Water and Sodium Disorders Flashcards
Usual IV Fluid Needs
- 1-10 kg: 100 mL/kg
- 11-20 kg: 1000 mL + 50 mL/kg for each kg >10
- > 20 kg: 1500 mL + 20 mL/kg for each kg > 20
Factors Effecting Fluid Requirements
- Age (more for young, less for old)
- Environment (humidity/temperature)
- Increased fluid need conditions (burns, diarrhea, dehydration, fever)
- Decreased fluid need conditions (CHF, renal failure, fluid overload, mechanical ventilation)
Monitoring Fluid Therapy
- Measure intake and output
- Intake from food/IVs
- Output from urine, stool, GI
- Daily weights are useful for fluid balance
Fluid Therapy Assessment
- In»_space; Outs assessed as positive fluid balance
- Out > In assessed as negative fluid balance
- Usually Ins are a little greater than outs due to insensible fluid loss
Fluid Imbalance Goals
- Correction of volume depletion: input»_space; output
- Fluid Overloaded CHF: Output > Input
ECF
- Extracellular Fluid
- Important to adequately perfuse tissues and organs
- Volume depletion occurs with decreased ECF
- Regulated by kidneys, ADH, Renin, prostaglandins
Signs of Mild Volume Depletion (<10%)
- Thirst
- Decreased urine output
- Increased hematocrit
- Increased urine sp. gravity
Signs of Modest Volume Depletion (20%)
- Dry mucous membranes
- Tachycardia
- Orthostatic Hypotension
- Increase BUN/Cr
- CNS (apathy, drowsy)
Signs of Severe Volume Depletion (30%)
- Hypotension
- Weak Pulse
- CNS (stupor, coma)
- Skin cool, pale, poor turgor
- Pronounced oliguria
- Leads into shock
“Effective Osmole”
- Can’t move freely across cell membranes
- Sodium is the main one
- Osmolality is maintained between 275-290 mOsm/kg
- Maintenance results from vasopressin (ADH), thirst, and renal fxn
Calculated Osmolality
2 * (Na+) + BUN/2.8 + Glucose/18
About 10 mOsm/kg less than actual since certain solutes are ignored
Distribution of IV Fluids
- D5W: 40% ECF/60% ICF
- 0.9% NaCl and Lactated Ringers: 100% ECF
- 0.45% NaCl: 70% ECF/30% ICF
Distribution of D5W
- Iso-osmolar: 278 mOsm/L
- Dextrose taken into cell via insulin and free water is left behind and distributed to all body compartments
Isotonic Crystalloid Solutions
- NS, Lactate Ringers
- Only distribute into ECF
- LRs may be preferred for fluid rescusitation (less hyperchloremia and renal dysfxn)
Sodium/Water Regulation
- Sodium is actively removed from ICF to ECF and is a main osmolality determinant in ECF
- Filtered by glomerulus and 50-90% reabsorbed in proximal tubule
- Aldosterone increase sodium reabsorption (less fluid excretion)
- Antidiuretic Hormone increases free water reabsorption
- [Na+] = 135-145 mEq/L, serum concentration may NOT reflect total body Na+
Classifications of Na/Water Disorders
Hyponatremia
- Hypertonic
- Isotonic
- Hypotonic (hyper/iso/hypovolemic)
Hypernatremia
- Hypervolemic
- Euvolemic
- Hypovolemic
Hypertonic Hyponatremia
- Na < 135
- > 295 mOsm/kg
- Excess non-sodium osmoles in ECF (glucose, mannitol)
- Increased ECF dilutes ECF and makes serum sodium concentration low (total body is normal)
- Sodium drops by 1.7 for each 100 mg/dL increase in glucose
Hyponatremia Treatment
- Determine symptoms related to hyponatremia and if they are related to tonicity or volume
- Address accordingly based on tonicity or volume
- If tonicity: raise [Na+] to normal but avoid increasing too quickly (osmotic demylination syndrome)
- Treat/remove underlying cause
Hypovolemic Hypotonic Hyponatremia
- Na+ deficit > water deficit
- Signs/symptoms generally associated with ECF depletion
- Causes: GI/renal/extra-renal losses, latrogenic (replace sodium-rich fluid losses with sodium free fluids
- Intact thirst mechanism and replacing fluids with hypotonic fluids
- Determine if renal or extrarenal if sodium concentration is high (>20) or low (<20) respectively
Hypo/Hypo/Hypo Treatment
- Restore vital organ perfusion
- Decrease fluid losses: hold diuretics and administer antiemetics
- Replace sodium/volume loss with crystalloid (20 mL/kg and infuse rapidly)
- Monitor for symptom resolutions and [sodium]
Hypervolemic Hypotonic Hyponatremia
- Excess total body Na+ and ECF, ECF > Na+
- Causes: CHF, cirrhosis, less “effective” circulating plasma volume
- Presentation: acute weight gain, pulmonary congestion, edema,
- *Usually no severe symptoms from hypo-osmolality**
Hyper/Hypo/Hypo Treatment
- Restrict salt and water
- Fluid restrict to 1-1.2 L/day
- Sodium restriction to 1-2g/day
- May use loop diuretics to remove water
Euvolemic Hypotonic Hyponatremia
- Excess total body water, minimal change in ECF and normal total body Na
- Hypotonicity symptoms: cerebral cellular swelling, vomiting, confusion, agitation
- If Na < 120: seizures, coma, death
- Symptom severity related to decrease and rate of hyponatremia
- Causes: SiADH or excessive free water intake
SiADH
- Syndrome of Inappropriate ADH
- Release ADH or ADH-life substance to reabsorb inappropriate free water
- Appear euvolemic, minimal free water excretion => decreased, concentrated urine
- Exclude hypocortisolism, renal failure, and hypothyroidism to diagnose