Fluid and Blood Flashcards
What is the importance of euvolemia?
- Euvolemia is important to ensure optimal cellular perfusion of oxygen and nutrients and to avoid peripheral interstitial oedema
Osmolality
the number of osmoles of solute per kilogram of solvent (Osm/kg)
Normal plasma osmolality is 275 – 295 mOsm/kg
2(Na) + Urea + Glucose
Osmolarity
the number of osmoles of solute per litre of solution (Osm/L)
Total body water
60%
60ml / 100ml : 600ml / 1000ml : 600ml : 1kg
Total Blood volume
60-65 ml/kg
Fluid compartments and their volumes in the body
- Total Body Water (TBW) = 60% of Body Weight (70 kg man) 42 L
- Intracellular Fluid (ICF) 2/3 of TBW 28 L
- Extracellular Fluid (ECF) 1/3 of TBW 14 L
- Interstitial Fluid 3/4 of ECF 10.5 L
- Plasma 1/4 of ECF 3 L
- Transcellular Fluid Small component (not fractional) 0.5 L
Starling forces
there is an outwardly directed hydrostatic pressure in arterial side of capillaries leading
venous side, there is an inwardly directed oncotic pressure which induces reabsorption
Glycocalyx
fuzzy-like coat of glycoproteins (carbohydrate-portion and protein-portion) that covers cell membranes of epithelial cells
Carbohydrate-portion contributes to cell-to-cell recognition, communication, and intracellular adhesion
protein-free space creates a difference in protein concentration, resulting in a colloid pressure from the inside to the outside of the vasculature
The glycocalyx binds proteins
**Glycocalyx ensures a competent barrier so that fluid doesn’t leak out unnecessarily and it covers adhesion-receptors so that it is not activated inappropriately
Damage to glycocalyx can be caused by:
- Reperfusion injury after a period of ischaemia e.g. unclamping of artery or crush injury
- Inflammation e.g. sepsis
- Trauma including surgery
- Arteriosclerosis
- Hyperglycaemia
- Hypervolaemia causes atrial natriuretic peptide to be released from the atria which causes direct enzymatic breakdown of glycocalyx
Tissue oedema will develop if:
- The oncotic (colloid osmotic) pressure decreases due to low serum protein.
- The hydrostatic pressure (Pc) increases.
- The permeability of the membrane increases as a result of capillary endothelial damage (as occurs in systemic inflammatory response syndrome)
What happens when there is damage to the glycocalyx?
In the case of a damaged glycocalyx there is shedding, and this exposes the adhesion receptors (SIRS and clotting happens inappropriately) and the barrier function is also compromised (interstitial space now opens for large proteins as well as intravascular fluid leaking = forms oedema). Once destroyed, full reconstitution of this glycocalyx takes several days.
Why is hypovolemia so dangerous?
In a hypovolemic patient: if fluid is given it will have 100% effect meaning that all of the fluid will remain intravascularly. However, in a normovolaemic patient: if fluid is given, only 40% of the fluid will remain intravascularly and 60% of the fluid will enter the interstitial space. This is the direct effect of inappropriate volume, as well as the release of ANP
it causes hypoperfusion, causing ischemia and possible lactate formation with organ failure.
What is dangerous about fluid overload?
it damages your vascular barrier and causes ARDS (which increases dead space), prolonged ileus, compartment syndrome, and inevitably prolonged hospitalization
How to maintain euvolemia
Maintenance fluids normal saline & Ringer’s lactate
Zero-balance approach to fluid management patient must maintain the same body weight postoperatively, as preoperatively (can be achieved by replacing losses and a background infusion of <2 mol/kg/hour using crystalloids (maintenance fluids)
what is Goal-directed fluid therapy:
individualised fluid management, with or without inotropes, guided by cardiovascular measures of fluid responsiveness whilst also avoiding fluid overload
1. Assess fluid status prior to surgical incision
2. When fluid is thought to be needed, you give a bolus and then reassess > crystalloids for maintenance, colloids for bolus
What is a fluid challenge?
The definitive test for fluid responsiveness
rapid infusion of 3ml/kg bolus and want to see an increase in stroke volume of at least 10%
How to interpret a fluid challenge?
Fluid responsive patients have ‘preload reserve’ and will have an increase in stroke volume (and usually CO too) when fluid is administered
The presumption is that increased cardiac output will lead to increased oxygen delivery (DO2) and increased tissue oxygenation
what are Static parameters?
indicates what is happening at some point in time, but it cannot demonstrate whether there is capacity to advance along the Frank Starling curve
trend monitoring
example of Static Parameters of measuring intravascular volume status:
Central venous pressure
Clinical endpoints:
- Blood pressure
- Heart rate
- Urine output
- Plasma lactate & arterial acidosis
- CXR (Chest X-ray)
What are dynamic parameters?
uses heart-lung interactions to predict the volume responsiveness and they are superior for indicating volume responsiveness as they use changes in preload
manifests as a swing in the a-line
Dynamic Parameters of measuring intravascular volume status:
- Stroke Volume Variation (SVV)
- Pulse Pressure Variation (PPV)
- Passive Leg Raise Test
Monitors: - Invasive = Pulmonary artery catheter (Gold Standard)
- Minimally Invasive:
Esophageal Doppler
LiDCO®, PiCCO®, EV1000
Other causes of swinging a-line
constrictive pericarditis
pneumothorax
cardiac tamponade
bronchospasm
pulmonary embolus
Interpretation of vol depleted patient’s parameters
In a volume-depleted patient, the magnitude of the changes in your pulse pressure and stroke volume is exaggerated if the change is >10-13% then the patient is fluid responsive and requires a fluid bolus
What do you do if a patient falls in the grey zone of 9-13% change in pulse pressure and stroke vol?
use static parameters to determine their need for fluid therapy
