Postoperative pain management with incisional local anesthetic infiltration

We read with interest the recent study¹ by Fitzpatrick et al on the use of incisional local anesthetic (LA) infiltration in dogs undergoing ovariohysterectomy (OHE). We commend the authors for investigating a modality of perioperative multimodal analgesia widely used in human and veterinary medicine. We were surprised when this study did not reveal a positive effect on postoperative pain, as this is contrary to the results of at least one other veterinary study² and many human studies,^3–5 including large systematic reviews. The documented positive effects of incisional LA infiltration include improved resting and dynamic pain scores, decreased opioid consumption, and decreased incidence of chronic postoperative pain syndromes.

One potential reason for the lack of effect merits further attention. The authors of the study are commended for adopting a strong multimodal approach to pain management, including administration of opioids and NSAIDs. At the same time, it is plausible that this aggressive approach, although quite appropriate in the clinical setting, may have precluded the ability to discern differences between groups. That is, although differences may have existed, they may have been below the sensitivity of the Glasgow composite measures pain score system and von Frey filament technique. Admittedly, it is difficult to design a study of analgesic treatment in which the differences between groups are maximized, the impacts of confounding ancillary treatments minimized, and standards of humane care maintained.

Another confounder in this study was the variability in technique for LA administration. This study used several inexperienced operators, in contradistinction to other published studies in which LA was administered by a single, experienced operator, minimizing error and eliminating interoperator variability. Additionally, although injections were made in the area of the planned incision for this study, the variability in incision lengths implies that some patients’ incisions may have exceeded the length of the block. The authors also report errors and adverse events, including splenic laceration, suggesting improper technique and bupivacaine disbursement in some patients. Such errors may have resulted in an ineffective block or iatrogenic inflammation and pain unassociated with the surgical incision.

Those accustomed to using incisional LA infiltration and experiencing perceived benefits in clinical practice are unlikely to be deterred from its use by this study. Our greater concern is that without critical analysis of this study, readers may conclude that incisional LA infiltration is ineffective and need not be part of pain management for dogs undergoing OHE or other surgical procedures.

We applaud the authors for investigating incisional LA infiltration, for using a multimodal analgesic protocol in dogs undergoing OHE, for incorporating a validated pain scale, and for using a quantitative tool for assessment of peri-incisional analgesia (von Frey filaments). However, we caution against overinterpretation and encourage the pursuit of further well-controlled studies of this and other multimodal analgesic techniques. Readers are encouraged to review the totality of veterinary and human literature on incisional LA infiltration, which supports demonstrable improvement in patient comfort associated with this technique.

Mark E. Epstein, dvm, dabvp

President, International Veterinary

Academy of Pain Management

Gastonia, NC

Benjamin M. Brainard, vmd, dacva, dacvecc

Department of Small Animal

Medicine and Surgery

College of Veterinary Medicine

University of Georgia

Athens, Ga

Patrice M. Mich, dvm, ms, dabvp, dacva

OrthoPets Center for Animal Pain

Management and Mobility Solutions

Denver, Colo

Rachael E. Carpenter, dvm

Ruffian Equine Medical Center

Elmont, NY

Alexander T. Hawley, dvm, ms, dacva

The Sams Clinic

Mill Valley, Calif

The authors respond:

Thank you for your comments on our study. We agree with you that line blocks have shown some benefits on postoperative analgesia in several studies. However, whether this is true in conjunction with a multimodal analgesia protocol is not universally recognized in the literature, especially for patients undergoing abdominal surgery,^1–5 and this is one of the reasons why we performed our study. Our study only showed that under controlled conditions with a standard treatment of pain, the line block did not make a difference in management of postoperative pain. No matter what our preconceived ideas or clinical biases are, we are obligated to report the results as they occurred.

