Fluid & Electrolytes Flashcards
What’s the TBW of an adult male & female
- Adult Male: TBW is approximately 60% of body weight. For a man weighing 70 kg, this translates to around 42 liters of water in the body.
- Adult Female: TBW is lower, around 50% of body weight. This difference is due to body fat, which contains less water than muscle.
What are the Factors Influencing TBW:
- Age: As people age, TBW decreases because muscle mass tends to decrease while fat increases, which holds less water.
- Sex: Women typically have more body fat than men, leading to a lower percentage of body water.
- Obesity: In obese individuals, TBW is also lower as fat tissue contains less water compared to lean tissue.
What’s the Distribution of Body Water both %&L
TBW is divided into two major compartments:
1. Intracellular Fluid (ICF): This is the water contained inside cells, making up 40% of body weight or about 28 liters in a 70 kg adult.
- The intracellular space is essential for cellular metabolism and the exchange of nutrients and waste between the inside and outside of the cell.
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Extracellular Fluid (ECF): This includes all the water outside of cells and accounts for 20% of body weight, about 14 liters in a 70 kg adult. ECF is further divided into:
- Intravascular Fluid (Plasma): This is the fluid portion of blood and makes up 4% of body weight, approximately 2.8 liters. Plasma is crucial for transporting blood cells, nutrients, and waste products.
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Extravascular Fluid:
- Transcellular Fluid: About 1% of body weight, around 0.7 liters, this includes specialized fluids such as gastrointestinal secretions, cerebrospinal fluid, and fluids in the eyes and joints. These fluids serve specific functions for. protection and lubrication.
- Interstitial Fluid: Makes up 15% of body weight, approximately 11 liters. This fluid surrounds the cells and helps in the exchange of nutrients, gases, and waste between the blood and the cells.
Neonatal vs. Adult TBW and ECF explain why?
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Full-term Neonates: Babies are born with a higher percentage of TBW, about 75% of their body weight. This is essential for their higher metabolic needs and rapid growth.
- ECF in neonates: Around 35% of body weight is ECF at birth, indicating a larger proportion of fluid outside the cells compared to adults. This decreases over time.
- By 2 Years of Age: TBW decreases to 65%, and ECF reduces to 20%, aligning more closely with adult values. The intracellular fluid (ICF) remains relatively constant throughout life.
What’s Interstitial Fluid and transcellular Fluid
The interstitial fluid and plasma are separated by a capillary membrane, which is highly permeable. This membrane allows for the rapid transfer of substances like water, electrolytes, and small molecules between the two compartments, except for larger protein molecules and blood cells. Because of this, interstitial fluid and plasma function as one fluid compartment, allowing for efficient exchange of nutrients and waste.
Transcellular Fluid
Transcellular fluids include:
- Gastrointestinal secretions: These help with digestion.
- Cerebrospinal fluid (CSF): This surrounds the brain and spinal cord for protection and nutrient transport.
- Joint fluids (synovial fluid) and fluid in the eye: These help reduce friction and protect sensitive structures.
What’s Extracellular Fluid (ECF) and Its Functions
The ECF is often referred to as the “inland sea” because of its role in maintaining the environment for cells, similar to how the ocean sustains marine life. It plays the following critical roles:
- Transport of nutrients and oxygen: The ECF carries essential nutrients from the gastrointestinal tract and oxygen from the lungs to cells.
- Waste removal: It also collects waste products and carbon dioxide from cells and transports them to organs such as the kidneys, liver, and lungs for excretion.
Analogy: Think of the ECF like a delivery system that provides what cells need to function and removes what they no longer need, just like how the sea nourishes marine life and carries away waste.
Key Takeaways
- Total Body Water and its distribution are vital for proper bodily functions, and changes in fluid compartments can lead to significant health issues.
- Intracellular fluid is the largest compartment, while the extracellular fluid plays a critical role in transporting essential substances to and from cells.
- Plasma and interstitial fluid together make up most of the ECF and are vital for maintaining nutrient and gas exchange.
- Neonates have higher TBW and ECF percentages, which decrease as they grow, reflecting changes in their physiological needs.
This breakdown helps us understand how water is distributed in the body and why maintaining fluid balance is critical for survival. Each compartment plays a specific role in keeping the body functioning properly.
