Atlas of Procedures in Neonatology, 4th Edition

Physiologic Monitoring

9

Continuous Blood Gas Monitoring

  1. Kabir Abubakar

Pulse Oximetry

  1. Definitions
  2. Arterial oxyhemoglobin saturation measured by an arterial blood gas analysis is referred to as SaO2.
  3. Arterial oxyhemoglobin saturation measured noninvasively by pulse oximetry is referred to as SpO2.
  4. Purpose
  5. Noninvasive arterial oxygen saturation monitoring
  6. Pulse rate monitoring
  7. Trending of SpO2and pulse rate over time
  8. Background
  9. Principles of oxygen transport
  10. Approximately 98% of the oxygen in the blood is bound to hemoglobin.

The amount of oxygen carried in the blood is related directly to the amount of hemoglobin in the blood and to the partial pressure of unbound, dissolved oxygen in the blood (PO2) (1). The relationship of arterial PO2, in near–term infants, to percent saturation measured by pulse oximeter is shown in Fig. 9.1.

  1. The relationship between blood PO2and the amount of oxygen bound to hemoglobin is presented graphically as an oxygen–hemoglobin affinity curve (Fig. 9.2). Percent oxygen saturation is calculated below:
  2. Principles of pulse oximetry
  3. Based on the principles of spectrophotometric oximetry and plethysmography (2)
  4. Determine arterial saturation and pulse rate by measuring the absorption of selected wavelengths of light

Oxygenated hemoglobin (oxyhemoglobin) and reduced hemoglobin (deoxyhemoglobin) absorb light as known functions of wavelengths. By measuring the absorption levels at different wavelengths of light, the relative percentages of these two constituents and SpO2 are calculated.

  1. Utilizes a sensor composed of two light-emitting diodes (LEDs) as light sources and one photodetector as a light receiver. The photodetector is an electronic device that produces a current proportional to the incident light intensity (3).
  2. One LED emits red light with an approximate wavelength of 660 nm.

Red light is absorbed selectively by deoxyhemoglobin.

  1. The other LED emits infrared light with an approximate wavelength of 925 nm.

Infrared light is absorbed selectively by oxyhemoglobin.

  1. Utilizes the different absorption of the wavelengths when transmitted through tissue, pulsatile blood, and nonpulsatile blood (Fig. 9.3).
  2. The photodetector measures the level of light that passes through without being absorbed.
  3. During the absence of pulse (diastole), the detector establishes baseline levels for the absorption of tissue and nonpulsatile blood.
  4. With each heartbeat, a pulse of oxygenated blood flows to the sensor site.
  5. Absorption during systole of both the red and the infrared light is measured to determine the percentage of oxyhemoglobin.
  6. Because the measurements of the change in absorption are made during a pulse (systole), these pulses are counted and displayed as heart rate.
  7. Indications
  8. To monitor oxygenation in infants suffering from conditions associated with:
  9. Hypoxia
  10. Apnea/hypoventilation

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  1. Cardiorespiratory disease
 

FIG. 9.1. Arterial PO2 versus pulse oximeter percent saturation in near-term newborn infants in whom pulse saturation was fixed by adjusting FiO2 first and then measuring PaO2. Values are means ± SD. (From 

Brockway J, Hay WW Jr. Ability of pulse O2 saturations to accurately determine blood oxygenation. Clin Res. 1988;36:227A

, with permission.)

  1. Bronchopulmonary dysplasia

Pulse oximetry is the optimal mode of monitoring for larger infants with bronchopulmonary dysplasia. Whereas PO2 monitors may underestimate PaO2 in this population, oximetry has been found to be reasonably accurate for these infants (4). The pulse oximeter requires no patient preparation or calibration time, has a rapid response time, and is readily adaptable to different patient populations (5).

 

FIG. 9.2. Factors affecting hemoglobin–oxygen affinity. 2,3-DPG, 2,3-diphosphoglycerate. (From 

Hay WW Jr. Physiology of oxygenation and its relation to pulse oximetry in neonates. J Perinatol. 1987;7:309

, with permission.)

 

FIG. 9.3. Tissue composite showing dynamic as well as static components affecting light absorption. (From 

Wukitch MW, Petterson MT, Tobler DR, et al. Pulse oximetry: analysis of theory, technology and practice. J Clin Monit. 1988;4:290

, with permission.)

