(P) Lec 4: Acid-Base Balance (Part 2) Flashcards
Blood Buffers
- A buffer in both plasma and cells
- Contains charges on their surface
Plasma Proteins
Plasma Proteins
What are the acidic and basic components?
Acidic: Carboxyl group (COOH)
Basic: Amino group
- Proteins are considered ____, meaning they can have either a positive or negative charge
- A negative charge makes them capable to bind with ____
- Amphoteric
- Hydrogen ions
Plasma Proteins
- In an acidic medium, the ____ act as a base as the amino group accepts hydrogen ions forming an ____ ion
- In an alkaline medium, ____ donates hydrogen ions
- Proteins; ammonium
- COOH
Plasma Proteins
The more this group is contained in histidine, the better the plasma proteins will be in acting as a buffer
Imidazole
Plasma Proteins
This protein accounts for the greatest buffer as it has 16 histidine residues
Albumin
Parameters of Interest
Refers to the negative logarithm of hydrogen ion activity with a formula of “-log[H]”
pH
Parameters of Interest: pH
What is the normal pH value range of the body?
7.35-7.45
Acidosis is less than 7.35 while alkalosis is more than 7.45
Parameters of Interest: pH
The optimum pH for arterial blood
7.40
Parameters of Interest: pH
The pH that represents the difference of arterial and venous blood because of the chloride isohydric shift
0.03 pH
Parameters of Interest: pH
What type of blood sample can be used to measure pH, pCO2, and HCO3?
Venous blood
Note: Applicable in cases of patients with fever
Parameters of Interest: pH
Venous blood can be used to measure pH, pCO2, and HCO3, except for what?
pO2 (partial pressure of oxygen)
Parameters of Interest: pH
The pH decreases by ____ per each Celsius above 37ºC
0.015
Parameters of Interest: pH
TOF: The lower the temperature, the lower the pH
False (inversely proportional)
Parameters of Interest: pH
Significance of the body pH
1. For proper (physiologic/anatomical) functioning of cells and tissues
2. Any change can alter (enzyme/hormone) activity
3. Nerve conduction and muscle (relaxation/contraction) are pH dependent
4. All (metabolic/catabolic) processes are pH dependent
5. The uptake, transport and (binding/release) of O2 and CO2 are pH dependent
- Physiologic
- Enzyme
- Contraction
- Metabolic
- Release
Parameters of Interest: Ventilation
What is the normal pCO2?
35-45 mmHg
Parameters of Interest: Ventilation
If pCO2 is < 35 mmHg and > 45 mmHg, what 2 conditions are related?
- < 35 mmHg - respiratory alkalosis
- > 45 mmHg - respiratory acidosis
Note: CO2 binds with water to form H2CO3, so an increase in CO2 means higher acidity
Parameters of Interest: Ventilation
This is the index of efficient gas exchange
pCO2
Parameters of Interest: Ventilation
Total CO2 values differ from arterial and venous whole blood, what are those value ranges?
- 19-24 mmol/L (WB arterial)
- 22-26 mmol/L (WB venous)
Parameters of Interest: Metabolic Process
To evaluate the ____, the parameter used is ____; the organ is the one responsible for the reclamation and excretion of said substance
- Kidneys
- Bicarbonate
Parameters of Interest: Metabolic Process
What is the normal HCO3 level?
21-28 mEq/L
Parameters of Interest: Metabolic Process
If HCO3 is < 21 mEq/L and > 28 mEq/L, what 2 conditions are related?
- < 21 mEq/L - metabolic acidosis
- > 28 mEq/L - metabolic alkalosis
Parameters of Interest: Metabolic Process
____ is the basic component while ____ is the acidic component of this buffer system
- Bicarbonate
- Carbonic Acid
Parameters of Interest: Metabolic Process
It is refered to as “metabolic” because it is being regulated by the kidneys but it can also be called as ____ acidosis/alkalosis
Non-respiratory
Note: “Metabolic” refers to its relation to bicarbonates
Parameters of Interest: Degree of Oxygenation
Adequate oxygenation will produce a normal pO2 of what?
