Things you need to know in surgical dept 2: Acid Base balance & Oxygen therapy

Posted: September 16, 2012 by kiamseong in Surgery, Uncategorized

(i)     ABG interpretation


pH 7.35-7.45

pO2 80-100 mmHg

pCO­2 35-45 mmHg

HCO3 22-26

*To convert mmHg to kPa divide 7.5

(ii)    If pH>7.45

pCO2 < 35

HCO3 >26

Respiratory Alkalosis

Metabolic Alkalosis








-salicylates poisoning

-profuse vomiting



(iii)  If pH<7.35

pCO2 > 45

HCO3 <22

Respiratory Acidosis

Metabolic Acidosis

         NAGMA                          HAGMA

Respiratory failure -RTA


-Addison ds

-Pancreatic fistula

-NH­4 ingestion


Increase in organic acid production

-lactoacidosis-shock, sepsis,hypoxia

-uric acid

-ketone-DM, alcohol

-drug – metformin, metanol

*anion gap = [ Na + K ]– [ Cl + HCO3 ]

(iv)  Oxygen dissociation curve

Left side of curve – ­pH ¯T ¯DPG (2,3 dephosphoglycerate)
Right side of curve – ¯pH ­T ­DPG (2,3 dephosphoglycerate)

p50 – point where saturation of Hb reaches 50% (at pO2=26.6)

ICU point (PaO2, SaO2) = (60mmHg, 91%) = lowest acceptable paO2 in ICU patient because further drop beyond this point lead to drastic drop in SaO2

Mixed venous point at SaO2 = 75%

(v)   Indication for intubation

ü  To deliver positive pressure ventilation

ü  Airway protection from aspiration

ü  During surgical procedures involving neck and head in non-supine position

ü  Neuromuscular paresis

ü  Procedures increases intracranial pressure

ü  Profound disturbance n consciousness

ü  Severe pulmonary and multi-systemic injury


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