Lec4 Respiratory compensation mechanism PDF

## Learning Objectives At the end of the lecture students should be able to * Describe the compensation of pH disturbances by the respiratory system * Describe compensation of pH disturbances due to respiratory diseases * Describe respiratory acidosis and respiratory alkalosis * Interpret the...

## Learning Objectives At the end of the lecture students should be able to * Describe the compensation of pH disturbances by the respiratory system * Describe compensation of pH disturbances due to respiratory diseases * Describe respiratory acidosis and respiratory alkalosis * Interpret the respective ABGs in various clinical disorders ## Your Patient * Shortness of breath * Chest tightness * Trouble sleeping caused by shortness of breath, coughing * A whistling or wheezing sound when exhaling ## Normal Bronchial Tube vs. Inflamed Bronchial Tube of an Asthmatic This image depicts two depictions of bronchial tubes. One is labeled "Normal bronchial tube" and the other is labeled "Inflamed bronchial tube of an asthmatic". The normal bronchial tube shows relaxed smooth muscles, and alveoli, which are small air sacs in the lungs. The inflamed bronchial tube, which is found in an asthmatic, shows the smooth muscles as tightened, with swelling and mucus. ## ABG in Acute Asthma | Severity | pH | PaO₂ | PaCO₂ | HCO₃ | |---|---|---|---|---| | Mild | ↑ | → | ↓ | → | | Moderate | → | ↓ | → | → | | Severe | ↓ | ↓↓ | ↑ | ↓ | *Beware the following:* * Speechless patient * PEFR < 50% * Respiration Rate > 25 * Tachycardia > 110 (pre ß2 agonist) ## Asthma with Respiratory Acidosis * Respiratory acidosis: * Cellular Respiration * CO₂ produced continuously * (Asthma) ↓ ability of the lungs to remove CO₂ * CO₂ will accumulate rapidly * ↑PaCO₂ (hypercapnia) * ↓HCO₃-/PaCO₂ ratio * ↓PH $pH = pK + log_{10} \frac{[HCO_3]}{[H_2CO_3]}$ ## Acid-Base Balance This image depicts a scale. The left side of the scale shows H₂CO₃, and the right side shows HCO₃-. The scale is titled at an angle, so that the side with HCO₃- is higher than the side with H₂CO₃. The picture is meant to show that the body's pH is balanced when the levels of HCO₃- and H₂CO₃ are relatively equal. * Acidosis: PH< 7.36 - The scale is tipped further towards the H₂CO₃ side * Normal: PH 7.35 - 7.45 - The scale is balanced * Alkalosis: PH > 7.44 - The scale is tipped further towards the HCO₃- side ## Acid Base Disturbances * Acidosis: is due to either accumulation of acid or loss of base...PH<7.36 * Alkalosis: is due to either accumulation of base or loss acid...PH>7.44 * Respiratory: denote that the primary event is alveolar ventilation dysfunction * Metabolic: denote that the primary event is abnormal gain or loss of Non Carbonic Acid. * Simple: consist of one primary event and its compensatory response * Mixed: a combination of primary events are present *for example:* patient with respiratory acidosis from COPD, with metabolic acidosis from uncontrolled DM. or from large doses of steroids. ## Definitions of Acid-Base Terms **Disorders in the blood** * Acidemia. A low blood pH (less than 7.36) * Alkalemia. A high blood pH (greater than 7.44) * Hypocapnia. A low PaCO2 (less than 36 mm Hg) * Hypercapnia. A high PaCO2 (greater than 44 mm Hg) **Disorders in the patient** * Metabolic acidosis. A primary disorder that causes a decrease in the plasma bicarbonate and lowers the blood pH. * Metabolic alkalosis. A primary disorder that causes an increase in the serum bicarbonate and, raises the blood pH. * Respiratory acidosis. A primary disorder that leads to an increased PaCO2 and, lowers the blood pH. * Respiratory alkalosis. A primary disorder process that leads to a decreased PaCO₂ and raises the blood pH. * Compensatory process. Not a primary acid-base disorder, but a change that follows a primary disorder. A compensatory process attempts to restore the blood pH to normal and is not appropriately termed acidosis or alkalosis. ## Regulation of blood pH. To maintain the blood pH at 7.35-7.45, there are three primary systems that regulate the hydrogen ion concentration in the body fluids. 