  1. To monitor response to therapy
  2. Resuscitation (6)

Pulse oximetry is also a significant adjunct to monitoring in the delivery room. With the use of pulse oximetry, SpO2 values can be obtained within 1 minute after birth (7, 8, 9) (Fig. 9.4).

  1. Monitoring effectiveness of mask ventilation (10) or during placement of an endotracheal tube
  2. To monitor side effects of other therapy
  3. Suctioning
  4. Positioning for laryngoscopy (6, spinal tap, etc.
  5. For low-birthweight infants <1,000 g (11, 12)
 

FIG. 9.4. Mean arterial oxygen saturation (SaO2) values measured by pulse oximetry from the time of cord clamping. Values are means ± SD. (From 

House JT, Schultetus RR, Gravenstein N. Continuous neonatal evaluation in the delivery room by pulse oximetry. J Clin Monit. 1987;3:96

, with permission.)

  1. It is optimal to use pulse oximetry for oxygen monitoring in the very low-birthweight infant because of its
  2. P.60

  3. noninvasiveness. Pulse oximetry can be used reliably in very low-birthweight infants with acute as well as chronic lung disease (11).
  4. Pulse oximetry also offers an advantage for precise fraction of inspired oxygen (FiO2) control during neonatal anesthesia because of the short response time to changes in SpO2(13).
  5. Limitations
  6. Decreased accuracy when arterial saturation is <65%

Pulse oximetry will overestimate SpO2 at this level; therefore, blood gas confirmation is imperative (14, 15, 16).

  1. Not a sensitive indicator for hyperoxemia (1)

Pulse oximeter accuracy does not allow for precise estimation of PO2 at saturations >90%. Small changes in O2 saturation (1% to 2%) may be associated with large changes in PO2 (6 to 12 mm Hg) (1).

  1. Because pulse oximeters rely on pulsatile fluctuations in transmitted light intensity to estimate SpO2, they are all adversely affected by movement (3, 17 and 19).

In some cases, the pulse oximeter may calculate an SpO2 value for signals caused by movement, or it may reject the signal and not update the display. Usually, the heart rate output from the oximeter will reflect the detection of nonarterial pulsations, indicating either “0” saturation or “low-quality signal” (3). However, advances in microprocessor technology have led to improved signal processing, which makes it possible to minimize motion artifact and monitor saturation more accurately during motion or low-perfusion states.

  1. Significant levels of carboxyhemoglobin or methemoglobin can yield erroneous readings (carboxyhemoglobin absorbs light at the 660-nm wavelength) (18). However, carboxyhemoglobin levels of <3% will not affect the accuracy of the instrument.
  2. SpO2may be overestimated in darkly pigmented infants.

Some oximeters will give a message such as “insufficient signal detected” if a valid signal is not obtained (18, 19).

  1. Erroneous readings can occur in the presence of high fetal hemoglobin (18).

A smaller effect on accuracy is noted when fetal hemoglobin levels are <50% (20, 21 and 22). With a predominance of fetal hemoglobin, an SpO2 of >92% may be associated with hyperoxemia (22). However, whereas saturations may appear adequate, PO2 may be low enough to produce increased pulmonary vascular resistance (SpO2/PO2 curve shift to the left).

Because infants with chronic lung disease and prolonged oxygen dependence are older and have less fetal hemoglobin, SpO2 readings obtained from these patients may be more accurate than those obtained from neonates with acute respiratory disorders at an earlier age (23). The same situation exists in infants who have undergone exchange transfusion because of decreased levels of fetal hemoglobin (24).

  1. Light sources that can affect performance include surgical lights, xenon lights, bilirubin lamps, fluorescent lights, infrared heating lamps, and direct sunlight.

Although jaundice does not account for variability in pulse oximeter accuracy (24), phototherapy can interfere with accurate monitoring. Therefore, appropriate precautions should be taken, such as covering the probe with a relatively opaque material (1).

  1. Do not correlate SpO2values with laboratory hemoximeters (18).

Most laboratory oximeters measure fractional oxygen saturation (all hemoglobin including dysfunctional hemoglobin) as opposed to functional oxygen saturation (oxyhemoglobin and deoxyhemoglobin excluding all dysfunctional hemoglobin).

