Evaluation of Intraoperative Infusion Solution Using a Complete Anhepatic Model in Baby Pigs

How is depth of anaesthesia assessed in experimental pigs? A scoping review

BACKGROUND

Despite the large number of pigs involved in translational studies, no gold standard depth of anaesthesia indicators are available. We undertook a scoping review to investigate and summarize the evidence that sustains or contradicts the use of depth of anaesthesia indicators in this species.

METHODS

Medline, Embase and CAB abstract were searched up to September 22nd 2022. No limits were set for time, language and study type. Only original articles of in vivo studies using pigs or minipigs undergoing general anaesthesia were included. The depth of anaesthesia indicators reported in the selected papers were divided in two categories: A, indicators purposely investigated as method to assess depth of anaesthesia; B, indicators reported but not investigated as method to assess depth of anaesthesia.

RESULTS

Out of 13792 papers found, 105 were included after the screening process. Category A: 17 depth of anaesthesia indicators were found in 19 papers. Studies were conducted using inhalant anaesthetics as the main anaesthetic agent in the majority of the cases (13/19 = 68.4%), while 3/19 (15.8%) used propofol. The most investigated depth of anaesthesia indicators were bispectral index (8/19 = 42.1%) and spectral edge frequency 95% (5/19 = 26.3%). Contrasting results about the specific usefulness of each depth of anaesthesia indicators were reported. Category B: 23 depth of anaesthesia indicators were found in 92 papers. The most reported depth of anaesthesia indicators were: motor response following a stimulus (37/92 = 40.2%), depth of anaesthesia scores (21/92 = 23.3%), bispectral index (16/92 = 17.8%) and spectral edge frequency 95% (9/92 = 9.8%).

CONCLUSION

Results highlight the lack of scientifically valid and reliable indicators to ensure adequate depth of anaesthesia in pigs.

Usability of the SedLine® electroencephalographic monitor of depth of anaesthesia in pigs: a pilot study

To investigate the usability of the SedLine® monitor in anaesthetized pigs. Five juvenile healthy pigs underwent balanced isoflurane-based general anaesthesia for surgical placement of a subcutaneous jugular venous port. The SedLine® was applied to continuously monitor electroencephalographic (EEG) activity and its modulation during anaesthesia. Computer tomography and magnetic resonance were performed to investigate the relationship between electrodes' positioning and anatomical structures. The pediatric SedLine® EEG-sensor could be easily applied and SedLine®-generated variables collected. An EEG Density Spectral Array (DS) was displayed over the whole procedure. During surgery, the EEG signal was dominated by elevated power in the delta range (0.5-4 Hz), with an underlying broadband signal (where power decreased with increasing frequency). The emergence period was marked by a decrease in delta power, and a more evenly distributed power over the 4-40 Hz frequency range. From incision to end of surgery, mean SedLine®-generated values (± standard deviation) were overall stable [23.0 (± 2.8) Patient State Index (PSI), 1.0% (± 3.8%) Suppression Ratio (SR), 8.8 Hz (± 2.5 Hz) Spectral Edge Frequency 95% (SEF) left, 7.7 Hz (± 2.4 Hz) SEF right], quickly changing during emergence [75.3 (± 11.1) PSI, 0.0 (± 0.0) SR, 12.5 (± 6.6) SEF left 10.4 (± 6.6) SEF right]. Based on the imaging performed, the sensor does not record EEG signals from the same brain areas as in humans. SedLine®-DSA and -generated variables seemed to reflect variations in depth of anaesthesia in pigs. Further studies are needed to investigate this correlation, as well as to define the species-specific brain structures monitored by the EEG-sensor.

