Acid Base Balance

pH<7.35 => acidosis

pH>7.45 => alkalosis

major extracellular buffering system of body HCO3-/H2CO3

H2O + CO2 << H2CO3 << H+ + HCO3-

le Chatelier's principle usually followed.

1. PaCO2 controlled by changes in ventilation (normal value 35-45 mm Hg) 40 is usual value.

acidosis compensated by hyperventilation (lt shift), alkalosis by hypoventilation (rt shift).

2.HCO3- (22-30 meq/L) 24 is usual value

acidosis compensated by renal reabsorption of bicarbonates by tubular cells from tubular fluid,collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH₃ buffer, alkalosis compensated by excretion of more bicarbonate from kidney, by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of glutamine metabolism and ammonia excretion

major extracellular buffer- bicarbonate & ammonia

major intracellular buffer- proteins & phosphates

For usual calculation, look for the primary defect in terms of acidosis or alkalosis by pH value.

Next is identifying the primary defect in terms of metabolic or respiratory acidosis or alkalosis, both the reason and effect being in the same direction in terms of change in hydrogen ion concentration.

Third is to identify the compensatory mechanism, if any

Organophosphorous Poisoning

Setting: Agricultural poison, often accidental due to contact,inhalation or ingestion

Victim: Agricultural workers, handlers of organophosphorous compounds

Clinical features: Often smell of organophosphorous compounds

Cholinergic effects: miosis+bradycardia+parasympathetic activation+increased secretion of glands+muscular contraction+urinary incontinence most often

Diagnosis: Cholinesterase activity Plasma vs Red cell If that in plasma decreases,and red cell constant,implies exposure mild. If both affected southwards,severe form of exposure. In tissue samples at room temperature,cholinesterase activity can be assessed till 1-2 days,at temp 4-8 degrees,can be assessed even after months.

Clinical diagnosis: iv injection of 2 ml atropine relieves most symptoms,whereas in normal subjects it causes atropinization (mydriasis+cycloplegia+abolition of light reflex+tachycardia+sympathetic activation+decreased secretion of glands+voluntary muscle relaxation+sphincter tone rise+body temperature rise)

Treatment: Atropine 2-4 mg iv repeat every 10-15 minutes till patient stabilizes usual maint dose 40 mg/day max 1000 mg/day

Oximes: Pralidoxime