Question 1
A therapist is monitoring a child on the mechanical ventilator who is hemodynamically stable. The PetCO2 is 48 mm Hg. If accurate, what should be the PaCO2?

43-48 mm Hg

45-48 mm Hg

50-53 mm Hg

 

Exactly the same as PetCO2
PetCO2 can be used as a surrogate for the arterial partial pressure of CO2 (PaCO2) within physiologic limits. Normally, PetCO2 is 2-5 mmHg below PaCO2. The reason for this is the proportion dead-space ventilation.

 

Question 2  
What is volumetric capnography able to determine?
 
I. Airway dead space
II. Alveolar tidal volume
III. Shunt fraction
IV. Alveolar minute volume

II, III, and IV only

I only

I, II, and IV only

I, II, III, and IV
 
The concentration of CO2 is plotted against exhaled tidal volume to determine relevant ventilation data such as airway dead space, alveolar tidal volume, and extrapolation of CO2 elimination and alveolar minute ventilation.

 

Question 3
The respiratory therapist has initiated iNO at 20 ppm for an infant with pulmonary hypertension. After 2 hours a blood gas test reveals a 10% improvement in SaO2. What should the therapist do?
Keep iNO at 20 ppm and wait at least 2 hours before considering any change.

Increase iNO to 30 ppm and keep the same FiO2.

Keep iNO at 20 ppm and wean the FiO2 by 10%.

Increase iNO to 30 ppm with no changes in FiO2.
 
Several studies have used an increase in oxygen saturation of 20% over baseline as an indication that the infant is responsive.

 

Question 4
 
Vascular smooth muscle is largely dependent on which of the following
intracellular ions?

Na+

K+

 

Ca2+

Mg2+
 
Current understanding suggests that vascular smooth muscle is largely dependent on intracellular calcium ion (Ca2+) concentration. Smooth muscle tissue comprises bundles of myofibrils, threadlike contractile fibers encased by the sarcoplasmic reticulum, a network of tubes or channels that store Ca2+.

 

Question 5
 
Which of the following medications contributes to an increased right-to-left intrapulmonary shunting?
 
Dobutamine
Dopamine
Prostacyclin
Prostaglandin A
 
The intravenous vasodilators nitroprusside and prostacyclin will relax pulmonary vasculature globally, reducing pulmonary vascular resistance, but will also increase pulmonary blood flow past nonfunctioning alveoli and intrapulmonary right-to-left shunt.

 
Question 6
 
The therapist is performing a routine assessment and ventilator check on a patient who is receiving heliox near the wye adapter of the ventilator circuit. He notices a serious discrepancy between the set tidal and the exhaled volume. What should the therapist do to correct this situation?
 
Administer heliox through the heliox-approved inlet of the mechanical ventilator
Add a 16-inch piece of corrugated tubing between the wye adapter and the place on the inspiratory limb where heliox is administered
Reduce the liter flow on the heliox
Adjust ventilator settings to compensate for the lower viscosity of heliox


The safest method to deliver helium–oxygen mixtures via mechanical ventilation is to connect an 80/20 heliox mixture to the heliox-approved inlet of the mechanical ventilator. The practitioner then uses the ventilator’s oxygen concentration control to adjust helium and oxygen to the desired mixture. This allows the practitioner to deliver a helium concentration up to the 80% helium. It is important to note that ventilators may not function properly with helium as a source gas.

 
Question 7
 
The therapist taking care of an infant on iNO observes that the NO2 levels have been increasing. In order to correct the situation he increases the inspiratory flow of the ventilator. What will be some of the limitations associated with this change?
 
I. It reduces time of contact between NO and O2.
II. It affects the mean airway pressure because it changes the inspiratory time.
III. It may increase the delivered tidal volume.
IV. It reduces the mean airway pressure and increases the inspiratory time.
 
I only
II and IV only
I, II, and III only
II, III, and IV only
 

Decreasing the NO or oxygen concentration is usually not an option; therefore, to reduce NO2 delivery to the patient, reduce the duration of contact between NO and oxygen. Two methods accomplish this: (1) increase the inspiratory flow or (2) add the NO as close to the patient as possible. Each of these methods has practical limitations. Increasing the ventilator flow will reduce the time of contact between NO and oxygen before reaching the patient, but it may also affect inspiratory time, tidal volume, mean airway pressure, and so on.
 
