All Things Sodium & the Brain in the PICU

Welcome to PICU Doc On Call, A Podcast Dedicated to Current and Aspiring Intensivists.

I'm Pradip Kamat and I'm Rahul Damania. We are coming to you from Children's Healthcare of Atlanta - Emory University School of Medicine.

Here's the case:

A 6-year-old child with a known h/o craniopharyngioma who has been endocrinologically intact with exception of needing thyroid replacement was admitted to the PICU prior to craniotomy to proceed with further tumor resection as well as the removal of a secondary cyst impacting his brainstem. The patient is receiving Keppra for seizures and per mother, he has recently been significantly more sleepy at school.

On POD Op day 5: the PICU the bedside nurse notices increased urine output (6cc/kg/hr to as high as 10cc/kg/hr). Initially, there was an increase in Na to 157mEq/L within 48-72 hours the serum Na dropped to 128mEq/L

To summarize key elements from this case, this patient has:

• Increase UOP
• Rapidly increasing Na initially followed by a drop
• All of which brings up a concern for Na abnormality post craniotomy

In today’s episode, we will be breaking down all things Sodium & the Brain. We will discuss diagnostic & management frameworks related to three pathologies:

1. Central Diabetes Insipidus
2. Syndrome of inappropriate Anti-Diuretic Hormone or SIADH
3. Cerebral Salt Wasting

These diagnoses can certainly be seen individually inpatients or as a spectrum of diseases — as we go through each of these diagnoses, pay particular attention to patient characteristics and lab abnormalities. Namely, serum sodium, serum osm, and urine osm.

To build the fundamentals, lets first start with classic nephrology saying: Serum Na represents Hydration

This takes us into a brief review of normal physiology — talking about three important hormones:

1. ADH
2. Aldosterone
3. Atrial Natriuretic Peptide (ANP)

Let’s go through a quick multiple-choice question.

A patient is recently started on DDAVP for pan-hypopituitarism. The medication acts similarly to a hormone that is physiologically synthesized in which of the following from which are in the body?

A. Paraventricular Nucleus of the Hypothalamus

B. Supraoptic Nucleus of the Hypothalamus

C. Anterior Pituitary

D. Vascular Endothelium

The correct answer here is B the Supraoptic Nucleus of the Hypothalamus. Remember that ADH is synthesized in the hypothalamus and released from the posterior pituitary.