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NR202 Test 3 Arterial Blood Gasses

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Components of ABGs
•pH: measure of concentration of H+ ions

–Basics

•the body will try to compensate to pull pH into normal

•the body functions best with pH of 7.35-7.45

•the pH affects many body functions especially O2 transport
Compensation
The body will compensate in an attempt to keep the pH within normal limits

•If the disorder is metabolic, compensation is achieved by altering respirations

–increasing or decreasing pCO2 to bring pH to normal

•If the disorder is respiratory, compensation achieved by retaining or increasing excretion of bicarbonate
Which system would compensate in the patient with diabetic ketoacidosis?
a. Respiratory
b. Metabolic
c. Cardiac
d. Endocrine
a. Respiratory
Mechanism of pH control
The body uses several mechanisms to buffer acids and bases.
•Bicarbonate buffer
–1st to react - works immediately

–accepts or donates H+ ions to neutralize strong acids/bases

–CO2 + H2O = carbonic acid (H2CO3) = H+ + HCO3 (bicarbonate)

HCO3 = bicarbonate



•Plasma proteins (albumin, globulin, etc)
–largest buffering system in the body

–may attract or release H+ ions

–works in conjunction with liver



•Hemoglobin
–chloride shift

•if Cl enters hemoglobin, bicarbonate leaves the hemoglobin

•if Cl leaves hemoglobin, bicarbonate enters the hemoglobin
Mechanism of pH control
Lungs
–2nd line of defense - takes 10-30 min

–H+ causes a corresponding change in respiratory rate

–carbonic acid is exhaled as CO2 & H2O

–if body function is normal the lungs correct 50-75% of the imbalance

–Plays most vital role

•ie kidneys excrete 40-80 mEq H+ per day, slower

•ie lungs excrete 15,000-20,000 mEq H+ per day, minutes



–if there is a bicarbonate loss, lungs hyperventilate

•blow off CO2



–if there is a bicarbonate excess, lungs suppress resp (rate & depth)

•increase carbonic acid available to neutralize bicarbonate
Which patient might have an impaired plasma protein buffering system? The patient:
a. That is morbidly obese
b. With high cholesterol
c. With chronic alcohol abuse
d. That has a 40 pack year smoking history
With chronic alcohol abuse

Chronic alcohol abuse causes liver failure. The liver is necessary for a properly functioning plasma protein buffering system.
Mechanism of pH control
⬢Cells
•Cells
–work in 2-4 hr

–soak up or release H+ ions in exchange for K+

–if pH is low (acid), then H+ ions enter cells and K+ leaves

–opposite true if alkalotic

–actual amount of K+ in body is unchanged but has shifted locations
Mechanism of pH control
Kidneys
–most thorough and more selective

–slowest to act - takes few hrs to several days

–selective regulation of bicarbonate

–excretes excess H+ ions as phosphoric acid or ammonium via urine
What might the nurse observe if the patient has a fruity smell to his breath?
a. Decreased U/O
b. Increased U/O
c. Cheynne Stoke Respirations
d. Kussmaul Respirations
d. Kussmaul Respirations

A fruity smell may indicate the patient is in metabolic acidosis. Kussmaul respirations are the bodies way of blowing off CO2 (acid) and compensating for acidosis.
What electrolyte imbalance would the nurse monitor for with this patient? (before compensation)
a. Hyponatremia
b. Hypernatremia
c. Hypokalemia
d. Hyperkalemia
d. Hyperkalemia

In acidemia the body throws K+ out of the cell and into the blood, and H+ into the cell to reduce the H+ ions in the blood--to reduce the pH.
Hypoxia
•pO2: partial pressure of O2 dissolved in arterial blood

–normally 80-100 mm Hg

•SaO2: % or hemoglobin that is saturated with oxygen

–normally >95%
Causes of hypoxia
–decreased inspired O2 ie. altitude

–hypoventilation: state of decreased alveolar ventilation caused by decreased tidal volume or respiratory rate or both, such as:

•drug OD

•excessive sedation or analgesia

•head injury

•sleep apnea

•some neuromuscular disease

•some thoracic deformities (kyphoscoliosis)
Signs of hypoxia
⬢Early signs
increased heart rate

