Surgical Physiology

Question 1

total body water (TBW) & distribution

Answer 1

*TBW varies from 45-70%, depending on age/gender/diseases/IV fluids
*distributed into several compartments:
1. extracellular compartment (40% TBW):
1a. intravascular/plasma space (25% of extracelluar)
1b. extravascular/interstitial space (75% of extracellular)
2. intracellular compartment (60% TBW)

Question 2

extracellular vs. intracellular water electrolyte composition

Answer 2

*extracellular water: primarily sodium, chloride, bicarbonate
*intracellular water: primarily potassium, organic phosphate, and sulfate

recall: salty banana = sodium outside, potassium inside

Question 3

fluid maintenance requirements - in a healthy adult

Answer 3

approximately 30 mL/kg body weight/24 hours

Question 4

fluid maintenance requirements after volume resuscitation

Answer 4

4-2-1 formula:
4 mL/kg for the first 10 kg body weight
2 mL/kg for the second 10 kg body weight
1 mL/kg for all additional weight

Question 5

hypernatremia - clinical manifestations

Answer 5

*thirst, restlessness, irritability, ataxia, altered mental status
*commonly seen in free water deficit (diabetes insipidus, significant renal conditions)

Question 6

hyponatremia - clinical manifestations

Answer 6

*headache, delirium, nausea, malaise, lethargy, confusion; if more severe, acute seizures & coma

Question 7

hypokalemia - clinical manifestations

Answer 7

*if severe ( < 3.0): fatiuge, weakness, cramps, constipation, ileus
*EKG changes: flat T-waves, ST depression, appearance of U waves
*may occur as a result of isotonic fluid loss (SIADH, adrenal insufficiency, hyperglycemia)
*increased K+ loss can result from emesis, diarrhea, diuretic use, DI, and metabolic alkalosis

Question 8

hyperkalemia - clinical manifestations

Answer 8

*if severe: weakness, flaccid paralysis
*EKG changes: peaked T-waves, prolonged PR and QRS intervals
*can result from any catabolic state (trauma, burns, prolonged illness, hemolysis, renal failure, adrenal insufficiency)

Question 9

treatment of hyperkalemia

Answer 9

*varies based on rapidity of rise of serum K+ and underlying cause
1. IV glucose + IV regular insulin (shifts K+ intracellularly)
2. sodium bicarb (corrects metabolic acidosis)
3. calcium gluconate (stabilizes the cardiac membrane)

Question 10

acid-base status and serum potassim

Answer 10

*alkalosis→ shifts K+ into cells
*acidosis → shifts K+ out of cells

Question 11

hypercalcemia - clinical manifestations

Answer 11

*chronic/classically: nephrolithiasis (stones), pathologic fractures (bones), moans, groans
*EKG changes: short QT interval
*if severe ( > 12) and acute: weakness, confusion, vomiting, anorexia, abd pain, polyuria
*common causes include hyperparathyroidism, cancer, hyperthyroidism, renal insufficiency, and prolonged immobilization

Question 12

hypocalcemia - clinical manifestations

Answer 12

*confusion, seizures, carpopedal spasm, perioral paresthesias, tetany, Trousseau sign (inflating BP cuff causes carpopedal spasm), Chvostek sign (tapping facial nerve causes face twitches)
*EKG changes: QT prolongation with severe deficits
*common causes include hypoparathyroidism, pancreatitis, severe trauma/crush injuries, nec fasc, and severe renal failure

Question 13

hypermagnesemia - clinical manifestations

Answer 13

*occur when mag > 4
*hyporeflexia, weakness, lethargy, paralysis, ileus, respiratory failure
*EKG changes: prolonged PR, QRS, and QT intervals

Question 14

hypomagnesemia - clinical manifestations

Answer 14

*occur with levels < 1.2
*confusion, tetany, seizures
*EKG changes: prolonged PR and QT intervals, wide QRS, presence of U waves, Torsades de pointes

Question 15

hyperphosphatemia - clinical manifestations

Answer 15

*s/s attributable to hypocalcemia (confusion, seizures, spasms, etc)
*common causes include severe crush injury, muscle breakdown, and severe renal failure

Question 16

hypophosphatemia - clinical manifestations

Answer 16

*if severe ( < 1): weakness, impaired diaphragmatic function, ileus, confusion, stupor
*common causes include hyperparathyroidism and malnourishment (eg. alcoholics)

