Renal dysfunction is commonly seen in hospitalized stroke patients. Ischemic stroke is frequently associated with renal dysfunction and nearly a third of patients hospitalized with intracerebral haemorrhage (ICH) have chronic kidney disease (CKD) (estimated glomerular filtration rate [e-GFR] < 60ml/minute per 1.73m ²) ^{1, 2} . The severity of the impairment and the requirement of renal replacement therapy for these patients in the course of their treatment are important management issues not currently well addressed by the literature. It has been established that good overall medical care can greatly influence the outcome of patients with stroke ³ . Cerebrovascular accident itself has a high burden of morbidity and mortality, and additionally, CKD is an independent predictor of poor clinical outcome and mortality after an initial stroke ^{4, 5} . Co-existence of adverse conditions, such as anemia, oxidative stress, platelet dysfunction, electrolyte imbalance and hyperhomocysteinemia, in patients with CKD have been implicated as the reason why these patients have poorer outcomes compared to the normal population ⁶ . Moreover, even mild stages of CKD increases the risk of future ischemic and haemorrhagic strokes ⁷ . e-GFR decreased <40mL/min indicates that the risk of symptomatic stroke in the general population is increased by 3.1 times ⁸ . Hence proper and routine evaluation of renal function in hospitalized patients with cerebrovascular accident needs to be ensured to improve the outcome of these patients.

Since there is inadequate knowledge concerning the trend of renal function in hospitalized stroke patients and a lack of clear guidelines regarding the need for renal replacement in these type of patients, we conducted an observational study of the trends in renal function in all stroke patients hospitalized at our centre.

A prospective study was conducted at the National Institute of Neurological and Allied Sciences, a 100-bed, tertiary care neuro-centre in Kathmandu, Nepal. Stroke patients admitted between December 2014 and April 2015 were recruited to the study. The Institutional Review Board of the National Institute of Neurological and Allied Sciences approved the study (6/2014). The review board confirmed that as this is a descriptive study with no active interventions performed on the patients and their personal identity was not disclosed, no informed consent from the patients was required.

Non-probability, consecutive sampling was performed; all patients with haemorrhagic and ischemic stroke admitted during the study period were enrolled into the study. Patients admitted less than 5 days were excluded as trend analysis was not possible in them. The mean e-GFR at admission and at one week interval was calculated. Serum urea and creatinine were evaluated on alternate days throughout their hospital stay, and the e-GFR was calculated as per the Modification of Diet in Renal Disease Study group formula: e-GFR (mL/minute per 1.732m ²) = 186 X [serum creatinine] ^{- 1.154} X age ^{- .203} X [.742 if female] X [1.21 if of African descent] ⁹ . Renal impairment was defined when the e-GFR was < 60mL/minute per 1/73m ².

All data were taken from patient hospital records. If data was not available, the information was sought from the patients’ relatives, which was obtained as part of routine care. The primary outcome measure was the occurrence of renal impairment during the hospital stay. The trend of renal function and the need for renal replacement in these patients were analyzed over the duration of admission in the hospital. Demographic, clinical profile and the trend in renal function of patients with haemorrhagic stroke were compared with those of ischemic stroke. The number of patients who had renal impairment according to our criteria was analyzed and any surgical interventions carried out on these patients were recorded. Of the patients that developed renal impairment, the ones that required renal replacement were strictly followed. Since renal replacement is not available at our centre, the patient were monitored when they were moved to nearby hospitals.

Data were entered in IBM SPSS (version 20; SPSS Inc., Chicago, IL, USA) and Pearson's chi square test, Fischer's exact test and independent variable t-test were applied. Line graphs were made to show the trends in the e-GFR in all the patients.

Renal failure is a rare primary cause of death in patients following stroke; however, impaired renal function is a significant predictor of both short and long term mortality in these patients. The Oxford Community Stroke Project reported that stroke survivors tend to die 2.3 times more than the matched general population every year post-stroke, and non-stroke cardiovascular diseases is the most common cause of death following the first year of initial stroke ¹⁰ . Calculated e-GFR ≥ 51.27ml/min predicts a better long term survival in stroke patients after adjustment of confounders (age, neurological state, ischemic heart disease, hypertension, smoking and diuretic use). MacWalter et al. suggested the use of ACE inhibitors in this subgroup of patients, as they had higher risk of mortality ¹¹ .

Hypertension is attributed to a large share of patients progressing to end stage renal failure ¹² . In the present study, 23 out of 25 patients with haemorrhagic stroke had hypertension (14 uncontrolled and 9 newly diagnosed). However, 18 out of 27 patients with ischemic stroke had a normal blood pressure (9 without history of hypertension and 9 controlled). Even the patients with well-regulated blood pressure continued to have renal impairment, i.e. 5 out of 9 patients. Additionally, 4 out of 11 patients without hypertension, 4 out of 9 patients with controlled hypertension, 12 out of 22 patients with uncontrolled hypertension and 5 out of 10 patients with newly diagnosed hypertension developed renal impairment, which was not statistically significant (independent t-test, p=0.793). Therefore, in our patients, hypertension did not play a significant role in predisposing patients to renal impairment.

