Survive or thrive after ICU: what’s the score?

AKI is a frequent complication in critically ill patients and portends poor short and long-term outcomes, including an increase in readmissions, cardiovascular events, and progression to chronic kidney disease (CKD) [1]. The impact on health related quality of life (HRQOL) has been studied less. Further, it is not known which aspects of HRQOL are most affected and why, and how this could shape post-critical care management. Some of these questions have been addressed in the follow-up study of The Artificial Kidney Initiation in Kidney Injury (AKIKI) trial by Chaibi et al. [2].

AKIKI was a large French multicentre randomised controlled trial on renal replacement therapy (RRT) initiation strategy for AKI [2]. Chaibi et al. examined longer-term survival, renal outcomes and HRQOL in 316 patients (51% of total population) who survived 60 days after randomization. Their median follow-up was up to 3.35 years [Interquartile range (IQR) 1.89—4.09]. Survival rate was 39.4% at three years following inclusion, with age being the only predictor om mortality. Over a quarter of patients had worsening renal function whilst 5% needed chronic dialysis. HRQOL was assessed using the Eq-5L instrument at a median of 3 years post randomisation. Although the response rate was low at 35%, overall HRQOL following an ICU admission with AKI was low. Population normative data for the EQ-index is generally 0.80–0.85 [3] and the median index value in this study was 0.67 (IQR 0.40 to 1.00). Interestingly, HRQOL scores were not influenced by need for chronic dialysis.

These findings are consistent with a body of literature that was summarized in a comprehensive meta-analysis published in 2014 [3]. The meta-analysis included 18 studies over a 18 year period in which six different HRQOL assessment tools (SF-46, EQ-5L, NHP, HUI3, MOS-SF-20, SF-12) were used and assessments were made over a median of 10.5 months ranging from 2 to 14 years after ICU admission [3]. Overall, HRQOL was markedly impaired among survivors of AKI compared to the general population and this was mainly driven by limitations in physical function, mobility and ambulation compared to psychosocial domains. Interestingly, the majority of studies found a similar degree of reduction in HRQOL in patients experiencing AKI or receiving RRT when compared to similarly critically ill patients without severe AKI. Notably, at 1 year post ICU admission, more than 80% of respondents would undergo ICU admission again if needed to survive [4].

Since that publication, several other studies have examined HRQOL outcomes with similar findings (Table 1). Further, additional scoring systems have been introduced, notably the clinical frailty score (CFS). Frailty, although more common with age but not confined to the elderly, complicates acute and chronic disease and is considered a marker of a limited existence [5]. It can be assessed using the CFS, a validated measure of clinical frailty with scores ranging from 1 (very fit) to 7 (severely dependent). There are recognized limits to the CFS, and although not a classic HRQOL scoring system, it is objective, easy to obtain and easy to teach [6]. In a prospective multicentre observational study enrolling older critically ill patients with AKI, frailty was defined as having a CFS > 5. The study found 28% of survivors were considered frail at 6 months, of whom 57% were not back at baseline (pre-ICU level) with only 4% transitioning to not frail and a further 4% becoming frail [5]. A follow-up of the BRAIN ICU study, a prospective cohort of critically ill adults with acute respiratory failure and/or shock enrolled found that severity of AKI was associated with increasing frailty at both 3 and 12 months compared to baseline measurements [6]. These studies further corroborate the ongoing decline in physical function of patients who suffer AKI as part of their critical illness. They also highlight the link between frailty and HRQOL and the complexity of assessing HRQOL specifically related to survival after AKI.

Table 1 Selected studies exploring quality of life and frailty in AKI survivors

There are additional limitations to interpreting HRQOL data following critical illness. First, the findings are impacted by the heterogeneity in study design and participants, timing of assessment, and tools used. Second, most studies reported a high loss to follow-up [3]. Despite this, there are useful signals, including the absence of difference in HRQOL based on stage of AKI or implementation of acute RRT [3, 6, 7]. This suggests that the process that led to AKI drives ongoing worse outcomes rather than AKI per se. More recently, worse cardiovascular outcomes have been reported for patients who survive AKI during hospitalisation, particularly in those with increased proteinuria [1]. Measuring and monitoring such outcomes provide valuable data of the long-term effects of AKI. However, the day to day effects long after ICU admission are less well studied, nor how the effects of changing socio-economic status following critical care influence HRQOL measurements at the time of testing [8].

The study by Chaibi and colleagues provides important data to our field on how patients survive after critical illness. However, it is unclear how these results should influence clinical management. Should rehabilitation, optimisation of nutrition and psychosocial support to reduce frailty be as much part of follow-up care after AKI as measuring urinary albumin and serum creatinine? The study by Chaibi et al. serves as a reminder that more research in AKI survivors is urgently needed to inform management strategies so that patients with AKI do not just survive but thrive after ICU.