  1. Use of normal adult values for hemoglobin, 2,3-diphosphoglycerate, and, in some cases, PCO2can lead to errors in the algorithm to calculate SpO2with some blood gas analysis instruments (18).
  2. Although pulse oximeters can detect hyperoxemia, it is important that type-specific alarm limits are set (25).

To avoid hyperoxemia, a minimal sensitivity of at least 95% is required.

  1. Pulse oximeters rely on detecting pulsatile flow in body tissues; therefore a reduction in peripheral pulsatile blood flow produced by peripheral vasoconstriction results in an inadequate signal for analysis.
  2. Pulse oximeters average their readings over several seconds depending on oximeter type and internal settings. Oximeters with a long averaging time may not be able to detect acute and transient changes in SpO2.
  3. Venous congestion may produce venous pulsations, which can produce low readings.
  4. The pulse oximeter only provides information about oxygenation. It does not give any indication of the patient's carbon dioxide elimination.
  5. In summary, it is optimal to make some correlation between SpO2and PO2 throughout a reasonable range of SpO2 (lower, 85% to 88%; higher, 95% to 97%) before relying completely on SpO2 for oxygen and/or respirator management (23, 26).

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FIG. 9.5. Pulse oximeter. Vertical column indicates pulse. (Courtesy of Nellcor, Pleasanton, CA, USA.)

  1. Equipment
  2. Manufacturer-specific sensor and monitor (Fig. 9.5) with
  3. Display of SpO2and pulse rate and a pulse indicator
  4. Adjustable alarm limits for SpO2as well as pulse rate
  5. Battery-powered operation
  6. Neonatal sensor, either disposable or reusable
  7. Disposable sensors have become the standard from the standpoint of infection as well as quality control.
  8. Disposable neonatal sensors are available in different sizes, depending on the site to be used.
  9. Precautions
  10. Use only with detectable pulse.

Cardiopulmonary bypass with nonpulsating flow, inflated blood pressure cuff proximal to the sensor, tense peripheral edema, hypothermia, low perfusion state secondary to shock or severe hypovolemia, and significant peripheral vasoconstriction may interfere with obtaining accurate readings (5).

  1. Assess the sensor site every 8 hours to be certain that the adherent bandage is not constricting the site and that the skin is intact.
  2. Whenever possible, the SpO2sensor should not be on the same extremity as the blood pressure cuff.

When the cuff is inflated, the SpO2 sensor will not detect a pulse, will not update SpO2 values, and will alarm. Use of ace bandages on the extremities to increase central venous return may also interfere with the function of the sensor.

  1. Malpositioned sensor: When a probe is not placed symmetrically, it can allow some light from the LED emitters to reach the photodetector in the sensor without going through the tissue at the monitoring site and will therefore produce falsely low readings. This is called the penumbra effect.
  2. To avoid possible transfer of infection, do not share pulse oximetry probes between patients.
  3. Technique
  4. Familiarize yourself with the system before proceeding.
  5. Select an appropriate sensor and apply it to the patient.
  6. Ear lobe, finger, toe, lateral side of the foot, or across the palm of the hand. (Placing the sensor in a position matching that of the peripheral arterial line, if present, may avoid discrepancies caused by intracardiac or ductal shunts when trying to correlate SpO2with arterial PO2.)
  7. For neonates 500 g to 3 kg, anterior-lateral aspect of a foot (Fig. 9.6) (1).
  8. For infants weighing >3 kg, use the palm, thumb, great toe, or index finger (1).
  9. Align the LEDs (light source) and the detector so they are directly opposite each other.
  10. Reusable sensors should be applied with nonadhesive elastic wrap.
  11. Tighten sensor snugly to the skin but not so as to impede circulation. The probe should then be left in place for several seconds until extremity movement stops and the signal is stable.
  12. Secure the sensor to the site to prevent tugging or movement of the sensor independent of the body part.
  13. Cover the sensor to reduce the effect of intense light levels, direct sunlight, or phototherapy.
  14. Attach the sensor to the system interconnecting cable and turn on the monitor. (Attaching the sensor to the baby before connecting the cable to the monitor will shorten the time taken for data acquisition and display of SpO2information.)
  15. Calibration of the system is not required (internal autocalibration).
  16. After a short interval, if all connections are correct, the monitor will display the pulse detected by the sensor. If the pulse level is adequate, it will display

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SpO2 and pulse rate. If the pulse indicator is not synchronous with the patient's pulse rate, reposition the probe. If, after repositioning the sensor, the pulse detector is still not indicating properly, change the sensor site.