Question 8
 
Which of the following features or characteristics apply to mainstream capnography?
 
I. The mainstream capnograph contains narrow tubing that can become occluded with mucus.
II. Mainstream capnography generally employs infrared spectrometers.
III. The mainstream capnograph does not add much weight to the breathing circuit.
IV. The mainstream capnograph is placed at the proximal end of the endotracheal tube.
 
I and II only
II and IV only
I, II, and III only
I, III, and IV only
 

Gases from an exhaled breath can reach the sample chamber in one of two ways. Mainstream capnographs are used in ventilated patients, with placement at the proximal end of an endotracheal tube (see Figure 9-5 in the textbook). This method employs infrared spectrometers. Sidestream capnograph analyzers continuously aspirate a sample of gas through a small tube to the analyzer.

 
Question 9
 
During the administration of aerosol therapy, how does a heliox mixture compare with an air–oxygen mixture as a carrier gas?
 
Less aerosol is deposited with heliox.
More aerosol is deposited with heliox.
The two gas mixtures are equally efficient.
Definitive data are not available.
 
Patients who use the helium–oxygen mixtures show more improvement in expiratory peak flows than a group using air. Aerosol has deeper and prolonged deposition in the lung when it is delivered with heliox as the carrier gas.

 
Question 10
 
An infant on high-flow nasal cannula also requires administration of albuterol every 6 hours. The flow of the cannula was adjusted from 4 to 5 liters per minute. How could this affect the aerosol delivery to this infant?
 
It will be unchanged.
It will decrease.
It will increase.
 

 
It will increase only if the infant’s respiratory rate increases.
 

Heliox has been shown to reduce turbulence and improve aerosol delivery in a range of clinical settings. Ari and colleagues assessed the effects of heliox on medication delivery by comparing with 100% oxygen while testing the infant, pediatric cannulas running at flows of 3 and 6 Lpm, and adult cannulas running at 10 and 30 Lpm. At higher flows they found that heliox increased aerosol deposition compared to oxygen. At lower flows there was less benefit from the use of heliox compared to oxygen in the pediatric and adult cannulas and no benefit for the infant.

 
Question 11
 
Which of the following parameters of mechanical ventilation are affected negatively by the use of heliox?
 
PEEP
Plateau pressure
Peak pressure
Volume
 
The primary obstacle to heliox delivery via a mechanical ventilator is error in volume and flow measurement. Many mechanical ventilators rely on gas density to measure flows and volumes. Most errors result from underestimation of flow due to the low-density characteristics of helium. Volume is typically a mathematical integration of flow and time; therefore, volumes will be equally affected.

 
Question 12
 
What is the purpose of administering helium–oxygen gas mixtures to patients?
 
To reduce the work of breathing
To improve gas exchange
To increase the functional residual capacity
To improve pulmonary compliance
 
It is important to note that helium is not used to treat the underlying cause of increased airway resistance but rather to decrease the work of breathing until more definitive therapies are effective. When helium is combined with oxygen, the resulting gas mixture density is one third that of air.

 
Question 13
 
What is the normal gradient between PaCO2 and end-tidal CO2 (PaCO2 minus end-tidal CO2)?
 
-2 to -5 mm Hg
2 to 5 mm Hg
-5 to -10 mm Hg
5 to 10 mm Hg

 
Question 14
 
What is the primary physiologic activity of inhaled nitric oxide?
 
Bronchodilation
Pulmonary vasodilation
Systemic vasodilation
Cerebral vasodilation
 
The underlying principle of inhaled nitric oxide (iNO) is its selectivity as a pulmonary vasodilator. Inhaled NO will relax only pulmonary smooth muscle adjacent to functioning alveoli. Atelectatic or fluid-filled lung units will not participate in iNO uptake.

 
Question 15
 
What clinical parameter is critically important to monitor when mechanical ventilation is administered?
 
Blood pressure
Heart rate
Temperature
Respiratory rate
 
In mechanically ventilated children, increasing intrathoracic pressure (by increasing positive end expiratory pressure, for example) can reduce venous return, resulting in decreased BP.

 
Question 16
 
The therapist is treating a very irritable young child with upper airway obstruction. Which oxygen device will be the most appropriate to administer the greatest concentration of helium?
 
