Advanced Cardiopulmonary Monitoring

5 Advanced Cardiopulmonary Monitoring


Note 1: This book is written to cover every item listed as testable on the Entry Level Examination (ELE), Written Registry Examination (WRE), and Clinical Simulation Examination (CSE).


The listed code for each item is taken from the National Board for Respiratory Care’s (NBRC) Summary Content Outline for CRT (Certified Respiratory Therapist) and Written RRT (Registered Respiratory Therapist) Examinations (see http://evolve.elsevier.com/Sills/resptherapist/). For example, if an item is testable on both the ELE and the WRE, it will simply be shown as: (Code: …). If an item is only testable on the ELE, it will be shown as: (ELE code: …). If an item is only testable on the WRE, it will be shown as: (WRE code: …).


Following each item’s code will be the difficulty level of the questions on that item on the ELE and WRE. (See the Introduction for a full explanation of the three question difficulty levels.) Recall [R] level questions typically expect the exam taker to recall factual information. Application [Ap] level questions are harder because the exam taker may have to apply factual information to a clinical situation. Analysis [An] level questions are the most challenging because the exam taker may have to use critical thinking to evaluate patient data to make a clinical decision.


Note 2: A review of the most recent Entry Level Examinations (ELE) has shown an average of 2 questions (out of 140), or 1% of the exam, will cover advanced cardiopulmonary monitoring. A review of the most recent Written Registry Examinations (WRE) has shown an average of 3 questions (out of 100), or 3% of the exam, will cover advanced cardiopulmonary monitoring. The Clinical Simulation Examination is comprehensive and may include everything that should be known by an advanced level respiratory therapist.



MODULE A





1. Capnography (exhaled CO2 monitoring)





c. Perform the bedside procedure (Code: IB9c and IIIE3d) [Difficulty: ELE: R; WRE: Ap, An]


The capnometer is a device that measures the concentration of CO2 in a gas sample from a patient. The principle of operation of most bedside units is based on carbon dioxide’s absorption of infrared light in a narrow wavelength band (4.3 μ). Infrared light at this wavelength is passed through the gas sample to a receiving unit. The difference between what is transmitted and what is received is directly related to how much carbon dioxide is in the gas sample. In other words, the greater the difference between the sent and the received infrared light, the greater the concentration of carbon dioxide in the gas sample.


The capnometer is calibrated by comparing a gas sample without carbon dioxide (possibly room air) with a second gas sample containing a known amount of carbon dioxide. The first gas sample without CO2 should give a “zero” reading. Adjust the calibration control to zero if needed. The second sample usually contains 5% to 10% carbon dioxide. The capnometer should display a CO2 level that matches the amount in the known gas sample. Adjust the calibration control as necessary. The carbon dioxide level can be documented as a percent or fraction (FACO2) or as a partial pressure (PACO2).


The capnograph is a strip chart recorder that provides a copy of the patient’s exhaled carbon dioxide curve. There are at least two paper speeds that are useful for different purposes. The fast speed is most useful for evaluating sudden changes in the patient’s condition. Each individual breath is easily seen (Figure 5-1). The slow speed is most useful for trend monitoring (Figure 5-2).




Two different gas sampling methods exist: mainstream and sidestream. The mainstream method involves having the infrared sensing unit at the airway; usually it is attached directly to the endotracheal/tracheostomy tube. If the patient is on a ventilator, the sampling adapter must be placed between the endotracheal tube and the ventilator circuit (with or without mechanical dead space). All inspired and expired gas passes through the sensor (Figure 5-3).



