Blood Gases

Question 1

Significance of hyperventilations and hypoventilation

Answer 1

In relation to [H+], hypervent. aims to blow off CO2 that would be produced in excess in order to buffer excess acidity.

Meanwhile hypovent. aims to maintain and keep equilibrium to favour the maintenance of [H+]

Question 2

Significance of A/B balance at the proximal distal tubule

Answer 2

Control of carbonate reabs therefore

• HCO3- back to blood if ACIDIC
• less if pH is high

Question 3

Significance of A/B balance at the collecting duct

Answer 3

excretion of [H+]

1) via ATPase pumps, K+ exchange

meanwhile Cl- is exchanged for HCO3- to blood
Cl- reabs via co-transporter to blood

Question 4

METABOLIC ACIDOSIS and causes

Answer 4

HCO3 <22mmol/l =

ANION GAP = 18mmol + or normal difference between cations and anions = anions LOWER than cations

• high gap = loss of HCO3- exacerbates
• normal gap = Cl- compensates for HCO3- loss

Question 5

RESPIRATORY ACIDOSIS and its causes

Answer 5

PCO2 > 6.0kPa = will be high = excess H+

*hypovent. = resp obstruction, disease
 weak muscles = dystrophy, GBS, MND
* drugs = opiods, sedatives
* Burns
* COPD excacerbation; Interstitial

Question 6

normal pH range

Answer 6

7.35 - 7.45

Question 7

METABOLIC ALKALOSIS

Answer 7

HCO3- > 26mmol/l

• loop diuretics
• vomiting
• antacids
• HYERPERALDOSTERONISM
• oedema

Question 8

RESPIRATORY ALKALOSIS

Answer 8

PCO2 < 4.6kPa = less carbonic acid = more alkaline

• HYPERVENT = anxiety, hypoxia
• pumonary embolism = hypervent d/t hypoxic
• brain tumour
• drugs = salicylates (aspirin)

Question 9

What is a hyperchloraemic acidosis

Answer 9

Normal anion gap w/ metab. acidosis d/t Cl- compensating for major HCO3- loss.

A ddisons
B icarb loss
C hloride XS (excess saline)
D iuretics

Question 10

Causes of High Anion Gap

Answer 10

M etformin/methanol
U raemia
D ka
P aracetamol
I ron
L actic acidosis
E thylene glycol (anti-freeze)
S alicylates (aspirin)

Question 11

Respiratory Compensation mechanisms

Answer 11

DKA = metab acidosis = Kussmaul Breathing = deep rapid, = attempt to expel carbon

• in metab. acidosis, CO2 will interestingly be lowered as body attempts ot blow off carbonic acid and thus H+
• CO2 retention may occur in metabolic alkalosis

Question 12

Metabolic compensation mechanisms

Answer 12

compensation by kidneys takes time, 2-3days = HCO3- changes

• ACUTE = nil compensation in HCO3-
• CHRONIC = HCO3- excretion in order to lower pH often in resp acidosis

Question 13

Mixed acidosis

Answer 13

raised CO2 and lowered HCO3-

= cardiac arrest
= multi-organ failure

Question 14

nterpret this ABG:

pH 7.37

PaO2 10.1kPa

PaCO2 8.1kPa

HCO3 30 mEq/L

Answer 14

compensated respiratory acidosis

Question 15

Other parameters

Answer 15

PO2 = assess alongside inspiratory

Base Excess = if co2 normal , measure of how much H+ to return pH to normal
-3 = met. acid
+3 = met alkalosis

Na
K
Cl
= calculate anion gap

Ca = hyper = cardiac arrest etc.

Haematocrit = blood conc = raised = dehydration

Tot Bilirubin = raised = haemolysis or liver disease