62 Section II ■ Physiologic Monitoring

Ensure that the entire circuit and all the ports are fluid

filled and bubble-free.

5. If using disposable transducers, connect the reusable

interface cable to the transducer and to the monitor.

Turn the monitor on.

6. Secure the transducer at the patient’s reference level,

defined as the midaxillary line (heart level). If using

transducer holders, level the reference mark on the

holder at the patient’s reference level.

7. Connect the distal end of the circuit to the patient’s

catheter, ensuring that the catheter hub is filled with

fluid and is bubble-free.

8. Start the infusion pump. The pump rate cannot exceed

the flow rate of the flush device.

9. Open the stopcock connected to the transducer to air

(shut off to the patient, open to atmosphere).

10. Zero/calibrate the monitor according to the manufacturer’s instructions.

11. Close the stopcock connected to the transducer (open

to the patient).

12. Set the monitor pressure waveform scale to one that

accommodates the entire pressure wave.

13. Observe the waveform obtained. If the wave appears to

be damped (flattened, poorly defined, with slow rise

time), check the circuit for air bubbles starting at the

Fig. 9.6. Arterial pressure waveforms: normal arterial waveform

(top); dampened arterial waveform (middle); arterial waveform

with spike caused by catheter whip or inappropriate tubing (bottom). (Note that figure demonstrates waveform appearance only

and not actual pressure values.)

A B

Fig. 9.7. Pressures obtained by direct measurement through umbilical artery catheter in healthy newborn infants during first 12 hours of life. Broken lines represent linear regressions; solid lines represent

95% confidence limits. A: Systolic pressure (top) and diastolic pressure (bottom). B: Mean aortic pressure

(top) and pulse pressure (systolic–diastolic pressure amplitude) (bottom). (From Versmold HT, Kitterman

JA, Phibbs RH, et al. Aortic blood pressure during the first 12 hours of life in infants with birth weight 610

to 4,220 grams. Pediatrics. 1981;67:611, with permission of American Academy of Pediatrics.)

Chapter 9 ■ Blood Pressure Monitoring 63

distal end (Fig. 9.6). If no air bubbles are detected, then

gently flush the catheter.

14. Once a stable pressure reading is obtained, set the

alarm limits. Mean arterial pressure value is optimally

used to set alarm limits (Fig. 9.7).

15. Zero the transducer every 8 hours.

16. When blood samples are drawn from the line, flushing

should be done gently with a syringe using a minimal

amount of heparinized saline solution.

H. Complications (Table 9.3)

1. Defective transducer

2. Cracked Luer-lock connections, causing leaks, low

pressure readings, or blood to back up in the line

3. Air bubbles in the line

4. Malfunctioning infusion pump not providing continuous flush, causing the line to clot off

5. Defective reusable transducer interface cable (disposable transducer system)

6. Erroneous readings caused by the transducer not being

properly set at the patient’s reference level. Lower readings occur when the transducer is high; higher readings

occur when the transducer is lower than the patient’s

reference level.

7. Problems associated with catheters

8. Tip of the catheter lodging against the wall of the vessel

(will cause the pressure wave to flatten and the pressure

to rise slowly as a result of the continuous infusion)

9. Transducer not zeroed to atmosphere (static pressure

trapped by stopcock valve and a syringe stuck in the

port that should be opened to air). This will cause lower

or negative pressure readings.

10. Loss of blood if stopcock is left open and third port is

not capped.

11. Fluid overload if a pressurized IV bag is used instead of

an infusion pump and the fast flush mode is used to

clear the line (20)

Table 9.3 Trouble-shooting for Intravascular Pressure Monitoring

Problem Cause Prevention Treatment

Damped pressure

tracing

Catheter tip against vessel wall Usually unavoidable Reposition catheter while observing

waveform

Partial occlusion of catheter tip by clot Use continuous infusion of normal saline

or ½ normal saline with 0.5–1 U

heparin/mL of fluid

Remove line if possible. If line

removal is not an option, then

aspirate clot with syringe and

flush with heparinized saline

Clotting in stopcock or transducer, or blood in

system

Flush catheter carefully after blood withdrawal and re-establish continuous

infusion; back-flush stopcocks to

remove blood

Change components

Abnormally high or

low readings

Change in transducer level. A 10 cm change in

height will alter the pressure reading by 7.5

mm Hg. Note: If the cannula is inserted into

the radial artery, raising the hand will not

effect the measurement as long as the transducer is maintained level with the hearta

.