Dry Weight Dr Rosna

DRY WEIGHT Dr Rosnawati Yahya Consultant Nephrologist Hospital Kuala Lumpur

INTRODUCTION Cardiovascular (CV) disease is the primary cause of mortality in maintenance hemodialysis (HD) patients.

INTRODUCTION Poor control of hypertension is, in great part, responsible for this situation. Several factors are involved in the pathogenesis of hypertension, but the main one is extracellular volume (ECV) overload.

INTRODUCTION Establishing and maintaining normal extracellular volume (ECV) is required to achieve normotension. The achievement of an optimal fluid status, as expressed by "dry weight" (DW), should allow for controlling blood pressure (BP) in the large majority of HD patients .

BODY WATER INTRACELLULAR FLUID INTRA VASCULAR FLUID INTERSTITIAL FLUID EXTRACELLULAR FLUID

BODY WATER INTRACELLULAR FLUID 2/3 TBW 28 L INTRAVASCULAR FLUID 3.5 L 70kg man TOTAL BODY WATER:42 L INTERSTITIAL FLUID 10.5 L

Sodium and water balance Extracellular volume is about 15 L; sodium is the most prevalent cation in ECV. Physiologically, urine is the only exit route for sodium.

Sodium and water balance When the kidney fails, no alternative route compensates for the lack of sodium output and it accumulates, thereby increasing body osmolality. Subsequent increased thirst and water ingestion results in the accumulation of isotonic saline in the ECV.

Sodium and water balance In dialysis, the patients who do not restrict sodium in their diets develop a water & salt excess between dialyses. In CRF : ECV increases even if the overload is not such that edema is obvious. Patients with advanced CRF are particularly sensitive to sodium load . Hypertension appears, even with a relatively low normal sodium intake. This peculiar sensitivity to sodium load increases as CRF progresses

Sodium and water balance For each 9 g sodium chloride, the patient's serum osmolality increases and stimulates thirst enough to drive a 1-L fluid intake. There is no reason to convince the patient to tolerate thirst and to restrict fluid intake to reduce the interdialytic weight gain, because excess dietary sodium, not fluid, is the real culprit

Sodium and water balance A low salt diet is the most important tool to reduce interdialytic weight gain. In end-stage renal disease, it is impossible for the kidney to adjust the ECV, the dialyzer must do this.

Dry weight ideal postdialysis weight that allows a constantly normal blood pressure to be maintained without using antihypertensive medications. "that body weight at the end of dialysis at which the patient can remain normotensive until the next dialysis without antihypertensive medication" Dry weight is not the actual postdialysis weight. It is the ideal postdialysis weight allowing for a normal BP.

Dry weight The patterns of euvolemia are mandatory: normotension per se does not exclude saline overload hypotension during dialysis does not necessarily indicate that the patient has reached DW.

Evaluation of fluid status (extracellular volume)

Evaluation of fluid status (extracellular volume) An increase in predialysis BP is the main sign of saline (salt & water) overload. Low BP postdialysis or postural hypotension persisting more than a few hours suggest saline depletion. Short-term weight variations allow for the quantitative estimation of changes in ECV.

Evaluation of fluid status (extracellular volume) Intravascular volume can be assessed by examining the jugular veins in the supine patient or by central venous pressure measurement. Edema can be present in advanced stages of saline overload, but a severe saline overload can also exist without any edema.

Evaluation of fluid status (extracellular volume) Cardiothoracic ratio on x ray changes in hematocrit, total protein, and serum albumin may be of great help in evaluating ECV changes

Dry weight Assessment: Clinical Blood pressure JVP Oedema/ascites Lungs examinations Weighing scale. Advantages Cheap Immediate universally available at the patient's bedside. Disadvantages: Unreliable Insensitive inaccurate.

Dry weight Assessment: non-clinical inferior vena cava diameter, atrial natriuretic peptide (ANP) Bioimpedance blood volume monitoring

Dry weight Assessment: non-clinical There is no necessity in the clinical day-to-day practice to know the absolute value of ECV. All we really need is to achieve the ECV value at which the patient is without signs of dehydration or fluid overload and remains normotensive without antihypertensive medications.

Pathophysiology of dry weight

Pathophysiology of dry weight normal kidney functions 24 hrs/day HD is discontinuous, a few hours every 2 or 3 days: to a peak-and-valley situation. The patient gains one to several liters of ECV during the interdialytic period.

