Nutrition And Fluids

Question 1

What is MOVU?

Answer 1

Minimum obligatory volume of urine to dissolve waste products
0.5-1ml/kg/h. About 30 ml/h in average human. Or 1l per day.

Question 2

Effects of crystalloids v colloids on fluid volume/compartments.

Answer 2

Crystalloids: electrolytes in water. No oncotic pressure. Easily distributed in ECF spaces. Eg. Normal saline 0.9% isotonic; 5% dextrose hypotonic. Hartman’s solution (lactate, K, Ca with NaCl) aka physiological.
Initially: only in ECF (plasma is only 3l of 14l in ECF) so only 214ml stay in plasma (distribution time in minutes). 1l IV dextrose 5% (hypotonic) dilutes ECF relate to ICF. SO 70ml would stay in plasma.
Colloids: contain large molecules so increase IV oncotic pressure = draw fluid back into circ. Stay in circ for longer. Maintain BP. No O2 carrying capacity. E.g. Haemaccel/volplex containing gelatine.
500ml colloid IV would all stay IV. No change in osmotic pressure, no distribution into cells (ICF).

Question 3

Insensible fluid losses?

Answer 3

In faeces, from lungs (500ml) from sweat/skin (500ml) per day.
In total unavoidable losses= 1.5-2l per day. In healthy adult at rest. Up to 3l if & activity.
Salt losses: K 60mM, Na 100mM per day.

Question 4

First post-op day est fluid prescription.

Answer 4

~2l on day 1. As water tends to be retained more due to stresses of surgery. 2l 5% dextrose. NB. Don’t just prescribe dextrose alone for several days. Pt will be hyponatraemic. Normal saline every 3rd bag.

Question 5

Third space losses?

Answer 5

8l of secretion reabsorbed into bowel per day. If post-op ileus= fluid secreted is not reabsorbed (completely). = reduced ECF = fluid depleted. 
But you don't know the size so- rely on urine output.
Sudden diuresis (d2/3) ?recovery from ileus.
Pancreatitis: several litres of fluid lost into peritoneal cavity. But very difficult to tell how much! -> Vigorous replacement to maintain urine output + correct electrolytes according to daily U&Es.

Question 6

What percentage of body is water? In an average 70kg man how much of each fluid does he have?

Answer 6

2/3 water (increase with age and Female)
70kg man= 42l water
ICF -28l
ECF-14l
Plasma- 3l
Interstitial- 10l
Transcellular 1l

Question 7

A 70yo male presents to A&E with syncope, dyspnoea, and peripheral oedema. His CXR shows Kerley B lines, batwing shadowing, and a heart >50% of the thorax diameter. What do you expect his blood results to show? How would this guide your management?

Answer 7

DD: Congestive cardiac failure causing pulmonary oedema
Expected blood results: Hypovolaemic hyponatraemia
Management: normal physiological response to CCF, so treat the underlying cause,I.e. Heart failure. Otherwise: Fluid restriction, consider diuretics, use hypertonic solutions if needed.

Question 8

80yo F is referred by her GP with increasing dyspnoea, low sodium, and an abnormal CXR. Explain the pathological process underlying this presentation. What else would you expect to elucidate from her history?

Answer 8

Euvolaemic hyponatraemia. Suspected SIADH, from a bronchial carcinoma, likely to be a small cell lung cancer secreting ADH inappropriately. Expect increased exposure to carcinogens e.g. Large pack history.

Question 9

A 15yo known type 1 diabetic presents to A&E after found to be vomiting and sluggish at school. What do you expect to find on his blood results and his clinical examination? What is the underlying pathology.

Answer 9

Expect clinical examination: confusion, fruity breath (ketones), kussmaul respiration- deep and rapid with occasional apnoeas (air hunger to compensate for acidosis)
Bloods: high glucose, high ketones (large osmolar gap), acidotic with very low pCO2, high K
DD: Diabetic ketoacidosis due to not taking insulin (makes you gain wt). Metabolic acidosis due to ketones, attempted respiratory compensation by hyperventilation. Hyperkalaemia due to movement of H into ICF in exchange for K, hopefully will resolve on fixing the DKA e.g. Insulin.

Question 10

Management of Hyperkalaemia?

Answer 10

If <6 or >6and no symptoms or ECG signs- treat it promptly. Treat the underlying cause and review drugs, monitor carefully until downwards trend established.
If >6 and symptoms or ECG changes
Anyone with
- hyperkalaemia (any) and ECG changes
- K>6 with symptoms/signs
- K>7
should be treated as a medical emergency.

Question 11

Emergency management of Hyperkalaemia

Answer 11

Get help from Med Reg. And do ABCDE…
Repeat test URGENTLY but do not delay treating
Give IV Ca gluconate
Give IV insulin. And dextrose IV
If still uncontrollable consider dialysis/haemofiltration.
Monitor BM for at least 6h after last admin of insulin.

Question 12

Which hormones control sodium and water excretion respectively?

