Dr. Muhammad Rafique

Assistant Prof. Pediatrics

Normal Acid Base Balance

Lungs and kidneys maintain acid base balance.

Co2 is produced by body metabolism.

Kidneys excrete endogenous acid produced.

Three main endogenous sources of acids are;

1 -Dietary protein metabolism.

2-Incomplete glucose metabolism produce

lactic acid.

Normal Acid Base Balance-Cont--

Incomplete triglycerides metabolism produces ketoacids (ketones) like beta-hydroxybutaric acid and acetoacetic acid etc.

3 -Stool loss of H2Co3.

H+ formed from endogenous acid production are neutralized by H2Co3 regeneratd by kidneys, decreasing H+ level.

H+HCo3- Co2+H2o

Normal Acid Base Balance

During metabolic acidosis hyperventilation can lower the Co2 level, decreasing H+ conc. and thus increasing pH.

Increase in HCo3- causes reaction to right side increase Co2 and decrease H+ ions.

During respiratory acidosis, increase renal HCo3- generation decreases H+ & increases pH.

Lungs can regulate only Co2 & kidney onlyHCo3-

Renal mechanism of Acid Base Balance

Kidneys regulate serum HCo3- by changing its excretion in urine.

Normal adult has GFR 180 L / 24 hours.

Proximal CT reabsorb 85 % filtered HCo3-.

Ascending limb of loop of Henle absorbs 15%.

Adequate acid excretion needs urinary buffers

Coll. duct secrets H+ ions that acidifies urine.

H+ pump cannot lower urinary pH below 4.5

Acid Base Disturbance Acid base status can be determined by

patient’s blood gases and electrolytes.

Normal values are :

PH = 7.35 - 7.45

PCo2 < 45 mm Hg

Po2 > 55 mm Hg

H2Co3 = 24+ 4meq/l

So2 > 92%

Metabolic Acidosis It is caused by accumulation of net acid :

Ingestion of acid e.g. salicylate intoxication

excesseve production of acid e.g. lactic

acidosis, ketoacidosis.

decreases excretion of acid e.g. renal failure

Excessive loss of HCo3- e.g. diarrhoea, renal disease.

Metabolic Acidosis—cont. Treatment:

1- Body compensate it with hyperventilation,

leading to reduction in PCo2 and returning

pH to normal.

2-Renal tubular acidosis and other causes are

treated with alkalinizing agents like HCo3-

or citrate.

Metabolic Alkalosis

It is caused by loss of H+ or increase in base.

Most common cause is diuretic use causing volume depletion and K and Cl depletion.

It results due to increased HCo3 reabsorption

& aldosteronism with increased H+ secretion.

Other causes are recurrent vomiting, dietary

Cl- deficiency and chronic K depletion.

Metabolic Alkalosis---cont. Compensation is by hypoventilation to raise

PCo2 slightly.

Treatment:

- Intravascular volume repletion.

- K and Cl replacement.

- Treatment of underlying cause.

Respiratory Acidosis

Caused by accumulation of Co2 due to pulmonary hypoventilation.

Main causes are:

- respiratory failure as a result of pulmonary disease

- neuromuscular disease

- CNS depression.

Compensation by renal conservation of HCo3- and increased excretion of H ions.

Treatment:

- adequate ventilation maintenance.

Respiratory Alkalosis Caused by excessive loss of Co2 as a result of

hyperventilation e.g.

. salicylate intoxication

. head injury

. hysteria.

Compensation:

. increased renal HCo3- excretion

Treatment :

. cause of hyperventilation.

Fluid & Electrolytes Maintenance These are amounts required daily to maintain

homeostasis in a resting basal state.

Maintenance water requirements are 1500ml/m2/d

surface area = 4 x weight+7/weight+90

Maintenance fluid can also be calculated as:

100ml/kg for body weight 1-10 kg

50ml/kg for body weight 11-20 kg

25 ml/ kg for body weight >20 kg

Maintenance Fluid & Electrolytes Maintenance water is needed for:

. Insensible water loss from skin & lungs---40%

. fecal losses ------------------------------------5-10%

. Urinary losses --------------------------------50-55%

Maintenance electrolytes are :

. Sodium ----- 2-3meq/Kg

. Potassium-- 2-3meq/Kg

. Chloride----- 2-3meq/Kg

Dehydration

Fluid and electrolytes disturbances in children are commonly due to GIT illnesses (like diarrhoea, vomiting) and renal disease.

Dehydration -usually due to acute gastroenteritis (loss of water due to diarrhoea and vomiting) with inadequate oral fluid intake.

Fever, hyperventilation, sweating and increased metabolic rate increase water requirement.

Isotonic Dehydration

70% of dehydration in diarrhoea.

S. sodium level is 130-150 meq/l

Net sodium and water loss is proportionate.

ECF tonicity remains normal and there is net loss of water from ICF.

Hypotonic Dehydration

It is 20% in diarrhoea.

S. sodium level is <130meq/l.

Sodium loss is in excess of water e.g. cholera

Losses are mainly from ECF.

Classical signs of dehydration are :

loss of skin turgor, dry mucous membrane, sunken anterior fontanel and seizures etc.

Hypertonic Dehydration

This type of dehydration is 10 % in diarrhoea.

S. sodium level is >150 meq/l.

Water loss is in excess of sodium.

Water loss- mainly from ICF and ECF is well preserved.

Classical signs :

. Skin may feel doughy .

Neurological signs:

. Irritability, lethargy , seizure.

Hyponatremia

S. sodium <130meq/l ,common elec. abnormality.

Common causes- hyperglycemia, hyperlipidemia, hypovolemia like DKA, GIT losses, SIADH, CF .

Treat fluid overload, restrict fluid + diuretics.

Treating symptomatic hyponatremia, rapidly increase Na upto 120 then slowly in 24-36 hours.

Na required (meq/l) = desired - pt.’s Na xWt.x 0.6

Don’t raise or lower Na level > 15meq/l/day.

Hypernatremia

S. sodium>150 meq/l.

Main causes: greater loss of H2O in excess of Na (insensible water loss), insufficient ADH secretion (central diabetes Insipidus),reduced renal response to ADH(nephrogenic DI) , excessive salt intake.

Treatment: replace fluid slowly not in <48 h .

If shock, give 20ml/Kg plasma /N/S in20-30 m

Rapid correction cause cerebral oedema.

Hypokalemia Serum K less than 3.0 meq/l.

Causes: diarrhoea, vomiting, DKA, starvation, RTA, diuretic therapy, inadequate I/V therapy.

There is muscle weakness, paralytic ileus, cramps, areflexic paralysis, lethargy, confusion .

ECG- low, voltage&T wave, U wave, prolonged QT.

Treat: underlying cause, Give oral K supplement.

I/V K infusion very slowly, not >40meq/l in fluid .

Hyperkalemia

S. potassium > 5.5 meq/l.

Causes include: renal failure, Sudden oligurea, massive hemolysis, congenital adreno-cortical hyperplasia, tissue necrosis and tissue destruction.

There is listlessness, mental confusion, bradycardia, arrhythmia and later cardiac arrest.

ECG: increased PR interval, widened QRS complex. Tented T wave, heart block & ventricular fibrillation.

Treatment:Calcium, I/V glucose & insuline,NaHCo3, salbutamole nebulization, kayexalate& p.dialysis etc

Thank you for your attention!