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Sodium profiling and UF profiling in hemodialysis

These are temporary, individualized strategies for patients who develop intradialytic hypotension (IDH), cramps, or poor tolerance of fluid removal. They should be prescribed and set by the nephrologist/dialysis unit protocol, not applied routinely to every patient.

There is no universal machine “profile number”. A profile called “1”, “2”, “linear”, or “step” differs by manufacturer. Select the shape and actual values, not the profile number alone.

1. Sodium profiling

What it is

Dialysate sodium is set higher at the beginning of dialysis and then gradually reduced to the prescribed usual sodium by the end.

Why it works

Early higher dialysate sodium:

Maintains plasma osmolality
Reduces water shift from the blood into cells
Improves vascular refill
Can reduce symptomatic hypotension, nausea, cramps, and disequilibrium symptoms

Main problem

It can cause a positive sodium balance, leading to:

Thirst
Higher interdialytic weight gain (IDWG)
Hypertension
Edema/fluid overload
Higher ultrafiltration requirement at the next dialysis

The textbook notes that intradialytic sodium gain increases thirst and IDWG, which then raises UF requirements and can worsen hypotension in later sessions. Comprehensive Clinical Nephrology, 7th Edition, Individualized Dialysate Sodium Prescription. Current evidence also advises that sodium modeling be used cautiously because of sodium loading and hypervolemia, as summarized in this dialysis volume-management review.

Sodium profile graph

A. Usual and preferred profile: descending / tapering profile

Dialysate Na
mmol/L

145 |●
143 |  ●
141 |    ●
139 |       ●
138 |----------●------------------> Time
       Start     Mid        End

Higher sodium initially
Falls gradually
Must end at the patient's prescribed baseline dialysate sodium, commonly around 136-140 mmol/L, depending on the unit prescription.
Do not finish with a high sodium concentration.

B. Step sodium profile

Dialysate Na

145 |───────────
142 |           ───────────
139 |                      ───────────
138 |                                 ● End
    Start        1/3          2/3       End

This uses discrete drops rather than a smooth slope.

C. Linear profile

Dialysate Na

145 |●
    |  ●
    |    ●
    |      ●
138 |--------●------------------------> Time

A continuous decline from the initial sodium to the final sodium.

D. Avoid: high sodium throughout

145 |──────────────────────────────────
    Start                             End

This is not sodium profiling. It promotes sodium loading, thirst, large IDWG, and hypertension.

Practical sodium settings

Common concept

Parameter	Typical principle
Starting dialysate sodium	Modestly higher than usual prescription
End dialysate sodium	Return to prescribed baseline by end of dialysis
Shape	Linear or step-down
Goal	Reduce IDH without net sodium loading
Monitoring	BP, symptoms, thirst, post-dialysis weight, IDWG, predialysis serum sodium

A unit may use a starting sodium around 142-145 mmol/L and taper to 138 mmol/L, but this is not a universal prescription. It depends on serum sodium, BP, IDWG, residual renal function, and machine capabilities.

Do not confuse these two values

Serum sodium: patient blood sodium, commonly about 135-145 mmol/L.
Dialysate sodium: sodium concentration in the dialysis fluid.

A patient with serum Na 130 mmol/L does not automatically need a high sodium profile. The cause and chronicity of hyponatremia must be assessed by the nephrology team.

Indications for sodium profiling

Consider only for selected patients with:

Recurrent symptomatic IDH
- BP fall with dizziness, syncope, nausea, yawning, cramps, chest discomfort, or need for saline.
IDH despite correcting basic causes
- Reassess dry weight.
- Reduce excessive UF rate.
- Avoid eating during dialysis if relevant.
- Review antihypertensive timing.
- Consider cooler dialysate.
- Increase dialysis time or frequency.
High osmotic shift risk
- Short dialysis time with substantial solute removal.
- Dialysis disequilibrium risk in selected situations.
Severe cramps or symptoms related to rapid osmolar reduction, after other causes are addressed.

Relative contraindications / situations to avoid

Avoid routine sodium profiling, or use only with strong justification, in:

Hypertension
Large IDWG
Chronic volume overload / edema
Heart failure with congestion
Frequent pulmonary edema
Patients persistently thirsty after dialysis
High predialysis serum sodium or hypernatremia
Patients who already need aggressive UF because of sodium and fluid excess

Harrison’s notes that high dialysate sodium and sodium modeling may be undesirable in patients with hypertension or large interdialytic weight gains. Harrison’s Principles of Internal Medicine, 22nd ed., Dialysate. A 2024 systematic review also evaluated the relationship between lower dialysate sodium and IDWG.

2. UF profiling

What it is

UF profiling means changing the ultrafiltration rate during the session while keeping the same total planned fluid removal.

The usual aim is:

Higher UF earlier, when the patient is relatively more fluid overloaded and plasma refill may be better
Lower UF later, when intravascular volume becomes more vulnerable

Unlike sodium profiling, UF profiling does not intentionally add sodium.

Basic UF profile graph

A. Standard UF: constant rate

UF rate
mL/hour

600 |──────────────────────────────────
    Start                             End

For example, 2.4 L over 4 hours:

[ 2400\text{ mL} \div 4\text{ hours} = 600\text{ mL/hour} ]

B. Descending or front-loaded UF profile

UF rate
mL/hour

900 |●
800 |  ●
700 |    ●
600 |      ●
500 |         ●
400 |            ●
    +----------------------------------> Time
       Start        Mid                 End

Area under the curve must equal the prescribed total UF volume.