In our study, some degree of renal impairment was seen in 64% of patients with haemorrhagic stroke and 33.3% of patients with ischemic stroke. Ovbiagele et al. have reported renal impairment in nearly a third of patients with ICH; and Mishra and colleagues in 38.46% of such patients ^{1, 13} . Use of mannitol could be a confounding variable in our study. Dziedzic et al. found that the use of mannitol decreased intra cranial pressure, caused transient elevation of urea and creatinine, but did not cause anuria or oliguria ¹⁴ . The higher incidence of renal impairment seen in the haemorrhagic stroke subgroup may be due to the inhererent difference in the management of haemorrhagic and ischemic stroke, in regards to the use of mannitol, nephrotoxic drugs, various antibiotics, etc. This study is unable to explore this possibility in detail; however, as all these patients were managed in the same institution, over the same period of time, and the baseline management in both these groups is grossly similar, we found it interesting to highlight this difference. As ours is a tertiary care centre receiving referred cases from all over the country, selected severe patients could have been enrolled into our study. Of 614,454 patients admitted with ICH in hospitals in the USA between 2005 and 2011, 41694 (6.8%) had acute renal failure (ARF), with 700 patients (1.7%) requiring in-hospital dialysis. These patients with ARF had higher rates of moderate-to-severe disability and in-hospital mortality ¹⁵ .

After excluding patients with a history of renal disease, dehydration, nephrotoxic drugs use or septicemia, transient renal impairment was found in 30 of 78 patients (38.46%) with acute ICH. Renal functions normalized in 2–4 weeks ¹⁵ . Hence, only a small percentage of patients with ICH who develop renal impairment, need renal replacement. Only one of the 25 patients with ICH and two of the 27 patients with ischemic stroke required renal replacement in our study. This finding is coherent with Saheed et al., who found that of only 700 (1.7%) of 41, 694 patients with some renal impairment requiring renal replacement in 614,454 patients with ICH admitted in the USA ¹⁵ . The Oxford Community Stroke Project further states that renal failure is a rare primary cause of death in post-stroke patients, but is a significant predictor of increased mortality in both the short and long term ^{10, 16} .

The size of the hematoma did not predispose patients to renal impairment in our study, as the average hematoma volume in the group of patients that developed renal impairment was 29.23 ± 24.23mL and in the patients that did not develop renal impairment was 28.61± 42.24 (p=0.966). In a similar study by Cutting et al. (2004), there was no correlation between admission GFR and ICH volume (p=0.77), and patients with GFR <60 versus patients with GFR ≥ 60mL/min/1.73 m ² also had similar ICH volumes (median 10.8mL vs 11.4mL; p=0.54) ¹⁷ . However, Molshatzki and colleagues (2011) were of the opinion that patients with larger ICH were predisposed to having more severe renal impairment. In their no renal impairment group, mild impairment group and the moderate to severe impairment group, the median hematoma volumes were 15.3mL, 16.6mL and 50.2mL, respectively (p=0.009) ¹⁸ . In addition, patients with moderate/severe impairment exhibited a 2.3-fold higher hematoma volume than the other groups (p=0.04). In our study, the location of the hematoma did not have any association with the severity of the renal impairment. Molshatzki et al. concluded that patients with moderate to severe renal impairment had a > 6-fold higher odds of lobar location of the bleed (95% CI = 1.59-24.02) as compared to the patients with no impairment.

The mean e-GFR (mL/minute per 1.732m ²) on the day of admission in the haemorrhagic stroke group was significantly lower (64.79 ± 25.85) compared to the ischemic stroke group (86.04 ± 26.09) in our study. In Hao et al.’s (2010) study, the mean e-GFR at admission in the haemorrhagic and ischemic stroke groups were comparable 77.57 ± 51.73 vs 77.07 ± 29.89 (p=0.285) ¹⁹ . Patients presented to our centre at various times following the index stoke; hence, the days mentioned are not the days after the stroke event, but the days after admission to the hospital. This is a limitation of our study as the values mentioned do not reflect the trend profile of renal parameters following stroke.

Small vessel disease is a generalized condition affecting the vascular beds in the brain, kidneys and retina. Makin and colleagues (2015) tried to study the relation of small vessel (lacunar) stroke with renal impairment with the hypothesis that lacunar infarction would be associated with more renal impairment compared to cortical stroke; however, there was no such difference ²⁰ . We are not able to comment on this as we have not categorized ischemic stroke into these subgroups in this study.

Renal impairment is commonly seen in stroke patients and is more common in the haemorrhagic variety, particularly in the initial days of the ictus. The impairment however is transient and rarely requires renal replacement therapy. The volume of the intracerebral bleed, its location and whether the patients were surgically or conservatively managed did not predispose them to renal impairment.

Raw data for renal impairment in stroke patients is available from http://dx.doi.org/10.7910/DVN/EILQSZ ²¹ .

Coding schema for Excel spreadsheet (schema included in SPSS version): SN, Serial Number; age (1, <20; 2, 21–30; 3, 31–40; 4, 41–50; 5, 51–60; 6, 61–70; 7, 71–80; 8, 81–90); sex (0- female, 1-male); location, location of the bleed; IVE, intraventricular extension (1-yes, /- no); Renal_impair, patients that developed renal impairment (1-yes, 0-no); Renal_replace, patients that required renal replacement (1-yes, 0-no); Volume, volume of bleed in millilitres; htnhth, hypertension (0-absent, 1-controlled, 2-uncontrolled, 3-newly diagnosed), sbp, systolic blood pressure in mmHg at admission; dbp, diastolic blood pressure in mmHg at admission; MAP, mean arterial pressure at admission; operation (EVD, external ventricular drain; VP shunt, ventriculoperitoneal shunt; evacuation, evacuation of bleed or infarction); interv, intervention (1, conservative management (haemorrhagic); 2, evacuation of hematoma; 3, CSF drainage; 4, conservative (Infarction); 5, decompressive craniectomy; 6, decompression and evacuation of the infarction); egfr1, estimated glomerular filtration rate at day 1; Meaneffr, mean egfr of each patient; Meandrop, maximum drop in egfr during the hospital stay of the patient as compared to the day of admission.

NOTE: The hospital stay can be determined by counting the number of egfrs recorded.