Question 1

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?

Accepted Answer

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 2

While working in the NICU with a mechanically ventilated newborn who is being monitored for PetCO₂, the therapist observes the following capnogram. What interpretation should the therapist make of this capnogram?

Accepted Answer

Rebreathing is characterized by an elevation in the A-B phase of the capnogram, with a corresponding increase in ETCO₂. It indicates the rebreathing of previously exhaled carbon dioxide. Rebreathing can be caused by allowing an insufficient expiratory time or by inadequate inspiratory flow (see Figure 9-7 in the textbook).

Question 3

What clinical parameter is critically important to monitor when mechanical ventilation is administered?

Accepted Answer

In mechanically ventilated children, increasing intrathoracic pressure (by increasing positive end expiratory pressure, for example) can reduce venous return, resulting in decreased blood pressure.

Question 4

While attending to a neonatal patient in the 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?

Accepted Answer

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 5

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.

Accepted Answer

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 6

The therapist is assessing a mechanically ventilated infant and observes that the transcutaneous electrode temperature is set between 41 and 44°C. What action does the therapist need to take at this time?

Accepted Answer

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.

Question 7

Which of the following conditions will preclude the use of indirect calorimetry? I. Cuffed endotracheal tubes II. Circuit leaks III. FiO₂ 0.40 IV. HFOV

Accepted Answer

Conditions that preclude the use of indirect calorimetry include uncuffed endotracheal tubes, cuff or ventilator circuit leaks >10% to 15%, FiO₂ >50%, need for high-frequency ventilation or extracorporeal membrane oxygenation, and active chest tube leakage.

Question 8

Which of the following is the main physiologic factor responsible for deriving accurate transcutaneous data?

Accepted Answer

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 9

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

Accepted Answer

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 10

What is the purpose of indirect calorimetry?

Accepted Answer

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 11

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?

Accepted Answer

PetCO₂ can be used as a surrogate for the arterial PaCO₂ within physiologic limits. Normally, PetCO₂ is 2 to 5 mm Hg below PaCO₂. The reason for this is the proportion dead space ventilation.

Question 12

Why do transcutaneous oxygen tension (PO₂) and carbon dioxide tension (PCO₂) values differ from PaO₂ and PaCO₂ measurements?

Accepted Answer

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 13

The following capnogram was obtained from a newborn infant receiving mechanical ventilation.  How should the therapist evaluate this capnogram?

Accepted Answer

Obstruction of the expiratory flow of gas will be noted as a change in the slope of the B-C phase of the capnogram. The B-C phase may diminish without a plateau. Obstruction can be caused by a foreign body in the upper airway, increased secretions in the airways, the patient having bronchospasms, or partial obstruction of the ventilator circuit (see Figure 9-8 in the textbook).

Question 14

How is the percentage of functional hemoglobin that is saturated with oxygen determined via pulse oximetry?

Accepted Answer

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 15

Which of the following is volumetric capnography able to determine?
I. Airway dead space
II. Alveolar tidal volume
III. Shunt fraction
IV. Alveolar minute volume

Accepted Answer

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 16

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?

Accepted Answer

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.

Quiz 9: Noninvasive Monitoring in Neonatal and Pediatric Care

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?

While working in the NICU with a mechanically ventilated newborn who is being monitored for PetCO2, the therapist observes the following capnogram. What interpretation should the therapist make of this capnogram?