  1. Once reliable operation is achieved, set the high and low alarm limits.
  2. Although pulse oximeters can detect hyperoxemia, it is important that type-specific alarm limits are set and a low specificity is accepted (25). Type-specific alarm limits should be guided by normative values for SpO2depending on postnatal age (Fig. 9.7).
  3. The optimal alarm limit, defined as having a sensitivity of 95% or more, associated with maximal specificity, will differ depending on which particular monitor is used.

In general, low-limit SpO2 values are defined as 87% to 89%; higher-limit SpO2 values are defined as 94% to 95%.

  1. Default (starting point) alarm limits for a newborn (26): high limit >94% to 95%; low limit <87% to 90%.

Note that SpO2 is a more sensitive indicator of hypoxemia and decreased tissue oxygenation than is PaO2. Lower alarm limits should be individualized to alert the user when the oxygenation requirements of the given patient are not satisfied.

 

FIG. 9.6. Disposable sensor applied to foot.

 

FIG. 9.7 The oxygen dissociation curve at various postnatal ages. (From 

Oski FA, Delivoria-Papadopolous POM. The red cell 2,3-diphosphoglycerate and tissue oxygen release. J Pediatr. 1970;77:941

, with permission.)

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  1. Complications
  2. Management based on erroneous readings caused by a misapplied sensor or conditions affecting instrument performance (27, 29)
  3. Burn resulting from electrical short (28)
  4. Limb ischemia if applied too tightly, particularly in an edematous limb

Transcutaneous Blood Gas Monitoring

Transcutaneous measurements of oxygen and carbon dioxide are useful in the neonatal intensive care unit because they provide continuous and relatively noninvasive estimation of arterial blood gases.

  1. Definitions
  2. Transcutaneous measurement of oxygen is referred to as PtcO2.
  3. Transcutaneous measurement of carbon dioxide is referred to as PtcCO2.
  4. Purpose
  5. Noninvasive blood gas monitoring of PO2and PCO2
  6. Trending of PO2and PCO2over time
  7. Background
  8. Transcutaneous monitoring measures skin-surface PO2and PCO2to provide estimates of arterial partial pressure of oxygen and carbon dioxide. The devices increase tissue perfusion by heating the skin and then electrochemically measuring the partial pressure of oxygen and carbon dioxide.
  9. Accomplished by two electrodes contained in a heated block that maintains the electrodes and the skin directly beneath it at a constant temperature (30) (Fig. 9.8)
  10. Arterialized capillary oxygen levels are more accurately measured by heating the skin to establish hyperemia directly beneath the sensor.
  11. The electrodes are covered with an electrolyte solution and sealed with a semipermeable plastic membrane.
  12. A modified Clark electrode is used to measure oxygen.
  13. It produces an electrical current that is proportional to PO2.
  14. Measured current is converted to PO2and then corrected for temperature.
 

FIG. 9.8. A: Principle of cutaneous PO2 measurement by heated oxygen sensor. B: Temperature profile of cutaneous tissue. C:Cross section of cutaneous oxygen sensor. (Courtesy of Kontron Medical Instruments, Ergolding, Germany.)

  1. A Severinghaus electrode is used to measure CO2.
  2. pH-sensitive glass electrode
  3. CO2diffuses from the skin surface through the membrane. The CO2changes the pH of the electrolyte solution bathing the electrode.

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  1. The measured pH is converted to PCO2and then corrected for temperature.

Conversion of electric current and pH to PO2 and PCO2, respectively, is based on conversion equations adjusted by a two-point calibration. This is part of the setup and calibration process.

  1. Indications
  2. To approximate arterial PaO2and PaCO2for respiratory management
  3. To monitor the effect of therapeutic ventilatory maneuvers (30, 31, 32, 33 and 34), particularly in infants who have combined oxygenation and ventilation problems
  4. For stabilization and monitoring during transport (31, 35, 36)
  5. To reduce the frequency of arterial blood gas analysis (37)
  6. To determine by a noninvasive and continuous method the regional arterial oxygen tension (38, 39 and 40)
  7. To infer regional arterial blood flow (40, 41, 42 and 43), e.g., in the lower limbs of infants with duct-dependent coarctation of the aorta
  8. Contraindications
  9. Skin disorders (e.g., epidermolysis bullosa, staphylococcal scalded skin syndrome)
  10. Relative contraindications
  11. The very low-birthweight infant (44, 45)
  12. Severe acidosis
  13. Significant anemia
  14. Decreased peripheral perfusion
  15. PtcO2may underestimate PaO2(46).
 

