Hi Mr PaCO2. | Resp acid: Hi CO2, resp alk Low CO2. (hi paco2 lo, lo ph hi, lo bicarb hi)

Resp acidosis: COPD
Raised CO2 and acid = Lack of ventilation = RESP ACIDOSIS. COPD/asthma. Status. MG.

Met acidosis:
DKA ==> Metabolic acidosis. Low bicarb and acid. if Low CO2 –> resp compensation.
Raised AG: Lactate, Ketoacidosis, Ureamia from renal failure, poisoning e.g. salicycates or anti-freeze.
No increase in AG – lost bicarb and raised Cl e.g. RTA or severe diarrhoea.

Respiratory alkalosis –> Low Co2 and high PH –> Hyperventiliation (which causes low serum Ca.)
Resp alkalosis: PE, Pneumonia, anaemia, high altitude hypoxia, meningitis, anxiety. Early asp overdose = resp alkalosis with hyperventilation.

Met alk: VOM! (Co2 tends not to correct this.)
Vom. Diuretics (low K+ –> met alk; cf resp alk –> low Ca). Conn’s.

Resp acid = raised CO2. Resp alk = low Co2.

Resp acidosis (hi Co2):
a) Lungs COPD/CF/Pulm oedema. b) Opiates. c) MS/Guillian-barre.
Treat with NIPPV/IPPV/Naloxone etc.

Metabolic acid (lo bicarb):
RF/DKA/Lactate/DIARRHOEA. (Ergo, compensate via resp alk).

Resp alk (lo Co2):
Hyperventilation (PE, acute aspirin!), Hypoxia. Head injury. Tx: O2.

Met alk (hi bicarb):
Vomiting of protons/GI fistula – loss of protons. Diuretics causes metabolic alkalosis as does vomiting, while diarrhoea causes metabolic acidosis.
Met alk: Compensate badly by BRADYPNEOA – low RR.

-3 BE = acid! +3 BE = alk. Alkalosis give rise to Spasm/low K+.
If PCO2 abnormal = resp issue; if bicarb abnormal = met issue.
Compensation: patient’s cannot over-compensate. FiO2 of 0.4 if on 40% venturi.


Hi PaCo2 Lo (Hi-Lo’s smoking bar) 6 to 4.5
Lo Bicarb Hi 22-26
Lo pH Hi 7.35-7.45

If on same side: cause. If other side: compensation.


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