Lots of confounding factors can change the results of scientific studies and should be considered when reading the literature. For studies evaluating postoperative analgesia, confounding factors include, but are not limited to, the type of surgery, the technique used to provide analgesia (eg, timing related to the surgery), and the surgical technique (eg, amount of soft tissue trauma). The type of surgery (eg, penetration of a major cavity inducing visceral pain) is a major confounding factor. Anesthesia of only the subcutaneous tissue and abdominal wall along the incision is likely not a great contributor to postoperative analgesia after any abdominal surgery. The effect of a line block is probably going to be more pronounced for surgeries involving only the skin and the subcutaneous tissues, such as resection of a small skin mass. To minimize the effect of confounding factors, we decided to test our hypothesis with a single elective surgical procedure that involved the abdominal cavity (ovariohysterectomy). The surgery had to be performed by veterinary students with limited surgical experience. Therefore, the amount of soft tissue trauma was likely higher than would have been the case if the surgery had been performed by a single, more experienced surgeon. Also, we used positive and negative controls in our study to try to minimize the effect of confounding factors related to the technique of injection.

You mentioned that the length of the incision varied (14-mm difference between groups) because of the students’ inexperience. The line block may have missed a small part of the incision in one group, given that the injection was performed before the incision was made. In our study, however, line blocks were performed in a wide expanse around the incision site. Therefore, even with the variability in incision length (14 mm), we do not believe any part of the incision was missed.

As you mentioned, we use a combination of an NSAID and an opioid for routine postoperative pain control at our institution. It would have been unethical to perform our study without providing this standard treatment to all patients. Also, we believe that line blocks would not typically be used alone in a clinical situation. Therefore, to test their effect in conjunction with the standard treatment seemed more realistic to us. In this situation, the addition of a line block did not make a difference. We might have shown a beneficial effect of a line block if we had not provided other analgesia and waited for dogs to become painful before additional analgesia was given, but this was not the point of our study.

Finally, one could question whether it is detrimental to perform a line block even if it does not provide any supplemental analgesia. More than likely not, since the complication rate related to the line block was not high.

Eric Monnet, dvm, phd

Heather Weir, dvm

Department of Clinical Sciences

College of Veterinary Medicine

Colorado State University

Fort Collins, Colo

Courtney Fitzpatrick, dvm

Department of Clinical Sciences

College of Veterinary Medicine

Cornell University

Ithaca, NY

Questions conclusions in study of blood pressure measurement system

Although I would welcome a well-designed study that compares the newer generation of oscillometric blood pressure monitoring devices in cats, the study by Acierno et al¹ unfortunately does not allow any conclusions to be drawn. The invasive blood pressure measurement system used by the authors in this study cannot be considered valid. The natural frequency of the device used for direct blood pressure measurements is listed at 16.6 Hz, as measured in a dog (this already poses issues since generally it is not acceptable to test the system in other species). For accurate direct blood pressure measurement, the system should have a natural frequency at least ten times the frequency being measured,² although other authors have stated that six to eight times is adequate.³ Importantly, the system has to be able to deal with all frequencies encountered. In cats, heart rates are often 180 beats/min (3 Hz) or higher. Thus, the minimum frequency a system would have to have for direct measurement of blood pressure in cats is 18 Hz (assuming maximum heart rate of 180 beats/min and a range six times this frequency). The figure in the article that the authors quote as validating their system does show their system to be in the acceptable range; however, the simulated patients had a heart rate of 94 or 118 beats/min. Frequency has also been shown to decrease with time, so that 16.6 Hz has to be considered the best possible scenario, unless all the data were generated on the same day within a few hours.⁴ It is likely the performance of the system was considerably worse than the 16.6 Hz reported. Dynamic response needs to be checked at least once per shift and anytime the system has been opened or a component changed.⁵ This would apply to every patient in this study, which was clearly not done. A 24-gauge dorsal pedal artery catheter could very likely have suffered from attenuation, a problem that causes direct blood pressure measurements to become inaccurate as a result of turbulence.⁶ The small catheter size, arterial spasm, small artery used, and likelihood that the catheter would have to go around a bend in the tarsal region all make attenuation likely. Placement of a larger catheter in the femoral artery with local anesthetics to minimize vasospasm could have minimized attenuation. There also does not appear to have been much attention to routine flushing; air bubbles are always present, and every effort needs to be taken to minimize these (it is usually not possible to completely eliminate them). Using only the flush device on the catheter has been shown to be inadequate in clearing bubbles and avoiding errors.⁴

I realize there are limitations to what can be done in client-owned animals; however, the limitations in this study make any conclusions impossible. The gold standard used in this study was incapable of recording blood pressures accurately.