FIG. 9.9. Combined transcutaneous PO2/PCO2 and SpO2 monitor. (Courtesy of Radiometer.)

  1. Equipment—Specifications
  2. Transcutaneous monitor components
  3. Dual electrode
  4. Electrode cleaning kit
  5. Electrolyte and membrane kit
  6. Contact solution
  7. Double-sided adhesive rings
  8. Calibration gas cylinders with delivery apparatus
  9. Digital display shows values for PtcO2, PtcCO2, and site of sensor (Fig. 9.9).
  10. Monitor with controls for both high and low alarm limits, and for electrode temperature. The monitor may also have a site placement timer that will alarm as an indication to change the site of the electrode.
  11. Precautions
  12. Be aware that:
  13. Equilibration requires approximately 20 minutes once the electrode is placed, with the response time for PtcO2being much faster than that for PtcCO2. Therefore, management changes based on transcutaneous values should be guided by values that have been consistent for at least 5 minutes.
  14. Periodic correlation with PO2from appropriate arterial sites is recommended (46).

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  1. PtcO2may underestimate PaO2 in the infant with hyperoxemia (PaO2 >100 mm Hg), with reliability of PtcO2 measurement decreasing as PaO2 increases (47, 48, 49 and 50).
  2. PtcO2may underestimate PaO2in older infants with bronchopulmonary dysplasia (51, 52).
  3. Transcutaneous blood gas measurements are affected by the state of the infant.

Values during feeding or active sleep can be lower (53).

  1. Pressure on the sensor (e.g., infant lying on sensor) may restrict blood supply, resulting in falsely low PtcO2values.
  2. Manufacturers' parts are not interchangeable. Only supplies of the same brand and designated for the monitor should be used.
  3. To avoid skin burns, change electrode location at leastevery 4 hours.
  4. PtcO2may underestimate PaO2in the presence of:
  5. Severe acidosis
  6. Severe anemia
  7. Decreased peripheral perfusion
  8. Technique
  9. Familiarize yourself with the system before proceeding.
  10. Perform routine electrode maintenance, if there is any question as to the status of the electrode.
  11. Remove the membrane, rinse the electrode with deionized water, and dry with a soft lint-free tissue or gauze.
  12. Clean the electrode using the solution provided in the cleaning kit; abrasive compounds or materials should never be used (they will permanently damage the electrode).
  13. Rinse the electrode with deionized water and dry with lint-free tissue.
  14. Apply the electrolyte solution.
  15. Place a new membrane on the electrode. Avoid finger contact, and always handle the membrane inside its protective package or with plastic tweezers.
  16. Perform two-point gas calibration using the device-specific apparatus, as per manufacturer's instruction.
  17. Use an alcohol pad to clean and degrease the skin site where the sensor is to be placed.
  18. Apply double-sided adhesive ring to the sensor.
  19. Apply one drop of contact solution to the skin site.
  20. Peel the protective backing from the adhesive ring, place the sensor on the skin over the contact solution, and press the sensor to the skin.
  21. For best results, place the sensor on a location with good blood flow.
  22. Appropriate sites include the lateral abdomen, anterior or lateral chest, volar aspect of the forearm, inner upper arm, inner thigh, or posterior chest (Fig. 9.10) (54).
  23. Although large differences between pre- and postductal PaO2values are uncommon in premature infants with hyaline membrane disease, preductal location of the electrode is optimal for prevention of hyperoxemia (55).
  24. Choose a site devoid of hair.
  25. Avoid bony prominences.
  26. Avoid areas with large surface blood vessels (Fig. 9.10).
 

FIG. 9.10. Cutaneous PO2/PCO2 sensor applied to the back.

