Cardiopulmonary, blood and peritoneal fluid alterations associated with abdominal insufflation of carbon dioxide in standing horses

Pathophysiology of intraabdominal hypertension and abdominal compartment syndrome and relevance to veterinary critical care

BACKGROUND

Increased intraabdominal pressure, termed intraabdominal hypertension (IAH), is reported as an independent cause of morbidity and mortality in the human ICU but, until recently, has been rarely described in veterinary species outside of experimental models. Failure to identify severe IAH leads to organ dysfunction, termed abdominal compartment syndrome, and rapidly becomes fatal without therapeutic intervention. Although the veterinary community has been slow to address the concept of IAH and associated comorbidities, recent companion and large animal case series and experimental studies suggest IAH may also be common in veterinary species and correlates well with risk factors and grading systems already described in the human literature.

PATHOPHYSIOLOGY

Increasing abdominal pressures exert deleterious local effects through visceral ischemia and reperfusion injury as well as systemic effects on the cardiovascular, pulmonary, renal, and central nervous systems. Even mild grades of IAH increase systemic vascular resistance, impede venous return, increase pulmonary wedge pressure, and decrease pulmonary function. More severe grades cause azotemia, oliguria, decreased coronary blood flow, hypoxia, increased intracranial pressure, and death.

IMPORTANCE

Many of the common diseases in veterinary patients are associated with IAH, including gastric dilatation-volvulus, colon volvulus, closed pyometra, hemoperitoneum, ascites, uroperitoneum, and hydrops. Monitoring of the veterinary patient is difficult, but several experimental studies validate both the presence of IAH and the ability to monitor abdominal pressures in large and small animal species. Moreover, prompt recognition of IAH and subsequent treatment is feasible in the veterinary ICU.

KEY POINTS

Increasing abdominal pressures exert deleterious local effects through visceral ischemia and reperfusion injury as well as systemic effects on the cardiovascular, pulmonary, renal, and central nervous systems. Increases in central venous pressure, systemic vascular resistance, pulmonary wedge pressure, and a decreased cardiac output by way of both decreased preload and increased afterload have been documented as a result of intraabdominal hypertension (IAH). Direct diagnosis of IAH is achieved by blind or ultrasound-guided abdominal needle puncture attached to a water manometer or direct pressure monitoring transducer. Transvesicular measurement of intraabdominal pressure (IAP) is relatively noninvasive, and many patients that would benefit from rapid diagnosis of IAH and abdominal compartment syndrome already have indwelling bladder catheters. Recommendations for interventions are based on the assigned grade of IAH (mild, moderate, severe).

KEY POINTS

If IAH is strongly suspected or diagnosed, abdominal wall compliance may be improved through judicious use of neuromuscular blockers and sedation. Decompression, either minimally invasive or surgical, is absolutely recommended for IAPs consistently above 20 mm Hg, especially in the presence of signs attributed to secondary organ dysfunction.

Evaluation of the effects of medial saphenous venous pressures as an indirect method of measurement of intra-abdominal pressures in the horse

OBJECTIVE

To evaluate the effect of changes in intra-abdominal pressure (IAP) on medial saphenous venous pressure (MSVP) and hemodynamics in normal horses.

DESIGN

Experimental, in-vivo study.

SETTING

University Teaching Hospital.

ANIMALS

Convenience sample of 7 mixed breed horses; 5 geldings, and 2 mares.

INTERVENTIONS

Pneumoperitoneum was induced in horses under standing sedation with carbon dioxide gas using a laparoscopic insufflator for a total of 60 minutes to simulate clinical elevation in IAP. Pressure was increased stepwise to 20 mm Hg over 30 minutes, and maintained at that pressure for 30 minutes to evaluate the effect of sustained intra-abdominal hypertension. The MSVP and vital parameters were recorded, along with direct arterial blood pressure from the transverse facial artery.

MEASUREMENTS AND MAIN RESULTS

As IAP increased, MSVP increased in a stepwise manner, in concert with changes in IAP. The consistency in measurement between MSVP and IAP was high (intraclass correlation coefficient = 0.92; P < 0.001) and repeated measures correlation was excellent (r = 0.98; P < 0.001). Heart rate was unchanged over the course of the experiment (P = 0.09), however, respiratory rate increased with increasing IAP (P < 0.001). Arterial blood pressure also increased with insufflation (P < 0.001), with a significant difference at an IAP of 15 mm Hg (P = 0.04).

CONCLUSIONS

This report provides preliminary data demonstrating a strong correlation between equine MSVP and changes in IAP, similar to that observed in other species. Further investigations are needed to evaluate this relationship, and to confirm these results in clinical patients.

