Med-Surg Respiratory System, part 2: Diagnostic Tests
by Cathy Parkes August 18, 2021 Updated: December 07, 2022 5 min read
In this article, you'll learn the diagnostic tests and expected lab values for the respiratory system. We'll cover the ones you need to know most for Med-Surg Nursing exams and practice, including arterial blood gas, pulse oximetry, pulmonary function tests, bronchoscopies and thoracentesis.
The Med-Surg Nursing video series follows along with our Medical-Surgical Nursing Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
As part of your Med-Surg education, it's important to learn about the diagnostic tests and expected labs for each body system that you are studying. When you learn about diseases and disorders of the respiratory system, you will learn about the diagnostics, including when lab values are out of the normal range. If you know what the expected lab values are and what they are a measure of, this can help you better understand the diseases and disorders.
Check out our Lab Values Flashcards if you want to learn and retain all the lab values you need for the NCLEX in one place!
Arterial Blood Gas (ABG)
An arterial blood gas (ABG) is a test run on an arterial blood sample which can provide information on a patient's acid-base balance and ventilation by measuring the amount of oxygen, carbon dioxide, and bicarbonate present in the blood. These tests are often ordered for critical care patients, but not always, and can also occur in a med-surg/telemetry unit.
If you'd like in-depth studying on ABGs and to learn how to interpret ABGs, we have Arterial Blood Gas Interpretation Flashcards and a video series on ABG Interpretation.
There are five components in an ABG, and the first three listed here are the most important for being able to interpret the results:
- Partial pressure of carbon dioxide (PaCO₂)
- Bicarbonate (HCO₃)
- Partial pressure of oxygen (PaO₂)
- Oxygen saturation (SaO₂)
pH expected range
On an ABG, the normal range for pH is between 7.35 and 7.45. A pH under 7.35 indicates the blood is acidic and over 7.45 indicates the blood is alkalotic.
PaCO₂ expected range
On an ABG, the normal range for PaCO₂ is between 35 and 45 mmHg. PaCO₂ below 35 mmHg indicates presence of respiratory alkalosis due to hyperventilation OR compensation for metabolic acidosis.
HCO₃ expected range
On an ABG, the normal range for HCO₃ is between 22 and 26 mEq/L. HCO₃ under 22 mEq/L indicates metabolic acidosis or compensation for respiratory alkalosis.
PaO₂ expected range
On an ABG, the normal range for PaO₂ is between 80 and 100 mmHg. A PaO₂ less than 80 mmHg indicates poor oxygenation in the arterial blood.
SaO₂ expected range
On an ABG, the expected range for SaO₂ is between 95 - 100%. SaO₂ is the measure of hemoglobin saturation in the arterial blood. An SaO₂ level under 95% indicates hypoxemia which may be due to anemia, pneumonia, COPD, asthma, ARDS, pneumothorax, pulmonary embolism, or pulmonary edema.
ABG values can be difficult to interpret without some extra practice. Remember to check out our Arterial Blood Gas Interpretation Flashcards for help!
Pulse oximetry (SpO₂)
Pulse oximetry is another way to assess respiratory status. The expected range for SpO₂ is between 95 - 100%.
It is an expected finding for patients with COPD to have SpO₂ levels in the low 90s.
What's the difference between SpO₂ and SaO₂?
SaO₂ and SpO₂ are both a measurement of hemoglobin saturation in the blood. However, SpO₂ is measured with a pulse oximeter (a device that goes on the fingertip) so it is a much less invasive technique to collect this lab value than the arterial blood sampling that is needed with an ABG. Theoretically, these values should be the exact same. In practice, they are usually pretty close, within a small margin of error.
Pulmonary function tests
Pulmonary function tests are tests that measure lung function, and they include things like spirometry, lung volume test, gas diffusion test, and more.
Spirometry is the most common pulmonary function test and it measures things like forced vital capacity (FVC—how much air can be exhaled), and peak expiratory flow (PEF—the rate at which air can be exhaled).
Pulmonary function tests can be helpful in diagnosing asthma and COPD in patients.
A bronchoscopy is a procedure in which a tube is inserted into the patient's airway that allows for visualization of the airway as well as collection of specimens.
-Scopy comes from the Greek skopia/skopeo which means to view. So, any procedure ending in -scopy will involve the use of an instrument for viewing. Like colonoscopy!
Want to know more word hints to recognize unfamiliar terms? Check out our Medical Terminology and Abbreviations Flashcards.
Pre-bronchoscopy nursing care includes making sure the patient has not had anything to drink (been NPO) for the prescribed amount of time (4-8 hours) before the procedure and preparing patients for sedation.
