Abstract

Marine mammal respiratory physiology differs from terrestrial mammals in that breath-holding results in oxygen storage challenges. These animals rely on hemoglobin and myoglobin oxygen storage while the alveoli collapse under pressure. As breath is held longer (sometimes for extended minutes), hypoxia increases with a concomitant increase in carbon dioxide.¹ Capnometers noninvasively measure expired carbon dioxide (CO₂), a by-product of metabolism excreted via the lungs, in millimeters of mercury. Although capnometers are usually used for anesthetic monitoring, another use is point-of-care testing to determine the ventilatory status of a non-anesthetized patient. A pilot study was developed to monitor baseline end-tidal carbon dioxide (ETCO₂) values for individual cetaceans at the Shedd Aquarium.

Pacific white-sided dolphins (Lagenorhynchus obliquidens, n=5) and beluga whales (Delphinapterus leucas, n=5) at the Aquarium were monitored via a Microcap® handheld capnometer (Oridion Capnography, Inc., Needham, MA, USA). Many new capnometers can be used on non-intubated patients by placing the probe within the exhaled stream of gases. For this study, the probe was held above the blow hole to capture passive exhalations while the animal was at rest in a voluntary sternal “layout” position in the water. The dolphins participated in 15–18 sessions and the belugas in 10–11 sessions each. Each session consisted of capturing ETCO₂ from 2 consecutive passive exhalations per animal, yielding between 30–36 exhalations per dolphin and 20–22 exhalations per beluga. The mean ETCO₂ was generated for each individual animal for each session; all sessions were then combined for each animal and an overall mean ETCO₂, standard deviation (SD) and standard error of the means (SEM) was derived per animal.

Since there are no published reference ranges for these species, the information in this study has provided the Aquarium with individual animal reference ranges of ETCO₂. This information will be used to monitor the pulmonary health of each cetacean at the Aquarium, and as a baseline to compare to during times of illness.² In the future, cetacean population norms for ETCO₂ could be achieved if multiple institutions within the aquarium community participated in a larger study.

Literature Cited

1.  Pabst, D.A., S.A. Rommel, W.A. McLellan. 1999. The Functional Morphology of Marine Mammals. In: Reynold, J.E and Rommel, S.A. (eds). 1999. Biology of Marine Mammals. Smithsonian Institution Press. Washington, D.C.

2.  Van Elk, C.E., N. Epping, and S.J.M Gans. 2001. Pulmonary function measurements in dolphins using capnography. Vet. Rec. 149: 308–309.