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Questions and Answers
Which buffer system primarily helps to maintain acid-base balance in the blood?
Which buffer system primarily helps to maintain acid-base balance in the blood?
What is the primary role of the kidneys in acid-base balance?
What is the primary role of the kidneys in acid-base balance?
Which acid-base imbalance results in increased pCO2 levels and decreased pH?
Which acid-base imbalance results in increased pCO2 levels and decreased pH?
How does the Henderson-Hasselbalch equation assist in understanding acid-base disorders?
How does the Henderson-Hasselbalch equation assist in understanding acid-base disorders?
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Which factor has the least impact on the shape of the oxygen dissociation curve?
Which factor has the least impact on the shape of the oxygen dissociation curve?
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What indicates that the body is attempting to compensate for an acid/base imbalance?
What indicates that the body is attempting to compensate for an acid/base imbalance?
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If a patient's pH is 7.32, what condition does this indicate?
If a patient's pH is 7.32, what condition does this indicate?
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Which scenario suggests a respiratory issue in acid/base balance?
Which scenario suggests a respiratory issue in acid/base balance?
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What is the first step in assessing acid/base balance?
What is the first step in assessing acid/base balance?
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What should be done if pCO2 and HCO3 are both abnormal?
What should be done if pCO2 and HCO3 are both abnormal?
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What are the products of the dissociation of H2CO3?
What are the products of the dissociation of H2CO3?
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How do changes in CO2 concentration affect breathing rate?
How do changes in CO2 concentration affect breathing rate?
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What is the role of the kidneys in regulating blood pH?
What is the role of the kidneys in regulating blood pH?
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What constant value is used as the pKa for blood pH in the Henderson-Hasselbach equation?
What constant value is used as the pKa for blood pH in the Henderson-Hasselbach equation?
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Which of the following is a necessary condition for adequate tissue oxygenation?
Which of the following is a necessary condition for adequate tissue oxygenation?
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What is the approximate normal value of HCO3- in the blood?
What is the approximate normal value of HCO3- in the blood?
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In the Henderson-Hasselbach equation, which component represents the weak base?
In the Henderson-Hasselbach equation, which component represents the weak base?
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What occurs during the process of gas exchange in the lungs?
What occurs during the process of gas exchange in the lungs?
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What does a pH reading of 7.39 indicate in the context of metabolic acidosis?
What does a pH reading of 7.39 indicate in the context of metabolic acidosis?
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In the context of Example #8, why is the patient considered partially compensated?
In the context of Example #8, why is the patient considered partially compensated?
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Which step is taken to determine the primary concern in a compensated acid-base imbalance?
Which step is taken to determine the primary concern in a compensated acid-base imbalance?
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What is indicated by a pCO2 value of 42 in Example #10?
What is indicated by a pCO2 value of 42 in Example #10?
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Which conclusion can be drawn from a HCO3 level of 15 in Example #9?
Which conclusion can be drawn from a HCO3 level of 15 in Example #9?
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What is the main function of buffers in the body?
What is the main function of buffers in the body?
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What happens to pH as hydrogen ion concentration increases?
What happens to pH as hydrogen ion concentration increases?
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Which of the following statements accurately describes the role of the kidneys in acid-base balance?
Which of the following statements accurately describes the role of the kidneys in acid-base balance?
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What is the normal pH range for human blood?
What is the normal pH range for human blood?
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Which equation represents the relationship between pH and hydrogen ion concentration?
Which equation represents the relationship between pH and hydrogen ion concentration?
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What is observed in a state of acidosis?
What is observed in a state of acidosis?
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Which system is considered the body's first line of defense against extreme changes in hydrogen ion concentration?
Which system is considered the body's first line of defense against extreme changes in hydrogen ion concentration?
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In the Henderson-Hasselbalch equation, what does a decrease in pH indicate about hydrogen ion concentration?
In the Henderson-Hasselbalch equation, what does a decrease in pH indicate about hydrogen ion concentration?
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Which ion is primarily excreted by the kidneys to maintain acid-base balance?
Which ion is primarily excreted by the kidneys to maintain acid-base balance?
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What is the main waste product of aerobic metabolism that affects acid-base balance?
What is the main waste product of aerobic metabolism that affects acid-base balance?
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What constitutes respiratory acidosis based on the pH, pCO2, and HCO3 values?
What constitutes respiratory acidosis based on the pH, pCO2, and HCO3 values?
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In which scenario is the patient's condition classified as fully compensated?
In which scenario is the patient's condition classified as fully compensated?
