CLASS 15 - IMPAIRED GAS EXCHANGE, ACID-BASE BALANCE AND RELATED THERAPIES Flashcards
What are the 2 forms in which hydrogen circulate in our bodies?
- volatile hydrogen in carbonic acid
2. nonvolatile form of hydrogen and organic acids
What is the normal range for arterial blood pH?
7.35-7.45
If the arterial pH is below 7.35 what state is the patient in?
acidotic (low pH = acidic)
if the arterial pH is above 7.45 what state is the client in?
alkalotic state
Define ventilation
The process of inhaling oxygen into the lungs and exhaling carbon dioxide fom the lungs
What might impair ventilation?
Ventilation may be impaired by the unavailability of oxygen or by any disorder affecting the nasopharynx and lungs.
Inadequate bone, muscle, or nerve function can reduce inhalation, prevent full thoracic expansion, or limit full mvmt of the diagram
Define transport
Transport refers to the availability of hemoglobin and its ability to carry oxygen from alveoli to cells for metabolism and to carry carbon dioxide produced by cellular metabolism from cells to alveoli to be eliminated
Define perfusion
Refers to the ability of blood to transport oxygen-containing hemoglobin to cells and return carbon dioxide-containing hemoglobin to the alveoli.
What might be a cause of inadequate / impaired perfusion?
Inadequate or impaired perfusion can be caused by decreased cardiac output as well as by thrombi, emboli, vessel narrowing, vasoconstriction, or blood loss
Why are ABGs so significant?
ABGs are an essential diagnostic tools for clients in acute respiratory distress. They tell us about homeostasis and allostasis in the body.
ABGs provide the most information about how the body is adapting or declining in the case of respiratory disorders.
This information will guide medical care and nursing interventions.
Identify the normal atterial blood gas values for the following parameters:
- pH
- pCO2
- Bicarbonate (HCO3-)
- PO2
- Base excess
- pH: 7.35-7.45
- pCO2: 35-45 mmHg
- Bicarbonate (HCO3-): 21-28 mmol / L
- PO2: 80-100 mmHg
- Base excess: plus or minus 2 mmol/L
Define pH
What does a high pH indicate?
What does a low pH indicate?
pH refers to the balance of hydrogen ions in arterial blood
a high pH indicates the blood is alkaline (low conc of hydrogen)
a low pH indicated the blood is acidic (high conc of hydrogen)
what does PaCO2 measure in the arterial blood?
PaCO2 measures the amount of carbon dioxide in the blood.
Indicates how well the lungs are excreting carbonic acid.
what does HCO3- measure in the arterial blood?
Measures the amount of bicarbonate in the arterial blood.
Indicates how well the kidneys are excreting metabolic acid.
what does PaO2 measure in the arterial blood?
PaO2 measures the amount of oxygen in the arterial blood.
What is base excess?
Base excess is an indicator of how well the buffers are managing metabolic acid.
Cellular metabolism generates carbonic acid (____) in the form of ___ + ___ and metabolic acids. _______ cellular metabolism produces more of these acids.
H2CO3
CO2 + H2O
Increased
Where is CO2 abundant in the body? Where is it low? Is it a weak acid or strong acid?
CO2 is abundant in the tissues
Low in the lung capillaries.
Weak acid, easily dissociated from H2CO3 into H+ and HCO3-
What are the 4 regulatory systems used to maintain the acid-base balance in our body?
1) Buffers
2) Lungs
3) Kidneys
4) Potassium Exchange
What is the function of a buffer?
What is the downside to buffer systems?
A buffer is a fast-acting regulatory system.
Buffer systems provide immediate protection against changes in H+ concentration in the ECF. They function to keep the pH in a narrow limit of stability when too much acid or base is released into the system.
A buffer will absorb or release a hydrogen ion as needed.
Downside is that once a primary buffer system reacts, they are consumed which leaves the body less able to withstand further stress until the buffers are replaced.
Identify the 4 primary buffer systems that exist in the ECF.
1) Hemoglobin system
2) Plasma protein system
3) Carbonic acid bicarbonate system
4) Phosphate buffer system
Describe the function of the Hemoglobin system.
Maintains the acid-base balance via chloride shift. Chloride is an electrolute that shifts in an out of cells in response to the levels of oxygen in the blood.
For each chloride molecule that leaves a RBC, a bicarbonate ion enters
For each chloride molecule that enters a RBC, a bicarbonate ion leaves.