  1. Secure the sensor cable to prevent tugging of the electrode when the cable is manipulated.
  2. Allow 15 to 20 minutes for site equilibration before taking readings.
  3. Note the time at which the sensor was placed on the skin, so that the site can be changed after a 4-hour period (maximum site time). When changing the sensor site:
  4. Use an alcohol pad to help loosen the adhesive and peel gently from the skin.
  5. Inspect the skin site for signs of sensitivity to heat or to the adhesive. In the event of skin irritation, either lower the sensor temperature or change the site more frequently; mild erythema after sensor removal is typical.
  6. Peel adhesive ring off the sensor.
  7. Flush the membrane surface with de-ionized water.
  8. Gently blot excess water and dry the sensor.

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  1. Recalibrate if instructed to do so by the manufacturer's guidelines.

Most manufacturers recommend recalibration every 4 to 8 hours.

  1. Remember that response time for gas measurements is slow and values will not always immediately reflect physiologic changes.
  2. Average 90% response time for O2is 15 to 20 seconds.
  3. Average 90% response time for CO2is 60 to 90 seconds.

TABLE 9.1 Poor Correlation of PtcO2 and PaO2

Problem

Technical Solution

Clinical

PtcO2 < PaO2

1. Improper calibration

2. Insufficient warm-up period after electrode application

3. Insufficient heating temperature

1. Recalibrate

2. Allow longer warm-up period

3. Increase heating temperature

1. Presence of shock

2. Use with high-dose tolazolinea, Isuprel, dopamine

3. Obstructive heart disease with hypoperfusion

4. Edema

5. Severe hypothermia

PtcO2 > PaO2

 

1. Improper calibration

2. Reading taken immediately after electrode application

3. Air bubble beneath membrane or leak to atmosphere

4. Excessive heating temperature

1. Recalibrate

2. Allow longer warm-up period

3. Reapply electrode

4. Attempt calibration at lower temperature

1. Right-to-left ductal shunt with preductal electrode and postductal arterial sample

2. General anesthesiab

tc, transcutaneous.
aIn the presence of tolazoline, Ptc O2 measurements appear to be accurate at lower doses (1–2 mg/kg/h), becoming increasingly inaccurate as dosage increases (43).
bEffect depends on concentration and type of membrane.

  1. Complications
  2. Skin blisters or burns (44, 56, 57)
  3. Management based on erroneous readings if the unit was not calibrated properly or site precautions were not adhered to (Table 9.1)

Continuous Umbilical Artery PO2 Monitoring (58, 59)

The following method for monitoring PO2 and the subsequent method for monitoring blood gases are included for completeness;, however, the editors are not aware of any current commercial source of the required equipment in the United States.

  1. Purpose
  2. Continuous arterial PO2monitoring from the umbilical artery

Continuous PaO2 monitoring through the umbilical artery offers a means for determining precise data on a continuous basis.

  1. Trending of PaO2over time
  2. Background
  3. Dual-purpose biluminal catheter
  4. A miniature polarographic bipolar oxygen electrode is incorporated into the tip of a bilumen umbilical catheter.
  5. The small lumen contains the wires for the electrode.
  6. The larger lumen can be used for blood sampling, infusion, blood pressure monitoring, and sampling for instrument calibration.
  7. The electrode is covered by a gas-permeable membrane, under which is a layer of dried electrolyte. The probe is packed dry, and then is activated before use. Water vapor from the activating (hydrating) solution diffuses through the membrane to form a thin layer of liquid electrolyte on the surface of the electrode.
  8. While it is in the artery, the electrode will produce an electrical current proportional to the PO2in the blood.
  9. The device is calibrated to the PO2value obtained from a blood sample drawn from the catheter.
  10. Contraindications
  11. Previous history of or evidence of compromise to the vascular supply of the lower extremities or the buttock area

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  1. History of previous complications related to an umbilical arterial line
  2. Peritonitis
  3. Necrotizing enterocolitis
  4. Omphalitis
  5. Omphalocele
  6. Equipment

Previously commercially available monitoring systems have been withdrawn from the market recently because of high production costs.

  1. Precautions

See also Chapter 28.