The sidestream method employs a capillary tube placed so that a small sampling of the patient’s exhaled gas can be drawn into the capnometer for analysis. It is not necessary for the patient’s entire breath to pass through the sampling adapter; therefore it can be used in an unintubated patient by taping the sampling catheter a short distance into a nostril. If the patient is on a ventilator, the sampling adapter must be placed between the endotracheal tube and the ventilator circuit (with or without mechanical dead space). Remember that the patient’s exhaled tidal volume (VT) and minute volume (imageE) are reduced by the amount that is drawn into the capnometer (Figure 5-4).




d. Interpret the results from the procedure (Code: IB10c, IIIE4e) [Difficulty: ELE: R, Ap; WRE: An]


It is known that carbon dioxide diffuses from the higher concentration in the tissues to the venous blood and to the lungs to be exhaled. Figure 5-5 shows the normal physiology behind capnography. This diffusion or “flow” of CO2 results in a measurable gradient or difference. In a healthy, upright sitting person, a close relationship exists between carbon dioxide levels in both venous blood and arterial blood and the amount of exhaled carbon dioxide gas. The carbon dioxide level at the end of exhalation is most frequently monitored during patient care. This is called the end-tidal carbon dioxide pressure (PetCO2). When ventilation and perfusion match well, as in a healthy upright person, the gradient between the arterial carbon dioxide level (PaCO2) and the PetCO2 is between 2 and 3 torr, with a range of 1 to 5 torr. The gradient will show the PetCO2 level to be less than the PaCO2 level. This is because the PetCO2 value is an average of exhaled carbon dioxide levels from all lung areas.



Box 5-1 lists normal values of capnography. Three factors influence capnography’s use and the interpretation of the results. (1) The first factor is the patient’s metabolism. The average resting adult produces about 200 mL of CO2 per minute, and fever and exercise increase this value. Hypothermia, sleep, and sedation decrease CO2 production. Exhaled CO2 is monitored during a cardiopulmonary resuscitation (CPR) attempt to determine the effectiveness of circulation and ventilation attempts and to decide if the efforts should be continued or stopped. If no carbon dioxide is being exhaled despite proper CPR procedures, the physician may conclude that the patient’s metabolism has stopped altogether and death has occurred. There would then be nothing to gain by continuing cardiopulmonary resuscitation (CPR) efforts.



(2) Although not a major factor, the patient’s cardiac output is another factor that influences the use of capnography. Sepsis, which might double a patient’s cardiac output, reduces the PCO2 level only a few torr (millimeters of mercury [mm Hg]). Cardiogenic shock, which reduces the cardiac output, raises the partial pressure of CO2 (PCO2) only a few torr.


(3) The third and most important factor is alveolar ventilation. A doubling of alveolar ventilation, under steady-state conditions for carbon dioxide production, results in a halving of the PCO2 levels in arterial blood and alveolar gas. However, a reduction of alveolar ventilation to half of its previous level will result in the PaCO2 and PACO2 levels being doubled (Figure 5-6).



Tidal volume (VT) and respiratory rate are directly related to alveolar ventilation. Of the two, tidal volume is more important because it relates to the patient’s dead space (VD) to VT ratio (VD/VT). A decrease in the patient’s VT level results in less alveolar ventilation and a rise in PCO2 level. Conversely, an increase in the VT level results in more alveolar ventilation and a drop in the PCO2 level.


Capnography is most accurate and correlates best with the PaCO2 level if the patient’s ventilation and perfusion match. The more ventilation and perfusion mismatching there is, or the more unstable the pulmonary perfusion, the wider or less reliable is the gradient between the patient’s arterial carbon dioxide and alveolar carbon dioxide levels. The following procedures should be performed to help understand the patient’s condition and interpret the capnography results.




Remember that mm Hg (millimeters of mercury) and torr (Torricelli) are equivalent units of pressure. The National Board of Respiratory Care (NBRC) uses these two units for different items in its questions. It uses mm Hg for blood pressure measurements and torr for blood gas values (such as PaCO2 and PimageO2). However, in questions regarding capnography, the NBRC has used both mm Hg and torr in its questions that relate to exhaled CO2 (such as PACO2 and PetCO2).