Describe the function of the Plasma Protein System
Functions w the liver to vary the number of hydrogen ions in the chemical stucture of plasma proteins.
Describe the function of the phosphate buffer system.
Present in all cells and body fluids especially the kidneys. Neutrolizes excess hydrogen ions.
Describe the function of the carbonic acid bicarbonate system
primary buffer system in the body
maintains a ratio of 20 parts bicarbonate (HCO3-) to 1 part carbonic acid (H2CO3)
Which part of the body controls the concentration of carbonic acid?
Controlled by the excretion of CO2 in the lungs. Rate + depth of respiration change in response to the changes in CO2.
Which part of the body controls the bicarbonate concentration?
Kidneys. They selectibely retain or excrete bicarbonate in response to the body’s needs.
Describe the lungs as a regulatory system for blood pH.
The lungs are the body’s second line of defense. Interact with the buffer system to maintain acid-base balance
inactivate only the H+ ions carried by carbonic acid
How do the lungs compensate when the body is in a state of acidosis? alkalosis?
Acidosis - lungs increase the body’s respirations as a mechanism to excrete more CO2
Alkalosis - HOLD HYDROGEN IONS; pH increases and the resp rate and depth decrease, CO2 is retained, carbonic acid increases to neutralize and decrease the strength of excess bicarbonate.
Describe the kidneys as a regulatory system for blood pH.
Slower but provides a more inclusive + selective response
Restore bicarbonate by excreting hydrogen ions and retaining bicarbonate ions
Results in diffusion of ammonia into the kidneys, which combines with excess hydrogen to be excreted in the urine (= phosphoric acid).
Describe potassium exchange as a regulatory mechanism for acid-base balance in the blood
Body changes potassium levels by drawing hydrogen ions into the cells or by pushing them out of the cells.
Potassium level changes to compensate for hydrogen level changes.
What happens with potassium exchange when the body is in a state of acidosis?
in acidosis, the body protects itself from the acidic state by moving hydrogen ions into the cells. Therefore potassium moves out to make room for hydrogen ions and the potassium levels increase.
what happens with potassium exchange when the body is in a state of alkalosis?
In alkalosis the cells release hydrogen ions into the blood in an attempt to increase the acidity of the blood, this forces the potassium into the cells and therefore potassium levels decrease.
What is alkalosis?
Occurs when more hydrogen ions are present in the ICF than ECF.
What is acidosis?
Hydrogen in ECF increases, therefore Hydrogen ions move into ICF, equal amt pf potassium moves out of the cell to compensate.
Is a change in the concentration of carbonic acid a respiratory or metabolic imbalance?
How is this compensated?
Respiratory imbalance.
This change will be compensated by metabolic changes in the concentration of bicarbonate.
Is a change in the concentration of bicarbonate a metabolic or respiratory imbalance?
How is this compensated?
Metabolic imbalance.
Compenseated by respiratory changes (increase or decrease in RR)
Does a carbonic acid excess result in acidosis or alkalosis?
Excess results in acidosis.
Does a carbonic deficit result in acidosis or alkalosis?
Deficit results in alkalosis.
Does a bicarbonate excess result in acidosis or alkalosis?
Alkalosis
Does a bicarbonate deficit result in acidosis or alkalosis?
Acidosis
Define acidosis.
Situation in which there is too much acid in the body and acid excretion is not able to keep up with acid production or intake.
pH will be below 7.35.
What is respiratory acidosis? Why is it called this?
Condition of too much carbonic acid in the body.
Lungs excrete carbonic acid.
What is metabolic acidosis?
Excess metabolic acid, occurs when the base bicarbonate has been lost from the body.
Define alkalosis.
Condition of too little acid in the body. Acid excretion exceeds production, or too much base bicarbonate has been added to the buffer system.
Define respiratory alkalosis.
Too little carbonic acid
Define metabolic alkalosis
Too little metabolic acid
What is typically the cause of acid-base imbalances?
Acid-base imbalances typically occur as a consequence of another underlying condition.
What are the risk factors for developing an acid-base imbalance?
excessive production or intake of metabolic acid
altered acid buffering due to loss / gain of bicarbonate
altered acid excretion
abnormal shift of H+ into cells
What are the clinical manifestations of Respiratory Acidosis (increased PCO2)?
