Dehydration
The renal feedback loop between the tubules and glomerulus of the kidney that regulates GFR
What is tubuloglomerular feedback
Explain the expected BUN concentration in dehydration (high or low) and explain why
Increased BUN.
In dehydration, the kidneys reabsorb as much water back into circulation as possible. This causes more urea to be reabsorbed. Dehydration also decreases RBF leading to a decreased GFR and less solutes filtered out of the bloodstream.
Ammonia is generated when proteins are digested. NH3 travels to the liver and converted into urea then excreted from kidneys.
If BUN is low it can indicate there's a problem with the liver or malnutrition.
Inc BUN indicates something is impairing adequate excretion from the kidneys
Dehydration can adversely affect brain ___ and ___ leading to worsening psychiatric and neurological conditions.
What is volume and structure
Give an example that would cause Hyperosmotic Volume contraction and its influence on both ECF and ICF volume and osmolarity
ex. Running a marathon
ECF V: Decrease, O: increase
ICF V: Decrease, O: increase
Many bicarbonate transporters are linked with reabsorption of this ion
What is sodium?
HCO3- plays a key role in acid-base regulation so most of the filtered HCO3- is reabsorbed.
HCO3- is freely filtered at the glomerulus and 70-80% is reabsorbed in the early proximal tubule, 15% in the thick ascending limb of the LH, and 5% in the collecting duct.
Since HCO3- follows Na+ its often increased in volume depletion and hemorrhage.
Decrease in brain volume can lead to a compensatory increase in ___ which may fill the open space as cells shrink.
What is CSF volume.
The basic response to decreased renal perfusion caused by hypovolemia (6 steps)
1. Lower RBF lowers the GFR, leading to less filtered fluid entering the tubule.
2. Macula densa cells in distal nephron sense
3. They signal the juxtaglomerular cells in the afferent arteriole.
4. Cells dilate the afferent arteriole and secrete renin
5. afferent arteriole dilation helps keep the GFR normal even during hemorrhage
6. Higher renin increases salt and water reabsorption via RAAS system, helping restore volume
The dry environment caused by dehydration causes both of these molecules to "stick" to themselves, making their count appear elevated.
What is RBCs and Glucose
Name key neuro and physical exam findings seen in dehydration.
Obtunded (low or absent consciousness)
Sunken eyes
Dry mucous membranes, skin turgor, and elevated HR
A 3-year-old boy is brought to the emergency department with a history of
unintentional ingestion of seawater while swimming in the sea. The amount of
seawater ingested is unknown. There is no history of vomiting. On physical
examination, the boy appears confused and is asking for more water to drink. His
serum sodium is 152 mmol/L (152 mEq/L). Which of the following changes in body
fluid volumes and osmolality are most likely to be present in this boy?
A. Decreased ECF volume, unaltered ICF volume, unaltered body osmolality
B. Decreased ECF volume, decreased ICF volume, increased body osmolality
C. Increased ECF volume, unaltered ICF volume, unaltered body osmolality
D. Increased ECF volume, increased ICF volume, decreased body osmolality
E. Increased ECF volume, decreased ICF volume, increased body osmolality
E. Increased ECF volume, decreased ICF volume, increased body osmolality
Rationale: Correct answer E: The boy has ingested an excessive amount of seawater
which has resulted in hypernatremia, which leads to increased extracellular fluid (ECF) volume, decreased intracellular fluid (ICF) volume, and increased body osmolality. The
boy is excessively thirsty due to hypernatremia and the hyperosmolality of plasma. Seawater is a hypertonic fluid.
Explain the normal K+ value seen in our patient.
98% of K+ is found intracellularly and the balance depends on intake, excretion, and distribution. Our pt's K+ intake was low but her her decrease in total K+ was most likely not shown on the blood test because of the increased reabsorption of K+ in the kidneys along with the increased movement of K+ from ICF to ECF.
During dehydration the Hyperosmolarity of the ECF draws water from the cells causing the intracellular K+ concen to increase. This forms a favorable concentration gradient for K+ to move ICF --> ECF.
