Inferior vena cava diameter and collapsibility index as a marker of fluid status in regular hemodialysis patients

Patients with renal failure suffer from fluid overload which is a risk factor for mortality and morbidity. Therefore, fluid status assessment in patients on regular hemodialysis is very important. Dry weight assessment by clinical parameters is not always reliable. We evaluate the role of inferior vena cava ultrasound in estimating fluid overload in regular hemodialysis patients. A total of 45 persons, 30 end-stage renal disease patients on regular hemodialysis in group A (18 men and 12 women) and 15 healthy persons in group B (10 men and 5 women), were included in the study. The patients in group A ages ranged from 29 to 70 years with a mean of 48.38 ± 12.70 years and in group B ages ranged from 25 to 55 years with a mean of 34.93 ± 8.26. By clinical methods, the mean dry weight was 68.37 kg (68.37 ± 10.42). After HD mean, IVCe decreased from 2.01 ± 0.29 to 1.79 ± 0.22 cm (P < 0.001) similarly, mean IVCi decreased from 0.99 ± 0.48 to 0.64 ± 0.39 cm (P < 0.001). Changes in IVCD were significantly correlated with alterations in body weight following dialysis (P < 0.001). The IVC-CI increased significantly after dialysis (P < 0.001). IVCD and its IVC-CI reflected alterations in fluid status (P < 0.001). Considering the clinical parameters of fluid status, following HD mean, heart rate increased from 81.80 ± 5.15 beats per minute to 89.87 ± 6.42, (P < 0.001), systolic blood pressure decreased from 130 ± 18.43 mmHg to 113.33 ± 15.27 (P < 0.001), and diastolic blood pressure decreased from 80.17 ± 10.12 mmHg to 71.50 ± 9.29 (P < 0.001). It was found a significant correlation between IVCD and IVC-CI with ultrafiltration of hemodialysis. Thus, IVC ultrasound can be used in dry weight assessment in ESRD patients on regular HD by measurement of IVCD and IVC-CI before and after hemodialysis.


Background
Sixty years ago, Belding Scribner developed a blood access device which is used for repeated hemodialysis and became known as the Scribner shunt [1]. The development of the Scribner shunt opened the door for the creation of grafts and fistulas [2,3]. One of the vital functions of the kidney is the regulation of fluid homeostasis [4]. Patients with renal failure suffer from fluid overload which is a risk factor for mortality and morbidity [5,6]. So, accurate assessment of fluid status in hemodialysis patients is very important and represents a big challenge as the achievement of euvolemia is dependent on the skills of the treating physician. Dry weight definition is "the lowest post-dialysis weight at which patients are vitally stable with minimal symptoms of hypervolemia or hypovolemia" [7]. Overestimation of dry weight may lead to chronic fluid overload, edema, hypertension, and cardiac complications [8], while underestimation may lead to hypovolemia followed by complications like hypotension, nausea, headache, and muscle cramps [9]. Clinical parameters (heart rate, blood pressure, venous congestion, and lower limb edema) are not specific for fluid assessment and not always reliable. Therefore, optimal estimation of fluid status should include a combination of clinical and technical assessment methods [10]. Central venous pressure (CVP) [11], lung ultrasound [12], inferior vena cava (IVC) ultrasound [13], bio-impedance spectroscopy (BIS), and levels of atrial natriuretic peptide [14] can be used in the fluid status assessment. Recently, IVC ultrasound machines are available everywhere and can be easily used as it is considered a non-invasive evaluation method [15]. It can be very helpful in fluid management in the perioperative period, in trauma resuscitation, and ICU patients [16]. In this study, we used ultrasound to measure inferior vena cava diameter (IVCD) during inspiration (IVCi) and expiration (IVCe) in ESRD patients on regular hemodialysis before and after dialysis.

Aim
This study aims to evaluate the role of IVC collapsibility index and diameter measured by ultrasound in estimating fluid overload in regular hemodialysis patients to get the ideal dry weight.

Study design
A controlled cross-sectional study was conducted between 5 January and 15 March 2021.

