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General Surgery 1 > Fluids > Flashcards

Fluids Flashcards

1
Q

Fluids

A
  • Fluids mean water
  • Water composes around 50-70% of lean body weight.
  • Slightly higher in men.
  • Most concentrated in skeletal muscle.
  • A newborn is 95% water.
  • An elderly person is about 40% water.
  • In obese people, water is a smaller percentage of body weight as well.
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2
Q

Electrolytes

A
  • Means salt
  • Salts (e.g., NaCl) dissociate in water.
  • They become minerals with an electric charge, also known as electrolytes.
  • Cations: Na+, K+, Mg+, Ca2+
  • Anions: Cl-, HCO3-, PO43- (and other phosphates), and negatively charged proteins.
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3
Q

Electrolytes in fluid

A
  • Osmolality: Concentration of a solution expressed as the total number of solute particles per kilogram.
  • Osmolarity: Concentration of a solution expressed as the total number of solute particles per liter.
  • Because a liter of H2O weighs one kilogram, these two terms are sometimes used interchangeably.
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4
Q

Molecular diffusion

A
  • the spontaneous movement of molecules from areas of high concentration to areas of low concentration.
  • If you have two solutions of different concentrations that are separated by a semipermeable membrane, the tendency of those solutions to equalize their concentration by moving across the membrane is called the osmotic pressure gradient.
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5
Q

How is the rate of osmosis influenced

A
  • The rate of osmosis is influenced by many factors:
    • The concentration of each solution (the greater the difference, the greater the osmotic pull).
    • Temperature.
    • Surface area to volume ratio.
    • The permeability of the membrane (if more permeable, water will diffuse faster then solutes).
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6
Q

Two types of solutes

A
  • There are two kinds of solutes (aka osmoles):
    • Effective osmoles, which DO NOT freely move across a membrane (e.g., electrolytes).
    • Ineffective osmoles, which DO freely move (e.g., urea, ethanol, methanol).
  • The concentration of a solution, minus ineffective osmoles, is called tonicity.
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7
Q

three types of tonicity

A
  • Isotonic (270-300 mOsm/L): no osmotic activity.
  • Hypertonic (>300 mOsml/L): pulls fluid from cell.
  • Hypotonic (<270 mOsm/L): fluid goes into cell.
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8
Q

intracellular fluid vs extracellular fluid

A
  • Intracellular fluid (ICF): water contained within cell membranes. [~30L, ~40% of body weight]
  • Extracellular fluid (ECF): water contained outside cell membranes. [~14L, ~20% of body weight]
    • Interstitial [~9L, ~15% of body weight]
    • Intravascular [~5L, ~5% of body weight]
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9
Q

composition of fluids

A
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10
Q

where do our fluids come from

A
  • We drink them!
  • Around 2 liters a day
  • (1.3L water, 0.7L food)
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11
Q

where do our fluids go?

A
  • 800-1500ml in urine
  • 0-250ml in stool
  • 600-900ml through skin and lungs
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12
Q

what makes us thirsty

A
  • In the hypothalamus, osmoreceptors trigger thirst when ECF is hypertonic (i.e, we’ve lost water but held on to our electrolytes).
  • The renin-angiotensin system triggers thirst with baroreceptors in response to hypovolemia.
  • Oropharyngeal dryness
  • Psychological factors
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13
Q

Fluid deficits

A
  • Decreased intake
    • Decreased thirst
    • Depressed level of consciousness
    • Malnutrition
  • Increased fluid loss
    • GI: vomiting, diarrhea
    • Renal: diuresis
    • Vascular: hemorrhage
    • Skin: burns, fever
    • Lungs: tachypnea, mechanical ventilation
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14
Q

fluid overload

A
  • Heart failure
  • Liver failure
  • Renal failure
  • Iatrogenic
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15
Q

Cholera

A
  • An infection of the small intestine by Vibrio cholerae.
  • Vomiting and watery diarrhea (losing 10 to 20 liters a day).
  • Mortality in untreated patients is 50-60%.
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16
Q

second asiatic cholera pandemic (1827-1835)

A
  • Starts in India, spreads to Russia by 1829, spreads to England by 1831, spreads to the United States by 1832.
  • Millions die.
  • Thought to be a blood disorder, and so is treated by blood letting, with abysmal results.
  • In 1831, a Scottish physician named O’Shaughnessy recognizes that dehydration and “universal stagnation” of blood flow is the primary pathology.
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17
Q

