This document discusses relative blood volume (RBV) monitoring and its potential applications in dialysis. It provides an overview of RBV monitoring principles, compartmental fluid shifts, and RBV profiles in relation to intradialytic hypotension. While RBV monitoring shows promise for fluid management and blood pressure control, evidence from studies is mixed. The largest study to date found RBV monitoring increased mortality and hospitalizations. Further research is still needed to fully understand the clinical utility and appropriate applications of RBV monitoring.

1. Relative Blood Volume
Monitoring and
Applications in Dialysis
Christos Argyropoulos MD, PhD FASN
Division of Nephrology, University of New Mexico

2. Disclosures
• Nothing to disclose

3. Learning Objectives
• Understand the physiologic principles of R(elative)
B(lood) V(olume) monitoring
• Describe compartmental fluid shifts and RBV
profiles in relationship to the Guyton Curve
• Evidence supporting the use of RBV for
• BP management in ESRD
• Setting the target EDW in dialysis patients
• RBV in acute dialysis settings

4. Physiologic Principles of
Real Time RBV
monitoring

5. Non Invasive Vascular Monitoring:
the “critline”
• Continuous Hct
• Continuous BV change
• Continuous O2 saturation
• Recirculation
• Access Blood Flow

6. • (Overload) Remove more fluid without Intradialytic
Morbidity
• (Dehydration of Intravascular space)
Remove fluid without Intradialytic Morbidity
• (Hypoxemia) Ability to Determine and Treat
Hypoxemia in HD patients
• (ABF) Access Blood Flow measurements (not going to
be discussed)
Potential Applications of Crit-Lines

7. Emitter
Blood Flow
Blood
Chamber
Detector
Crit-Line Monitor Technology

8. Crit-Line vs Coulter Counter
5 10 15 20 25 30 35 40 45 50 55 60 65
5
10
15
20
25
30
35
40
45
50
55
60
65
Coulter Counter Hct
Crit-LineHct
R = .998
SD = ± 1.04
n = 52

9. O2 Saturation Accuracy
IL-482 Co-Oximeter
Crit-LineO2

10. Total Blood
Volume (BV)
Red Cell
Volume
(RCV)
Test tube represents
circulating blood volume
Hct =
RCV
BV
Plasma
Volume
Fundamental Parameter: Hematocrit (Hct)

11. 0 1 2 3 4
0
-5
-10
-15
-20
-25
27
29
31
33
35
%BV(Loss)
Hct
Hct =
RCV
BV
X 100
Hematocrit and Blood Volume
∆𝑅𝐵𝑉 =
𝐶0
𝐶 𝑡
−1 × 100%

12. HCT Thresholds, RBV
profiles and non-invasive
monitoring of
compartmental fluid shifts

13. 2
Intra-
cellular
Space Extra-
cellular
Space
Intra-
Vascular
Space
Circulating
Blood Volume
Toxins
Fluid
Toxins
Fluid
Toxins
Fluid
Dialyzer
Three Compartment Model
23 Liters 17 Liters 5 Liters

14. BVM Profile Screen

15. Fluid Removal Profiles
0
1
2
3
4
5
6
7
8
5 10 15 20 25 30 35 400
Adapted from Guyton, AC:
Textbook of Medical Physiology, 1991, pg.324
Normal
Death
Hypovolemia
C
B
AEdema
BloodVolume(liters)
Extracellular Fluid Volume (liters)
Shift
Due
to:
Low O2
Meds
UFR
Na+
Temp
Posture
TIME 03:37 HCT 30.7 BV - 0.0 SAT 94
-20
0
-10
5
BV
BV Profile A
TIME 03:20 HCT 34.7 BV -12.6 SAT 94
-20
0
-10
5
BV
BV Profile C
TIME 3:08 HCT 37.4 BV -18.4 SAT 91
-20
0
-10
5
BV
BV Profile B

16. 0
1
2
3
4
5
6
7
8
5 10 15 20 25 30 35 400
Adapted from Guyton, AC:
Textbook of Medical Physiology, 1991,
pg.324
Normal
Death
A
Edema
BloodVolume(liters)
Extracellular Fluid Volume (liters)
TIME 03:25 HCT 31.2 BV 0.2 SAT 98
-20
0
-10
5
BV
PROFILE A: < 3% RBV/hour

