acid / base balance - miami county, ks · pdf fileobjectives zdefine an acid, a base, and the...

Acid / Base BalanceAcid / Base Balance

ObjectivesObjectivesDefine an acid, a base, and the measure of pH.Define an acid, a base, and the measure of pH.Discuss acid/base balance, the effects of Discuss acid/base balance, the effects of acidosis or alkalosis on the body, and the acidosis or alkalosis on the body, and the mechanisms in place to maintain balance and mechanisms in place to maintain balance and homeostasis.homeostasis.Describe the role and actions of the bicarbonate Describe the role and actions of the bicarbonate buffer system.buffer system.Explain the actions of the respiratory and renal Explain the actions of the respiratory and renal systems in maintenance of acid/base balance.systems in maintenance of acid/base balance.Identify the type of imbalance based on lab Identify the type of imbalance based on lab values.values.

Acids, Bases, and SaltsAcids, Bases, and Salts

Chemical compounds in the body can be Chemical compounds in the body can be proton donors or acceptorsproton donors or acceptors

Proton donors are acidsProton donors are acidsProton acceptors are basesProton acceptors are bases

Acids and bases react to neutralize each Acids and bases react to neutralize each other forming saltsother forming salts


pH is the scientific method pH is the scientific method of expressing the acidity or of expressing the acidity or alkalinity of a solution.alkalinity of a solution.Normal pH of human blood Normal pH of human blood is 7.35 is 7.35 –– 7.45.7.45.7 is considered neutral. A 7 is considered neutral. A change in pH of 1 is a 10X change in pH of 1 is a 10X increase or decrease in increase or decrease in hydrogen ion concentration. hydrogen ion concentration. A pH of 6 is 10X more acidic A pH of 6 is 10X more acidic than a pH of 7.than a pH of 7.

AcidosisAcidosis

In the body, a pH In the body, a pH < 7.35 represents < 7.35 represents acidosis. Acidosis causes:acidosis. Acidosis causes:

Hyperventilation (compensatory response).Hyperventilation (compensatory response).Right shift of the oxygenRight shift of the oxygen--hemoglobin hemoglobin dissociation curve.dissociation curve.Depression of myocardial contractility.Depression of myocardial contractility.Sympathetic stimulation.Sympathetic stimulation.Hyperkalemia (KHyperkalemia (K++ shift out of cells).shift out of cells).

AlkalosisAlkalosisA pH of A pH of > 7.45 is considered to be alkalosis. > 7.45 is considered to be alkalosis. Alkalosis cAlkalosis causes:auses:

A shift of the oxygenA shift of the oxygen--hemoglobin dissociation curve to hemoglobin dissociation curve to the left.the left.Inhibits the respiratory drive.Inhibits the respiratory drive.Arrhythmias.Arrhythmias.Cerebral vasoconstriction with decreased cerebral Cerebral vasoconstriction with decreased cerebral blood flow.blood flow.Increased neuromuscular excitability including Increased neuromuscular excitability including carpopedal carpopedal spasm.spasm.Causes HCauses H++ shift into cells leading to shift into cells leading to hypokalemiahypokalemia..

Mechanisms to maintain normal pH Mechanisms to maintain normal pH and homeostasis include:and homeostasis include:

The buffer systemsThe buffer systemsThe respiratory systemThe respiratory systemThe renal systemThe renal system


The Buffer SystemsThe Buffer Systems

pH balance is maintained by buffers in the pH balance is maintained by buffers in the blood. The buffer systems are the:blood. The buffer systems are the:

Bicarbonate buffer systemBicarbonate buffer systemPhosphate buffer systemPhosphate buffer systemSulfate buffer systemSulfate buffer system

Buffer SystemsBuffer Systems

Function to change strong acids or strong Function to change strong acids or strong bases into weak ones.bases into weak ones.Most buffers are a weak acid and a salt of Most buffers are a weak acid and a salt of that acid which functions as a weak base.that acid which functions as a weak base.If strong acids are present, HCOIf strong acids are present, HCO33

--

(bicarbonate) will react with acid.(bicarbonate) will react with acid.If strong bases are present, HIf strong bases are present, H22COCO33(carbonic acid) will react with base.(carbonic acid) will react with base.

The Buffer SystemsThe Buffer Systems

Bicarbonate Buffer SystemBicarbonate Buffer System

Important ECF and ICF bufferImportant ECF and ICF bufferActs continually and immediatelyActs continually and immediatelyMaintains 1 carbonic acid molecule for Maintains 1 carbonic acid molecule for every 20 bicarbonate molecules.every 20 bicarbonate molecules.