Close-fitting nonrebreathing mask
Close-fitting partial rebreathing mask
Nasal cannula
High flow nasal cannula
 
Spontaneously breathing patients with upper or lower airway obstruction can be given heliox via mask. Because the goal of heliox therapy is to reduce the density of the inspired gas, it is important to deliver the greatest concentration of helium. Therefore, the patient must be able to tolerate the lowest possible fractional concentration of inspired oxygen (FiO2), and room air entrainment must be minimized, resulting in a higher fractional concentration of inspired helium (FiHe). Nasal cannulas (with the exception of high flow nasal cannulas) and simple masks allow far too much room air entrainment, thereby diluting the helium concentration. Therefore, a close-fitting nonrebreathing mask should be used. This limitation makes the treatment of young patients difficult. Children in distress may not tolerate the tightly fitting mask required to minimize air entrainment.

 
Question 17
 
Why do transcutaneous oxygen tension (PO2) and carbon dioxide tension (PCO2) values differ from PaO2 and PaCO2 measurements?
 
Because of the lag time between the cardiac output and the time the blood reaches the transcutaneous electrode site
Because the skin is much more permeable to oxygen than carbon dioxide
Because oxygen is consumed and carbon dioxide is produced in transit from the left ventricle to the electrode site
Because metabolism in the tissue consumes oxygen and produces carbon dioxide at the site of the electrode
 
Transcutaneous measurements of PO2 and PCO2 require a heating element, built into the sensor, which elevates the temperature in the underlying tissue. Increasing the skin’s temperature increases capillary blood flow to the tissues, making it more permeable to gas diffusion. The tissue under which the sensor is placed will continue to consume oxygen and produce carbon dioxide (according to their metabolic demands). Consequently, measured values obtained with a transcutaneous monitor will differ from arterial values. Generally, the PO2 is slightly lower than in the arteries, and the PCO2 is slightly higher.

 
Question 18
 
As the therapist applies a pulse oximeter finger probe to a neonate who is receiving supplemental oxygen, she notices that the SpO2 reading is 100%. What should the therapist do in this situation?
 
The therapist should continue monitoring the patient because the reading is accurate.
The therapist should obtain an arterial blood sample to confirm PaO2 level.
The therapist should switch to using a capnometer.
The therapist should reduce the fraction of inspired oxygen.
 
The sensitivity of pulse oximetry to detect the presence and degree of hyperoxia may be limited in the neonatal patient. If the oximeter is reading an SpO2 of 100%, the arterial oxygen tension (PaO2) could be between 90 and 250 mm Hg. However, many neonatal intensive care units will target an SpO2 below a certain threshold in order to reduce the risk of retinopathy of prematurity in premature babies.

 
Question 19
 
Inhaled NO has been administered to an infant for nearly 4 hours. The respiratory therapist notices suboptimal response and suggests HFOV. What is the principle behind the potential benefit of adding this ventilatory modality to this infant?
 
HFOV improves ventilation and reduces the formation of NO2.
Lung volumes are optimized with HFOV and further enhance the effects of iNO.
The high frequency accelerates the diffusion of NO through the alveolar surface.
HFOV reduces the need for higher doses of iNO.
 
If lung volume is optimized with HFOV, this could further enhance the effects of iNO. The use of HFOV improves oxygenation response to iNO.

 
Question 20
 
An infant has been receiving iNO for the last 3 days. Which important level should be monitored when ordering a co-oximetry?
 
Methemoglobin
Carboxyhemoglobin
Reduced hemoglobin
Oxyhemoglobin
 
The half-life of iNO is extremely short, about 5 seconds. Once NO crosses the vascular endothelium, it is rapidly bound by hemoglobin, forming nitrosyl hemoglobin (methemoglobin). Methemoglobin production results from the oxidation of the iron in the hemoglobin. The quantity of methemoglobin depends on iNO concentration and concurrent nitrate-based drug therapy (e.g., nitroprusside, nitroglycerin). If the methemoglobin level is excessive, a reduction in iNO or other nitro-based vasodilators is warranted.

 
Question 21
 
How is the percentage of functional hemoglobin that is saturated with oxygen determined via pulse oximetry?
 
The percentage of red light that lands on the photodiode represents the SpO2 (oxygen saturation as determined by pulse oximetry).
The percentage of infrared light that reaches the photodetector reflects the SpO2.
The ratio of the red and infrared light that reaches the photodiode signifies the SpO2.
 
