Thursday, November 20, 2014

EDELMAN IS THE ROOT OF ALMOST ALL GOOD IN NEPHROLOGY

Almost all the formulas we use in the management of the disorders of water homeostasis are derived from the Edelman equation. I am presenting where these formulas come from for the math aficionados.

Edelman equation

·         Original Edelman equation (J Clin Invest. 1958;37:1236-56):
[Na+] = {1.1 x (Nae + Ke)/TBW} – 25.6
Where [Na+] = plasma sodium concentration, Nae=total body exchangeable sodium, Ke=total body exchangeable potassium, TBW = total body water.

·         Simplified Edelman equation: [Na+] = (Na + K)/TBW
·         [Na+] x TBW = Na + K
·         Na + K = [Na+] x TBW

Calculating Free Water Deficit (FWD)

Method #1 (Using baseline weight, certainty about what % of body weight is water)

1.       Assuming only pure water has been lost, the total body sodium and potassium remain constant so the total body sodium and potassium at baseline (Na + K)baseline and the total body sodium and potassium after water loss (Na + K)current are equal:

·          (Na + K)baseline = (Na + K)current

2.       Total body sodium and potassium can be expressed as sodium concentration ([Na+]) multiplied by total body water (TBW):

·         [Na+]baseline x TBWbaseline = [Na+]baseline x TBWcurrent
·         TBWcurrent = [Na+]baseline x TBWbaseline/[Na+]current … (1)

3.       Free water deficit can be expressed as:

·         FWD = TBWbaseline – TBWcurrent … (2)

4.       Then replacing (1) in (2):

·         FWD = TBWbaseline – ([Na+]baseline x TBWbaseline)/[Na+]current
·         FWD = TBWbaseline x (1 – [Na+]baseline/[Na+]current)

5.       If [Na+]baseline is considered normal at 140 mEq/L then:

·         FWD = TBWbaseline x (1 – 140/[Na+]current)

Method #2 (Using current weight, uncertainty about what % of body weight is water)

1.       Assuming only pure water has been lost, the total body sodium and potassium remain constant so the total body sodium and potassium at baseline (Na + K)baseline and the total body sodium and potassium after water loss (Na + K)current are equal:

·         (Na + K)baseline = (Na + K)current

2.       Sodium and potassium masses can be expressed as sodium concentration ([Na+]) multiplied by total body water (TBW):

·         [Na+]baseline x TBWbaseline = [Na+]current x TBWcurrent
·         TBWbaseline = [Na+]current x TBWcurrent/[Na+]baseline … (1)

3.       Free water deficit can be expressed as:

·         FWD = TBWbaseline – TBWcurrent … (2)

4.       Then replacing (1) in (2):

·         FWD = [Na+]current x TBWcurrent/[Na+]baseline – TBWcurrent
·         FWD = TBWcurrent x ([Na+]current/[Na+]baseline - 1)

5.       If [Na+]baseline is considered normal at 140 mEq/L then:

·         FWD = TBWcurrent x ([Na+]current/140 - 1)

Calculating Rate of Infusion of Hypertonic Saline

Method # 1: Na deficit formula

Deriving Na deficit formula

1.       Na deficit = Nagoal – Nacurrent … (1)

2.       Since Na + K = [Na+] x TBW, then Na = [Na+] x TBW – K … (2)

3.       Replacing (2) in (1)
·         Na deficit = TBWgoal x [Na+]goal – Kgoal – {TBWcurrent  x [Na+]current – Kcurrent}

4.       Assuming TBW and K remain constant, so TBWgoal = TBWcurrent, and Kgoal = Kcurrent, then TBW = TBWgoal = TBWcurrent and K is cancelled out from equation:

·         Na deficit = TBW x [Na+]goal – TBW x [Na+]current
·         Na deficit = TBW x ([Na+]goal – [Na+]current)

5.       Since now we aim for an increase in [Na+] of 6 mEq/L, so [Na+]goal – [Na+]current = 6 mEq/L then:

·         Na deficit = TBW x 6 mEq/L

Calculating volume of infusate

·         Volume of infusate = Na deficit x (1000 mL/513 mEq)

Calculating rate of infusion

·         Rate of infusion = volume of infusate/24h

Method #2: Adrogue-Madias formula

Deriving Adrogue-Madias formula

1.       [Na+] = (Na + K)/TBW … (Edelman equation)

