Acid/BaseBalances

By: Diana Blum MSNMCC NURS 2140

04/22/2023 2

Acid /Base Balance• Acid base balance is the regulation of free

hydrogen ions in extra-cellular fluid.

• Acids: dissociate in solution to release H+.

• Bases: combine with free H+ and remove it from solution.

HomeostasisHydrogen ion: smallest ionic particle and very

reactiveSmall changes can alter protein and enzyme functioning

Affects organ function: heart, kidneys, lungsAffects clotting cascadeAffects drug metabolism

Plasma PH: indicator of hydrogen ion concentrationEx: pH of 7.50 is equivalent to 50 nmol/L of hydrogen ionAs Hydrogen ion increases pH decreases and vice versa

LifepH range compatible with life is 6.8-7.8

AcidsForm hydrogen ions and are proton donors

Ex: HCL gives up H+ ion when added to blood

Strong acids give up hydrogen easilyLower PH

Weak acids keep a grip on their hydrogen ions Higher PH

BasesCombine with hydrogen ions Proton acceptors

Ex: NaHCO3- (sodium bicarb) removes hydrogen when added to blood

Carbon Dioxide/Respiratory Acid

Potential acidWhen dissolved it becomes carbonic acid

Body metabolism will constantly produce288L/day produced and excreted by

ventilation

Metabolic AcidNot many produced on daily basisMain acids are:

LacticPyruvicKetoacidsBeta hydroxybutyric

Eliminated by kidneys or Metabolized by liver

Defense MechanismsFirst: Buffering2nd : Changing CO2 level3rd : changing the level of HCO3 -

Buffers

Buffer SystemsHelps minimize change in pHReact quickly to prevent excess changesPrimary Buffers: carbonic acid and bicarbAerobic metabolism:

Anaerobic metabolism:

Buffer continuedExcess CO2 exhaledBicarb is retained by glomerular filtration and also

excreted by renal tubuleSo what really happens???

Intracellular Buffer is phosphateProtein buffers in blood are plasma protein and

hemoglobinBone is a buffer

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The (blood)Bicarbonatebuffer system

The Respiratorybuffer system.

The Renal buffersystem.

Acts in seconds.20 HCO3- areReleased forevery 1 H+

Acts in minutes.Changes in rate anddepth of breathing.

Acts in hours orDays. DissociatesH2CO3 into H2Oand CO2

Balance in the body is maintained by three buffer mechanisms

R.O.M.E.

Respiratory OppositeExample: pH low PCO2 high HCO3 ok=

respiratory acidosisMetabolic Equal

Example: pH is high HCO3 is high it is metabolic

Categories of InterestRespiratory Acidosis:

Respiratory Alkalosis:

Metabolic Acidosis:

Metabolic Alkalosis:

Lungs

The LungsRegulate plasma pH on minute to minute basis by

regulating carbon dioxide.CO2 measured as partial pressure in arterial

blood=PaCO2Depth and rate of ventilation will alter

Minute Ventilation= how much air moved in 1 minuteIncrease= blowing off CO2 to compensate

Dead Space} wasted ventilation/no part in gas exchange

Lungs continuedRespiratory center=Hypercarbic Drive= response to acute respiratory

acidosisDeterminant of ventilation

Hypoxic Drive= Drive to breath…responds to low oxygen levels, high CO2, and acidosis

Hyperventilation: low PaCO2/hypocapniaHypoventilation: high PaCO2/ hypercapniaKussmals respirations: rapid deep breaths and attempt

of lungs to correct pH by decreasing respiratory acid (compensation)

Kidneys• Secrete hydrogen ions• Reclaim bicarb during the filtering process

in the glomerulas.• Ammonia

NormspH: 7.35-7.45pCO2: 35-45HCO3: 22-26RR=12-20

Interpretation• 1} Assess the pH• 2} Is it Respiratory or Metabolic

– Look at PaCO2 – Look at Bicarb level

• 3} Compensation– Complete or partial

1}

2}

2}

Imbalances• Result from disease, organ dysfunction,

pathologic reasons

Respiratory Acidosis

• Referred as primary hypercapnia• Excess CO2 decreases pH

– Regulated by RR• Management:

– Treat underlying cause– Sodium Bicarb not always given– BiPAP– CPAP– Vent

Respiratory Alkalosis

• Lower than normal PaCO2• Elevated pH• Excessive /deep ventilation causes CO2 to be blown off thereby

increasing pH• Alveolar over ventilation

• Other Causes: hypoxemia, neuro issues, pregnancy• Changes serum electrolytes• Management: treat underlying cause

– Breath into a paper bag– Reassure– Be calm – Explain procedures

Metabolic Acidosis

• Increase in total acid level thereby decreasing pH• Induced in 2 ways:

– adding H+ ion or excreting H+ from dietary metabolism

– Decrease in plasma bicarb to <22• Other Causes: ETOH, DM, Aspirin OD, Antifreeze

ingestion, GI disturbances• Management: assess anion gap, monitor

electrolytes and ABGs, treat underlying cause, sodium bicarb admin is controversial

Metabolic Alkalosis

• Increase Bicarb and pH• Other Causes: depletion in K+, Cl-,

volume depletion• Hypomagnesaemia may also occur• Management: correct volume or electrolyte

depletion, may get steroids, dialysis,HCL IV in severe cases

Compensation • Body’s normal way to normalize pH by

neutralizing the opposite mechanism• Important to know cause and effectIf you only treat compensatory response

only pH will become more abnormal

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Compensated ? / Uncompensated?