Pathophysiology of dry weight At the initiation of each HD session: the patient is saline overloaded, or "wet." He needs to lose the weight gained during the interdialytic period to return to the last postdialysis weight. Wt : 62 kg Wt 58 kg

Pathophysiology of dry weight If this weight has been found to be too high, the planned ultrafiltration (UF) must be increased. IDWG = 3 kg Set UF = 3.2 kg allow about 200 ml extra for blood return + fluid & food taken during HD If it has been found to be too low, the planned UF must be decreased. IDWG = 1kg Set UF =1.2 kg

Pathophysiology of dry weight DRY WEIGHT : 58kg 2 3 2.5 2 4 2.5 3 2 IDWG (kg) 2.2-2.5 3.2-3.5 2.7-3.0 2.2-2.5 4.2-4.5 2.7-3.0 3.2- 3.5 2.2-2.5 UF target (litres) 58 58 58 58 58 58 58 58 Post wt (kg) 60 61 60.5 60 62 60.5 61 60 Pre wt (kg) wed mon fri wed mon fri wed mon

Pathophysiology of dry weight The water and salt subtraction from the plasma volume creates a disequilibrium situation between the plasma and interstitial spaces. Water & salt removal from plasma/ intravascular space

Pathophysiology of dry weight Refilling from interstitial (and intracellular) spaces has started but is not yet completed (it takes about 4 hours).

Pathophysiology of dry weight At the end of the HD session, plasma volume reaches a nadir. At disconnection the patient is hypovolemic, or "dry," and may have a postural BP drop that will disappear within a few hours.

Pathophysiology of dry weight Plasma volume preservation during UF is linked to the initial interstitial volume status. The higher it is, the faster the refilling During the session, as the patient gets less and less volume overloaded, his refilling capacity decreases and the hazard of hypotension increases.

Pathophysiology of dry weight Blood pressure usually remains stable during the first two thirds of the session. In some patients, hypotension, rather than being compensated by an adequate hemodynamic response, may be complicated by a vasovagal syncope

Pathophysiology of dry weight In fact, several factors modulate cardiovascular compensation: extracorporeal temperature dialysate buffer calcium concentration.

Pathophysiology of dry weight The heart's ability to compensate for an acute volume change is: most important. impaired by reduced left ventricular compliance, which is very common in HD patients. Poor LV compliance or LV function leads to poor cardiac output thus causing hypotension

Assessing Dry Weight at the bedside: clinical information ie BP, JVP, oedema one can guess where the patient stands in terms of ECV and prescribe a target post-dialysis weight. When BP is normal both before and after dialysis, and no disturbing postural hypotension symptoms occur after a few hours, the patient is probably at DW.

Assessing Dry Weight If BP is elevated even slightly, DW is reduced by a few hundred grams. If, on the other hand, the patient experiences an orthostatic hypotension that persists more than a few hours after disconnection, then post-dialysis weight is increased. The trial-and-error process can be alleviated by ambulatory BP measurement, which gives a more objective view of the real BP than intermittent measurements.

Assessing Dry Weight The use of weight as surrogate of extracellular volume is acceptable in chronic dialysis patient who maintained their lean and fat body mass. It is more difficult if the lean and fat body mass fluctuates, for example during or after catabolic events (surgical procedure, hospitalization) the patient loses lean and fat body mass; therefore, prescribed DW must be lowered to maintain a steady ECV. If the patient's food intake improves and lean and fat mass increase, patients fail to notice. If same DW is given, the patient may develop hypotension

“ Failure” of Dry Weight

“ Failure” of Dry Weight A large proportion of patients are reported to be hypertensive in spite of being at their "dry weight.“ This is, in almost all cases, due to: the DW has been overestimated the correctly estimated DW could not be achieved.

“ Failure” of Dry Weight Problems may occur in clinical evaluation of DW. 4 things to remember: Dry weight is a mobile target. Because weight is used as the surrogate of ECV, any factor of weight variation must be identified and measured when evaluating DW. Dry weight must be readjusted on a regular systematic basis because appetite and nutrition keep changing all the time and food intake is difficult to appreciate.

“ Failure” of Dry Weight Problems may occur in clinical evaluation of DW. 4 things to remember: Clinical symptoms are unspecific and sometimes discordant. For instance, a grossly volume-overloaded patient may get hypotension and cramps during HD, especially if the session time is short and the UF rate is high. Dry weight must not be modified on the basis of a single symptom or data point, but on a cluster of information.