–restlessness

–increased BP

–anxiety

–HA

–fatigue

–cool & dry skin

–arrhythmias
Signs of hypoxia
Middle signs
–air hunger

–increased respiratory rate

–confusion
Late signs
–cyanosis

–diaphoresis

–coma that leads to death
Other Points About Hypoxia
–pO2 <60: the peripheral chemoreceptors are stimulated to increase rate & depth of respirations

–Increased HR is 1st sx of hypoxia

–Increased CO is most important compensatory mechanism

–muscle arterioles dilate

–skin, kidney, & splanchnic vessels constrict, shunting blood to vital organs

–pulmonary capillaries vasoconstrict in reponse to alveolar hypoxia

–most common signs are from the CNS—LOC
Nursing Interventions
–O2

–elevate HOB (Head of bed)

–TCDB (turn cough deep breathe)

- Fluids and expectorants

–VS

–Auscultate lungs

–Incentive spirometrey

–Monitor SaO2

–assess & treat cause

•pain

•decreased resp rate

•infection

•pulmonary edema

–hyperoxygenate pre/post respiratory suctioning
The patient with COPD has smoked 3 packs of cigarettes per day for 30 years. His ABGs are: pO2 85, pCO2 40, and HCO3 24. He has some thick secretions which are difficult to expectorate. What would the most appropriate nursing intervention be?
a. A
d. Encourage fluids and check orders for an expectorant


This patients oxygen level was fine, so he did not need oxygen; his bicarbonate was wnl, and there is no evidence of metabolic acidosis. Endotracheal suctioning is only performed if there is an endotracheal tube. His priorty need was to thin and expectorate his secretions.
Oxygen Toxicity
Causes
–intubated patients on mechanical ventilation with high O2 concentrations for extended periods may develop oxygen toxicity

–extended periods of high O2 concentrations wash out in nitrogen

–this leads to the development of signs depends upon lungs, oxygen tension, & duration of exposure
Oxygen Toxicity
⬢Signs
–sinus & ear pain

–decreased mucociliary clearance

–mucosal swelling & inflammation

–atelectasis

–depressed ventilatory drive

•bradypnea, hypoventilation, decreased TV,

–decreased serum albumin & hematocrit
Oxygen Toxicity
Treatment
–attempt other modality, besides increasing O2, to improve oxygenation; such as:

•pressure support, PEEP, CPAP, IPPB

•aerosol therapy

•chest physiotherapy

•medications
Which action would be indicated if the patient's ABGs returned with a PO2 of 60, although receiving 100% O2 per mechanical ventilation?
a. Increase O2 to 120%
b. Add PEEP
c. Increase morphine
d. Add a nasal cannula
b. Add PEEP
What should the nurse assess for on the patient whose pulse and blood pressure have increased?
a. Ear pain
b. Increased sputum
c. narcotic overdose
d. hypoxia
a. Ear pain
Carbon Dioxide
⬢pCO2 -
Define
Definition: pressure exerted by dissolved CO2 in the blood

–normal 35-45

–hypercapnia (45+)
causes of hypercapnia/hypoventilation
Hypercapnia is an excess of carbon dioxide in the blood caused by hypoventilation of the alveoli
–decreased respiratory drive

–increased dead space

–increased CO2 production

–neuromuscular diseases

–diseases of the medulla

–some obstructive or restrictive lung diseases
–Signs of hypercapnia
•early

–hypoventilation

–vasodilation

•middle

–HA

–hallucinations

–drowsiness

•late

–cyanosis

–lethargy, coma, death
Treatment of hypercapnia

–Nursing interventions
improve ventilation

⬢teach & encourage pursed lip breathing, and deep breathing and coughing exercises

⬢if on ventilator, MD may increase either rate or tidal volume

⬢may need to include interventions listed under hypoxia also
Which patients have the highest risk for developing hypercarbia?
a. The COPD patient recieving 100% oxygen per mask
b. The post surgical patient who is recieving high doses of morphine.
c. The post heart cath patient who is eating lu
a. The COPD patient recieving 100% oxygen per mask
b. The post surgical patient who is recieving high doses of morphine.
⬢Hypocapnia
Definition:
Hypocapnia is a less than normal level of carbon dioxide in the blood. Usually caused by increased ventilation and release of CO2.
Hypocapnia
causes
⬢anxiety-may cause increased respirations

