Acid- base

Dr Ardra Thorat
MS (Shalyatantra)

Acid base balance
 Regulation of H+ ion balance is similar in some ways
to the regulation of the other ions in the body, to
achieve Homeostasis.
 Precise regulation of pH (7.35-7.45) is necessary for
normal cellular enzymatic reactions & for normal ionic
conc.
8/7/2020 2Dr Ardra B. Thorat

A Hydrogen ion is single free proton release from
Hydrogen atom
 Acid- molecules containing hydrogen atom that
can release H+ ion is solutions.
e.g HCl, H2CO3 (carbonic acid)
 Base- it is an ion/molecule that can accept H+ ion
e.g- HCO3 – (bicarbonate ion)
Normally blood H+ ion conc. Is maintained within
tight limits around normal values of about
0.00004mE/L (40nEq/L) normal variation is about 3-
5nEq/L , because normal H+ ion conc. Is very low and
small in no. it is customary to express H+ conc. In
logarithm scale .
pH is inversely proportional to the H+ ion conc.

1
pH = log -------- = - log [H+]
[H+]
e.g normal H + ion conc. Is 40nEq/L
(0.00000004 Eq/L) :. Normal pH is
pH= -log[0.00000004]
pH= 7.4

pH & H+ ion conc. In Body fluids
H + Conc. mEq/L pH
Extracellular
fluid
Arterial blood 4.0 x 10 -5 7.40
Venous blood 4.0 x 10 -5 7.35
Interstitial
fluid
4.0 x 10 -5 7.35
Intracellular
fluid
1 x 10 -3 to 4 x 10 -5 6.0 to 7.4
Urine 3 x 10 -2 to 1 x 10 -5 4.5 to 8.0
Gastric HCl 160 0.8

Acid – Base Terminology
Clinical terminology Criteria
Normal pH 7.4 (7.35 to 7.45)
Acidaemia pH < 7.35
Alkalaemia pH > 7.45
Normal PaCO2 40 (35 to 45) mm of Hg
Respiratory acidosis
(failure )
PaCO2 > 45 mm of Hg & low
pH
Respiratory alkalosis
(Hyperventilation)
PaCO2 < 35 mm of Hg & high
pH
Normal HCO3 24 (22-26) mEq/L
Metabolic acidosis HCO3 < 22 mEq/L & low pH
Metabolic Alkalosis HCO3 > 26 mEq/L & high pH

Basic physiology of Acid Base
regulation
1. Buffers: buffers are chemical/ any substance which
either release or accept H+
*Buffer + H+ H Buffer
*The Bicarbonate buffer system
CO2 + H2O H2CO3 H+ + HCO3-
*The phosphate buffer system
HCl + NaH2PO4 NaH2PO4 + NaCl
NaOH + NaH2PO4 Na2HPO4 + H2O
*Protein : imp intracellular buffer = H+ + Hb
HHb

Arterial Blood Sample
<7.4 pH > 7.4
Acidosis Alkalosis
Metabolic Respiratory Metabolic Respiratory
HCO3- PCO2 HCO3- PCO2
< 24 mEq/L > 40mm of Hg >24 mEq/L < 40mm of Hg
Respiratory Renal Respiratory Renal
Compensation Compensation Compensation
Compensation
PCO2 HCO3- PCO2 HCO3-
<40mm of Hg >24 mEq/L > 40mm of Hg < 24 mEq/L

Metabolic acidosis
 Definition – it is characterized by fall in plasma HCO3 &
fall in pH (below 7.35).
(The PaCO2 is reduced secondarily by
hyperventilation, which minimizes the fall in pH)
 Pathophysiology – metabolic acidosis can result from
1. Loss of base – HCO3 via GIT or kidneys (diarrhea
NaHCO3- ion loss, proximal RTA )
2. Overproduction of metabolic acids in body
3. Ingestion / infusion of acids or potential acids
4. Failure of H+ excretion by kidney – renal tubular
acidosis or reabsorption of HCO 3- ions

 Metabolic acidosis is a condition in which there is too
much acid in the body fluid

Causes
 It can also occur when the kidneys are not removing
enough acid from the body.
There are several types of metabolic acidosis.
 Diabetic acidosis develops when acidic substances,
known as ketone bodies, build up in the body. This
most often occurs with uncontrolled type 1 diabetes. It
is also called diabetic ketoacidosis (DKA)
 Hyperchloremic acidosis results from excessive loss
of sodium bicarbonate from the body. This can occur
with severe diarrhea.

 Lactic acidosis results from a buildup of lactic acid. It
can be caused by:
1. Alcohol
2. Cancer
3. Exercising intensely
4. Liver failure
5. Medicines, such as salicylates
6. Prolonged lack of oxygen from shock, heart failure,
or severe anemia
7. Seizures

 Other causes of metabolic acidosis include:
1. Kidney disease (distal renal tubular acidosis and
proximal renal tubular acidosis)
2. Poisoning by aspirin, ethylene glycol (found in
antifreeze), or methanol
3. Severe dehydration

Symptoms
 Metabolic acidosis itself most often causes rapid
breathing.
 confused or very tired.
 Severe metabolic acidosis can lead to shock or death.
 In some situations, metabolic acidosis can be a mild,
ongoing (chronic) condition.

