Supportive Diagnostics in Fluid Therapy

Question 1

Indications for blood testing in patients receiving fluid therapy.
How often?

Answer 1

Warranted for any patient sick enough to be hospitalised and receive fluid therapy.
Every 24-48hrs, but sooner if clinical signs of complications. Tailored to patient and underlying disease process.

Question 2

Lab tests to monitor fluid therapy.
How do these help?

Answer 2

PCV, total solids
Blood Urea Nitrogen (BUN) and Creatinine.
USG
Lactate
Glucose
Electrolytes
(Acid-base status)

Helps for diagnosis and identifying issues that may be caused by fluid therapy.

Question 3

1. What constraints may there be on tests performed?
2. What other methods could be used to monitor a patient undergoing fluid therapy?

Answer 3

1. Owner finances
2. PE, bwt, urine output.

Question 4

1. Common electrolytes measured in practice?
2. Electrolyte most common to see derangements in?

Answer 4

1. Potassium, sodium, chloride
2. Potassium

Question 5

1. Term for potassium too high
2. ” “ too low
3. Why is it important to be vigilant with potassium?

Answer 5

1. Hyperkalaemia
2. Hypokalaemia
3. Needs to be maintained in a very narrow range and patients do not tolerate deviations out of this range very well.

Question 6

Why is hyperkalaemia such a problem?
Symptoms and PE findings?
Causes of hyperkalaemia?

Answer 6

Life threatening effects upon myocardial conduction and therefore effective contraction.

Bradycardia, ECG abnormalities (large T wave), heart standstill

Urethral obstruction, uroabdomen, hypoadrenocorticism (Addison’s), anuric/oliguric renal failure, GI disease, body cavity effusion.

Question 7

Management of hyperkalaemia.

Answer 7

Stabilisation and treatment priority.
- IVFT – isotonic crystalloid.
- Calcium gluconate (may need diluting)– Makes myocytes in heart more resistant to effects of hyperkalaemia.
- Glucose +/- soluble insulin (stims own endogenous insulin production, causing glucose to be transported from EC space to IC space, taking potassium with it) (soluble insulin for critical patients that cannot mount a response).
Continuous monitoring – ECG
Diagnosis and treatment of underlying cause.

Question 8

1. What type of patient is hypokalaemia most common in?
2. How life threatening is hypokalaemia?
3. Clinical signs? – In severe cases?
4. Common causes of hypokalaemia?

Answer 8

1. Critically ill patients – often inappetant and on long term IVFT.
2. Less immediately life threatening.
3. Non-specific – Weakness, lethargy, ileus, anorexia. – Resp muscle weakness and hypoventilation if severe.
4. GI tract losses e.g. v+d, urinary tract losses e.g. CKD, post-obstructive diuresis, some diuretics, mineralocorticoid excess, Insulin/glucose containing fluids, inappetence/anorexia, long-term IVFT with low potassium conc.

Question 9

Management of hypokalaemia.

Answer 9

Address underlying cause.
Potassium supplementation.
(IV)- Potassium chloride added to saline or Hartmann’s
- Never bolus!
Oral supplementation available for patients with chronic disease and hypokalaemia e.g. CKD.

Question 10

Common adjuncts/supplements to fluid therapy.
From common to rare.

Answer 10

Potassium
Glucose and some medications e.g. Metaclopramide.
Sodium bicarbonate. – rare.

Question 11

1. Define acidaemia.
2. Define alkalaemia.
3. What is a ‘base’?
4. Give examples of buffers.

Answer 11

1. Blood pH of <7.35.
2. Blood pH of >7.45
3. Alkali chemicals that react with acids to form salts. Can act as ‘buffers’, accepting H+ when there is a surplus and donating H+ when there is a shortage.
4. Bicarbonate
   Haemoglobin
   Some plasma proteins.

Question 12

Measuring acid-base.

Answer 12

Need IN-HOUSE blood gas machine.
– Results affected by storage of blood so cannot e sent away.
Most commonly found in SA hospitals and equine hospitals.
Rarely found in primary care practices.

Question 13

Samples needed for blood gas analysis?

Answer 13

Blood from arteries and veins.
‘Normal’ ranges for arterial and venous blood samples are different. (Must make machine aware where the sample came from).
Only blood from arteries can be used to assess resp function.

Question 14

4 main types of acid-base disturbance.
Which are common (and in what patients?) and which are uncommon?

Answer 14

Metabolic acidosis – most common in in unwell patients.
Metabolic alkalosis – uncommon.
Respiratory acidosis – most common in anaesthetised patients.
Respiratory alkalosis – uncommon,

Question 15

How does metabolic acidosis happen?

Answer 15

• Loss of base – e.g. bicarbonate with severe d+.
• Failure to excrete acid – e.g. H+ ions in some patients with renal failure.
• An accumulation of acid e.g. lactic acid in patients with shock.

Question 16

What does the body do about metabolic acidosis?
What will the blood gas result look like?

Answer 16

Attempts to increase body’s pH back to normal.
Body tries to ‘blow off’ more carbon dioxide so hyperventilation.

Low blood pH (rarely overcompensate) and a low pCO2 (hyperventilated).

Question 17

How does metabolic alkalosis happen?

Answer 17

A relative increase in bicarbonate levels.
- Excessive administration of bicarbonate.
- Loss of acid e.g. pyloric obstruction due to FB, causing pure gastric vomiting (no bicarbonate from proximal duodenum).

Question 18

What does the body do about metabolic alkalosis?
Why is the body’s ability to compensate in this way limited?
What will you see on the blood gas results?

Answer 18

Body attempts to lower pH by increasing blood CO2 levels by hypoventilation.
Limited due to hypoventilation causing hypoxia causing stimulation of ventilation.
High pH (rarely overcompensate) and high CO2 (hypoventilation).

Question 19

How does respiratory acidosis happen?

Answer 19

A rise in blood CO2.
Any disease/state that results in hypoventilation.
- Upper airway obstruction
- BOAS
- Pleural space disease e.g. pleural effusion
- Pulmonary disease e.g. pulmonary oedema
- CNS depression e.g. anaesthetic drugs
- Depression of neuromuscular respiratory function e.g. tetanus.

Question 20

What does the body do about respiratory acidosis?
What will be seen on the blood gas result?

Answer 20

Attempts to increase blood pH.
Kidneys will retain more bicarbonate and excrete more H+ ions.
V slow process.

Low pH (patients rarely overcompensate), high pCO2. Bicarbonate increases in time.

Question 21

How does respiratory alkalosis happen?

Answer 21

Caused by a fall in blood CO2.
Caused by any disease/state which results in hyperventilation.
- Hyperthermia
- Pain
- Stress

Question 22

What does the body do about respiratory alkalosis?
What will be seen on the blood gas result?

Answer 22

Attempts to lower pH.
By increasing elimination of bicarbonate via the kidneys.

High pH (rarely overcompensate) and low pCO2. Bicarbonate will decrease in time.

Question 23

How do acid-base imbalances in the patient alter your approach to fluid therapy?

Answer 23

• Hartmann’s may be chosen for acidotic patients as it contains a lactate buffer.
• 0.9% NaCl slightly acidifying so is the fluid of choice for alkalotic patients.
• Appropriate management of shock and dehydration is more important!
• If good perfusion of kidneys and lungs, the patient will be able to do the fine-tuning.
• Sodium bicarbonate can be administered to patients with acidosis. – very rarely needed.
  – Great risk of causing metabolic alkalosis – NEVER administer without access to blood gas analysis.