Speaking Out

Dear Editor,

We have read with great interest the article of Austin B, et al., titled Laparoscopic Ovariohysterectomy in Nine Dogs (

). The authors measured pre- and postoperative creatine kinase (CK) blood level to determine if CK activity could be used as an appropriate indicator of surgical stress in the dog. Based on the results of their study, they conclude that CK is not a predictable indicator of surgical stress. We do not agree with this opinion.

The authors have done only two blood samples (before induction and 12 hours after surgery) to determine serum CK activity. The protocol for blood sampling should have been designed to obtain a complete profile of CK plasma activity before, during, and after surgery to allow an accurate estimation of the Area under the Curve (AUC). This indicator is indeed much more appropriate than a comparison between two values at fixed times. Due to interindividual variability, it is obvious that only two blood-sampling times are not enough to allow an accurate estimation for assessing muscle damage. By measuring the AUC, it is also possible to determine an estimate of the amount (in gram) of muscle damage.¹ This approach has already been used with success in dogs to assess quantitative muscle damage induced by intramuscular (IM) injection,² electromyography,³ anesthesia with halothane or propofol,⁴ or exercise.⁵

Moreover, the experimental protocol does not distinguish the effect of surgical stress and other factors on CK elevation. The authors performed an IM injection of acepromazine before starting surgery. Intramuscular injections are known to dramatically increase CK activity up to 24 hours postinjection (with some drugs, elevations >1000 IU/L within hours following injection).² Therefore, it is not possible in their study to identify if the elevation was actually due to surgery or to the IM injection. Anesthesia may cause CK elevation; CK activity is known to increase for up to 2 days following halothane anesthesia (C_max = 2366 IU/L after 5 hours of halothane anesthesia).⁴ Such potential confounding factors should have been documented by using control dogs (i.e., sham-operated but anesthetized using the same drug combination). Therefore, even if the aim of this study was perfectly relevant, we think that no valid conclusion can be drawn here for the use of CK as a predictive indicator of surgical stress.

Nevertheless, we agree completely with the authors that determining CK activity in the field of surgery could be very useful, either as a marker of surgical stress or as a non-invasive method of quantifying surgical trauma.