·         [Na+]current = (Nacurrent + Kcurrent)/TBWcurrent
·         [Na+]current x TBWcurrent = (Nacurrent + Kcurrent) … (1)

2.       [Na+]goal will be the new [Na+] that results when we administer 1L of an infusate containing Nainfusate and Kinfusate, then:

·         [Na+]goal = (Nacurrent + Kcurrent + Nainfusate + Kinfusate)/(TBWcurrent + 1) …(2)

3.       Substracting [Na+]current from both terms of equation (2), then:

·         [Na+]goal – [Na+]current = (Nacurrent + Kcurrent + Nainfusate + Kinfusate)/(TBWcurrent + 1) – [Na+]current

4.       But [Na+]goal – [Na+]current is the same as change in [Na+], then:

·         Change in [Na+] = (Nacurrent + Kcurrent + Nainfusate + Kinfusate)/(TBWcurrent + 1) – [Na+]current
·         Change in [Na+] = {(Nacurrent + Kcurrent + Nainfusate + Kinfusate) – (TBWcurrent + 1) x Nacurrent}/(TBWcurrent + 1)
·         Change in [Na+] = {Nacurrent + Kcurrent + Nainfusate + Kinfusate – ([Na+]current x TBWcurrent –[Na+]current)}/(TBWcurrent + 1) … (3)

5.       Replacing equation (1) in (3), then:

·         Change in [Na+] = {Nacurrent + Kcurrent + Nainfusate + Kinfusate – (Nacurrent + Kcurrent) - [Na+]current}/(TBW + 1)

6.       Cancelling out Nacurrent + Kcurrent then:

·         Change in [Na+] = {Nainfusate + Kinfusate - [Na+]current}/(TBWcurrent + 1)

Calculating volume of infusate

·         Volume of infusate = {1000 mL x (Change in [Na+])goal}/(Change in [Na+])
·         Volume of infusate = {1000 mL x 6 mEq/L}/(Change in [Na+])

Calculating rate of infusion

·         Rate of infusion = volume of infusate/24h





Tuesday, November 18, 2014

SEVERE CHRONIC HYPONATREMIA: A Pathophysiological Rumination.

[This is the final post in the five-part series covering some important and often overlooked (and under-published) issues and concepts in the management of severe hyponatremia. While this is not, by any means, an exhaustive discussion of the topic, I hope that these posts will not only help the readers enhance their understanding of the pathophysiology of severe hyponatremia but also help them manage it more effectively with a lot less stress and mental anguish.]


PART 5: A CALCULATED APPROACH
In this video post, I discuss --- what I find to be --- an extremely useful method of calculating the dose of sodium chloride based infusions and predicting response to therapy while treating chronic severe hyponatremia.


Posted by Hashim Mohmand

Monday, November 17, 2014

Michelle P Winn Endowed Lectureship, ASN 2014

At this year's ASN Kidney Week in Philadelphia Andrey Shaw, MD, presented the inaugural Michelle P Winn Endowed Lectureship. Dr Shaw was not only a longtime collaborator of Michelle’s but also a very close personal friend making him the perfect choice for this inaugural lectureship. Dr Shaw delivered an excellent talk interweaving highlights from Michelle’s stellar career with examples of Michelle’s fun loving and genuine kindhearted nature. I was lucky enough to work in Michelle’s lab from 2012 to 2014. She cared greatly about all her mentees both professionally and personally. She was a huge inspiration and a friend.

Michelle did her undergraduate studies at the University of North Carolina before going to medical school at East Carolina University. She then entered Duke University for residency and fellowship before joining the Duke faculty. Despite spending most of her career at Duke she remained a true Tar Heel (UNC) fan!

