Designed, Produced and maintained by

Bhavani Shankar Kodali MD

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 Capnography in Veterinary Sedation

It has been recognized that monitoring respirations in patients during sedation for out of the operating room procedures is valuable in preventing the occurrence of hypoxic episodes. The value of monitoring respirations using capnography has migrated to veterinary anesthesia to protect lives of precious animals. The picture below demonstrates the use of capnography during sedation in Rhino in Africa. (courtesy: Robin W. Radcliffe, DVM, DACZM, Rhino Conservation Medicine Program, Adjunct Assistant Professor of Wildlife and Conservation Medicine International Rhino Foundation / Fossil Rim / Cornell University)

 

Morkel et al, measured acid-base balance and ventilation during sternal and lateral recumbancy in 36 field immobilized black Rhinoceros receiving oxygen insufflation. The animals were immobilized in Namibia from a helicopter, by remote intramuscular injection of etorphine HCl, azaperone, and hyaluronidase. They measured PETCO2, PVCO2, SPO2, HCO3 in lateral position and sternal position. For a similar PCO2, PETCO2 was higher in sternal position as compared to lateral recumbency position. The authors atrribute this to decreased physiological dead space as a result of better ventilation upon assuming sternal position from later recumbency. It would have been interesting to determine airway flows and ventilation in the two postions. Analysis of capnograms in the two positions would have also been useful. The additional information could determine if there was partial airway obstruction in the lateral position. Nonetheless, a notable feature of this study was that all animals were acedemic and hypoxic on capture. The information in this study will be very useful to improve the care of these animals upon capture.

Reference:

Morkel P.vdB, Radclifee RW, Jago M, Preez P du, et al. Journal of Wildlife Diseases 2010;46(1):236-45.

 

 

Capnography during conscious or procedural sedation -What is the present concern?

Bhavani Shankar Kodali MD
Propofol and other sedatives, although administered in good faith to produce conscious or light sedation, can often result in inadvertent deep sedation comparable to general anesthesia.(1,2) in a study by Ramsay etal, the authors observed that 74% of their patients crossed into general anesthesia as indicated by patient state index levels (PSI) below 70 measure by PSA 4000 that measures sedation depth. This can result in putting patients at significant risk for possible complications that includes respiratory depression. Therefore, it is rational, or even may be mandatory, to monitor oxygenation and ventilation. Since hypoventilation, airway obstruction and apnea precede the actual development of hypoxia, capnography plays a significant role in detecting these precursors. This enables corrective measures to be initiated and thus avoiding hypoxia. There is considerable debate in the literature regarding the safety of propofol administration outside of the operating rooms for sedation Some consider it is safe, whereas others think it is not. These concerns are illustrated in a debate in the American Journal of Gastroenterology. (3) Under these circumstances, it is wise to monitor ventilation and oxygenation as adequately as one can, and also be proficiently trained in taking care of sedated patients.

Hypoventilation and apnea generally occur before hypoxia
Capnography helps to facilitate identification of apnea and enable corrective measures to be instituted
1 Ramsay E etal. ASA Annual Meeting 2004. Abstract - A 68.

2. Nurse administered propofol puts patients at risk. Anesthesiology News 2005;31:3:1.

3. Debate on the use of propofol by Non anesthesiologists. Am J Gastroenterology 2004;99:7:1207-11
       


Carbon dioxide sampling devices for procedural sedation

Bhavani Shankar Kodali MD

The devices for carbon dioxide sampling can be assembled from the items shown in pictures (1,2). Several varieties of end-tidal carbon dioxide sampling devices are available commercially (3).


Capnograms during procedural sedation

Bhavani Shankar Kodali MD


Carbon dioxide wave forms may not be as perfect in shape as those obtained in intubated patients (1-4). However, a change form baseline capnograms during procedural sedation may indicate increased depth of sedation (5-7). In the least, one has to determine the cause of the change in the co2 waveforms from baseline. Is it due to sampling problems or increased depth of sedation?

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Capnograms during over sedation (Compare to baseline capnograms on the left)


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