Anthony P Carr, Dr med vet, dacvim

Department of Small Animal

Clinical Sciences

Western College of

Veterinary Medicine

Saskatoon, SK, Canada

The authors respond:

The direct blood pressure measurement system used in this study was both appropriate and valid. Frequency bandwidth requirements, as described by Dr. Carr, were once used to evaluate the dynamic response of catheter-transducer systems; however, these fail to properly characterize second-order systems.¹ Nevertheless, the natural frequency of the catheter-transducer system used in this study was more than six times the mean patient frequency, which satisfies frequency bandwidth requirements.² The suitability of our system for directly measuring blood pressure in cats was demonstrated by the fast flush test, which determines the dynamic response of the catheter-transducer system and has been described in the human^1,3 and veterinary literature.⁴ The fast flush test measures the dynamic response of the instrumentation from the tip of the needle to the transducer and is not influenced by patient factors.^1,3 Although the damping coefficient range for our catheter-transducer system was determined in a dog, it appeared quite adequate for the actual study population.

Dr. Carr also suggests that attenuation effects associated with the 24-gauge catheter used in this study were not properly accounted for and could have influenced our results. A fundamental principal of the fast flush test is that it incorporates the entire blood pressure monitoring system from the tip of the needle to the transducer.^1,3 Therefore, the attenuation caused by the catheter was included in our model.

Furthermore, Dr. Carr expresses concern that dynamic response of the blood pressure measurement system can change over time and that reused equipment could have a dynamic response that was less than we reported. We agree. As stated in our report, a new catheter, pressure transducer, and pressure line set were used for each patient.

Dr. Carr states, “There also does not appear to have been much attention to routine flushing; air bubbles are always present….” We refer readers to the materials and methods section, which clearly states, “The direct blood pressure monitoring system was periodically flushed to prevent clots and to remove air bubbles that could have changed the damping coefficient of the system.”

While we welcome discourse over the methods employed in this study, we believe that Dr. Carr has demonstrated inattention to critical details presented in the manuscript. In addition, we are curious about Dr. Carr's association with a veterinary oscillometric blood pressure manufacturer, and we believe that the details of this association should have been clearly disclosed to readers.

Mark J. Acierno, mba, dvm, dacvim

Diana Seaton, dvm

Anderson da Cunha, dvm, dacva

Department of Veterinary

Clinical Sciences

School of Veterinary Medicine

Louisiana State University

Baton Rouge, La

Mark A. Mitchell, dvm, phd

Department of Veterinary

Clinical Medicine

College of Veterinary Medicine

University of Illinois

Urbana, Ill

Thoughts on the threat of Ehrlichia ruminantium infection

The reference point article “Recognition of the threat of Ehrlichia ruminantium infection in domestic and wild ruminants in the continental United States” by Dr. Kasari et al¹ provides an excellent review of a tick-borne disease that, if introduced to the United States, would threaten livestock and wildlife in North America. I would like to add one clarification to this review. The authors state, “Calves, kids, and lambs also have natural resistance against heartwater during the neonatal period, and resistance appears to be unrelated to the immune status of the respective dam.” This statement is based on earlier work by DuPlessis and Malan² and Neitz and Alexander.³ In a study by Deem et al,⁴ it was found that immunity to heartwater was present up to six to nine weeks after birth in calves born in heartwater-endemic areas, was not entirely innate, and was influenced by extraneous factors, including colostrum intake. These findings extended the four-week period that innate calfhood immunity was believed to last and challenged the belief that calfhood immunity was innate and not influenced by the dam's previous E ruminantium exposure.⁵ This study is important in terms of the epidemiology and control of heartwater, especially in endemic regions. The beneficial qualities of colostrum are directly related to the dam's previous exposure to E ruminantium ⁴ Thus, the best control methods in heartwater-endemic areas are those that ensure continual exposure to E ruminantium (eg, minimal strategic acaracide applications).⁶ Immune resistance in the dams would then be passively transferred to their offspring through colostrum-derived E ruminantium-specific immune factors.⁴ Additionally, if vaccination is used on calves born to heartwater-naïve dams, it would appear that these calves may not have as great a resistance to clinical infection as previously believed.⁴

