# Internal Medicine/Fluid and Electrolyte Disturbances
## Composition of Body Fluids

The human body is composed of various fluids, each with its own unique composition and function. These body fluids play crucial roles in maintaining homeostasis, transporting nutrients, eliminating waste, and facilitating physiological processes. Here, we explore the primary body fluids and their key components:
* Blood Plasma:
** Water: Blood plasma is approximately 90% water, making it the largest component.
** Solutes: Plasma contains a wide range of solutes, including electrolytes (sodium, potassium, calcium, magnesium, chloride, bicarbonate), proteins (albumin, globulins, fibrinogen), glucose, hormones, waste products (urea, creatinine), and gases (oxygen, carbon dioxide).
* Intracellular Fluid (ICF):
** Water: The ICF is found within the body's cells and constitutes about two-thirds of the total body water.
** Solutes: The primary solutes in ICF are potassium, magnesium, phosphate ions, and proteins.
* Extracellular Fluid (ECF):
** Interstitial Fluid: This fluid surrounds and bathes the body's cells. It contains ions, glucose, fatty acids, hormones, and waste products.
** Blood Plasma: As mentioned earlier, blood plasma is part of the ECF and contains water and various solutes.
** Lymph: Lymph is a component of the ECF that is found in the lymphatic vessels. It is similar in composition to interstitial fluid.
* Cerebrospinal Fluid (CSF):
** Water: CSF is primarily composed of water, providing buoyancy and cushioning for the brain and spinal cord.
** Solutes: CSF contains electrolytes, glucose, and proteins, albeit in different concentrations compared to blood plasma.
* Synovial Fluid:
** Water: Synovial fluid is a lubricating fluid found in joint cavities and is mostly water.
** Solutes: It contains electrolytes, hyaluronic acid, and proteins, which contribute to joint lubrication and nutrition.
* Peritoneal Fluid:
** Water: Peritoneal fluid fills the peritoneal cavity in the abdominal region and is primarily composed of water.
** Solutes: It contains electrolytes, white blood cells, and small amounts of proteins, serving as a lubricating and protective fluid for abdominal organs.
* Amniotic Fluid:
** Water: Amniotic fluid surrounds the developing fetus during pregnancy and is mostly water.
** Solutes: It contains electrolytes, fetal skin cells, and various proteins, contributing to fetal protection and development.
* Saliva:
** Water: Saliva is predominantly water, facilitating digestion and oral hygiene.
** Solutes: It contains electrolytes (sodium, potassium, bicarbonate), enzymes (amylase, lipase), mucus, and antibacterial compounds.
* Tears:
** Water: Tears are primarily composed of water, moistening and protecting the eyes.
** Solutes: They contain electrolytes (sodium, potassium, chloride), proteins, and lysozyme (an enzyme with antibacterial properties).
* Sweat:
** Water: Sweat is mainly water, assisting in thermoregulation by evaporative cooling.
** Solutes: It contains electrolytes (sodium, potassium, chloride), urea, lactate, and small amounts of metabolic waste products.
The composition of body fluids varies to meet the specific functions of each fluid and the unique requirements of different body regions and systems. Maintaining the proper balance and composition of these fluids is essential for overall health and the normal functioning of the human body.