⬢early stages of hypoxia-early signs of hypoxia increases respirations in an attempt to overcome the hypoxia

⬢hyperventilation (also mechanical ventilation)
Signs of hypocapnia
⬢hyperventilation (rapid & deep)

⬢HA

⬢vertigo

⬢paresthesia

⬢tetany

⬢carpopedal spasm

⬢syncope
Nursing interventions for person in hypocapnia
rebreathe technique (paper bag)

⬢hold breath

⬢emotional support

⬢rebreathing mask

⬢sedation
Which acid-base abnormalities would most likely be observed in a patient recently extubated, but still receiving high doses of Morphine and Ativan.
a. Decreased pH, increased pCO2, increased pO2
b. Decreased pH, increased pCO2, decreased pO
b. Decreased pH, increased pCO2, decreased pO2


Morphine and Ativan both reduce ventilation and lead to retaining CO2 which then in turn causes a decreased pH. With a decreased ventilation the O2 will also decrease.
Bicarbonate
Base or alkaline substance (metabolic component)

–normal 22-26

–High bicarbonate

•vomiting or NG tube loss (loss of HCL from upper GI tract)

•conditions leading to renal excretion of H, K, Cl

–diuretics, corticosteriods, Cushing's disease, Aldosteronism

–ingestion of large amounts of bicarbonate
Low bicarbonate
–loss of bicarbonate from lower GI tract

•diarrhea•
Base Excess
Represents excess of other bases in blood

⬢Increased: metabolic alkalosis

⬢Decreased: metabolic acidosis

⬢Normal: -2 to +2
What might the nurse observe in the patient with diarrhea?
a. hyperventilation
b. hypoventilation
c. dyspnea
d. bradypnea
a. hyperventilation
The patient with diarrhea has a base deficit leading to an acid excess. The body will attempt to compensate by releasing CO2, exhibited by hyperventilation.
Interpretation of ABGs
General Hints:
–pO2 tells oxygenation status, not acid-base state

–pCO2 is related to respiratory system

–HCO3 is related to metabolic system

–The body tends not to over compensate
Interpretation of ABGs
General Hints:
Respiratory and metabolic system
If the problem is in the respiratory system, it cannot compensate itself

•the metabolic system will compensate

–If the problem is in the metabolic system, it cannot compensate itself

•the respiratory system will compensate
Interpretation of ABGs
General Hints:
-pCO2 and HCO3-explain highs and lows
–pCO2 forms carbonic acid so is considered an acid

•high pCO2 causes pH to drop (toward acidosis)

•low pCO2 causes pH to climb (toward alkalosis)

–HCO3 (bicarbonate) is considered a base

•high HCO3 causes pH to climb (toward alkalosis)

•low HCO3 causes pH to drop (toward acidosis
Interpretation of ABGs
⬢Step 1
Assess pH

⬢if >7.45, then alkalosis

⬢if<7.35, then acidosis

⬢if WNL, which way is it leaning?
Interpretation of ABGs
⬢Step 2
–Compare pCO2 to pH

–If the pH and pCO 2 are moving in opposite directions it is a respiratory disorder

–If the pH and pCO2 are moving in the same direction it is a metabolic disorder


Ph and PCO2 opposite directions = resp acidosis

Ph and PCO2 saMe directions = Metabolic acidosis


Ph and PCO2 opposite direction = resp alkalosis

Ph and PCO2 saMe directions = Metabolic alkalosis
Interpretation of ABGs
Step 3:
–Compare HCO3 to pH

•if HCO3 >26, then it is either metabolic alkalosis or the body is attempting to compensate for resp. acidosis (high pCO2)

•if HCO3 <22, then it is either metabolic acidosis or the body is attempting to compensate for resp. alkalosis (low pCO2)
Interpret the following:

⬢pH 7.23 PCO2 67 HCO3 35

⬢pH 7.48 PCO2 48 HCO3 32

⬢pH 7.30 PCO2 40 HCO3 30

⬢pH 7.49 PCO2 30 HCO3 17
⬢pH 7.23 PCO2 67 HCO3 35
Respiratory Acidosis: the body is attempting to compensate by increasing bicarbonate

⬢pH 7.48 PCO2 48 HCO3 32
Metabolic alkalosis: The body is attempting to compensate by retaining CO2 to increase acidity.

