Acid-Base Balance By: Hannah - PowerPoint Presentation

Slide1

Acid-Base Balance

By: Hannah

Coakley

2/27/2014

Slide2

Quick Review: Acids

Acids are compounds which function as

hydrogen (H+) donors

in biochemical equations/solutes

The more free H+ ions available for donation, the more acidic the compound

Many foods that are “acidic” in taste are actually metabolized into basic compounds in the body

Slide3

Quick Review: Bases

Bases are compounds which can

accept H+ ions

.

This is accomplished by having an

excess of OH- (hydroxide) ions

The terms “basic” and “alkaline” are used interchangeably

Slide4

Quick Review: pH

pH is the

–log

of H+ concentration in any given solute

Its range spans from 0 – 14

A lower pH implies a high H+ concentration (acidic). A higher pH implies a low H+ concentration (basic)

Slide5

The pH Scale

Slide6

Role of pH in the Body

Intra and extracellular pH levels are tightly regulated:

Slide7

Acids & Bases in the Body

The body naturally produces

more H+

than OH- ions

This occurs in several ways:

-- The metabolism of fats (fatty acids) and proteins (amino acids)

-- The byproduct of cellular respiration

: where carbonic acid breaks down into CO

2

and H20 to be breathed out by the lungs

Slide8

The Chemical Buffer

System

Works to regulate pH by taking up or releasing H+ ions accordingly

Protects neutrality, usually by pairing a weak acid with a base

Also functions by substituting a strong acid or base for a weak one

Slide9

Methods of Excretion

The other primary way to maintain pH homeostasis is through the excretion of excess acids or bases.

Respiratory excretion

of CO

2

using rate and depth of breath

Renal excretion,

which

eliminates acids and can also regulate the amount of circulating bicarbonate (

HCO

3

-

)

Slide10

pH Balance Visualized

Slide11

Defining Acidosis and Alkalosis

Acidosis:

pH< 7.35

Primary effect is in suppression of the CNS



decreased

Ca binding to protein,

high

I-Cal

Weakness

, coma, death

Alkalosis:

pH > 7.45

Primary effect is in overstimulation of CNS & PNS



increased Ca binding to protein, low I-

C

al

L

ightheadedness

, spasms/

tetany

, death

Slide12

Metabolic vs

Respiratory

Metabolic Acidosis



loss of

relative concentration of bicarbonate ion (< 22

mEq

/L)

(

Symptoms:

Headache, lethargy, N/V/D, coma)

Metabolic Alkalosis



excess of

relative concentration of bicarbonate ion (> 26

mEq

/L)

(

Symptoms:

electrolyte depletion,

tetany

, slow and/or shallow breathing, tachycardia)

Slide13

Metabolic vs

Respiratory

Respiratory Acidosis



carbonic acid excess

leading to

hypercapnia

(p

CO

2

> 45 mm Hg)

(

Symptoms:

warm, flushed skin



vasodilation

, breathlessness, hypoventilation, disorientation, tremors)

Respiratory Alkalosis



carbonic acid deficit

leading to

hypocapnia

(p

CO

2

< 35 mm Hg)

(

Symptoms:

dizziness, lightheaded, numbness of extremities)

Slide14

Compensatory Mechanisms

Depending upon the

primary

acid-base imbalance, the body will compensate using a

secondary

mechanism in order to return pH homeostasis to the body

Slide15

Compensation: Metabolic

Metabolic Acidosis



Increased Ventilation to eliminate excess CO2 (Hyperventilation)

K+ & PO4 shifting from ICF to ECF to function as a buffer (H+ shifts into the cells)

Metabolic Alkalosis



Decreased ventilation (Hypoventilation)

limited by constraints of hypoxia

Slide16

Compensation: Respiratory

Respiratory Acidosis



Kidneys eliminate excess H+ ions, retain Bicarbonate ions

Respiratory Alkalosis 

Kidneys conserve H+ ions and excrete excess

Bicarb

ions

K+ shift from ECF to ICF to increase circulating H+ (sudden low serum K+)

Slide17

Calculating the Anion Gap

Slide18

Interpreting the Anion Gap

If the Anion gap is > than 26

mEq

/L this is considered

normochloremic

acidosis

If the anion gap is WNL (6 – 12

mEq

/L), this is considered

hyperchloremic

acidosis

Slide19

Understanding Base Excess

Slide20

Mixed Acid-Base Disorders

More than one acid/base disturbance can occur concomitantly in the body

If unexpected lab values are noted, there is good reason to suspect a mixed acid-base disorder

Slide21

Treatment Strategies: Metabolic

Acidosis

If

H

yperchloremic

:

IV-Lactate solution is given, this is converted to

bicarb

in the liver, thus raising the relative concentration of bicarbonate in the blood

(shift of K+ back into ICF and may cause a need for it to be

repleted

)

If

Normochloremic

:

Identify and correct sources of excess acids

Slide22

Treatment Strategies: Metabolic

Alkalosis

Saline Responsive

(urine Cl- < 10

mEq

/L)

IV-

NaCl

solution is given to physiologically replace the excess bicarbonate ions in the blood with Cl

** Administration

of

KCl

is also essential, as adequate K+ buffer in the ECF is essential to fully correcting the alkalosis

Slide23

Treatment Strategies: Respiratory

Acidosis

-- Treat the underlying dysfunction or disease

-- Restore appropriate ventilation

-- Add IV-lactate to aid in compensatory

bicarb

production

-- Ensure that the patient is not being overfed, as this will prolong acidosis (via excess CO2 production)

Slide24

Treatment Strategies: Respiratory

Alkalosis

-- Treat underlying dysfunction or disease

-- Attempt to slow respiration

-- Add IV-

Cl

to aid in compensatory replacement of excess

bicarb

-- Replete K+ as needed, since K+ shifts

intracellularly

in exchange for H+ in the ECF

Slide25

Correcting Acid/Base Imbalance:

Step By Step

Analyze the pH

2) Analyze the pCO

2

3) Analyze the HCO

3

4) Match the pCO

2

or the HCO

3

with the pH

5) Assess AG and BE

6) Assess directionality/compensation

7) Analyze the pCO

2

and O

2

saturation

Slide26

Check Your Knowledge

Scenario #1a:

pH: acidic // CO2: high // HCO3: high

What is the primary imbalance? Is there evidence of compensation?

#1b

:

What if HCO3 was normal? Low?

Slide27

Take Home:

What is the RD’s Role?

Monitoring

Treatment (Repletion of electrolytes and fluids)

Maintenance (appropriate TF or TPN)

Slide28

Thank You!

Slide29

References

Brantley, Susan. The ABCs of ABGs.

Support Line.

UT Medical Center, Knoxville, TN.

Langley, Ginger. Fluid, Electrolytes, and Acid-Case Disorders.

A.S.P.E.N Nutrition Support Core Curriculum,

2007.

Gilmore, Diane M. Acid Base Balance and Imbalance.

Arkansas State University, Dept of

Pathophysiology

,

2012.

Ebihara

, L. & West, John. Acid-Base Balance, A Respiratory Approach.

Repiratory

Physiology, The Essentials.

2011

Jaber

, Bertrand. Metabolic Acidosis.

Tufts University Open Courseware, Renal

Pathophysiology

.

2007.

Kibble, Jonathan D.& Colby R. Halsey, 

Medical Physiology: The Big Picture. 2009

.

Skujor

, Mario & Mira

Milas

.

Endocrinology

. Cleveland Clinic: Center for Continuing Education. 2013