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88 Cards in this Set
- Front
- Back
What is the effective circulating volume?
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is that portion of the ECF that is contained in the vascular space and is effectively perfusing the tissues
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Is effective circulating volume a measurable entity? it refers to?
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no, but rather refers to the rate of perfusion of the capillaries
-ie, the sites of exchange between blood and tissue cells |
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In general, the effective circulating volume varies directly with?
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the ECF volume in normal subjects
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Is some disease states, the effective circulating volume and ECF may be?
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dissociated
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In congestive heart failure patients, the effective circulating volume is?
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reduced, due to a primary decrease in CO
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What compensatory mechanisms occur in CHF patients with a decreased effective circulating volume?
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sodium and water retention by the kidney leads to an increase in ECF (and plasma) volume
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Maintenance of effective circulating volume is essential for?
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delivery of adequate oxygen and energy substrates to tissues, and for removal of C02 and metabolic end-products
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Maintenance of effective circulating volume is closely linked to regulation of?
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sodium balance
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Sodium loading (retention) leads to?
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volume expansion
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Sodium loss leads to?
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volume depletion
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What are the two steps in response to variations in effective circulating volume?
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1. Volume change is sensed by multiple receptors
2. Activation of effector mechanisms that act together to restore normovolemia |
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What is the location of the primary receptors? 3
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1. carotid sinus and aortic arch (baroreceptors)
2. atria of the heart 3. afferent arterioles in the kidney (JG cells) |
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What variable are the volume receptors actually sensing?
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pressure (stretch)
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Pressure and volume are usually ________ related.
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directly
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The rate of discharge of the stretch-sensitive nerve endings in the carotid sinuses and aortic arch are proportional to?
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the degree of stretch
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Afferent activity from the receptors in the carotid sinuses and aortic arch is directed to?
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the vasomotor centers in the medulla and to the paraventricular nuclei (ADH secretion) in the hypothalamus
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What does volume depletion do to activity of the stretch receptors in the carotid sinuses and aortic arch?
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tends to decrease stretch and afferent activity directed to the brain which causes a reflex increase in both vasomotor center output and ADH secretion
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What does volume expansion cause?
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increased pressure, increased afferent activity and reflex decrease in vasomotor output and ADH secretion
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Atrial stretch receptors detect?
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the degree of atrial filling
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Volume expansion has what effect on atrial stretch receptors?
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increases filling and stretch, reflex decrease in ADH secretion and release of ANP into the circulation
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Volume depletion has what effect on the atrial stretch receptors?
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decrease filling and stretch, reflex increase in ADH secretion and decreased release of ANP into the circulation
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Renin secretion from JG cells of afferent arteriole is _______ related to?
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inversely, the degree of stretch of the arteriolar wall
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What does volume depletion do to afferent arteriole stretch?
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reduces stretch which increases renin secretion and increases angiotensin II production and aldosterone release
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What does volume expansion do to renin secretion?
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suppresses it
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What 3 effector mechanisms are involved in volume regulation?
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1. SNS
2. RAS 3. Renal sodium excretion |
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SNS outflow from the medulla vasomotor centers is regulated, in part, by?
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input from peripheral baroreceptors (inverse relationship)
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What is the response of the SNS to decreased effective circulating volume?
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Decreased venous return, CO, BP, baroreceptor stimulation, increased sympathetic tone
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Pharmacologic blockade of SNS in hypovolemic patients can cause?
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marked hypotension
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Volume expansion reduces?
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sympathetic output from vasomotor centers to minimize changes in CO and BP, and to facilitate sodium excretion
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Secretion of renin from JG cells of afferent arteriole is influenced by?
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sympathetic nervous system activity - direct relationship (beta-1 adrenergic receptors)
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Degree of stretch of afferent arteriole is?
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independent of SNS input, inverse relationship
-myogenic response |
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What converts angiotensin I to II?
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ACE
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Angiotensin II is a potent?
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vasoconstrictor
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Angiotensin II stimulates secretion of? which promotes?
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aldosterone from the adrenal cortex which promotes sodium reabsorption in principal cells of the CCT AND stimulates sodium reabsorption in PCT
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When are renin secretion and angiotensin II formation enhanced?
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in hypovolemic states such as sodium restriction/loss, hemorrhage, or decompensated heart failure
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If you were to administer a pharmacologic blockade of the renin-angiotensin system in hypovolemic states would would happen?
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marked hypotension
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Renal sodium excretion varies directly with?
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effective circulating volume
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Volume expansion causes?
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increased sodium excretion
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Volume depletion causes?