As stated by the authors, if E ruminantium were introduced to the US mainland, domestic and wild ruminants would be most at risk to develop heartwater disease.¹ I applaud the authors for this excellent review and would second the recommendation that all practicing veterinarians in North America become familiar with this important foreign animal disease.

Sharon L. Deem, dvm, phd, daczm

St Louis Zoo WildCare Institute

St Louis, Mo

The author responds:

The authors thank Dr. Deem for her kind words about our review article on heartwater and for echoing our position that all practicing veterinarians in North America should become familiar with this important foreign animal disease. We would also like to thank Dr. Deem for her clarifying remarks about calfhood immunity to this disease. She provides evidence that immunity can last several weeks longer than reported in this review. The extended period of immunity is due, in part, to passive immunity gained from ingesting colostrum that contains Ehrlichia ruminantium-specific antibodies produced by dams with previous exposure to this disease agent. It is hoped that veterinary practitioners who read our review article on heartwater will incorporate this additional information into their knowledge base for this disease.

Thomas R. Kasari, dvm, mvsc, dacvim, dacvpm

National Surveillance Unit

Centers for Epidemiology

and Animal Health

Veterinary Services, APHIS, USDA

Fort Collins, Colo

More on the importance of diversity in veterinary medicine

The Association of American Veterinary Medical Colleges (AAVMC) wishes to comment on a letter published in the September 15, 2010, issue of JAVMA¹ that raised questions concerning the necessity of and strategies to promote diversity in the veterinary profession. We welcome the opportunity to tackle such important questions.

To advance veterinary medical education and ensure a strong future for the US veterinary medical workforce, the AAVMC has assigned a high priority to working towards a more diverse profession by focusing efforts to increase enrollment of students and recruitment of faculty from underrepresented populations. The US Census Bureau reports that the racial and ethnic population demographics of the United States are changing so rapidly that by 2050, individuals who identify themselves as white or Caucasian will no longer make up the racial majority in this country. Pet ownership is changing as well, as is the historical assumptions about who owns pets, how their medical care is managed, and how the relationships are presented. Yet, veterinary medicine remains one of the least diverse professions in the United States. We believe that a diverse workforce will be much better positioned to meet the evolving needs of society.

Our graduates are serving multiple populations with competence and professionalism. Data from other professions and industry, however, clearly show that historically, minorities have been and continue to be underserved in receiving care and services, resulting in negative health outcomes and health disparities, and that increasing diversity through the delivery of care and services makes the greatest difference in closing these gaps. Although there is a dearth of studies in this area for the field of veterinary medicine, there is every reason to suggest that these findings would be applicable to the US pet- and animal-owning population. Therefore, we believe that a veterinary education must include lessons on self-awareness, basic cultural acuity, and the impact that biases can have on providing quality services and running optimally successful practices.

Diversity can no longer be dismissed as a “politically correct” endeavor of the veterinary medical profession. Improving our diversity is essential to the profession's long-term success and sustainability. As educators, we are committed to graduating veterinarians who are well positioned to contribute to the strength of the profession medically, socially, and economically. These principles are central to the oath taken by all veterinarians at graduation in the United States. We applaud the AVMA, which under the leadership of Dr. Larry Corry, immediate past president of the AVMA, and Dr. Larry Kornegay, president of the AVMA, has provided increased attention to and leadership of these efforts. We invite everyone in the profession to join us in this endeavor.

