Even though I am kind of an old guy with a fake knee I still think I know what it's like to be a student. For instance I understand and believe that the question; "What's on the exam?" is totally legitimate. In my courses I try to make if very clear what will be on the exam. Maybe not the exact specific questions but I try to leave little doubt about what content is relevant. For instance in this course you will absolutely need to now normal ABG values, causes of respiratory failure (table 41-2 Egans) and the physiological indicators for ventilatory support (table 41-3 Egans) for a start. Questions on these will be on the quizzes and exams!
Notice I'm giving a little plug to promote the fact that reading the text is good and starting off with reading Chapter 41 of Egans would be a very good idea.
Our first week will not be an idle one. We will be getting into the material very quickly, see the course map from D2L for details.
One uncomfortable element at the beginning of the course is that we do a very brief introduction to ABG interpretation. We need this background information but your ANPH 221 course is really where you will be learning the bulk of ABG interpretation. ABG interpretation is a critical concept and will be tested in both courses and used frequently in all your courses. The reason I say it's uncomfortable is that ABG interpretation is a very deep subject that we will only briefly touch on and learn how to do basic classification using a table method.
In class the first week we will also have a little review of the history of mechanical ventilation. This is really just a nice introduction to the meat of the first module which is the "Indications for Mechanical Ventilation". There will be not questions on quizzes or exams about the history of mechanical ventilation. The quizzes and exams will be inundated with questions about the indications for mechanical ventilation. I make it clear that the students must totally understand the numbers and elements of information contained in Table 41-3 of Egans (Physiological Indicators for Ventilatory Support) and this material will be part of quizzes and exams for the entire course, and even future courses in mechanical ventilation. So I guess I'm trying to tell you a good place to get started.
Many class days I will have worksheets for you to do. Some class time will be given for these but often they are completed at home. Worksheets are reviewed in class and the answers are not published. I have found that if I publish the answer sheets students are less likely to work on them and wait for the answers. I do not publish the answers. You will need to ask questions in class or review the material in the text and with other students to ensure you have the correct answers.
Okay enough for one sessions.
Al
Wednesday, December 22, 2010
Monday, December 20, 2010
Solution, Solutions
Okay; one of the first things you will learn about me as an instructor is that I often answer my own questions. This is often true but not always. Don't give me any grief if I don't occasionally provide the answers and you have to check with your classmates or the confirm your work with the texts. I do answer questions in class at any time on any assignment.
Okay back to our problem.
There really are two solutions. The first, as we often must do in medicine, we have to make some assumptions. The assumption we are going to make is that the patients' compliance is linear. This is seldom true but often true enough for the range of ventilating volumes and pressures we are using with most patients. Like all assumptions you need to be cognoscente of making it and realize that it may not apply or alter your observations at the bedside.
present C 25 = Change in volume 800ml / unknown new pressure in lungs X
Cross multiply to solve for the unknown pressures X; so now
unknown pressure X = 800ml / 25 ml/cmH2O
X = 32 cmH2O
So this pressure, 32cmH2O is the expected increase in pressure that would result from increasing the lung volume from FRC (functional residual capacity) with an additional 800ml. You can think of it as inflating a stiff balloon with 800ml of volume.
Now let us consider the second answer, what if the lung compliance is not linear? How would this affect our estimation? It is possibly a valid answer to say that the exact pressures could not be calculated without measuring the dynamic compliance of the lungs. We will discuss and demonstrate this in class. So if the actual lung compliance of the patient at the higher volume is lower, then our calculated pressure would be low. The actual pressures in the patients' lungs would be higher than calculated.
If the actual patients' lung compliance is higher at the larger volume, and this can be true, then our calculated pressures would be high. The actual lung pressures would be lower than our calculated value.
Comments or questions let me know below.
Al
Okay back to our problem.
There really are two solutions. The first, as we often must do in medicine, we have to make some assumptions. The assumption we are going to make is that the patients' compliance is linear. This is seldom true but often true enough for the range of ventilating volumes and pressures we are using with most patients. Like all assumptions you need to be cognoscente of making it and realize that it may not apply or alter your observations at the bedside.