81-100 mmHg
Parameters of Interest: Degree of Oxygenation
Other terms for low pO2
Hypoxemia/Hypoxia
Parameters of Interest: Degree of Oxygenation
Give the types of hypoxia:
1. 61-80 mmHg
2. 41-60 mmHg
3. 21-40 mmHg
- Mild
- Moderate
- Severe
Parameters of Interest: Degree of Oxygenation
This reflects the availability of gas in blood but not its content within the RBC
pO2
Parameters of Interest: Degree of Oxygenation
TOF: Higher altitudes result to lower ranges of arterial pO2
True
Parameters of Interest: Degree of Oxygenation
Excessive oxygen supply can cause ____, that is when the buffering capacity of hemoglobin comes in whenever there is oxygen excess in the body
Acidosis
Parameters of Interest: Degree of Oxygenation
TOF: The degree of dissociation of oxygen with hemoglobin will also determine the pO2 level
True
Parameters of Interest: Degree of Oxygenation
The interrelated parameters (acidosis or alkalosis):
1. ↑ pH
2. ↑ pO2
3. ↑ HCO3
- Alkalosis
- Alkalosis
- Acidosis
Parameters of Interest: Degree of Oxygenation
The interrelated parameters (acidosis or alkalosis):
1. ↓ pH
2. ↓ pO2
3. ↓ HCO3
- Acidosis
- Acidosis
- Alkalosis
Additional Parameters
- The ratio of oxygen bound to the carrier protein Hgb, with the total amount of Hgb capable of binding oxygen
- How much oxyhemoglobin is present in the blood
Oxygen Saturation
Additional Parameters: Oxygen Saturation (SO2)
What is the normal value of SO2?
> 90% (ideally 95%)
Additional Parameters
This determines how much oxyhemoglobin is present in the blood
Fraction of Oxyhemoglobin (FO2)
Additional Parameters: Fraction of Oxyhemoglobin (FO2)
What is the normal FO2 value?
> 95%
Additional Parameters
Give the 4 forms of hemoglobin
- Oxyhemoglobin (O2Hgb)
- Deoxyhemoglobin (HHgb) - can readily bind with O2
- Carbon Monoxide Hemoglobin (COHgb)
- Methemoglobin - when iron is oxidized than reduced (no capability to bind with O2)
Hemoglobin-Oxygen Dissociation
This is a ____ curve that presents the relationship between oxygen saturation and % saturation of Hgb and pO2
Sigmoid
Hemoglobin-Oxygen Dissociation
- The position of the curve reflects the affinity that Hgb has for ____
- Hemoglobin holds on to O2 until the O2 tension in the tissue is reduced to ____ mmHg
- Oxygen
- 60 mmHg
Hemoglobin-Oxygen Dissociation
True or False (for each number):
1. If ever the tissue has more than 60mmHg of oxygen tension, the hemoglobin will give off oxygen to that tissue but only in minute amounts
2. Less than 60mmHg of oxygen tension is the time that hemoglobin gives off its oxygen to the tissue in exchange for the CO2
- False (if more than 60mmHg, it will not give off oxygen at all)
- True
Hemoglobin-Oxygen Dissociation
Familiarize with the 4 factors affecting the curve
- H+ ions
- CO2 levels
- Body temperature
- 2,3 DPG levels
Oxyhemoglobin Dissociation Curve
This shift refers to when hemoglobin has a reduced affinity for oxygen as it cannot anymore combine with hemoglobin
Right
Oxyhemoglobin Dissociation Curve
This shift refers to when hemoglobin has a higher affinity with oxygen; the oxygen binds to hemoglobin which improves oxygen uptake
Left
Oxyhemoglobin Dissociation Curve
Shift to the Left or Right?
- Increased temperature
- Increased 2,3 DPG level
- Increased hydrogen ion (pH is acidic)
Right
Hemoglobin-Oxygen Dissociation
Shift to the Left or Right?