17. 0
1
2
3
4
5
6
7
8
5 10 15 20 25 30 35 400
Adapted from Guyton, AC:
Textbook of Medical Physiology, 1991, pg.324
Normal
Death
BBloodVolume(liters)
Extracellular Fluid Volume (liters)
TIME 03:25 HCT 34.7 BV -17.3 SAT 94
-20
0
-10
5
BV
PROFILE B: < 3 to 8% RBV/hour

18. %BV
1 2 3 4
-20
-10
0
5
A -3 to -8% slope in BV per hour (a “B” profile) is generally safe for patients who
have a urinary output of less than 1000 mls per day – unless they reach their
HCT Threshold

19. Exceptions to the 3-8% RBV profile
Minimal changes in HCT (a flat line) are also
acceptable when the patient is:
• Near HCT threshold
• UFR at minimum (<300-400 ml. per hour)
• Polyuric renal failure (why?)
• Diarrhea (why?)
• Little or no wt gain (assuming their EDW has been
correctly set)
• Double Amputee (why?) or Poor Ejection Fx (why?)

20. Intradialytic Hypotension and the “C”
profile
Time (hours)
%BV
SystolicBloodPressure


  


  
 
0 1 2 3 4
0
10
-10
-20
-30
0
25
50
75
100
125
150
UFR = 1428 ml/hr



UF Off
BP cuff: post- facto measurement RBV : predictive measurement

21. HCT Threshold
• Definition: The HCT at which the patient experiences
symptoms of morbidity.
• Maximum degree of hemoconcentration ( UFR) a patient may
tolerate before symptoms occur
• Rule of thumb…. Until you establish a Threshold
set the HCT Limit at 15% of the starting HCT.
• Review it every 3 weeks: it can change as the RBC mass
changes with EPO titration.

22. Just because a patient “Crashes”
It does NOT Mean they are “DRY”!!!
Time (hr)
%BV
1 2 3 4
-20
-10
0
5
8.0 L
Removed
7.0 L
Goal

23. 0 1 2 3 4
Time (hours)
0
10
-10
-20
-30
BVChange(%)
1
2
Refill: An Indicator of Over-hydration
Dynamic crit line monitoring : try to investigate after a crash or when challenging
DRY
WET

24. Causes of Intradialytic Hypotension
• Posture
• Low O2 saturation
• Medications / Antihypertensives
• Incorrect Ultrafiltration rate
• Hypotonic environment / Hypoalbumemia
• Dialysate at body temperature or warmer: core body heating
• Splanchnic vasodilatation secondary to food ingestion
• Electrolyte / Acid-Base Imbalances
• Severe anemia / Occult hemorrhage
• Unstable cardiovascular status / Arrhythmias / Pericardial
tamponade / MI
• Septicemia
• Dialyzer reaction, Hemolysis and Air embolism

25. 6 reasons for a “wet crash”
• O2 below 90% for Graft
or fistula and below
60% for a CVC
• Position
• UFR higher than plasma
refill
• Medications that cause
vasodilatation
• Temperature
• Hypotonic internal
environment: i.e.: low
Na+

26. Effects of Intradialytic Hypotension
• Tissue Hypoxia
• Adenosine release causing decrease in PVR
• Changes in Mental status / Seizures / Stroke
• Vision changes
• Silent cardiac ischemia / MI
• Ischemia / Infarct to the gut
• Decrease in Residual Renal Function
• Ischemia = decrease in URR

27. 02 Delivery 20+ % of HD patients have intradialytic
Hypoxemia; up to70% are sleep apneics.
0 1 2 3 4
Time (hours)
80
85
90
95
OxygenSaturation
Sleep Apnea Profile
Sleep
Complimentary Oxygen Delivery Issues

28. • Oxygen saturation: The percent to which the
hemoglobin is filled with oxygen.
• Must interpret in relationship to HGB / HCT
• 90 to 100% is considered normal for arterial sats:
thru access needles
• > 60 % for mixed venous sats: CVC lines
Oxygen Saturation

29. Intradialytic Oxygen Therapy
Increasing Oxygen:
• Increases Vascular tone / Vasoconstriction
• Increases Peripheral Vascular Resistance
• Increases Plasma Refill
One of the measures suggested for preventing/treating IDH

30. Application of RBV for
Fluid, EDW and BP
management in ESRD

31. Water : The Most Important Uremic Toxin ?
• A patient at their EDW should be:
- asymptomatic and
- normotensive
- on minimum blood pressure medications
- while preserving organ perfusion and
- maintaining existing residual renal
function

32. Volume Overload Indices In Stable
Hemodialysis Patients
Blood Purif 2013;35:202–208
𝑆𝑙𝑜𝑝𝑒4ℎ =
∆𝐵𝑉 (%/ℎ)
𝑈𝐹(𝐿) 𝑆𝑒𝑠𝑠𝑖𝑜𝑛 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 (ℎ𝑜𝑢𝑟𝑠)

33. Curves A,B,C or 1—6 ?
Blood Purif 2013;35:202–208

34. Curves A,B,C or 1—6?
Blood Purif 2013;35:202–208
Take home points:
• Slope4h : highest dynamic range
• A flat curve is truly a sign of FO
• Only 11% of the variability of the BVM marker can be explained by FO.