She received her training in classical human genetics from Drs Jeffery and Peggy Vance at the Duke Center for Human Genetics. In collaboration with another longtime friend and collaborator and early mentor at Duke, Dr Peter Conlon, Michelle began investigating the genetic heterogeneity of FSGS.
  • Together Drs Winn and Conlon collected what is now one of the largest Familial FSGS datasets in the world.
  • Michelle’s early work linked familial FSGS in one large family from New Zealand to a locus on chromosome 11.
  • Following this she identified TRPC6 as the cause for FSGS in this family. This was a seminal paper published in Science and introduced an ion channel and calcium into the burgeoning field of podocyte biology. 
  • Michelle’s further work on TRPC6 made a huge contribution to the understanding of the biology of TRPC6 in kidney disease. 
Michelle was also very interested in other inherited kidney diseases.
  • She described linkage of a gene causing MPGN type III, 
  • identified TNXB mutations causing vesicoureteral reflux, 
  • was involved in studies of genetic factors influencing the development and progression of IgA nephropathy 
  • a hybrid CFHR3-1 gene causing familial C3 glomerulopathy. 
  • Her work also helped to define the disease burden and impact of other FSGS causing genes such as INF2, NPHS2 and PLCe1
Towards the end of her career and even while fighting her illness she remained very involved and continued to contribute in a huge way to the field we all love.
  • She discovered Anillin a new gene causing FSGS, 
  • a new mutation in the WT1 gene 
  • added further insights into the function and regulation of TRPC6 in podocytes. 
Michelle was a leader in her field of podocyte biology and renal genetics. In 2007 Michelle won the ASN Young Investigator Award. I am sure that if her life had not been tragically cut short she would have been awarded the highest honors our specialty has to offer. The creation of the Michelle P Winn Endowed Lectureship is testament to this probability. Michelle was a beautiful person and will be missed by all who knew her.

Tuesday, November 11, 2014

Blogger night at #KidneyWk14 on Thursday

Thursday night at 8:30 pm, Blogger Night (after the ASN Presidents Reception). If you like the Neph Social Media Crew from Twitter, Renal Fellow Network, AJKDblog or NephJC, join us for drinks at Field House Philly sports bar. Look for Joel in his AJKD hat.

Sunday, November 9, 2014

Nephrology fellows events at ASN #KidneyWk14

Welcome Reception: Nov 12th: 6-7PM
Marriott Downtown, Grand Ballroom, Salon H

Fellows In Training Bowl (Mystery Case Debate): Nov 14th 2-3PM
Convention Center, Room  119A

Fellows In Training Bowl (Jeopardy game Nephrology Challenge): Nov 14th 3-4PM
Convention Center, Room  119A

Meet the Experts Session Nov 15th  9:30AM - 10:30AM (Meeting the ASN Award Winners)
Convention Center, Hall D

Fellows Forum Nov 15th 10:30-11:30AM
Convention Center, Room 203

Fellows Poster Discussion Section Nov 15th 2-3PM
Convention Center, Room 112

h/t Kenar Jhaveri

Thursday, November 6, 2014

NephJC Live at ASN Kidney Week 2014

The Nephrology twitter journal club will come to life on Saturday 15th November at Kidney Week in Philadelphia. NephJC co-founders Dr Joel Topf and Dr Swapnil Hiremath will co-host the event at the Double Tree hotel.

There will be 2 live presentations on the day, both of which are sure to stimulate active discussion. There will be a study, presented by Dr. Deirdre Sawinski of University of Pennsylvania, looking at transplanting HIV positive kidneys into seropositive donors. Dr Francis Wilson will also present his RCT on acute kidney injury.

The event is filling up so please visit www.nephjc.com before this Sunday November 9th to register. For those of us who cannot make it to Philadelphia, the event will, as ever, be live tweeted using #NephJC.

Wednesday, November 5, 2014

Preventing PD Peritonitis: What's the Evidence?

Peritoneal dialysis associated peritonitis is the second commonest cause of death among PD patients (35/1000 years) and the most common cause of treatment failure. It confers a CV risk of 7 times normal for 6 months following the bacteremia, so we need to remain ever vigilant when dealing with PD patient, and its worth refreshing our knowledge on how to prevent this feared complication. There is a paucity of high quality evidence for many of the most fundamental questions in PD. Such is the lack of evidence, the International Society for Peritoneal Dialysis (ISPD) have issued a consensus document where they state they are unable to issue formal guidelines.