Post-bronchoscopy nursing care includes ensuring that the patient's gag reflex has returned before providing food or beverage and monitoring the patient for a pneumothorax. Also, provide patient teaching that a sore, dry throat and blood-tinged mucus are expected.
A thoracentesis is a procedure to remove fluid or air from the pleural cavity via insertion of a needle into a patient's posterior chest (thorax).
Pleural effusion is excess fluid in the pleural cavity that can make it hard to breathe. A thoracentesis may be done to treat the pleural effusion by removing the fluid, but also as a diagnostic procedure to collect the fluid for analysis to determine the cause of the effusion. A thoracentesis can help diagnose congestive heart failure, tuberculosis, cancer, and other diseases.
Patient positioning will be the most important nursing activity before and during a thoracentesis, because it is required to provide access to the pleural cavity.
For the procedure, a patient must sit upright, and their arms should be supported on their bedside table or on pillows. They also need to remain still. Advise the patient not to talk, move, or cough when the thoracentesis is being performed.
Post-thoracentesis, monitor the patient for complications like a pneumothorax, bleeding, or hypotension. A chest x-ray can be performed if complications are suspected.
Advise your patient to take big, deep breaths to help expand the lungs after the procedure—if the lungs have been cramped and prevented from expanding by the pleural effusion, they have room now, so the deep breaths help with expansion.
Our teaching on respiratory labs and diagnostics is intended to help prepare you for Medical-Surgical nursing exams. TheMedical-Surgical Nursing video series is intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI and NCLEX.
Hi, I'm Cathy with Level Up RN. In this video, we are going to talk about respiratory system diagnostic tests and labs. At the end of the video, I'm going to give you guys a little quiz to test your knowledge of some of the facts I'll be going over in this video.
Let's start off by talking about arterial blood gases or ABGs. So I actually have a whole other playlist that is totally dedicated to ABGs and interpreting ABGs. So if you need any help with that, then definitely check that out at some point.
So ABGs assesses the acid-base balance and the oxygenation of critical-care patients and patients with acute or chronic respiratory disorders using a sample of their arterial blood.
There are five key components of ABGs.
The first is the pH, which should be between 7.35 and 7.45.
Then we have PaCO2, which is the partial pressure of carbon dioxide. That should be between 35 and 45.
Then we have bicarbonate or HCO3. That should be between 22 and 26.
Then we have our PaO2, which is the partial pressure of oxygen. That should be between 80 and 100.
And then we have our SaO2, which is, really, the oxygen saturation of the arterial blood. That should be between 95 and 100 percent.
So another way that we can assess our patient's respiratory status is through pulse oximetry. So the patient's SpO2 should be between 95 and 100 percent.
However, if we have a patient with COPD, they will often have SpO2 levels that are in the low 90s. And that is expected for a patient with this condition.
And then lastly, we have pulmonary function tests or PFTs, and these can be really helpful in diagnosing asthma and COPD in patients.
All right. Now, let's talk about a bronchoscopy, which is insertion of a tube into the patient's airway that allows for visualization of that airway as well as the collection of specimens.
In terms of nursing care, pre-procedure we want to make sure the patient has been NPO for the prescribed amount of time, which varies between four and eight hours. We also want to provide the prescribed medications which allow for sedation of the patient during the procedure.
Then post-procedure, we want to make sure that the patient's gag reflex has returned before we provide them anything to eat or drink. You also need to provide patient teaching that a sore, dry throat and blood-tinged mucus is expected. And then, of course, you want to monitor your patient for complications such as a pneumothorax, which we will talk more about as we go into detail about critical-care topics in this video playlist.
Next, let's talk about a thoracentesis, which involves the insertion of a needle into the patient's posterior chest to remove fluid or air from the pleural space.
So pre-procedure, you want to have the patient sit upright, and their arms should be supported on their bedside table or on pillows. And during the procedure, they need to remain perfectly still. So you need to advise them not to talk, move, or cough when the thoracentesis is being performed.
After the procedure, you're going to want to monitor them for complications such as a pneumothorax, bleeding, or hypotension. A chest x-ray can be performed if complications are suspected. And then you want to advise your patient to take nice, big, deep breaths to help expand those lungs after the procedure.
Okay. You guys ready for your quiz? I have three questions for you.
First question. An SpO2 of 90% is an expected finding in a patient with COPD. True or false? The answer is...true.
Question number two. Before allowing a patient to eat or drink after a bronchoscopy, what assessment do you need to make? The answer is...you need to make sure that the patient's gag reflex has returned.
Question number three. How would you position your patient for a thoracentesis? The answer is...you would have them sit upright with their arms supported on the bedside table or on pillows.
So hopefully you did well on that quiz. If not, you can go back and watch the video or review our cards again. Take care, and good luck studying.
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