Nephrosplenic Space Ablation in Horses After Homologous Pericardium Implant Using a Laparoscopic Stapler

This study aimed to describe and evaluate a laparoscopic technique to promote nephrosplenic space ablation in horses using a homologous pericardium implant, preserved in 98% glycerin and fixed using laparoscopic polydioxanone staples. In this experimental study, six Arabian horses without previous related abdominal diseases were used. The surgical procedures were performed in the standing position under sedation with alpha-2 agonists and opioids, associated with local infiltration of the local anesthetic in the portal sites. The horses were restrained in a stock, and the left flanks were clipped and aseptically prepared. Three portals were created on the left flank, and the homologous pericardium implant, measuring 10 × 5 cm, was introduced into the abdominal cavity covering the nephrosplenic space, positioned between the dorsal border of the spleen and perirenal fascia, fixed with polydioxanone staples using a laparoscopic stapler. Physical examination and blood and peritoneal fluid sample collection were performed on days 0, 1, 3, 7, 14, 30, and 60 of the postoperative period, and an exploratory laparoscopy was performed on day 60 to assess the effectiveness of the technique and eventual complications. There were no difficulties or significant complications during the surgical procedure, and the total average time to perform was 49.83 minutes (±10.19). In the postoperative period, there was a significant increase (P < .05) in the plasma fibrinogen concentration on days 7 and 14 compared with the preoperative moment. The total nucleated cell count in the peritoneal fluid increased (P < .05) on days 1, 3, 7, 14, and 30. After 60 days of the surgical procedure, the physical examination and laboratory data were within the normal range. Exploratory laparoscopy performed on day 60 revealed complete occlusion of the nephrosplenic space, and it was not possible to differentiate the pericardium implant from the scar tissue, not even in the histological evaluation performed on the collected samples. In two horses, omentum adhesion was observed in the region where the implant was fixed, and in two others, a synechia was observed between the implant area and mesocolon without association with clinical complications. The animals were followed up for 36 months at surgery, and no colic signs were observed along this period. It was concluded that the technique of ablation of the nephrosplenic space, using homologous pericardium preserved in 98% glycerin, fixed by polydioxanone staples by laparoscopy, was simple to perform, effective, and free of clinical complications during the period of evaluation, and its use may be indicated as a surgical option in clinical cases of horses with recurrent nephrosplenic entrapment.

Evaluation of the effects of intraabdominal hypertension on equine central venous pressure

OBJECTIVE

To evaluate the effect of changes in intraabdominal pressure (IAP) on central venous pressure (CVP) in normal horses.

DESIGN

Experimental, in vivo study.

SETTING

University Teaching Hospital.

ANIMALS

Convenience sample of 7 mixed breed horses-5 geldings and 2 mares.

INTERVENTIONS

Pneumoperitoneum was induced in horses under standing sedation with carbon dioxide gas using a laparoscopic insufflator for a total of 60 minutes to simulate clinical elevation in IAP. Pressure was increased stepwise to 20 mm Hg over 30 minutes, and maintained at that pressure for 30 minutes to evaluate the effect of sustained intraabdominal hypertension. CVP was obtained from the cranial vena cava, concurrent with pressure obtained from the peritoneal cavity.

MEASUREMENTS AND MAIN RESULTS

CVP increased as IAP increased up to 12 mm Hg, and declined as IAP increased further. The changes in CVP over time were significantly different (P < 0.03). Repeated measures correlation was positive, and highest, for mean CVP as IAP increased from 0 to 12 mm Hg (r = .70; 95% CI, .43-.85; P < 0.0001). Correlation of mean CVP with insufflation pressure became negative as IAP increased further from 15 to 20 mm Hg (r = -.47; 95% CI, -.66 to -.21; P = 0.0006).

CONCLUSIONS

This report provides preliminary data demonstrating a biphasic trend in equine CVP caused by changes in IAP, similar to that observed in other species. Further investigations are needed to evaluate this trend and to confirm these results in clinical patients.