Okay with that said, we now assume a constant lung compliance for the patient. The present "C" (compliance) of the patient is 25ml/cmH2O. Now we know the equation for calculating is; C= volume / pressure. Using this equation we can solve for the change in pressures with the increased volume. I like to set this up as a proportion;
present C 25 = Change in volume 800ml / unknown new pressure in lungs X
Cross multiply to solve for the unknown pressures X; so now
unknown pressure X = 800ml / 25 ml/cmH2O
X = 32 cmH2O
So this pressure, 32cmH2O is the expected increase in pressure that would result from increasing the lung volume from FRC (functional residual capacity) with an additional 800ml. You can think of it as inflating a stiff balloon with 800ml of volume.
Now let us consider the second answer, what if the lung compliance is not linear? How would this affect our estimation? It is possibly a valid answer to say that the exact pressures could not be calculated without measuring the dynamic compliance of the lungs. We will discuss and demonstrate this in class. So if the actual lung compliance of the patient at the higher volume is lower, then our calculated pressure would be low. The actual pressures in the patients' lungs would be higher than calculated.
If the actual patients' lung compliance is higher at the larger volume, and this can be true, then our calculated pressures would be high. The actual lung pressures would be lower than our calculated value.
Comments or questions let me know below.
Added Later: Graph of idealized lung compliance, lower zone = low compliance with alveolar collapse, middle zone =best compliance with open lung, upper zone = low compliance due to alveoli over inflation.
Al
Sunday, December 19, 2010
Introductory Problem
Here is an example problem that is very applicable to the RESP 220 course and uses the information you have obtained from your ANPH classes.
If a patient has a total lung compliance of 25ml/cmH2O and you fill the lungs with 800ml of air, from resting functional residual capacity, what would the pressure be in the lungs (in cmH2O). Note that you have held the 800ml of air in the lungs until the volume and pressure is totally equal in all areas of the lungs thus there is no flow and no effects of resistance. What all this means is that the pressures in the lungs and the pressure readings on the mechanical ventilator would be the same.
Problems like the one above are critical to our understanding of lung and ventilator mechanics. It's okay if you struggle with this problem for a while.
Post your answer as a comment and I will check in to see if you are correct.
Al
If a patient has a total lung compliance of 25ml/cmH2O and you fill the lungs with 800ml of air, from resting functional residual capacity, what would the pressure be in the lungs (in cmH2O). Note that you have held the 800ml of air in the lungs until the volume and pressure is totally equal in all areas of the lungs thus there is no flow and no effects of resistance. What all this means is that the pressures in the lungs and the pressure readings on the mechanical ventilator would be the same.
Problems like the one above are critical to our understanding of lung and ventilator mechanics. It's okay if you struggle with this problem for a while.
Post your answer as a comment and I will check in to see if you are correct.
Al
Friday, December 17, 2010
Welcome to My Blog
This is my blog and I am going to post anything that interests me about Respiratory Therapy and the SAIT RT Program. During this winter term my blog usually focuses on RESP 220 (Introduction to Mechanical Ventilators) course but all topics are open.
I am just getting back to classes after a short break to get a new right knee installed and am looking forward to 2011 and getting to know the first year students.
My first week starting back to work takes me to Hawaii where I am presenting and attending an international educational conference from Jan. 3-7. I know it is a tough way to start the New Year but someone has to do the dirty work.
There are some great resources for students these days with the Faculty at SAIT being excellent but I find students can often use an excellent resource like the Merck Manuals particularly as a quick resource for pathology (http://www.merckmanuals.com/professional/index.html). This online resource is the first place I go to get background info on almost any diseases.
Another source of interest is the CBC radio program “White Coat, Black Art”. This program deals with many issues such as; stress related to shift work, ethical problems, medical errors, and just about anything to do with medicine. It’s a fantastic professional look at the dynamics of medicine in Canada and you can choose to listen to any of the Podcasts you like at this website: http://www.cbc.ca/whitecoat/. If you get a little tired of studying relax by listening to a few of these podcasts.
The key about a blog like this is that it is not a mechanism for me to rant and rave. It’s a forum where I may introduce a topic or put forth my views on a topic but it really is important for you to participate with your comments. I will do my best to respond to any and all comments in a timely manner.
Check the D2L course website for the RESP 220 course map and the first modules Power Point slides. I’ll see you in class January 10.
Al
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