⬢pH 7.30 PCO2 40 HCO3 30
Metabolic acidosis
If teh body were trying to compensate the pCO2 would be decreasing--to decrease the acid content in the body.
⬢pH 7.49 PCO2 30 HCO3 17
The body is attempting to compensate by getting rid of HCO3 (base)
Interpret the following:

⬢pH 7.30 PCO2 30

⬢pH 7.28 PCO2 68

⬢pH 7.48 PCO2 50

⬢pH 7.32 PCO2 25
⬢pH 7.30 PCO2 30
Metabolic acidosis because both pH and the pCO2 are moving down in the same direction. It is acidosis because the pH is less than 7.35
⬢pH 7.28 PCO2 68
Respiratory acidosis because the pH is moving down and the pCO2 is moving up (opposite directions)
⬢pH 7.48 PCO2 50
Metabolic alkalosis because the pH is greater than 7.45 which makes it alkalotic, and it is metabolic because the pCO2 is moving in the same direction.
⬢pH 7.32 PCO2 25
metabolic acidosis
Determining Compensation
⬢No Compensation: pH abnormal
–other system is not trying to compensate

–HCO3 & pCO2 - one is normal the other is not

–pH 7.23 pCO2 50 HCO3 24

Which system needs to correct this? The metabolic or renal system. The above ABGs indicate respiratory acidosis. If compensation were taking place the HCO3 would be increasing, but it is not
⬢Partial Compensation:
–other system is trying to compensate, but pH is still abnormal

–pH, pCO2, & HCO3 are all abnormal

–pH 7.33 pCO2 33 HCO3 17
This is an example of metabolic acidosis (pH and pCO2 are moving in the same direction, and a deficit of HCO3)
There is partial compensation because the pCO2 is decreasing in an attempt to decrease the total acid in the body
–ie. Renal failure and intact respiratory system

–ie. Diabetic ketoacidosis
Total Compensation
–other system has completely compensated, bringing pH into normal range

•pH normal

•pCO2 & HCO3 abnormal

–pH 7.37 pCO2 60 HCO3 30
The primary imbalance was respiratory acidosis.
The HCO3 has increased to bring the pH back into normal range. In total compensation the pH is always within normal range, but the pCO2 and HCO3 are both abnormal.

–ie. Chronic lung disease
Mixed Gases
Both respiratory and metabolic disorders cause acidemia or alkalemia

–ie. pH 7.30 pCO2 60 & HCO3 18
So the disorder is mixed acidosis. Both an excess of carbon dioxide and a deficit of HCO3 cause acidosis

–ie. Renal failure with respiratory failure


•pH: 7.25 pCO2: 56 HCO3: 15
An excess of carbon dioxide and a deficit of HCO3 lead to acidosis. So the disorder is both respiratory and metabolic.
•pH: 7.55 PCO2: 26 HCO3: 30
An excess of HCO3 and a deficit of carbon dioxide exist. This leads to mixed alkalosis
Respiratory Acidosis
⬢Possible causes
–CNS depression

–pneumothorax

–hypoventilation

–bronchial obstruction

–atelectasis

–pulmonary infections

–heart failure

–pulmonary embolism
Respiratory Acidosis
⬢S/S
–dyspnea

–restlessness

–HA

–tachycardia

–confusion

–lethargy

–dysrythmia

–respiratory distress

–drowsiness

–decreased LOC
Respiratory Alkalosis
⬢Possible causes
–anxiety

–fear

–pain

–hyperventilation

–fever

–salicylates

–gram neg septicemia

–pregnancy
Respiratory Alkalosis
⬢S/S
–light-headedness

–confusion

–decreased concentration

–spasms

–palpitations

–sweating

–dry mouth

–blurred vision
Metabolic Acidosis/Alkalosis
caused by
⬢Due to either base deficit (HCO3) or accumulation of fixed acids (fatty acids)

⬢Stronger than carbonic acids--consume bicarbonate
Metabolic Acidosis
⬢Possible causes
–Increased acids

•renal failure

•ketoacidosis

•anaerobic metab.

