Fluid overload. Hansen. 2021. Frontiers

Question 1

What is the definition of fluid overload in terms of body weight gain?

Answer 1

5-10% body weight gain

Question 2

What is the definition of hypervolemia?

Answer 2

Hypervolemia is the state of excessive blood volume and increased mean circulatory filling pressure

Question 3

What is the mean circulatory filling pressure (MCFP)?

Answer 3

Mean circulatory filling pressure is defined as the average transmural pressure of the circulatory system when the heart and blood flow is stopped, and it is determined by blood volume and autonomic control of vascular smooth muscle

Question 4

What is the MCFP most similar to?

Answer 4

post-capillary venule pressure

Question 5

What is the driving force for blood flowing back to the heart?

Answer 5

pressure gradient between post-capillary venule pressure (i.e., MCFP) and right atrial pressure (i.e., central venous pressure)

Question 6

How does IV fluid therapy increase CO?

Answer 6

intravenous fluid administration will increase the pressure gradient between peripheral veins and RA pressure –> increased blood flowing back to heart –> increased preload –> increased CO

Question 7

How can IV fluid administration lead to edema?

Answer 7

increased venous/venule pressure –> will require higher capillary pressure to achieve forward flow of blood –> increased capillary pressure favor movement of fluid from capillary into interstitial space

Question 8

Name 4 conditions leading to water retention/impaired water excretion

Answer 8

1. heart disease
2. kidney disease
3. liver disease
4. excessive AVP (vasopressin) secretion

Question 9

How can sepsis or tissue injury from trauma lead to water retention?

Answer 9

increased levels of interleukin-6 lead to excessive AVP secretion

Question 10

How does inflammation promote edema formation?

Answer 10

inflammation –> disruption of collagen fibrils (responsible for interstitial matrix) –> increased compliance of the interstitial compartment –> reduction of interstitial fluid pressure
inflammation: break down of integrin links of cells to collagen and breakdown of cytoskeleton –> loosening the matrix –> decreased interstitial fluid pressure –> favors fluid movement from capillary into interstitium

Question 11

how is interstitial fluid accumulation self-exacerbating?

Answer 11

tissue weight increase > 10-20% causes further increase of compliance of interstitium –> even larger volumes can accumulate
maintains edema once it has begun

Question 12

what are the 3 main ways in which systemic inflammation (E.g., sepsis/sirs) causes fluid overload?

Answer 12

• increased vasopressin release (mediated by interleukin-6)
• breakdown/damage of interstitial matrix
• decreased albumin (e.g., acute-phase response, dilution from fluid therapy)

Question 13

how does an increase in extravascular water impair the lungs?

Answer 13

• impairs gas exchange
• decreased lung compliance
• increased work of breathing

Question 14

how does fluid overload in the systemic circulation impair organs?

Answer 14

• decreased oxygen diffusion and energy substrate delivery
• obstructs capillary blood flow and lymphatic drainage
• disrupts organ structure/architecture
• impairs cell-to-cell interaction

Question 15

which organs are the most sensitive to fluid overload?

Answer 15

• lungs

- organs in rigid structures or capsules (brain, kidneys, liver)

Question 16

what is more harmful, an excess in extracellular or intracellular fluid volume? what proved this

Answer 16

extracellular fluid overload is more harmful
changes in sodium (key determinant of extracellular fluid volume) correlates better with respiratory dysfunction than fluid balance

Question 17

what are the 2 ultrasound techniques used to predict fluid-responsiveness of patients? which one is “better”?

Answer 17

• assessment of caudal vena cava collapsibility
• comparison of CVC diameter to that of the intraabdominal aorta
• the latter is more sensitive and specific

Question 18

What is a main issue of most studies investigating the fluid responsiveness of septic patients and their conclusions on indications to give fluids or not?

Answer 18

• most of these studies only evaluate fluid responsiveness within the first few minutes of treatment
• increase in CO from fluid administration in septic patients has shown to fade within 20 min in half of the patients
• we don’t know if the transient increase in CO is worth the then developing tissue edema

Question 19

what are the 4 stages of fluid therapy in the critically ill?

Answer 19

1. rescue
2. optimization
3. stabilization
4. de-escalation

Question 20

Administering albumin solutions instead of crystalloid solutions in critically ill humans has shown little improvement in most outcome measures. What are benefits that argue for administration of CSA or plasma?

Answer 20

• these patients generally require less total fluids for resuscitation and optimization
• may have a lower tendency to develop fluid overload