CHAPTER 12. ARTERIAL BLOOD GAS SAMPLING
Indications105
Contraindications106
Equipment107
Practical procedure107
Femoral artery puncture109
Complications109
Gustav Magnus (1802–1870) made the first consistent analyses of blood gases in 1837. He obtained his blood samples from both horses and ‘commoners who for a small sum permitted themselves to be bled’. Magnus went on to estimate the oxygen capacity of blood in 1845. However, modern blood gas analysis is the accumulation of the work of numerous brilliant men, namely Cremer (1865–1935), Haber (1868–1934), Hasselbalch (1874–1962), Van Slyke (1883–1971), Henderson (1878–1942), Astrup (1915–2000), Clark (1918–2005) and Severinghaus (1922–). These men pioneered the construction and refinement of the hydrogen, oxygen and carbon dioxide electrodes. Furthermore, they also constructed formulae to explain the relationships between the directly measured values of haemoglobin, oxygen tension, acidity and carbon dioxide, and the derived calculations of base deficit and bicarbonate.
INTRODUCTION
Arterial blood gas sampling provides useful information in the assessment of both respiratory function and acid–base balance. The usual site of puncture is the radial artery, although femoral and brachial arteries are common alternatives when the radial approach proves to be difficult. It is important to understand the anatomy of vessels in the area (Fig. 12.1) prior to puncture to ensure successful sampling, and to minimize discomfort and complications to the patient.
INDICATIONS
CONTRAINDICATIONS
ALLEN’S TEST
Allen’s test helps to ensure that while you are performing a radial puncture, the ulnar artery is capable of perfusing the hand. Ask the patient to clench a fist. Obstruct the radial and ulnar arteries using the index and second finger of both your hands on the respective arteries simultaneously. This prevents arterial flow into the hand. Ask the patient to open their hand while you are still occluding both arteries. Now release the pressure on the ulnar artery while still occluding the radial artery. This allows the ulnar artery blood to flow into the hand. Look for a change in colour from white to pink of all digits of the hand. This demonstrates that blood flow to the hand would be adequate should cannulation of the radial artery lead to its obstruction. This positive Allen’s test is a prerequisite to radial cannulation and is a necessary precaution prior to puncture for gases. A negative Allen’s test is a warning that digital ischaemia is a significant risk following radial artery cannulation for any period of time.
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