Overview of Blood Gas Temperature Correction
The first machine used to measure gases in the blood was developed thanks to the efforts of John Severinghaus, Leland Clark, and a few other inventors. This revolutionary tool played a pivotal role in improving how we care for seriously ill patients. While today’s blood gas devices have evolved from that original design by Severinghaus, the core processes for detecting blood gases have largely remained the same.
It’s interesting to note that currently, these devices often heat up to about 37 degrees Celsius. For many patients, this temperature is close enough to their body temperature to give accurate readings. However, in patients who are too hot (hyperthermic) or too cold (hypothermic), the device’s temperature could impact the accuracy of the readings for oxygen levels (PO2), carbon dioxide levels (PCO2), and the balance between acidity and alkalinity in the blood (pH).
In this context, we will be focusing on how arterial blood gases, which are gases present in the blood that runs through the arteries, are detected. We’ll also look at how the readings may be managed in relation to temperature adjustments.
Anatomy and Physiology of Blood Gas Temperature Correction
The changes in temperature are influenced by factors like physical properties of gas, the human body’s process of breaking down food and turning it into energy (what we call metabolism), and the acid-base buffering system – the system our body uses to keep our body’s acidity (pH) under control. There’s a scientific principle called Henry’s law which says that when the temperature goes up, gas dissolves less in a solution. Clark and Severinghaus electrodes are devices used to measure the amounts of oxygen and carbon dioxide gases. As per Henry’s law, when the temperature rises, these gases are less likely to dissolve, which results in an increased prediction of their presence.
In simple terms, Henry’s law means the amount of gas that can dissolve in water is proportional to the pressure of the gas above the water. As the temperature rises, the ability for a gas to dissolve decreases, meaning more gas is present and more pressure is created by it.
When we look at our bodies, carbon dioxide (CO2), which is released during metabolism, mostly exists as bicarbonate dissolved in our blood. As our blood heats up, a chemical reaction occurs increasing the amount of CO2 in the blood. According to a scientific equation known as the Henderson-Hasselbach equation, a rise in CO2 levels causes a drop in blood pH, meaning the blood becomes more acidic. The reverse is also true – as our blood cools down, the pH can increase or become less acidic.
Blood oxygen levels also rise following Henry’s law. In addition, the patient’s hematocrit, or the proportion of red blood cells in the blood, can affect these levels. The amount of oxygen in the blood can be influenced by the temperature effect on a protein called hemoglobin, which carries oxygen in the blood. As our blood temperature increases, more oxygen is released and can be detected. However, in severely anaemic patients who have lower levels of red blood cells, this increase in oxygen levels might not be as high as expected when the blood is heated. It is important to consider this when looking at blood tests results.
The Bohr and Haldane effects are two principles related to how changes in acidity and carbon dioxide levels affect oxygen’s ability to bind to hemoglobin. These have a minor influence on blood gas levels compared to the effect of temperature.
Why do People Need Blood Gas Temperature Correction
It’s crucial when treating a patient to consider how their body temperature might affect their health. For instance, when a patient’s body temperature is lower than normal, they might have lower levels of carbon dioxide and oxygen in their blood, as well as higher levels of certain chemicals that indicate acid build-up in the body. On the other hand, when a patient’s body temperature is higher than normal, they might have higher levels of carbon dioxide and oxygen in their blood, with more acid present when compared to standard blood test values.
One common situation where body temperature adjustment of blood tests is often noted is in cardiac surgeries or the period following a serious heart condition, where the body’s tissues don’t get as much blood supply as they need. Consequently, the tissues need to operate without enough oxygen, leading to more acid build-up. Depending on the blood supply to the brain and concerns for increased pressure in the skull due to high carbon dioxide levels in the blood (which can increase blood flow to the brain), or the contrasting effect of decreased blood flow in states of low carbon dioxide levels, medical professionals might select one of two common methods to manage the patient.
The first method, known as alpha-stat, aims to maintain normal blood values for carbon dioxide, amount of acidity (pH) and oxygen, as observed in the laboratory at a standard body temperature of 98.6°F (37°C), regardless of the patient’s temperature. This approach is believed to be suited for patients at risk of decreased blood flow to the brain, as it uses a higher estimate of blood carbon dioxide levels to guide the treatment and seeks to maintain stable cellular health and blood flow regulation to the brain.
The second method, known as pH-stat, targets normal blood values adjusted for the patient’s body temperature. This approach is thought to be suitable for patients at risk of increased pressure within the skull, as it utilizes blood test values adjusted to a lower body temperature with lower carbon dioxide levels. However, it’s important to state that, regardless of the method chosen, there’s no evidence showing better brain recovery with one strategy over the other. Some sources suggest that The Royal College of Anesthetists in the United Kingdom generally prefers the alpha-stat method.