What are Electrolytes
Electrolytes are minerals that dissolve in body fluids and help regulate key physiological functions, such as fluid balance, nerve signaling, and muscle contraction. Understanding how electrolytes are distributed between the intracellular and extracellular compartments is essential for fluid therapy and maintaining the body’s electrolyte balance.
List some Intracellular & extracellular ions and their function
Potassium (K⁺) is the most important intracellular cation (positively charged ion). Its concentration inside cells is about 140 mmol/L, making it essential for maintaining electrical stability in cells, particularly in nerve and muscle cells, where it helps with action potential and muscle contraction. Potassium’s high intracellular concentration creates a gradient compared to its much lower concentration outside cells, and this difference is crucial for many cellular processes.
- Magnesium (Mg²⁺) is present at 15 mmol/L within cells. Magnesium is vital for enzyme function, particularly those involved in energy production (ATP generation).
- Sodium (Na⁺) is relatively low in the intracellular space at 8 mmol/L. Sodium’s major role is in the extracellular fluid, but its small presence inside the cell helps with regulating the sodium-potassium pump, which is essential for maintaining cell volume and generating electrical signals.
- Phosphates (PO₄³⁻), at 26 mmol/L, and proteins (9 mmol/L) are the main intracellular anions (negatively charged ions). These play a role in maintaining intracellular pH and energy storage, particularly in the form of ATP (adenosine triphosphate), which contains phosphate.
Extracellular Ions
Sodium (Na⁺) is the most important extracellular cation, with a concentration of 135–145 mmol/L. Sodium is critical for maintaining fluid balance and osmotic pressure. It helps draw water into the extracellular space, maintaining blood volume and pressure. It also plays a significant role in nerve transmission and muscle function.
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Other Extracellular Cations:
- Potassium (K⁺): Around 3.6–5.2 mmol/L in the extracellular fluid. This low concentration of potassium in the blood and extracellular space is tightly regulated because even small changes can cause serious issues, such as abnormal heart rhythms.
- Calcium (Ca²⁺): About 2.1–2.6 mmol/L. Calcium is essential for muscle contractions, nerve signaling, blood clotting, and bone health.
- Magnesium (Mg²⁺): 0.7–0.9 mmol/L in the extracellular space, where it supports many enzymatic reactions.
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Main Extracellular Anions:
- Chloride (Cl⁻): 95–105 mmol/L. Chloride helps maintain fluid balance and electrical neutrality across cell membranes by following sodium.
- Bicarbonate (HCO₃⁻): 24–29 mmol/L. Bicarbonate acts as a buffer to maintain the body’s acid-base balance by neutralizing excess acids in the blood.
Electrolyte Composition Similar to Seawater
An interesting observation is the similarity between the electrolyte composition of extracellular fluid (ECF) and seawater. This resemblance is sometimes used to describe the extracellular fluid as an “inland sea” because it surrounds cells and provides them with nutrients, much like seawater sustains marine life.
For example:
- Seawater has 478 mmol/L of sodium (Na⁺), 10 mmol/L of potassium (K⁺), and 26 mmol/L of magnesium (Mg²⁺), similar to the ratios found in human extracellular fluid. This historical analogy suggests that the body’s extracellular environment reflects an ancient marine origin.
What are the daily fluid losses(how?) and gains in the body?
Fluid and Electrolyte Requirements
Fluid Losses: The body loses water and electrolytes through several routes:
- Pulmonary and Cutaneous (skin): About 1700 mL/day is lost from breathing and sweating.
- Urine: Around 1500 mL/day is excreted through the kidneys.
- Feces: Typically, around 200 mL/day is lost in stool.
This results in a total daily water loss of about 3400 mL in tropical climates.
Water Gain:
- Endogenous production: The metabolism of carbohydrates, proteins, and fats generates 200 mL/day of water.
- Net water requirement: The body needs about 3200 mL/day of water in tropical climates to make up for the losses mentioned above.
However, surgical patients who are on parenteral fluid therapy (intravenous fluids) often do not pass feces due to fasting or the effects of surgery. As a result, they require around:
- 3 liters of water per day in tropical climates.
- 2.3 liters in temperate regions.