Example only:

Hour 1: 800 mL
Hour 2: 700 mL
Hour 3: 500 mL
Hour 4: 400 mL
----------------
Total : 2400 mL

This may be a useful shape only if the early UF rate is safe for that particular patient.

C. Step-down UF profile

UF rate

800 |─────────
650 |         ─────────
500 |                  ─────────
350 |                           ─────
    Start       1 h       2 h      End

D. Avoid: increasing UF late in dialysis

UF rate

300 |●
500 |  ●
700 |    ●
900 |       ●
    +----------------------------------> Time

This is generally poorly tolerated because intravascular volume is often lowest late in treatment. It may provoke late-session hypotension and cramps.

3. How to set UF profiling safely

Step 1: Calculate total UF target

[ \text{UF target} = \text{Pre-HD weight} - \text{Target post-HD weight} + \text{fluids given during HD} ]

Example:

Pre-HD weight:        72.8 kg
Target post-HD weight:70.5 kg
Intradialytic intake: 0.2 L
--------------------------------
UF target:            2.5 L

Step 2: Calculate the average UF rate

[ \text{UFR} = \frac{\text{UF volume in mL}}{\text{treatment time in hours} \times \text{post-HD/target weight in kg}} ]

Example:

[ \frac{2500}{4 \times 70.5} = 8.9\text{ mL/kg/hour} ]

Step 3: Set a maximum UFR first

A practical safety approach is to avoid UFR above 10 mL/kg/hour when possible. Some programs use 13 mL/kg/hour as a warning threshold, but it should not be treated as a goal or routinely acceptable rate.

The 10 mL/kg/hour value is a useful clinical caution point, especially in hypotension-prone patients. A recent IDH review recommends avoiding high UFR, generally over 10 mL/kg/h, and using longer treatments when necessary. See this IDH prevention review.

Example of why this matters

For a 60-kg patient dialyzed for 4 hours:

[ 60 \times 4 \times 10 = 2400\text{ mL} ]

So a UF goal above 2.4 L in 4 hours exceeds 10 mL/kg/h. The safer response is usually:

extend treatment time,
add an extra session,
reduce IDWG through salt/fluid counseling,
reassess target weight,

rather than use a more aggressive UF profile.

Step 4: Choose the profile shape

If appropriate, select a mild descending profile, not an extreme front-load.

The exact hourly rates are machine- and patient-specific. Ensure:

Total UF equals prescribed target
No interval exceeds the patient-specific maximum UFR
The patient is monitored throughout, especially in the first hour
The target weight is reassessed if there is recurrent IDH

4. Indications for UF profiling

Possible indications:

Recurrent IDH or cramps, especially late in dialysis.
Poor tolerance of a constant UF rate despite a reasonable total UF target.
Patients with evidence of better early vascular refill and late-session hypotension.
Selected patients with autonomic dysfunction, ischemic heart disease, or reduced cardiac reserve, only after correcting basic factors.
High IDWG, but only as a temporary strategy. It does not replace sodium restriction or longer dialysis.

Evidence for UF profiling alone remains limited. A review of BP and volume management notes that randomized evidence independent of sodium profiling or blood-volume monitoring is scarce. The profile should therefore be judged by patient outcomes, not used automatically.

5. Contraindications / when not to use UF profiling

There are few absolute contraindications to changing a UF curve, but do not use it as a way to force fluid removal in the following situations:

Situation	Why it is unsafe
UF target is too high	Profile does not make excessive removal safe
Early-session hypotension	A front-loaded profile may worsen it
Active hypovolemia or inaccurate low target weight	Fluid removal is the wrong intervention
Sepsis, bleeding, vomiting, diarrhea	Risk of intravascular depletion
Acute cardiac ischemia or unstable arrhythmia	Hemodynamic instability
Severe peripheral vasculopathy or poor refill	Less ability to maintain circulating volume
Recurrent IDH with low UFR	Investigate cardiac disease, autonomic dysfunction, infection, malnutrition, dialysate factors, and target weight
Patient has persistent overload due to dietary sodium excess	Treat sodium intake and dialysis time, not just the UF curve

6. Sodium profiling vs UF profiling

Feature	Sodium profiling	UF profiling
What changes?	Dialysate sodium concentration	Fluid removal rate
Typical graph	High early sodium, taper down	Higher early UF, taper down
Main intended benefit	Maintain osmolality and BP	Match UF to plasma refill
Main risk	Sodium loading, thirst, IDWG, hypertension	Early hypovolemia/hypotension if too aggressive
End setting	Return to usual prescribed dialysate Na	Total UF must equal prescribed volume
Routine use?	No	No
Best use	Selected, refractory IDH after basic correction	Selected intolerance to constant UF

7. Practical order for recurrent intradialytic hypotension

Before using either profile, check:

Is target weight too low?
Is UFR too high? Aim to reduce it, often by increasing dialysis duration.
Is IDWG excessive? Review dietary sodium intake.
Is the patient eating during dialysis?
Are antihypertensives being taken immediately before dialysis?
Could cooler dialysate help?
Are there cardiac, autonomic, infectious, bleeding, or arrhythmic causes?
Only then consider a carefully monitored UF profile, and rarely a sodium profile.

For many hypotension-prone patients, avoiding positive sodium balance and using individualized cool dialysate is preferable to routine sodium profiling. Comprehensive Clinical Nephrology, 7th Edition, Impaired Cardiovascular Regulation.

Key take-home

Sodium profile graph: start a little higher and finish at usual sodium.
UF profile graph: usually higher early and lower late, but never exceed the patient-safe UFR.
Do not use “profile number 1/2/3” without knowing the dialysis machine brand and its programmed curve.
Do not use profiles to compensate for an excessive UF target or very high IDWG.

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