Acid Base Ined 2014

8/12/2019 Acid Base Ined 2014

http://slidepdf.com/reader/full/acid-base-ined-2014 1/39

BLOOD GASES AND

ACID – BASE DISORDERS

Dr. Wan Nedra Sp. A

Pediatricts Departement

University of YARSI



LEARNING OBJECTIVES

By the end of the session, the student will be

able to:

1. Identify the causes of acid base imbalance

in children.

2. Recognise the clinical manifestations that

may be seen in a child with acid baseimbalance.

3. Interpret blood gas analysis.



CAPILLARY BLOOD GASES:pH: Same as arterial or slightly lower (Normal = 7.35-7.40)

pCO2: Same as arterial or slightly higher (Normal = 40-45)

pO2: Lower than arterial (Normal = 45-60)

O2 Saturation: >70% is acceptable.



blood gas machines

• The blood gas machines in most labs

actually measure the pH ,the pCO2 and the

pO2.

• The [HCO3-] and the base difference are

calculated values using the Henderson-

Hasselbalch equation



For a rough estimate of [H+]

• [H+] = (7.80 -pH) x100.

• This is accurate from a pH 7.25 to 7.48;

• 40 mEq/L = [H+] at the normal pH of 7.40.

• pH is a log scale, and for every change of 0.3 in

pH from 7.40 the [H+] doubles or halves.

• For pH 7.10 the [H+] = 2 x 40, or 80 nmol/L, andfor pH 7.70 the [H+] = 1/2 x40, or 20 nmol/L.



pCO2 and pH

• A change in pCO2 up or down 10 mm Hg is

associated with an increase or decrease in

pH of 0.08 units.

• As the pCO2 decreases, the pH increases;

as the pCO2 increases, the pH decreases.



base deficit and base excess

• A pH change of 0.15 is equivalent to a base

change of 10 mEq/L.

• A decrease in base (i.e, [HCO3-]) is termed

a base deficit, and an increase in base is

termed a base excess.



Acidosis and alkalosis

• Acid-base disorders are very common clinical problems.

• Acidemia is a pH <7.37, and• alkalemia is a pH >7.44.

• Acidosis and alkalosis are used to describe howthe pH changes.

• The primary causes of acid-base disturbances areabnormalities in the respiratory system and in themetabolic or renal system.



normal compensatory response

• Any primary disturbance in acid-base homeostasis

invokes a normal compensatory response.

• A primary metabolic disorder leads to respiratorycompensation, and a primary respiratory disorder

leads to an acute metabolic response due to the

buffering capacity of body fluids.

• A more chronic compensation (1-2 days) due to

alterations in renal function.



Mixed acid-base disorder

• Most acid-base disorders result from a single primary disturbancewith the normal physiologic compensatory response and are calledsimple acid-base disorders.

• In certain cases, however, particularly in seriously ill patients, twoor more different primary disorders may occur simultaneously,resulting in a mixed acid-base disorder.

• The net effect of mixed disorders may be additive (eg, metabolicacidosis and respiratory acidosis) and result in extreme alterationof pH;

• or they may be opposite (eg, metabolic acidosis and respiratoryalkalosis) and nullify each other’s effects on the pH.







INTERPRETATION OF BLOOD GASES

Step 1:

• Determine if the numbers fit.

• The right side of the equation should be within about10% of the left side.

• If the numbers do not fit, you need to obtain another

ABG



INTERPRETATION OF BLOOD GASES

Step 2:

determine if an acidemia (pH <7.37)

or an alkalemia (pH >7.44) is present.



Step 3: Identify the primary disturbance as

metabolic or respiratory.

• For example, if acidemia is present, is the pCO2 >44 mm Hg (respiratoryacidosis), or is the [HCO3 -] <22 mmol/L (metabolic acidosis).

• In other words, identify which component, respiratory or metabolic, isaltered in the same direction as the pH abnormality.

• If both components act in the same direction (eg, both respiratory [pCO2 >44 mm Hg] and metabolic [HCO3 - <22 mmol/L] acidosis are present),then this is a mixed acid-base problem.

• The primary disturbance will be the one that varies from normal thegreatest, that is, with a [HCO3 -] = 6 mmol/L and pCO2 = 50 mm Hg, the

primary disturbance would be a metabolic acidosis, the [HCO3 -] is aboutone-quarter normal, whereas the increase in pCO2 is only 25%.



Step 4:

• Calculate the anion gap.

• Anion gap = Na+ - (Cl- + HCO3 -).

• Normal anion gap is 8-12 mmol.



Step 5:

If the anion gap is elevated• Then compare the changes from normal between the

anion gap and [HCO3 -].

• If the change in the anion gap is greater than thechange in the [HCO3 -] from normal, then a metabolic

alkalosis is present in addition to a gap metabolic

acidosis.

• If the change in the anion gap is less than the change in

the [HCO3 -] from normal, then a non gap metabolic

acidosis is present in addition to a gap metabolic

acidosis.



METABOLIC ACIDOSIS: DIAGNOSIS AND

TREATMENT

• Metabolic acidosis represents an increase in

acid in body fluids .

• Reflected by a decrease in [HCO3 -] and acompensatory decrease in pCO2.



Anion Gap Acidosis:

• Anion gap >12 mmol/L; caused by a

decrease in [HCO3 -]

• balanced by an increase in an unmeasuredacid ion from either endogenous production

or exogenous ingestion (normochloremic

acidosis).