- Decreased temperature
- Decreased 2,3 DPG level
- Decreased hydrogen ion (alkalosis)
- Carbon monoxide is present
Left
Acid-Base Disorders
TOF: When there is compensation happening in the body, it alters the factor primarily affected by the pathologic process (e.g. if the kidneys are defective, it is also what compensates to restore order)
False (it should be the organ NOT primarily affected)
Ex.: If the kidney is down, what compensates is the lungs
Acid-Base Disorders
What are the 2 types of compensations?
- Fully - pH returns to normal
- Partially - pH is near/approaching normal
Acid-Base Disorders
Refers to when the pH is still the same as the first result (no improvement)
Uncompensated
Acid-Base Disorders
Which among the lungs and kidneys:
1. Compensate slow but is long term and complete
2. Compensate immediately but is short term and incomplete
- Kidneys
- Lungs
Acid-Base Disorders
- Aka non-respiratory acidosis
- Caused by decreased bicarbonate (therefore decreased pH)
- Is seen in increased amounts of acid production and reduced renal excretion of acids
Metabolic Acidosis
Acid-Base Disorders
Seen in the ff. conditions:
- Diabetic ketoacidosis
- Lactic acidosis
- Renal/kidney failure
- Diarrhea (excessive loss of bicarbonates)
- Administration of acid-producing substances
Metabolic Acidosis
Acid-Base Disorders
- Presents with hyperkalemia and hyperchloremia
- Compensations happen in the lungs via hyperventilation (primary) as the kidneys retain the bicarbonates (secondary)
Metabolic Acidosis
Acid-Base Disorders
- Refers to the increased rate or depth of breathing in order to blow off CO2
- Refers to when the patient is breathing into a paper bag
- Hyperventilation
- Hysterical hyperventilation
Acid-Base Disorders
- Aka non-respiratory alkalosis
- Caused by excess bicarbonate levels
Metabolic Alkalosis
Acid-Base Disorders
Seen in:
- Excess administration of sodium bicarbonate
- Ingestion of bicarbonate-producing salts (sodium lactate, acetate, and citrate)
- Vomiting (excessive loss of acid)
- Prolonged used of diuretics which augment renal excretion of hydrogen ion therefore it decreases hydrogen ion level (decreasing the acidic part in the blood)
Metabolic Alkalosis
Acid-Base Disorders
- Presents with hypokalemia and hypochloremia
- Compensation happens in the lungs via hypoventilation (increases retention of CO2 in the blood)
Metabolic Alkalosis
Acid-Base Disorders
- Caused by excessive CO2 accumulation (hypoventilation)
- Presents with decreased elimination of CO2 in the lungs/decreased alveolar ventilation
Respiratory Acidosis
Acid-Base Disorders
Seen in:
- Hypoventilation
- Drugs such as barbiturates, morphine and alcohol
- Lung disease (COPD, bronchopneumonia, and chronic hypercarbia)
- Decreased cardiac output (CHF)
Respiratory Acidosis
Acid-Base Disorders
- Compensation happens in the kidneys by retaining bicarbonates/increasing the secreation of hydrogen ions
- Due to the decrease in acidity, it will normalize the body’s pH
Respiratory Acidosis
Acid-Base Disorders
- Caused by an increased rate of alveolar ventilation leading to excessive CO2 loss
- Presents with hypokalemia
- Compensation happens in the kidneys by reclaiming hydrogen ions to the blood leading to the decreased reabsorption/increased secretion of bicarbonate
Respiratory Alkalosis
Acid-Base Disorders
Seen in the ff conditions:
- Hypoxia
- Hyperventilation
- Fever, anxiety, and severe pain
- Pulmonary emboli
- Aspirin overdose (salicylates)
- Gram (-) sepsis
Respiratory Alkalosis
Methods for Blood Gases and pH
Blood gas analyzers use ____ with either macro-electrochemical or micro-electrochemical sensors as their sensing device whether it’s for pH, pO2 or pCO2
Electrodes
Methods for Blood Gases and pH
- The specimen is ____
- It is to be collected in an ____ manner
- The anticoagulant of choice is ____
- The syringe and needle need to be ____
- Specimen should be ____ and/or transported in ____
- Arterial blood
- Anaerobic
- Heparin (lithium)
- Pre-heparinized
- Chilled (4ºC); ice
Methods for Blood Gases and pH
If the arterial blood is collected aerobically, what would happen to the pH, pO2, and pCO2?