The best resources I have found on the topic are a Kidney International supplement from 2006, and the ISPD document already mentioned. In the first instance, which patients are at risk of developing peritonitis? The best described risk factors are hypoalbuminemia (similar to the association in haemodialysis patients), Staph aureus  carriage at inception of dialysis (HR 1.53), initiation of PD early after catheter insertion (HR 0.98/day), PD after transplant failure (HR 2.18), lower hemoglobin (HR 0.88/gram/l), faster PD transport rates (HR 2.92) and previous peritonitis. A special risk group to consider are those PD patients undergoing invasive procedures such as endoscopy or IUD insertion. There is evidence that antibiotic prophylaxis using cephalosporins may help reduce peritonitis rates.

The cornerstone of peritonitis prevention is minimizing contamination risk with effective hand washing and immaculate exchange technique. Specialized nurse-led training is key. If peritonitis occurs, retraining and re-education are the most important interventions. Home visits by PD nurses can cut recurrence rates in half, and should be performed where possible. A Cochrane review could find no RCT data to support any particular insertion technique, catheter type, number of cuffs or positioning. It demonstrated that of all catheter-related interventions designed to prevent peritonitis in PD, only disconnect (twin-bag and Y-set) systems have been proved to be effective. Topical antibiotic prophylaxis is a standard of care and there are multiple RCTs demonstrating the efficacy of mupirocin cream application at the exit site. Ointment is to be avoided as it can erode the catheter polymer.  In contrast, nasal mupirocin is more difficult to justify. Cochrane point out that while there is trial data that nasal mupirocin reduces exit-site/tunnel infection, it has no effect on peritonitis rates. Preoperative intravenous prophylaxis reduces early peritonitis but not exit-site/tunnel infection. 

Recent published trials in the area of antimicrobial prophylaxis have been disappointing. They include the Honeypot study, discussed previously on RFN, which demonstrated the application of honey to exit sites approximately doubled the risk of developing peritonitis in diabetic patients. The MP3 study published in JASN in 2012 found polysporin to increase rates of fungal exit site infections without any improvement in primary outcomes of exit site infection or peritonitis. Finally, a special mention goes to cats, who are responsible for at least 25 case reports of pastuerella peritonitis, as well as an assortment of other bugs. Not to be outdone, rodents feature  in the case reports also, coining the term “hamster bite peritonitis” caused by pastuerella aerogenes.
In summary, technique and continuing re-education are of fundamental importance, as are topical antibiotics to prevent exit site infection.  Beyond this, trial data are severely lacking and local opinion and consensus must guide practice.

Authored by Eoin O'Sullivan

Friday, October 31, 2014

SEVERE CHRONIC HYPONATREMIA: A Pathophysiological Rumination.

PART 4: CONTROL ISSUES

1. Losing Control: In the preceding posts, I explained how sudden emergence of water diuresis as the predominant mechanism by which rapid overcorrection of serum sodium happens in cases of severe chronic hyponatremia.  Few situations or more stressful in nephrology than when we suddenly find that serum sodium has increased by 12 mmol or more within a few hours. The usual scurried response is the immediate administration of 5% dextrose water, DDAVP are both. There has recently been some evidence that using DDAVP with D5W rapidly re-lower the sodium is well tolerated. But, as it was illustrated in this  paper, the response to these therapies is very unpredictable with the usual clinical course being a rather erratic series of rises and falls in serum sodium.


Two mechanisms are responsible for the vast majority of cases of overcorrection due to emergence of water diuresis.  (1) a sudden drop in plasma ADH/AVP levels due either to resolution of a transient source of ADH secretion or repletion of subclinical hypovolemia and (2) in cases of solute depletion hyponatremia, the sudden availability of solute (in the form of saline solutions or protein load) in the setting of an appropriately suppressed ADH. The common feature of both these phenomena is the very low level of plasma ADH which allows water diuresis.