Study area and population
The study was carried out at the dialysis unit of the Internal Medicine department, in cooperation with the Radiology department, Faculty of Medicine, Bab Al Shaeria University hospitals. The study was conducted on 45 persons classified into two groups as follows: All patients were subjected to the following: 1. Full history taking 2. Full clinical examination 3. Weight and height measurement 4. Dry weight assessment by clinical parameters: symptoms, weight, blood pressure, heart rate, and lower limb edema before and after HD 5. Echocardiography to exclude heart failure 6. Abdominal ultrasound to exclude liver cirrhosis 7. Chest x-ray 8. Inferior vena cava diameter (IVCD) measurement by ultrasound before and after hemodialysis 9. Calculation of Kt/v 10. Laboratory investigations: complete blood count (CBC), kidney functions (serum urea and serum creatinine before and after HD), blood chemicals (serum Na, Ca, K), and liver functions (albumin, PT) For normal group:

Full history talking 2. Full clinical examinations 3. Weight and height measurement 4. Measurement of inferior vena cava diameter (IVCD) by ultrasound
Laboratory investigations: complete blood count (CBC), kidney functions (serum urea and serum creatinine), blood chemicals (serum Na, Ca, K), and liver functions IVCD was measured 1.5 cm below the diaphragm in the hepatic segment in the supine position. IVCD was measured during normal inspiration and expiration. IVC diameter at inspiration ranges from 0 to 14 mm at rest and expiratory diameter of 15 to 20 mm at rest. IVC collapsibility index (IVC-CI) is defined as (IVCe − IVCi)/ IVCe [17].

Statistical analysis
Data were handled using SPSS software version 20. We presented the qualitative data as frequencies and percentages and quantitative data as mean, standard deviation, range, and median. To compare two groups of quantitative data, we used independent t test and paired t test. We used the ROC curve to compare between variables. We used the following criteria to determine the P value.

Results
Considering demographic data, a total of 45 persons were included the study and were classified in two groups:  Table 1).
Considering IVC parameters, in group [A] before hemodialysis, the mean of IVCe was 2.013 ± 0.298, the mean of IVCi was 0.99 ± 0.487, and the mean of IVC-CI was 0.527 ± 0.189, while in group [B], the mean of IVCe was 1.68 ± 0.174, the mean of IVCi was 0.8 ± 0.141, and the mean of IVC-CI was 0.525 ± 0.054 (Table 2).
Following ROC curve, the difference in IVCi and IVC-CI of both groups was not significant (P > 0.05). However, the difference in IVCe was significant (P < 0.05). The area under the ROC curve of IVCe was significantly higher than 0.5 concluding that the expiratory IVC could differentiate between HD patient and normal one (Fig. 1).
Following the ROC curve, the differences in IVCe and IVC-CI before and after HD sessions were significant (P < 0.05). The area under the ROC curves of the IVCe and IVC-CI were significantly higher than 0.5 concluding that IVCe and IVC-CI could identify the efficacy of ultrafiltration among HD patients (Fig. 2).
According to the dry weight method, 22 patients were hypervolemic, 6 were euvolemic, and 2 were hypovolemic before dialysis, and after dialysis, 7 were still hypervolemic, 21 were euvolemic, and 2 were hypovolemic. According to the IVC-CI, 16 were hypervolemic, 8 euvolemic, and 6 hypovolemic before dialysis. After dialysis, 7 were hypervolemic, 5 euvolemic, and 18 were hypovolemic. Thus, there were a significant number of patients who became hypovolemic after dialysis according to the IVC-CI.

Discussion
The results in our study suggest that clinical parameters are not always reliable and not specific for fluid status assessment. Hypovolemic complications such as dizziness, headache, and muscle cramps result from the underestimation of dry weight. In extreme cases, intradialytic hypotension is common which endangers perfusion to vital organs. In our patients, hypovolemic symptoms occurred in fifteen instances. After dialysis, the patients' blood pressure is expected to increase (paradoxical hypertension) or to decrease (depending on the degree of hypovolemia) compared to pre-dialysis blood pressure with a rise in heart rate which is an indicator of hypovolemia [18]. On the other hand, overestimation of the dry weight may cause chronic fluid overload and complications such as hypertension and congestive heart failure [19]. Therefore, optimal estimation of fluid status should include a combination of clinical and technical assessment methods. One of these methods is the central venous pressure measurement but is considered an invasive method for evaluation and cannot be used routinely [20]. Another method is lung ultrasound but is not accurate and has some limitations [21]. Bioimpedance and levels (BIS) of atrial natriuretic peptide are available but require special machines and are not very accurate [22,23]. At the same time, ultrasound machines are available and can be easily used to measure IVCD in hospitals during inspiration and expiration [24]. Previous studies in adults and children have used IVCD to estimate the intravascular volume in HD patients and to correlate well the ultrafiltration [25,26]. This study has been done to evaluate the role of IVCD and CI in regular hemodialysis patients compared with healthy individuals. IVCe, IVCi, and IVC-CI were measured before and after HD and were correlated well with the amount of ultrafiltration achieved via dialysis. In our study, IVCD decreased significantly following dialysis and correlated well with the changes in weight, and IVC-CI increased significantly after ultrafiltration. We have taken IVC-CI < 0.40 as hypervolemic, IVC-CI

Funding
We did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations
Ethics approval and consent to participate