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When you look at blood gas results in animals, you learn about their acid-base balance. These numbers help you make fast choices in emergencies. Many animals get metabolic acidosis, and this happens a lot in dogs. The table below lists the most common acid-base problems in dogs:
Acid-Base Imbalance Type | Frequency in Normokalemic Dogs | Frequency in Hypokalemic Dogs | Notes |
|---|---|---|---|
Normal anion gap metabolic acidosis | Most common, more frequent in hypokalemic group | More frequent (47.8% vs 31.7%) | May happen from losing bicarbonate through the kidney or stomach; linked to distal renal tubular acidosis |
Metabolic acidosis (hyperchloremic, hyperlactatemic) | 31.7% (traditional analysis) | 47.8% (traditional analysis) | Hyperlactatemia found in 84% of IMHA dogs when they arrive |
Unmeasured ions (anion effect) | 87.3% (semquantitative) | 89.2% (semquantitative) | Unmeasured anions are seen more than cations; it is not clear if this matters for health |
Alkalotic albumin effect | 66.7% | 83.1% | Low albumin is common in IMHA, and it can make acid-base results harder to understand |
Multifactorial acid-base disturbances | Present in both groups | Present in both groups | This means there are mixed effects from unmeasured ions, albumin, hyperchloremia, and hyperlactatemia |
Metabolic alkalosis | Less common | Less common | This does not play a big part in hypokalemia |
You can see that some acid-base problems, like hyperchloremic metabolic acidosis, do not happen as much in animals as in people. In animals, it usually takes a lot more fluids to cause these changes. When you check blood gas results, you should look for these differences to help your patients in the best way.
Always look at the pH first. This tells you if the blood is acidic or basic. It helps you know how to start your analysis.
Use PaCO2 and HCO3 numbers to see if the problem is from breathing or from metabolism.
Check if the body is trying to fix the problem. Compare the expected changes in PaCO2 or HCO3. This shows if the disorder is balanced.
Figure out the anion gap when bicarbonate is low. This helps you find hidden acid problems or loss of bicarbonate.
Follow a step-by-step plan or use a checklist. This helps you read blood gas results with confidence and give better care to patients.
When you look at arterial blood gas results, you learn about acid-base balance and oxygen in animals. You should know what normal abg levels are for each part. The table below lists normal abg values for dogs, cats, and horses:
Parameter | Units | Dog | Cat | Horse |
|---|---|---|---|---|
pH | - | 7.31–7.42 | 7.24–7.40 | 7.32–7.44 |
PaCO2 | mmHg | 29–42 | 29–42 | 36–46 |
HCO3 | mEq/L | 17–24 | 17–24 | 24–30 |
PaO2 | mmHg | 85–95 | 85–95 | 94 |
pH tells you if blood is more acidic or basic. It helps you see if acid-base balance is normal. If pH is between 7.36 and 7.44, the animal's acid-base balance is healthy. A low pH means acidemia and shows acidosis. A high pH means alkalemia and shows alkalosis. You check pH first when looking at arterial blood gas results. This helps you find the main acid-base problem.
Tip: Always look at pH before other numbers. It helps you decide what to do next in blood gas analysis.
PaCO2 tells you how well the animal gets rid of carbon dioxide. It shows the breathing part of acid-base balance. High PaCO2 means the animal cannot breathe out enough CO2, which causes respiratory acidosis. Low PaCO2 means the animal breathes out too much CO2, which causes respiratory alkalosis. High PaCO2 happens in animals with airway problems or weak muscles. Low PaCO2 happens in animals that are excited, in pain, or have a fever.
High PaCO2: Neuromuscular disease, airway block, pleural space problems.
Low PaCO2: Sepsis, pain, lung blood clots, excitement.
HCO3, or bicarbonate, shows the metabolic part of acid-base balance. You use it to see if the animal has metabolic acidosis or alkalosis. Low HCO3 means metabolic acidosis, often from losing bicarbonate or gaining acids like lactate or ketones. High HCO3 means metabolic alkalosis, often from losing chloride by vomiting or kidney issues. You use HCO3 with pH and PaCO2 to understand the whole acid-base picture.
Low HCO3: Metabolic acidosis (loss of bicarbonate, gain of acids).
High HCO3: Metabolic alkalosis (loss of chloride, more bicarbonate).