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Which step involves determining whether the pCO2 or HCO3 value is furthest from the normal reference?
Which step involves determining whether the pCO2 or HCO3 value is furthest from the normal reference?
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A patient has a pCO2 of 70 and an HCO3 of 15. What is the classification of their acid-base status?
A patient has a pCO2 of 70 and an HCO3 of 15. What is the classification of their acid-base status?
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What is the expected outcome if the HCO3 is found to be abnormal in relation to the patient's pH?
What is the expected outcome if the HCO3 is found to be abnormal in relation to the patient's pH?
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If both pCO2 and HCO3 are normal, what classification does the patient fall under?
If both pCO2 and HCO3 are normal, what classification does the patient fall under?
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How is metabolic alkalosis indicated through pH, pCO2, and HCO3 levels?
How is metabolic alkalosis indicated through pH, pCO2, and HCO3 levels?
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In the context of compensated states, what defines a partially compensated situation?
In the context of compensated states, what defines a partially compensated situation?
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Study Notes
Blood Gases and Buffer Systems
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Lesson Objectives:
- Describe chemical and physiological systems in acid/base balance (bicarbonate, phosphate, protein, hemoglobin). Include role of kidneys and lungs.
- Use Henderson-Hasselbalch equation to predict pH/bicarbonate of a sample.
- Define and describe 4 major acid/base imbalances: metabolic acidosis/alkalosis, respiratory acidosis/alkalosis.
- Explain compensation mechanisms for each imbalance.
- Use Henderson-Hasselbalch to determine acid/base disorders and compensatory status.
- Describe O2 transport and assessment for patient O2 status.
- Describe pH, pCO2, 2,3-DPG/BPG, temperature effects on O2 dissociation curve shape.
- Describe measurement principles of pH, pCO2, pO2 and various hemoglobins.
- Explain clinical significance of pH, pCO2, pO2, bicarbonate, carbonic acid, base excess, O2 saturation, fractional oxyhemoglobin, hemoglobin oxygen binding capacity, oxygen content, and total CO2.
- Discuss collecting and handling blood gas samples (syringes, anticoagulants, mixing, icing, capillary vs. venous vs. arterial samples).
- Describe methods for measuring various hemoglobins, pH, and blood gas parameters.
- Describe QA/QC processes, proficiency testing and delta checks to assess blood gas quality.
- Discuss reasons for discrepancies between O2 saturation calculated by blood gas analyzer and measured by a co-oximeter.
Acid/Base Balance
- Acid: A substance donating hydrogen (H+) ions when dissolved in water.
- Base: A substance accepting hydrogen (H+) ions when dissolved in water.
- pH: Represents the measurement of the body's regulation of H+ ions, calculated as the negative logarithm of the hydrogen ion concentration. Normal range for blood pH is 7.35-7.45. A lower pH indicates more hydrogen ions (more acidic), a higher pH indicates less hydrogen ions (more basic).
- Henderson-Hasselbalch Equation: Mathematically shows that for every 1 pH unit decrease, the hydrogen ion concentration in the blood increases tenfold.
Buffer Systems
- Buffers: Resist changes in pH, achieved through a combination of a weak acid and its corresponding salt base.
- Buffering Systems: Produce desirable outcomes by combining correct acid/base combinations. Bicarbonate/Carbonic acid buffering system is an example.
- Bicarbonate/Carbonic acid buffering system: H2CO3 dissociates into CO2 and H2O, allowing CO2 elimination by the lungs and hydrogen elimination in water by the kidneys. Changes in CO2 concentration can speed up / slow down bicarbonate concentration.
- Effectiveness of pH: pH = pKa + log [CA-]/[HA] (pKa is the dissociation / ionization constant; defines relative strength of acid or base).
Role of Lungs & Kidneys in acid/base balance
- Transport of CO2: CO2, a waste product of most aerobic metabolic processes, easily diffuses out of tissues and into surrounding capillary plasma/RBCs. Dissociation of carbonic acid causes a concentration gradient due to increased bicarbonate in RBCs. Rate is determined by the body’s need for O2.
- Lungs: Efficiently exchange CO2 for fresh O2 when dissolved plasma CO2 equals CO2 in the lungs.
- Kidneys: Reabsorb needed bicarbonate and excrete acids (primarily ammonium ions and hydrogen).
- Regulation of Hydrogen Ions (pH): Body produces ~150g of H+ per day. Blood pH is regulated by lungs (respiratory) and kidneys (metabolic), that store and excrete excess hydrogen to maintain homeostasis. The extremely narrow pH range (7.35-7.45) is required for life.
