Urinary Elimination, Fluid Balance, and Assessment of I & O

Water Content of the Body (Differences in populations)

• Accounts for approx 60% of adult weight

• Varies with sex, body mass and age

• Men have more water content than women, because men have more lean tissue (less fat cuz fat contains less water than lean tissue)

• Infants have a body water content of approx 70-80% while older adults have a content of approx 45-55%. This makes both populations more vulnerable to fluid-related problems.

Functions of Body Water (6)

• In constant motion.

• Transport nutrients, electrolytes and O2 to cells and carry waste away.

• Regulate body temp

• Lubricates joints and membranes

• Medium for food digestion

• Water shifts between compartments

Body Fluid Compartments

• Intercellular (60% of body fluid inside cells)

• Extracellular (outside cells)

  • Interstitial (between cells in tissue. Ex: between individual skin cells)

  • Intravascular (in blood and plasma)

  • Transcellular (Contained within epithelial lines spaces. Ex: pleural cavity)

Osmosis

• Movement of WATER through a semipermeable membrane from an area of high concentration to an area of low concentration

Osmotic Pressure

• Pressure needed to counter osmosis.

Colloid Osmotic Pressure

Water being pulled from the intracellular fluid into the intravascular compartment (bvs) due to a greater solute concentration in the plasma

This solute concentration exists due to plasma proteins such as albumin (greatest), globulins, and fibrinogen

Hydrostatic Pressure

"Force exerted by fluids within a compartment", in the case of intravascular fluid, is caused by heart contractions. Thus, hydrostatic pressure (bp) is greater in the arterioles than the veins, causing a pressure gradient, allowing blood to flow through the capillaries

Diffusion

• Movement of IONS AND MOLECULES across a semipermeable membrane from an area of high conc to low conc.

Filtration

• Movement of SOLUTES AND SOLVENTS across a semipermeable membrane AT THE CAPILLARY LEVEL OF CIRCULATION

Forces and Values of Filtration

• The force behind filtration is hydrostatic pressure (the force a fluid exerts due to gravity and/or fluid movement). In the capillaries, hydrostatic pressure is generated by the pumping action of the heart. 

• Filtration results in 2-4L of fluid per day entering the interstitial fluid from the intravascular space. 

• Filtration is important for urine production

Body response to dehydration

• During dehydration your blood osmolality increases. Osmoreceptors in the hypothalamus detect this change and make you thirsty. In addition to that, they tell the posterior pituitary to increase ADH which increases renal water reabsorption by increasing the permeability of the tubules and collecting duct to water. Both these actions make fluid balance normal again

Natriuretic Peptides

• Natriuretic peptides are released when there’s too much blood volume (ANP released by the heart). These peptides facilitate diuresis by increasing Na+ and water loss. Natriuretic peptides also block the release of ADH and aldosterone and reduce thirst. 

Aldosterone

• Aldosterone is released by the adrenal cortex in response to hyperkalemia (lots of K) or hyponatremia (less Na) to counteract hypovolemia (low blood volume). Aldosterone acts on distal renal tubules to reabsorb sodium, and excrete K and H

GI Fluid Regulation w/ values

• Your gastric lumen receives 1.5L of fluid from intestinal secretions, 1.5L from pancreatic juice, 0.5-1L from bile, 1.5L from gastric secretions, 1.5L from saliva swallowing, and 2L from drinking. In total it receives about 8.9L of fluid

• Your intestines absorb 8.8L and therefore only 100mL is lost in feces

• Diarrhea and vomiting can result in significant imbalance and loss.

Insensible Water Loss

• 600mL-900mL of water a day is lost from the skin and lungs, but this can change depending on fever and exercise. 

Symptoms of Hypervolemia

• Increased cardiac symptoms (turn up the heart)

• Weight gain and edema

Average Adult I&O

• Intake

  • Oral fluids: 1.1-1.4L

  • Food: 0.8-1L

  • Metabolism Generates: 0.3L

• Output

  • Skin: 0.5-0.6L

  • Lungs: 0.4L

  • GI: 0.1-0.2L

  • Urine: 1.2-1.5L

• Total intake and output should be equal at around 2.2-2.7L

What urine rate is a cause for concern?

• Hourly output of <30mL/hour for 2 hours is cause for concern.

Urethra sizes

• Urethra is 3-4cm in females and 18-20cm in males

Urge to void

• Urge to void first felt when bladder is 250-300mL full

• Strong urge at 500mL

Positive vs Negative Balances

• Positive Balance: Input>Output

• Negative Balance: Input<Output

Adult and Infant Urine Rates

• Adults urinate approx 1.5-1.6L of urine a day. Approx every 4-5hours

• Up to age 2: 2mL/kg/hour

• Age 2+: 1mL/kg/hr

How does Age Influence Fluid Imbalances in the Body

Infants: Have more water and therefore have more oppurtunity for defecits

Children (2-12): Less ability to regulate imbalnces. Frequent illness can affect imbalances
Adolesence: More metabolism = greater need for hydration

Older adults: Less ability to compensate for imbalances.

Fluid volume deficit (FVD)

aka hypovolemia, condition where body losses an excessive amount of fluid

Fluid volume excess (FVE)

aka hypervolemia, condition where body contains/retains an excessive amount of fluid

How can urinary retention affect fluid imbalances in the body?

Accumulation of urine in the bladder due to the bladder's inability to empty , causing feelings of discomfort, pressure, tenderness, restlessness, and diaphoresis. Can result in UTI and UI

What are 7 types of urinary incontinences?

Transient UI= caused from factors outside of urinary system

Urge UI= Involuntary loss of urine with urgency, frequency, or nocturia

Stress UI= Involuntary loss of urine upon physical exertion

Mixed UI= Urge + Stress UI

UI assoc with chronic retention of urine = involuntary loss of urine when bladder does not completely empty with a high residual urine volume

Functional UI = loss due to inability to reach toilet

Neurogenic bladder dysfunction = lower urinary tract dysfunction, causing urge incontinence, frequency, and retention

What urine characteristics should be noted during a urinary assessment?

Color

• Normal: pale straw

• Amber/ Bleeding: dark red from kidney or liver dysfunction, bright red from bladder or urethra/ also influenced by food and medication

Clarity

• Normal: Transparent

• Cloudy+Foamy: Renal disease, bacteria

• Mucous: normal w/ pts with urinary diversions, increased production= UTI

Odor

• More concentrated = stronger

• Incontinent = ammonia odour

• Diabetes mellitus or starvation = sweet-fruity odor

Amount

• (<30ml/hr for 2 hours is concerning)

How should urine collection be adjusted for pediatric patients?

- Offering water 30 minutes before collection

- Using terms that children can understand

-Use of potty chair or toilet seat instead of receptacles

-Use of clear plastic single use bags for toddlers that are not potty trained

What are the steps to using a bladder scanner

1. Identify patient and perform hand hygiene

2. Place patient supine with head slightly elevated, expose abdomen

3. Turn scanner on, clean before use

4. Palpate pubic bone, apply ultrasound gel to midline abdomen above pubic bone

5. Place scanner on gel and apply light pressure, point downward slightly toward bladder