When a patient has fever how will that affect their fluid requirements
If a patient develops a fever (1°C rise in body temperature), about 12% extra water is added to the daily requirement to replace water lost through increased sweating.
What are the Electrolyte Requirements in Tropical Regions for Na, K?
What are amount is lost via what method
In tropical climates, where sweating is more intense due to heat, sodium and potassium losses differ:
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Sodium:
- Urine: 114 mmol/day.
- Sweat: 10–16 mmol/day.
- Feces: 10 mmol/day.
- Total sodium loss: 130–140 mmol/day.
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Potassium:
- Urine: 50 mmol/day.
- Sweat: Negligible.
- Feces: 10 mmol/day.
- Total potassium loss: 60 mmol/day.
For a surgical patient on parenteral therapy (not passing feces), the daily electrolyte requirements in the tropics are:
- Sodium: 130 mmol.
- Potassium: 50 mmol.
In temperate regions, the requirements drop slightly to:
- Sodium: 80–110 mmol/day.
- Potassium: 60 mmol/day.
Energy Requirement
The body’s energy needs are met through a balance of carbohydrate, protein, and fat metabolism.
- Glycogen: The body’s stored carbohydrate reserve is small, only about 400 grams, providing around 1600 kcal of energy. This is quickly used up within the first 24 hours of starvation or fasting.
- After glycogen stores are depleted, the body turns to fat for energy, providing 75-90% of the energy, with the remaining coming from protein.
In surgical patients, preventing acidosis (a condition where the body becomes too acidic) is critical. If 100-150 grams of glucose (providing 1674–2508 kJ) is given daily, it reduces the body’s need to break down protein for energy. This is why surgical patients often receive 2 liters of 5% glucose per day intravenously to provide energy.
For prolonged IV therapy, 5 grams of glucose per kilogram of body weight per day is recommended. Sorbitol, which can be infused in higher concentrations (up to 30%), may also be used to provide more energy.
- Electrolyte Balance: The balance of electrolytes between intracellular and extracellular compartments is essential for maintaining cell function, fluid balance, and nerve signaling.
- Fluid Requirements: Water losses increase in tropical climates, and surgical patients often need additional fluids due to factors like fever and sweating.
- Energy Needs: Surgical patients require sufficient energy from glucose to prevent protein breakdown and acidosis, which is managed by administering IV glucose and sometimes sorbitol.
Understanding these principles helps in managing fluid and electrolyte therapy, ensuring that patients maintain optimal hydration and energy balance.
Which vitamin do you think will be deficient in a post-operative or critically ill conditions?
Vitamins and Minerals:
Patients often have inadequate stores of essential vitamins and minerals, especially in post-operative or critically ill conditions. Important considerations include:
- Vitamin C: Essential for collagen production, which is critical for wound healing, and serves as a scavenger of free radicals. Daily intake should be 100-200 mg.
- Vitamin B Complex: Important for carbohydrate and protein metabolism and should also be supplemented.
- Multivitamins and Trace Elements: In prolonged therapy, supplements of magnesium, zinc, and chromium, among others, should be considered to prevent deficiencies.
What’s the summary of Daily Requirements (Tropics):
And These needs are met through what solutions:
In tropical regions, the daily requirements are as follows:
- Water: 3 liters per day.
- Sodium: 130 mmol (equivalent to 2 mmol/L).
- Potassium: 50 mmol (equivalent to 1-2 mmol/L).
- Carbohydrate: 100 g, or approximately 2 g/kg/day.
These needs are met through the following solutions:
1. Ringer’s Lactate (1 Liter): Provides 130 mmol/L sodium, 4 mmol/L potassium, 4 mmol/L calcium, 111 mmol/L chloride, and 27 mmol/L bicarbonate.
2. 5% Dextrose (2 Liters): Supplies fluid along with glucose to prevent protein catabolism.
3. Potassium Chloride (50 mmol): Added separately to meet the potassium requirement.
4. Vitamin B complex and Vitamin C: Added to ensure adequate metabolic support.
Calculation of Maintenance Fluids:
For critically ill patients, maintenance fluids are calculated at an hourly rate, tailored to the patient’s condition. The combination of different fluids ensures the required intake of sodium and potassium.
