Respiratory Part 3: Arterial Blood Gases MS II

Carbon Dioxide

-95% of the CO2 generated in the tissues is carried in the red blood cells -Approximately one-half of the (95%) CO2 is directly bound to hemoglobin* (at a site different from the one that binds oxygen) *No effect on pH -The other ½ is converted by the enzyme carbonic anhydrase into: +bicarbonate ions (basic) that diffuse back out into the plasma and +hydrogen ions (H+) that bind to the protein portion of the hemoglobin (thus having no effect on pH). -A small portion of carbon dioxide, about 5 percent, remains unchanged and is transported dissolved in plasma

Metabolic Acidosis (More H+ ions): S&S (Do not have to know)

-ABG: (Decrease) # pH, (Decrease) HCO3 -arrhythmias, hypotension -lethargy, coma, disorientation -Kussmaul's breathing

Respiratory Acidosis (More H+ ions): S&S (Do not have to know)

-ABG: (Decrease) # pH, (Increase) PaCO2 -BP changes, headache -Hypoventilation, restlessness -Confusion, tachycardia

Respiratory Alkalosis (Fewer H+ ions): S&S (Do not have to know)

-ABG: (Increase) # pH, (Decrease) PaCO2 -dizziness, light-headedness -hyperventilation, paresthesia -palpitations -muscle cramps and spasms

Metabolic Alkalosis (Fewer H+ ions): S&S (Do not have to know)

-ABG: (Increase) # pH, (Increase) HCO3 -arrhythmias, confusion -apathy, stupor, restlessness -Slow respirations

Relationship between Carbon Dioxide and Bicarbonate ions

-Carbon dioxide (CO2) in the plasma combines with water forming carbonic acid, which dissociates into a hydrogen ion (H+) and bicarbonate ions: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3− -Reversible Chemical combination

Examples of compensation

-Example: pH - 7.36 Normal (<7.4) likely acidosis PaCO2 - 25 - alkalosis HCO3 - 17 - acidosis Interpretation: Compensated metabolic acidosis Example: pH - 7.44 Normal (>7.4) likely alkalosis PaCO2 - 50 - acidosis HCO3 - 32 - alkalosis Interpretation: Fully compensated metabolic alkalosis -Example: pH - 7.52 - alkalosis PaCO2 - 50 - acidosis HCO3 - 35 - alkalosis Interpretation: Partially compensated metabolic alkalosis If the non-matching values is outside the normal range (opposite of the disorder), there is at least some compensation taking place. In partial compensation, 3 values are abnormal.

ABG Interpretation

-First, does the patient have an acidosis or an alkalosis (pH) -Second, what is the primary problem - metabolic or respiratory (Why is the pH is high or low) -Third, is there any compensation by the patient - respiratory compensation is immediate while renal compensation takes time -The pH determines the primary problem -It would be extremely unusual for either the respiratory or renal system to overcompensate -After determining the primary and compensatory acid/base balance, evaluate the effectiveness of oxygenation

Compensation Review

-If the pH is normal and the PaCO2 and HCO3 are abnormal. Take the median of your pH (7.40) pH < 7.40 is acidosis pH > 7.40 is alkalosis Reexamine your PaCO2 and HCO3 if they match with the pH. (acidosis or alkalosis)? If there is enough compensation to bring the pH to normal levels, the compensation is "Compensated". -Example: pH - 7.36 Normal (<7.4) likely acidosis PaCO2 - 25 - alkalosis HCO3 - 17 - acidosis Interpretation: Fully compensated Metabolic acidosis Example: pH - 7.44 Normal (>7.4) likely alkalosis PaCO2 - 50 - acidosis HCO3 - 32 - alkalosis Interpretation: Fully compensated metabolic alkalosis -Example: pH - 7.52 - alkalosis PaCO2 - 50 - acidosis HCO3 - 35 - alkalosis Interpretation: Partially compensated metabolic alkalosis If the non-matching values is outside the normal range (opposite of the disorder), there is at least some compensation taking place. In partial compensation, 3 values are abnormal.

HCO3 = 22mmHg-26mmHg (Bicarbonate)

-Metabolic Component (Basic) -Amount of bicarbonate dissolved in the arterial blood -Kidney's normally excrete H+ (acid) and retain HCO3 (base) ***NCLEX: may change the number a little.

SaO2 = 95 - 100%*

-Oxygen saturation (O2 sat) -Percentage of available oxygen that is attached to the hemoglobin *How can this be measured? Pulse ox (SpO2), can check SaO2 and PaO2 with ABGs. ***Do not have to remember: Left Shift: Left shift will increase oxygen's affinity for hemoglobin: +in a left shift condition (alkalosis, hypothermia, etc.) oxygen will have a higher affinity for hemoglobin) Right Shift: A right shift decreases oxygen's affinity got hemoglobi: + In a right shift (acidosis, fever, etc.) oxygen has a lower affinity for hemoglobin/ Blood will release oxygen more readily.