2. Gaining Back the Control:  So how can we prevent the sudden water diuresis which is the hallmark of serum sodium overcorrection? We’ve argued above that the lack of sufficient ADH or sudden turning off of the ADH secretion is responsible for the sudden loss of free water in the urine. To address this issue specifically, in this paper by Sood et al, the Rochester group tested a very simple yet brilliant idea: why not keep the SIADH state from turning off by creating a robust iatrogenic state of SIADH? This was achieved by giving IV DDAVP 2mg every 8 hours (1 mg was tried as well but there was some breakthrough diuresis; also q6hr schedule was also tried). What this does is, by greatly reducing urine output, stabilize the denominator in Edelman’s equation (i.e. almost eliminated changes in TBW, see figure in previous post) and turn the patient into the proverbial beaker, into which now sodium, potassium and water can be added as needed to control the rate of sodium correction. In their series of 25 patients with starting serum sodium of less than 120 mEq/L, quoting directly from the abstract, “Mean changes in serum sodium levels during the first and second 24 hours of therapy were 5.8 +/- 2.8 (SD) and 4.5 +/- 2.2 mEq/L, respectively, without correction by >12 mEq/L in 24 hours or >18 mEq/L in 48 hours and without a decrease during therapy.” There was no difference in the predicted and actual correction of sodium and there were no adverse effects associated with the treatment.
Essentially, by converting the patients into human "beakers" by inducing iatrogenic SIADH and then infusing 3% saline at the desired rate allow for safe and predictable rise in serum sodium without any complications.
Our experience with this protocol has been extremely gratifying.  When this protocol was used very carefully, the serum sodium correction graph was almost invariably an almost straight line: Something that we almost never see with the traditional method of treatment of severe hyponatremia.
Once a serum sodium is between 125 and 130 mmol/L DDAVP can be discontinued while closely watching the patient.

There are a few important points that need to be mentioned here.
#1 --- It has to be clarified to the nursing staff that the DDAVP needs to be given exactly every 8 hours and the dose cannot be missed.  If the dose is missed, there can be breakthrough large volume diuresis in about 10-12 hours from the last dose which can cause overcorrection.
#2 --- The water content of all fluids given/ingested will be retained.  Therefore a very strict fluid restriction needs to be enforced.  In the IV fluids being given to the patient's in the form of infusions with antibiotics etc. need to be accounted for by calculation.
#3 --- in patients with congestive heart failure lasix can be used if it seems like fluid overload is becoming a problem.
#4 --- if a double-lumen PICC line is being used for 3% saline infusion and for drawing labs, the hypertonic infusion should be held for a few minutes before a drawing serum sodium level.  Recirculation can give a falsely elevated sodium level.  An important clue in this situation would be that there would be no large change in urine output that would be expected with a true sudden rise in serum sodium.
This protocol is somewhat opposite of what we have traditionally been taught regarding treatment of severe hyponatremia.  Given how stress-free and easy the management of severe hyponatremia has become with this for me and other colleagues, I expect this protocol to gain more widespread acceptance over the next few years.  I would also like to know if anybody has had experience with this protocol, good or bad.
Hyponatremia remains a clinical challenge but is also fun and stimulating at the same time.  A little time spent on determining the physiology at work and using more quantitative methods of choosing the doses of 3% saline coupled with good results for the patient make it very rewarding as well.

Posted by Hashim Mohmand

Tuesday, October 28, 2014

FSGS biomarker updates—suPAR, B7-1, CD40 and more…

FSGS is the most common glomerular disorder causing end-stage kidney disease in the USA with a high post-transplant recurrence rate of 20-50%. Furthermore, the treatment of post-transplant recurrent FSGS is extremely challenging. While reading a recent article on biomarkers predicting post-transplant recurrent FSGS by Delville et al. (discussed below), it seemed a good idea to cover recent advancement in FSGS research. 

 suPAR (soluble plasminogen activator receptor) 
Since the first report by Wei et al. of suPAR as a circulating permeability factor causing FSGS, there has been extensive research to elucidate its role in FSGS. Although administration of suPAR molecule to mice was initially thought to be sufficient to cause proteinuria mimicking FSGS, via activation of integrin beta 3 and derangement of actin cytoskeleton, the situation does not seem that straightforward. As Reiser et al. discussed, there are challenges to overcome: existence of different suPAR isoforms with different disease modifying effects; heterogeneity of FSGS itself, which make it complicated to interpret correlation between levels of suPAR and disease activity; involvement of suPAR in other disease process, including cardiovascular disease (KI 2014). However, suPAR remains an intriguing molecule and potential biomarker in FSGS disease process.