The first IV

A
  • In 1832, a colleague of O’Shaughnessy’s, Dr. Thomas Latta, injects 6 pints of fluid into a sick, elderly woman. Her clinical improvement is swift and dramatic, but she relapses and dies several hours later.
  • In 1833, Latta successfully resuscitates a critically ill 52-year-old woman with 330ml of fluid over 12 hours. He treats 25 patients with this therapy, and reports a 33% survival rate.
18
Q

the colloidal solution

A
  • In 1834, Dr. John Mackintosh comments that “it would be advisable to make the fluid resemble as much as possible the serum of blood, by adding albumin obtained from egg.”
  • Perhaps because of this, IV infusions of milk became standard practice. The first attempts are by Drs. Bovell and Hodder using cows milk, with 5 out of 7 patients dying. Goat—and later human—milk is used, until 1884, when saline infusions are demonstrated to be more beneficial than milk infusions.
19
Q

the most beneficial solution

A
  • In 1876, Dr. Sydney Ringer, a clinical pharmacologist, introduces Ringer’s solution, a solution containing 8gm NaCl, 0.3gm KCl, and 0.33gm CaCl in one liter of distilled water.
  • Thirty-five years later, an American pediatrician named Alexis Hartmann added lactate to the recipe, creating “lactated Ringer’s solution.”
  • Resuscitation = loading someone up with fluids – any event other than maintenance fluids
20
Q

blood transfusions

A
  • In 1849, after a study demonstrated that blood transfusions had a mortality rate of 30%, the procedure was deemed a success.
  • Landsteiner discovers three of the four blood groups in 1901, Jansky discovers the fourth in 1907.
  • Blood transfusions save countless soldiers’ lives in World War I.
  • The first blood bank is established in Leningrad in 1932.
21
Q

technology breakthroughs

A
  • In 1950, Dr. Carl Walter introduces the plastic bag as a new vessel for collecting blood (and, by extension, for delivering intravenous fluids).
  • Also in 1950, Dr. David Massa, an anesthesiology resident at the Mayo Clinic, invents the modern plastic intravenous infusion cannula, referred to as the Massa needle, or the Rochester plastic needle (after Rochester, Minnesota, home of the Mayo Clinic).
  • Finally, routine IV therapy becomes possible.
22
Q

fluid and electrolytes in the surgical patient

A
  • Good fluid and electrolyte management is essential for both preoperative and postoperative patients.
  • These patients, for various reasons, will have difficulty with the maintenance of normal fluid and electrolyte equilibrium.
23
Q

Normal fluid requirements

A
  • For an average-sized adult, the daily requirement of water is about 2 to 3 liters.
  • Humans require 1500ml of water for every square meter of surface area.
  • An average adult has a surface area of about 1.7 square meters. 1.7 x 1500 = 2.55 liters a day.
  • Thus, an adult needs around 100-125 ml/hr of IV fluid to meet his or her daily fluid requirements.
24
Q

Daily fluid requirements for pediatric patients

A
25
Q

fluid requirements in elderly patients

A
  • Daily Fluid Requirements
  • 1500ml PLUS 10-15ml per kg over 20
26
Q

daily electrolyte requirements

A
  • Sodium: 1-2 mEq/kg (~140mEq)
  • Potassium: 0.5-1 mEq/kg (~70 mEq)
  • Glucose: ~500 kcal
  • Glucose provides calories vital for brain, renal, and RBC function. Also will reduce the risk of the body going into “starvation mode,” thus protecting the body’s stores of protein.
27
Q

types of crystalloid fluids

A
28
Q

crystalloids

A
  • Crystalloid fluids are aqueous solutions of mineral salts.
  • They are administered as maintenance fluids in NPO patients, used for hypovolemic resuscitation in trauma, used to maintain intravascular volume in sepsis patients, etc.
  • They are relatively cheap, and generally well tolerated.
29
Q
A
30
Q

colloids

A
  • Fluids that, in addition to mineral salts, also have large proteins. For example, albumin contains a protein that has a molecular weight of 69,000.
  • The proteins are too big to move out of the intravascular space, so they remain there and keep it hypertonic, drawing fluid from the ICF compartment.
  • Giving 250ml of albumin will achieve the same effect from infusing four liters of crystalloid. They expand plasma volume better, and are less likely than crystalloids to cause edema.
31
Q