Successful laparoscope-assisted orchiectomy in three cryptorchid sheep

Three adult Corriedale cryptorchid sheep were subjected to laparoscope-assisted orchiectomy of the retained testicles. One (n = 2) or both (n = 1) the testicles were missing in their scrotal sac and inguinal regions. Ultrasonography was used to locate the retained testicles and their distance from the abdominal surface. The animals were restrained in dorsal recumbency and Trendlenburg posture under lumbosacral epidural anaesthesia using 2% lignocaine hydrochloride. Two laparoscopic ports were created in the caudal abdomen adjacent to the retained testicles. They were identified by their ovoid shape, white glistening surface (Tunica albuginea) and typical vasculature. Laparoscope-assisted exteriorization of the testicles after enlarging the ports, ligation of their blood supply and resection of the spermatic cord was performed successfully. The scrotal testes in two rams were then subjected to routine Burdizzoo castration. The laparoscopic port sites healed without complications and all the animals continued to do well subsequently. From this case report, it is concluded that in sheep the laparoscopy; a minimally invasive procedure can confirm abdominal retention of testicle/s and may also be used for their retrieval in a single sitting. Although total laparoscopic procedure is expected to reduce the incision size further but requires advanced laparoscopic instruments and expertise.

Laparoscopic evaluation of the small intestine in the standing horse: Technique and effects

OBJECTIVE

To evaluate the feasibility and clinical outcomes after laparoscopic evaluation of the small intestines via laparoscopy.

STUDY DESIGN

Prospective pilot study.

ANIMALS

Healthy adult horses (n = 5).

METHODS

Horses were restrained in standing stocks and received an infusion of detomidine. One port was placed in the left last intercostal space and 3 ports were placed in the right paralumbar fossa. The small intestine was run with atraumatic laparoscopic grasping forceps, from the duodenocolic plica to the ileocecal plica. Postoperative pain was scored every 4 hours for the first 48 hours. Horses were monitored via physical examinations for 2 weeks. Second look laparoscopy was repeated at 2 weeks, to run the small intestine and assess iatrogenic changes. An exploratory celiotomy was performed in 2 horses, 2 months later and long-term follow-up was recorded in 3 horses.

RESULTS

Laparoscopic evaluation of the entire small intestine was successfully completed twice in every horse. This evaluation lasted 39 ± 21.2 minutes (mean ± SD), while total surgery time was 73 ± 34.1 minutes. Postoperative physical examinations remained normal in all horses, and pain scores were scored as mild. The only abnormalities at second look laparoscopy consisted of multifocal petechiae and ecchymoses in all horses, resolved by 2 months in the 2 horses explored via celiotomy. Three horses with long-term follow-up were healthy 8 months after the study.

CONCLUSION

Running the small intestine laparoscopically is a feasible procedure in standing normal horses, and does not cause significant discomfort nor complications.

Laparoscopic cryptorchidectomy in standing bulls

Laparoscopic cryptorchidectomy without insufflation was applied in 10 standing bulls aged 3 to 15 months. Nine bulls were preoperatively pointed out intra-abdominal testes by computed tomography. Preoperative fasting for a minimum of 24 hr provided laparoscopic visualization of intra-abdominal area from the kidney to the inguinal region. Surgical procedure was interrupted by intra-abdominal fat and testis size. It took 0.6 to 1.5 hr in 4 animals weighing 98 to 139 kg, 0.8 to 2.8 hr in 4 animals weighing 170 to 187 kg, and 3 and 4 hr in 2 animals weighing 244 and 300 kg to complete the cryptorchidectomy. In conclusion, standing gasless laparoscopic cryptorchidectomy seems to be most suitable for bulls weighing from 100 to 180 kg.

Effect of laparoscopic abdominal surgery on splanchnic circulation: Historical developments

With the developments in medical technology and increased surgical experience, advanced laparoscopic surgical procedures are performed successfully. Laparoscopic abdominal surgery is one of the best examples of advanced laparoscopic surgery (LS). Today, laparoscopic abdominal surgery in general surgery clinics is the basis of all abdominal surgical interventions. Laparoscopic abdominal surgery is associated with systemic and splanchnic hemodynamic alterations. Inadequate splanchnic perfusion in critically ill patients is associated with increased morbidity and mortality. The underlying pathophysiological mechanisms are still not well understood. With experience and with an increase in the number and diversity of the resulting data, the pathophysiology of laparoscopic abdominal surgery is now better understood. The normal physiology and pathophysiology of local and systemic effects of laparoscopic abdominal surgery is extremely important for safe and effective LS. Future research projects should focus on the interplay between the physiological regulatory mechanisms in the splanchnic circulation (SC), organs, and diseases. In this review, we discuss the effects of laparoscopic abdominal surgery on the SC.

