Checking IDs at the Membrane
In what direction does water move when there is a difference in solute concentration across a cell membrane?
Water moves via osmosis from an area of low solute concentration to an area of higher solute concentration
What two age groups may be most susceptible to volume depletion, electrolyte imbalance and dehydration?
infants/young children and elderly individuals
What is another route of administration for fluids, other than IV?
Oral
What are the 7 components of a BMP and the 3 main cellular categories measured in a CBC?
BMP: sodium, potassium, chloride, bicarb, creatinine, BUN, glucose
CBC: RBC (red blood count), Hemoglobin, Hematocrit, WBC (white blood count), Platelet count
What are the four cardinal techniques used during a physical exam to assess a patient’s condition?
Inspection, Palpation, Percussion, and Auscultation
How many sodium and potassium ions are moved by the primary cell pump for every molecule of ATP it burns?
The Na+/K+-ATPase moves three sodium ions out and two potassium ions in
List 3 symptoms of dehydration in infants/children
Crying without tears, no wet diapers for 3+ hours, and unusual lethargy
What is the tonicity of Lactated Ringer’s solution and what does it contain/what is in it?
Isotonic to the body; ~275mOsm/L
Contains NS (normal saline), K+, Ca2+, and a lactate buffer
Why would a clinician order a CBC for someone experiencing similar symptoms to Samantha?
to rule out signs of underlying conditions such as infection (indicated by elevated WBC), anemia (indicated by low RBC or hemoglobin, which could cause fatigue or dizziness), blood disorders (such as issues with platelets or bone marrow)
What physical sign of volume depletion is observed when a patient's skin loses its ability to "bounce back" quickly after being pinched?
Diminished skin turgor
Why can’t electrolytes like sodium or chloride just pass through the cell membrane on their own?
They are charged particles, which the hydrophobic lipid membrane refuses to let through without a specific transporter
How low do sodium levels typically drop until moderate-severe symptoms of hyponatremia are visible? (think: what was Samantha’s sodium level)
Below ~120-125mEq/L
What is 5% dextrose solution used for and why?
5% Dextrose is clinically used to treat hypernatremia and is effective because the glucose is rapidly metabolized, leaving behind "free water" that creates a hypotonic gradient to shift fluid into the intracellular space
What are the purposes of measuring Blood Urea Nitrogen (BUN) and Creatinine in an athlete after a race, and what might elevated levels indicate?
Assess kidney function, renal flow, and glomerular filtration.
Elevated BUN: kidneys aren’t getting enough blood flow due to volume depletion
Elevated creatinine: signals increased kidney stress due to injury, reduced perfusion, or if accompanied with dark urine or muscle pain, may be indicative of rhabdomyolysis
When a clinician uses the OPQQRST framework to elaborate on a patient's chief concern, they are documenting which specific component of the complete history?
The History of Present Illness (HPI).
When running a race, we think it is good to drink water. Why was Samantha's consumption of 4 liters of water problematic?
The "free water" intake induced dilutional hyponatremia by lowering her extracellular osmolality, which forced a massive osmotic shift of water into her cells
When Samantha presented to the ER, her vitals were normal. However, in adults experiencing severe dehydration, we expect to see: ___ blood pressure and ___ heart rate. WHY?
Hypotension (LOW blood pressure): Volume depletion → lowered ECF volume = lowered plasma volume → Decreased pressure pushing against the vessels
Tachycardia (RAPID heart rate): In response to lowered plasma/blood volume, heart pumps faster in order to get adequate blood flow to the organs
Why is a hypertonic solution like 3% saline the specific treatment for Samantha’s confusion, rather than a standard isotonic fluid like 0.9% normal saline or Lactated Ringer’s?
A hypertonic solution creates a powerful osmotic gradient that forces water to shift from the intracellular fluid (ICF) back into the extracellular fluid (ECF), which physically shrinks her swollen brain cells
In the context of intense physical exertion what does a low value of bicarbonate typically signify? How can "marked elevations" in blood glucose levels complicate the interpretation of a patient's sodium levels?
Low bicarbonate indicates metabolic acidosis (pH < 7.35), which is associated with intense exertion due to lactic acid production or impaired tissue perfusion.
Marked elevations of glucose can draw water to the extracellular space and lower sodium osmolality causing need for correction, also known as hypotonic hyponatremia.
Instead of a comprehensive "head-to-toe" assessment, why would an ER clinician choose a focused physical exam for Samantha, and which three specific systems must be prioritized?
Focused exam is used to prioritize the most relevant systems in an acute setting; the priorities for Samantha are the Neurologic, Respiratory, and Cardiovascular systems.
How does the Na+/Ca2+ Exchanger (NCX) link a patient’s sodium levels directly to their cardiac stability, and why could a severe drop in extracellular sodium lead to a life-threatening heart rhythm?
The NCX relies on the sodium electrochemical gradient to pump calcium out of the cell; when extracellular sodium is too low, the exchanger can reverse or fail, causing an intracellular calcium buildup that triggers arrhythmias
Samantha drank 4L of water during her race. If she had not drank any water at all and had been sweating profusely, what may have happened to her? Explain the mechanism.
She would experience hyperosmotic volume contraction. In severe cases or if she had not drank water after the race, she could even faint from too much ICF volume leaving her cells.
A 45-year old man presents to the ER. He complains that he is extremely tired, becoming confused, and has had muscle cramps over the last 4 days. He works 12-hour days in construction in the Texas heat, sweating a lot, and notes that he has not been drinking water in the last few days because his Brita filter broke and he refuses to drink tap water. What fluids do you give and why?
He has extreme volume depletion and ECF is hyperosmotic.
First, give normal saline to remediate the volume depletion.
Then, give 5% dextrose to restore the osmolality of the ECF.
What are the two primary mechanisms by which an athlete can develop exercise-associated hyponatremia (serum sodium < 135 mEq/L), and what specific clinical data allows a provider to distinguish between these two causes?
1. Over-hydration with Hypotonic Fluids that exceed what the kidneys can excrete during or after exercise (Most Common)
2. Substantial Sodium and Water Loss through sweat (Less Common). If the athlete then attempts to replenish these losses with only pure water, they further dilute the remaining extracellular sodium concentration.
How to Decipher Between the Two:Obtain a thorough history
In a complete history, how does the Review of Systems (ROS) function as a tool for identifying "pertinent negatives" differently than the History of Present Illness (HPI)?
The ROS uses a systematic series of yes/no questions across all organ systems to screen for symptoms the patient may have overlooked, while the HPI focuses strictly on the details and context surrounding the Chief Concern.