 B7-1 (CD80)
A case series in the NEJM from Peter Mundel’s group in the end of 2013 brought us to an excitement for personalized treatment of a subgroup of B7-1 positive FSGS patients. They found strong B7-1 stain in primary FSGS as well as post-transplant recurrent FSGS. These patients were successfully treated with abatacept (CTLA4-Ig), resulting in complete remission of proteinuria. The hypothetical pathophysiological mechanism was via direct interaction of B7-1 and integrin beta 1 causing podocyte actin cytoskeleton changes. However, it was followed by comments and larger case series (AJKD 2014) questioning specificity of the immunostaining and treatment effect of abatacept. Exploration of this costimulatory molecule in FSGS was just started and further research is needed. 

Micro RNA(s) as biomarkers for FSGS disease activity 
A group from China suggested that certain micro RNAs are associated with disease activity (level of proteinuria) and progression (Zhang et al. CJASN and AJKD 2014). Potential candidates are miR-186 (involved in cell cycle control, AKT and insulin signaling etc.) and miR-125b (involved in NFkB signaling etc.). However, their contribution to pathogenesis is not clear so far.

 Pre-transplant antibody panel (including anti-CD40) to predict post transplant recurrent FSGS
Expanding potential FSGS biomarkers is the publication by Delville et al. The authors did a beautiful translational work using human serum in protein arrays, validation of specific auto-antibodies and further experimentation using cell cultures and animals models. The authors elegantly showed that pre-transplant antibody panel, especially anti-CD40 antibody, can predict risk of post-transplant recurrent FSGS.
In more detail, they started by comparing pre-transplant sera of non-recurrent FSGS (nrFSGS) vs recurrent FSGS (rFSGS), identifying 789 autoantibodies upregulated only in rFSGS but not in nrFSGS. Then those antibodies were enriched for those Ab with antigen targets expressed in kidney (151 autoAbs) and more specifically in glomeruli (10 autoAbs). They validated the 7-antibody panel (CD40, CGB5 (chorionic gonadotropin b), PTPRO (protein tyrosine phosphatase receptor O), FAS (TNF receptor superfamily member 6), P2RY11 (P2Y purinoceptor 11), SNRPB2 (small nuclear retinoid X receptor a), and APOL2 (Apolipoprotein 2)) in rFSGS vs nrFSGS cohort, and obtained ROC AUC of 0.92. Surprisingly, anti-CD40 itself had a high ROC AUC (0.77). Then, the involvement of rFSGS-anti-CD40 IgG to enhance FSGS recurrence was confirmed in vitro—rFSGS-anti-CD40 IgG caused actin cytoskeleton derangement in podocyte cell culture—, as well as in vivo—co-injection of rFSGS-anti-CD40 IgG and suPAR molecule markedly enhanced proteinuria (in a suPAR-dependent manner), which was inhibited by CD40-blocking antibody or in CD40 knockout mice. This suggests that by checking pre-transplant anti-CD40 antibody, we may be able to identify a high risk FSGS recurrence group. To manage these patients, current options are: peritransplant plasmaphresis or rituximab. Interesting to see if CD40 antagonist or blocking antibody can play a role in preventing/treating rFSGS in the clinic...

Naoka Murakami

Friday, October 24, 2014

SEVERE CHRONIC HYPONATREMIA: A Pathophysiological Rumination (Part 3)

PART 3: THE DANGERS OF "DEPLETION"

In my previous post concerning chronic severe hyponatremia, I explained how over corrections of serum sodium of large magnitude required a dilute large volume diuresis, often precipitated by resolution of a transient source of ADH secretion.  In this post I will discuss two phenomena which are particularly dangerous as they carry significant risk of producing large volume water diuresis.

1.  Subclinical Volume Depletion: As mentioned in my previous post, we noticed during our review of a large number of cases of severe hyponatremia treated with 3% saline that most of the patients whose serum sodium eventually overcorrected responded to small volumes of 3% saline as if they were volume depleted, with sudden emergence of water diuresis.  Interestingly, most of these patients were initially considered to be euvolemic by experienced nephrologists. 
This very interesting paper reviewed the literature concerning the value of physical examination in diagnosing volume depletion.  The conclusion, rather humbling, was that other than in cases of severe volume depletion our physical exam was quite inaccurate in diagnosing volume depletion.  This is especially concerning considering that establishing a patient's volume status forms the major decision point in the ubiquitous diagnostic algorithm for hyponatremia. 
According to the paper, reliable signs of volume depletion usually are visible with the loss of about 20% of the intravascular volume.  The ADH secretion and response to volume depletion starts with volume losses as low as 5-8% of the effective intravascular volume.  This implies that the patient may have significant ADH secretion, contributing to the relative excess water retention causing hyponatremia, while clinically appearing euvolemic.  It also means small volume bolus may switch off this ADH secretion, causing water diuresis and sudden rise in serum sodium.
Subclinical volume depletion as a contributor to hyponatremia should always be considered a possibility especially when starting therapy with 3% saline.

