Respiratory - Acid & Base Flashcards
Which two organs are mostly involved in acid base regulation?
Lungs and kidneys
What does reduced ventilation cause?
Respiratory acidosis
Increased retention of CO2 in blood causes a shift of equilibrium in the below equation right causing an increase in proton concentration.
What are the causes of respiratory acidosis?
Impair CNS respiratory drive
e.g. Opioid overdose
Impair neuromuscular transmission/muscular weakness
e.g. Obesity e.g. Guillain-Barre
Pulmonary disorders
Obstructive, restrictive, and parenchymal
e.g. COPD
What does increased ventilation cause?
Respiratory alkalosis
CO2 is blown off, so equilibrium shifts to the left
Causes of respiratory alkalosis?
Stimulation to Over breathe
- CNS (Stroke, Anxiety “Medical student”)
- Hypermetabolic (Thyrotoxicosis)
- Drugs (Aspirin overdose)
- Iatrogenic (sometimes on purpose)
Response to Hypoxaemia
- Asthma
- PE
- Altitude
Compensation to Metabolic Acidosis
What are the kidney’s two main responsibilites in acid base regulation?
1) Reabsorption of filtered bicarbonate
2) Excretion of the fixed acids (acid anion and associated H+)
What are the caues of metabolic acidosis?
Increased acid intake
Increased acid production
(e.g. ketoacidosis)
Increased acid retention
(e.g. renal failure)
Loss of alkali
(e.g. Renal Tubular Acidosis)
(e.g. methanol)
What are the two types of metabolic acidosis?
Low anion gap met. ac.
High anion gap met. ac.
What is the cause of low anion gap?
- Loss of alkali/HCO3- is cause
- E.g. proximal renal tubular acidosis
- E.g. GI loss HCO3-
What are the causes of high anion gap?
- Production of additional acid is cause
- E.g. diabetic ketoacidosis, lactic acidosis, methanol poisoning, ethylene glycol poisoning
Methanol / Metformin
Uraemia
Diabetic ketoacidosis (and alcoholic/starvation ketoacidosis)
Propylene glycol
Isoniazid
Lactate
Ethylene glycol
Salicylates
Caues of metabolic alkalosis?
Acid loss
e.g. Gastric acid loss due to vomiting
Alkali administration
e.g. Taking 4 bottles of Gaviscon
Intracellular shift of hydrogen ion
e.g. H+ in hypokalemia
Kidney associated
What acid base abnormality does Hypokalaemia cause?
Metabolic alkalosis
K+ moves out of cells to compensate for low K in blood. H+ in turn moves inside cells causing the alkalosis
14 yr old male patient brought to A&E by mother. The patient seems to be passing in and out of consciousness and vomited upon arrival. The patient appears short of breath and is clutching his abdomen in pain. The A&E registrar performed an Arterial Blood Gas, the results of which are:
pH: 7.12 (7.35-7.45)
pO2: 11.5 (10–14)
pCO2: 3.2 (4.5–6.0)
HCO3: 9 (22-26)
BE: -17 (-2 to +2)
a) Respiratory Acidosis with partial compensation
b) Metabolic Acidosis with partial compensation
c) Respiratory Alkalosis no compensation
d) Respiratory Alkalosis with partial compensation
e) None of the above
b) Metabolic Acidosis with partial compensation
pH is low - acidosis
BE is low - acidotic picture, acid comes from metabolism
CO2 is NOT high - it’s low to compensate metabolic acidosis
A 16 year-old girl with no previous medical history collapses at school and is brought to A&E. On examination she appears thin and has lanugo hair.
- pH: 7.56 (7.35-7.45)
- pO2: 10.7 (10–14)
- pCO2: 6.0 (4.5–6.0)
- HCO3: 31 (22-26)
- BE: +5 (-2 to +2)
a) Respiratory Acidosis with partial compensation
b) Metabolic Acidosis with partial compensation
c) Respiratory Alkalosis no compensation
d) Metabolic Alkalosis with partial compensation
e) None of the above
d) Metabolic Alkalosis with partial compensation
A 32 year-old man presents to the emergency department having been found collapsed. He looks unkempt and is malodorous.
pH: 7.25 (7.35-7.45)
pO2: 11.1 (10–14)
pCO2: 3.2 (4.5–6.0)
HCO3: 11 (22-26)
BE: -15 (-2 to +2)
Potassium: 4.5
Sodium: 135
Chloride: 100
Metabolic Acidosis
With raised anion gap
A 23 year-old lady with asthma presents to A&E with difficulty in breathing. Her initial ABG on 15 litre of oxygen shows:
- pH: 7.54 (7.35-7.45)
- pO2: 10.0 (10–14)
- pCO2: 3.2 (4.5–6.0)
- HCO3: 24 (22-26)
- BE: +0 (-2 to +2)
- Other values within normal range
a) Respiratory Acidosis with partial compensation
b) Metabolic Acidosis with partial compensation
c) Respiratory Alkalosis no compensation
d) Respiratory Alkalosis with partial compensation
e) None of the above
c) Respiratory Alkalosis no compensation
You are called to see a 54 year old lady on the ward. She is three days post-cholecystectomy and has been complaining of shortness of breath. Her ABG is as follows:
pH: 7.49 (7.35-7.45)
pO2: 7.5 (10–14)
pCO2: 3.9 (4.5–6.0)
HCO3: 22 (22-26)
BE: -1 (-2 to +2)
a) Respiratory Acidosis with partial compensation
b) Metabolic Acidosis with partial compensation
c) Respiratory Alkalosis no compensation
d) Respiratory Alkalosis with partial compensation
e) None of the above
c) Respiratory Alkalosis no compensation
Type 1 Respiratory Failure
Low PO2
Normal/Low PCO2
Ventilation-perfusion mismatch
E.g. Pulmonary Embolism
A 64 year old gentleman with a history of COPD presents with worsening shortness of breath and increased sputum production. His oxygen saturations are now 89%.
pH: 7.21 (7.35-7.45)
pO2: 7.2 (10–14)
pCO2: 8.5 (4.5–6.0)
HCO3: 29 (22-26)
BE: +4 (-2 to +2)
a) Respiratory Acidosis with partial compensation
b) Metabolic Acidosis with partial compensation
c) Respiratory Acidosis with no compensation
d) Respiratory Alkalosis with partial compensation
e) None of the above
a) Respiratory Acidosis with partial compensation
Type 2 Respiratory Failure
Low PO2
High PCO2
Impaired gas exchange
E.g. COPD exacerbation
71 year-old Man
History of diabetes mellitus and a long smoking history (45 pack-years)
Presents to the emergency department with worsening shortness of breath
On auscultation of the chest there are wide spread crackles and you notice moderate ankle oedema.
- pH: 7.20(7.35-7.45)
- pO2: 8.9 (10–14)
- pCO2: 6.3 (4.5–6.0)
- HCO3: 17 (22-26)
- BE: -8 (-2 to +2)
- Other values within normal range
Mixed respiratory and metabolic acidosis