Willie Reed, dvm, phd

Dean, School of Veterinary Medicine

Purdue University

West Lafayette, Ind

President, AAVMC

Warwick Arden, bvsc, phd

Interim Provost, North Carolina

State University

Raleigh, NC

Past-President, AAVMC

Gerhardt Schurig, dvm, phd

Dean, Virginia-Maryland Regional

College of Veterinary Medicine

Virginia Tech

Blacksburg, Va

President-Elect, AAVMC

An experience in removal of a foreign body from the trachea

I read with great interest the article “Use of a unique method for removal of a foreign body from the trachea of a cat”¹ in the September 15, 2010, issue of JAVMA and would like to make some comments.

I graduated in 1949 and spent my career in small animal practice. The instruments described in this article were not available or had not even been developed during my practice days. Sometimes common sense outweighs sophistication.

One Sunday, a good client called to have a Shetland Sheepdog examined because of respiratory distress. Radiography revealed a piece of gravel about the size of a large pea located in the distal part of the trachea.

Once anesthetized, the dog was placed on the surgical table in dorsal recombency with the rear legs secured with ropes and the table was tilted with the dog's head down to about a 65° angle. A mouth speculum was used to hold the mouth open, and the owner pulled the dog's tongue out while I compressed the sides of the dog's thorax. The piece of gravel fell to the floor, much to the relief of the owner.

I suspect that most veterinarians don't have an over-the-wire balloon catheter or access to fluoroscopy. In my case, gravity and compression of the thoracic wall resulted in a similar successful outcome.

Donald D. Reeser, dvm

Kernersville, NC

Implementation required to improve the profession's future

The latest in a decades-long series of self-studies of the veterinary profession, the North American Veterinary Medical Education Consortium (NAVMEC)¹ recently completed three national conferences. Attendees examined the essential attributes of veterinarians and studied various models of the veterinary curriculum that might enable the profession to adapt more nimbly to the changing needs of 21st century society. What should we expect from NAVMEC? Are we prepared to accept its recommendations prima facie?

The ability to self-criticize—to examine ourselves reflectively, as if through the eyes and ears of others—is a rare talent. The Scottish poet Robert Burns once mused, “…to see ourselves as others see us…would from many a blunder free us, and foolish notion ” Introspection is not science; nevertheless, we use it as the basis of strategic planning.

In the excellent book A Sense of Urgency, renowned Harvard business professor John Kotter² states that more than 70% of all organizations fail to implement critically needed changes in their operations. The reasons are complacency (lack of urgency), fear of change, and narrow vision, not systemic structural problems or external obstacles. Seventy percent is a shocking statistic, and it seems that veterinary medicine is a part of it. Kotter distinguishes between true urgency and false urgency. True urgency comes from skilled self-examination, careful selection of top-priority issues, and unequivocal focus on new opportunities. False urgency is unproductive behavior that stems from lack of introspection, anxiety from failure to discard clutter (unimportant topics), and inabilty to recognize opportunities and hazards. Veterinary medicine's consistent inability to adopt previous self-studies^3,4 belongs in the latter category of urgency. As Kotter says, “…run-run, meet-meet, talktalk, defend-defend, and go home exhausted.” (To which I would add, write-write, report-report, recommend-recommend, and go home confused and frustrated.) Activity is not the same as productivity. And all too often, publishing a report is proclaimed as “mission accomplished”; everyone heaves a sigh of relief, and there is little further action. The report seems more important than the system it was intended to improve.

The NAVMEC's nine-member board of directors was chosen wisely to include representation from the major national veterinary groups. I have every reason to expect the board to deliver a well-balanced report that includes important recommendations and implementation strategies. The next step will be for the Association of American Veterinary Medical Colleges to publish and promote the findings. However, the actual implementation is up to us. Whom shall we trust to get the job done? And who is prepared to lead? Without leadership, consensus, and concerted efforts, especially among deans and college faculties, once again little will happen.

It is obvious that we have to prepare ourselves well for the future. Therefore, we must honor the NAVMEC board's opinions and recommendations. There is only one thing guaranteed in this exercise: if we fail, we are in trouble and society will not bail us out.

“No one can guarantee success…, but only deserve it.”

—Winston S. Churchill

Peter Eyre, dvm&s, bsc, bvms, phd

Professor and Dean Emeritus

Virginia-Maryland Reginal

College of Veterinary Medicine

Virginia Tech

Blacksburg, Va