HH22

0 + CO0 + CO22

↔↔

HH22

COCO33

↔↔

HH++

+HCO+HCO33

--

HendersonHenderson--Hasselbalch EquationHasselbalch Equation

Typically found as sodium bicarbonate Typically found as sodium bicarbonate (NaHCO(NaHCO33

--).).HCl + NaHCO3

→

H2

CO3

+ NaCl

20:1 ratio is maintained20:1 ratio is maintained

Bicarbonate buffer system is continually working Bicarbonate buffer system is continually working with its action within seconds. In an acidic with its action within seconds. In an acidic environment, it acts on a strong acid to create environment, it acts on a strong acid to create carbonic acid. The carbonic acid is then broken carbonic acid. The carbonic acid is then broken down into carbon dioxide and water. In an down into carbon dioxide and water. In an alkaline environment, free hydrogen is created alkaline environment, free hydrogen is created and bicarbonate is placed in reserve or and bicarbonate is placed in reserve or eliminated by the kidneys.eliminated by the kidneys.The bicarbonate buffer system will react The bicarbonate buffer system will react depending on what is needed for homeostasis.depending on what is needed for homeostasis.

Bicarbonate Buffer SystemBicarbonate Buffer System

Phosphate Buffer SystemPhosphate Buffer SystemImportant intracellular buffer.Important intracellular buffer.

HH22

POPO44

-- ↔↔

HPOHPO44

22--

+ H+ H++

Sulfate Buffer SystemSulfate Buffer SystemIntracellular and systemic bufferIntracellular and systemic buffer

SOSO44

22--

Other Buffer SystemsOther Buffer Systems

BufferingBufferingHH22

0 + CO0 + CO22

↔↔

HH22

COCO33

↔↔

HH++

+HCO+HCO33

--

In both the bicarbonate and the phosphate In both the bicarbonate and the phosphate buffering systems, the addition of more buffering systems, the addition of more acid will shift the equilibrium to the left, acid will shift the equilibrium to the left, consuming the excess Hconsuming the excess H++..On the other hand, an increase in pH in On the other hand, an increase in pH in alkaline conditions with lower Halkaline conditions with lower H++ will cause will cause the equilibrium to shift to the right restoring the equilibrium to shift to the right restoring the pH to more acid conditions.the pH to more acid conditions.

Respiratory SystemRespiratory System

Respiratory system Respiratory system takes minutes to takes minutes to correct an correct an imbalance. It imbalance. It eliminates or eliminates or retains carbon retains carbon dioxide which dioxide which quickly converts to quickly converts to carbonic acid.carbonic acid.

Respiratory SystemRespiratory SystemIs a back up to Is a back up to the buffer system.the buffer system.Takes 1 to 3 Takes 1 to 3 minutes to be minutes to be effective.effective.The main The main contribution is the contribution is the removal of COremoval of CO22..

Renal system Renal system takes hours to takes hours to correct an correct an imbalance by imbalance by retaining or retaining or excreting excreting bicarbonate bicarbonate and / or and / or hydrogen ions. hydrogen ions. Slow, but very Slow, but very precise.precise.

Renal SystemRenal System

Renal SystemRenal SystemRequires hours to Requires hours to days to be effective.days to be effective.Main contribution is Main contribution is the longthe long--term term maintenance of maintenance of acidacid--base balance base balance by the removal or by the removal or reabsorption of Hreabsorption of H++

and HCOand HCO33--..

Urinary Control of pHUrinary Control of pH

The kidneys can excrete varying amounts of The kidneys can excrete varying amounts of hydrogen ions or bicarbonate into the urine.hydrogen ions or bicarbonate into the urine.Excess HExcess H++ can be excreted resulting in a net can be excreted resulting in a net increase in HCOincrease in HCO33

--, raising the blood pH., raising the blood pH.HCOHCO33

-- can be eliminated, lowering blood pH.can be eliminated, lowering blood pH.

