Iowa Neonatology Handbook: Procedures

Collection of Arterial Blood Gas Samples

Iowa Neonatology Fellows
Peer Review Status: Internally Peer Reviewed

I. Due to the persistent, continuing incidence of retinopathy of prematurity (ROP), any infant in an increased ambient oxygen concentration must have his arterial oxygen tension or saturation monitored. Retinal changes have been noted in children whose PaO2s have not been higher than 100 mm Hg.

II. An ill infant without an indwelling arterial catheter should have arterial O2 tension monitored by arterial puncture, or PO2 catheter, or transcutaneous PO2 monitor. An acceptable alternative would be continuous pulse oximetry with upper limits of saturation in the low 90's, but caution should be used to prevent exposure to high amounts of oxygen. If questions arise regarding the appropriate level of oxygen saturation, peripheral arterial puncture should be performed.

III. Frequency of sampling depends on the clinical situation and the reliability of the other monitoring devices. Generally, a change in respirator or CPAP setting should be followed by a capillary or arterial sample within 15 minutes to an hour. If performing a peripheral arterial puncture for blood gas purposes, note should be made of the location, as many infants have shunting through the ductus arteriosus that may effect the interpretation.

IV. Blood gas sampling with peripheral arterial puncture or indwelling arterial catheter requires 0.1 ml of blood. If electrolytes, ionized calcium and hematocrit are also run in the NICU laboratory, 0.3 ml of blood are obtained. Generally, the tuberculin syringe should be heparinized by withdrawing 0.1-0.2 ml of 100 U/ml heparin solution, coating the surfaces and disposing of the remainder. Excessive heparin left in the syringe will dilute the sample, decrease the pH value and lower the PaCO2. If using blood in the syringe for other labs, including spun hematocrit in the NICU lab, heparin cannot be used and one must notify the blood gas technician to run the sample immediately.

V. Arterial puncture, although not as commonly used in NICU's as other methods of monitoring, can be performed with relative ease, using the radial temporal, posterior tibial, or dorsalis pedis artery. The brachial and femoral artery should be used only in emergency situations, because of the risk of complications at those sites. Indwelling catheters may be placed in the radial, posterior tibial or dorsalis pedis artery but should not be placed the temporal or brachial artery.

VI. Prep the site with 3 alcohol swabs and wear appropriately fitting gloves. Goggles or eyeglasses are also recommended. The artery should be easily palpable or visible with transillumination. If using the radial artery, an Allen test should be performed prior to puncture. An arm board may be useful to prevent extreme dorsiflexion of the wrist which makes the procedure more difficult. A 25 gauge butterfly needle, with TB or 3 ml syringe should be used. The bevel up position should be used, except in the most superficial arteries. The angle of insertion should be 25o for a superficial and 45o for a deep artery, against the flow of the artery. Blood should flow spontaneously or with gentle suction.

VII. After the needle is removed, continuous pressure should be applied for 5 minutes, with care not to squeeze with the fingertips. If hematoma formation is prevented, the artery may be used multiple times. Observe the extremity for 15-20 minutes after the procedure for arterial spasm.

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