Question

A 16-year-old girl with a history of poorly controlled asthma presents to the emergency department with worsening shortness of breath. She is in severe respiratory distress despite receiving albuterol every 2 hours at home. She is placed on a cardiopulmonary monitor and a pulse oximeter. Vitals signs are as follows: heart rate 120 beats per minute, respiratory rate 30 breaths per minute, blood pressure 125/90 mm Hg, temperature 37.5°C, oxygen saturation 86% on room air. You are asked to initiate continuous albuterol at 15 mg/hr and to obtain a blood gas. After obtaining the arterial blood gas supplies, you enter the room, introduce yourself to the patient, and describe the procedure to her.

Prior to performing the radial artery puncture, you perform the modified Allen’s test. The color of the palm changed from blanched to pink in <5 seconds.

You proceed with the procedure, obtain a sample for analysis, and apply pressure to the puncture site until bleeding has stopped. The blood gas is analyzed with a point-of-care blood gas machine. The arterial blood gas test indicates a pH of 7.54, CO2 of 26 mm Hg, PaO2 of 60 mm Hg, bicarbonate level of 22 mEq/L, base excess of 0.8 meq/L and Pa. A chemistry panel demonstrates a sodium level of 138 mEq/L and chloride level of 103 mEq/L. The physician asks you to interpret the arterial blood gas and to make recommendations for care.

1. If the patient was unable to follow your direction for the modified Allen’s test, describe how you would assess collateral circulation.

Answer 1

It is possible quickly to check the patency of the ulnar
collateral circulation in the unconscious patient with a
pulse meter, preferably one which displays a trace on an
oscilloscope. The pulse detector is placed on the thumb
of the hand which is chosen for radial arterial cannula-
tion, and the gain is adjusted on the pulse monitor, so
that a satisfactory trace is displayed on the oscilloscope.
Both radial and ulnar arteries are compressed at the
wrist. The trace will go flat. When the pressure on the
ulnar artery is released, the trace reappears if the ulnar
artery is patent. Failure to demonstrate an ulnar trace
suggests that the ulnar collateral circulation is in-
adequate, and that another site be chosen for arterial
cannulation