## Hypovolemia

Hypovolemia, often referred to as volume depletion, is a critical medical condition characterized by a significant decrease in the volume of blood plasma circulating within the body. This reduction in blood plasma volume results in an insufficient supply of blood to vital organs, potentially leading to life-threatening consequences. Understanding the intricacies of hypovolemia, its causes, diagnostic measures, and treatment strategies is essential for healthcare professionals and individuals alike.
Causes of Hypovolemia: Renal Factors
Hypovolemia can be attributed to various factors, with some originating in the kidneys (renal causes). These causes include:
* Excessive Urinary Loss: Certain medical conditions and scenarios can lead to excessive urinary loss of critical electrolytes like sodium (Na+), chloride (Cl–), and water. This results in hypovolemia. Notable contributors include:
** Osmotic Diuresis: When the urine contains high levels of endogenous solutes such as glucose or urea, the kidneys struggle to efficiently reabsorb Na+-Cl– and water. This leads to osmotic diuresis, a primary cause of hypovolemia.
** Diuretic Use: Pharmacological diuretics, commonly prescribed for various health issues, selectively target different sites along the nephron to increase urinary Na+-Cl– excretion. This mechanism often leads to fluid loss and can result in hypovolemia.
** Medications: Some medications, including acetazolamide, trimethoprim, and pentamidine, can inadvertently induce natriuresis (excessive sodium excretion), contributing to hypovolemia.
** Hereditary Defects: Genetic mutations affecting renal transport proteins can impair the reabsorption of filtered Na+-Cl– and water, potentially leading to hypovolemia.
* Mineralocorticoid Abnormalities: Conditions such as mineralocorticoid deficiency, mineralocorticoid resistance, or inhibition of the mineralocorticoid receptor can diminish the reabsorption of Na+-Cl– in the distal nephron, ultimately causing hypovolemia.
* Tubulointerstitial Injury: Injuries affecting the renal tubules, as seen in interstitial nephritis, acute tubular injury, or obstructive uropathy, can significantly reduce the reabsorption of Na+-Cl– and water by the kidneys, contributing to hypovolemia.
Causes of Hypovolemia: Extrarenal Factors
In addition to renal causes, various extrarenal factors can lead to hypovolemia. These extrarenal factors encompass:
* Gastrointestinal Loss: The gastrointestinal (GI) tract plays a crucial role in fluid balance. Daily, approximately 9 liters of fluid enter the GI tract—2 liters through ingestion and 7 liters through secretion. However, nearly 98% of this fluid is absorbed, resulting in minimal fecal fluid loss (100–200 mL per day). Hypovolemia can occur when GI functions are compromised, as seen in vomiting, diarrhea, or impaired gastrointestinal reabsorption.
* Skin and Respiratory Loss: "Insensible losses" refer to the fluid that evaporates from the skin and respiratory tract and is not readily measurable. In healthy adults, this loss typically ranges from 500 to 650 mL per day. Factors such as fever or prolonged exposure to heat can increase insensible losses, potentially leading to hypovolemia. Furthermore, hyperventilation, particularly in ventilated patients, can elevate insensible losses through the respiratory tract.
* Sweating: Profuse sweating, especially in hot and humid conditions, can result in both hypovolemia and hypertonicity if water and sodium are not adequately replaced. The composition of sweat is hypotonic compared to plasma, meaning it has lower salt concentration.
* Fluid Accumulation: In some cases, excessive fluid accumulates within specific compartments within the body, contributing to intravascular hypovolemia. Conditions that alter Starling forces, such as sepsis, burns, pancreatitis, nutritional hypoalbuminemia, and peritonitis, can lead to the phenomenon known as "third spacing," where fluid accumulates in interstitial spaces.
* Distributive Hypovolemia: Fluid accumulation within specific compartments, such as the bowel lumen in gastrointestinal obstruction or ileus, can also result in distributive hypovolemia. Retroperitoneal hemorrhage or extracorporeal hemorrhage may lead to hypovolemia when significant blood loss occurs within an expandable space.
Diagnostic Evaluation of Hypovolemia:
Accurate diagnosis is crucial for effective management of hypovolemia. It involves a comprehensive assessment that considers both clinical presentation and laboratory findings.
* Clinical Assessment: A meticulous medical history and physical examination form the foundation of diagnosing hypovolemia. Symptoms often include fatigue, weakness, thirst, dizziness, oliguria (reduced urine output), cyanosis, abdominal and chest pain, and confusion. Physical examination may reveal decreased jugular venous pressure, orthostatic tachycardia (an increase in heart rate when standing up), and orthostatic hypotension (a drop in blood pressure upon standing). In severe cases of fluid loss, individuals may exhibit peripheral cyanosis, cold extremities, oliguria, and altered mental status.
