Sodium & Water Patient Assessment & Therapeutics for Pharmacists

Sept 2026

Instructor

Peter Loewen, B.Sc.(Pharm), ACPR, Pharm.D., FCSHP, RPh | peter.loewen@ubc.ca phone 604-506-8011
Associate Professor | Faculty of Pharmaceutical Sciences
Faculty, Collaboration for Outcomes Research & Evaluation (CORE)
Researcher, UBC Center for Cardiovascular Innovation (CCI)

Pre-Session Objectives

PRIOR TO arriving at the session, participants should be able to describe

1. the distribution of total body water (TBW).
2. the influence of changes in TBW on serum Na concentration.
3. the pathophysiology and clinical presentation of diabetes insipidus and SIADH.
4. the clinical parameters for assessing ECF status and ICF status.

Preparation for the session

1. Get Loewen’s Sodium & Water Assessment & Therapeutics 1-pager
2. Install “MedCalc”, “MedMath”, “Mediquations”, "QxCalculate", "Medal", MedCalX", or equivalent on your phone and find the fluid&lytes tools in there. Find formulas for “Water deficit”/“Free water deficit”, “Change in serum sodium”, and “Fractional excretion of Na”.

3. Ingelfinger, J., Sterns, R. Disorders of Plasma Sodium - Causes, Consequences, and Correction. NEJM 2015;372(1), 55-65.
4. Read Freda BJ, Davidson MB, Hall PM. Evaluation of hyponatremia: A little physiology goes a long way. Cleveland Clin J Med 2004;71:639-50.
5. #170 Hypernatremia is Easy - Curbsiders podcast

Pre-session self-assessment

1. The proportion of Total Body Water (TBW) that is intracellular is approximately

(a) 1/3
(b)  2/3
(c)  1/8
(d)  20%

2. Loss of extracellular fluid (e.g. blood) typically causes which of the following effects ACUTELY (e.g., within the first 6 hours):

(a)   a rise in serum sodium concentration
(b)   a drop in serum sodium concentration
(c)   excretion of very dilute urine
(d)   no effect on serum sodium concentration

3. Which of the following drugs may cause diabetes insipidus (circle as many as apply)

(a)  demeclocycline
(b)  carbamazepine
(c)  sertraline
(d)  lithium
(e)  enalapril

4. SIADH is

(a)  euvolemic hyponatremia with excretion of concentrated urine
(b)  hypervolemic hyponatremia with oliguria
(c)  euvolemic hyponatremia with excretion of dilute urine
(d)  euvolemic hypernatremia with excretion of dilute urine

5. Which of the following is not a direct measure of a patient’s volume status

(a)  symptoms of severe postural dizziness
(b)  postural change in HR
(c)  serum creatinine/BUN ratio
(d)  serum sodium concentration
(e)  postural change in SBP
(f)   JVP

By the end of the session, and upon reflection & practice, learners should be able to

describe the differences between water and volume, dehydration/hypertonicity, and volume depletion
using physical assessment and laboratory parameters, diagnose the type of water-related defect a patient exhibits (e.g. hypovolemia, hyponatremia, hypernatremia, SIADH)
demonstrate an APPROACH to evaluating water-related problems in a patient and their potential causes
design a detailed therapeutic plan for treating the water-related disorder, including:
- selecting and writing orders for an appropriate crystalloid solution (if required) or other drug therapy.
- determining how much crystalloid to administer, including infusion rate.
- conducting an appropriate monitoring plan.

Required Skills

1. assess your patient for postural BP and HR changes
2. assess your patient's JVP | Jugular venous pressure: a cardinal sign | More about JVP

Why Na and H2O Matter in Pharmacotherapy Practice

Your patient is on multiple antihypertensives and today complains of dizziness on rising. BP reasonably well controlled. Should you decrease the dose of an antihypertensive?
Your patient with HFrEF has been told to restrict their salt intake. Is this a good idea?
Your patient with parkinson's disease seems to be developing postural hypotension. Does he need midodrine?
You're consulted about a patient with severe hyponatremia and recent SSRI initiation. Is the hyponatremia drug-induced?
Your CHF patient needs to be started on ACE-I. Her SCr is 155. How worried about a rise in SCr upon starting ACE-I are you?
Your CHF patient is stable on ramipril 10mg, B-blocker, and furosemide 40mg. Lately his SCr has been creeping up. Physicians intends to decrease the ramipril dose because everybody knows ACE-I can cause renal failure. Is this a good idea?
Your patient with HTN is admitted to hospital with CAP and has a serum Na of 129. Admitting physicians documents that the patient's HCTZ is being held due to "HCTZ-induced hyponatremia" and that it should not be restarted. Is this sensible?
Your patient has recurrent angina despite amlodipine+NTG patch. You believe metoprolol will be indicated, but are worried about his standing BP of 110/70 and postural drop. Can his anti-ischemic therapy be augmented?
Ever been asked to "please procure some demeclocycline"? Know what tolvaptan is?
Your vancomycin-treated patient is starting to show signs of GFR decline. Is it due to vancomycin?