A review of equine laparoscopy

Minimally invasive surgery in the human was first identified in mid 900's. The procedure as is more commonly practiced now was first reported in 1912. There have been many advances and new techniques developed in the past 100 years. Equine laparoscopy, was first reported in the 1970's, and similarly has undergone much transformation in the last 40 years. It is now considered the standard of care in many surgical techniques such as cryptorchidectomy, ovariectomy, nephrosplenic space ablation, standing abdominal exploratory, and many other reproductive surgeries. This manuscript describes the history of minimally invasive surgery, and highlights many of the techniques that are currently performed in equine surgery. Special attention is given to instrumentation, ligating techniques, and the surgical principles of equine minimally invasive surgery.

Compartment syndrome: pathophysiology, clinical presentations, treatment, and prevention in human and veterinary medicine

OBJECTIVE

To review the human and veterinary literature pertaining to all forms of compartment syndrome (CS).

DATA SOURCES

Data sources included scientific reviews and original research publications from the human and veterinary literature.

HUMAN DATA SYNTHESIS

While CS affecting the extremities has been recognized in people for decades, other forms of CS in the abdominal and thoracic cavities are recently gaining more attention. The role of CS in critically ill people is a rapidly growing area of interest. More research on prevention and treatment of CS is being conducted in people because some studies have found mortality rates as high as 80% for those suffering from these conditions.

VETERINARY DATA SYNTHESIS

While a significant amount of experimental studies of CS have been performed on small animals, there is a marked lack of primary veterinary studies. The majority of the veterinary literature includes case reports and series, and many of these studies were published over a decade ago. However, the increased recognition of CS in people has sparked an interest in veterinary critical care medicine and this has been demonstrated by the recent increased evaluation of compartment pressures in veterinary patients.

CONCLUSIONS

CS is a complex clinical condition where increased pressure within a compartment can cause significant adverse effects within the compartment as well as throughout the body. Systemic inflammatory responses and local ischemia-reperfusion elements can contribute to the detrimental effects seen in CS. This cascade of events results in increased mortality rates and contributes to the development of CS elsewhere. A better understanding of CS will help veterinarians improve patient care and outcome. Future studies on incidence, prevention, and treatment of CSs in the critical care patient are needed in veterinary medicine.

Effect of sedation with detomidine and butorphanol on pulmonary gas exchange in the horse

BACKGROUND

Sedation with alpha2-agonists in the horse is reported to be accompanied by impairment of arterial oxygenation. The present study was undertaken to investigate pulmonary gas exchange using the Multiple Inert Gas Elimination Technique (MIGET), during sedation with the alpha2-agonist detomidine alone and in combination with the opioid butorphanol.

METHODS

Seven Standardbred trotter horses aged 3-7 years and weighing 380-520 kg, were studied. The protocol consisted of three consecutive measurements; in the unsedated horse, after intravenous administration of detomidine (0.02 mg/kg) and after subsequent butorphanol administration (0.025 mg/kg). Pulmonary function and haemodynamic effects were investigated. The distribution of ventilation-perfusion ratios (VA/Q) was estimated with MIGET.

RESULTS

During detomidine sedation, arterial oxygen tension (PaO2) decreased (12.8 +/- 0.7 to 10.8 +/- 1.2 kPa) and arterial carbon dioxide tension (PaCO2) increased (5.9 +/- 0.3 to 6.1 +/- 0.2 kPa) compared to measurements in the unsedated horse. Mismatch between ventilation and perfusion in the lungs was evident, but no increase in intrapulmonary shunt could be detected. Respiratory rate and minute ventilation did not change. Heart rate and cardiac output decreased, while pulmonary and systemic blood pressure and vascular resistance increased. Addition of butorphanol resulted in a significant decrease in ventilation and increase in PaCO2. Alveolar-arterial oxygen content difference P(A-a)O2 remained impaired after butorphanol administration, the VA/Q distribution improved as the decreased ventilation and persistent low blood flow was well matched. Also after subsequent butorphanol no increase in intrapulmonary shunt was evident.

CONCLUSION

The results of the present study suggest that both pulmonary and cardiovascular factors contribute to the impaired pulmonary gas exchange during detomidine and butorphanol sedation in the horse.

Laparoscopic intestinal exploration and full-thickness intestinal biopsy in standing horses: a pilot study

OBJECTIVE

To assess a laparoscopic technique for equine intestinal biopsy.

STUDY DESIGN

Experimental study.

ANIMALS

Seven adult horses.