2. Arterial–end-tidal carbon dioxide gradient



a. Perform the bedside procedure (Code: IB9c and IIIE3d) [Difficulty: ELE: R; WRE: Ap, An]


The arterial–end-tidal carbon dioxide gradient [P(a-et)CO2] is useful, because once it is reliably determined the patient’s ventilatory condition can be monitored by capnography alone. Drawing an arterial blood sample to measure the PaCO2 level is less necessary if the patient is stable.


The normal gradient is 2 to 3 torr, with a range of 1 to 5 torr. However, most patients using capnography are not normal. The possible gradient ranges from 6 to 20 torr in unstable patients with cardiopulmonary abnormalities. For example, the patient who is breathing shallowly may have an end-tidal CO2 level that is greater than the arterial CO2 level. This is because the patient is not exhaling completely to empty alveolar gas. Therefore determining each patient’s own gradient is important.


Follow these steps:









b. Interpret the results from the procedure (Code: IB10c, IIIE4e) [Difficulty: ELE: R, Ap; WRE: An]


Review the components of a fast-speed capnography tracing in Figure 5-1 to understand a normal person’s expiratory pattern. Figure 5-7 shows eight different abnormal fast-speed capnography tracings. See the figure legend for an explanation of each problem. As the patient returns to normal, the tracing should approach that shown in Figure 5-1.


image

Figure 5-7 A series of abnormal fast-speed capnography tracings. A, A mechanically ventilated patient with a malfunctioning exhalation valve. Note that the baseline CO2 level is elevated because the patient’s exhaled breath is measured during an inspiration. Correction of the exhalation valve should result in normal inhalation and exhalation. B, This rapidly rising baseline gas pressure and failure to return to baseline is usually seen when moisture or secretions block the capillary tube. Clearing the obstruction enables the patient’s gas to again reach the analyzer. C, Distortions in the tracing from incomplete exhalation. These may be caused by hiccups, chest compressions during CPR, or inconsistent tidal volume efforts during an asthma attack. D, An obstructive lung disease patient with ventilation and perfusion mismatching. There is no alveolar plateau with a stable CO2 level. Inhaling a bronchodilator should result in the tracing returning closer to normal. E, A patient with restrictive lung disease showing no plateau of alveolar gas emptying. This is because the alveoli do not empty evenly. F, A sudden drop in carbon dioxide level in the middle of an exhalation indicates that the patient attempted inspiration. This “cleft” is usually seen when a patient who has been pharmacologically paralyzed begins to regain movement. G, Uneven carbon dioxide levels seen at the end of exhalation can be caused by the following: (1) the patient’s heartbeat pumping fresh blood and CO2 to the emptying lungs; the cardiogenic oscillations should match the heart rate; (2) the ventilator’s exhalation valve is fluttering open and closed. H, The alveolar plateau is biphasic. This has been seen in patients with lungs that are different in compliance and ventilation/perfusion matching (e.g., single lung transplantation).


(From Shapiro BA, Peruzzi WT, Templin R: Clinical application of blood gases, ed 5, St Louis, 1994, Mosby.)



3. Arterial–residual volume alveolar carbon dioxide gradient




b. Interpret the results from the procedure (Code: IB10c, IIIE4e) [Difficulty: ELE: R, Ap; WRE: An]


When comparing the normal (solid line) tracing in Figure 5-8 with the image/image mismatching (dashed line) tracing, note the increased gradient at end-tidal CO2. With continued exhalation to residual volume, the left heart failure and COPD patients have a narrowing of the gradient. This can be used clinically to follow these patients’ progress and response to treatment. The patient with a large pulmonary embolism will not have such a narrowing of the gradient as he or she exhales to residual volume. This patient’s gradient will narrow to normal as the embolism is resolved and the physiologic dead space returns to normal.




Past exams have often had one question that requires the interpretation of capnography results, especially the end-tidal CO2 value (PetCO2). Examples include a change in alveolar ventilation, shallow breathing, and CPR attempt.