- pO2 and pH - increased
- pCO2 - decreased
Methods for Blood Gases and pH
The powdered form of the anticoagulant heparin must be used because excessive amounts of the liquid form can lead to ____
Dilution
Methods for Blood Gases and pH
Around how many mL of heparin should be present in the glass/plastic syringe?
1-3mL
Methods for Blood Gases and pH
Excess heparin in the syringe should be expelled becauses it causes a/an (upward/downward) shifting of blood pH
Downward
Note: Increased CO2 causes a decrease in pH
Methods for Blood Gases and pH
This test is a screening test for collateral circulation before proceeding with the arterial puncture
Allen’s Test
Methods for Blood Gases and pH
Analyze the samples ASAP as ____ might happen therefore decreasing the pH of the blood
Glycolysis
Specimen Considerations
Bubbles or gaps during collection should be avoided as it affects pCO2 and pO2 in what manner?
- pCO2 - decreased
- pO2 - increased
Specimen Considerations
____ errors and protein coating in ____ are the common causes of analytical error
- Temperature
- Electrodes
Specimen Considerations
The specimen should be chilled to prevent ____ consumption by the RBC that could result to the release of acidic metabolites that then alter the pH
Oxygen
Methods of Measurement
Refers to the amount of current flow that indicates the presence of your parameter; you are measuring the amount of current flow that serves as an indicator for the oxygen present
Amperometric
Methods of Measurement
Refers to the change in the voltage that indicates the activity of the analyte or of that parameter; whenever there is a change in voltage, that indicates the activity of the analyte—either it is the pH or pCO2 that is being measured
Potentiometry
Methods of Measurement
These 2 methods have electrochemical cells made up of two opposite electrodes that are immersed in a liquid that will conduct the current
Potentiometry and Amperometry
Methods of Measurement (Potentiometry and Amperometry)
The site where cations travel (positively charged ions); where reduction occurs
Cathode (negative electrode)
Methods of Measurement (Potentiometry and Amperometry)
The site where anions or negatively charged ions migrate; the site of oxidation
Anode (positive electrode)
Methods of Measurement (Potentiometry and Amperometry)
- This is a process of gaining electrons by a particle
- Refers to the loss of electrons by a particle
- Reduction
- Oxidation
Methods of Measurement (Potentiometry and Amperometry)
pH and pCO2 are measured using what 2 electrodes:
1. This electrode reacts to the responsive of the ions of interest. Increased concentration or activity of the ions leads to an increase in the force exerted by those ions
2. Acts as the basis electrode
- Measuring electrode
- Reference electrode
Methods of Measurement (Potentiometry and Amperometry)
This piece of equipment measures the potential difference between the two electrodes
Volt meter
Methods of Measurement
What are the 3 potentiometry electrodes for measuring pH?
- Silver-silver chloride electrode
- Calomel electrode (Hg-HgCl2)
- Glass electrode
The 3 Potentiometry Electrodes for Measuring pH
- Serves as the measuring electrode; uses a chloride electrode
- Serves as the reference electrode; uses mercuric mercury chloride
- Uses a glass membrane that is sensitive to hydrogen ions
- Silver-Silver Chloride Electrode
- Calomel Electrode (Hg-HgCl2)
- Glass Electrode
Methods of Measurement
The ____ shows the difference between the two electrodes measured based on the hydrogen ion concentrations of a given sample
pH meter
Methods of Measurement
For pCO2 (potentiometry), this is known as a modified electrode, it has an outer semipermeable membrane that allows CO2 to diffuse into a layer of electrolytes that contains a bicarbonate buffer which covers the glass of the pH electrode.
