categorized as <120 mmHg, 120-129 mmHg, 130-139 mmHg, 140-149 mmHg, 150-159 mmHg, and ≥160 mmHg. Time spent in each SBP category was gathered and represented in 30-day increments. The study’s primary outcomes were the time to mortality and the time to all-cause hospital readmission.   

The researchers adjusted Cox proportional hazards regression for demographics, comorbidities, and lab values. To assess associations over time, they calculated hazard ratios (HRs) at 60, 90, 120, 180, 270, and 365 days after discharge. 

Timing relative to hospital discharge significantly affected associations of SBP with both mortality and hospital readmission rates. There were clear, time-dependent mediations on associations in all groups. Patients with SBP 130-139 mmHg had the most favorable risk level for mortality and hospital readmission and the lowest mortality risk at most time points. 

The SBP 130-139 mmHg group had a statistically significant increase in mortality risk compared to patients with SBP of ≥160 mmHg at 60 days (adjusted HR [aHR], 1.20; 99% CI, 1.00-1.44). No association with mortality was observed at 90, 120, and 180 days, but there was a statistically significant decrease in mortality risk by 270 days (aHR, 0.72; 99% CI, 0.59-0.90) that endured at 365 days (aHR, 0.58; 99% CI, 0.45-0.76).  

Patients with SBP ≥160 mmHg had the lowest projected mortality at 60 days but the highest projected mortality of all groups except those with SBP <120 mmHg at 365 days. Patients with SBP 120-129 mmHg had a significantly higher risk of mortality than patients with SBP ≥160 mmHg through the first 180 days, but there were no statistical differences between those groups at 270 or 365 days. Patients with SBP <120 mmHg had the highest risk of mortality at each time point, including at 60 (aHR, 2.20; 99% CI, 1.85-2.62) and 365 days (aHR, 1.82; 99% CI, 1.47-2.25).  

Patients with SBP 130-139 mmHg had the lowest risk of readmission at most time points and a significantly lower risk of readmission by 180 days. This was also the only group without a statistically higher risk for readmission at 60 days compared to patients with SBP ≥160 mmHg. Patients with SBP ≥160 mmHg or greater had the lowest projected readmission rate at first, but the highest rate at every time point after approximately six months.  

The study’s limitations include possible residual confounding, ascertainment bias, and bias related to the level of medical care. There is also inadequate data to determine whether medication regimens were adjusted in this population to achieve blood pressure goals and limited generalizability due to participants being largely male. 

“In this retrospective cohort study of patients post-AKI there were substantial variations in the associations of SBP with mortality based on time from discharge,” the authors summarized. “Risks of mortality and readmission relative to elevated blood pressure were highest in the immediate postdischarge period, with a shift toward lower mortality and readmission at later time points. Veterans with SBP between 130 and 139 mmHg had the most favorable risk level over time of any group. These findings may have important implications for the timing and targets for blood pressure control used in post-AKI care.” 

Source: JAMA Network Open.