When a Person Should Avoid Blood Gas Temperature Correction
There’s essentially no harm in adjusting the temperature of a patient’s blood gas levels, making it a procedure with no known drawbacks. However, experts still haven’t reached a consensus on the potential long-term benefits in choosing the alpha-stat or pH-stat approach over the other. So, it’s best for doctors to consider each patient’s unique situation when deciding which method to use.
Equipment used for Blood Gas Temperature Correction
The doctor can adjust the temperature in real-time during your treatment, or they can use proven methods available on handheld devices and other equipment.
Managing your body’s balance of acidity and alkalinity (pH-stat management) needs a machine called an oxygenator that can adjust how much carbon dioxide your body gets. This process also requires a device to analyze the gases in your blood while the treatment is ongoing.
Who is needed to perform Blood Gas Temperature Correction?
When you need to have your blood gases checked, several medical professionals get involved. First, there’s the doctor who orders the blood test. This doctor decides what specific tests you need based on your health condition.
Next, there’s the expert who is responsible for getting the blood sample. They do this through arteries (the blood vessels that carry blood away from your heart) or veins (the vessels that return blood to your heart). This could be a doctor, nurse, or medical technician.
Once they’ve gotten the blood sample, a lab technician collects it. This technician is specially trained to handle blood in a way that keeps it safe for testing.
After the sample has been drawn, a responsible person transports it to the lab for processing. This ensures that your blood sample gets analyzed in a timely manner so that the results come back quickly.
The final step is the lab processing. The lab personnel analyze your blood and write up a report on the findings. These findings provide your doctors with valuable information about your health condition.
Preparing for Blood Gas Temperature Correction
Drawing blood for testing is a process that requires careful preparation and proper training. The person taking the blood sample needs to be well-trained. Additionally, before taking the blood sample, the patient’s body temperature needs to be noted because this could affect the test result.
The blood sample needs to be transported quickly to the lab where it will be processed. During this process, it’s also critical to keep the blood sample at a consistent temperature. These steps are important to ensure the accuracy of the blood test result.
How is Blood Gas Temperature Correction performed
Body temperature has an impact on blood gas values. Simply put, a decrease in body temperature can alter the values of oxygen (PO2), carbon dioxide (PCO2), and pH in blood. Here’s the breakdown:
For each 1°C drop in body temperature below normal (37°C or about 98.6°F), the oxygen level (PO2) in blood decreases by 5mmHg, carbon dioxide level (PCO2) decreases by 2mmHg, and the pH level increases by 0.012. On the flip side, when body temperature rises above 37°C, the level of carbon dioxide in the blood increases by 4.6% for each 1°C increase.
Healthcare providers have some formulas to estimate these changes. For example, one formula is called logcPao2. This helps to calculate the changes in oxygen level, based on a factor (f) related to temperature difference and oxygen level.
Another formula known as the Nunn method, helps determine how carbon dioxide levels change with different temperatures. This formula uses the PatcCO2 code and takes into account the difference in temperature from the normal 37°C.
However, it’s important to note that these formulas are based on general data and might not account for specific characteristics of an individual patient.
Possible Complications of Blood Gas Temperature Correction
In the past, it was usual to cool tubes used for blood gas tests to slow down white blood cell activity. Doing this would cause a higher PCO2 reading and a lower estimation of PO2 and pH. PCO2 refers to the amount of carbon dioxide in the blood, while PO2 is the level of oxygen and pH measures acidity. These readings tell us how well your lungs are working.
However, this practice of cooling is not recommended anymore. Nowadays, we use PVC or plastic syringes, which can let out oxygen when they get cold. This can lead to underestimating the true oxygen level in your blood.
The best way to get accurate readings is to run these tests quickly. We aim to test for PO2 within 15 minutes of drawing the blood to avoid interference from metabolism in the blood cells. All other values should be processed within 30 minutes.
It’s also important to know that other factors can lead to incorrect blood gas results. These can include trapping an air bubble in the sample, shaking the sample too much, drawing blood from a line that has fluid other than blood, or not using the right technique to collect the blood.
What Else Should I Know About Blood Gas Temperature Correction?
There’s some debate about the usefulness of adjusting blood gas values based on temperature in patient care. This means that doctors should only consider the temperature while evaluating blood gases when it’s specifically asked for. However, it’s critical to know how temperature can affect blood gases. Not being aware of this influence can potentially cause incorrect readings and misguided medical decisions.
Just to clarify, ‘blood gases’ are measurements that show how much oxygen and carbon dioxide is in your blood. These measurements are often used to check how well your lungs are working. Sometimes, the results need to be adjusted for temperature, especially when the body’s temperature is not normal, but this isn’t always necessary or helpful.