35. Crit-Line Intradialytic
Monitoring Benefit
(CLIMB) Study
J Am Soc Nephrol 16: 2162–2169, 200
Can Crit-Line monitoring
improve fluid removal and
reduce morbidity in ESRD?

36. CLIMB Study Flowchart and Study
Characteristics
J Am Soc Nephrol 16: 2162–2169, 200

37. Implementation of the intervention in
CLIMB was variable and inconsistent
J Am Soc Nephrol 16: 2162–2169, 200

38. Application of RBV did not modify BP in CLIMB
J Am Soc Nephrol 16: 2162–2169, 200

39. Application of RBV increased mortality
and hospitalizations
J Am Soc Nephrol 16: 2162–2169, 200
Mortality at 6 mo was greater in the Crit-Line than the
conventional monitoring group (8.7 and 3.3%, respectively; P
0.021 by log-rank test).

40. Using RBV to manage BP & estimated
EDW in stable chronic dialysis patients
Hypertension. 2010;55:305-311
Hypertension. 2009;53: 500–507
Prevalent HD patients (>3 mos on HD) with
interdialytic ambulatory BP > 135/85
Intervention
probed pts EDW
by decreasing
until symptoms
occurred

41. Using RBV to manage BP & estimated
EDW in stable chronic dialysis patients
Hypertension. 2010;55:305-311
Hypertension. 2009;53: 500–507
When EDW is not probed, pts
w/o change in slope had no
change in BP
When EDW is probed, pts who
go from flap to steep had the
largest, most robust BP changes
“Flat” < 1.33%/hr
Prespecified analysis of a trial in
which change in EDW => affects
slope
Does not establish that tracking of
slope is useful in adjusting dry
weight

42. Problems with the measurement of RBV
Blood Purif 2012;33:177–182
RBV ≠ Absolute Blood Volume
Fahraeus effect (F-cell) = hematocrit
mixed blood / central hematocrit varies
during HD
• Postural changes in the first 30 mins
• Observed decrease in RBV under-
estimates changes in total blood
volume
? Not as good in preventing
hypotension
? Better at managing overload

43. RBV and ScvO2 in Acute
Dialysis Settings

44. RBV Monitoring in Acute Dialysis In the ICU
Kidney International, Vol. 62 (2002), pp. 1075–1080
Only prospective study to date included 20 patients dialyzing in the ICU for a total of
57 treatments (less than 2 weeks worth of data in our service)
?? Any takers for a quality project

45. RBV Monitoring of Acute Dialysis In the ICU
Kidney International, Vol. 62 (2002), pp. 1075–1080

46. Access: Catheter
Normal 60-80 %
SvO2
Venous Blood
Lower O2 Saturation

47. ScvO2
ScvO2
Venous Blood
Lower O2 Saturation
Cardiac Output (L/min) = Oxygen
consumption (ml/minute) Art O2
content - Ven O2 Content
 ScvO2 = CO = BP (BP = CO X PVR)

48. Continuous monitoring of SvO2 is a
sensitive parameter of cardiac output
C. O. = Heart Rate x Stroke Volume
Nephrol Dial Transplant (2017) 1–
doi: 10.1093/ndt/gfx271
Unanswered questions:
1. could changes in acute patients (dialyzing with CVCs) be inferred to
stand for myocardial stunning?
2. Could we trend SvO2 to prevent IDH in acute dialysis patients?

49. Conclusions
• The value of RBV monitoring remains highly uncertain
• Inconsistent application of RBV monitoring may even
be associated with worse clinical outcomes
• At present the device seems more able to identify
volume overloaded patients than prevent hypotension
• Standardization of measurements are important given
postural changes around the start of dialysis
• Further studies are needed to probe the utility of other
device channels (e.g. SvO2) in acute and chronic
settings
• Modifications of the standard critline readout to
estimate the absolute blood volume may be useful in
future applications