72 Section II ■ Physiologic Monitoring

c. Peel adhesive ring off the sensor.

d. Flush the membrane surface with deionized water.

e. Gently blot excess water and dry the sensor.

f. Recalibrate if instructed to do so by the manufacturer’s guidelines.

Most manufacturers recommend recalibration

every 4 to 8 hours.

11. Remember that response time for gas measurements is

slow and values will not always immediately reflect

physiologic changes.

a. Average 90% response time for O2 is 15 to 20 seconds.

b. Average 90% response time for CO2 is 60 to 90 seconds.

12. Complications

13. Skin blisters or burns (23)

14. Management based on erroneous readings if the unit

was not calibrated properly or site precautions were not

adhered to (Table 10.1)

Continuous Umbilical Artery PO2

Monitoring (24,25)

The following method for monitoring PO2 and the subsequent

method for monitoring blood gases are included for completeness. The editors are not aware of any current commercial

source of the required equipment in the United States.

A. Purpose

1. Continuous arterial PO2 monitoring from the umbilical artery

 Continuous PaO2 monitoring through the umbilical

artery offers a means for determining precise data on a

continuous basis.

2. Trending of PaO2 over time

B. Background

1. Dual-purpose biluminal catheter

a. A miniature polarographic bipolar oxygen electrode

is incorporated into the tip of a bilumen umbilical

catheter.

b. The small lumen contains the wires for the electrode.

c. The larger lumen can be used for blood sampling,

infusion, blood pressure monitoring, and sampling

for instrument calibration.

d. The electrode is covered by a gas-permeable membrane, under which is a layer of dried electrolyte.

The probe is packed dry and is then 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.

e. While it is in the artery, the electrode will produce

an electrical current proportional to the PO2 in the

blood.

f. The device is calibrated to the PO2 value obtained

from a blood sample drawn from the catheter.

C. Contraindications

1. Previous history of or evidence of compromise to the vascular supply of the lower extremities or the buttock area

2. History of previous complications related to an umbilical arterial line

3. Peritonitis

4. Necrotizing enterocolitis

5. Omphalitis

6. Omphalocele

D. Equipment

Previously commercially available monitoring systems have

been withdrawn from the market recently because of high

production costs.

Table 10.1 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