Regulation of H+ (cont'd)
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Buffer Systems (cont'd):
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- H2CO3 dissociates to CO2 + H2O, allowing CO2 elimination by the lungs, and hydrogen to be eliminated as water by the kidneys.
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- Changes in CO2 concentration can speed up or slow down bicarbonate concentration.
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- Bicarbonate concentration can be altered (metabolically) by the kidneys.
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- Other major buffer systems: Phosphate and other major buffer systems.
pH: Respiratory Regulation
- Lungs: Blood pH is affected by respiratory ventilation. O2 inhaled diffuses into the blood, which then diffuses into tissue cells. CO2 created diffuses into the blood then alveoli, and is eliminated via respiration. Minimal H+ concentration changes between venous and arterial blood.
pH: Metabolic Regulation
- Kidneys: Regulate acid/base balance by filtering/excreting acids and bases. Bicarbonate (HCO3-) is filtered and then reabsorbed into the bloodstream.
Henderson-Hasselbalch Equation (cont'd)
- pH is the negative log of hydrogen ion concentration.
- pKa is the pH at which equal concentrations of protonated and unprotonated solutions exist; constant at 6.1 for blood.
- A⁻ is the hydrogen proton acceptor (e.g., bicarbonate).
- HA is the hydrogen proton donor (e.g., carbonic acid).
Oxygen and Carbon Dioxide Exchange
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Seven conditions necessary for adequate tissue oxygenation:
- Available atmospheric oxygen
- Adequate ventilation
- Gas exchange between lungs and arterial blood
- Loading of O2 onto hemoglobin
- Adequate hemoglobin
- Adequate oxygen transport
- Release of O2 to tissue
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Factors influencing amount of O2 moving through the lungs:
- Destruction of alveoli
- Pulmonary edema
- Airway blockage
- Inadequate blood supply
- Diffusion of CO2 and O2
Oxygen Transport
- Disturbances in O2 and CO2 conditions can result in poor tissue oxygenation (hypoxia). pO2, along with pH and pCO2, are measured to evaluate patients' O2 status.
- Most O2 in arterial blood is transported to tissues via hemoglobin.
- Oxyhemoglobin (O2Hb): O2 reversibly bound to hemoglobin.
- Deoxyhemoglobin (HHb): Hemoglobin is not bound to O2 but capable of forming a bond when O2 is available (reduced hemoglobin).
- Carboxyhemoglobin (COHb): Hemoglobin bound to CO.
Assessing Oxygen Status
- Four parameters used to assess a patient's oxygen status:
- Oxygen saturation (SO2 or O2 sat)
- Amount of O2 dissolved in plasma (pO2)
- Fractional (percent) oxyhemoglobin (FO2Hgb)
- SO2 trends assessed via transcutaneous (TC) pulse oximetry (SpO2)
Hemoglobin/Oxygen Dissociation
- O2 releases/dissociates from carrier hemoglobin into tissues.
- Dissociation of O2 from adult hemoglobin (Hb) is characteristically S-shaped.
- Dissociation curve shape and Hb affinity for O2 affected by pH, pCO2, body temperature, and 2,3-DPG levels.
Oxygen Saturation Measurement
- O2 saturation is the ratio of hemoglobin already bound to oxygen compared to all available hemoglobin. Normal is typically 95-100%.
- O2 saturation is determined via a co-oximeter spectrophotometer. Number of wavelengths in the instrument determines what can be measured. Interfering substances can cause issues.
pH, PCO2 & PO2 Measurement
- Blood gas analyzers measure pH, pCO2 and pO2 via electrodes.
- Techniques include amperometry (Clarke electrode, which measures pO2) and potentiometry(change in voltage, which measures pCO2, pH, etc).
- Electrochemical cells use opposing electrodes immersed in a sample. Cathode end is negative, attracting cations, and reduction occurs. Anode end is positive, attracting anions, and oxidation occurs.
Types of Measurement Devices
- Electrochemical sensors(macroelectrodes and microelectrodes), which are used in blood gas instruments for clinical measurement, often use thick/thin film technologies or circuitry. Optical sensors (using fluorescent dyes) have also been used.
Blood Gas Instrument Calibration
- pH and blood gas measurements are sensitive to temperature. pH electrodes are calibrated with two buffer solutions. Two gas mixtures of known pCO2 and pO2 levels are used, including a lower end gas mixture of (0% O2, 5% CO2) and an upper end gas mixture of (20% O2, 10% CO2). Most instruments are self-calibrating and have alarms signaling calibration issues. Temperature corrections are made via 37°C testing.