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decreased sodium excretion (urine can be virtually sodium free)
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Adjustments in sodium excretion are due primarily to?
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adjustments in sodium reabsorption by the tubules
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What are factors that affect sodium reabsorption? 3
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1. aldosterone
2. atrial natriuretic peptide 3. filtration fraction (FF) |
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Aldosterone promotes?
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sodium reabsorption in CCT
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ANP inhibits?
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sodium reabsorption in MCT
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Increased FF does what?
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enhances proximal tubular sodium reabsorption; decreased FF has opposite effect
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ECF volume determined by?
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absolute amounts of sodium and water present
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ECF osmolality determined by the ratio of?
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solutes (primarily sodium salts) to water
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Sweating leads to loss of hypoosmotic fluid which causes a?
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rise in Posm and fall in ECF volume
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Infusion of isotonic saline causes a?
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rise in ECF volume but no change in Posm
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So ECF volume and ECF osmolality can?
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vary independently
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Osmoregulation is achieved by?
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regulation of water balance; sodium is not directly affected unless there are concurrent changes in ECF volume
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Volume regulation is achieved primarily by?
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regulation of sodium excretion; the hypovolemic stimulus for ADH secretion, however, also promotes water retention to help restore normovolemia
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Crystalloid solutions contain?
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water and electrolytes; no colloids
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What is the replacement of blood loss ratio?
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3:1 to 4:1, 3-4mL of crystalloid solution per mL of blood loss
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what is the intravascular "half-life" of crystalloid solutions?
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20-30 min
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Balanced solutions have an?
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electrolyte composition similiar to that of ECF
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Lactated ringers solution
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most physiological replacement fluid, though slightly hypotonic (273mosm/kg H20)
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LR contains?
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lactate, which is converted to bicarbonate
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What are other examples of balanced solutions?
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PlasmaLyte and Normosol-R
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Normal saline is what type of solution?
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isotonic and isosmotic solution
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Normal saline has a?
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chloride concentration that is higher than that of ECF
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NS administered in large amounts can cause?
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hyperchloremic (non-anion gap) metabolic acidosis
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NS is the preferred replacement fluid (over LR) in patients with?
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brain injury, hyperkalemia, or hypochloremic metabolic alkalosis
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What is the preferred solution for dilution of packed RBCs prior to transfusion?
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NS
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Hypertonic saline solutions
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3% may be used for treatment of severe, symptomatic hyponatremia
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What solutions have been used for treatment of hypovolemic shock?
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3%-7.5% saline
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5% dextrose in water (D5W) is a?
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hypotonic solution (253 mosm/kg H20)
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D5W is used to provide?
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free water, as the dextrose (glucose) is metabolized, but does not cause hemolysis
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Why is D5W most commonly used?
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used to provide glucose and prevent hypoglycemia in diabetic patients who have been administered insulin
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D5W may also be used to treat?
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hypernatremia
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What is the replacement ratio for colloid solutions?
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1:1
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What is the intravascular "half-time" of colloid solutions?
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much longer than that of crystalloids
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What is Plasmanate composition?
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5% albumin, 5% plasma protein fraction
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What is the colloid osmotic pressure of Plasmanate?
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20 mmHg
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The preparation of Plasmanate involves?
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heating to destroy infectious agents
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Plasmanate is appropriate for treating?
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conditions with large protein losses eg, peritonitis, burns
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Dextran solutions are?
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water-soluble glucose polymers
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Dextran 70 (Macrodex) has an average polymer MW of?
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70,000
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6% dextran 70 expands the vascular volume the same as?
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5% albumin
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Dextran 40 (Rheomacrodex) has an average MW of?
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40,000
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Dextran 40 is not used to?
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expand plasma volume; used in vascular surgery to reduce blood viscosity, improve microcirculatory blood flow, and prevent thrombosis
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Dextrans have?
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antiplatelet activity and can increase bleeding time
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Dextrans may cause?
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anaphylactic or anaphylactoid reactions
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Dextran polymers are enzymatically degraded to?
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glucose
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Hydroxyethyl starch is a?
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synthetic colloid- very effective plasma volume expander; less expensive than albumin and nonantigenic
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Hespan is 6% hydroxyethyl starch in?
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NS
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Hextend is 6% hydroxyethyl starch in?
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solution that contains electrolytes, glucose, and lactate; the polymer molecules are smaller than those of Hespan
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Hetastarch preparations may interfere with?
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clotting and raise PTT - more likely with Hespan
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Pentastarch contains?
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smaller hydroxyethyl starch molecules
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