Severinghaus Electrode
Severinghaus Electrode (pCO2 potentiometry)
What happens is that when CO2 is present in the sample and the electrode is covered with the ____ buffer, it will combine, producing now carbonic acid and will be converted (dissociated) to become ____ and ____. The hydrogen ion activity here is the one being measured by the pH electrode and the activity related to pCO2
Bicarbonate; Hydrogen ions and CO2
Methods of Measurement
For the polarography-amperometry method of pO2, what are the 2 electrodes used?
- Clarke Electrode
- TC Electrode
pO2 (Polarography-Amperometry)
This electrode measures the amount of current flow in a circuit that is related to the amount of oxygen being reduced at the cathode
Clarke Electrode
pO2 (Polarography-Amperometry)
This electrode is prone to error in measurement either because of:
- Protein buildup
- Bacterial contamination (bacteria can make use of the oxygen level therefore decreasing the result)
- Increased WBC in blood (decreasing the O2 level)
- Room temperature-exposed sample (the RBC consumes the O2 present, releasing acidic metabolites)
Clarke Electrode
pO2 (Polarography-Amperometry)
This electrode:
- Is non-invasive
- Can be performed on neonates or infants wherein this electrode is only applied on the skin directly, no need for the blood
TC Electrode
pO2 (Polarography-Amperometry)
This electrode’s principle:
- Oxygen diffusing from the capillary bed going to the tissue is now being measured by electrodes
- One factor that can affect the electrode is heating which can increase tissue perfusion
TC Electrode
Other Methods of Measurement
In FO2 (fractional oxyhemoglobin), which refers to the actual percent of oxyhemoglobin present on the sample, is being measured by the use of ____ that use different wavelengths for different forms of hemoglobin which has different absorbance capacities
Co-oximeters
Other Methods of Measurement
Give the wavelengths for the measurement of the ff. forms of Hgb:
1. Oxyhemoglobin
2. Cyanmethemoglobin
3. Methemoglobin
- 575nm
- 540nm
- 630nm
Other Methods of Measurement
This instrument allows for transcutaneous measurement in determining O2 saturation
Pulse Oximeter
Factors Affecting Blood Gas and pH
Temperature (37ºC ± 0.1º):
Depending on the degree of fever, pO2 will fall by ____ and pCO2 will rise by ____
7% and 3%
Factors Affecting Blood Gas and pH
In elevated plasma protein concentrations, what analyte is the most affected?
Note: Protein coating the electrodes alters the results
pO2
Factors Affecting Blood Gas and pH
- Bacterial contamination causes a false ____ or ____ value of pO2
- Bacterial contamination is common in what electrode?
- Decrease; Low
- Glass membrane/electrode
Factors Affecting Blood Gas and pH
During improper transport of the specimen, air exposure (bubbles) can cause what effects for pO2 and pCO2?
- pO2 - increases (rapid)
- pCO2 - decreases by 4mmHg in 2 minutes
Sample Problem
If both parameters (pCO2 & HCO3) are increased and decreased, and are both pointing to acidosis, what is that phenomenon called?
Mixed/Combined Acidosis (both organs have a problem therefore no compensation happens)
Sample Problem
If both parameters (pCO2 & HCO3) are increased and decreased, and are both pointing to alkalosis, what is that phenomenon called?
Mixed/Combined Alkalosis (both organs have a problem therefore no compensation happens)
Sample Problems
- pH: 7.35 (normal but near acidic)
- pCO2 (acid): 75 mmHg (increased)
- HCO3 (base): 37 mmol/L (increased)
Note: The near acidic pH of the blood is caused by the increased pCO2
- Fully Compensated (due to an increased HCO3 and the return of the pH to normal)
- Respiratory (due to the contribution of pCO2)
- Acidosis (due to the borderline pH)
Clue: If both pCO2 and H3CO2 are increased or decreased (not reversed), the compensation has happened
Sample Problems
- pH: 7.48 (alkalotic)
- pCO2 (acid): 54 mmHg (increased)
- HCO3 (base): 38 mmol/L (increased)
Note: The basic pH of the blood is caused by the increased HCO3
- Partially Compensated (due to an increased pCO2 and the near return of the pH to normal)
- Metabolic (due to the contribution of HCO3)
- Alkalosis (due to the increased pH)
