The purpose of this text is to assist clinicians in better understanding the indications for testing umbilical cord blood gases, in recognizing the pitfalls involved in collecting and handling specimens, and in correctly interpreting umbilical cord blood gas values.

To illustrate these points, I use a series of clinical cases drawn from actual experience with patients. The information is presented by category, and most often each successive case within the category is of increasing complexity. Some of the cases are old and some relatively new. The care provided was not necessarily optimal or even acceptable. As with every endeavor, regular practice produces better results. In many situations, more than one interpretation of umbilical cord gases is possible. Of critical importance is the reasoning behind the interpretations. In general, much additional information is provided, both antenatal and postnatal, along with the blood gas results. Of course, not all of this information is available as the baby is being delivered; however, the goal is correct interpretation of cord blood gas results. It is important to make sense of the data, not simply to note the presence of respiratory or metabolic acidosis or mixed acidosis. Fairly often, this requires integrating information about the fetal monitoring strip, details of the delivery, the follow-up blood gas results taken directly from the infant and other post-delivery information.

In each example, the clinical and laboratory data are presented first, with my own interpretation presented on the following page. This will allow readers to compose their own thoughts prior to reading my conclusions and, more importantly, to develop the reasoning behind them.

The objectives of this text are to help the reader to:

(1) Become familiar with normal umbilical cord blood gas values;
(2) Understand the usual relationship between pH and blood gas values found in the umbilical vein and the umbilical artery;
(3) Recognize how best to interpret the results when technical problems have occurred;
(4) Recognize patterns of abnormal umbilical cord blood gas values and understand their pathophysiology;
(5) Recognize when asphyxia has been associated with delivery and when it has not;
(6) Be able to decipher even complex issues in the interpretation of umbilical cord blood gas results, and,
(7) To boldly interpret where no one has interpreted before.

Following each of the first two sections and the interpretation of each case presentation, “Key Points” are listed.

Jeffrey J. Pomerance, MD, MPH

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