1. Buffers system 2. Respiratory Regulation 3. Renal Regulation ## Acid-Base Buffer systems This is a diagram. * The left side of the diagram indicates the buffer system, which retains or excretes H+. * The diagram shows a human body. * The lungs are depicted on the human body, and show a CO₂ symbol to represent the respiratory system. * The bottom of the human body depicts H and HCO₃. * The right side of the diagram shows the renal system, which excretes or retains H+, HCO₃- , Na+, K+, Cl-. ## Respiratory Acidosis | Symptom | Cause | |---|---| | Breathlessness | Pneumonia | | Restlessness | Emphysema | | Rapid, Shallow Respiratory | Asthma | | Lethargy and disorientation | Chronic obstructive lung disease | | Drowsiness, Dizziness, Disorientation | Depression of respiratory center | | Tremors, convulsions, coma | Pulmonary edema | | Death | Retention of CO₂ by Lungs | The PaCO2 is elevated above the upper limit with a normal blood pH (7.35 to 7.45) or near-normal pH secondary to renal compensation and an elevated serum bicarbonate (HCO₃- > 30 mm Hg). ## Causes Of Respiratory Acidosis * Airway obstruction due to bronchitis, bronchospasm, emphysema, etc. * Lung diseases like fibrosis, pneumonia, etc. * Respiratory center depression by anesthetics, sedatives, cerebral trauma, tumors, etc. * Extrapulmonary thoracic diseases like flail chest, kyphosis and scoliosis * Neural diseases like polymyelitis, paralysis of respiratory muscles ## Causes of Acidosis This diagram shows an arrow labeled "Acidosis PH - 17.4" pointing up from the bottom to the top of the image. On the left side of the image, there is a loop, which is labeled "Metabolic Acidosis" and contains symbols. * Inside the loop, there is a person lying in a hospital bed, there are 2 arrows pointing to the person, with labels "Shock", and "Sepsis." * Above the person is a symbol of diarrhea, and one arrow from the diarrhea to the person, and another to the loop, both pointing to the symbol, labeled "Severe Diarrhea." * Below the person on the loop, there are two arrows pointing to the person and the loop, both labeled "Renal Failure." * On the loop there is an arrow pointing to the person, labeled "Salicylate OD." * Another arrow points to the person and the loop, labeled "Diabetic Ketoacidosis" On the right side of the diagram, there is a loop, which is labeled "HYPOVENTILATION" and contains symbols. * Inside the loop, there is an arrow pointing to the person, labeled "Drug Overdose." Another arrow points to the person, labeled "Pulmonary Edema." Another arrow points to the person, labeled "Chest Trauma." Another point points to the person, labeled "Neuromuscular Disease." * The person is depicted as having a large arrow in their chest, labeled "co₂". * An arrow points to the person, labeled "Airway Obstruction/COPD" * An arrow points to a box labeled "Respiratory Acidosis", labeled "PH↓" and "CO₂↑." ## Decreased Ventilation This is a diagram showing the negative feedback loop that results in increased ventilation when PCO₂ rises. * The diagram shows a flow chart that starts with "Decreased ventilation." * Arrows lead to "Increased arterial PCO₂." * One arrow points to "Blood pH," another arrow points to "Plasma CO₂." * From "Plasma CO₂" arrows point to "CSF" and "Blood." * From "CSF" arrows point to "Chemoreceptors in medulla oblongata" and "Respiratory center in medulla oblongata." * From "Respiratory center in medulla oblongata" arrows point to "Spinal cord motor neurons." * From "Spinal cord motor neurons" arrows point to "Respiratory Muscles." * From "Respiratory Muscles" arrows point to "Increased ventilation." ## Compensation This diagram depicts two sets of lungs. * The left set of lungs has an arrow pointing to the lungs from the outside, and a yellow arrow exiting the lungs. The arrow entering the left lung is labeled "PCO₂↑," and the arrow exiting the left lung is labeled "HCO₃-↓." * The right set of lungs has a yellow arrow entering the lungs, and an arrow pointing to the lungs from the outside. The arrow entering the right lung is labeled "HCO₃-↑," and the