•Starvation

–Loss of base

•diarrhea

•intestinal fistulas
Metabolic Acidosis
S/S
–HA

–confusion

–restlessness

–lethargy

–weakness

–stupor/coma

–Kussmaul respiration

–N/V

–warm flushed skin
Metabolic Alkalosis
⬢Possible causes
–gain of base

•excess use of bicarb

•excess ingestion of antacids

•lactate use in dialysis

–loss of acids

•vomiting

•NG sx

•hypokalemia

•diuretics
Metabolic Alkalosis
⬢S/S
–muscle twitching/cramping

–tetany

–dizziness

–lethargy

–weakness

–confusion

–seizures

–coma

–N/V
Which acid-base abnormality would the patient with chronic bronchitis have?
a. Decreased pH, increased pCO2
b. Increased pH, decreased pCO2
c. Normal pH, increased pCO2
d. Decreased pH, normal pCO2
c. Normal pH, increased pCO2

In chronic bronchitis the body has had time to adapt or compensate fully. So the pH is normal although the pCO2 is increased.
The nurse receives an arterial blood gas (ABGs) report for a client on continuous nasogastric suctioning. The ABG report is as follows: pH 7.48, PaCO2 46, and HCO3 28. The nurse would interpret these blood gases to be which of the following?

a
c. Metabolic alkalosis

Metabolic alkalosis occurs as a result of loss of hydrogen and chloride ions from continuous nasogastric suctioning. In metabolic alkalosis, the pH is >7.45 and the PaCO2 is > 45.
Assessment; Physiological Integrity; Analysis
A 32-year-old female, overdosed on an unknown sedative, presents with severe respiratory depression and decreased level of consciousness. Arterial blood gases are pH 7.31, PaCO2 47, and HCO3 24. The nurse interprets these as which acid-base disorder?
a. Uncompensated respiratory acidosis

Respiratory acidosis occurs in conditions such as sedative overdose and COPD, which cause hypoventilation. In respiratory acidosis, carbon dioxide is retained and the pH is decreased. The HCO3 will elevate with compensation.
Assessment; Physiological Integrity; Analysis
A client with salicylate poisoning presents to the Emergency Department. The arterial blood gas results are pH 7.32, PaCO2 32, and HCO3 11. The nurse interprets these blood gases to be which of the following?

a. Metabolic alkalosis
b Me
b. Metabolic acidosis

In situations such as salicylate poisoning, DKA, fasting, and starvation, metabolic acidosis occurs because of a loss of bicarbonate from the extracellular fluid due to increased acid production. In metabolic acidosis, the pH is < 7.35, and the HCO3 is < 22 mEq/L.
An elderly male is receiving mechanical ventilation. The arterial blood gases for this morning are pH 7.48, PaCO2 33, and HCO3 24. The nurse would interpret these blood gases as which of the following

a. Uncompensated respiratory acidosis
c. Uncompensated respiratory alkalosis

Respiratory alkalosis occurs in conditions causing hyperventilation, such as mechanical over-ventilation, fever, and pulmonary embolus. In respiratory alkalosis, the pH is elevated and the PaCO2 is decreased. The bicarbonate decreases with compensation.
Assessment; Physiological Integrity; Analysis
The client's arterial blood gases (ABG) reveal metabolic acidosis. Which of the following medications is indicated? [Hint]
a. Sodium chloride
b. Ammonium chloride
c. Sodium bicarbonate
d. Potassium chloride
c. Sodium bicarbonate

Sodium bicarbonate acts by directly raising the pH of body fluids. It is the drug of choice to restore the pH of the plasma to normal limits.
Which medications treat alkalosis
Ammonium chloride-For severe cases of alkalosis.
or
Sodium chloride with Potassium chloride. This combination increases the renal excretion of bicarbonate ion, which indirectly increases the acidity of the blood
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