1 - Response to Injury, Fluids, and Nutrition 2026

~50-60%

In general, water constitutes approximately how many percent of total body weight?

Body fat

Lean tissues (e.g., muscle and solid organs) have higher water content than fat and bone.

Total body water (TBW) is relatively constant for a person and is primarily a reflection of ___

60%

In an adult male, total body water (TBW) comprises how many percent of total body weight?

50%

Due to higher adipose tissue and lower muscle mass

In an adult female, total body water (TBW) comprises how many percent of total body weight?

80%

In a neonate, total body water (TBW) comprises how many percent of total body weight?

40% ICF

20% ECF

The 60% total body water is divided into __% intracellular fluid (ICF) and __% extracellular fluid (ECF)

5% plasma

15% interstitial fluid

Extracellular fluid (ECF) comprises 20% of total body weight. ECF is further divided into __% plasma and __% interstitial fluid

Na+

What is major cation found in extracellular fluid?

K+, Mg2+

What are the cations found in intracellular fluid

Cl-, HCO3-

What are the anions found in extracellular fluid?

PO4-, proteins

What are the anions found in intracellular fluid?

Skin

The lungs contribute 25%

On average, the ___ contributes 75% of insensible water losses

Saliva

Recall your Physio: as saliva is formed, sodium and chloride are reabsorbed, while potassium and bicarbonate are secreted into saliva

Fluid A: Na 10 K 26 Cl 10 HCO3 30

Fluid B: Na 60 K 10 Cl 130 HCO3 0

Fluid C: Na 140 K 5 Cl 100 HCO3 24

Fluid D: Na 140 K 5 Cl 75 HCO3 115

Fluid A corresponds to the composition of what body fluid?

Stomach

The high chloride composition best reflects the acidic gastric juice secreted by the stomach for digestion

Fluid A: Na 10 K 26 Cl 10 HCO3 30

Fluid B: Na 60 K 10 Cl 130 HCO3 0

Fluid C: Na 140 K 5 Cl 100 HCO3 24

Fluid D: Na 140 K 5 Cl 75 HCO3 115

Fluid B corresponds to the composition of what body fluid?

Blood (plasma)

Fluid A: Na 10 K 26 Cl 10 HCO3 30

Fluid B: Na 60 K 10 Cl 130 HCO3 0

Fluid C: Na 140 K 5 Cl 100 HCO3 24

Fluid D: Na 140 K 5 Cl 75 HCO3 115

Fluid C corresponds to the composition of what body fluid?

Pancreas

Pancreatic duct cells actively secrete bicarbonate into pancreatic juice, giving it the highest HCO₃⁻ concentration of any GI fluid

Fluid A: Na 10 K 26 Cl 10 HCO3 30

Fluid B: Na 60 K 10 Cl 130 HCO3 0

Fluid C: Na 140 K 5 Cl 100 HCO3 24

Fluid D: Na 140 K 5 Cl 75 HCO3 115

Fluid D corresponds to the composition of what body fluid?

Extracellular volume deficit

Acute volume deficit is associated with cardiovascular and central nervous system signs.

Chronic volume deficit displays tissue signs such as decrease in skin turgor and sunken eyes, in addition to acute signs.

What is the most common fluid disorder in surgical patients?

Loss of GI fluids

Typically from nasogastric suction, vomiting, diarrhea, or enterocutaneous fistula

What is the most common cause of volume deficit in surgical patients?

0.9% pNSS or plain Lactated Ringer's

Surgical patients often experience contraction of the extracellular fluid compartment. What appropriate IVF preparations may be given to expand the ECF compartment?

Lactated Ringer's (LR)

What is the IV fluid preparation that most closely approximates the composition of plasma?

2300 mL/day or approx. 100 mL/hr

First 10 kg: 4 mL/kg/hr or 100 ml/kg/day

Next 10-20 kg: 2 mL/kg/hr or 50 ml/kg/day

Each kg >20 kg: 1 mL/kg/hr or 20 ml/kg/day

Based on the Holliday-Segar method, what is the daily maintenance fluid requirement for a 35/M who weighs 60 kg?

