Fluids, acid-base and electrolytes Flashcards
5 mechanism of oedema formation:
- Venous hypertension
- Hypoproteinemia
- ↑microvascular permeability
- Impaired lymph flow
- ↑negativity of interstitial fluid pressure
4 mechanism of antiedema formation:
- ↑ interstitial hydrostatic pressure
- ↑ lymph flow
- ↓ interstitial colloid osmotic pressure
- ↑ trans-serosal flow in organs with potential spaces
characteristics that lead to longer half-life for artifical colloids:
larger MW
High molar substitutions
higher C2:C6 ratio
e,g, VetStarch 6% 130/0.4/9:1
Means:
6% - 6% tetrastarch solution
130 – Average MW in kDa
0.4 – 4 hydroxyethyl group substitutions per 10 glucose molecule
9:1 – C2:C6 ratio
Definition of fluid responders:
10-15% increase in stroke volume
Implicated mechanism for coagulopathy secondary to HES:
decreased platelet function
decreased concentrations of von Willebrand factor, factor VIII coagulant activity (FVIII:C), factor VIII-related antigen, factor VIII ristocetin cofactor
impaired fibrinogen polymerization
a dilutional coagulopathy.
what does CVP measure?
hydrostatic pressure of the intrathoracic vena cava just outside of the RA. Approximate RA pressure that’s similar to right ventricular pressure at end diastole, approximate preload
Predominant gas type for room air embolism:
Nitrogen
At or above which COP can the risk of oedema be decreased?
15mmHg
Osmolal gap that indicates unmeasured solutes
Osmolal gap > 10mOsm/kg above calculated indicates an unmeasured solute is present in large amounts.
Other than unmeasured solutes what else can confound an increased osmolal gap
- secondary to pseudohyponatremia secondary to hyperlipidaemia, marked hyperglycaemia or hyperproteinemia
- activiated charcoal containing propylene glycol or glycerol
Possible mechanisms for AKI from HES usage:
Renal tubular damage due to
i) hyperoncotic induced renal dysfunction => decreased GFR
ii) HES reabsorbed into PT cells via pinocytosis => osmotic nephrosis, cellular oedema, apoptosis
what is urine osmolality used for?
To assess concentrating ability of the kidneys especially if many high MW molecules could be present
Net effect of PTH:
increase Ca and decrease phosphate
Net effect of calcitriol
increases both calcium and phosphate
What is the active vitamin D?
Calcitriol
What is the Ca-P product?
total Ca (mg/dL) x phosphate (mg/dL)
What happens when Ca-P product > 60
increases risk of mineralisation
Effect of acidosis on phosphate:
↓ HPO42- due to renal elimination with H+
Main sites of Mg reabsorption in the kidneys
Loop of Henle
List 7 functions of Mg:
- Production and use of ATP
- Co-enzyme for membrane Na-K ATPase pump
- Calcium ATPase and proton pumps
- Protein and nucleic acid synthesis
- Regulation of vascular smooth muscle tone
- Cellular second messenger systems
- prevent apoptosis
List 5 adverse effects for bicarb therapy:
- electrolytes: increase Na, decrease K and Ca
- decrease tissue oxygenation due to increased Hgb affinity to oxygen
- intracellular acidosis
- paradoxic CSF acidosis
- hypercapnia
Listed 4 differences between distal RTA and proximal RTA
- distal RTA is a problem with H+ excretion in collecting duct, where proximal RTA is a problem with bicarb reabsorption in PT
- urine pH > 6 in distal RTA and ph < 5.5 in proximal RTA despite acidemia
- when NH4Cl is administered, urine pH remains > 6 in distal RTA
- when alkali is administered to normalise plasma bicarb urinary excretion of bicarb in proximal RTA increase > 15%, where distal RTA remains normal < 5%. Therefore larger doses of bicarb is required for proximal RTA tx.
Electrolytes correlate well between venous and arterial samples, except for which one?
Chloride is lower in systemic venous blood due to the Hamburger effect (chloride shift)
Which parameters (2) differ between IO samples and venous/arterial samples:
potassium and PCV
Name 3 ways sodium/lithium heparin can affect blood gas analysis
- false hypoCa or Mg due to chelation
- artificial increase NaCl and decrease K (dilutional)
- artifically elevate PaO2
Recommendation to keep heparin < ___% of blood volume
4%
If a blood gas sample is left out at room temp, at what rate can lactate form?
0.01mmol/L per minute with concomitant decrease BE and pH
What can cause artificial hyperkalaemia in a blood gas sample (3):
hemolysis, thrombocytosis, leukocytosis
Main finding of 2017 Critical care medicine article: Cl content of fluids used in large volume resus is associated with reduced survival
-Chloride load was significantly associated with mortality even when controlling for total fluids, age and baseline severity.
- each 100mEq increase in Cl load associated with 5.5% increase in hazard of death over one year
- relationship between chloride load and hyperchloremic acidosis and AKI is less clear
most common side effects (3) of bicarb therapy found in 2018 BICARB-ICU trial?
metabolic alkalosis
hypernatraemia
hypocalcaemia
(no life-threatening complications)
What did the BICARB-ICU study find? 3 main findings:
Overall population: Sodium bicarbonate infusion was not associated with improvement in organ failure at day 7 and cause of death at day 28 in patients with severe metabolic acidemia
Patients with AKI at enrolment: Na bicarb decreased primary composite outcome and day 28 mortality
Bicarb decreased need for RRT during ICU stay
