acid base fall 2008

8/14/2019 Acid Base Fall 2008

1/34

Robin Connell MS RN

Fall 2008

Acid/Base Disorders


2/34

Objectives

Define Acid/ Base influence in the body

Know the normal values of the components of BloodGas

Relate abnormal Blood Gases to ElectrolyteDisturbances

Discuss Treatment options for those with complexmetabolic disorders

Correlate patient diagnosis to potential acid/basedisturbances

2


3/34


4/34

pH Scale


5/34

Human pH Scale


6/34

Acid / Base

Acid = a substance that can donate hydrogen ionsH2CO3 (carbonic acid) ( H+) + (HCO3-)

Base is a substance that can accept hydrogen ions

HCO3- + (H+) H2CO3

PaCO2- is controlled by the lungs and refers to thepressure exerted by dissolved CO2 gas in blood.

PaO2-refers to the pressure exerted by dissolved oxygen inthe blood

6


7/34

pH in the Human Body

Normal Range pH 7.35 7.45

How does the body maintain this narrow normal

range?Chemical buffering mechanisms: Kidneys & Lungs

The more (H+) the more acidic the solution.

Compatibility with life pH 6.8 7.8. This range

equals a ten fold difference in (H+) concentration

7


8/34

pH Laboratory Test

pH is most optimally determined by arterial blood gas

analysisBlood Gases can be done by one certified in this

procedure

RNs, RPT, Physicians


9/34

Normal Arterial Blood Gas ValuesPH 7.35-7.45 pH< 7.35 acidosis

PaCO2 35-45 < 35 (respiratory alkalosis)

>45 (respiratory acidosis)

Pao2 80-100mmHg

HCO3 22-26 mEq/L

9


10/34

Respiratory System

Lungs are the initial and primary organ in the control

of pH

Changes in the rate and the depth of respiration canhave significant and immediate affects on the pH of

the individual

Kidneys have a secondary affect and are called into

action if the respiratory system can not affect a changein the pH.

10


11/34

Chemical Buffering Mechanisms

Buffering results in a change in the amount of H+ ions

through release or removal of H+ ions

Bodys Major Buffer is bicarbonate (HCO3-) andcarbonic acid (H2CO3)

Normally there are 20 to1 Ratio HCO3- to H2CO3 if

this ratio is upset the pH will change

Buffers prevent major changes in the pH of bodyfluids

by removing or replacing H+

11


12/34

BuffersBodys major extracellular buffer is the bicarbonate-

carbonic acid buffer system

CO2 is a potential acid; when dissolved in H2O

(CO2+H2O)=H2CO3 so when CO2 carbonic acid is

also and vice versa

Kidneys regulate the bicarbonate level in the ECF

( In the presence of respiratory acidosis and most

metabolic acidosis kidneys excrete H+ and conservebicarbonate ions)

12


13/34

Buffers

Lungs under influence of respiratory center (Medulla)

control CO2 (and thus carbonic acid)

It adjusts ventilation in response to the amount of

CO2, and to a lesser extent O2

CO2 has an immediate effect on respiratory efforts;

but declines over time for the next 1-2 days. So after 2

days elevation of blood CO2 has only a weak effect asa respiratory stimulant.

13


14/34

LungsPartial pressure of O2 in arterial blood (PaO2)

influences respiration, but does not do so unless PaO2

falls below 60mmHg

Lungs compensate for metabolic disturbances by either

conserving or retaining CO2

Metabolic acidosis respirations is = elimination of

CO2 (lighten the acid load)

Metabolic alkalosis respiration is = retention ofCO2 (increasing the acid load)

14


15/34

Effects of pH on Potassium

Generally acidic states cause potassium to shift from

the cells ECF plasma potassium concentration

The opposite happens in alkalemia; potassium shifts

the cells the plasma potassium concentration.

(metabolic and respiratory)

Hypokalemia is commonly present in patients in

patients with metabolic alkalosis15


16/34

AcidemiaA shift in potassium out of the cells can occur in acidemia

(metabolic or respiratory) respiratory being a weaker stimulus

H+ ions shift the cells to correct the low plasma pH topreserve cellular electroneutrality cellular potassium shift from

the cells the ECF

Hyperkalemia is less marked when do to lactic acidosis orketoacidosis then when due to renal failure or diarrhea

Hyperkalemia does occur in untreated diabectic ketoacidosis,due more to insulin lack

16


17/34

Metabolic Acidosis

Clinical disturbance characterized by pH and

bicarbonate concentration

Lungs hyperventilate to CO2 concentration


18/34

Anion GapMetabolic Acidosis can be divided into two forms depending on

the values of the serum anion gap

Anion Gap (AG) = Na+ - (CL- + HCO3-)= 8-12mEq/L

or

Anion Gap (AG) = Na+ + K+ - (CL- + HCO3-) = 12-16mEq/L

Anion Gap reflects normally unmeasured anions (phosphates,sulfates, and protein in plasma)

An Anion Gap 16 suggests excessive accumulation of

unmeasured anions

18


19/34


20/34

Clinical Manifestations

Headache, confusion, drowsiness, RR and depth ofrespirations, N/V, peripheral vasodilation, Cardiac

Output occurs when pH 7.0, BP, cold clammy skin,

dysrhythmias and shock

Lactic Acidosis-most commonly seen in patients with

significant cardiopulmonary problems and sepsis.