“ Failure” of Dry Weight Problems may occur in clinical evaluation of DW. Four main points to remember The lag time of some weeks between change in ECV and change in BP must be accounted for in the probe for DW. One should not expect an immediate BP response to changes in ECV. This is true when DW increases as well as when it decreases.

“ Failure” of Dry Weight Problems may occur in clinical evaluation of DW. Four main points to remember An important difficulty in clinical evaluation of DW comes from the common confusion between DW and interdialytic weight change. Interdialytic weight changes are first-order oscillations of weight due to the intermittent nature of HD, but DW is the short-term stable value that allows the BP to be normal.

“ Failure” of Dry Weight Clinical Scenario If a normotensive patient has edema, shortness of breath or a high venous pressure (or full jugular veins), or an enlarged heart on chest x ray, -> suspected of being saline overloaded. Studies have shown that a proportion of normotensive patients have an increased ECV (fluid overloaded) according to bioimpedance. BP is the target of ECV control, it is important to assess ECV.

“ Failure” of Dry Weight Clinical Scenario antihypertensive treatment is a major source of failure to achieve DW . low BP is artificially maintained by the medication, even if the patient is not really "dry“.

“ Failure” of Dry Weight Clinical Scenario One of the main potential problems in achieving DW is insufficient dialysis time: insufficient time allocated for UF. A shorter HD session leads to more hypertension, and at the same time hypotension When session time is shortened, UF rate is increased and hypotension occur.

“ Failure” of Dry Weight Clinical Scenario This has several bad effects: The patient has a poor perception and acceptance of HD and asks for a shorter session. The nurse has to cut down the UF rate or give saline, so prescribed DW is not achieved. The physician wrongly re-evaluates DW. Often he prescribes a higher dialysate sodium (Na profiling). This, reduces the diffusive sodium drag from the patient and leads to increased osmolality, thirst, and interdialytic weight gain. Consequence: the patient does not achieve DW

“ Failure” of Dry Weight Clinical Scenario Another potential factor in achieving an adequate ECV is the existence of so-called hypotension-prone patients Risk factors: left ventricular hypertrophy (LVH) and impaired diastolic relaxation Poor LV function impaired cardiac output

Assessment BP –pre and post dialysis No of antihypertensives Look for: Pedal/sacral oedema Feels for apex beat JVP Lungs bases

Assessment If BP OK :pre/post on 0 or 1 anti hypertensives and clinically no sign of fluid overload : continue current dry weight If BP OK : on 2 or more anti hypertensives and clinically no sign of fluid overload : CXR –assess CTR: if cardiomegaly : reduce DW If normal CTR : continue DW increased antihypertensives Further assessment ( bioimpedance)

Assessment If BP high :with or without anti hypertensives and clinically no sign of fluid overload : CXR –assess CTR: if cardiomegaly : reduce DW If normal CTR : continue DW increased antihypertensives Further assessment ( bioimpedance) If BP high and clinically with sign of fluid overload : reduce DW

Which is more important? restricting fluid Versus restricting sodium on weight gain between dialyses

Management of Dry Weight Sodium intake must be reduced to the lowest level . Telur masin Ikan masin/pekasam Belacan Cincaluk Budu Keropok

Management of Dry Weight If the patient is followed in the clinics before HD start, the growing difficulty in controlling ECV and BP as CRF worsens is a good opportunity to show him the benefit of a low salt diet. The period of dialysis initiation needs the restriction to be especially tight.

Management of Dry Weight When starting dialysis, the lower the interdialytic weight gain, the easier it is to reduce the ECV to the level required to achieve normotension. It is easier to ask this effort of the patient at the start of dialysis when he is looking for a rapid improvement of his status.

Management of Dry Weight A multidisciplinary approach is needed to educate the patient and caregivers A low sodium diet of 2-3 gm. , daily fluid restriction (30-40 oz/day or 1000 to 1200 cc/day) is needed for the average 60 Kg patient

Management of Dry Weight Accurate pre- and post-dialysis weights, to measure the weight gain in between dialysis treatments is essential. Average interdialysis weight gains are 3% of estimated DW during the midweek days 30-50 % higher over the weekend interval.

Dry Weight Dr Rosna

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