Lab Rounds

Shawn DowlingPGY-2

Case 78 yo M. Brought in by EMS from

NSG home c/o generalized weakness, V, D for

past 2-3 days Brief GTC seizure while nurses are

checking patient in PMHx: HTN (on HCTZ), allergies: ex-wife

Physical Exam VS: HR-110, BP110/70, T/RR/sats N Stopped seizing but still altered

sensorium (?post-ictal), GCS 13-14 Fluid: looks dry Chest/abdo/extremeties – N Neuro: no focal abnormalities, neck

supple

Want to order anything NOW?

Want to order anything NOW? Chemstrip

Want to order anything NOW? Chemstrip The paramedics had noticed this

by his bedside

Want to order anything NOW? Chemstrip – 8.0 ABG

Na – 108, K - 3.0, Cl - 90

Objectives Acute Hyponatremia

Touch of physiology DDx The Na calculating game How and when to use HTS

FOR INDEPTH REVIEW OF HYPONATREMIA SEE MORITZ’S PRESENTATION FROM 2003

Sodium H20 makes up 60% of total body

weight (:. TBW = 0.6 x wgt(kg)) H20 is distributed between 3 compartments

Intracellular space (ICS) Interstitial space (ISS) Intravascular space (IVS)

Na is the predominant cation in the ECS and is distributed primarily in the TBW

ExtracellularSpace

Na+ balance primarily controlled by renin-angiotensin-aldosterone system

Na governs the movement of fluid between these compartments

Water balance largely driven by Na+ balance and ADH

Fluid Distribution

Intracellular (2/3) Extracellular (1/3)

IVS(1/3)

ISS(2/3)

TBW = wgt (kg) x 0.6

Distribution of TBW (and Na):

Hyponatremia DDx(abridged

version)

“TRUE” Na Hypovolemic

GI/insensible losses Poor H20 intake Diuretics

Euvolemic SIADH Psychogenic

polydipsia Hypervolemic

CHF Cirrhosis Nephrotic syndrome

Lab Error PseudoNa*

lipids/proteins No longer an issue

Redistributive (osm) Hyperglycemia Mannitol

*No longer an issue since the lab uses

a different technique to calculate Na

Making the Diagnosis Hx in particular ROS, PMHx, Meds Physical exam: hypo-,eu- or

hypervolemic Labs:

Serum electrolytes (ABG if needed urgently) Urine lytes, Cr (if not on diuretics or have

not received fluids yet) Urine Osmols Serum Glucose

Approach to sodium Need to determine:

1. Is the patient symptomatic?2. Is this an acute or chronic process?3. Do I need to intervene emergently?

Seizure? Comatose? Focal Neuro Deficits?

S/Sx Sx

HA Lethargy N,V Anorexia Dizzy Confusion

Signs Psychosis Confusion Focal Neuro

deficits Ataxia Seizures Comatose

37M. Diabetic. Glucose 35 Na – 126 How do you correct the sodium for

the glucose?

Back to our case His Na is 108. What info do you need to calculate

his Na deficit? What is his Na deficit?

Fluid Distribution

Intracellular (2/3) Extracellular (1/3)

IVS(1/3)

ISS(2/3)

TBW = wgt (kg) x 0.6

Distribution of TBW:

Calculating Na deficit His wgt is 60kg. Since Na is primarily distributed in

the Total body water which is wgt(kg) x 0.6*

(Desired Na-actual Na) x TBWOr

The drop in Na x where the Na is distributed

***Some sources suggest using 0.5 for females/elderly males and 0.45 for elderly females – probably not important acutely

(140-108) x 0.6x60kg= (32) x 36=1152mEq of Na

How quickly can we replace Na? Why? How are we going to calculate how

much to replace over 24 hours? What solution are you going to use?

Pt is not seizing, no focal deficits, no coma

Na correction CANNOT correct sodium quicker than

10-12mEq/24 hours, 0.5 mEq/hr rule is not absolute – this rule

can be broken as long as 10-12/day is not Risk of over-aggressive Na

replacement is central pontine myelinolysis Demyelination of the pons, flaccid

paralysis and death -- BAD

Determining how much Na to give What is the Na content of…

NS RL HTS (3%)

Determining how much Na to give What is the Na content of…

NS – 154mEq RL – 130mEq HTS (3%) – 513mEq

Calculating volume of fluid His Na deficit is 1152mEq, but we

only want to increase 10-12mEq/24H (Desired Na-actual Na) x TBW

(118-108) x 36 360mEq

NS 360/154 = 2.33 L over next 24 hours – check lytes Q2-4H to ensure not correcting too quickly

The Divine Brine – HTS HTS (3%) – Na content is 513mEq

Indications Moderate-Severe hyponatremia (<120) And 1 of the following

Seizures Focal neuro deficit Comatose

Dose: 3cc/kg ½ half given over 10 minutes, 2nd ½ given over 50 minutes

Then STOP & check lytes (usually Na by 3-6mEq). STILL LTD BY 10-12mEq/DAY

Summary1. Order Urine lytes prior to giving fluid2. Calculate target Na

(Goal Na - actual Na) x TBW & DO NOT EXCEED

3. HTS saline indications Seizure Focal neuro deficits Comatose

4. HTS: 3cc/kg, 1st ½ over 10min, 2nd ½ over next fifty minutes, then STOP & check lytes

Usu by 3-6 mEq, STILL ltd by 10-12mEq/24hrs

References EMRAP March 2006 Yeates K. Salt and Water: A simple

Approach. CMAJ. Feb 2004;170, 365-69 Rosen’s Harrison’s Moritz’s presentation 2003