2.  Solute Depletion Hyponatremia: The so called "Tea and Toast Diet " hyponatremia and "Beer Potomania" are examples of solute depletion hyponatremia.  As nicely described by Dr. Berl, our solute intake limits our ability to excrete free water.  Even with a maximally dilute urine of around 50 mOsm/L, a person consuming a 300 mOsm/d diet can only excrete 6 L of urine (300/50=6).  Such a person will become hyponatremic with drinking more than 6 L of fluids a day because any water in excess of 6 L per day excretory capacity will be retained in the body.  It is important to note that this water retention is not due to ADH secretion.  ADH is often suppressed in such patients.  The renal danger of this pathophysiological mechanism is that whenever such patient is "presented" with solute (IV normal saline, high-protein meal which would generate BUN or even 3% saline!), without a high ADH level to prevent it, the added solute is used to rapidly excrete free water that has been "trapped" in the body. 
As an example, consider the case of the 26-year-old female that I briefly alluded to in the previous post.  She presented with a serum sodium of 108 mEq/L after being on an exclusively alcohol diet for the last 2 weeks.  She received 2 L of normal saline in the ER (154 mEq x2 = 308 mEq of Na). Using the Edelman equation (see figure) and an initial total body water of 32 L, if we do not account for urine output, that amount of added NaCl would have raised the serum sodium to about 111 mEq/L. But the actual rise of serum sodium was to 131 mEq/L in about 5 hours accompanied by almost 7 liters of dilute urine output. Her kidneys used the roughly 300 mEq of sodium in the NS bolus to excrete more than 6 liters of maximally dilute urine (300/50=6 L, remember the earlier calculation?) and almost perfectly accounts for the 23 mEq/L rise in serum sodium (by reducing the denominator, TBW).
This would have also happened if she had received the same amount of NaCl in the form of 3% saline as in such cases the volume of infusate matters less than the amount of solute delivered.
I hope this case illustrates how dangerous solute depletion hyponatremia can be and how easy it can be to precipitate an overcorrection of serum sodium in such patients. This raises a very important question: if even treatment with 3% saline is so unreliable in patients with chronic severe solute depletion hyponatremia, how can we safely treat such patients? That will be the subject of my next post.
In conclusion, subclinical volume depletion and solute depletion pose a particularly tricky challenge in the management of chronic hyponatremia as sudden rises in serum sodium level can happen rather easily in these patients with, what would otherwise seem to be, rather innocuous treatment with saline solutions.

Posted by Hashim Mohmand

Monday, October 20, 2014

SEVERE CHRONIC HYPONATREMIA: A Pathophysiological Rumination (Part 2)

PART 2: THE PEE IS THE KEY
I mentioned in the previous post that severe hyponatremia is multifactorial and that the contributing etiological factors in any given case may be transient and reversible.  In this post I would like to stress the importance of closely monitoring the urine output of the patient in addition to frequent monitoring of the plasma sodium.  Urine output is an extremely important clinical parameter that needs to be monitored closely but is not really mentioned in textbooks and handbooks.
Overcorrection by more than 12 mEq/L in 24 hours is not easy to achieve if the patient has a stable state of antidiuresis.  In an anuric patient with total body water of 32 L and a starting serum sodium of 108 mEq/L would require an infusion of more than 750 mL of 3% saline: a prescription not many of us would order.  In fact, during our review of cases of severe hyponatremia we found that the very popular Adrogue-Madias equation grossly underestimated the sodium correction in the majority of patients.  Most of the patients' sodium corrected far in excess of what the equation predicted.
The reason for that is that these equations treat the patients as if they were beakers that we can add sodium to and watch the plasma sodium rise as predicted.  However, unless the patient is on dialysis or in oliguric renal failure, they also lose free water in the urine, a fact that the equation does not take into consideration.  In fact, in our case series every patient that had an overcorrection of sodium beyond the desire goals, and had adequate documentation of ins and outs, had a documented large volume dilute diuresis.  Invariably, such large-volume water diuresis emerged suddenly as if an ADH switch was turned off, suggesting resolution of a transient source of ADH secretion.
While small, sudden increases in serum sodium are certainly possible with the addition of too much sodium to the system, very large and dangerous increases require simultaneous loss of free water.  A very illustrative case is one of a 26-year-old female I managed a couple of years ago.  She presented with a serum sodium of 108 mEq/L and received the inescapable 2 L of normal saline bolus in the ER and about 5 hours later her serum sodium was 131 mEq/L. With an estimated total body water of 32 L (and using the Edelman equation, see figure), if we considered her oliguric and try to account for the rise in serum sodium slowly on the basis of addition of sodium chloride to the system, we would require about 1.9 L of 3% saline to be infused in a 5 hour period!  However it is perfectly explained by the almost 7 L of water diuresis that emerged with the 2 L saline bolus.  More on this case in a later post.