The sum of the amount of red and infrared absorbed by the tissue determines the SpO2.
A pulse oximeter sensor has two light-emitting diodes (LEDs) that function as light sources and a photodiode that measures the amount of light from the LEDs (see Figure 9-1 in the textbook). One LED emits red light, and the other diode emits infrared light. The sensor is placed over a translucent part of the body (finger, toe, earlobe, etc.). As the light from the diodes passes through the blood and tissue, some of the light from both the red and the infrared diodes is absorbed by oxyhemoglobin. The photodiode then measures the amount of light that passes through the body without being absorbed. Because oxyhemoglobin (hemoglobin bound with oxygen) and deoxyhemoglobin (hemoglobin not bound with oxygen) absorb significantly different amounts of light, the proportion of oxyhemoglobin (expressed as a percentage) is determined (see Figure 9-2 in the textbook).

 
Question 22
 
Which of the following conditions will preclude the use of indirect calorimetry?
 
I. Cuffed endotracheal tubes
II. Circuit leaks
III. FiO2 40%
IV. HFOV
 
I, II, and III only
II and III only
II and IV only
I, III, and IV only
 
Conditions that preclude the use of indirect calorimetry include: uncuffed endotracheal tubes, cuff or ventilator circuit leaks >10-15%, FiO2 >50%, need for high-frequency ventilation or extracorporeal membrane oxygenation, and active chest tube leakage.

 
Question 23
 
What accounts for the difference between PaCO2 and end-tidal CO2?
 
Dead-space ventilation
 
Inadequate respiratory rate
 
Postductal oxygen concentration
 
Spontaneous ventilation

 
Question 24
 
The therapist has applied a bandage-type pulse oximetry probe too tightly to an infant’s finger. What problem can be expected to occur in this situation?
 
The SpO2 will read erroneously low.
The SpO2 will read erroneously high.
The monitor will display a message indicating inadequate pulse.
The monitor will display fluctuating SpO2 values between being erroneously low and high.
 
Correct application of the sensor is crucial to the quality of readings from the pulse oximeter. The sensors should be placed firmly to avoid falling off or motion artifact, but care should be taken to avoid overtightening and compromising local circulation.
 
Question 25
 
Which of the following is the main physiologic factor responsible for deriving accurate transcutaneous data?
 
Heart rate
Minute ventilation
Peripheral perfusion
Ventilation-perfusion ratios
 
Changes in perfusion can adversely affect the accuracy of transcutaneous measurements. The skin reacts to cold, shock, and certain drugs by contracting the superficial blood vessels, opening larger, deeper arterioles to achieve a shunting effect. Capillary blood flow is reduced on exposure to cold temperatures in order to reduce the loss of body heat. Shock and certain medications can also divert blood from capillaries to the central circulation. In all cases of reduced capillary perfusion, the capillary blood that is measured using a transcutaneous monitor may reflect measurements associated with venous blood, with a considerably lower PO2 and higher PCO2 (compared to values obtained with good capillary perfusion). If a patient has poor skin integrity, transcutaneous monitoring may also be contraindicated.

 
Question 26
 
Which of the following substances prevents the release of Ca2+ from the sarcoplasmic reticulum?
 
Intracellular cGMP
EDRF
cGMP-dependent kinase
Calmodulin
 
In the body, the process of smooth muscle relaxation uses cyclic guanosine monophosphate (cGMP) to reduce Ca2+ levels. In smooth muscle cells cGMP activates cGMP-dependent kinase, preventing the release of Ca2+ from the sarcoplasmic reticulum, resulting in smooth muscle relaxation. In the early 1980s researchers reported a potent smooth muscle–relaxing agent, endothelium-derived relaxing factor (EDRF), now understood to be endogenous nitric oxide.

 
Question 27
 
Which of the following inhaled anesthetic gases has/have demonstrated the possibility to treat status asthmaticus?
 
I. Halothane
II. Thromboxane
III. Isoflurane
IV. Sevoflurane
 
II only
I, II, and III only
I, III, and IV only
II, III, and IV only
 
Of the several inhaled anesthetics used clinically for anesthesia, only halothane, isoflurane, enflurane, and sevoflurane have been widely reported as potential treatments for status asthmaticus.

 
Question 28
 
What is the potential benefit of adding heliox to patients who have status asthmaticus while undergoing mechanical ventilation?
 
To improve pulmonary compliance
To reverse bronchospasm
To minimize air trapping
To facilitate the removal of tracheobronchial secretions
 
The use of heliox mixtures has been advocated to minimize air trapping and hemodynamic compromise and to reduce peak inspiratory pressures.

