Arterial Blood Gases Flashcards
what can you get from your ABGs?
- pH
- PaCO2
- PaO2
- HCO3
- base excess
normal pH on ABG
7.35-7.45
normal PaCO2
35-45mmHg
normal PaO2
80-100mmHg
normal HCO3-
22-26mEq/L
normal base excess
-2 to +2mmol/l
what are the rates of oxygen flow in nasal cannulae?
- 1L/min - 24%
- 2L/min - 28%
- 3L/min - 32%
- 4L/min - 36%
types of oxygen delivery devices
- nasal cannulae
- venturi masks
- simple oxygen masks
- non-rebreather mask
when can you say that a patient is hypoxaemic?
when the patient’s PaO2 is below 10kPa, below 8kPa, they are in respiratory failure
features of type 1 respiratory failure
- hypoxaemia
- normocapnia
features of type 2 respiratory failure
- hypoxaemia
- hypercapnia
why does type 1 respiratory failure occur?
ventilation/perfusion mismatch
why does type 2 respiratory failure occur?
alveolar hypoventilation
causes of hypoventilation
- increased resistance due to airway obstruction
- reduced compliance of the lung tissue/chest wall
- reduced strength of the respiratory muscles
- drugs acting on the respiratory centre reducing overall ventilation
what happens if the pH drops and CO2 levels increase?
respiratory acidosis
what condition causes
- a drop in pH
- inc in CO2
- inc in HCO3-
respiratory acidosis with metabolic compensation
what condition causes:
- an inc in pH
- a drop in CO2
respiratory alkalosis
what condition causes:
- an inc in pH
- a drop in CO2
- a drop in HCO3
respiratory alkalosis with metabolic compensation
what is the base excess?
another surrogate marker of metabolic acidosis or alkalosis
what does a high base excess entail?
an abnormally high HCO3- in the blood
what does a low base excess entail?
a low HCO3- in the blood
what types of compensation can happen?
- respiratory
- metabolic
how long would respiratory compensation take to kick in and do its work?
immediately by either increasing or decreasing alveolar ventilation to regulate the CO2 levels
how long would metabolic compensation take to work?
a few days
what would indicate that a person is suffering from a mixed acidosis/alkalosis?
the levels of CO2 and HCO3- would be going to opposite directions (i.e. CO2 increasing, HCO3 decreasing)
causes of respiratory acidosis
- respiratory depression
- guillain-barre
- asthma
- COPD
- iatrogenic
causes of respiratory alkalosis
- anxiety
- pain
- hypoxia
- pulmonary embolism
- pneumothorax
- iatrogenic
causes of metabolic acidosis
- increased acid production/acid ingestion
- decreased acid excretion/rate of GI and renal HCO3 loss
lab characteristics of metabolic acidosis
- low pH
- low HCO3
- low BE
what is the normal anion gap range?
4-12mmol/L
what conditions increase the anion gap?
- diabetic ketoacidosis
- lactic acidosis
- aspirin overdose
what decreases the anion gap?
- gastrointestinal loss of HCO3-
- renal tubular acidosis
- Addison’s disease
features of metabolic alkalosis on an ABG?
- high pH
- high HCO3-
- high BE
causes of metabolic alkalosis
- gastrointestinal loss of H+
- renal loss of H+
- iatrogenic
which conditions cause metabolic alkalosis?
- vomiting
- diarrhoea
- use of loop/thiazide diuretics
- heart failure
- nephrotic syndrome
- cirrhosis
- Conn’s syndrome
features of a mixed respiratory and metabolic acidosis
- low pH
- high CO2
- low HCO3-
causes of a mixed metabolic and respiratory acidosis
- cardiac arrest
- multi-organ failure
features of mixed respiratory and metabolic alkalosis
- high pH
- low CO2
- high HCO3-
causes of a mixed respiratory and metabolic alkalosis
- liver cirrhosis in addition to diuretic use
- hyperemesis gravidarum
- excessive ventilation in COPD