In conclusion, very close monitoring of urine output should be an important and integral part of the early management of severe hyponatremia.  The sudden emergence of water diuresis is often the earliest sign of a rising serum sodium and should prompt a stat plasma sodium check. I have often relied upon a well documented q2hr urine output in ICU setting more so than the q2-4hr sodium levels which are fraught with the issue of delayed venipuncture and delays in reporting.

Posted by Hashim Mohmand

Monday, October 13, 2014

SEVERE CHRONIC HYPONATREMIA: A Pathophysiological Rumination (Part 1)


INTRODUCTION:
Severe chronic hyponatremia (<120 mEq/L) remains the #1 reason nephrologists lose sleep on call nights and rightly so.  The fear of overcorrection and the risk of central pontine myelinolysis (CPM) or osmotic demyelination syndrome (ODS), however uncommon they actually might be, has been drilled into our brains since the beginning of medical school.
In this post and the few that follow, I will attempt to address some aspects of chronic severe hyponatremia which have traditionally not been included when hyponatremia is taught or written about or have only recently been backed by some evidence and have not yet made their way into the textbooks. The recently released guidelines also did not address some of these issues. While this is not, by any means, an exhaustive discussion of the topic, I hope that these posts will not only help the readers enhance their understanding of the pathophysiology of severe hyponatremia but also help them manage it more effectively with a lot less stress and mental anguish.

PART 1: THINK OUTSIDE THE ALGORITHM
The Schrier-Berl algorithm for diagnosis of hyponatremia has been used successfully for decades for teaching, and for reasoning through the differential diagnosis at the bedside.  It is an integral part of every medicine textbook and pocket handbook. It takes us to our diagnosis through 3 decision points: Plasma osmolarity, volume status and urine sodium sequentially.  While the algorithm holds true for the garden variety mild to moderate hyponatremia, it almost invariably breaks down in case with very severe hyponatremia.

During our extensive review of cases of severe hyponatremia treated with 3% saline, we seldom came across a case in which there was only one isolated cause for hyponatremia.  Rather, they were almost always two or more possible etiologies.  In addition, many patients that were initially considered to be euvolemic by experienced nephrologists, responded to 3% saline as if they were volume depleted.  Lastly, the clinical course of these patients during the hospitalization seemed to suggest many of these causes of inappropriate release of ADH were transient and reversible (SSRIs, acute nausea, postop state etc.). The patients' physiology seemed to change from time to time, with overcorrection of sodium invariably accompanied by large-volume water diuresis as these transient sources of ADH were "switched off."
It was, however, the paper by Sood et al that finally looked at the possible different etiologies for cases of severe hyponatremia as shown in the table (see image), which I consider the single most important table in all of recent hyponatremia literature.  They showed for the first time for multiple etiologies and processes are at play, some fixed and some transient in generating severe hyponatremia.

It is of paramount importance, that in the workup of hyponatremia, especially severe cases, we do not limit our reasoning through the differential diagnosis to comply with the algorithm that we have so familiar with but constantly look for multiple etiologies and transient causes of SIADH, especially subclinical volume depletion (low urinary sodium can be helpful here), as often it is the resolution of these causes that leads to the large-volume water diuresis and overcorrection. 
Posted by Hashim Mohmand