Treatment of Metabolic Acidosis1. Correct any underlying disorder (control diarrhea, etc).

2. Treatment with bicarbonate should be reserved for severemetabolic gap acidosis.

If the pH <7.20, correct with sodium bicarbonate.

The total replacement dose of [HCO3 -] can be calculated as

follows:

3. Replace with one-half the total amount of bicarbonate over 8-12 h and reevaluate.

• Be aware of sodium and volume overload during replacement.

• Normal or isotonic bicarbonate drip is made with 3 ampules NaHCO3 (50 mmol NaHCO3/ampule) in 1 L D5W.



METABOLIC ALKALOSIS:

• Metabolic alkalosis represents an increase

in [HCO3 -] with a compensatory rise in

pCO2.









RESPIRATORY ACIDOSIS:

DIAGNOSIS AND TREATMENT

• Respiratory acidosis is a primary rise in pCO2

with a compensatory rise in plasma [HCO3 -].

• Increased pCO2 occurs in clinical situations in

which decreased alveolar ventilation occurs.



Differential Diagnosis

1. Neuromuscular Abnormalities with Ventilatory Failure

2. Central Nervous System Drugs, Sedative,,Central sleep apnea

3. Airway Obstruction

a. Chronic (COPD)

b. Acute (asthma)c. Upper airway obstruction

d. Obstructive sleep apnea

4. Thoracic/Pulmonary Disorders

a. Bony thoracic cage: Flail chest, kyphoscoliosis

b. Parenchymal lesions: Pneumothorax, pulmonary edema,

c. Large pleural effusionsd. Scleroderma

e. Marked obesity (Pickwickian syndrome)



Treatment of Respiratory Acidosis

• Improve Venti lation:

Intubate patient and place on ventilator,

increase ventilator rate, reverse narcotic

sedation with naloxone (Narcan), etc



RESPIRATORY ALKALOSIS:

• Respiratory alkalosis is a primary fall in

pCO2 with a compensatory decrease in

plasma [HCO3 -].• Respiratory alkalosis occurs with increased

alveolar ventilation.



Differential Diagnosis1. Central stimulation

a. Anxiety, hyperventilation syndrome, pain

b. Head trauma or CVA with central neurogenic hyperventilation

c. Tumors

d. Salicylate overdose

e. Fever, early sepsis

2. Peripheral stimulation

a. PEb. CHF (mild)

c. Interstitial lung disease

d. Pneumonia

e. Altitude

f. Hypoxemia:

3. Miscellaneous

a. Hepatic insufficiency

b. Pregnancy

c. Progesterone

d. Hyperthyroidism

e. Iatrogenic mechanical overventilation



Treatment of Respiratory

Alkalosis

• Correct the underlying disorder.

• Hyperventi lation Syndrome: Best treated

by having the patient rebreathe into a paper

bag to increase pCO2, decrease ventilator

rate



32

KIDNEYS

Excrete / reabsorb

H+ / HCO3-

LIVER

METABOLISM

PRODUCES H+

BLOOD

BUFFERS

Protein,Bicarbonate &

Phosphate

LUNGS

Eliminate CO2

METABOLISM

CO2

HCO3-

H+

Protein bufferssynthesisedH+

H+



33

PCO2 in

arterial

bloodPCO2 in

CSF

PCO2 in

arterial

blood

expiration

of PCO2

H+ in CSF

stimulation of

central

chemoreceptors

frequency of

impulses to

medullary

rhythm

generator

rate and

depth of

ventilation

more CO2

crosses

blood brain

barrier

RESPONSE TO

HYPERCAPNIA



34

Blood Gas Case Studies.

1. Anna is a 3 month old baby who has been in hospital forone week. She has been tested RSV +ve. She is having

severe difficulty in breathing.

PH 7.15

Paco2 9.25 kPa

BE -1 mmol

What is Anna’s acid base status?



35

2. Badu is a 15 year old who has been involved in a RTA. He

was driving a stolen car. He has been admitted to your wardawaiting police investigation. He is very anxious. He begins

to hyperventilate.

PH 7.6 Paco2 3.15 kPa

BE +3 mmol

What is Budu’s acid base status?



36

3. Rani is a 10 year old newly diagnosed diabetic. She has

presented to A & E. She has been acutely unwell since thismorning. It is now 2pm.

PH 7.10

Paco2 4.2 kPa BE -10 mmol

What is Rani’s acid base status?



37

4. Andrew is a 4 week old baby. He has vomited postfeeds since 1 week old. This vomiting has worsened, he

has come to your ward for investigation into pyloric

stenosis.

PH 7.75

Paco2 5.8 kPa

BE +8.7 mmol

What is Andrew’s acid base status?



38

5. Jessica is a 10 year old newly diagnoseddiabetic. She has presented to A & E. She has been

acutely unwell since Monday morning but her parents

felt she would get better today. It is now Tuesday

2pm.

PH 7.3

Paco2 3.35 kPa

BE -5.9 mmol

What is Jessica’s acid base status?



END OF SESSION EVALUATION

39

• Please answer the following questions:1. How has your ability to relate theory to practice

changed as a result of this session?

2. What was the most valuable aspect of thissession?

3. What was the most unclear aspect of this

session?

Selamat Belajar..

Documents

Acid Base Ined 2014