Badoe’s Maintenance Solution can be used in tropical regions. This solution contains:
???
- Sodium (43.3 mmol/L)
- Potassium (16 mmol/L)
- Calcium (1.3 mmol/L)
- Chloride (51.7 mmol/L)
- Bicarbonate (9 mmol/L)
- Sorbitol (100 g/L)
Three liters of this solution provide the following:
- Water: 3 liters (daily requirement).
- Sodium: 130 mmol.
- Potassium: 48 mmol.
- Sorbitol: 300 g, which supplies about 3,000 J (780 kcal) of energy. This energy source reduces the body’s need to break down its own protein and fat stores for energy.
What are the enefits of Badoe’s Maintenance Solution:?
- It serves as a comprehensive solution for daily fluid, sodium, and potassium needs.
- Reduces the need for separate solutions like normal saline, dextrose, or potassium chloride, which are sometimes in short supply.
- It helps maintain sodium levels throughout the day, which encourages urinary excretion and prevents fluid overload.
- The sorbitol component provides a significant amount of energy and spares the body’s endogenous protein and fat from being broken down.
- Sorbitol metabolism: Sorbitol is processed by the liver into fructose, which can enter glycolysis or be converted into glycogen or blood glucose.
- This solution does not cause thrombophlebitis (inflammation of the veins due to clot formation).
What are the things you keep in mind when using badoes solution?
Cautions:
- Badoe’s Maintenance Solution should not be used in patients with liver disease or acidosis, as sorbitol is metabolized by the liver and can produce lactic acid.
- It should also be avoided in neonates.
- It appears to be safe for diabetic patients despite the sorbitol content.
This section outlines the essential fluid, electrolyte, and vitamin management strategies for post-operative or critically ill patients, particularly in the tropics, with a focus on simplifying treatment through solutions like Badoe’s Maintenance Solution.
Water Infusion Rate Calculation:
The formula for calculating the water infusion rate based on body weight is:
& Total water infusion rate for a 70kg man
- 4 mL/kg/hr for the first 10 kg of body weight
- 2 mL/kg/hr for the next 10 kg of body weight
- 1 mL/kg/hr for the remaining body weight
For a 70 kg man, the calculation is as follows:
- First 10 kg: ( 4 \text{ mL/kg/hr} \times 10 \text{ kg} = 40 \text{ mL/hr} )
- Next 10 kg: ( 2 \text{ mL/kg/hr} \times 10 \text{ kg} = 20 \text{ mL/hr} )
- Remaining 50 kg: ( 1 \text{ mL/kg/hr} \times 50 \text{ kg} = 50 \text{ mL/hr} )
Total water infusion rate: ( 40 \text{ mL/hr} + 20 \text{ mL/hr} + 50 \text{ mL/hr} = 110 \text{ mL/hr} )
This equals a daily water requirement of ( 110 \text{ mL/hr} \times 24 \text{ hrs} = 2.6 \text{ L/day} ).
What are the Sodium and Potassium Requirements:
For sodium and potassium, the requirements are based on body weight as well:
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Sodium: 1-2 mmol/kg/day
For a 70 kg man, sodium requirement is:
( 1 \text{ mmol/kg/day} \times 70 \text{ kg} = 70 \text{ mmol/day} )
( 2 \text{ mmol/kg/day} \times 70 \text{ kg} = 140 \text{ mmol/day} )
So, the daily sodium requirement is 70-140 mmol/day. -
Potassium: 0.5-1 mmol/kg/day
For a 70 kg man, potassium requirement is:
( 0.5 \text{ mmol/kg/day} \times 70 \text{ kg} = 35 \text{ mmol/day} )
( 1 \text{ mmol/kg/day} \times 70 \text{ kg} = 70 \text{ mmol/day} )
So, the daily potassium requirement is 35-70 mmol/day.
Dehydration:
Dehydration refers to the loss of water, but in the clinical context, it also involves the loss of electrolytes, particularly sodium. It commonly affects the extracellular fluid (ECF) but can also involve the intracellular fluid (ICF).
What are the Types of DehydrationDehydration & eachs characteristics
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Acute Dehydration:
- Cause: Rapid loss of ECF, as seen in conditions like acute intestinal obstruction, peritonitis, or diarrhoea.