- neurological
- cardiovascular
- neuromuscular
- respiratory
Neurological
- Drowsiness
- Disorientation
- Dizziness
- Headache
- Coma
Cardiovascular
- decreased BP
- VFIB releated to hyperkalemia from compensation
- warm, flushed skin related to peripheral vasodilation
Neuromuscular
- seizures
Respiratory
- hypoventilation with hypoxia (problem bc lungs unable to compensate when there is a respiratory problem)
What are the clinical manifestations of Metabolic Acidosis (decreased bicarbonate)?
- neurological
- cardiovascular
- GI
- Respiratory
Neurological
- Drowsiness
- Confusion
- Headache
CV
- decreased BP
- dysrhythmias related to hyperkalemia from compensation
- warm, flushed skin related to peripheral vasodilation
GI
- nausea, vomiting, diarrhea, abdominal pain
Respiratory
- deep, rapid respirations (compensatory action by the lungs) resulting in hyperventilation
How does the body attempt to compensate for resp acidosis? What usually causes it?
usually caused by hypoventilation, corrected by hyperventilation.
kidneys will increase secretion of H+ and produce more ammonia to be excreted in the urine.
How does the body attempt to compensate for metabolic acidosis?
Increased secretion of H+ and more NH3 production, respiratory compensation results in hyperventilation
What are the clinical manifestations of respiratory alkalosis (decreased PCO2)?
- neurological
- cardiovascular
- neuromuscular
- respiratory
Neurological
- lethargy
- light-headedness
- confusion
Cardiovascular
- tachycardia
- dysrhythmias related to hypokalemia from compensation
GI
- nausea
- vomiting
- epigastric pain
Neuromuscular
- tetany
- numbness
- tingling of extremities
- hyperreflexia
- seizures
Respiratory
- hyperventilation (lungs can’t compensate when there is a respiratory problem.
What are the clinical manifestations of metabolic alkalosis (increased bicarbonate)?
- neurological
- cardiovascular
- GI
- neuromuscular
- respiratory
Neurological
- dizziness
- irritability
- nervousness
- confusion
Cardiovascular
- tachycardia
- dysrhythmias related to hypokalemia from compensation
GI
- anorexia
- nausea
- vomiting
Neuromuscular
- tremors
- hypertonic muscles
- muscle cramps
- tetany
- tingling of fingers + toes
Respiratory
- hypoventilation (compensatory action by the lungs).
What are the 6 steps to ABG analysis?
1) pH - acidotic or alkalotic?
2) PaCO2 - resp acidosis or alkalosis?
3) HCO3 - metabolic acidosis or alkalosis?
4) match pH with step 2 or 3
5) is there compensation occurring?
6) assess PaO2 and O2sat
Carbonic acid can be in the form of ___ and ___
CO2 and H2O
What are the critical values for PaO2 and Sp O2?
PaO2: less than 40 mmHg
SpO2: less than 75%.
What are some considerations a nurse should take when a patient has a pao2 greater than 70 and an spo2 above 95?
this is adequate unless the patient is hemodynamically instable or has an O2 unloading problem.
With low cardiac output, dysrhythmias, a leftward shift of the oxygen-hemoglobin disocciation curve, higher values may be desirable.
(high margin for error)
Benefits of a higher arterial O2 level must be balanced against the risk of O2 toxicity.
What are some nursing considerations that should be taken when the patient has a pao2 of 60 mmHg and an SPO2 of 90%?
Adequate in almost all patient, values are at a steep part of the oxygen-hb dissociation curve. Oxygenation is adequate but the margin of error is less than for higher values.
What are some nursing considerations that should be taken when the patient has a pao2 of 55 mmHg and an SPO2 of 88%?
This is adequate for patients with chronic hypoxemia or if no cardiac problems occur.
These values are used as the criteria for the prescription of continuous O2 therapy.
What are some nursing considerations that should be taken when the patient has a pao2 of 40 mmHg and an SPO2 of 75%?
This is inadequate but may be acceptable on a short term basis if the patient also has CO2 retention.
In this situation, respiration may be stimulated by a low PaO2. O2 therapy at a low concentration (~25%) will gradually increase the paO2.
What are some nursing considerations that should be taken when the patient has a pao2 below 40 mmHg and an SPO2 of below 75%?
This is inadequate.
Tissue hypoxia and cardiac dysrhythmias can be expected.
What is the most important indicator of oxygenation in the body?
PaO2.
Describe the relationship between PaO2 and O2.