MODULE B






2. Perform the bedside procedure (ELE Code: IB9l) [Difficulty: ELE: R, An]


The procedure is the mathematical comparison of a person’s dead space volume with tidal volume. Steps in the traditional procedure follow (Figure 5-9):








b. Determine the dead space volume


Place both carbon dioxide values into this formula, which is derived from the original Bohr formula:



image



In which:


VD VT or VD the patient’s physiologic dead space


VT = the average exhaled tidal volume


PaCO2 = the patient’s arterial carbon dioxide pressure


PĒCO2 = the patient’s average exhaled carbon dioxide pressure


The following example is based on a normal adult:



image



The patient’s physiologic VD volume = 150 mL. (Note that this equation must be used when the patient’s tidal volume is known.)


In addition, the preceding equation allows calculation of the patient’s VD/VT ratio. In this example, it is 150/500, 0.3, or 30%, depending on how it is written.


The recent advent of volumetric capnography technology allows the patient’s dead space to be rapidly determined. These units can simultaneously measure the patient’s exhaled tidal volume and the variable percentage of carbon dioxide found during the exhalation (Figure 5-10). The computer that is integrated with the volumetric capnography unit then calculates the volume of dead space as a fraction of the exhaled tidal volume. Figure 5-11 shows how volumetric capnography can be set up to measure the dead space of a patient requiring mechanical ventilation. This technology permits the rapid assessment of a patient as treatment is being performed. For example, if a patient had a large pulmonary embolism resulting in significant dead space, a clot-dissolving medication such as streptokinase (Kabikinase or Streptase) or alteplase (Activase) would be given. These “clot buster” medications will rapidly dissolve the patient’s pulmonary embolism. With volumetric capnography, the dead space volume can be monitored as it normalizes when blood flow through the lungs is restored.







3. Interpret the results of the VD/VT calculation (Code: IB10l) [Difficulty: ELE: R, Ap; WRE: An]


The normal adult’s VD/VT ratio ranges from 0.2 (20%) to 0.4 (40%). Anatomic dead space is normally greater in men than in women. The normal 3-kg neonate’s dead space to tidal volume ratio is 0.3 (30%). Physiologic dead space (also known as respiratory dead space) is gas that is ventilated into the lungs but does not take part in gas exchange. This is because the alveoli are not perfused or are underperfused for the amount of gas that they receive.


Physiologic dead space is composed of the following:




The following conditions or pulmonary disorders can cause the ratio to vary from the normal range:






MODULE C





1. Blood pressure





c. Perform blood pressure measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]


The general steps in measuring blood pressure were described in Chapter 1. The BP is usually measured on either of the patient’s arms. Necessary equipment includes the proper size of blood pressure cuff, a sphygmomanometer to measure the pressure, and a stethoscope to hear the sounds of bloodflow returning through the brachial artery. Figure 5-12 shows the basic elements of the procedure. The cuff is inflated to a pressure that is greater than the patient’s systolic pressure. As the pressure in the cuff is gradually decreased, the first sound heard (Korotkoff sounds) is the systolic pressure. The pressure reading at which this sound ceases is the diastolic pressure. Blood pressure measurement can usually be performed manually by a respiratory therapist or other trained health care professional. If BP measurement is needed on a frequent basis, an automated blood pressure measurement system can be set up on the patient’s arm. This unit can be programmed to measure the BP on a schedule and can also have high and low blood pressure alarm limits established as a safety feature.






2. Central venous pressure (CVP) monitoring



a. Review central venous pressure measurement data in the patient’s chart (Code: IA8b) [Difficulty: ELE: R; WRE: Ap]


The central venous pressure (CVP) is the pressure measured in a patient’s superior vena cava, just above the right atrium. See Figure 5-13. Review previous patient data to understand whether there is an abnormality. Compare the current data with the earlier information to determine if there has been a change in the patient’s condition. See Box 5-2 for normal values.







d. Perform central venous pressure measurement (Code: IB9e) [Difficulty: R, Ap, An]


