Determining Total Flow

Figure 1.  Photos taken by Janelle Gardiner
September 15, 2014

Air-Entrainment Devices

Figure 2

Figure 3

An air-entrainment mask is sometimes referred to as a Venturi mask.  An air-entrainment mask is capable of delivering a precise amount of oxygen.  "The mask is usually supplied with several color-coded adapters that change the rate of oxygen flow past the air entrainment port" (Aehlert, 2007, p. 66).  See figure 1.  As oxygen is flowing through the device, the air-entrainment ports, or colored adapters, allows for the mixture of air and oxygen to be delivered to the patient at a precise amount.  This is called a Venturi principle.

Each colored adapter is noted for a different fraction of inspired oxygen (FiO2), ranging from 24-50%.  The colored adapter changes the rate at which the oxygen flows through the device, and influences the amount of room air (21% oxygen) to be entrained.  In this case the air-entrainment ports remain the same size.  The flow injection port changes size in each color.  This is what changes the amount of oxygen delivered.

Figure 2 is a picture of a different type of air-entrainment mask.  In this mask, the size of the air-entrainment port is adjustable to determine the amount of oxygen to be delivered (Aehlert, 2007).  Figure 3 is a picture of an air-entrainment nebulizer.  The amount of oxygen delivered by the nebulizer is based on the same Venturi principle, as the air-entrainment port is adjustable for varying FiO2 delivery (White, 2013).

Total Flow

When using an air-entrainment device, a respiratory therapist needs to ensure the flow to a device is adequate to meet the patient's inspiratory flow demand.  The total flow to the device must meet or exceed their demand to ensure the set FiO2 is being delivered. 

The total flow delivered to the patient can be determined by using this formula:

Total flow = (air to oxygen entrainment factor) (set liter flow to the device)

Instructions for determining the air to oxygen entrainment ratios will be provided in another discussion.  For now, use the following table to determine the factor to use to calculate total flow.  The FiO2 and liter flow to the device will be provided in the given scenario.  

FiO2	Air:O2 Entrainment Ratio	Factor (Air + O2 from ratio)
24	25:1	26
28	10:1	11
40	3:1	4
50	1.7:1	2.7
60	1:1	2
100	0:1	1

Case One:

The physician's order for the patient in room 316 reads "Venturi mask at 40%".  You note that the Venturi mask indicates that the device must have 6 liters of oxygen flowing through it.  What is the total flow delivered to the patient?

Respond to the discussion with your answer.  Then provide your peers with another scenario to allow them to have practice calculating total flow.

Recommendations for teaching total flow:

When teaching students the concept of total flow, include methods to address the needs of visual, auditory, and kinesthetic learners.  Auditory learners will benefit from hearing the lecture, and the description of how total flow is determined.  They may also benefit from hearing the device in use and the varying flows through the device as the air-entrainment port is changed.  Visual learners will benefit from seeing the types of mask, the varying sizes of injection ports and air-entrainment ports, and seeing the calculations performed.  Kinesthetic learners will learn best by using the mask or air-entrainment nebulizer, adjusting the size of the port, changing the color-coded pieces, and connecting the device to oxygen while adjusting the flow.  

References:

Aehlert, B.  (2007).  ACLS Study Guide (3rd ed.).  VitalBook file: C. V. Mosby.  

White, G. C. (2013).  Basic clinical lab competencies for respiratory care: An integrated approach (5th ed.).  Clifton Park, NY: Delmar.

Enterovirus D68

In the first week of class we discussed infection control.  You may recall our discussion included the spread of infection, importance of hand washing, and isolation procedures.  You may wish to review appropriate chapters in your textbooks (Kacmarek, Stoller, & Heuer, 2013; White, 2013).  In current news, there is a rare virus, Enterovirus D68, traveling west and could affect Utah.  As of September 12, 2014 the Centers for Disease Control and Prevention (CDC), reports no confirmed cases in Utah.  On the map below, the dark green states are those with confirmed cases of Enterovirus D68 (CDC, 2014).

Centers for Disease Control and Prevention (2014, September 12).

Click on the links below to learn more about the virus.

CDC on Enterovirus D68

KSL 5 News, Enterovirus potential in Utah

As you gather information, consider how it applies to the things you have recently learned about the spread of infection.  Perform your own research and then contribute to the discussion below by considering some of the following:

• What infection control measures should be taken if Enterovirus 68 is confirmed in patients in Utah hospitals?  In class we discussed standard, contact, droplet, and airborne precautions.  Which of these would apply here?  Support your answer with additional resources.
• As a clinician, what are your responsibilities?  By what signs and symptoms will you recognize the virus?  Who is at greatest risk?  Support your answer with additional resources.
• Post PDFs of literature or links to other good sources of information on the subject.  In your comments, discuss why you feel it is important for you or your peers to know this information.