METHODS

Food but not water was withheld for 36 hours before laparoscopy. In 3 horses (group A) standing, right laparoscopic access to different small intestinal segments was compared with ventral median celiotomy access. Inaccessible segments were identified at necropsy. In 4 horses (group B), the feasibility of obtaining full-thickness duodenal and cecal biopsies and any associated morbidity were evaluated. Biopsy specimens were collected during standing right laparoscopy using a 2-step procedure and intracorporeal suturing technique, and abdominal lavage was performed. Horses were monitored clinically and by abdominal fluid cytology and microbial culture, and repeat laparoscopy was performed on day 6.

RESULTS

Standing right flank laparoscopy provided good observation of small intestinal segments and enabled manipulation of all but 15-20 cm of the duodenum and approximately 40 cm more ileum compared with ventral median celiotomy. Group B horses had no complications, no adhesions, and no bacterial growth from peritoneal fluid samples. None of the horses had signs of abdominal pain.

CONCLUSION

A 2-stage intestinal biopsy technique performed during standing, right flank laparoscopy may be a safe alternative to exploratory celiotomy and biopsy in normal horses.

CLINICAL RELEVANCE

Right flank laparoscopy allows biopsy of intestinal segments including duodenum and 50% more of the ileum than is accessible by ventral median celiotomy. This technique should be evaluated in clinical patients.

Electroencephalographic and electromyographic changes during the use of detomidine and detomidine-butorphanol combination in standing horses

Clinically, the use of detomidine and butorphanol is suitable for sedation and deepening of analgosedation. The aim of our study was to establish the influence of detomidine used alone and a butorphanol-detomidine combination on brain activity and to evaluate and compare brain responses (using electroencephalography, EEG) by recording SEF90 (spectral edge frequency 90%), individual brain wave fractions (beta, alpha, theta and delta) and electromyographic (EMG) changes in the left temporal muscle in standing horses. Ten clinically healthy cold-blooded horses were divided into two groups of five animals each. Group I received detomidine and Group II received detomidine followed by butorphanol 10 min later. SEF90, individual brain wave fractions and EMG were recorded with a pEEG (processed EEG) monitor using computerised processed electroencephalography and electromyography. The present study found that detomidine alone and the detomidine-butorphanol combination significantly reduced SEF90 and EMG, and they caused changes in individual brain wave fractions during sedation and particularly during analgosedation. The EMG results showed that the detomidine-butorphanol combination provided greater and longer muscle relaxation. Our EEG and EMG results confirmed that the detomidine-butorphanol combination is safer and more appropriate for painless and non-painless procedures on standing horses compared to detomidine alone.

Recent advances in equine abdominal surgery

Laparoscopy is a minimally invasive procedure that has applications as a diagnostic, therapeutic and prognostic technique. Specialized equipment is necessary to perform equine laparoscopy, and there is a large range of instruments, both disposable and non-disposable available. Laparoscopic procedures described include ovariectomy, cryptorchidectomy, adhesiolysis and herniorrhaphy. Laparoscopy can be performed in a standing or dorsally recumbent position, depending on surgeon preference, patient status and the procedure to be performed. Stapling equipment is frequently used in gastrointestinal surgery in horses. Advantages include decreased surgical time and a decrease in the risk of contamination. Stapling equipment is often used in creating anastomoses, both in the large and small intestines, as well as in vessel ligation. New surgical techniques intended to decrease adhesion formation include the use of carboxymethylcellulose and bioresorbable patches. Indwelling abdominal drains can be used for peritoneal lavage following surgery and also appear to decrease the risk of adhesion formation. Improvements in post-operative care, including the treatment of post-operative ileus and endotoxaemia can significantly improve the outcome of horses that have undergone surgery for abdominal disorders. Recommendations for the use of prokinetic agents in horses with ileus vary widely. Prokinetic agents include local anaesthetics, macrolide antimicrobials, cholinergic agonists and dopamine antagonists. Endotoxaemia is common in horses following surgery for gastrointestinal disorders. The antibiotic polymyxin B binds to the circulating endotoxin molecule, decreasing its half-life in the intra-vascular space and reducing associated inflammation. This drug appears to be an effective and affordable treatment option for horses with endotoxaemia. The use of specific cyclooxygenase inhibitors in veterinary medicine have been studied recently. Selective cyclooxygenase-2 inhibitors may provide comparable anti-inflammatory and analgesic properties to the non-selective non-steroidal anti-inflammatory drugs. These drugs appear to have similar clinical effectiveness and will hopefully minimize deleterious side effects. The optimal healing of ventral midline incisions in horses is related to many factors including appropriate suture patterns and bite size, in addition to appropriate post-operative exercise recommendations. Recent advances in surgical techniques and post-operative care should decrease the morbidity and mortality associated with abdominal surgery. This article provides an overview of some of these advances.

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