Page 157 - Libro 2

8 — Indirect Assessment of Arterial Disease
137
Figure 8-18 The proper patient position in an ice bath used for cold sensitivity testing.
A large container is needed for the hand immer- sion, and a “bath basin” as used routinely in hospi- tal settings works very well. Placing the basin on a small table in front of the patient facilitates immer- sion and prevents accidental spills.
Cold immersion should be for 30 to 40 seconds, fol- lowed by immediate removal of the gloves. If the hands do get water on them directly, they should be “pat- ted” dry rather than rubbed briskly. Digital waveforms (Fig. 8-19) and/or temperatures should be measured immediately at 2 minutes, 5 minutes, and 10 minutes. Normal digital tracings and/or temperatures should re- turn to preimmersion status within 10 minutes to be categorized as normal (Fig. 8-20; also see Table 8-4f), with 􏰁10 minutes being consistent with cold sensitivity.
Figure8-20 Normalandabnormaltemperaturemeasurements following cold sensitivity testing using ice water immersion. A normal response is one where temperatures return to base- line measurements within 10 minutes following removal from the cold stimulus.
If the study is abnormal, the pulse and/or tem- perature should be verified prior to releasing the patient.
THE ALLEN TEST
An application of the Allen test can use PPG waveforms to indicate adequacy of hand perfu- sion from the radial and ulnar arteries, combined and individually. It is necessary to establish the contribution to digital perfusion from each artery prior to certain surgical procedures. These proce- dures include the creation of a dialysis fistula or graft and radial artery harvest prior to coronary bypass procedures. The PPG transducer is affixed to the middle finger or the forefinger and pulses are recorded. The radial and the ulnar arteries are compressed sequentially to verify whether or not pulses are maintained (Fig. 8-21). The intent is to detect that pulse amplitude is not abolished when the arteries are compressed. This confirms that flow into the hand will not be interrupted if the radial artery is used to feed the fistula or graft or if harvested for bypass.
Pathology Box 8-1 summarizes some of the com- mon arterial pathology observed in the lower and upper extremities. It also lists the indirect testing re- sults associated with these abnormalities.
Pre 2 5 10 15 25
Time
PPG Waveform
Digital Temperature
Immediately
Reduced amplitude
􏰄20°C (68°F)
2 minutes
Increase in amplitude
20°–25°C (68° to 77°F)
5 minutes
Sharp peak returning
25°–30°C (77° to 86°F)
10 minutes
Return to preimmersion
30°–33°C (86° to 91°F)
Normal
Abnormal
Figure 8-19 Normal and abnormal digital PPG waveforms recorded during cold sensitivity testing. Pre indicates initial waveforms recorded at room temperature. The numbers 2, 5, 10, 15, and 25 indicate the minutes after removal from an ice water bath.