colloids and controversy

A
  • In the 1990s, several studies showed a survival benefit for trauma patients treated with crystalloid vs colloid.
  • In 2004, the SAFE Study (n=7000) showed no difference in mortality, ICU, hospital days, or days on a ventilator between patients treated with crystalloid vs colloid. Head injury patients had a greater mortality with colloids than with crystalloid (33% vs 20%).
  • In 2010, Dr. Joachim Boldt, a leading colloid researcher, was fired from his hospital, and is now under criminal investigation for allegedly falsifying his research.
  • Both crystalloids and colloids can increase the permeability of the intravascular compartment (due to the increase in hydrostatic pressure), thus causing edema. Edema from colloids takes longer to resolve than edema from crystalloids.
  • Finally, albumin costs 65 times more than equivalent crystalloid. Starch-based colloids cost 13 times more.
32
Q

bottom line of colloids in fluid replacement therapy

A
  • Use of colloids in fluid replacement therapy is currently undergoing a dramatic reevaluation in the medical community.
  • There appear to be only a small group of patients who can benefit from administration of colloids; e.g. elderly patients who cannot tolerate high volume resuscitation, severe diarrhea with low serum albumin, nephrotic syndrome, etc.
  • Stick with crystalloids unless instructed otherwise.
33
Q

Fluid Derangements

A
  • Surgical patients are at great risk for fluid derangements intra-operatively and post-operatively.
  • Insensible losses during surgery, coupled with blood loss, can be very significant.
  • Intra-operative fluid issues are mainly dealt with by anesthesia.
  • As PAs, we get to deal with the patient post-operatively.
34
Q

Assessing fluid status

A
  • As a general rule, it is safe to assume that a patient just leaving the OR is going to be down 1 to 2 liters of fluid.
  • Review history (procedure, I & Os, PMH, pre-op weight)
  • Review BP, HR, RR, skin turgor, cap refill, lung sounds.
  • Check urine output, blood tests, CVP, chest X-ray.
35
Q

the perfect patient

A
  • Healthy and young before surgery, with no comorbidities.
  • Normotensive with regular heart rate between 60-100. CVP is between 3-8. Lungs are clear.
  • Urine output is between 50-100ml/hr.
  • Labs are within normal limits: Na+ is 135-145, K+ is 3.6-4.8, creatinine is <1.2.
36
Q

the dry patient

A
  • History of being NPO for a while, is elderly, was having diarrhea or vomiting pre-op, is diabetic, I & O’s indicate fluid deficit.
  • Low BP, tachycardia, low CVP, weighs less than pre-op by several kg, decreased skin turgor and capillary refill.
  • Urine output is less than 30ml/hr.
  • Labs: elevated Na+ and K+, elevated creatinine.
37
Q

the overloaded patient

A
  • Higher risk in people with history of heart failure, renal failure/insufficiency, elderly patients. Fluid intake is greater than recorded output.
  • Raised CVP, lung crackles, weight is above pre-op by several kg.
  • Na+ may be low.
  • Chest X-ray shows pulmonary edema.
38
Q

treating the perfect patient

A
  • If able to take PO, heplock the IV when the patient begins to eat.
  • Remove the foley.
  • Check electrolytes daily for 24 or 48 hours.
  • Monitor for signs of fluid overload or fluid deficit while in house.
39
Q

Treating the dry patient

A
  • Give an initial isotonic fluid bolus, 500-1000ml. Use smaller amounts in elderly patients.
  • Follow vital signs, urine output, blood pressure.
  • Follow labs for electrolyte abnormalities.
  • If you’re concerned about the patient’s fluid status, consider placing a foley (or keeping the current foley in) to track urine output more closely.
40
Q

treating the overloaded patient

A
  • Restrict fluid intake. If patient requires maintenance fluids, give 500ml over first 24 hours (20ml/hr).
  • Consider diuretics (e.g., Lasix) if patient has signs of pulmonary edema.
  • Follow electrolytes closely, and correct abnormalities.
  • Severe cases in the setting of renal failure may require dialysis.
41
Q

4 2 1 rule

A
  • 1st 10kg give 4ml/kg/hr
  • For 2nd 10kg give 2 ml/kg/hr
  • For the remaining kg give 1ml/kg/hr
  • Ex:
    • 30 kg pt
    • 4 x 10 = 40
    • 2 x 10 = 20
    • 1 x 10 = 10
    • 40 + 20 + 10 = 70
42
Q
A

General Surgery 1 (9 decks)

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