Where the PaO2 is high (in the lung), O2 is easy uploaded to the Hgb.
Where PaO2 is low, O2 is easily released from the Hgb into the plasma so it can go to the tissue.
What does PaO2 represent in the body?
dissolved O2 available for cell uptake.
What does O2sat represent in the body?
amt of oxygen on hb.
What do we use the oxygen-hb dissociation curve for?
We use O2sat to estimate the PaO2.
The oxy-hb dissociation curve is used to account for the conditions that alter oxy-hb affinity and to determine how the body’s affinity for O2 on hemoglobin impacts oxygenation at a tissue level.
When we look at the curve, we are eamining if what is happening in the body is normal or if there is a shift to the left or a shift to the right.
Which 3 conditions alter oxygen-hb affinity?
pH
Temperature
PCO2
What causes a left shift on the oxy-hb dissociation curve?
how does pH change? Temperature? PCO2?
What is happening in terms of oxygen affinity when there is a shift to the left?
A left shift is caused by alkalotic states - due to increased pH (decreased hydrogen ions), low temperature, and low PCO2.
In a left shift there is an increase in oxygen affinity. This means that it is easy to bind the O2 to the hemoglobin BUT it is harder to release into the tissue.
Therefore the PaO2 is lower than normally expected despite the high O2sat.
What causes a right shift on the oxy-hb dissociation curve?
how does pH change? Temperature? PCO2?
What is happening in terms of oxygen affinity when there is a shift to the right?
Due to acidotic states.
- decreased pH (increased hydrogen ions)
- high temperature
- increased PACO2
In a right shift, there is a DECREASE in oxygen affinity. This means that it is harder to keep the oxygen on the hemoglobin, but it is easier to release into the tissue. This means that the PaO2 is higher than normally expected in comparison to the O2 saturation.
Define hypercapnia (hypercarbia). What is is typically caused by?
Hypercapnia is a condition arising from too much carbon dioxide in the blood.
Often caused by hypoventilation or disordered breathing where not enough oxygen enters the lungs + not enough catbon dioxide is emitted.
What are the 4 primary mechanisms for the development of hypercapnia in the body?
1) abnormalities of airways + alveoli (ex - airway obstruction, air trapping with outflow obstruction)
2) abnormalities of the CNS (ex - suppressed respiratory drive)
3) abnormalities of the chest wall (ex - flail chest, rib fractures, clinical obesity).
4) Neuromuscular Conditions (ex - muscular dystrophy, myasthenia gravis, MS, or stroke)
What are the mild symptoms of hypercapnia on assessment?
- dizziness
- drowsiness
- excessive fatigue
- headaches
- feeling disoriented
- flushing of skin
- SOB
What are the severe symptoms of hypercapnia on assessment?
- confusion
- coma
- depression or paranoia
- hyperventilation
- irregular heartbeat or arrhythmia
- loss of consciousness
- muscle twitching
- panic attacks
- seizures.
What is the main cause of hypoventilation?
High PaCO2 level bc adequate ventilation is necessary for the removal of CO2.
Ventilation is also required for oxygenation, and hypoventilation leads to low o2sat and subsequently low PaO2.
What is a diffusion disturbance?
Occurs when oxygen transport across the alveolocapillary membrane is impaired.
What are some potential causes of a diffusion disturbance?
May be caused by:
- decrease in lung surface area for diffusion
- inflammation
- fibrosis of the alveolovapilarry membrane
- low alveolar oxygenation
- extremely short capillary transit time
Describe the process of ventilation.
Oxygen goes into the alveoli and carbon dioxide exits.
Describe the process of perfusion.
Deoxygenated bloos from your heart goes to the pulmonary capillarie.s, CO2 exits your blood through the alveoli and the oxygen is absorbed.
What is a shunt?
The shunt is a condition in which blood from the R side of the heart enters the L side w/o taking part in any gas exchange. Results in mixed blood which will lead to decreased perfusion.
What is the V/Q ratio?
the amt of air that reaches your alveoli divided by the amount of blood flow in the capillaries in your lungs.
What happens in a V/Q mismatch?
Part of the lung receives oxygen without blood or blood flow without oxygen.
What are alveoli?
Small sacs at the end of your bronchioles.
What are the 4 mechanisms of Hypoxemia?
Hypoventilation (decreased respirations)
Diffusion Disturbance
Shunt
V/Q perfusion mismatch