* Laboratory Tests: Blood tests provide crucial insights into the physiological changes associated with hypovolemia. Routine chemistries may show elevated levels of blood urea nitrogen (BUN) and creatinine, indicating a decrease in glomerular filtration rate (GFR). Creatinine, in particular, serves as a reliable measure of GFR. However, BUN levels can be influenced by various factors, including increased tubular reabsorption, hyperalimentation, catabolic states, and gastrointestinal bleeding. Therefore, creatinine is preferred in assessing renal function.
In cases of hypovolemic shock, additional tests may reveal evidence of hepatic and cardiac ischemia through liver function tests and cardiac biomarkers, respectively. Electrolyte imbalances and acid-base disorders can be detected through routine blood tests as well. For instance, metabolic acidosis may result from bicarbonate loss due to diarrheal illnesses, while severe hypovolemic shock can lead to lactic acidosis characterized by an elevated anion gap.
* Urine Analysis: In hypovolemia, the body's neurohumoral response stimulates increased reabsorption of sodium (Na+) and water in the renal tubules. Consequently, urine sodium concentration is typically less than 20 mM in nonrenal causes of hypovolemia, and urine osmolality exceeds 450 mOsm/kg. Additionally, the reduction in glomerular filtration rate (GFR) and distal tubular sodium (Na+) delivery may result in impaired renal potassium (K+) excretion, leading to elevated plasma potassium concentrations. However, it's important to note that in certain situations, such as hypochloremic alkalosis due to vomiting, diarrhea, or diuretic use, urine sodium concentration may exceed 20 mM, and urine pH may be higher than 7.0 due to increased filtered bicarbonate (HCO3–). In such cases, urine chloride (Cl–) concentration becomes a more accurate indicator of volume status, with values below 25 mM suggesting hypovolemia.
Treatment of Hypovolemia:
Effectively managing hypovolemia requires a multifaceted approach aimed at restoring normal fluid balance and addressing ongoing fluid losses. The treatment strategy varies depending on the severity of hypovolemia and the underlying cause.
* Oral Hydration: Mild cases of hypovolemia can often be managed with oral hydration and a resumption of a normal diet. Individuals with mild symptoms may benefit from increasing fluid intake through oral rehydration solutions.
* Intravenous (IV) Hydration: Severe hypovolemia typically necessitates intravenous fluid therapy. The choice of IV fluid depends on the underlying pathophysiology:
** Isotonic Saline (0.9% NaCl): Isotonic saline, with a sodium concentration of 154 mM (millimoles per liter), is the primary resuscitation fluid for patients with normonatremic or hyponatremic severe hypovolemia. This solution effectively restores circulating volume.
** Colloid Solutions: Although colloids like intravenous albumin have been used in various clinical scenarios, they are not definitively superior to isotonic saline for the purpose of volume resuscitation in patients with severe hypovolemia.
** Hypertonic Solutions: Hypernatremic patients, who have elevated blood sodium levels, require a different approach. They should receive hypotonic solutions such as 5% dextrose if there has been only water loss, as seen in diabetes insipidus (DI). For cases involving water and sodium chloride (Na+-Cl–) loss, hypotonic saline solutions (1/2 or 1/4 normal saline) may be administered. The administration of free water should be adjusted as needed based on frequent monitoring of serum chemistry values.
** Bicarbonate Solutions: Patients with bicarbonate loss and accompanying metabolic acidosis, often resulting from conditions like severe diarrhea, may require intravenous bicarbonate. Options include isotonic bicarbonate solutions (e.g., 150 meq of Na+-HCO3– in 5% dextrose) or more hypotonic bicarbonate solutions in dextrose or dilute saline.
** Blood Transfusions: Individuals with severe hemorrhage or anemia may require red blood cell transfusions. This intervention is particularly crucial when blood loss is substantial and hematocrit levels need to be maintained below a certain threshold (e.g., a hematocrit of 35%).
In conclusion, hypovolemia is a complex medical condition characterized by a decrease in blood plasma volume, which can result from various renal and extrarenal factors. Prompt and accurate diagnosis, often accompanied by intravenous fluid therapy, is paramount for effectively managing hypovolemia and preventing its potentially life-threatening complications. Healthcare professionals play a vital role in identifying the underlying causes of hypovolemia and tailoring treatment strategies to the individual needs of patients.

