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Airless identification of the epidural space in infants and children.

Probable venous air embolisms were reported in two pediatric patients during caudal (1) or intervertebral (2) epidural anesthesia. These reports have alerted us to the danger of air for use in the loss-of-resistance (LOR) technique or in confirmation of the correct placement of epidural catheters in infants and children. The authors of one report (2) were unable to find the study on the comparison of the LOR-to-air and the LOR-to-saline technique in the pediatric population. However, Dalens and Chrysostome (3) had performed the comparison. They found that the LOR-to-saline technique resulted in more subarachnoid penetrations than the LOR-to-air technique in 357 pediatric patients. However, the LOR-to-air technique produced patchy anesthesia ("painful gaps") in 4.2% of patients. In addition, they proved that the LOR-to-carbon dioxide (COJ technique is as reliable as air and did not produce painful gaps. Even if the CO, was injected inadvertently into the venous system, CO, would be absorbed rapidly. This technique seems to be a reasonable alternative to the traditional technique using air. However, we have to have CO, cylinders in our operating rooms. The other reliable method of airless identification of the epidural space in infants and children is the use of the microdrip chamber prepared with saline (4,5). The microdrip infusion set is connected to the epidural needle. When the needle enters into the epidural space, dripping of saline in the chamber is observed. Only a few drips of saline and practically no air are injected into the epidural space to identify the space. The overall success rate of this method was 97.7% (4). In contrast to CO, cylinders, microdrip infusion sets are readily available in the operating rooms. Masao Yamashita, MD Anaesthetist-in-Chief Ibaraki Children's Hospital Mito, japan collected the blood samples for the catecholamine determination from an antecubital vein. This approach, however, may lead to unreliable catecholamine levels. Various authors reported with regard to epinephrine that a highly variable and unpredictable extraction upon passage through tissues (2-6) occurred. This makes venous sampling an invalid indicator of epinephrine's and also norepinephrine's arterial concentration, especially when the epinephrine secretion increases (5,6). It is well known that venous levels greatly underestimate the epinephrine response to stress (4,6). Using a central venous sampling site, as was done in another recent article (7), raises the question of the exact location of the catheter tip, because measured epinephrine levels in central venous blood depend greatly on the catheter's location, inasmuch as the inferior caval vein mainly contributes to the amount of circulating epinephrine. The ideal blood collecting site for determination of reliable epinephrine concentrations is the pulmonary artery. Mixed venous blood will most reliably reflect the adrenomedullary secretion, but there may be ethical limitations to inserting a pulmonary catheter in patients without a medical indication. The use of arterial blood can provide an alternative (3,5,6), even though some catecholamine uptake of the lungs has to be considered (3,4,6). Norepinephrine levels determined in the aorta are about 20% lower than in the pulmonary artery (41, whereas epinephrine is affected to a much lesser extent (4,5). Therefore, arterial blood has been recommended for epinephrine measurements (3-6), mainly because the net removal of catecholamines is more calculable in the lungs than in the other tissues, and the plasma concentrations to which target organs are actually exposed are best reflected by arterial catecholamine levels. Friedrich K. Piihringer, MD Marco Gottardis, MD Wilhelm Furtwangler, MD Reinhard Germann, MD Clinic for Anaestlzesia and