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Jennifer Welder - online ppt lecture NURS 7000

pH: definition, normal levels, acidosis levels, alkalosis levels

pH: measure of hydrogen ion concentration
normal levels: 7.35 - 7.45
< 7.35 = acidosis
>7.45 = alkalosis

What are the three regulatory mechanisms of acid/base balance, and at what speed do they react?

buffers - immediate
respiratory system - minutes to hours
renal system - 2-3 days for maximal response but can maintain balance indefinitely in chronic imbalances

What do buffers do? Give a few examples.

Act chemically to IMMEDIATELY neutralize acids; Cannot maintain pH without adequate resp and renal function. Ex: carbonic acid - bicarbonate, hgb buffers

How does the respiratory system regulate acid/base?

Eliminates CO2. Resp center in medulla controls breathing. CO2 enters RBCs and combines with H2O to form carbonic acid. This dissociates into hydrogen ions and bicarb. Hgb buffers the hydrogen and bicarb diffuses into the plasma.

How does the renal system regulate acid/base?

Eliminates hydrogen ions, reabsorbs bicarb. The kidneys also excrete a portion of the acid produced by cellular metabolism. The pH of urine can fluctuate from 4-8 as a compensatory mechanism.

Respiratory vs Metabolic imbalances

Respiratory: affect carbonic acid concentration

Metabolic: affect bicarb

Acidosis can be caused by _______ in carbonic acid (_______ acidosis) or _______ in bicarbonate (_______ acidosis)

increase in carbonic acid = resp acidosis
decrease in bicarb = metabolic acidosis

Respiratory acidosis is caused by _____ in carbonic acid. This can be caused by _______.

resp acidosis - increase in carbonic acid
caused by: hypoventilation, resp failure

How do the kidneys compensate for respiratory acidosis?

Kidneys conserve bicarb and secrete hydrogen ions into the urine. This begins within 24 hours.

Respiratory alkalosis is caused by _____ in carbonic acid. This can be caused by _____.

Respiratory alkalosis - decrease in carbonic acid
caused by: hyperventilation, hypoxemia from acute pulmonary disorders

Metabolic acidosis is caused by ____ in bicarbonate. This can be caused by ____.

metabolic acidosis - decrease in bicarbonate
caused by: ketoacidosis, lactic acid accumulation (shock), severe diarrhea, kidney disease

What are some compensatory mechanisms for metabolic acidosis?

Increased CO2 excretion by lungs (deep and rapid); kidneys excrete acid

Metabolic alkalosis is caused by ____ in bicarbonate. This can be caused by ____.

metabolic alkalosis - increase in bicarbonate
caused by: prolonged vomiting or gastric suction, gain of bicarb for some reason

What are some compensatory mechanisms for metabolic alkalosis?

Decreased resp rate (increase plasma CO2)
Renal excretion of bicarb

What are the steps of interpreting ABGs?

1. evaluate pH
2. analyze PaCO2
3. Analyze bicarb
4. Determine if CO2 or HCO3 match the alteration
5. Decide if body is attempting to compensate

What are NORMAL values for:
pH, PaCO2, HCO3, PaO2, SaO2, base excess?

pH: 7.35-7.45
PaCO2: 35-45 mmHg
HCO3: 22-26 mEq/L
PaO2: 80-100 mmHg
SaO2: >95%
Base excess: +/- 2.0 mEq/L

Interpret:
pH 7.30
PaCO2: 25 mmHg
HCO3: 16 mEq/L

1. pH: acidosis
2. PaCO2: low = resp alkalosis
3. HCO3: low = metaolic acidosis
4. Metabolic acidosis matches pH
5. CO2 does not match, but is moving in opposite direction which indicates that the lungs are attempting to compensate.

METABOLIC ACIDOSIS with partial compensation.

Mnemonic ROME

Respiratory values are Opposite (decreased pH = increased PaCO2)

Metabolic values are Equal (decreased pH = decreased HCO3)

Interpret:
pH 7.36
PaCO2: 67 mmHg
PaO2: 47 mHg
HCO3: 37 mEq/L

1. pH: normal
2. PaCO2: high = resp acidosis
3. HCO3: high = metabolic alkalosis
4. PaO2: low

RESP ACIDOSIS

Interpret:
pH 7.18
PaCO2: 38 mmHg
HCO3: 15 mEq/L
PaO2: 70 mmHg

1. pH: acidic
2. PaCO2: normal
3. HCO3: low = metabolic acidosis
4. PaO2: low

metabolic acidosis

Interpret:
pH 7.60
PaCO2: 30 mmHg
HCO3: 22 mEq/L
PaO2: 60 mmHg

1. pH: alkaline
2. PaCO2: low = resp alkalosis
3. HCO3: normal
4. PaO2: low

respiratory alkalosis

Interpret:
pH 7.58
PaCO2: 35 mmHg
HCO3: 50 mEq/L
PaO2: 74 mmHg

1. pH: alkaline
2. PaCO2: normal but on the low end
3. HCO3: high = metabolic alkalosis
4. PaO2: normal

Metabolic alkalosis

Interpret:
pH 7.28
PaCO2: 28 mmHg
HCO3: 18 mEq/L
PaO2: 70 mmHg

1. pH: acidic
2. PaCO2: low = respiratory alkalosis
3. HCO3: low = metabolic acidosis
4. PaO2: normal

Metabolic acidosis with partial compensation (CO2 going in opp direction)

Why might a potassium level be altered in a patient with acid-base imbalance?