Question 17

expected compensations in metabolic acid-base disorders

Answer 17

*metabolic acidosis: PCO2 expected to decrease 1.2 mmHg for every 1 decrease in HCO3
*metabolic alkalosis: PCO2 expected to increase 0.7 for every 1 increase in HCO3

Question 18

solute concentrations of normal saline (0.9%)

Answer 18

Na+: 154
Cl+: 154
K+:
HCO3-:
Ca+:
Glucose:

Question 19

solute concentrations of lactated ringers (LR)

Answer 19

Na+: 130
Cl+: 1-9
K+: 4
HCO3-: 28
Ca+: 2.7
Glucose:

Question 20

solute concentrations of D5 1/2 NS

Answer 20

Na+: 77
Cl+: 77
K+:
HCO3-:
Ca+:
Glucose: 50

Question 21

solute concentrations of D5 1/2 NS + 20 KCl

Answer 21

Na+: 77
Cl+: 97
K+: 20
HCO3-:
Ca+:
Glucose: 50

Question 22

normal saline (0.9%) crystalloid fluid

Answer 22

*ubiquitously used for dehydration and hypovolemia
*considered an “isotonic fluid”
*concentration of NaCl is higher than found in humans
*typically the first-line fluid used in trauma resuscitations, head injuries, acute neurologic conditions where hyponatremia should be avoided

Question 23

lactated ringers (LR) crystalloid fluid

Answer 23

*commonly used for resuscitation
*more isotonic than NS, with less NaCl
*widely used with equal efficacy as NS in most circumstances
*advantages: more physiologic levels of sodium & chloride
*considerations: think before using in pts with hyperkalemia or renal dysfunction

Question 24

D5 1/2 NS (5% dextrose in 1/2 normal saline)

Answer 24

*a common IV fluid used for maintaining fluid balance & providing calories
*a combination of 5% dextrose in 0.45% NaCl
*dextrose helps decrease hypotonicity and provides caloric content, stimulating insulin release and preventing protein catabolism

Question 25

D5 1/2 NS + 20 KCl (5% dextrose in 1/2 NS with 20 mEq of KCl)

Answer 25

*addition of KCl results in an almost isotonic solution with solute concentrations approach that of stomach fluid

Question 26

hypertonic saline

Answer 26

*solutions range from 2% to > 23% *can be used to treat pts with head injury, hypovolemic shock, spontaneous subarachnoid hemorrhage, or refractory hyponatremia *advantages: volume expansion, reduction of cerebral edema via osmotic effects, scavenging of oxygen free radicals *use with caution

Question 27

hemostasis - review of steps

Answer 27

1. vasoconstriction 2. platelet aggregation 3. coagulation 4. fibrinolysis

Question 28

prothrombin time (PT)

Answer 28

*measures the EXTRINSIC factors that lead to clotting (esp. factors II, V, VII, or XI) *also used as a surrogate to reflect the function of the liver (INR) *more affected by warfarin / vitamin K

Question 29

partial thromboplastin time (PTT)

Answer 29

*measures the function of the INTRINSIC factors that lead to clotting (esp. factors VIII, IX, XI, or XII) *more affected by heparin *elevated in pts with hemophilia

Question 30

heparin

Answer 30

*anticoagulant agent *accelerates the effects of **antithrombin III** → a systemically anticoagulated state *the heparin-antithrombin III-complex inactivates several factors in the coag cascade, esp. **thrombin & factor X** *level of anticoagulation cnan be measured by checking the PTT

Question 31

low-molecular-weight-heparin (LMWH)

Answer 31

*acts primarily by **inhibiting factor Xa** *does not prolong PTT

Question 32

warfarin

Answer 32

*leads to a deficiency of vitamin K, leading to a **decrease in production by the liver of factors II, VII, IX, and X; proteins C and S** *level of anticoagulation is measured by checking the PT/INR

Question 33

acute hemolytic transfusion reaction

Answer 33

*a life-threatening reaction that occurs during or within 24h of a blood transfusion *mechanism: ABO incompatibility *caused by the recipient's antibodies attacking and destroying the donor RBCs *common sx: anxiety, chest pain, chills, flank pain, headaches *tx: stop transfusion, alert blood bank, ensure adequate hydration and diuresis