While other molecules may be “sexier,” said John Toffaletti, PhD, a patient with very low oxygen can die within half an hour without appropriate intervention. Toffaletti, together with Craig Rackley, MD, led a popular workshop on Sunday for the third year in a row titled, “Guidance for Evaluating the Hypoxemic Patient in the Critical Care Setting.”
“Oxygen is the most important of the blood gas parameters,” Toffaletti noted. But the AACC University session also looked beyond oxygen itself, exploring how this essential parameter affects pulmonary function and how clinical lab professionals must work with clinicians to quickly identify the specific cause of hypoxemia—for example, whether it’s a gaseous exchange problem or not enough air reaching the lungs.
The workshop was divided into two sections. Toffaletti went through the basic theory, including some of the blood gas concepts that are challenging but important, such as paO2 to FiO2 (P/F) ratio, oxygenation index (OI), determining interpulmonary shunting, and determining pulmonary dead space, among others. He pointed out that some calculations may be difficult, and the lab must know when it is clinically appropriate to perform them.
This theory then came to life in the clinical cases Rackley discussed in the later part of his presentation. For example, Rackley presented a case that highlighted the importance of calculating the P/F ratio and OI in determining the survival outcomes of patients in the ICU that have acute respiratory distress syndrome.
They also emphasized some common pre-analytical errors and how to avoid them. For example, using catheters to draw specimens can cause many problems, but the laboratory needs to know how to perform this correctly when it’s unavoidable. Inadequate mixing of heparinized blood also is a common mistake, but less well known is how this can affect hemoglobin, pO2, and O2 content.
Additionally, laboratories commonly transport blood gas samples by pneumatic tubes, but a normal pO2 or abnormal pO2 are effected differently, and quite significantly, by trapped air bubbles. Effects of metabolism and icing during transport and extracellular fluid contamination are other pre-analytical errors of note.
One of the attendees, Jane Tansiongco, a point-of-care coordinator from Pali Momi Medical Center in Hawaii, said she found the pre-analytical errors section Toffaletti covered especially helpful. She plans to stress these areas in her training during the next skills fair at her institution.