Acid Base Balances in Medical Surgical Nursing

ACID-BASE BALANCE
Introduction:
• Body desires homeostasis or equilibrium
• Acids and bases must be kept in balance to achieve homeostasis
• In a healthy person the following keeps the person in effective acid base balance
o Metabolic processes and buffers à produce acids open means partial
o Respiratory system




minimum
o Kidneys
• Health problems can lead to imbalances ·
o Diabetes mellitus
o Vomiting and diarrhea
o Respiratory conditions
• Acid à substance that can donate H+ to a base
o Carbonic acid
• Base à a substance that can accept or bind H+ mom
o Bicarbonate
• pH à reflects the overall H+ concentration in body fluids

pH & H+ Ion Concentration:
• acidity or alkalinity depends on H+ ion concentration
o H+ ions must be maintained within very narrow limits for normal body function
§ Acid-base imbalances occur when these limits are exceeded
• H+ ion concentration is usually expressed as negative logarithm
o Symbolized as pH
• Negative logarithm à low pH = high H+ concentration
• pH of 7.0 is neutral
• normal arterial blood = 7.35-7.45 • PH < 7.35 = acidosis
• INCREASED H+ IONS à INCREASE PH à pt is alkalotic • PH > 7.45 = alkalosis
• A pH lower than 6.8 or higher than 7.8 is usually fatal
• pH represents a balance between the percentage of H+ ions and the
% of bicarbonate ions

Acid Base Parameters:
Acidosis Normal Alkalosis
pH < 7.35 7.35-7.45 >7.45
pCO2 >45 35-45 mmHg <35
HCO3 <22 22-26 mEq/L >26
<21 21-28 mEq/L >28

, Respiratory & Metabolic Parameters:
• carbon dioxide is the respiratory parameter of acid base balance
o if there is too much CO2 à pt is acidotic
o slow shallow ventilation increases concentration of CO2 in the blood
• bicarbonate is the metabolic parameter of acid base balance

Acidosis:
• high concentration of H+ ions in the blood
o pH is low
• caused by too much or too lile base
• too much carbon dioxide
• too lile bicarbonate

Alkalosis:
• low concentration of H+ ions
o pH is too high
• caused by too much alkaline (bicarbonate) or too lile acid (H+ ions or CO2)
o too much bicarbonate leads to metabolic alkalosis
o too lile CO2 leads to respiratory alkalosis

Compensation:
• disease process can interfere with acid base balance
o respiratory à kidneys compensate
§ aempt to normalize pH
o metabolic à lungs compensate
§ normalizes pH

Acid-Base Regulation:
• acids must be neutralized & excreted to main acid-base balance
• 3 mechanisms by which it regulates acid-base balance
o Buffer system
o Respiratory system
o Renal system
• These regulatory mechanisms react at different speeds
• BUFFERS react immediately
o Primary regulator of acid-base balance
o Chemicals that combine w an acid or base to weaken or neutralize it
o Chemical buffer system is the 1st line of defense at cellular level to buffer excess acid or base
• RESPIRATORY SYSTEM responds in minutes à reaches max effect in hours
o Increased depth and rate of respirations causes CO2 to decrease à alkalosis (pH increases)
o Shallow and slow respirations cause CO2 to increase à acidosis (pH decreases)
• RENAL RESPONSE takes 2-3 days to response maximally
o Excrete acids and bases into the urine
o Kidneys can reabsorb bicarbonate or H+