Common Misconceptions and Sticking Points

1. Explain why serum sodium is a reflection of your patient's ICF.
2. Explain how giving your patient too much free water causes their serum sodium to go down. EXPLANATION
3. Explain how causing your patient to lose free water (eg, by administering a loop diuretic) causes their serum sodium to go up. EXPLANATION
4. Explain why giving your hypovolemic hyponatremic patient normal saline causes their serum sodium to go up.
5. Explain why it is a mistake to believe that hypernatremia causes ICF contraction, or hyponatremia causes ICF expansion.

Further learning on Na/H2O management

Hyponatremia

Adrogué HJ, Tucker BM, Madias NE. Diagnosis and Management of Hyponatremia. JAMA. 2022;328:280–291.
Chander S, Kumari R, Lohana AC, Rahaman Z, Parkash O, Shiwlani S, Mohammed YN, Wang HY, Chi H, Tan W, et al. Urea to Treat Hyponatremia Due to Syndrome of Inappropriate Antidiuretic Hormone Secretion: A Systematic Review and Meta-Analysis. Am J Kidney Dis. 2025;85:303–319.
Fahlén CB, Falhammar H, Skov J, Lindh JD, Mannheimer B. Thiazides and Risk of Hyponatremia by Age and Sex. JAMA Netw Open. 2026;9:e264642
Cohen DM, Ellison DH. Evaluating Hyponatremia. JAMA. 2015;313:1260–1261
Adams K, Kearney M, Lee K, Rhoney D, Smith M. Strength in Numbers: A Team-Based Approach to Managing Patients with Hyponatremia. Am J Medicine 2018
Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol 2014; 170: G1–G47
Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med 2013. pp. S1–42
Sushrut et al. Mortality after Hospitalization with Mild, Moderate, and Severe Hyponatremia. Am J Med (2009) 122, 857-865.
Chawla A, et al. Mortality and Serum Sodium: Do Patients Die from or with Hyponatremia? Clin J Am Soc Nephrol 6: 960–965, 2011.
Yeates KE, Singer M, Morton AR. Salt and water: a simple approach to hyponatremia. CMAJ 2004; 170:365-9
Oster JR, Singer I. Hyponatremia, hypoosmolality, and hypotonicity: tables and fables. Arch Intern Med 1999;159:333-6.
Nemerovski C, Hutchinson, DJ. Treatment of hypervolemic or euvolemic hyponatremia associated with heart failure, cirrhosis, or the syndrome of inappropriate antidiuretic hormone with tolvaptan: a clinical review. Clinical therapeutics. 2010;32(6):1015-32.

Hypernatremia

Kamel KS, Schreiber M, Harel Z. Hypernatremia. JAMA. 2022;327:774–775.
Sterns R. Evidence for Managing Hypernatremia: Is It Just Hyponatremia in Reverse? Clin J Am Soc Nephro 2019;14:CJN.02950319

Balanced crystalloids

McIntyre L, Fergusson D, McArdle T, English S, Cook DJ, Fox-Robichaud AE, Martin C, Marshall J, Pugliese M, Menon K, et al. A Crossover Trial of Hospital-Wide Lactated Ringer’s Solution versus Normal Saline. N Engl J Med. 2025. doi:10.1056/nejmoa2416761.)
Finfer S, et al. PLUS trial. Balanced Multielectrolyte Solution versus Saline in Critically Ill Adults. New Engl J Med. 2022;386(9):815–26.
MacDonald, N., Pearse, R. (2017). Are we close to the ideal intravenous fluid? British Journal of Anaesthesia 119(suppl_1), i63-i71.

Patient assessment

Drum B, Course BL, Kelly M, York A, Worrall E, Martins J, Johnson S, Liles EA. Does This Patient Have Volume Overload? JAMA. 2026;335. doi:10.1001/jama.2026.0446.
Elhassan MG, Chao PW, Curiel A. The Conundrum of Volume Status Assessment: Revisiting Current and Future Tools Available for Physicians at the Bedside. Cureus. 2021;13:e15253.
Bentzer P, Griesdale DE, Boyd J, MacLean K, Sirounis D, Ayas NT. Will This Hemodynamically Unstable Patient Respond to a Bolus of Intravenous Fluids? JAMA. 2016;316:1298–1309.