Fluid overload. Hansen. 2021. Frontiers Flashcards
What is the definition of fluid overload in terms of body weight gain?
5-10% body weight gain
What is the definition of hypervolemia?
Hypervolemia is the state of excessive blood volume and increased mean circulatory filling pressure
What is the mean circulatory filling pressure (MCFP)?
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
What is the MCFP most similar to?
post-capillary venule pressure
What is the driving force for blood flowing back to the heart?
pressure gradient between post-capillary venule pressure (i.e., MCFP) and right atrial pressure (i.e., central venous pressure)
How does IV fluid therapy increase CO?
intravenous fluid administration will increase the pressure gradient between peripheral veins and RA pressure –> increased blood flowing back to heart –> increased preload –> increased CO
How can IV fluid administration lead to edema?
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
Name 4 conditions leading to water retention/impaired water excretion
- heart disease
- kidney disease
- liver disease
- excessive AVP (vasopressin) secretion
How can sepsis or tissue injury from trauma lead to water retention?
increased levels of interleukin-6 lead to excessive AVP secretion
How does inflammation promote edema formation?
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
how is interstitial fluid accumulation self-exacerbating?
tissue weight increase > 10-20% causes further increase of compliance of interstitium –> even larger volumes can accumulate
maintains edema once it has begun
what are the 3 main ways in which systemic inflammation (E.g., sepsis/sirs) causes fluid overload?
- increased vasopressin release (mediated by interleukin-6)
- breakdown/damage of interstitial matrix
- decreased albumin (e.g., acute-phase response, dilution from fluid therapy)
how does an increase in extravascular water impair the lungs?
- impairs gas exchange
- decreased lung compliance
- increased work of breathing
how does fluid overload in the systemic circulation impair organs?
- decreased oxygen diffusion and energy substrate delivery
- obstructs capillary blood flow and lymphatic drainage
- disrupts organ structure/architecture
- impairs cell-to-cell interaction
which organs are the most sensitive to fluid overload?
- lungs
- organs in rigid structures or capsules (brain, kidneys, liver)