Modes of Ventilation:

This is a subject near and dear to many a Respiratory Therapist’s heart.  It is what defines our ability to manipulate the mechanical ventilator to a patient’s needs.  The primary need is oxygen delivery to the tissues, removal of carbon dioxide and the maintenance of normal pH.  A tall order when a patient has advance lung disease as with adult respiratory distress syndrome (ARDS).

You have already learned but maybe not mastered the basics of volume and pressure ventilation.  Now we will explore the many subtle nuances of how we can manipulate these two basic elements into the modes we use every day.

The kinds of problems we will look to solve in this course are the key control interactions.  For example in the mode of VC-CMV the ventilator controls are: rate, tidal volume, PEEP, flow, and FiO2.   A typical question we will explore may include a statement like; if you increase the rate what would happen to minute ventilation?  Another question might be what would happen to the I:E ratio when you increased the RR?  What would happen if to the mean airway pressure (Paw) with this increase in RR?

The questions are probably a little intimidating at this time, but by the end of the course you will have explored all these relationships and be more confident.

In class I have been impressed that many of you are considering what does this mean for the patient?  Isn’t that rate too low or minute ventilation too high?  What about those ventilator pressures?  All excellent questions because two elements are critical; maintaining the patient’s ABG’s to meet the clinical goals, and to minimize harm to the patient.  We can never eliminate all the harm we will do to the patient but ultimately the good of keeping them alive outweighs the bad.  We must always try to minimize the damage to the patient. 

Here is a challenge for you to think about.  Two adult patients with ideal body weights of 70kg are involved in a motor vehicle collision come into ER.   They are both unconscious and require mechanical ventilation.  One is set-up with volume ventilation, the other with pressure control.  Now I challenge you to think about the volume ventilator, what would should the initial settings be?  Initial settings Vt set for normal tidal volume about 8ml/kg or a Vt of 560 or round it to 550ml is set,  Rate 12 bpm, flow 60lpm, FiO2 1.0 because we don’t know anything about their oxygen needs at this time, PEEP of 5 because we think that is a fairly normal physiological level.

Now what about patient #2?  What PC level do we set?  How would or could we know?  We would need to know the patient’s lung compliance to be able to estimate the Vt delivered.  How could we know that?  The answer is I don’t know!  We could guess and set a safe PC level and see what happens and sometimes we do this.  Say PC level of 25, Ti 1.2 sec (longer than an expected TC*5 but we will have to check), Rate 12 bpm seems reasonable, FiO2 1.0, throw in +5 of PEEP just for fun.  Okay but what about our minute ventilation.  Are we meeting the patient’s needs?  With this mode we would need to check the Vt delivered (this would be recorded as the ventilator would measure it for us).  Then we could get an idea if the Vt with this PC level would be enough.  So here I hope I have highlighted one of the dilemmas about choosing a PC mode initially in an emergency situation.  There may be a few breaths or couple of ABG,s required before you can fine tune your ventilator.  Mind you VC may also require fine tuning as patients demands change and are dependent upon many factors.

This brings me to the last point today that is we need to meet the patient’s needs.  This means ventilating to ABG’s.  We use our expertise to fine tune the ventilator to minimize the lung damage caused by pressure, volume, and oxygen.  Generally speaking keep the Pplat less than 30 cmH2O, maintain a PaO2 of at least 60 mmHg (works out to about a SpO2 of 90%)  Thus the art of the RT is born!

See you in class!

Professionalism

This is hot topic for Faculty, Mentors, Employers, and our patients and they all have different elements of professionalism that are important to them and so we as students and working Therapists must be aware and meet their expectations.  This may sound daunting with all the legislation that outlines our professional conduct but in my opinion these legal elements rarely are the factors that cause problems or conflict.  It is the soft hard to define attitudes conduct and behaviors that are often the source of heated concern.