  1. Because this specialized catheter is stiffer and has a wider outer diameter than other umbilical artery catheters, there is the theoretical possibility of a higher rate of failure to insert and vascular spasm and interference with peripheral blood flow.
  2. Failure to insert this catheter does not imply that insertion of other arterial catheters will be unsuccessful.
  3. The electrode may fail to activate or may lose activation.
  4. The catheter should be removed slowly to ensure that physiologic vasospasm occurs with removal.
  5. Technique
  6. Use sterile procedure.
  7. Prepare the catheter according to the manufacturer's instructions.
  8. 4 Fr catheters are recommended for infants weighing less than 1,500 g.
  9. The technique for placement/insertion is the same as that used for the placement of conventional umbilical artery catheters. Either a high or low umbilical artery placement can be used (see Chapter 28).
  10. Verify catheter position by radiography.
  11. Draw blood sample for calibration.
  12. Calibrate the monitor according to the manufacturer's instructions.
  13. Complications

Same as for umbilical artery catheterization. See Chapter 28.

Continuous Umbilical Artery PO2, PCO2, pH, and Temperature Blood Gas Monitoring (60, 61,62, 63, 64 and 65)

  1. Purpose
  2. Continuous arterial blood gas monitoring from the umbilical artery

Continuous blood gas monitoring through the umbilical artery offers a means for determining precise data on a continuous basis.

  1. Trending of blood gas data over time
  2. Background
  3. A very thin, multiparameter, single-use disposable fiber-optic sensor
  4. Measures pH, PCO2, PO2, and temperature directly
  5. Introduced into the bloodstream via the umbilical artery catheter
  6. Port allows blood sampling, blood pressure monitoring, and drug infusion
  7. Calculated parameters include bicarbonate, base excess, and oxygen saturation.
  8. Delivers continuous ventilation, oxygenation, and acid balance information, while also conserving blood volume by reducing blood sampling
  9. Contraindications
  10. Previous history or evidence of compromise to the vascular supply of the lower extremity or the buttock area
  11. History of previous complications related to an umbilical arterial line
  12. Peritonitis
  13. Necrotizing enterocolitis
  14. Omphalitis
  15. Omphalocele
  16. Equipment

Previously commercially available monitoring systems have been withdrawn from the market recently because of high production costs.

  1. Precautions
  2. The fiber-optic sensor may fail as a result of excessive kinking during sensor insertion into the umbilical artery catheter.

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  1. The sensor should be removed slowly to ensure that there is no microthrombus release if heparinization of the catheter was suboptimal.
  2. See also Chapter 28.
  3. Technique
  4. Use sterile procedure.
  5. Insert umbilical artery catheter (see Chapter 28).
  6. Verify catheter position by radiography.
  7. Calibrate sensor following the manufacturer's instructions.
  8. Introduce the sensor into the umbilical artery catheter following the manufacturer's instructions.
  9. Complications

Same as for umbilical artery catheterization; see Chapter 28.

References

  1. Hay WW.Physiology of oxygenation and its relation to pulse oximetry in neonates. J Perinatol. 1987;7:309.
  2. Dziedzic K, Vidyasagar D.Pulse oximetry in neonatal intensive care. Clin Perinatol. 1989;16:177.
  3. Barrington KJ, Finer NN, Ryan CA.Evaluation of pulse oximetry as a continuous monitoring technique in the neonatal intensive care unit. Crit Care Med. 1988;16:1147.
  4. Solimano AJ, Smyth JA, Mann TK, et al. Pulse oximetry advantages in infants with bronchopulmonary dysplasia. Pediatrics. 1986;78:844.
  5. Bowes WA, Corke BC, Hulka J.Pulse oximetry: a review of the theory, accuracy and clinical applications. Obstet Gynecol. 1989;74:541.
  6. Sendak MJ, Harris AP, Donham RT.Use of pulse oximetry to assess arterial oxygen saturation during newborn resuscitation. Crit Care Med. 1986;14:739.
  7. House JT, Schultetus RR, Graverstein N.Continuous neonatal evaluation in the delivery room by pulse oximetry. J Clin Monit. 1987;96:96.
  8. Porter KB.Evaluation of arterial oxygen saturation of the newborn in the labor and delivery suite. J Perinatol. 1987;7:337.
  9. Deckardt R, Schneider K-T, Graeff H.Monitoring arterial oxygen saturation in the neonate. J Perinat Med. 1987;15:357.
  10. Maxwell LG, Harris AP, Sendak MJ, et al. Monitoring the resuscitation of preterm infants in the delivery room using pulse oximetry. Clin Pediatr. 1987;26:18.
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