The catheter is usually inserted into the right jugular vein or right subclavian vein and advanced to just above the superior vena cava. When set up for monitoring pressure, it measures the right atrial pressure (see Figure 5-15 for how to perform the procedure). Note that the stopcock must be kept at the midchest (midheart) level. Usually a mark is placed at this location (on the patient’s chest) for consistency. Raising the stopcock above the mark results in an incorrectly low reading. Lowering the stopcock below the mark results in an incorrectly high reading. See Figure 5-16. Clinical practice is very important in learning how to perform this procedure. It is important that the patient breathes spontaneously if at all possible. Peak pressures during inspiration on a mechanical ventilator may artificially raise the CVP reading. Positive end-expiratory pressure (PEEP) may also raise the CVP reading. If the patient cannot be removed from the ventilator, take the reading during exhalation. Make a note of the settings and that the reading was taken with the patient on the ventilator. Record the data in the patient’s chart or flow sheet.






Past exams have asked about the proper placement of the CVP stopcock or arterial pressure transducer at the midchest (midheart) location to ensure accurate pressure measurements. Usually a mark is placed on the patient’s chest for a consistent measurement point. Review Figure 5-16 for the effects of misplacement.



e. Interpret the results of the central venous pressure measurement (Code: IB10m, IIIE4c) [Difficulty: ELE: R, Ap; WRE: An]


As noted earlier, the CVP is a measure of the pressure in the right atrium. The two main factors that influence the right atrial pressure are the blood volume returning to it and the functioning of the right ventricle (see Box 5-2 for normal CVP readings).


A decreased CVP reading usually indicates that the patient is hypovolemic. Hypotension confirms this. An increased CVP reading may suggest one of the following possibilities:










Exam Hint 5-6 (ELE, WRE)


Memorize the values listed in Box 5-2. Expect to see several questions in which these values are used as patient data or as options to answer a question. The normal values must be understood to identify abnormal values and know why they are abnormal.


Memorize the values listed in Box 5-2. Expect to see several questions in which these values are used as patient data or as options to answer a question. The normal values must be understood to identify abnormal values and know why they are abnormal.



3. Pulmonary artery pressure monitoring




b. Recommend the insertion of a pulmonary artery catheter for additional data (WRE code: IC12) [WRE Difficulty: R, Ap, An]


To read the PAP, a pulmonary artery catheter (PAC) must be inserted through a vein and passed through the right atrium and right ventricle into the pulmonary artery. The common insertion sites, in descending order of preference, are the basilic vein in either the right or the left arm, the right internal jugular or subclavian vein, or the right or left femoral vein. The pulmonary artery catheter is also commonly called a Swan-Ganz catheter after the inventors who gave their names to a particular brand. The catheters are available in different lengths and diameters for pediatric and adult patients. See Figure 5-17 for a typical adult catheter.





d. Perform pulmonary artery pressure measurement (Code: IB9m, IIIE3e) [Difficulty: ELE: R, Ap; WRE: An]


Figure 5-17 is an illustration of a 7-French quadruple-lumen thermodilution pulmonary artery catheter. Besides measurement of PAP, it is capable of being used to measure cardiac output. Figure 5-18 illustrates how a pulmonary artery catheter could be arranged with a pressure transducer and pressure monitor. Figure 5-19 shows a representation of the series of pressure waveforms seen as the catheter is advanced through the heart and into the wedged position in a branch of the pulmonary artery. Figure 5-20 shows a larger cutaway view of the heart with a PAC and normal heart chambers and related pressures.





To obtain an accurate pulmonary artery pressure measurement, the equipment must be set up and calibrated properly, the distal lumen of the catheter must be patent with a continuous fluid-filled channel from the patient’s bloodstream back to the transducer, and the catheter’s balloon must be deflated. Clinical practice is important in understanding how to perform this procedure. Record the PAP data in the patient’s chart or flow sheet.


Jun 18, 2016 | Posted by in RESPIRATORY | Comments Off on Advanced Cardiopulmonary Monitoring

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