I have often heard individuals proclaim; “how being late is unprofessional and unacceptable behavior!”  Clearly this could be considered as true if the individual is wantonly late and has a casual attitude towards punctuality but is this often true?  In our complex world of public transit, required lining up for everything, and just the general chaos of daily life is it not more often true that being late is often out of our control.  To me stating; "that an individual should just have planned better", is arrogant and makes many unsubstantiated insinuations.  In my personal opinion I sometimes think it could be considered that unreasonable intolerance of behaviors such as lateness could be considered an unprofessional attitude in itself.  But I think we can all see why punctuality is a coveted trait in any profession where interdependence is a major operating factor.  So what can we do to demonstrate professionalism with regards to being on time?   In my opinion I think students can demonstrate professionalism in this regard by clearly  striving to be on time and then acknowledging the problem with the inevitable occurrence of being late occurs.  When late, give apologies first, rationale second, then confirmation of your acceptance of responsibility and finally outline how you will strive to not allow this to happen is all that we can offer and expect.  For acceptance by our colleagues and coworkers we must make sure that this problem is infrequent and genuinely something we will try to resolve.  I think we all know individuals who perhaps have a problem with time management or are often late.  I propose there are two approaches to this problem, if it is truly an attitude and callous disregard for others that is the cause of the problem then strict discipline with clear consequences maybe the solution.  But for those other problematic individuals that are trying their best but still are problematic then maybe we need to look inward for a broader definition of professionalism and look to understanding and tolerance rather than just anger and disgust towards the problematic individual.

I am using this example of problematic punctuality as an example of how we as professionals may need to set standards of conduct and behavior but also how truly professional behaviors force us to be tolerant and understanding when viewing the conduct and actions of others.

What do you think?

Week Four, Module 3, and Assignment 1

Well it’s hard to keep up a serious interest in blogging when so few of the class are reading this stuff but I hope to reward those of you reading it now!

I would like to give you few who do check this out a little heads up about next week.  The next chapters on Ventilator Classification are a real slog for students.  I’ve got some worksheets and a few things to try and keep us on track but it really pays to read ahead.  What seems to be the biggest obstacle is the new vocabulary we need to develop so that we can start to understand the performance aspects of mechanical ventilators.  Once this is established we can start our discussions about the modes of ventilation and some of the nuances of ventilating specific patients and adjusting the ventilator to meet their needs.

The essence of this next module is so that we can understand table 42-2, Specifications for some of the modes.  In this table we need to understand all the headings such as; Breathing Pattern, Control Type, Trigger, Limit, and Cycle.  Once these terms are understood we can begin to define the characteristics and unique aspects of each mode of ventilation.

The assignment for this course is actually a virtual laboratory experiment where you will derive the relationship of all ventilator controls for three common modes of ventilation.  For the assignment you will use the virtual ventilator models that I have derived for you.  These are useful because they allow you to control the ventilator and patient parameters, see the resulting outputs without being tangled up in alarms, and ventilator specific controls.  The input and outputs are clearly established in this assignment.  I test regularly and deeply on this subject matter.  It is an expectation that you understand the controls and the interactions. 

An example question would be; In the mode of VC-CMV if the patient’s compliance decreased what would happen to the Ti (inspiratory time) would it, go up, go down, or stay the same?  After completing the assignment you will be able to answer this question.  I hope you find the assignment challenging, fun, and worthwhile.


Please complete this form (click here for RESP 220 Feedback) and give me some feedback about the class.  All input into this form are anonymous.


Thank you

First Week of Classes

Wow our first week of classes is already over and I’m a little concerned because I had to start off with the dreaded “Blood Gas Introduction”.  Please be assured that this is an introduction to orient us to basic ABG values and the classification terminology.  You will notice there is no Power Point and few official notes except for the worksheets.  This is because ABG’s are part of mechanical ventilation in that we use the ABG’s as a guide to manage the patient.

That said; this next section on indications for mechanical ventilation is important and interesting.  Egans chapter 41 is some good reading and all the critical elements of the course are captured there.  Sometimes students comment that they are uncomfortable when Instructors mention different pathologies that cause respiratory failure.  I can totally empathize with you as pathology is a huge area of study and not yet something you have studied in detail.  The course survival mechanism for this is to look at the table 41-2 page 956 and maybe write out a very brief description for some of the basic pathologies.  I know this is work but a quick “Google” search or a “Wikipedia” search can give you all the basic info you need.  Some of the first pathologies you may be interested in and I tend to use in class are; adult respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), asthma, and pulmonary infections / pneumonia.  Remember you can always ask in class for me to describe the pathology but it’s hard to grasp my one sentence descriptions delivered off the cuff and on the fly.

My method of using worksheets and in-class exercises I hope works for you.  Notice that I will really emphasize key elements when making presentations and you may wish to focus on this when it comes time for review.

I really enjoy the sidebar discussions and questions in class so please speak up!

Al