PaO2 = 80mmHg - 100mmHg (Oxygen)

-Oxygen tension -The pressure exerted by the oxygen that is dissolved in the arterial blood ***The Patient's Oxygen Status (in plasma) ***Pressure encourages oxygen to bind to hemoglobin

PaCO2 = 35mmHg - 45mmHg*

-Respiratory component: because CO2 is stored in the lungs -High PaCO2 - blood more acidic -Low PaCO2- blood more alkaline -Lungs remove excess CO2 while breathing * Millimeters of mercury

Compensation Definition

-The body's attempt to return the acid/base status to normal (i.e. pH closer to 7.4) Primary Problem Compensation respiratory acidosis metabolic alkalosis respiratory alkalosis metabolic acidosis metabolic acidosis respiratory alkalosis metabolic alkalosis respiratory acidosis

Exchange of Gases

-The function of the respiratory system is to exchange two gases: oxygen and carbon dioxide. -The exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. -Inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.

Types of ABGs

-Uncompensated (nothing else in the body is not trying to fix it yet because the attack has just started, not enough time) -Partially compensated (body is acidic for a while, so body wants to change this, so it makes the patient breath fast so blow off CO2 [Kussmal] => making more basic, back to neutral) -Fully Compensated -Mixed (not discussed in these slides): +When two unrelated (independent) medical conditions impact ABGs. + Asthma attack (respiratory acidosis) + trouble with breathing because of pneumonia (can also make respiratory acidosis) Two different systems are causing problems, so your body cannot fix it.

Metabolic Acidosis: Causes

-diabetic ketoacidosis (Type I DM, breathing really fast, burning muscles) -severe diarrhea, starvation, burns -kidney failure, shock -lactic acidosis (running) -Rhabdomyolysis => breakdown with muscle, compartment syndrome

Definition of Terms

-pH - the logarithm of the concentration of H+ ions. -PaO2 - partial pressure of oxygen molecules dissolved in the blood (plasma) -PaCO2 - partial pressure exerted by the carbon dioxide molecules in the blood. (plasma) -HCO3 - concentration of the bicarbonate ions in the blood (plasma) *** Picture of arterial puncture sites: Allen's Test: 1) Compress radial and ulnar arteries. 2) Clench fist to blanch hand. 3) Release ulnar artery. 4) If the hand becomes flushed, there is adequate circulation. Put the container in ice and take it immediately to the lab, preserves oxygen and carbon dioxide

Metabolic Alkalosis: Causes

-severe vomiting, gastric suction, sever diarrhea -peptic ulcer, hypokalemia -excess administration of blood, NaHCO3

Steps in the Interpretation of ABG

1) First we look at the pH. (Normal 7.35 - 7.45) pH < 7.35 is acidosis pH > 7.45 is alkalosis Examples: a) pH 6.99 acidosis b) pH 7.43 Normal c) pH 7.52 Alkalosis d) pH 7.22 Acidosis 2) Look at the PaCO2 (Normal 35 - 45 mmHg) PaCO2 > 45 expect acidosis PaCO2 < 35 expect alkalosis If the PaCO2 matches with the pH, then the disorder is respiratory Examples: a) pH 6.99 CO2 48 Respiratory Acidosis b) pH 7.59 CO2 33 Respiratory Alkalosis 3) Look at the HCO3 (Normal 22 - 26 mEq/L) HCO3 < 22 expect acidosis HCO3 > 26 expect alkalosis If the HCO3 matches with the pH, then the disorder is metabolic. Examples: a) pH 6.99 HCO3 18 Metabolic Acidosis b) pH 7.50 HCO3 30 Metabolic Alkalosis If both PaCO2 & HCO3 match with pH = Combined problem

pH 7.45, PaCO2 30, HCO3 20

Fully compensated respiratory alkalosis

Respiratory Alkalosis: Causes

HYPER-VENTILATION -nervousness -anxiety, tetany, delirium tremens -strenuous exercise, fever, fear -hyperthyroidism, pain -pulmonary embolism -excessive mechanical ventilation (on a ventilator and its going too fast, so you are getting rid of too much CO2)

Respiratory Acidosis: Causes

HYPO-VENTILATION -chronic obstructive lung disease -(emphysema, bronchitis, asthma) -respiratory distress syndrome (ARDS), drug overdose, -pneumothorax, pneumonia -anesthesia, head trauma **Trapping of air with high CO2 = acidosis

Arterial Blood Gas (ABG)

Importance: 1) To detect disturbances of acid-base balance caused by respiratory disorder or a metabolic disorder, or both. 2) To assess adequacy of oxygenation and monitor blood gases during an acute illness.