Exams and Tests
 Arterial blood gas
 Basic metabolic panel, (a group of blood tests that
measure sodium and potassium levels, kidney
function, and other chemicals and functions)
 Urine pH
 Urine ketones or blood ketones
 Lactic acid test
 Other tests may be needed to determine the cause of
the acidosis.

Treatment
 Treatment is aimed at the health problem causing the
acidosis.
 In some cases, sodium bicarbonate (the chemical in
baking soda) may be given to reduce the acidity of the
blood

Metabolic alkalosis
 Increase sr. HCO3
 High pH
 Causes
 Loss of H + from upper GIT- vomiting
 Urine diuresis
 Addition of Alkali- multiple BT

c/ f
 CNS- increase neuromuscular excitability,
paraesthesia, light head ache,
 CVS- hypotension, cardiac arrhethmias
 weakness., muscle cramps, postural dizziness

 Sr. potassium & chloride usually low
 ABG
 Urinary chloride

Rx
 IV isotonic saline + KCL/ isolyte G
 Stop Treatment H2 inhibitors/ proton pump inhibitors

Respiratory acidosis
 Respiratory acidosis is a condition that occurs
when the lungs cannot remove all of the
carbon dioxide the body produces.
 This causes body fluids, especially the blood,
to become too acidic.

Cont..
 is a medical emergency in which decreased ventilation
(hypoventilation) increases the concentration
of carbon dioxide in the blood and decreases the
blood's pH (a condition generally called acidosis).
 Carbon dioxide is produced continuously as the body's
cells respire, and this CO2 will accumulate rapidly if
the lungs do not adequately expel it through alveolar
ventilation.
 Alveolar hypoventilation thus leads to an
increased PaCO2 (a condition called hypercapnia).
The increase in PaCO2 in turn decreases the
HCO3
−/PaCO2ratio and decreases pH.
8/7/2020 Dr Ardra B. Thorat 22

 pH
 H+
 PaCo2
 Retention of Co2
 Inadequate ventilation

Types of respiratory acidosis
 Acute respiratory acidosis, the PaCO2 is elevated
above the upper limit of the reference range (over 6.3
kPa or 45 mm Hg) with an accompanying acidemia
(pH <7.36).
 Chronic respiratory acidosis, the PaCO2 is elevated
above the upper limit of the reference range, with a
normal blood pH (7.35 to 7.45) or near-normal pH
secondary to renal compensation and an elevated
serum bicarbonate (HCO3
− >30 mm Hg).

Causes
 Diseases of the airways - asthma and chronic
obstructive lung disease
 Diseases of the chest/ crushing injury
 Diseases affecting the nerves and muscles that
"signal" the lungs to inflate or deflate
 Drugs that suppress breathing (including powerful
pain medicines, such as narcotics, and "downers,"
such as benzodiazepines), especially when combined
with alcohol
 Severe obesity, which restricts how much the lungs
can expand
 Obstructive sleep apnea

Cont..
 Anaestesia with too much muscle relaxant
 Lung disorder- emphysema, bronchopneumonia,
chronic bronchitis
 Respiratory centre depress by brain
injury/poison/alcohol

Chronic respiratory acidosis
 This leads to a stable situation, because the kidneys
increase body chemicals, such as bicarbonate, that
help restore the body's acid-base balance.
 Acute respiratory acidosis is a condition in which
carbon dioxide builds up very quickly, before the
kidneys can return the body to a state of balance.
 Some people with chronic respiratory acidosis get
acute respiratory acidosis because an illness makes
their condition worse.


c/f
 Causes
 systolic & diastolic BP- HTN
 restlessness

Exams and Tests
 Arterial blood gas, which measures oxygen and carbon
dioxide levels in the blood
 Basic metabolic panel
 Chest x-ray
 CT scan of the chest
 Pulmonary function test

Treatment
 Adequate ventilation
 Bronchodilator drugs to reverse some types of
airway obstruction
 ET- mechanical ventilation
 Noninvasive positive-pressure ventilation
(sometimes called CPAP or BiPAP) or a breathing
machine, if needed
 Oxygen if the blood oxygen level is low
 Treatment to stop smoking

Complications
 Poor organ function
 Respiratory failure
 Shock

Respiratory alkalosis
 Respiratory alkalosis is a condition marked by low
levels of carbon dioxide in the blood due to breathing
excessively.

Causes
 Anxiety
 High grade Fever
 Hyperventilation-during anesthesia AMBU with
excess muscle relaxant
 High altitude, dry atmosphere.
 CO poisoning
 Pregnancy
 Any lung disease that leads to shortness of breath can
also cause respiratory alkalosis (such as pulmonary
embolism and asthma).

Symptoms
 Dizziness
 Light-headedness
 Numbness of the hands and feet
 Some risk of respiratory arrest
 Palor
 BP

Exams and Tests
 Arterial blood gas, which measures oxygen and carbon
dioxide levels in the blood
 Basic metabolic panel
 Chest x-ray
 Pulmonary function test

Treatment
 Breathing into a paper bag -- or using a mask that
causes you to re-breathe carbon dioxide -- sometimes
helps reduce symptoms.

Acid- base

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