Recommendations for teachers:  Have the students research and find information with regard to infection control procedures for Ebola virus or other current infection control concerns.  

References:

Centers for Disease Control and Prevention (2014).  Enterovirus D68.  Retrieved from http://www.cdc.gov/non-polio-enterovirus/about/ev-d68.html 

Kacmerek, R. M., Stoller, J. K., & Heuer, A. J. (Eds.). (2013).  Egan’s fundamentals of respiratory care (10th ed.).  St. Louis, Missouri: Elsevier.
White, G. C. (2013).  Basic clinical lab competencies for respiratory care: An integrated approach (5th ed.).  Clifton Park, NY: Delmar.

Calculating Tank Time

As a respiratory therapist, it may become necessary for you to know the amount of time an oxygen tank or oxygen cylinder is expected to last when running at a given liter flow.  This can be determined by calculating tank time.  The following is an example of a scenario in which it would be necessary for you to calculate tank time:

Photo taken by Janelle Gardiner, September 15, 2014.

You are a respiratory therapist on the night shift at a 300-bed, level two trauma center.  You are asked by the charge nurse of the cardiovascular-thoracic unit to arrange for home oxygen for a patient who is being discharged in the morning.  The patient is a truck-driver from Boise, Idaho, who suffered a myocardial infarction on his route and subsequently underwent Coronary Artery Bypass Graft at your hospital.  The patient will be traveling home via his 18-wheeler.  It will take approximately eight hours for the patient to travel from your location to Boise, including adequate time for rest stops and meals.  The patient will be discharged on a nasal cannula at 4 LPM.  The nurse would like to know how many E cylinders the patient will need to ensure the patient has enough oxygen to get home.  The patient needs to know how long to expect one full E cylinder to last.  This will allow the patient to plan to change tanks at appropriate time intervals.

This tank time formula will be helpful in your calculations.

The following steps are provided to guide you in obtaining the information necessary to provide both the nurse and the patient with the information needed.

1. Identify the tank factor for the size cylinder being used.  To simplify, use a tank factor of 0.28 for an E cylinder, and 3.14 for an H cylinder.  For a more complete listing of tank factors, please refer to Table 37-4 in Egan's Fundamentals of Respiratory Care (Kacmarek, Stoller, & Heuer, 2013).
2. Note the liter flow for the particular scenario.
3. Assume a full cylinder contains 2200 psig.
4. Insert know figures into the formula.  Tank factor * psig in cylinder.
5. Divide the result of step 4 by the liter flow as noted in step 2.  This will give you the number of minutes the cylinder will last at the specified liter flow and pressure (psi) remaining in the cylinder.
6. Divide the result of step 5 by 60 to determine the number of hours and minutes one cylinder will last.

Photo taken by Janelle Gardiner

Contribute to the discussion by posting information needed by the nurse and the patient in the comments section below.  If you are the first to respond, provide a scenario of your own for the next person to use to calculate tank time.

Beyond Tank Time
For the patient to be completely prepared for discharge, they will need to know other things in addition to time intervals at which to change tanks.  Comment on what other patient education you could provide at the time of discharge.  What arrangements need to made in Boise?  Are there other ancillary services that need to be involved in discharge planning?


Recommendations for teaching tank time calculations:

• Provide the students with some relevant scenarios similar to the one provided above.  The scenarios can be for in-hospital transport, inter-hospital transport, or discharge for home use.  For optimal learning, the student should be able to find clinical relevance in the scenarios provided.
• Discuss with students the format for finding a similar scenario on the National Board for Respiratory Care (NBRC) Certified Respiratory Therapist exam.  Help the student understand that all questions will be asked in a multiple choice format.  The students must be able to perform these calculations without the use of a calculator, as the NBRC does not allow the student to use a calculator on the exam.  Therefore, you may suggest they can use a tank factor of three for an H cylinder, and 0.3 for an E cylinder to simply the calculations.  Historically, multiple choice responses are far enough apart from each other that these types of estimations can be made to arrive at the correct answer.  

References:

Kacmerek, R. M., Stoller, J. K., & Heuer, A. J. (Eds.). (2013).  Egan’s fundamentals of respiratory care (10th ed.).  St. Louis, Missouri: Elsevier.