Fluids, acid-base and electrolytes

Question 1

5 mechanism of oedema formation:

Answer 1

1. Venous hypertension
2. Hypoproteinemia
3. ↑microvascular permeability
4. Impaired lymph flow
5. ↑negativity of interstitial fluid pressure

Question 2

4 mechanism of antiedema formation:

Answer 2

1. ↑ interstitial hydrostatic pressure
2. ↑ lymph flow
3. ↓ interstitial colloid osmotic pressure
4. 4. ↑ trans-serosal flow in organs with potential spaces

Question 3

characteristics that lead to longer half-life for artifical colloids:

Answer 3

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

Question 4

Definition of fluid responders:

Answer 4

10-15% increase in stroke volume

Question 5

Implicated mechanism for coagulopathy secondary to HES:

Answer 5

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.

Question 6

what does CVP measure?

Answer 6

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

Question 7

Predominant gas type for room air embolism:

Answer 7

Nitrogen

Question 8

At or above which COP can the risk of oedema be decreased?

Answer 8

15mmHg

Question 9

Osmolal gap that indicates unmeasured solutes

Answer 9

Osmolal gap > 10mOsm/kg above calculated indicates an unmeasured solute is present in large amounts.

Question 10

Other than unmeasured solutes what else can confound an increased osmolal gap

Answer 10

• secondary to pseudohyponatremia secondary to hyperlipidaemia, marked hyperglycaemia or hyperproteinemia
• activiated charcoal containing propylene glycol or glycerol

Question 11

Possible mechanisms for AKI from HES usage:

Answer 11

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

Question 12

what is urine osmolality used for?

Answer 12

To assess concentrating ability of the kidneys especially if many high MW molecules could be present

Question 13

Net effect of PTH:

Answer 13

increase Ca and decrease phosphate

Question 14

Net effect of calcitriol

Answer 14

increases both calcium and phosphate

Question 15

What is the active vitamin D?

Answer 15

Calcitriol

Question 16

What is the Ca-P product?

Answer 16

total Ca (mg/dL) x phosphate (mg/dL)

Question 17

What happens when Ca-P product > 60

Answer 17

increases risk of mineralisation

Question 18

Effect of acidosis on phosphate:

Answer 18

↓ HPO42- due to renal elimination with H+

Question 19

Main sites of Mg reabsorption in the kidneys

Answer 19

Loop of Henle

Question 20

List 7 functions of Mg:

Answer 20

1. Production and use of ATP
2. Co-enzyme for membrane Na-K ATPase pump
3. Calcium ATPase and proton pumps
4. Protein and nucleic acid synthesis
5. Regulation of vascular smooth muscle tone
6. Cellular second messenger systems
7. prevent apoptosis

Question 21

List 5 adverse effects for bicarb therapy:

Answer 21

• electrolytes: increase Na, decrease K and Ca
• decrease tissue oxygenation due to increased Hgb affinity to oxygen
• intracellular acidosis
• paradoxic CSF acidosis
• hypercapnia

Question 22

Listed 4 differences between distal RTA and proximal RTA

Answer 22

• 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.

Question 23

Electrolytes correlate well between venous and arterial samples, except for which one?

Answer 23

Chloride is lower in systemic venous blood due to the Hamburger effect (chloride shift)

Question 24

Which parameters (2) differ between IO samples and venous/arterial samples:

Answer 24

potassium and PCV

Question 25

Name 3 ways sodium/lithium heparin can affect blood gas analysis

Answer 25

• false hypoCa or Mg due to chelation
• artificial increase NaCl and decrease K (dilutional)
• artifically elevate PaO2

Question 26

Recommendation to keep heparin < ___% of blood volume

Answer 26

4%

Question 27

If a blood gas sample is left out at room temp, at what rate can lactate form?

Answer 27

0.01mmol/L per minute with concomitant decrease BE and pH

Question 28

What can cause artificial hyperkalaemia in a blood gas sample (3):

Answer 28

hemolysis, thrombocytosis, leukocytosis

Question 29

Main finding of 2017 Critical care medicine article: Cl content of fluids used in large volume resus is associated with reduced survival

Answer 29

-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

Question 30

most common side effects (3) of bicarb therapy found in 2018 BICARB-ICU trial?

Answer 30

metabolic alkalosis
hypernatraemia
hypocalcaemia
(no life-threatening complications)

Question 30

What did the BICARB-ICU study find? 3 main findings:

Answer 30

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