Answer 12

Sodium excretion = aldosterone

Water excretion = ADH

Question 13

Where is aldosterone secreted? What causes it’s secretion

Answer 13

Secreted from adrenal cortex (glomerulosa).
Stimulated by renin-angiotensin system (RAAS) which is stimulated by a decrease in renal perfusion (Renin release).
It causes sodium reabsorption in DCT and water retention.

Question 14

How does the autonomic nervous system respond to a decrease in effective arterial blood volume?

Answer 14

Increased sympathetic activity -> systemic arteriolar VASOCONSTRICTION AND constriction of renal AFFERENT arterioles

Question 15

Where is sodium? Normal intake and excretion in 24h?

Answer 15

Sodium is primarily an extracellular cation (total approx 4000mmol or 4 moles) some is complexed in bone (30%)
Normal intake: 100-200mmol
Normal losses (Kidney, gut, skin) <20mmol
So the excess is excreted in urine.

Question 16

46yo M, received recent Vincristine therapy with packed red cells for progression of Acute Lymphoblastic Leukaemia. 4/7 later he had mild abdominal pain and distention, bowel sounds present, continuing mild constipation. 6/7 more abdominal distention and vomiting, reduced bowel sounds. What do you do?

Answer 16

Order abdominal x-ray: check for perforation and ileus (multiple fluid levels).
ABG
Prescribe IV fluids- with extra sodium.
Stop diuretics/opiates.
Nasogastric tube to aspirate contents.
Vincristine can cause neurotoxicity -> colonic demyelination/axonal degeneration -> constipation -> paralytic ileus (3rd space loss of sodium and water) -> hyponatraemia.
1000mmol of sodium is secreted into gut in 24h. Normally it’s reabsorbed- and can be fatal if not (i.e. Paralytic ileus)

Question 17

Sources of sodium losses in disease states

Answer 17

• Renal: 25 000 mmol filtered in 24h. It MUST be reabsorbed.
• GI: 1000mmol secreted in 24h. It must be reabsorbed.
  (Total body sodium = 4000mmol)

Question 18

What is Conn’s syndrome?

Answer 18

Excess mineralocorticoids:

Primary adrenal disease

Question 19

Commonest causes of Conn’s syndrome?

Answer 19

Adrenal adenoma
Bilateral hypertrophy of zona glomerulosa
GC remediable aldosteronism (Auto Dom, where ACTH controls Aldo)
Adrenal carcinoma

Question 20

Signs of Conn’s Syndrome?

Answer 20

Hypokalaemic, Alkalosis

Hypertension, High-normal Na

Question 21

Differentials for Conn’s Syndrome?

Answer 21

Liquorice, 11B hydroxysteroid dehydrogenase deficiency.

Question 22

Causes of hyperaldosteronism?

Answer 22

Primary: conn’s syndrome
Secondary: increased plasma renin activity (CCF, liver cirrhosis, nephrotic syndrome, Na losing nephritis, renal artery stenosis)

Question 23

How to distinguish 1o or 2o hyperaldosteronism?

Answer 23

Na: (1o normal-high) (2o <138)
HTN: in primary, occasional in secondary
CCF, ascites, nephrotic syndrome: rare in primary;
Plasma renin: low in 1o; high in 2a.

Question 24

How to screen for hyperaldosteronism? What is important pre-test?

Answer 24

[aldo]/[renin] in plasma.

Need to have stopped spironolactone at least 6w before

Question 25

How to confirm hyperaldosteronism?

Answer 25

Saline suppression test (4h): 2l saline in 4h (aldo should decrease)
Sodium loading and fludrocortisone (4d) risk of severe hypokalaemia

Question 26

How to differentiate Na v water depletion?

Answer 26

Isotonic depletion: Na (-), HCT+++, urine volume(-), urine conc(+). More effect on peripheral circulation UNLESS severe then plasma volume preservation > osmolality.
water depletion: Na+, HCT(+), urine volume—, urine conc+++

Question 27

What is the anion gap?

Answer 27

[Na + K] - [Cl + HCO3]

Normal: 10-18

Question 28

Causes of a raised anion gap?

Answer 28

MUDPILES: methanol/metformin, Ureamia, DKA, Paraldehyde, Iron, Lactate, Ethanol, Salicylates

Question 29

What is the cause of the normal anion gap?

Answer 29

Phosphate and lactate

Question 30

Initial management of DKA

Answer 30

NG tube: prevents inhalation
Rehydration
Insulin replacement
K replacement (total K is low)

Question 31

What must be done in the first hour of DKA management

Answer 31

PANICS
Potassium: check hourly; omit if ?anuria or serum level >5.5
Acidosis: check pH and ketones
Normal saline: 500ml over 15mins if syst<90; otherwise 1l in 1st hr
Insulin infusion: by wt, fixed rate, 0.1units/kg/hr
Catheter and cultures (urine, blood)
Stomach aspiration if drowsy; ET tube if no gag reflex.

Question 32

Venous fasting blood glucose diagnostic of diabetes

Answer 32

7.0

Question 33

Venous blood glucose diagnostic of diabetes 2h after oral glucose load (OGTT)

Answer 33

11.1

Question 34

HbA1c diagnostic of diabetes?

Answer 34

48mmol/mol