pH

Question 1

What is the effect of acidosis on tissue oxygenation efficiency?

Answer 1

Bohr effect
- Acidemia → rightward shift of the oxyhemoglobin dissociation curve ⇒ decrease affinity of Hb for O2 → less efficient O2 loading of Hb in the lungs

• Alkalosis → left shift ⇒ increase affinity of Hb for O2 → decrease O2 delivery to tissues

Question 2

What are the consequences of pH on the ionogram ?

Answer 2

Acidemia : ↗︎ [K+], [Ca2+]

Alkalosis : ↘︎ [K+], [Ca2+], [Mg2+], [P]

Question 3

What are the 2 types of lactic acidosis ?

Answer 3

Type A : caused by hypoxia (hypoxemia, anemia, hypoperfusion)

Type B : sepsis, activated leukocytes, any tissue undergoing a significant inflammatory response, catabolism… (normal O2 level)

Question 4

What are the GI causes of hyperchloremic acidosis in horses ?

Answer 4

Diarrhea : digestive bicarbonate loss and Na loss without Cl
.+ hypovolemia and renal retention of NaCl
⇒ hyperchloremic acidosis

So appropriate fluid therapy to adress hypovolemia and reevaluate the situation

Question 5

What are the renal causes of hyperchloremia in horses ?

Answer 5

• Compensatory response to alkalosis (physiologic) : renal retention of Cl-
• Chronic renal failure : failure of Cl- excretion
• Renal tubular acidosis (RTA) : type 1 (distal, inability to acidify the urine during metabolic acidosis) or type 2 (proximal). Primary or secondary (++ in horses) after exposure to aminoglycosides, TMPS, carbonic anhydrase inhibitors, NSAIDs, and tetracyclines.

Question 6

What are the causes of hypochloremia in horses ?

Answer 6

• Compensatory response to acidosis : hypoCl should not be corrected
• Gastric reflux or furosemide therapy : hypochloremic alkalosis. Assess fluid deficits and [K+].
• Hypoproteinemia in critical patients could contribute to metabolic alkalosis.

Question 7

What are the causes of respiratory alkalosis ?

Answer 7

Hyperventilation caused by :
- hypoxemia (PaO2 < 60 mmHg) → stimulation of ventilation
- central hyperventilation in neonatal encephalopathy
- stimulation of pulmonary neuroreceptors in pneumonia, pneumothorax, interstitial lung disease…
- secondary to pain, anxiety, fever, high adrenergic tone, pregnancy, sepsis, liver failure, heat exhaustion…

TT of the underlying cause.

Question 8

How to evaluate an acid-base disorder ?

Answer 8

1- Evaluate strong ions : abnormalities in Na+, K+ and Cl-, causes by renal and GI diseases.
2- Evaluate lactic acidosis
3- Abnormalities of the buffer base (usually mild)
4- Evaluate respiratory component and CO2 excretion