Acid Base Imbalance

Peggy D. Johndrow

2009

Must it be so complicated!

• Key concepts• pH• PC02• Base Excess

What I need to knowComponents

Two ComponentsRespiratory

Metabolic

What I need to knowRespiratory

Respiratory When breathing is inadequate carbon dioxide (respiratory acid) accumulates. Extra C02 combines with water to form carbonic acid which leads to an acid PH

Evaluate PC02

What I need to knowMetabolic

Metabolic When metabolism is impaired acid forms, poor blood supply stop oxidative metabolism and lactic acid forms. “Metabolic Acid”

Why do we care?

Variations in pH or PC02 are not causes of pathology (lab values)

Both may be well tolerated when circulation and oxygenation maintained

Abnormal levels of pH and PC02 are best indicators of trouble

Let’s Review

pH represents degree of acidity of fluid

Major concern pH of blood

Normal range 7.35-7.45

Incompatible with life value 6.8-7.8

Normal Blood pHKeeping pH within normal range involves balancing acids and bases in body fluidsNormal pH for arterial blood: 7.35 to 7.45Normal pH for venous blood: 7.31 to 7.41Changes from normal blood pH interfere with many normal functions by:Changing shape of hormones & enzymesChanging distribution of other electrolytes,

causing fluid & electrolyte imbalances.Changing of excitable membranesDecreasing effectiveness of many hormones &

medications

Acid-Base Chemistry

AcidsBasesBuffersBody fluid chemistry:Bicarbonate ionsRelationship between carbon dioxide and

hydrogen ionsCalculation of free hydrogen ion level

pH Control

Controlled precisely because even minor deviation from normal can affect body organs

Hydrogen ion concentration directly relates to pH

Acid pH

Higher hydrogen ion concentration more acid the fluid

More acid solution lower the pH

Sources of Acids

Incomplete breakdown of glucoseDestruction of cellsBicarbonate

Alkaline pH

Lower hydrogen ion concentration more alkaline the pH

More alkaline fluid higher the pH

Acid Base Balance Table

Mechanisms Regulate Acid Base Balance

pH Buffers: Bicarbonate-Carbonic Acid Buffer System

Lungs

Kidneys

Bicarbonate-Carbonic Acid Buffer System

Normal ratio 20 to 1

20 parts HC03- to 1 part H2C03

If alter 20:1 ratio pH will change (not value but ratio that determines pH)

What is carbonic acid?

Carbon dioxide(C02) potential acid when dissolved in H20 becomes carbonic acid (C02 + H20 = H2C03)Key:When C02 the H2C03 When C02 the H2C03

If either changes so the 20:1 ratio is no longer maintained results in acid base imbalance

Respiratory Acid-Base Control Mechanisms

Chemical buffers alone cannot prevent changes in blood pH, respiratory system second line of defense against changes:HyperventilationHypoventilation

Respiratory Mechanism Diagram

Lungs Alkaline

Excretion of carbon dioxide(C02)

Respiratory center regulates amount of C02 exhaled by controlling speed and depth of respirations

Increased respiration (tachypnea) C02 level decreases and blood pH becomes more base

Lungs Acid

Decreased respirations (bradypnea) C02 increases and the blood becomes more acidic.

By adjusting the speed and depth of respirations; the respiratory center and lungs are able to regulate blood pH minute to minute

Renal Acid-Base Control Mechanisms

Kidneys third line of defense against wide changes in body fluid pHStronger for regulating acid-base balance but take longer to completely respond than chemical & respiratory mechanisms Kidney movement of bicarbonateFormation of acidsFormation of ammonium

Kidneys

Excess acid excreted by kidneysHave ability to alter amount of acid or base excreted but generally process takes hours to daysCan retain or excrete hydrogen(H+) and Bicarbonate(HC03-) to restore balanceKidneys can’t compensate with renal failure or severe impairment

Compensation

Body attempts correct changes in blood pHpH below 6.9 or higher than 7.8 usually fatalRespiratory system more sensitive to acid-base changes; can begin compensation efforts within seconds to minutesRenal compensatory mechanisms much more powerful & result in rapid changes in ECF composition not fully triggered unless imbalance continues for several hours to days

Respiratory Compensation

Lungs compensate for acid-base imbalances of metabolic originExample: Prolonged running causes buildup of lactic acid, hydrogen ion levels in ECF increase, pH drops; breathing triggered in response to increased carbon dioxide levels to bring pH level back to normal

Renal Compensation

Healthy kidney can correct or compensate for changes in blood pH when respiratory system either overwhelmed or unhealthyExample: Person has chronic obstructive pulmonary disease, retains carbon dioxide in blood, blood pH level falls (becomes more acidic); kidney excretes more hydrogen ions & increases re-absorption of bicarbonate back into blood

