Today's Veterinary Practice

MAY-JUN 2013

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

Issue link: http://todaysveterinarypractice.epubxp.com/i/133843

Contents of this Issue

Navigation

Page 46 of 85

The PracTiTioner's acid–Base Primer: oBTaining & inTerPreTing Blood gases | STEP BY STEP: OBTAINING ARTERIAl BlOOD GAS SAMPlES What You Will Need • lithium heparin arterial blood gas syringe with needle (usually 25 gauge) or • 25-gauge needle and 3-ml syringe coated with liquid heparin (as described for venous sample collection)3 Step by Step: Obtaining an Arterial Sample 1. Clip and aseptically prepare the site chosen for arterial puncture; a metatarsal branch of the dorsal pedal artery is the most common site used. 2. Place the patient in lateral recumbency, using the recumbent limb. 3. With the nondominant hand, palpate the pulse between the second and third metatarsals. 4. With the dominant hand, slowly insert the needle at a 30o to 40o angle. continue very slowly advancing the needle, watching for a flash of blood in the needle's hub. • if no flash is seen, slowly back the needle out, watching for a flash (it is possible that the needle was inserted through the vessel and a sample can be obtained as the needle is backed out). • otherwise, once the needle is very superficial, redirect it if a sample has not yet been obtained. 5. once a flash is seen: • if an arterial blood gas syringe is being used, allow the syringe to automatically fill. • if a 3-ml syringe is being used, gently aspirate the plunger to withdraw blood. 6. after the quantity of blood needed has been obtained, remove the needle from the artery and apply pressure to the site, followed by application of a pressure bandage for 30 to 60 minutes.3 distally from the hock to the metatarsophalangeal joint. If the skin is very thick, make a small nick in the skin with the bevel of a 20-gauge needle prior to inserting the catheter, which prevents burring. 5. The artery travels dorsolaterally (see Figure 3, page 46), at an approximately 30o angle to a perpendicular line drawn between these 2 joints; angle the catheter appropriately. 6. once arterial blood has flashed into the catheter, advance it into the artery and remove the needle stylet. 7. Attach a t-piece to the catheter, inject a small quantity (1–1.5 ml) of heparinized saline, and tape the catheter in place as would be done for a standard iV catheter. 8. label the catheter as arterial to avoid inadvertent administration of injections through the catheter. Arterial Catheters in Cats arterial catheters are difficult to place in cats due to their small size. additionally, cats have less collateral circulation in their distal limbs and, therefore, are more predisposed to ischemic injury of the foot or tail after arterial catheterization. arterial catheters should not be left in cats for longer than 6 to 8 hours.4 Skill Set Required obtaining arterial blood samples requires more skill than that required for obtaining venous samples; the vessel cannot be seen and only palpated by pulse (with the exception of the auricular artery, which can often be seen and felt running down the middle of the dorsal aspect of the pinna). Practice, especially on anesthetized patients, and knowledge of the anatomic location of the artery are helpful when developing this skill. Step by Step: Placing an Arterial Catheter arterial catheters are extremely useful in patients that require repeat arterial blood gas sampling, such as those on mechanical ventilation. 1. Use of sedation or a local anesthetic, such as lidocaine, is recommended. Placement during general anesthesia is ideal. 2. Clip and aseptically prepare the site chosen for arterial puncture; a metatarsal branch of the dorsal pedal artery is the most common site used. The radial, coccygeal, femoral, and auricular arteries may also be catheterized; however, catheters at these sites are less well tolerated in awake patients and, therefore, more commonly used during anesthesia.3,4 3. Place the patient in lateral recumbency, using the recumbent limb. 4. Using an over-the-needle short catheter (usually 22-gauge), penetrate the skin between the second and third metatarsals and approximately 1/3 Figure 2. Obtaining an arterial blood gas sample from the dorsal pedal artery of a 2-year-old neutered male pitbull that was anesthetized for exploratory laparotomy and foreign body removal (from the pylorus of stomach) after presenting for vomiting May/June 2013 Today's Veterinary Practice 45

Articles in this issue

Archives of this issue

view archives of Today's Veterinary Practice - MAY-JUN 2013