Correlation of Sedline-generated variables and clinical signs with anaesthetic depth in experimental pigs receiving propofol

Most of currently available electroencephalographic (EEG)-based tools to assess depth of anaesthesia have not been studied or have been judged unreliable in pigs. Our primary aim was to investigate the dose-effect relationship between increasing propofol dose and variables generated by the EEG-based depth of anaesthesia monitor Sedline in pigs. A secondary aim was to compare the anaesthetic doses with clinical outcomes commonly used to assess depth of anaesthesia in this species. Sixteen juvenile pigs were included. Propofol infusion was administered at 10 mg kg-1 h-1, increased by 10 mg kg-1 h-1 every 15 minutes, and stopped when an EEG Suppression ratio >80% was reached. Patient state index, suppression ratio, left and right spectral edge frequency 95%, and outcomes from commonly used clinical methods to assess depth of anaesthesia in pigs were recorded. The best pharmacodynamic model was assessed for Patient state index, suppression ratio, left and right spectral edge frequency 95% in response to propofol administration. The decrease of Patient state index best fitted to an inhibitory double-sigmoid model (including a plateau phase). The increase of suppression ratio fitted a typical sigmoid Emax model. No relevant relationship could be identified between spectral edge frequency 95% values and propofol administration. A large variability in clinical outcomes was observed among pigs, such that they did not provide a reliable evaluation of propofol dose. The relationship between propofol dose and Patient state index/suppression ratio described in the present study can be used for prediction in future investigations. The evaluation of depth of anaesthesia based on common clinical outcomes was not reliable.

Influence of acetate- vs. lactate-containing fluid bolus therapy on acid-base status, electrolytes, and plasma lactate in dogs

Objective

Acetate- and lactate-containing fluids influence the acid-base and electrolyte status. This prospective, randomized, clinical study compared two balanced crystalloid solutions regarding their influence on acid-base status, electrolytes, and lactate values, when given to dogs as a resuscitation bolus of 30 mL/kg.

Material and methods

One hundred client-owned dogs presenting to the emergency service with signs of fluid deficits were randomly assigned to receive an intravenous bolus of 30 mL/kg of either a lactate- (LAC), or an acetate-containing solution (ACET). Before and after the bolus, vital parameters were assessed, and a venous blood gas analysis was performed.

Results

Both solutions performed equally well in decreasing the heart rate (ACET: −10 ± 27 bpm, LAC: −12 ± 30 bpm; p = 0.737). The acetate-containing solution caused a significant decrease in plasma lactate levels (p = 0.016), anion gap (p < 0.001), and potassium (p < 0.001), and a significant increase in chloride (p < 0.001), and ionized calcium (p = 0.014). The lactate-containing solution caused a significant decrease in anion gap (p < 0.001), sodium (p = 0.016), and potassium (p = 0.001), and a significant increase in chloride (p < 0.001). ACET causes a stronger decrease in plasma lactate (p = 0.015), sodium (p = 0.039), potassium (p = 0.006), and an increase in chloride (p < 0.001), and ionized calcium (p = 0.016) compared to LAC.

Conclusion

Both solutions caused mild changes in electrolyte concentrations and had minor influence on acid-base status when used for bolus therapy in dogs with fluid deficits. Further studies are needed to evaluate their influence on acid-base status, lactate, and electrolytes when used in larger volumes and for a longer time span.

Development of a Simple and Active Shunt System in the Anhepatic Stage for Surgical Training of Orthotopic Liver Transplantation

BACKGROUND

A pig model has been commonly used for technical training for clinical liver transplantation (LT). However, as the healthy pigs have no shunt bypassing the portal vein (PV), it is necessary to complete LT within 30 minutes after shutting off the PV flow. While a model that uses an ex vivo shunt system has been used to alleviate the constraints of the anhepatic phase, it has been often difficult to keep sufficient blood flow rate and prevent the intestinal congestion because the blood vessels were occluded easily with the suction pressure by using the conventional shunt system.

METHODS

We designed a portable shunt system and a novel connector that can prevent the blood vessel from occluding. The system can separately control the flow rate of PV and inferior vena cava (IVC) and detect whether the blood vessels were occluded. By reducing the solution volume in the circuit, the effected blood loss ex vivo could be minimized. The stability of this system was verified with 15 medical doctors in an advanced medical professional education course.

RESULTS

The system enabled the blood flow to maintain ≥ 20 mL/minute and prevented the intestinal congestion. The perioperative hemodynamics of the recipient were stable without a blood transfusion using 25 to 40 kg pigs. We confirmed that all LT training were completed, even 60 minutes after shutting off the PV flow.

CONCLUSIONS

Our system greatly contributed to training on LT for conducting the survival experiments.