PaO2 tells you how much oxygen is in the blood. Oxygen saturation shows how much hemoglobin carries oxygen. You use both to see how well the animal gets oxygen. PaO2 and oxygen saturation do not change at the same speed. When PaO2 drops below 70 mmHg, oxygen saturation drops fast. Low PaO2 and low saturation happen in animals with lung disease or trouble breathing. You need both numbers to check oxygen and find hypoxemia.
Note: PaO2 and oxygen saturation follow a curve. When PaO2 is low, small drops can make saturation fall a lot.
Arterial blood gas analysis gives you a clear look at acid-base balance and oxygen. You use these numbers to help treat and watch your patients.
When you look at blood gas results, use a clear plan. This helps you not make mistakes. It also helps you feel sure about your choices. Many veterinarians use steps to check arterial blood gas. You can use these steps each time you read a blood gas report.
Tip: Try using a checklist or a grid. Many people use six steps or a tic-tac-toe grid for abg results.
Start by looking at the pH. This number shows if the animal has acidemia or alkalemia. If pH is normal, acid-base balance is healthy. If pH is low, the animal has acidemia. If pH is high, the animal has alkalemia. This first step helps you with the rest of your check.
Step-by-step guide:
Check the pH value.
Decide if it is normal, low (acidemia), or high (alkalemia).
Write down what you find.
You always start with pH because it shows if there is an acid-base problem. It also helps you know if the disorder is compensated or not.
Next, find out if the problem is respiratory or metabolic. Look at PaCO2 and HCO3. These numbers show if the main issue is from the lungs or metabolism.
If PaCO2 changes like pH, it is respiratory.
If HCO3 changes like pH, it is metabolic.
You can use this table to help:
Parameter | Direction of Change | Primary Disorder Type |
|---|---|---|
PaCO2 | Opposite to pH | Respiratory |
HCO3 | Same as pH | Metabolic |
Check if the animal's signs match your findings. For example, high PaCO2 and low pH means respiratory acidosis. Low HCO3 and low pH means metabolic acidosis. Always match your findings to the animal's symptoms.
Note: Respiratory and metabolic disorders can happen together. You may see mixed acid-base problems in sick animals.
After you find the main disorder, see if the body tries to fix it. This is called compensation. The lungs or kidneys help bring pH closer to normal. Decide if the disorder is compensated or not.
In respiratory disorders, kidneys change HCO3.
In metabolic disorders, lungs change PaCO2.
Here are some rules:
In respiratory disorders, pH and PaCO2 move opposite.
In metabolic disorders, pH and HCO3 move together.
The body does not overcompensate. Compensation makes pH closer to normal but not perfect.
Respiratory compensation is fast. Metabolic compensation takes longer.
Use these guidelines to check for compensation:
Disorder Type | Compensation Mechanism | Expected Change |
|---|---|---|
Metabolic Acidosis | PaCO2 drops (lungs) | PaCO2 drops 0.7 mmHg for each 1 mEq/L drop in HCO3 |
Metabolic Alkalosis | PaCO2 rises (lungs) | PaCO2 rises 0.7 mmHg for each 1 mEq/L rise in HCO3 |
Respiratory Acidosis | HCO3 rises (kidneys) | Acute: HCO3 rises 0.15 mEq/L per 1 mmHg PaCO2; Chronic: 0.35 mEq/L |
Respiratory Alkalosis | HCO3 drops (kidneys) | Acute: HCO3 drops 0.25 mEq/L per 1 mmHg PaCO2; Chronic: 0.55 mEq/L |
If the compensation matches these numbers, the disorder is compensated. If not, it is not compensated or mixed.
Clinical Pearl: If you see more than one abnormal result or the compensation does not fit, you may have a mixed disorder. Always check the animal and use chemistry panels to find hidden problems.
Common methods for arterial blood gas interpretation:
Six-step process: pO2, pH, PaCO2, HCO3, main change, compensation.
Tic-tac-toe grid: Put pH, PaCO2, and HCO3 in a grid to see which values match.
You can use these tools to make blood gas analysis easier. Practice often to get better at it.