Metabolic AcidosisMetabolic Acidosis (HCO(HCO33

--

< 22mEq/L, pH < 7.4)< 22mEq/L, pH < 7.4)

Caused from either an accumulation of Caused from either an accumulation of acid in the blood or the loss of a base.acid in the blood or the loss of a base.Common causes include uncontrolled Common causes include uncontrolled diabetes mellitus, diarrhea, ASA overdose, diabetes mellitus, diarrhea, ASA overdose, renal failure, liver failure, starvation, renal failure, liver failure, starvation, alcoholism, ethylene glycol ingestion, or alcoholism, ethylene glycol ingestion, or after heavy exercise.after heavy exercise.Hyperventilation and respiratory alkalosis Hyperventilation and respiratory alkalosis can be a response to metabolic acidosis.can be a response to metabolic acidosis.

Metabolic AlkalosisMetabolic Alkalosis (HCO(HCO33

--

> 28 mEq/L, pH > 7.4)> 28 mEq/L, pH > 7.4)

Abnormal loss of acid or an accumulation Abnormal loss of acid or an accumulation of a blood base. Most often caused by of a blood base. Most often caused by either the renal Heither the renal H++ excretion or loss of HCl excretion or loss of HCl from the stomach, accompanied by from the stomach, accompanied by concurrent production of HCOconcurrent production of HCO33

--..Common causes include vomiting, Common causes include vomiting, constipation with excessive reabsorption constipation with excessive reabsorption of HCOof HCO33

--, ingestion of alkalis or licorice, , ingestion of alkalis or licorice, nasogastric suctioning, diuretics, steroid nasogastric suctioning, diuretics, steroid use, or blood transfusions.use, or blood transfusions.

Respiratory AcidosisRespiratory Acidosis (PCO(PCO22

> 45 mmHg, pH < 7.4)> 45 mmHg, pH < 7.4)

Occurs with a decrease of alveolar ventilation with Occurs with a decrease of alveolar ventilation with an increase in COan increase in CO22 levels (Hlevels (H22COCO33 ↑↑, pH , pH ↓↓).).Caused by any condition that impairs gas Caused by any condition that impairs gas exchange or lung ventilation.exchange or lung ventilation.

Chronic bronchitis, emphysema, cystic fibrosis.Chronic bronchitis, emphysema, cystic fibrosis.Rapid, shallow breathing with reduced tidal volume.Rapid, shallow breathing with reduced tidal volume.Trauma with injury to the brain stem or chest wall.Trauma with injury to the brain stem or chest wall.Narcotic, barbiturate, sedative overdose.Narcotic, barbiturate, sedative overdose.Myasthenia gravis, GuillainMyasthenia gravis, Guillain--Barre syndrome.Barre syndrome.Exhaustion.Exhaustion.

Respiratory AlkalosisRespiratory Alkalosis (PCO(PCO22

< 35 mmHg, pH > 7.4)< 35 mmHg, pH > 7.4)

Occurs with alveolar hyperventilation and Occurs with alveolar hyperventilation and the depletion of COthe depletion of CO22 and Hand H22COCO33..Caused by hyperventilation or overzealous Caused by hyperventilation or overzealous mechanical ventilation.mechanical ventilation.Anxiety, fever, pain.Anxiety, fever, pain.Pneumonia, ARDS, PE, CHF.Pneumonia, ARDS, PE, CHF.Trauma, hypoxemia, pregnancy, shock.Trauma, hypoxemia, pregnancy, shock.

Acid / Base DisturbanceAcid / Base DisturbancepH HCOpH HCO33

--

PCOPCO22

7.357.35--7.45 227.45 22--28 mEq/L 3528 mEq/L 35--45 mmHg45 mmHg

Respiratory acidosis Respiratory acidosis ↓↓

↑↑

if compensatingif compensating

↑↑

Respiratory alkalosis Respiratory alkalosis ↑↑

↓↓


↓↓

Metabolic acidosis Metabolic acidosis ↓↓

↓↓

↓↓


Metabolic alkalosis Metabolic alkalosis ↑↑

↑↑

↑↑if compensatingif compensating

Determining ImbalanceDetermining Imbalance

Think of the pH as the Think of the pH as the last name when trying last name when trying to name the imbalance.to name the imbalance.

If the number is below If the number is below 7.35, the last name is 7.35, the last name is acidosis.acidosis.If the number is above If the number is above 7.45, the last name is 7.45, the last name is alkalosis.alkalosis.7.4 is the midline or 7.4 is the midline or median.median.

Let’s give the imbalance a first name by Let’s give the imbalance a first name by looking at the partial pressure of carbon looking at the partial pressure of carbon dioxide (pCOdioxide (pCO22).).