1950 mL/day or approx. 81 mL/hr

For elderly patients or those with cardiac disease, adjust the 20 mL/kg/day for each kg above 20 kg to 15 mL/kg/day

Based on the Holliday-Segar method, what is the daily maintenance fluid requirement for a 68/M with known cardiac disease who weighs 50 kg?

Moderate (6-10% loss)

This stage of dehydration is characterized by beginning tachycardia and orthostatic hypotension, poor skin turgor, and oliguria.

HARD UP:

Hyperalimentation

Acetazolamide

Renal tubular acidosis

Diarrhea

Ureteroenteric fistula

Pancreaticoduodenal fistula

Causes of NAGMA can be remembered by:

MUDPILES:

Methanol

Uremia

Diabetic ketoacidosis

Propylene glycol, paraldehyde

Iron, isoniazid, infection

Lactic acidosis

Ethylene glycol

Salicylates

Causes of HAGMA can be remembered by:

AG = Na+ - (Cl- + HCO3-)

Given Na, Cl, and HCO3, how is the anion gap computed?

Normal anion gap metabolic acidosis (NAGMA)

Ureterosigmoidostomy is a form of urinary diversion after pelvic exenteration. This can lead to what acid-base disturbance?

Water of oxidation (insensible water gain)

Water produced by the chemical breakdown of food is a source of water for the body. This is called:

Colonic juices

Which body fluid has the highest potassium concentration?

Hypokalemia

Based on the electrolyte composition of colonic juices, what is the expected electrolyte disturbance in diarrhea?

Acidosis: hyperkalemia

Alkalosis: hypokalemia

When acidosis is present, the H⁺ ions move into cells via the H⁺-K⁺ pump, causing K⁺ to shift out of cells and resulting in hyperkalemia; in alkalosis, H⁺ ions leave cells and K⁺ moves in, causing hypokalemia.

Acidosis is a state of ___-kalemia, while alkalosis is a state of ___-kalemia

160 mEq/L

Symptoms of hypernatremia are rare until serum sodium concentration exceeds ___ mEq/L

1 mEq/L/hr

In hypernatremia, rate of fluid administration should be titrated to achieve decrease in serum sodium concentration of no more than __ mEq/L/hr

120 mEq/L

Symptomatic hyponatremia does not occur until serum sodium reaches less than ___ mEq/L

1 mEq/L/hr

If asymptomatic, correction should increase sodium level by no more than 0.5 mEq/L/hr

Symptomatic hyponatremia is corrected using 3% normal saline. The goal is to increase sodium by no more than ___ mEq/L/hr

Peaked T waves > flattened P waves > widened QRS complex > sine wave pattern

Arrange the following in order of earliest to latest manifestation of hyperkalemia:

Flattened P waves

Sine wave pattern

Widened QRS complex

Peaked T waves

Administration of 10% calcium chloride or calcium gluconate

When ECG changes are present in hyperkalemia, what is the immediate management?

Hypokalemia

T wave flattening and the presence of U waves is associated with what electrolyte disturbance?

>12 mEq/L

Treatment for hypercalcemia is required when it becomes symptomatic, which typically occurs at what serum level?

Primary hyperparathyroidism

In the outpatient setting, what is the likely cause of hypercalcemia?

Malignancy

In the inpatient setting, what is the likely cause of hypercalcemia?

2.5 mg/dL

Neuromuscular and cardiac symptoms of hypocalcemia do not occur until ionized Ca falls below __ mg/dL

Hypomagnesemia

Hypocalcemia will be refractory to treatment if this coexisting electrolyte abnormality is not treated first:

Administration of IV 10% calcium gluconate to achieve serum concentration of 7-9 mg/dL

What is the management for acute symptomatic hypocalcemia?

IV calcium chloride

IV calcium gluconate may also be used and is associated with lower risk of tissue necrosis and extravasation injury.

What is the management for acute symptomatic hypermagnesemia?

IV magnesium sulfate

What is the management for severe or symptomatic hypomagnesemia?

IV calcium gluconate

To counteract the side effects of a rapidly rising magnesium level during correction of hypomagnesemia, simultaneous administration of ___ is done