When you check arterial blood gas in animals, you often find acid-base imbalances. Metabolic acidosis is the most common problem you will see. In one study, 36% of 220 dogs had metabolic acidosis. About 28% of dogs had acidemia or alkalemia. Vomiting, diarrhea, dehydration, drinking a lot, and peeing a lot often happen with metabolic acidosis. These signs help you find the main problem fast.
You can look at this table to see common acid-base imbalances and their signs:
Imbalance Type | pH Change | Common Signs | Example Causes |
|---|---|---|---|
Metabolic Acidosis | Low (acidemia) | Vomiting, diarrhea, dehydration | Kidney failure, shock |
Metabolic Alkalosis | High (alkalemia) | Weakness, muscle twitching | Vomiting, diuretics |
Respiratory Acidosis | Low (acidemia) | Slow breathing, confusion | Airway block, lung disease |
Respiratory Alkalosis | High (alkalemia) | Fast breathing, anxiety | Pain, fever |
You must decide if the blood is acidic or alkalotic. This step helps you understand the animal's acid-base balance and what to do next.
If you see low HCO3 on an arterial blood gas, check the anion gap. The anion gap tells you if the drop is from extra acids or from losing bicarbonate. Use this table for help:
Mechanism causing decreased HCO3 | Expected Anion Gap | Strong Ion Difference | Chloride vs Sodium |
|---|---|---|---|
Accumulation of acids | Increased | Normal | Similar |
Bicarbonate loss/gain of chloride | Normal | Decreased | Chloride higher |
Tip: The anion gap can help you find hidden acid-base problems when HCO3 is low.
Sometimes, sick animals have more than one acid-base disorder. Mixed disorders happen when two or more problems change the acid-base balance at once. You can spot mixed disorders by checking if the compensation is what you expect. If it is not, you probably have a mixed disorder.
Here is a table that shows how to spot mixed acid-base disorders:
Case Description | pH | HCO3- | pCO2 | Expected Compensation | Observed vs Expected | Interpretation |
|---|---|---|---|---|---|---|
Acute renal failure | 7.27 | 12 | 27 | pCO2 = 27 | Matches | Simple metabolic acidosis |
Chronic respiratory acidosis | 7.33 | 29 | 57 | HCO3- = 29 | Matches | Simple respiratory acidosis |
Seriously ill dog | 7.05 | 12 | 44 | Not as expected | Not matching | Mixed metabolic and respiratory acidosis |
GDV (dog) | 7.38 | 12 | 21 | Not as expected | Not matching | Mixed metabolic acidosis and respiratory alkalosis |
Note: A normal pH does not always mean the acid-base balance is normal. Compensation or mixed disorders can hide the real problem.
There are some limits when you use arterial blood gas analysis:
Taking blood from an artery can be risky and hard, especially in sick animals.
You might get venous blood by mistake, which gives wrong results.
Venous blood gas values can change with blood flow and metabolism.
A normal pH does not mean there are no acid-base disorders because the body can compensate or have more than one problem.
You need to use all the information from arterial blood gases, signs you see, and chemistry panels to understand the whole situation.
You can learn blood gas results by using simple steps. First, check the pH level. Next, find out what the main problem is. Last, see if the body is trying to fix it.
Knowing normal blood gas numbers helps you find problems fast.
Understanding results helps you treat emergencies and helps animals get better.
Veterinary nurses and veterinarians collect and read blood samples.
You can get better by taking free classes and practicing with real cases.
Use easy tools and ask experts for help to feel sure.
Keep practicing blood gas analysis with real cases. It helps you make good choices for your patients.
You should look at pH before anything else. pH shows if blood is acidic or basic. This helps you figure out the animal's problem.
Venous blood gas gives some clues, but not about oxygen. Arterial blood is best for checking acid-base and oxygen levels.
See if the body tries to fix the pH. Use this table to help:
Disorder Type | Compensation Seen? |
|---|---|
Metabolic Acidosis | Lower PaCO2 |
Metabolic Alkalosis | Higher PaCO2 |
Respiratory Acidosis | Higher HCO3 |
Respiratory Alkalosis | Lower HCO3 |
The anion gap helps you find hidden acids in blood. It shows if low bicarbonate is from acid buildup or loss.
You might see strange pH, PaCO2, or HCO3 numbers. The body's fix does not match what you expect. You often see more than one abnormal value together.
Tip: Always check your results with the animal's symptoms for better care.