- Characterized by the sudden loss of fluids, particularly from the extracellular space.
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Chronic Dehydration:
- Cause: Gradual loss of both ECF and ICF over days or weeks, as seen in gastric outlet obstruction.
- There is significant loss of potassium in chronic dehydration.
Severity of Dehydration:
- Moderate Dehydration: When at least 4% of body weight is lost due to fluid depletion.
- For an average West African weighing 70 kg, moderate dehydration means the loss of at least 2.8 liters of fluid.
What are the Causes of Dehydration:
- Vomiting or nasogastric aspiration: These mechanisms cause significant loss of both fluids and electrolytes.
- Diarrhoea: Rapid loss of water and electrolytes through the gastrointestinal tract.
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Internal Fluid Shifts: Fluids shift into damaged or infected tissues, as seen in conditions like:
- Burns
- Peritonitis
- Pancreatitis: Known for causing substantial internal fluid shifts.
- Enterocutaneous fistulae: Abnormal connections between the gastrointestinal tract and the skin, causing significant fluid loss.
- Excessive Sweating: Can result in dehydration, especially in hot climates.
- Polyuria: Excessive urination, leading to water and electrolyte depletion.
In summary, fluid management in surgical and critically ill patients requires careful calculation of both water and electrolyte needs. Acute and chronic dehydration must be addressed promptly, with consideration for the underlying causes and the appropriate replacement of fluids and electrolytes.
The first 3 are the commonest causes.
Internal fluid-shifts: Interstitial fluid may be sequestered inan
area in continuity with the E. C. F. space and yet be functionally
unavailable to the compartment. This occurs in burns, infec-
tions with oedema and oedema in wounds or traumatized areas
of operation. Gastro-intestinal secretions may also accumulate
in the gut as in intestinal obstruction and be unavailable to the
E.C.F. space. The net result of this internal fluid shift, creating
a “third” fluid space, is to reduce the effective functional
extracellular fluid volume (E.F E.C.F. V) and cause dehydra-
tion which must be corrected. However, as the underlying
condition resolves, this internally shifted fluid “returns” func-
tionally to the ECF space, increases the E.F.E.C.F.V. and
causes diuresis.
Clinical features of Dehydration
A good history is always essential. The duration of the
illness, duration and approximate amount of vomiting and/or
diarrhoea, and the volume and degree of concentration of the
urine must be sought.
The main clinical features are.-
1. Dry, inelastic skin with loss of turgor.
2. Dry mouth.
3. Sunken eyes in severe cases.
4. Collapsed veins.
5. Tachycardia.
6. Scanty highly concentrated urine.
7. If the loss is mainly of gastric juice with loss of chlorides and hydrogen ions as well, metabolic alka-
losis may occur. In diarrhoea, loss of bicarbonates
causes metabolic acidosis.
8. With progressive fluid loss (about 3.5L), shock, with
bypotension and sweating supervenes.
What’s Internal Fluid Shifts: and how does apply to burns, infections with edema and post operative edema.
Internal fluid shifts occur when interstitial fluid (fluid between cells) gets sequestered in areas that are part of the extracellular fluid (ECF) space but becomes functionally unavailable for circulation. This situation is typical in conditions such as:
- Burns: The damaged tissues cause fluid to accumulate in the interstitial spaces, reducing available ECF.
- Infections with Edema: Infected tissues swell due to fluid accumulation, limiting the availability of fluid in the ECF compartment.
- Post-operative Edema: After surgery, fluid may collect in the traumatized tissues (such as the site of operation) and reduce the functional fluid volume in the body.
- Gastrointestinal Obstructions: In cases of intestinal obstruction, fluid can accumulate within the gut, effectively removing it from the ECF space.
These conditions create a “third” fluid space, meaning the fluid is present but unusable by the body’s normal fluid compartments. The net result is a reduction in functional extracellular fluid volume (EFECFV), leading to dehydration.
As the underlying cause resolves (e.g., the infection clears, the obstruction is relieved), the fluid that had shifted to the third space returns to the ECF. This return of fluid leads to an increase in the EFECFV, which often triggers diuresis (increased urine output) as the body works to balance fluid levels.