Calculated Parameters
- Directly measured results include pH, pCO2, pO2 and O2 saturation.
- Calculated results—HCO3, H2CO3, and TCO2—are provided when pH, pCO2 measurements are available. Bicarbonate includes bicarbonate and dissolved CO2 + CO2 bound to proteins. Base Excess (BE) can be calculated to assess metabolic base imbalances
- Exemplary values for each parameter are provided.
Quality Assurance (QA) & Proficiency Testing (PT)
- Preanalytic Considerations: Proper specimen collection (identifying patients and labeling specimens), collection personnel training and expertise, and proper specimen collection, handling, and transport time are all relevant. Equipment/materials should also be reviewed.
- Analytic Considerations: Commercially available liquid/gaseous control samples are used to validate results for matrix and concentration. Sealed glass containers are typically used, alongside split sample analysis across devices.
- Postanalytic Considerations: Result interpretation is critical.
- Proficiency testing programs are essential.
Common Sources of Error
- Incorrect collection devices (e.g., syringes).
- Incorrect form and concentration of anticoagulants (e.g., heparin).
- Speed of syringe filling.
- Failure to maintain anaerobic environment during collection/transport (air bubbles introduced to the sample).
- Inefficient sample mixing impacting heparin distribution and sample dissolution.
- Long storage or waiting time between collection and analysis.
Acid/Base Balance Disorders
- Primary Concerns: Acidosis (low blood pH) and alkalosis (high blood pH).
- Subclasses: Respiratory and metabolic (origin of the imbalanced chemical).
- Regulatory Mechanisms: These mechanisms help determine what is happening in the body (e.g., bicarbonate).
Respiratory Acidosis
- Definition: Blood pH too low, caused by a respiratory or metabolic condition and decreased lung function.
- Causes: Airway obstruction, sedatives, acute lung disease, chronic lung disease, opioids, weakness of respiratory muscles
- Compensation mechanisms attempt to restore blood pH via kidneys, increasing rate of bicarbonate reabsorption.
Metabolic Acidosis
- Definition: Blood pH too low, usually due to a kidney or GI dysfunction.
- Causes: Methanol, uremia, diabetic ketoacidosis, propylene glycol, iron tablets, isoniazid, lactic acid, ethylene glycol, salicylates, hyperalimentation, Addison's disease, renal tubular acidosis, diarrhea, acetazolamide, spironolactone, and saline infusion.
- Compensation mechanisms attempt to restore blood pH via lungs, increasing rate of hyperventilation in response.
Respiratory Alkalosis
- Definition: Blood pH too high due to hyperventilation.
- Causes: Panic attacks, anxiety attacks, salicylates (aspirin), tumors, pulmonary embolism, and hypoxemia.
- Compensation mechanisms attempt to restore blood pH via kidneys.
Metabolic Alkalosis
- Definition: Blood pH too high due to a loss of hydrogen or gain in bicarbonate.
- Causes: Loop diuretics, antacid use, vomiting, and aldosterone increase.
- Compensation mechanisms attempt to restore blood pH via lungs.
acid/base imbalance: 4 steps
- Step 1: Is pH outside normal range? (acidosis or alkalosis?)
- Step 2: Respiratory or metabolic issue? (Look at pCO2 and HCO3)
- Step 3: When both pCO2 and HCO3 are abnormal, determine which is furthest from 100%.
- Step 4: Is the patient compensated, partially compensated, or uncompensated? (review pH, HCO3, pCO2)
4 Step Process (cont'd)
- Used when results from one or more primary blood gas results (pH, pCO2, HCO3) are abnormal.
- Step 1: Classify the acid-base status (acidosis or alkalosis).
- Step 2: Determine the origin of imbalance (respiratory or metabolic).
- Step 3: Identify the primary disturbance among pCO2 and HCO3.
- Step 4: Determine compensation (fully, partially, or not compensated.).
Example Cases #7, #8, #9, and #10
- Detailed examples of using the 4-step process to evaluate blood gas results are provided to understand how to apply the principles taught, noting when and how compensation occurs.
Questions ???
- Contact information for questions about this material is available.
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Description
This quiz assesses your understanding of acid-base balance in the human body, focusing on buffer systems, kidney functions, and compensatory mechanisms. Answer questions related to the Henderson-Hasselbalch equation and acid-base disorders to test your grasp of these vital physiological concepts.
