basic fluids and electrolytes douglas p. slakey. why listen to this? essential for surgeons based...
TRANSCRIPT
Why Listen to This?• Essential for surgeons• Based upon physiology
– Disturbances understood as pathophysiology
Most abnormalities are relatively simple, and many iatrogenic
It’s All About Balance
• Gains and Losses– Losses
• Sensible and Insensible
• Typical adult, typical day– Skin 600 ml
– Lungs 400 ml
– Kidneys 1500 ml
– Feces 100 ml
• Balance can be dramatically impacted by illness and medical care
Fluid Compartments
• Total Body Water– Relatively constant– Depends upon fat content and varies with age
• Men 60% (neonate 80%, 70 year old 45%)
• Women 50%
TOTAL BODY WATERTOTAL BODY WATER60% BODY WEIGHT60% BODY WEIGHT
ICF
2/3
Predominant solute
K+
ECF
1/3
Predominant solute
Na+
HH22OO
(mEq/L) Plasma IntracellularNa 140 12K 4 150Ca 5 0.0000001Mg 2 7Cl 103 3
HCO3 24 10Protein 16 40
Electrolytes
Fluid Movement
• Is a continuous process• Diffusion
– Solutes move from high to low concentration
• Osmosis– Fluid moves from low to high solute concentration.
• Active Transport– Solutes kept in high concentration compartment– Requires ATP
Movement of Water• Osmotic activity
– Most important factor– Determined by concentration of solutes
Plasma (mOsm/L)
2 X Na + Glc + BUN
18 2.8
Third Space
• Abnormal shifts of fluid into tissues
• Not readily exchangeable
• Etiologies– Tissue trauma– Burns– Sepsis
Fluid Status• Blood pressure
• Check for orthostatic changes
• Physical exam
• Invasive monitoring– Arterial line– CVP– PA catheter– Foley
Fluid Imbalances
• Must assess organ function– Renal failure– Heart failure– Respiratory failure• Excessive GI fluid losses• Burns
Volume Deficit
• Most common surgical disorder• Signs and symptoms
– CNS: sleepiness, apathy, reflexes, coma– GI: anorexia, N/V, ileus– CV: orthostatic hypotension, tachycardia with
peripheral pulses– Skin: turgor– Metabolic: temperature
Dehydration
Chronic Volume Depletion
Affects all fluid components
Solutes become concentrated
Increased osmolarity
Hct can increase 6-8 pts for 1 L deficit
Patients at risk:
Cannot respond to thirst stimuli
Diabetes insipidus
Treatment: typically low Na fluids
HypovolemiaAcute Volume Depletion
Isotonic fluid loss, from extracellular compartmentDetermine etiology
Hemorrhage, NG, fistulas, aggressive diuretic therapyThird space shifting, burns, crush injuries, ascites
Replace with blood/isotonic fluid» Appropriate monitoring
» Physical Exam» Foley (u/o > 0.5 ml/kg/min)» Hemodynamic monitoring
Fluid Replacement
• Isotonic/physiologic– NS, LR
• Less concentrated– 0.45NS, 0.2NS– Maintenance
• Hypertonic Na
Fluid Replacement
• Plasma Expanders– For special situations– Will increase oncotic pressure– If abnormal microvasculature, will extravasate
into “third space”Then may take a long time to return to circulation
Fluid Replacement
• Maintenance– 4,2,1 “rule”
• Other losses (fistulas, NG, etc)– Can measure volume and composition!!!– Should be thoughtfully assessed and
prescribed separately if pathologic
Maintenance Fluid
• Daily Na requirement: 1 to 2 mEq/kg/day
• Daily K requirement: 0.5 to 1 mEq/kg/day
• AHA Recommended Na intake: 4 to 6 grams per day
How much Sodium is Enough???
» NS» 0.9% = 9 grams Na per liter
» 0.45 NS = 4.5 grams per liter» 125 ml/hour = 3000 ml in 24 hours» 3 liters X 4.5 grams Na = 13.5 GRAMS Na!
(If 0.2 NS: 3 liters X 2 grams Na = 6 grams Na)
Assessment of Disorders of Volume
and Electrolytes• Effects are variable and complex
• Simplified treatment algorithms cannot address the variable and complex nature of these disorders
• Acid - Base balance is integral with these disorders
Hyponatremia• Na loss
– True loss of Na– Dilutional (water excess)– Inadequate Na intake
• Classified by extracellular volume– Hyovolemic (hyponatremia)
• Diuretics, renal, NG, burns
– Isotonic (hyponatremia)• Liver failure, heart failure, excessive hypotonic IVF
– Hypervolemic (hyponatremia)• Glucocorticoid deficiency, hypothyroidism
Na Volume
Check Ur Na
< 10 mmol/L
VomitingDiarrhea3rd spaceHepatorenal
Adrenal InsufficiencyDiureticsSalt-Wasting SyndromeSIADH
> 20 mmol/L
SIADH• Causes
– Cancers (pancreas, oat cell)– CNS (trauma, stroke)– Pulmonary (tumors, asthma, COPD)– Surgical stress– Medications
• Anticonvulsants, antineoplastics, antipsychotics, sedatives (morphine)
SIADHToo much ADH
Affects renal tubule permeability
Increases water retention (ECF volume) Increased plasma volume, dilutional hyponatremia,
decreases aldosterone, increased GFR
Increased Na excretion (Ur Na >40mEq/L)
Fluid shifts into cellsSymptoms: thirst, dyspnea, vomiting, abdominal cramps,
confusion, lethargy
SIADH Treatment
• Fluid restriction– Will not responded to fluid challenge
(distinguishes from pre-renal cause)
• Possibly diuretics
Hypovolemia and Metabolic Abnormality
• Acidosis– May result from decreased perfusion
• Alkalosis– Complex physiologic response to more chronic
volume depletion
Hypernatremia
Relatively too little H2O
– Free water loss (burns, fever)– Diabetes insipidus (head trauma, surgery,
infections, neoplasm)• Dilute urine
– Nephrogenic DI• Kidney cannot respond to ADH
Hypernatremia
• Hypovolemic– GI loss, osmotic diuresis– Increased Na load (usually iatrogenic)
[0.6 X wt (kg)] X [Serum Na/140 - 1]
Free water deficit:
Hypernatremia Volume Replacement
• Example:
• Na 153, 75 kg person
• (0.6 X 75) X [(153/140) - 1]
• 45 X [1.093 -1]
• 45 X 0.093 = 4.2 Liters
Potassium
• 98% intracellular• 20 to 40 mEq/L of urine
– Kidneys cannot retain K
• Dietary sources– Chocolate, dried fruits, nuts– Fruits: oranges, bananas, apricots– Meats– Potatoes, mushrooms, tomatoes, carrots
Potassium and Ph
• Acidosis– Extracellular H+ increases, moves intracellular
forcing K+ extracellular
• Alkalosis– Intracellular H+ decreases, to keep intracellular
fluid neutral, K+ moves into cells
Hyperkalemia
• Associated medications– ACE inhibitors, beta-blockers, antibiotics,
chemotherapy, NSAIDS, spironolactone
• Treatment– Mild: dietary restriction, assess medications– Moderate: Kayexalate
• Do NOT use sorbitol enema in renal failure patients
Hyperkalemia
• Emergency (> 6 mEq/l)
• Treatment– Monitor ECG, VS– Calcium gluconate IV– Insulin and glucose IV– Kayexalate, Lasix + IVF, dialysis