• Uncompensated: Ph and one other value abnormal

• Partially Compensated: ( All values are abnormal)

• Completely Compensated: (pH is the only normal value)

• When compensation is present, we will see two imbalances. The question then becomes, which is the primary problem, and which imbalance is due to compensation.

• The clue is the pH. – If the pH is leaning toward acidosis or alkalosis,

then the parameter with the matching imbalance is the primary problem, and the other is due to compensation.

EXAMPLE• if the pH is normal in the presence of abnormal

pO2/pCO2 – compensated– (the body has compensated for the abnormality and is able

to maintain a normal pH)

• if the pH is abnormal in the presence of abnormal pO2/pCO2 – uncompensated– (the body's defense mechanisms are no longer adequate to

compensate, allowing the pH to move to an acidotic or an alkalotic state)

*Remember that compensation corrects the ph.

Examples•

Respiratory acidosis = low ph and high C02 hypoventilation (eg: copd, narcs or sedatives, atelectasis)*Compensated by metabolic alkalosis (increased HC03)

examples:ph 7.20 C02 60 HC03 24 (uncompensated respiratory acidosis)ph 7.33 C02 55 HC03 29 (partially compensated respiratory acidosis)ph 7.37 C02 60 HC03 37 (compensated respiratory acidosis)

• Respiratory alkalosis = high ph and low C02 hyperventilation (eg: anxiety, PE, pain, sepsis)*Compensated by metabolic acidosis (decreased HC03)

examples:ph 7.51 C02 26 HC03 25 (uncompensated respiratory alkalosis)ph 7.47 C02 32 HC03 20 (partially compensated respiratory alkalosis)ph 7.43 C02 30 HC03 19 (compensated respiratory alkalosis)

• Metabolic acidosis = low ph and low HC03 ex:diabetic ketoacidosis, starvation, severe diarrhea*Compensated by respiratory alkalosis (decreased C02)

examples:ph 7.23 C02 36 HC03 14 (uncompensated metabolic acidosis)ph 7.31 C02 30 HC03 17 (partially compensated metabolic acidosis)ph 7.38 C02 26 HC03 20 (compensated metabolic acidosis)

• Metabloic alkalosis = high ph and high HC03 ex. severe vomiting, k+ deficit, dieuretics*Compensated by respiratory acidosis (increased C02)

example:ph 7.54 C02 44 HC03 29 (uncompensated metabolic alkalosis)ph 7.50 C02 49 HC03 32 (partially compensated metabolic alkalosis)ph 7.44 C02 52 HC02 35 (compensated metabolic alkalosis)

Nursing ManagementPromote healthy behaviorsLimit conversations6 small meals a dayPositioningStress reduction techniques

Practice

• pH 7.33• PCO2 50• HCO3 26

Answer• Respiratory Acidosis

• pH low PCO2 high bicarb ok

• pH 7.52• PCO2 40• HCO3 30

Answer • Metabolic alkalosis

• pH high Bicarb high

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Acid base Problems

• pH 7.5, PaCO2 = 50 mm Hg, HCO3 =30 mEq/L• Metabolic Alkalosis Partially Compensated.

• pH 7.31, Pa CO2 = 50 mm Hg, HCO3 = 22 mEq/L• Respiratory Acidosis Uncompensated.

• pH 7.31, PaCO2 = 44 mm Hg , HCO3 = 20 mEq/l• Metabolic Acidosis Uncompensated.

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More, Acid / Base problems.• pH 7.47, PaCO2 = 48 mm Hg , HCO3 = 30 mEq/L• Metabolic Alkalosis Partially Compensated.

• pH 7.33, Pa CO2 = 40 mm Hg, HCO3 = 21 mEq/L• Metabolic Acidosis Uncompensated.

• pH 7.48, Pa CO2 = 44 mm Hg, HCO3 = 30 mEq/L• Metabolic Alkalosis Uncompensated

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Even more, Acid /Base Problems

• pH 7.33, PaCO2 = 49 mm Hg, HCO3 = 26 mEq/L• Respiratory Acidosis Uncompensated.• pH 7.48, PaCO2 = 33 mm Hg, HCO3 = 24 mEq/L• Respiratory Alkalosis Uncompensated.• pH 7.31, PaCO2 = 33 mm Hg, HCO3 = 20 mEq/L• Metabolic Alkalosis Partially Compensated.• pH 7.45, Pa CO2 = 34 mm Hg, HCO3 = 20 mEq/L• Respiratory Alkalosis Compensated.

• http://www.rnceus.com/course_frame.asp?exam_id=18&directory=abgs

• www.acid-base.com • http://micunursing.com/ • http://www.ocalaregional.com/CPM/ABG%20self%2

0learning%20module%2006.pdf

• http://www.m2hnursing.com/ABG/basic_questions.php

• http://www.madsci.com/manu/gas_acid.htm