Acidosis and Alkalosis

Metabolic caused by an imbalance in production and excretion of acids or bases by kidney

Respiratory caused primarily by lung or breathing disorders which affect CO2

Normal Arterial Values

Parameter Arterial Sample

pH 7.35-7.45

PaC02 35-45 mmHg

Pa02 80-100 mmHG

Oxygen Saturation 95-100%

Base Excess + or - 2

HC03- 22-26 mEq/L

Acid Base Guide

Disorder Initial Event Compensation

Respiratory Acidosis PaC02 or normal HC03 pH

Kidneys eliminate H+ and retain HCO3-

Respiratory Alkalosis PaC02 or normal HC03 pH

Kidneys conserve H+ and excrete HC03-

Metabolic Acidosis or normal PaC02 HC03- pH

Lungs eliminate C02 conserve HC03-

Metabolic Alkalosis or normal Pac02 HCO3- pH

Lungs ventilation to PC02 kidneys conserve H+ to excrete HC03-

Acid Base Key Concept

With Respiratory reverse relationship

Increase PaC02/HC02 Decrease pH

Decrease PaC02/HC02 Increase pH

Metabolic

acidosis all values decreased (equal)

alkalosis all values increased (equal)

Metabolic Acidosis

Excessive blood acidity characterized by inappropriate low level of bicarbonate

Increase in acid and blood becomes acidic

Metabolic Acidosis Causes

Kidney FailureDiabetic KetoacidosisLactic AcidosisPoison: Salicylate(overdose), Methanol(wood alcohol), paraldehyde, ethylene glycol (antifreeze),acetazolamide, ammonia chlorideLoss of base through GI tract (diarrhea, ileostomy or colostomy)

Metabolic Acidosis Symptoms

Mild Nausea, vomiting , fatigue, tachypnea

Moderate Extreme weakness, sleepy, confusion,

increased nausea

Severe Severe drop in BP, shock, coma, death

Metabolic Acidosis Treatment

Depends on cause

Treat underlying cause such as control diabetes or remove toxin from blood

Occasionally dialysis

Direct treatment Mild: IV fluids and underlying disorder Severe: bicarbonate IV (used with caution)

Metabolic Alkalosis

Condition in which the blood is alkaline because of an inappropriately high level of bicarbonate

Metabolic Alkalosis Causes

Body loses too much acid or ingest too much alkali from substance like bicarbonate of soda(baking soda for indigestion)

Excessive loss of Na or K affects kidneys ability to control blood acid-base balance

Diuretics (thiazides, furosemide, loop diuretics)

Loss of acid from vomiting or GI suction

Overactivity of adrenal gland (Cushing's or use of steroids)

Metabolic Alkalosis Symptoms

Mild Can have no symptoms at all Irritably, muscle twitching and muscle

cramps

Severe Prolonged contraction of and spasms of

muscle tetany

Metabolic Alkalosis Treatment

Replace water and electrolytes(NA and K)

Treat underlying cause

Severe occasionally dilute acid in the form of ammonium chloride is given IV

Respiratory Acidosis

Excessive blood acidity caused by build up of carbon dioxide

Respiratory Acidosis Causes

Anything that interferes with lungs ability to expel carbon dioxide adequately Emphysema, Chronic bronchitis, Asthma Severe pneumonia Pulmonary edema Over-sedation with narcotics sleeping medication

or overdose

Also with impairment of nerves or muscles that impair mechanics of breathing

Respiratory Acidosis Treatment

Improve lung function

Medications to improve lung function

Artificial respirations with a mechanical ventilator

Respiratory Alkalosis

Condition in which blood is alkaline because of rapid or deep breathing results in a low blood carbon dioxide

Respiratory Alkalosis Causes

Hyperventilation

Anxiety

Pain

Cirrhosis of the liver

Low oxygen levels in the blood

Fever

Aspirin(salicylate) overdose

Respiratory Alkalosis Treatment

Slow rate of breathing

Administer pain medication

Breathe into paper bag helps raise C02 level, person rebreathes C02 back in after breathing out.

Hold the breath as long as possible and repeat the sequence 6 to 10 times

Let’s Practice

http://www.mhhe.com/biosci/ap/ap_casestudies/cases/ap_case14.html

http://www.rnceus.com/abgs/abgframe.html

Acid Base References

http://www.tmc.tulane.edu/departments/anesthesiology/acid/default.html

http://qldanaesthesia.com/AcidBaseBook/Abindex.htm

Or type in acid base and see what helps you