21/34

Normal Anion Gap Acidosis

Diarrhea-direct loss of Bicarbonate in the stool, ECF

volume depletion, and concentration of the remaining

chloride, also referred to as hyperchloremic acidosis

Excessive chloride due to IV infusion

Use of diuretics

A reduced or negative anion gap is primarily causedby hypoproteinemia usually a rare occurance.


22/34

Metabolic Acidosis

ABGs look like: Bicarbonate 22 mEq/L pH 7.35

serum Bicarb level

Hyperkalemia may accompany shift K+ out of the cell

into the ECF

Hyperventilation to decrease CO2 as compensatory

mechanism

Management: correct metabolic defectif Cl- eliminate source

Give Bicarb for pH 7.1 or HCO3 10


23/34

Metabolic Acidosis

Example: Patient with diabetic ketoacidosis

pH = 7.05

HCO3 = 5 mEq/L( primary disturbance)PaCO2 = 12mmHg (compensatory

hyperventilation)

Base excess (BE) = -30

Acidosis depresses myocardial contractility, lowers thefibrillation threshold.


24/34

Metabolic AlkalosisExcess HCO3High pH (decreased H+ concentration)

High plasma bicarbonate concentration

Causes= by a gain in bicarbonate or loss of hydrogen

Compensation=lungs hypoventilate to increase PaCO2

Common causes = vomiting or gastric suction ( loss of H+

and CL- ionsOveruse of diuretics, Excessive alkali ingestion

24


25/34

Hypokalemia & Alkalosis

Kidneys conserve K+ H+ excretion increases

Cellular K+ moves out of the cell ECF to helpmaintain serum level. (as K+ leaves the cell H+ enters

to maintain electroneutrality.


26/34


27/34

Respiratory Acidosis

H2 CO3 Excess can be acute or chronicAcute is more dangerous

Renal compensation is very slow

High PaCO2 can quickly produce a sharp decrease inplasma pH

Causes: always due to inadequate excretion of CO2

(inadequate ventilation)

Pulmonary Edema, pneumothorax, atelectasis, overdoseof sedatives etc

27


28/34

Signs and Symptoms

PaCo2 pulse and Respiratory rate,BP, mentalcloudiness, and a feeling of fullness in the head

cerebrovascular vasodilation

Example: Acute Respiratory Acidosis

pH 7.26

PaCO2 56

HCO3 2428


29/34

Chronic Respiratory Acidosis

Patient may complain of weakness, dull headachepH may be low normal like 7.35 (if complete

compensation has occurred)

PaCO3 45 mmHg

Example: Chronic Respiratory Acidosis

pH 7.38

PaCO2 76

HCO3 42BE +14

Remember when PaCO2 is chronically elevated??????? 29


30/34

Respiratory Alkalosis

H2CO3 deficit due to hyperventilation causing excess

blowing off of CO2 decrease in Plasma H2CO3

Signs and Symptoms:

Fever, extreme anxiety, hypoxemia, gram negative

Bacteremia, Pulmonary Emboli, Excessive ventilation

by ventilators

30


31/34

RespiratoryAlkalosis

Acute: pH 7.52

PaCO2 30mmHg

HCO3 24

BE +2.5mEq/L

Chronic: pH 7.40

PaCO2 30

HCO3 18mEq/L

BE -5 31


32/34

Mixed Acid Base Imbalances

Respiratory Alkalosis Plus Metabolic AcidosisExample:

pH 7.4

PaCO2 18mmHg

HCO3 16mEq/L

BE -10

Examples of Disorders that cause mixed acid/baseimbalances: Cardiopulmonary Arrest, Salicylate

Intoxication, Renal failure and vomiting etc

32


33/34

Systemic Assessment of Blood Gas

First look at the pH:

Determine the primary cause of the disturbance this is

done by evaluating the PaCo2 and HCO3 in relation to

the pH

Determine if compensation has occurred

33


34/34

Questions??????

Practice on Blood Gas Problems

Look on-line

acid base fall 2008

Documents