Respiratory Compensation of Arterial Blood Gases

Increase in amount of exhaled carbon dioxide => decrease in H+ ions and respiratory alkalosis Example: Kussmal respiration with DKA Paper bag for nervousness (respiratory alkalosis)

Renal Compensation of Acid Base Balance

Kidney Nephron: (For Acidosis): •Retains bicarbonate •Excretes Hydrogen ions (For Alkalosis): •Retains Hydrogen ions •Excretes bicarbonate

Case 1

Little Billy got into some of dad's barbiturates. He suffers a significant depression of mental status and respiration. You see him in the ER 3 hours after ingestion with a respiratory rate of 4. A blood gas is obtained (after doing the ABC, of course). It shows pH = 7.16, paCO2 = 70, HCO3 = 23 Uncompensated Repiratory Acidosis (# 3) What is the acid/base abnormality? 1.Uncompensated metabolic acidosis 2.Compensated respiratory acidosis 3.Uncompensated respiratory acidosis 4.Compensated metabolic alkalosis

Case 2

Little Suzie has had vomiting and diarrhea for 3 days. In her mom's words, "She can't keep anything down and she's runnin' out." She has had 1 wet diaper in the last 24 hours. She appears lethargic and cool to touch with a prolonged capillary refill time. After addressing her ABC's, her blood gas reveals: pH=7.35, PaCO2=26, HCO3=12 Fully compensated Metabolic Acidosis (#4) What is the acid/base abnormality? 1.Uncompensated metabolic acidosis 2.Compensated respiratory alkalosis 3.Uncompensated respiratory acidosis 4.Compensated metabolic acidosis

Acid Base Controls

Lungs: -Control the carbonic acid by controlling the level of carbon dioxide (the more in the blood, the more acidic it is) Kidney: -Control H+ ion concentration and bicarbonate through various chemical reactions in the tubules

pH 7.40, PaCO2 60, HCO3 30

Mixed *** ONLY TIME YOU CAN HAVE A pH OF 7.40 IS IF IT IS MIXED

pH 7.35, PaCO2 45, HCO3 24

Normal

pH: 7.35, PaCO2 40, HCO3 22

Normal

ABG Assessment (Must memorize)

Overview: -Check pH and compare to normal: +7.35 to 7.45 -Check PaCo2: +Acid > 45 +Base < 35 -Check HCO3: +Acid < 22 +Base >26 -Note body's attempt to compensate

pH 7.20, PaCO2 55, HCO3 30

Partially compensated Respiratory Acidosis

pH 7.33, PaCO2 28, HCO3 17

Partially compensated metabolic acidosis

pH 7.55, PaCO2 50, HCO3 40

Partially compensated metabolic alkalosis

pH 7.30, PaCO2 65, HCO3 35

Partially compensated respiratory acidosis

pH 7.50, PaCO2 33, HCO3 19

Partially compensated respiratory alkalosis

pH 7.48, PaCO2 40, HCO3 28

Uncompensated Metabolic Alkalosis

pH 7.25, PaCO2 65, HCO3 25

Uncompensated Respiratory Acidosis

pH 7.28, PaCO2 56, HCO3 24

Uncompensated Respiratory Acidosis

Compensation

We start by reviewing uncompensated acid base balances: -Example pH - 7.18 - acidosis PaCO2 - 35 - normal HCO3 - 12 - acidosis Interpretation: Uncompensated Metabolic Acidosis -Example: pH - 7.46 - alkalosis PaCO2- 32 - alkalosis HCO3- 23 - normal Interpretation: Uncompensated Respiratory Alkalosis More uncompensated acid base balances: -Example pH - 7.18 - acidosis PaCO2 - 35 - normal HCO3 - 12 - acidosis Interpretation: Uncompensated Metabolic Acidosis Example: pH - 7.46 - alkalosis PaCO2- 32 - alkalosis HCO3- 23 - normal Interpretation: Uncompensated Respiratory Alkalosis Now look at compensation: -If the pH is normal and the PaCO2 and HCO3 are abnormal. Take the median of your pH (7.40) pH < 7.40 is acidosis pH > 7.40 is alkalosis +Reexamine your PaCO2 and HCO3 if they match with the pH. (acidosis or alkalosis)? +If there is enough compensation to bring the pH to normal levels, the compensation is "Compensated".

ABG Key

pH Acid < 7.35 Base > 7.45 PaCo2 Acid > 45 Base < 35 HCO3 Acid < 22 Base > 26

pH Normal Range

pH (normal): 7.35 - 7.45 (a little more basic than neutral [7.0])*** NEED TO KNOW THIS SLIDE -Measures the acidity or alkalinity of a solution -Based on the number of Hydrogen ions -The more H+ in the solution the more acidic the solution *** We are looking at what is in the plasma. -pH represents the number of H+ ions present in the blood. ** Picture of the scale of pH