The pig as a model for translational research: overview of porcine animal models at Jichi Medical University

To improve the welfare of experimental animals, investigators seek to respect the 3R principle (Replacement, Reduction, and Refinement). Even when large animal studies are essential before moving to clinical trials, it is important to look for ways to reduce the number of experimental animals used. At the Center for the Development of Advanced Medical Technology, we consider ‘medical’ pigs to be ideal preclinical model systems.

We have been using both wild-type and genetically modified pigs. We began using this approach about 10 years ago with a ‘total pig system’ to model human health and disease for the purposes of both medical skill education and the development of new devices and therapeutic strategies.

At our Center, medical students and residents use pigs to gain experience with surgical skills and train for emergency procedures after appropriate simulation training. Senior clinicians have also used these models to advance the development of innovative tools for endo- and laparoscopic procedures. The Center focuses on translational research for organ transplantation and stem cell therapy. Several pig models have been established for liver, intestine, kidney, pancreas, and lung transplantation. Mesenchymal stromal cells have been established in green fluorescent protein- and red fluorescent protein-transgenic pigs and tested to trans-differentiate organogenesis. A program to establish induced pluripotent stem cells in the pig is ongoing at our Center.

Here, we review our 10 years of activity in this field. Based on our experience in surgical education and research, experimental pigs are valuable models in translational research.

Education and research using experimental pigs in a medical school

Medium-sized animals such as miniature pigs are considered to be important for education and training in medical schools to master the skills required in surgical treatment. Much still remains to be done to establish total management for animal experiments using pigs. Improvement of the effective utilization of pigs is also required from the economical and ethical points of view. We have been providing a support system at a facility for experimental animals in a medical school for 3 years, and herein we introduce our personal experiments as an instructional lecture. Before starting surgical training using live pigs, sufficient education concerning animal ethics and dry laboratory training was completed. Four kinds of miniature pigs have been used as experimental animals; porcine rearing pens have been improved and a postoperative care system has been implemented. Moreover, staff at the center offer a preoperative service of anesthesia for surgical education, training, and research. Chronic experiments have increased to represent 35% and 48% of experiments using pigs in 2003 and 2004, respectively. Experimental pigs have undergone secondary use after being killed to reduce the number of animals used in experiments. Sharing and reuse have allowed effective use of miniature pig tissues and cells for research, and have reduced the number of animals used. We recommend that researchers consider use of our total systems because they can improve the quality of medical education and research and facilitate effective use of tissues and cells by sharing and reuse among different departments.

Naked plasmid DNA transfer to the porcine liver using rapid injection with large volume

The naked plasmid DNA transfer method of rapid injection with large volume has been useful for gene therapy in experimental study. However, only small animals like rodents have usually been reported on. In this study, the authors attempted to transfect naked plasmid DNA to the porcine liver by modified hydrodynamic method. We decided to transfer plasmid DNA to a part of the liver using the angio-catheter to reduce the liver damage. To discern the condition of injection, naked plasmid DNA-encoding green fluorescent protein (GFP) was transferred for use as a marker gene. The GFP gene expression was markedly observed in gene-transferred pig livers. In large animals, not only the naked gene quantity, the solution volume containing the plasmid DNA and the injection speed, but also the additional treatments of the portal vein and the hepatic artery preparation were crucial. We found that the following injection condition were needed: plasmid DNA, 3 mg; the solution volume, 150 ml and the injection speed, 5 ml/s. The portal vein and the hepatic artery were clamped during gene delivery and the blood flow of the portal vein was flushed out using normal saline. Cytotoxic T-lymphocyte antigen 4-immunoglobulin (CTLA4-Ig) gene was used to test for secretory protein. CTLA4-Ig gene was injected with a large volume of solution via the hepatic vein to the left outer lobe of the liver selectively. CTLA4-Ig was detected in the pig blood at a maximum serum level of 161.7 ng/ml 1 day after gene transfer, and the CTLA4-Ig was detected for several weeks. Our new technique of inserting a catheter into only a selected portion of the liver reduced liver toxicity and increased gene transfer efficiency. This is the first report of successful gene transfer, using a hydrodynamic method, to the segmental liver in pigs, and achieved more than enough secretory protein for the clinically therapeutic level in pigs.