arrow exiting the right lung is labeled "PCO₂↓." * If underlying problem is **metabolic** hyperventilation or hypoventilation can help: respiratory compensation. * If problem is **respiratory**, renal mechanisms can bring about metabolic compensation ## Causes of Alkalosis This diagram shows an arrow labeled "ALKALOSIS PH - 17.4" pointing up from the bottom to the middle of the image. On the left side of the image, there is a loop, which is labeled "HYPERVENTILATION" and contains symbols. * Inside the loop, there is a person depicted as breathing very hard. * Arrows point to the person, labeled "Anxiety," "High Altitudes," "Pregnancy", "Hypoxia" and "Fever." * Two arrows point to a symbol of lungs, one arrow is labeled "DHCO₃" and another arrow points to the symbol of the lungs, labeled "LOW." On the right side of the diagram, there is a loop, which is labeled "Metabolic Alkalosis" and contains symbols. * Inside the loop, there is a person with an antacid tablet in their hand, labeled "Antacids." * Arrows point to the person, labeled "Overuse of Antacids," "Loss of Gastric Juices." Another arrow points to the person, labeled "Potassium Wasting Diuretics" ## Remember * Respiratory compensation is always **FAST**...12-24 hrs * Metabolic compensation is always **SLOW**...5-7 days ## Compensation Mechanisms * **Chemical buffers** * On the scene in seconds * Already present in tissue and will handle minor changes in the acid-base balance. * **Respiratory** * Retention or elimination of CO₂ within minutes * Respiratory compensation can handle mild to moderate acid-base shifts. * **Renal** * Regulate bicarb (HCO₂) to combat hydrogen losses and gains * Starts in hours, but more permanent * When the other 2 mechanisms fail, the renal system slowly gets to work and requires up to 5 days to complete. ## Arterial Blood Gases * **Acidosis** < 7.4 > **Alkalosis** * PH 7.35 - 7.45 * PaCO₂ 35 - 45 * HCO₃ 22 - 28 * **ROME** * **R**espiratory Opposite: * PH ↑ PCO₂ ↑ Alkalosis * PH ↓ PCO₂ ↑ Acidosis * **M**etabolic Equal * PH ↑ HCO₃ ↑ Alkalosis * PH ↓ HCO₃ ↑ Acidosis * Uncompensated: CO₂ or HCO₃ normal * Partially Compensated: Nothing is normal * Compensated: PH is normal (7.4 baseline/neutral) ## Compensation $pH = 6.1 + log \left( \frac{[HCO_3]}{0.03 \times P_2CO_2} \right)$ | Initicial Abnormality | Body's Mechanism of Compensation | |---|---| | High HCO₃- | Increases P₂CO₂ | | Low HCO₃- | Decreases P₂CO₂| | High P₂CO₂ | Increases HCO₃- | | Low P₂CO₂ | Decreases HCO₃- | ## Goals of ABG Analysis With the given lab values, we need to determine if the interpretation is: 1. **Acidosis** 2. **Alkalosis** 3. **Metabolic** 4. **Respiratory** 5. **Fully Compensated** 6. **Partially Compensated** 7. **Uncompensated** ## What is an ABG? Arterial Blood Gas is a lab that shows us the status of a patient's chemical balance. The image depicts a healthcare worker drawing blood from someone's arm. ## What are the components of ABG? | Component | Description | |---|---| | PH | Measurement of acidity or alkalinity, based on the hydrogen (H+) 7.35 - 7.45 | | PaO₂ | The partial pressure oxygen that is dissolved in arterial plasma. 80 - 100 mm Hg| | PaCO₂ | The amount of carbon dioxide dissolved in arterial blood. 35 - 45 mmHg| ## ABG Analysis * STEP 0: Is this ABG Authentic? * STEP 1: ACIDEMIA or ALKALEMIA? * STEP 2: RESPIRATORY or METABOLIC? * STEP 3: If Respiratory - ACUTE or CHRONIC? * STEP 4: Is COMPENSATION adequate? * STEP 5: If METABOLIC - ANION GAP? * STEP 6: If High gap Metabolic Acidosis - GAP GAP? ## STEP0: Is this ABG Authentic? If the pH and the [H+] are inconsistent, the ABG is probably not valid. $[H+]=24(PaCO_3)$ $[HCO_3-]$ | H⁺ ion (mmol/L) | PH | |---|---| | 100 | 7.00 | | 79 | 7.10 | | 63 | 7.20 | | 50 | 7.30 | | 45 | 7.35 | | 40 | 7.40 | | 35 | 7.45 | | 32 | 7.50 | | 25 | 7.60 | ## How can I interpret an ABG Strip? **Step 1: Assess the pH ** * If below 7.35 = acidotic * If above 7.45 = alkalotic **Step 2:** **1-Assess the paCO₂ level** * If below 35 = Respiratory alkalosis element * If above 45 = Respiratory acidosis element **2-Assess HCO₃ value** * If below 