 
Question 29
 

While attending to a neonatal patient in the neonatal intensive care unit (NICU), the therapist notices that a transcutaneous electrode is affixed to the upper chest of the neonate. What should the therapist do at this time?
 
The therapist should only continue monitoring the patient since the transcutaneous electrode is properly placed.
The therapist should reposition the electrode on the neonate’s abdomen.
The therapist needs to move the transcutaneous electrode to the infant’s right shoulder.
The therapist should relocate the electrode on the sternum as close as possible to the heart.
 
The site should be a highly vascular area such as the earlobe, upper chest, abdomen, thighs, or the lower back if the patient is supine; bony areas and those with limited perfusion, such as over the spine, should be avoided.

 
Question 30
 
The therapist is evaluating a small tachypneic infant receiving heliox mixture 70:30 through an infant hood. Although the SpO2 has improved, the child shows signs of worsening work of breathing. What is the most probable mechanism to explain this situation?
 
The FiHe is too low in a 70:30 mixture to change work of breathing in this infant.
The flow going through the infant hood is inadequate.
A greater concentration of helium is present at the top of the hood and away from the infant’s nose and mouth.
The infant is breathing too fast; thus heliox is not reaching the airways.
 
Stillwell and colleagues investigated the use of heliox mixtures delivered through an infant hood. Not surprisingly, they found a greater concentration of helium at the top of the hood (due to its lower gas density), away from the infant’s nose and mouth. This resulted in a lower FiHe and therefore a denser gas being delivered to the infant.

 
Question 31
 
Although very small amounts of NO2 are present at the bedside, which health care workers need to exert special precautions to minimize exposure to NO2?
 
Nurses in the NICU
Air transport team members
Ground transport team members
Respiratory therapists in the NICU
 
At first, scavenging was advocated to reduce the possible harmful inhalation of nitrogen dioxide by other personnel in the vicinity. Studies have shown this to be unnecessary because of the relatively small amounts of NO2 present at the bedside. Modern hospitals have adequate room air exchange rates, and the chance of NO or NO2 accumulation is remote. A possible caveat involves interfacility transport. Pressurized aircraft may not allow an adequate cabin air exchange rate to ensure safety. The aircraft crew must be made aware of this so that proper measures are taken to reduce this risk.

 
Question 32
 
What is the purpose of indirect calorimetry?
 
To measure heat produced and lost from the body

 

To calculate energy expenditure by measuring VO2 and VCO2
To calculate resting energy expenditure
To measure gas exchange
 
Direct calorimetry extrapolates energy expenditure by measuring heat produced and lost from the body while indirect calorimetry combines measurements of VO2 and VCO2 into an equation to calculate energy expenditure. Most energy expenditure reports will contain results for VO2, VCO2, REE, and respiratory quotient (which is VCO2/VO2 and can be used to determine substrate utilization).

 
Question 33
 
A patient who has been admitted with status asthmaticus is receiving beta adrenergics every 2 hours and heliox with very limited response. What should the therapist suggest at this time?
 
Change heliox to 100% helium
Administer nitrogen
Administer inhaled anesthetics
Add iNO
 
Patients in status asthmaticus (SA) can be placed on helium–oxygen therapy as a temporizing measure to reduce the work of breathing until another therapy (b-agonists, methylxanthines, and corticosteroids) is effective. However, these patients frequently have bronchospasm that is refractory to conventional therapy. Certain volatile inhaled anesthetics are known for their bronchodilatory properties. Although no clinical trials have investigated the use of inhaled anesthetics (IAs) in the routine treatment of SA, several case reports exist.

 
Question 34
 
Which of the following inhaled anesthetics should the therapist recommend to administer via a face mask to a conscious, spontaneously breathing pediatric patient who has status asthmaticus?
 
Isoflurane
Enflurane
Sevoflurane
Halothane
 
Halothane is the gas of choice when delivering an inhaled anesthetic agent to a conscious, spontaneously breathing patient. The dose range for halothane is approximately 0.25% to 0.5%. The patient usually is sufficiently awake to communicate in short sentences. Bronchodilation is usually rapid (15 to 20 min). The patient benefits by the reduced resistance as well as the sedative effect.

 
Question 35
 
What is the product of the reaction between oxygen and nitric oxide?
 
