Fluids and Electrolytes 1 Flashcards
What does water loss lead to?
Water loss leads to increase in serum sodium and osmolality resulting in a stimulation of thirst and increased release ADH (acts on the kidneys)
In normal people this leads to an increase in water intake and reduced water excretion.
What is the minimum water intake required to maintain homeostasis (assuming normal temp and renal concentrating ability)?
500ml/d which would yield 500ml urine
What is the minimal obligatory water intake for normal adults?
Normal adults are considered to have a minimal obligatory water intake of 1600 mL/day
Ingested water- 500mL
Water in food- 800mL
Water from oxidation – 300mL
What is normal water loss in healthy adults and where does it come from?
Normal healthy individuals have obligatory water loss of 2.5-3L/24hr Loss from urine 500mL Skin- 500mL Respiratory Tract- 400mL Stool- 200mL
What are the factors affecting fluid requirements?
Age
Environmental Factors
Conditions with increased fluid needs
Conditions with decreased fluid need
What are the age factors affecting fluid requirements?
Neonates with larger fluid needs
Geriatric patients with smaller fluid needs
What are the environmental factors affecting fluid requirements?
Ambient temperature
Neonates- radiant warmers, ultraviolet phototherapy
What are the conditions with increased fluid needs that affect fluid requirements?
Burns, diarrhea, dehydration, fever
What are the conditions with decreased fluid needs that affect fluid requirements?
CHF, renal failure, iatrogenic fluid overload, mechanical ventilation
What determines the distribution of water between ECF and ICF compartments?
To tonicity (osmolality) of ECF
What is tonicity determined by?
The concentrations of effective osmoles in the ECF
What are effective osmoles?
Solutes that can not move freely across cell membranes (require active transport)
What is the main “effective osmole” in ECF?
Sodium
What reflects osmolality of body water?
Plasma osmolality
Unless abnormality of sodium and fluid resulting in redistribution between ICF and ECF
Rank the fluid compartments from most to least percentage of body water considering interstitial fluid, plasma, and intracellular fluid.
Intracellular fluid > Interstitial fluid > Plasma
What are the low pressure systems and what do they do?
Atria and pulmonary vasculature
In response to decreased wall stress (sign of decreased intravascular volume- in the heart and lungs) signal hypothalamus to release antidiuretic hormone (ADH) or vasopressin, while increased stress results in secretion of natriuretic peptide
What are the high pressure systems and what do they do?
Baroreceptors in aortic arch, carotid sinus, and juxtaglomerular apparatus
Stimulates the Renin-Angiotensin-Aldosterone system
What is renin released by?
Response of juxtaglomerular appraratus to decreased arteriolar wall of tension
Beta-1 innervation of juxtaglomerular apparatus
Tubuloglomerular feedback that senses distal nephron sodium release
What cleaves angiotenson to generate angiotensin I?
Renin
What cleaves angiotensin I to generate angiotensin II?
Angiotensin I is then cleaved by angiotensin converting enzyme (ACE) to Angiotensin II
Stimulation of Aldosterone secretion by adrenal gland
Increased reabsorption of NaCl from proximal tubule
Central stimulation of thirst and secretion of ADH
Arteriolar vasoconstriction
What type of solution is D5W?
Hypotonic
What type of solution is 1/2 NS (0.45%)?
Hypotonic
What type of solution is NS (0.9%)?
Isotonic
What type of solution is 3% saline?
Hypertonic
What type of solution is LR?
Isotonic
Dextrose
- Isotonic
- Small uncharged molecules able to cross capillaries and cell membrane: distributes to intracellular and extracellular compartments
- 1 liter 670ml ICF + 250ml interstitial + 80ml plasma
- Poor choice for volume replacement
- Not affected by osmolality D5, D10 and D50 distribute to all compartments
- Metabolized to CO2 + H2O soon after administration; provides calories
Saline- 0.2% (1/4NS) and 0.45% (1/2NS)
Distributes to intracellular, plasma and interstitial
1 liter 335ml ICF + 165ml plasma + 500ml interstitial fluid
1 liter distributes to ECF only 250ml plasma + 750ml interstitial
Can cause acidosis in large volumes
Useful in dehydration/hypovolemic state
Saline- 0.9% (NS)
Isotonic
1 liter distributes to ECF only 250ml plasma + 750ml interstitial
Can cause acidosis in large volumes
Useful in dehydration/hypovolemic state
Saline- 3%
Hypertonic; not commonly used
High solute in extracellular compartment draws water from intracellular compartment
Lactated Ringers
More physiologic isotonic solution than NS
Confined to extracellular compartment
1 liter -> 250ml plasma + 750ml interstitial
Safer than NS in large volume replacements
How do you monitor fluids?
Measure quantity of all intake and output
What are the sources of intake of fluids?
Oral intake from food and beverages
Intravenous intake including maintenance fluids and medications
What are the sources of output of fluids?
Urine
Stool
Gastrointestinal (From vomiting or gastric suctioning)
Other losses (chest tubes)
What is involved for the assessment in fluid monitoring?
Determine if In and Outs are balanced
May be desirable to have fluid imbalance
What is ins>outs assessed as?
Positive fluid balance
What is outs>ins assessed as?
Negative fluid balance
What is the goal for correction of dehydration?
Input>output
What is the goal for fluid overloaded CHF patient?
Output>input
What should be assessed for dehydration/volume depletion?
Pulses Capillary refill Blood pressure Urine output Mucus membranes HR Mental Status Skin tugor Fontanelle Skin/Extremities Tears/eyes Breathing
What systems should be the primary focus on PE to evaluate fluid overload?
Cardiac exam Abdominal Exam Extremities Lung Exam Blood pressure
What produces osmotic gradient that maintains water distribution between ICF and EFC?
Sodium distribution
What is a major determinant of ECG osmolality?
sodium is major determinant of ECF osmolality; chloride and bicarbonate also contribute
sodium is activity removed from ICF to ECF
What do sodium disorders result in?
Serum toxicity disorders
Do serum sodium concentrations always reflect total body sodium concentrations?
Not always
Serum sodium concentrations may be high but the total body sodium concentration may be high, normal or low
Serum sodium concentrations may be low but the total body sodium concentrations may be high, normal, or low