22 = Metabolic acidosis element * If above 26 = Metabolic alkalosis element ## Figure 1: Identifying the Primary Process * This is a flow chart. * The chart starts with "PH". * Arrows point from PH towards "Low", "Normal" and "High." * From Low, arrows point to "Acidemia," and from High arrows point to "Alkalemia." * From Acidemia, arrows point to "High PCO₂" and "Low HCO₃-." * From Alkalemia, arrows point to "Low PCO₂" and "High HCO₃-." * Underneath High PCO₂ it says "Respiratory Acidosis." * Underneath Low HCO₃- it says "Metabolic Acidosis" * Underneath Low PCO₂ it says "Respiratory Alkalosis" * Underneath High HCO₃- it says "Metabolic Alkalosis" ## Primary vs. Secondary Disturbances | Disorder | pH | [H+] | Primary Disturbance | Secondary Response | |---|---|---|---|---| | Metabolic acidosis | ↓ | ↑ | ↓ [HCO₃] | ↓ PCO₂ | | Metabolic alkalosis | ↑ | ↓ | ↑ [HCO₃] | ↑ PCO₂ | | Respiratory acidosis | ↓ | ↑ | ↑ PCO₂ | ↑ [HCO₃] | | Respiratory alkalosis | ↑ | ↓ | ↓ PCO₂ | ↓ [HCO₃] | ## Cases The image shows a cartoon drawing of a man with his arms outstretched. The word "cases" is in a header above the image. ## ABGs Practice This is a slide for ABGs practice. * pH 7.36 * PaCO₂ 43 * HCO₃ 22 Interpretation? a. Normal b. Respiratory acidosis c. Compensated respiratory acidosis d. Respiratory Alkalosis e. Compensated respiratory alkalosis f. Metabolic acidosis g. Compensated metabolic acidosis h. Metabolic alkalosis i. Compensated metabolic alkalosis ## ABGs Practice This is a slide for ABGs practice. A 55-year-old women with severe emphysema is experiencing increased breathlessness. Her ABG results are: * pH 7.30 * PaCO₂: 65 mmHg * HCO₃: 24 mEq/L Diagnosis: Acute respiratory acidosis pH: acidic, PaCO2 elevated, HCO3 normal a. Normal b. Respiratory acidosis c. Compensated respiratory acidosis d. Respiratory Alkalosis e. Compensated respiratory alkalosis f. Metabolic acidosis g. Compensated metabolic acidosis h. Metabolic alkalosis i. Compensated metabolic alkalosis ## ABGs Practice This is a slide for ABGs practice. A 28 year old man hyperventilating due to a panic attack. His ABG results are: * pH: 7.50 * PCO₂: 28 mmHg * HCO₃- : 25 mEq/L Interpretation? a. Normal b. Respiratory acidosis c. Compensated respiratory acidosis d. Respiratory Alkalosis e. Compensated respiratory alkalosis f. Metabolic acidosis g. Compensated metabolic acidosis h. Metabolic alkalosis i. Compensated metabolic alkalosis Answer: Respiratory alkalosis pH: Alkalotic PaCO2 is decreased HCO₃ is normal ## ABGs Practice This is a slide for ABGs practice. A 62 year old man with chronic bronchitis is experiencing worsening breathlessness. He has a history of COPD and is showing signs of increasing CO2 retention. His latest ABG result are: * pH: 7.32 * PaCO₂: 60 mmHg * HCO₃- : 30 mEq/L a. Normal b. Respiratory acidosis c. Compensated respiratory acidosis d. Respiratory Alkalosis e. Compensated respiratory alkalosis f. Metabolic acidosis g. Compensated metabolic acidosis h. Metabolic alkalosis i. Compensated metabolic alkalosis ## Analysis of Simple Acid Base Disorders and How They Are Compensated for By the Body This is a flow chart that depicts how the body compensates for acid base disorders. * The chart begins with "Arterial Blood Sample" * From "Arterial Blood Sample" an arrow points down to "PH?" * From "PH?" one arrow points to the left to "< 7.4" and another arrow points to the right to ">" * From "< 7.4" an arrow points to the right labeled "Acidosis" * From ">" an arrow points to the left labeled "Alkalosis." * From "Acidosis" one arrow points to the left labeled "Metabolic" and another arrow points to the right labeled "Respiratory" * From "Alkalosis" one arrow points to the left labeled "Metabolic" and another arrow points to the right labeled "Respiratory" * The bottom of the chart shows "Compensation" for each of the four types of acid base disorders. * Respiratory, Renal, Respiratory, Renal * From each compensation type, an arrow points downward to the value that is either corrected or exacerbated: * PCO₂ < 40 mm Hg, HCO₃- > 24 mEq/L, PCO₂ > 40 mm Hg, HCO₃- < 24 mEq/L