A 90-year-old woman is brought to the emergency department for evaluation of new onset confusion. Two days ago, her family noticed she decreased her oral intake. This morning, her family found her slumped over in a chair and unresponsive. She has a history of type 2 diabetes, dementia, and hypertension, for which she takes insulin, donepezil, and hydrochlorothiazide. One week ago, she was started on isoniazid, rifampin, ethambutol, and pyrazinamide for active pulmonary mycobacterium tuberculosis infection. Her temperature is 36.4°C (97.5° F), pulse is 80/min, respirations are 22/min, blood pressure is 110/60 mmHg, and oxygen saturation is 98% breathing room air. She appears stuporous. Physical examination shows conjugate eye deviation to the right and brisk reflexes with bilateral ankle clonus. Lung exam is normal. Laboratory studies show the following:
Sodium 138 mEq/L Potassium 5.6 mEq/L Chloride 95 mEq/L Bicarbonate 15 mEq/L Creatinine 1.2 mg/dL Glucose 120 mg/dL Arterial blood gas pH 7.21 PaCO2 40 mmHg PaO2 120 mmHg
D. Increased anaerobic metabolism
This patient's history of active tuberculosis treatment along with a low serum bicarbonate level suggests a diagnosis of high anion gap metabolic acidosis.
(HCO3-) decreases as it binds to excess hydrogen (H+)
Lastly, certain substances like isoniazid promote anaerobic metabolism and, in turn, lactic acid production.
A 4-year-old boy is brought to the clinic due to frothy urine over the past three days.
He had a sore throat ten days ago, which resolved spontaneously. His vital signs are
normal. Urine dipstick is positive for significant proteinuria. A condition is suspected
where large amounts of protein leak from the blood into the urine. Which of the
following is most likely present in this condition?
A. Movement of water from the interstitial space to the blood
B. Movement of water from the blood to the interstitial space
C. Movement of solutes from the interstitial space to the blood
D. Movement of solutes from the blood to the interstitial space
E. No net movement of water or solutes between the blood and the interstitial
space
B. Movement of water from the blood to the interstitial space
Rationale: Osmosis is the movement (i.e. passive diffusion) of water between two
solutions across a selectively permeable membrane, which primarily depends on solute
concentration in each solution. When there is a difference in concentration between two
solutions separated by a selectively permeable membrane, water passively diffuses
from an area of low concentration (i.e. hypotonic solution) to an area of high
concentration (i.e. hypertonic solution).
A 2-year-old boy presents to the emergency department due to persistent vomiting and diarrhea over the past week. His parent states, “He just cannot seem to keep anything down, whenever I feed him he just vomits it right back up.” The patient attends daycare, and his parent is unsure of any sick contacts. He is otherwise healthy, vaccines are up to date, and birth history was uncomplicated. Temperature is 37.5°C (99.5°F),pulse is 160/min, respirations are 26/min, blood pressure is 84/40 mmHg, and O2 saturation is 96% on room air. On physical exam the patient is crying but consolable and is noted to have diminished tear production. Which of the following best describes the most likely electrolyte abnormality present?
A. Hypernatremia
Sodium is primarily found in the extracellular fluid and is the primary driver of tonicity in the human body. Hypernatremia either occurs when more water is lost than sodium or when more sodium is retained compared to water. Most often, hypernatremia results from water losses. This includes losses through the skin, gastrointestinal tract, or kidneys. Common precipitants include heavy exercise without adequate water intake, gastroenteritis, and osmotic diuresis (e.g., mannitol, diabetes mellitus). Over ingestion or increased intake of sodium relative to water is less common but is encountered with massive salt intake or when hyponatremia is corrected too quickly.
A 47-year-old male presents to the emergency department with altered mental status. According to the paramedics, the patient was found obtunded in an alley with empty beer cans at his side. While nursing staff attempt to establish an IV, the patient begins seizing. Temperature is 37.0°C (98.6°F), pulse is 101/min, respirations are 11/min, blood pressure is 152/74 mmHg, and O2 saturation is 95% on room air. On physical exam, the patient appears disheveled with tetany in the upper and lower extremities bilaterally. The abdomen is soft and nondistended. The patient’s laboratory findings are demonstrated below:
Sodium 105 mEq/L Potassium 4.2 mEq/L Chloride 92 mEq/L HCO3- 20 mEq/L BUN 12 mg/dL Creatinine 1.1 mg/dL
B. Normal extracellular fluid status
Hyponatremia is classified based on the patient's volume status (e.g., hypovolemic, euvolemic, hypervolemic)
Hypervolemic hyponatremia occurs due to an enormous increase in total body water and less significant increase in total body sodium. (Ex. CHF)
hypovolemic hyponatremia occurs when there is significant sodium loss in comparison to a smaller water volume loss. (ex. diarrhea)
Euvolemic hyponatremia occurs when there is normal total body sodium but an increase in total body water. The condition is termed “euvolemic” since no edemais present. (ex. Etiologies include primary polydipsia, beer potomania, and SIADH)
The condition occurs secondary to overconsumption of electrolyte-poor liquid, such as beer, with little other sources of nutrition Poor electrolyte intake limits the formation of a normal renal urea gradient, leading to an inability to excrete sufficient free water and subsequent development of hyponatremia
.