If the arrow indicating the amount of COIf the arrow indicating the amount of CO22 is is pointing in the opposite direction of the pH pointing in the opposite direction of the pH arrow, the first name is “respiratory.”arrow, the first name is “respiratory.”If the arrow indicating the amount of COIf the arrow indicating the amount of CO22 is is pointing in the same direction of the pH arrow, pointing in the same direction of the pH arrow, the first name is “metabolic.”the first name is “metabolic.”


Bicarbonate or base excess will tell you if the Bicarbonate or base excess will tell you if the body is trying to correct the imbalance or not.body is trying to correct the imbalance or not.Remember bicarbonate always tries to maintain Remember bicarbonate always tries to maintain a 20:1 relationship with carbonic acid.a 20:1 relationship with carbonic acid.When it is metabolic, all the arrows will point the When it is metabolic, all the arrows will point the same direction and the amount of COsame direction and the amount of CO22 provides provides clues to determine if the body is compensating clues to determine if the body is compensating or not.or not.


For example, if your patient is not For example, if your patient is not breathing well and their pH is 7.3, they breathing well and their pH is 7.3, they are are acidoticacidotic. If they are not able to blow . If they are not able to blow off the carbon dioxide, the pCOoff the carbon dioxide, the pCO22 will be will be elevated telling you that the patient is in elevated telling you that the patient is in respiratory acidosis.respiratory acidosis.


If the bicarbonate HCOIf the bicarbonate HCO33-- is elevated, the is elevated, the

body is trying to correct the accumulation body is trying to correct the accumulation of COof CO2 2 or is “compensating.”or is “compensating.”


It is not completely “compensated” until the pH It is not completely “compensated” until the pH returns to within normal range. returns to within normal range. In this case, we look at the arrows and use the In this case, we look at the arrows and use the median number of 7.4 to determine if it is a median number of 7.4 to determine if it is a compensated acidosis or alkalosis, even though compensated acidosis or alkalosis, even though the pH may be between 7.35 the pH may be between 7.35 -- 7.45.7.45.So if the pH returns to 7.35 with pCO2 at 48 So if the pH returns to 7.35 with pCO2 at 48 mmHg with a BE of 30 mEq/L, the patient would mmHg with a BE of 30 mEq/L, the patient would be in a “compensated respiratory acidosis.”be in a “compensated respiratory acidosis.”


Example 1Example 1A 70 y.o. male is admitted to the ICU with acute A 70 y.o. male is admitted to the ICU with acute pancreatitispancreatitis. He is hypotensive, hypoxic, and in . He is hypotensive, hypoxic, and in acute renal failure with a respiratory rate of 48 acute renal failure with a respiratory rate of 48 breaths/minute. Blood gases show a pH of 7.1, breaths/minute. Blood gases show a pH of 7.1, PCOPCO22

of 22 mmHg and a BE of 21mEq/L. What of 22 mmHg and a BE of 21mEq/L. What is this patient’s condition?is this patient’s condition?

Severe metabolic acidosisSevere metabolic acidosis

Explain the cause of this condition.Explain the cause of this condition.Describe your treatment.Describe your treatment.

Example 2Example 2

A 6 week old male infant is admitted with a A 6 week old male infant is admitted with a history of projectile vomiting over 2 days. Blood history of projectile vomiting over 2 days. Blood gas analysis reveals a pH of 7.45, PCOgas analysis reveals a pH of 7.45, PCO22

of 48 of 48 mmHg and a BE of +11 mEq/LmmHg and a BE of +11 mEq/L

Compensated metabolic alkalosisCompensated metabolic alkalosis

If you responded to this call, describe your If you responded to this call, describe your assessment, possible cause, and treatment.assessment, possible cause, and treatment.

Example 3Example 3A 40 y.o. male patient is transported by EMS to A 40 y.o. male patient is transported by EMS to the ED. Patient is unresponsive with history of a the ED. Patient is unresponsive with history of a recent back injury. Patient had been found by his recent back injury. Patient had been found by his wife when she returned home from work. pH is wife when she returned home from work. pH is 7.27, PCO7.27, PCO22

is 58 mmHg, and BE is 28 mEq/L.is 58 mmHg, and BE is 28 mEq/L.

Respiratory acidosis Respiratory acidosis

What may be the cause of the respiratory What may be the cause of the respiratory acidosis? acidosis? What are the signs to look for?What are the signs to look for?How might you treat it?How might you treat it?

Questions?Questions?

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