Oxygen radicals
N2O
NO2
The two molecules do not react with each other.
 
When combined with oxygen, NO produces NO2, a toxic gas. Although rare, the patient as well as health care providers can be adversely affected. Factors influencing NO2 production are oxygen concentration, NO concentration, and time of contact between NO and oxygen.

 
Question 36
 
Where on the following normal capnogram is the end-tidal carbon dioxide (PetCO2) represented?

 

A
B
C
D
E
 
The normal capnogram can be divided into four phases (see Figure 9-6 in the textbook):Phase A-B: The inspiratory phase, during which the sensor detects no carbon dioxide
Phase B-C: The initial expiratory phase, during which carbon dioxide rapidly increases as the alveoli begin to empty

 

Phase C-D: The completion of expiration as the alveoli empty (alveolar plateau) and show a slight increase in carbon dioxide
Phase D-E: The beginning of inspiration as the waveform returns to zero

 
Question 37
 
The following choices are all disadvantages of a pulse oximeter except:
 
Artifact
Ease of use

 

Hypothermia
Poor tissue perfusion

 
Question 38
 
The therapist is using an oxygen flowmeter to deliver an 80:20 heliox mixture to a patient. The reading on the flowmeter is 10 L/minute. What is the actual flow received by the patient?
 
5.5 L/minute
10 L/minute

 

12.5 L/minute
18 L/minute
 
An 80:20 heliox mixture is 1.8 times more diffusible than oxygen. To correct for the difference in gas density, the indicated flow on the flowmeter is multiplied by 1.8. A 70:30 heliox mixture is 1.6 times more diffusible than oxygen. To obtain the accurate flow rate for this mixture, the indicated flow is multiplied by 1.6.

 
Question 39
 
The therapist has been asked to measure preductal oxygen saturation. Where could the therapist place the pulse oximeter probe?

 

 
Right thumb
Left thumb
Forehead
Left earlobe
 
Sensor placement on right arm or head will reflect preductal values while the left arm and the lower parts of the body will reflect postductal oxygen saturation values.

 
Question 40
 
After increasing the inspiratory flow of the ventilator to decrease the generation of NO2 the therapist notices many changes in the ventilator parameters. The therapist adds the NO into the inspiratory limb of the ventilator circuit close to the patient. What will be a limitation of the procedure?
 
A larger number of oxygen radicals are produced at this position.
Adding NO too close to the patient reduces proper mixing, which is necessary to ensure accurate NO measurement.
Adding NO in this position of the circuit is contraindicated.
The contact time between NO and O2 is too long to be clinically useful.
 
Adding NO into the inspiratory limb of the ventilator circuit close to the patient will reduce contact time, but it also creates monitoring difficulties. The practitioner must allow an adequate distance for proper mixing to ensure accurate NO measurement.

 
Question 41
 
The respiratory therapist has initiated nitric oxide for an infant with severe refractory hypoxemia. The initial dose was 20 ppm and titrated up to 30 ppm for the last 4 hours due to lack of response. However, there still is no response. What should the therapist do?
 
Increase iNO to 40 ppm
Increase iNO to 60 ppm
Increase iNO to 80 ppm
Discontinue iNO and consider a different therapeutic intervention
 
Studies have suggested that optimal dosing is usually in the 20- to 30-ppm range. Some infants will not respond positively. The Neonatal Inhaled Nitric Oxide Study (NINOS) trial indicated that only 6% of nonresponders will demonstrate a positive response when given NO at 80 ppm. Typically, a response would be seen almost immediately; however, it is recommended that the time allotted for determining an infant’s response last no longer than 4 hours to limit the exposure to NO.

 

Question 42
 
The therapist is assessing a mechanically ventilated infant and observes that the transcutaneous electrode temperature is set between 41° C and 44° C. What action does the therapist need to take at this time?
 
The temperature range set is appropriate; therefore, no action is necessary.
The therapist should increase the temperature range to 47° C to 48° C.
The temperature of the transcutaneous electrode needs to be reduced to 36° C to 38° C.
The electrode needs to be repositioned and maintained at the same temperature.
 
Selecting a sensor temperature is important to proper operation. The temperature range is usually 41° to 44° C. Heating of the sensor requires that the site be changed on a routine basis to prevent thermal injuries. The frequency of site changes ranges from 4 to 12 hours (depending upon the device and sensor temperature) but can be reduced if necessary.