## Sodium Disorders
### Introduction and Overview

Hypernatremia and hyponatremia are two common electrolyte disturbances that significantly affect a patient's health. They involve deviations in the levels of sodium (Na+) in the bloodstream. Maintaining the proper balance of sodium is crucial for various physiological processes, and when this balance is disrupted, it can lead to a range of symptoms and complications. Understanding the causes, symptoms, and management of hypernatremia and hyponatremia is essential for healthcare professionals to provide effective care and treatment.

### Hyponatremia

Definition: Hyponatremia is a medical condition characterized by a lower-than-normal concentration of sodium in the blood, specifically a serum sodium concentration below 135 millimoles per liter (mM).
Symptoms: The clinical presentation of hyponatremia can vary widely based on several factors, including the severity of the condition and the rate at which sodium levels drop. Patients with mild hyponatremia may be asymptomatic or experience vague symptoms, while severe cases can lead to life-threatening neurological disturbances. Common symptoms include:
* Neurological: Headache, confusion, altered mental status, seizures, and coma.
* Gastrointestinal: Nausea, vomiting, and abdominal pain.
* Muscular: Weakness and cramps.
* Cardiovascular: Hypotension and tachycardia.
* Respiratory: Respiratory arrest in severe cases.
Causes: Hyponatremia is often categorized based on the patient's volume status, distinguishing between hypovolemic, euvolemic, and hypervolemic hyponatremia. Key causes within each category include:
* Hypovolemic Hyponatremia: Loss of both sodium and water, commonly due to conditions like vomiting, diarrhea, or excessive sweating.
* Euvolemic Hyponatremia: A state of normal fluid balance with diluted sodium levels, often seen in conditions such as syndrome of inappropriate antidiuretic hormone secretion (SIADH) or psychogenic polydipsia.
* Hypervolemic Hyponatremia: An excess of both water and sodium, typically linked to congestive heart failure, liver cirrhosis, or renal disease.
Diagnosis: Diagnosing hyponatremia involves a combination of clinical assessment, laboratory tests, and an evaluation of the patient's medical history. Key diagnostic steps include:
* Measurement of serum sodium levels.
* Assessment of urine osmolality and sodium concentration.
* Determining the patient's volume status, which can be achieved through physical examination, blood pressure measurement, and assessment of edema.
Treatment: The management of hyponatremia primarily focuses on addressing the underlying cause while avoiding overly rapid correction of sodium levels. Treatment strategies vary depending on the type and severity of hyponatremia and may include:
* Fluid restriction: In cases of euvolemic or hypervolemic hyponatremia.
* Medications: The use of vasopressin receptor antagonists (vaptans) to increase urine output and correct sodium levels.
* Treating underlying conditions: Addressing the root cause of hyponatremia, such as heart failure or kidney disease.
* Monitoring: Frequent monitoring of sodium levels and clinical status to avoid complications associated with rapid correction.

### Management of Hyponatremia

Treatment Strategies: The management of hyponatremia is highly dependent on its underlying cause and the patient's clinical presentation. Specific approaches are employed for different forms of hyponatremia, including hypovolemic, euvolemic, and hypervolemic cases. Notably, the use of vasopressin receptor antagonists (vaptans) is discussed as a targeted pharmacological intervention.
Importance of Monitoring: Hyponatremia treatment necessitates close monitoring of the patient's condition, particularly due to the unpredictable nature of plasma sodium concentration changes during treatment. Monitoring includes regular assessment of serum sodium levels, clinical status, and response to treatment. It is emphasized that overly rapid correction of sodium levels should be avoided.
Special Considerations: This section delves into special considerations for the treatment of acute symptomatic hyponatremia, such as the administration of hypertonic saline. Additionally, it highlights the need for vigilant monitoring and supportive care, especially in cases where patients develop acute pulmonary edema or hypercapneic respiratory failure.

### Hypernatremia

Definition: Hypernatremia is characterized by an elevated concentration of sodium (serum sodium >145 mM) in the blood.
Causes: Hypernatremia often results from a combined deficit in both water and electrolytes. Excessive sodium intake can also lead to hypernatremia. Special emphasis is placed on high-risk groups, such as the elderly, who may have reduced thirst perception and limited access to fluids.
Overview of Common Causes: This subsection provides a comprehensive overview of the common causes of hypernatremia. It distinguishes between renal and nonrenal routes of water loss and discusses the role of central diabetes insipidus (DI) in rare cases.