In acidosis, hydrogen ions accumulate in the ICF so potassium shifts out of the cell to maintain a balance of cations across the cell membrane (hyperkalemia). In alkalosis, there are fewer hydrogen ions in the ICF so potassium shifts into the cell (hypokalemia).

Interpret:
pH 7.48
PaCO2: 44 mmHg
HCO3: 29 mEq/L
PaO2: 86 mmHg

1. pH: alklaline
2. PaCO2: normal
3. HCO3: high = metabolic alkalosis
4. PaO2: normal

metabolic alkalosis

What are clinical manifestations of metabolic alkalosis?

hypertonic muscles, cramping, reduced respiratory rate

What are clinical manifestations of metabolic acidosis?

hypotension, warm/flushed skin

Case Study:
Jeri has been on a 3-day party binge. Her friends are unable to awaken her, and assessment reveals LOC difficult to arouse. RR=8, shallow breathing pattern, diminished breath sounds.

What ABGs do you expect, and what is your treatment?

Because of diminished breathing patterns, expect a build-up of CO2 and decreased pH (respiratory acidosis). If the respiratory depression has lasted less than 24 hours, HCO3 will be normal; if greater than 24 hours, HCO3 may be elevated in response to compensation. PaO2 may be <80 because respiratory depression can lead to hypoxemia.

Determine cause of respiratory depression (opioids, alcohol) and treat accordingly.

Case Study:
Mayce presented to the ED after a sexual assault. She is in hysterics with emotional distress. RR=38, lungs are clear, SaO2 96%.

What ABGs do you expect, and what is your treatment?

Because she is breathing so quickly, expect PaCO2< 35 and pH >7.45 (respiratory alkalosis). HCO3 will be normal because this is not a long-term event.

Treatment: Encourage slow breaths, reduce anxiety. Administer CO2 by mask or by breathing into a paper bag.

Case Study:
Glen has a hx of fever, aches, chills, and feeling "ill." Cough produces yellow, thick sputum for 4 days. Temp is 38.4C, RR=20, lungs with crackles in LLL.

What ABGs do you expect, and what is your treatment?

Possibly pneumonia - possibly hypoxemia so PaO2<80 mmHg. This could lead to a build-up of CO2 in the body and decreased pH (respiratory acidosis).

Turn/cough/deep-breathe, administer oxygen, treat infection

Case Study:
Alan is 17 years old, history of symptoms consistent with diabetes. CBG is 484 mg/dL, RR= 28 and deep, breath is fruity, lungs are clear.

What ABGs do you expect, and what is your treatment?

Sounds like diabetic ketoacidosis, so pH< 7.35 and HCO3 < 20 mEq/L. PCO2 will be normal if acidosis is uncompensated but will be low if compensation has occurred. PaO2 will be normal.

Administer insulin, fluids, and electrolytes.

Case Study:
Anthony has a history of n/v x 1 week. Has been self-medicating with baking soda to control abdominal discomfort.

What ABGs do you expect, and what is your treatment?

Because of the baking soda, expect pH >7.45 and HCO3 > 30 mEq/L (metabolic alkalosis). Because it has been going for a week, compensation will have begun and PCO2 may be elevated > 45 mmHg

Treatment: Stop administration of baking soda, begin antiemetic drugs. IV replacement of fluids and electrolytes.

Describe a patient with the following ABGs and what the treatment might be:

pH 7.20
PaCO2: 58 mmHg
PaO2: 59 mmHg
HCO3: 24 mEq/L

1. pH 7.20 acidic
2. PaCO2: increased = respiratory acidosis
3. HCO3: normal
4. PaO2: low

Respiratory acidosis with hypoxemia. Possible respiratory infection or COPD. Hypoxemia = restlessness, confusion. Adventitious breath sounds, increased work of breathing, tachycardia, arrhythmias. Treatment of infection, oxygen therapy, bronchodilator therapy.

Describe a patient with the following ABGs and what the treatment might be.

pH 7.39
PaCO2: 38 mmHg
PaO2: 44 mmHg
HCO3: 24 mEq/L

1. pH normal
2. PaCO2: normal
3. HCO3: normal
4. PaO2: low

Because everything is normal except the PaO2, this indicate hypoxemic respiratory failure. Pneumonia, shock, pulmonary embolism, acute respiratory distress syndrome, pulmonary edema. Decreased LOC, restlessness, tachycardia, hypotension.

O2 thearpy, mobilization of secretions

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