### Clinical Features and Diagnosis of Hypernatremia

Clinical Manifestations: Hypernatremia leads to an increase in the osmolality of the extracellular fluid (ECF), resulting in cellular shrinkage. This section explores the clinical consequences of hypernatremia, with a particular focus on its neurological impact. Potential complications, including brain cell shrinkage, vascular complications, and osmotic demyelination, are discussed.
Diagnostic Approach: The diagnostic approach to hypernatremia is multifaceted. It involves evaluating serum and urine osmolality, as well as urine electrolyte measurements. The importance of differentiating central diabetes insipidus (DI) from nephrogenic DI is highlighted, along with the role of antidiuretic hormone (AVP) testing and copeptin levels.

### Treatment of Hypernatremia

Correction Approach: Effective management of hypernatremia necessitates a cautious approach to correction, focusing on slow and controlled correction of sodium levels to prevent complications such as cerebral edema. The concept of replacing the calculated free water deficit over 48 hours is emphasized. Exceptions are noted for patients with acute hypernatremia due to sodium loading, who may require more rapid correction.
Administration of Free Water: This section elaborates on various methods for administering free water, including oral, nasogastric tube, and intravenous (D5W) routes. The importance of monitoring blood glucose levels when using intravenous solutions is highlighted.
Additional Therapy: For specific cases of hypernatremia, additional therapeutic options are explored. Patients with central diabetes insipidus (DI) may respond to intravenous, intranasal, or oral desmopressin (DDAVP). Nephrogenic DI, particularly when caused by lithium, may benefit from amiloride therapy. Thiazides and nonsteroidal anti-inflammatory drugs (NSAIDs) are also considered for chronic management of polyuria associated with nephrogenic DI.

## Potassium Disorders
### Hypokalemia

Introduction to Hypokalemia Hypokalemia refers to a condition characterized by abnormally low levels of potassium (K+) in the bloodstream. Potassium is an essential electrolyte vital for maintaining various physiological processes, including muscle contraction, nerve function, heart rhythm regulation, and the balance of fluids in and out of cells.
Causes of Hypokalemia Hypokalemia can result from several underlying factors, including:
* Inadequate Dietary Intake: Not consuming enough potassium-rich foods, such as bananas, oranges, potatoes, and leafy greens.
* Gastrointestinal Loss: Conditions like severe diarrhea or vomiting can lead to excessive potassium loss through the digestive system.
* Renal Loss: Kidney disorders or the use of diuretic medications, which increase urine output, can cause the kidneys to excrete excess potassium.
* Transcellular Shift: In certain conditions, potassium can shift from the extracellular fluid into cells, reducing its concentration in the bloodstream.
Clinical Features of Hypokalemia Hypokalemia can present with various clinical symptoms, including:
* Muscle Weakness: Patients often experience muscle weakness, cramps, and even paralysis.
* Cardiac Arrhythmias: Low potassium levels can disrupt the normal electrical activity of the heart, leading to irregular heart rhythms.
* Fatigue and Weakness: Generalized fatigue, weakness, and lethargy are common complaints.
* Gastrointestinal Symptoms: Nausea, vomiting, and constipation may occur.
* Increased Urination: Polyuria, or increased urination, can result from renal potassium wasting.
ECG Changes in Hypokalemia Hypokalemia is associated with characteristic electrocardiogram (ECG) changes, including:
* ST-Segment Changes: ECG may show flattening of the T-waves, prominent U-waves, and even the development of a prolonged QT interval.
* Arrhythmias: Hypokalemia can lead to various cardiac arrhythmias, including ventricular ectopy, atrial fibrillation, and ventricular tachycardia.
Diagnosis of Hypokalemia Diagnosing hypokalemia involves a thorough evaluation of a patient's medical history, conducting a physical examination, and performing specific laboratory tests. Key diagnostic tests include measuring serum potassium levels, assessing kidney function, and conducting an ECG to identify cardiac abnormalities associated with low potassium levels.
Treatment of Hypokalemia The treatment of hypokalemia primarily aims to correct the underlying cause and replenish potassium levels in the body. Treatment options include:
* Dietary Changes: Increasing potassium-rich foods in the diet, such as bananas, oranges, potatoes, and spinach.
* Oral Potassium Supplements: Physicians may prescribe potassium supplements in tablet or liquid form.
* Intravenous Potassium: In severe cases or when patients cannot tolerate oral intake, intravenous potassium supplementation may be necessary.
* Addressing Underlying Causes: Identifying and treating underlying conditions contributing to hypokalemia, such as gastrointestinal disorders or kidney problems.
Monitoring and Follow-Up Patients with hypokalemia require ongoing monitoring of potassium levels, renal function, and ECG changes. Adjustments to treatment may be necessary to maintain normal potassium levels and prevent complications.

### Hyperkalemia

Introduction to Hyperkalemia Hyperkalemia is a medical condition characterized by excessively high levels of potassium (K+) in the bloodstream. Potassium is a critical electrolyte involved in various bodily functions, including muscle contraction, nerve transmission, and cardiac rhythm regulation. Elevated potassium levels can have serious effects on the heart and other vital organs.
Causes of Hyperkalemia Hyperkalemia can arise from several underlying factors, such as:
* Impaired Kidney Function: Kidney disorders, including acute kidney injury (AKI) and chronic kidney disease (CKD), can hinder the proper excretion of potassium, leading to its accumulation in the bloodstream.
* Medications: Certain drugs, such as potassium-sparing diuretics (e.g., spironolactone), ACE inhibitors, and angiotensin receptor blockers (ARBs), can elevate potassium levels.
* Transcellular Shift: Redistribution of potassium from cells into the extracellular fluid can occur due to tissue damage, acidosis, or insulin deficiency.
* Excessive Potassium Intake: Consuming large amounts of potassium-rich foods or supplements can lead to hyperkalemia.
Clinical Features of Hyperkalemia Hyperkalemia can manifest with a range of clinical symptoms, including:
* Cardiac Arrhythmias: Elevated potassium levels can disrupt the normal electrical activity of the heart, leading to severe cardiac arrhythmias, including ventricular tachycardia, fibrillation, and asystole.
* Muscle Weakness: Weakness and paralysis, especially in skeletal muscles, may occur.
* Nausea and Vomiting: Gastrointestinal symptoms like nausea, vomiting, and abdominal discomfort can be present.
* Altered Mental State: In severe cases, hyperkalemia may lead to confusion and altered consciousness.
ECG Changes in Hyperkalemia Hyperkalemia is associated with characteristic electrocardiogram (ECG) changes, including:
* T-Wave Changes: ECG may show tall, peaked T-waves.
* Prolonged PR Interval: An elongated PR interval can be observed.
* Widened QRS Complex: Hyperkalemia can result in a widening of the QRS complex.
* Sine Wave Pattern: In critical cases, a sine wave pattern may develop, indicating impending ventricular fibrillation or asystole.
Diagnosis of Hyperkalemia Diagnosing hyperkalemia involves evaluating a patient's medical history, conducting a physical examination, and performing specific laboratory tests. Key diagnostic tests include measuring serum potassium levels, assessing kidney function, and analyzing ECG findings to identify cardiac abnormalities associated with high potassium levels.
Treatment of Hyperkalemia The treatment of hyperkalemia aims to lower potassium levels promptly and address the underlying cause. Treatment options include:
* Calcium Infusion: Intravenous calcium gluconate or calcium chloride is administered to protect the heart and stabilize the cardiac membrane.
* Redistribution into Cells: Insulin and glucose, along with beta-2 agonists (e.g., albuterol), are used to shift potassium back into cells.
* Potassium Binders: Medications like sodium polystyrene sulfonate (SPS), patiromer, and sodium zirconium cyclosilicate (ZS-9) can help remove excess potassium from the body.
* Hemodialysis: In severe cases or when other measures are ineffective, hemodialysis is used to rapidly reduce potassium levels.
Monitoring and Follow-Up Patients with hyperkalemia require ongoing monitoring of potassium levels, ECG changes, and renal function. The underlying cause should be addressed to prevent recurrent hyperkalemia and associated complications.