Assessment of gut mucosal perfusion and colonic tissue blood flow during abdominal aortic surgery with gastric tonometry and laser Doppler flowmetry

Microcirculation during surgery

Throughout the long history of surgery, there has been great advancement in the hemodynamic management of surgical patients. Traditionally, hemodynamic management has focused on macrocirculatory monitoring and intervention to maintain appropriate oxygen delivery. However, even after optimization of macro-hemodynamic parameters, microcirculatory dysfunction, which is related to higher postoperative complications, occurs in some patients. Although the clinical significance of microcirculatory dysfunction has been well reported, little is known about interventions to recover microcirculation and prevent microcirculatory dysfunction. This may be at least partly caused by the fact that the feasibility of monitoring tools to evaluate microcirculation is still insufficient for use in routine clinical practice. However, considering recent advancements in these research fields, with more popular use of microcirculation monitoring and more clinical trials, clinicians may better understand and manage microcirculation in surgical patients in the future. In this review, we describe currently available methods for microcirculatory evaluation. The current knowledge on the clinical relevance of microcirculatory alterations has been summarized based on previous studies in various clinical settings. In the latter part, pharmacological and clinical interventions to improve or restore microcirculation are also presented.

The use of pulse pressure variation for predicting impairment of microcirculatory blood flow

Dynamic parameters of preload have been widely recommended to guide fluid therapy based on the principle of fluid responsiveness and with regard to cardiac output. An equally important aspect is however to also avoid volume-overload. This accounts particularly when capillary leakage is present and volume-overload will promote impairment of microcirculatory blood flow. The aim of this study was to evaluate, whether an impairment of intestinal microcirculation caused by volume-load potentially can be predicted using pulse pressure variation in an experimental model of ischemia/reperfusion injury. The study was designed as a prospective explorative large animal pilot study. The study was performed in 8 anesthetized domestic pigs (German landrace). Ischemia/reperfusion was induced during aortic surgery. 6 h after ischemia/reperfusion-injury measurements were performed during 4 consecutive volume-loading-steps, each consisting of 6 ml kg⁻¹ bodyweight⁻¹. Mean microcirculatory blood flow (mean Flux) of the ileum was measured using direct laser-speckle-contrast-imaging. Receiver operating characteristic analysis was performed to determine the ability of pulse pressure variation to predict a decrease in microcirculation. A reduction of ≥ 10% mean Flux was considered a relevant decrease. After ischemia–reperfusion, volume-loading-steps led to a significant increase of cardiac output as well as mean arterial pressure, while pulse pressure variation and mean Flux were significantly reduced (Pairwise comparison ischemia/reperfusion-injury vs. volume loading step no. 4): cardiac output (l min⁻¹) 1.68 (1.02–2.35) versus 2.84 (2.15–3.53), p = 0.002, mean arterial pressure (mmHg) 29.89 (21.65–38.12) versus 52.34 (43.55–61.14), p < 0.001, pulse pressure variation (%) 24.84 (17.45–32.22) versus 9.59 (1.68–17.49), p = 0.004, mean Flux (p.u.) 414.95 (295.18–534.72) versus 327.21 (206.95–447.48), p = 0.006. Receiver operating characteristic analysis revealed an area under the curve of 0.88 (CI 95% 0.73–1.00; p value < 0.001) for pulse pressure variation for predicting a decrease of microcirculatory blood flow. The results of our study show that pulse pressure variation does have the potential to predict decreases of intestinal microcirculatory blood flow due to volume-load after ischemia/reperfusion-injury. This should encourage further translational research and might help to prevent microcirculatory impairment due to excessive fluid resuscitation and to guide fluid therapy in the future.

Effects of Thoracic Epidural Anaesthesia on the Serosal Microcirculation of the Human Small Intestine

BACKGROUND

The effect of thoracic epidural analgesia (TEA) on splanchnic blood flow during abdominal surgery remains unclear. The purpose of this study was to examine whether the hemodynamic effects of TEA resulted in microcirculatory alterations to the intestinal serosa, which was visualized using incident dark-field (IDF) videomicroscopy.

METHODS

An observational cohort study was performed. In 18 patients, the microcirculation of the intestinal serosa was visualized with IDF. Microcirculatory and hemodynamic measurements were performed prior to (T1) and after administering a bolus of levobupivacaine (T2). If correction of blood pressure was indicated, a third measurement was performed (T3). The following microcirculatory parameters were calculated: microvascular flow index, proportion of perfused vessels, perfused vessel density and total vessel density. Data are presented as median [IQR].

RESULTS

Mean arterial pressure decreased from 73 mmHg (68-83) at T1 to 63 mmHg (±11) at T2 (p = 0.001) with a systolic blood pressure of 114 mmHg (98-128) and 87 (81-97), respectively (p = 0.001). The microcirculatory parameters of the bowel serosa, however, were unaltered. In seven patients, blood pressure was corrected to baseline values from a MAP of 56 mmHg (55-57), while microcirculatory parameters remained constant.

CONCLUSION

We examined the effects of TEA on the intestinal serosal microcirculation during abdominal surgery using IDF imaging for the first time in patients. Regardless of a marked decrease in hemodynamics, microcirculatory parameters of the bowel serosa were not significantly affected.

TRIAL REGISTRY NUMBER

ClinicalTrials.gov identifier NCT02688946.

Can sidestream dark field (SDF) imaging identify subtle microvascular changes of the bowel during colorectal surgery?

BACKGROUND

Recognition of a non-viable bowel during colorectal surgery is a challenging task for surgeons. Identifying the turning point in serosal microcirculatory deterioration leading up to a non-viable bowel is crucial. The aim of the present study was to determine whether sidestream darkfield (SDF) imaging can detect subtle changes in serosal microcirculation of the sigmoid after vascular transection during colorectal surgery.

METHODS

A prospective observational clinical study was performed at a single medical centre. All eligible participants underwent laparoscopic sigmoid resection and measurements were taken during the extra-abdominal phase. Microcirculation was measured at the transected bowel and 20 cm proximal to this point. Microcirculatory parameters such as Microvascular Flow Index (MFI), proportion of perfused vessels (PPV), perfused vessel density (PVD), total vessel density (TVD) and the Heterogeneity Index were determined. Data are presented as median (interquartile range) or mean ± standard deviation.

RESULTS

A total of 60 SDF images were acquired for 10 patients. Perfusion parameters and perfused vessel density were significantly lower at the transected bowel compared with the non-transected measurements [MFI 2.29 (1.96-2.63) vs 2.96 (2.73-3.00), p = 0.007; PPV 74% (55-83) vs 94% (86-97), p = 0.007; and PVD 7.61 ± 2.99 mm/mm² versus 10.67 ± 1.48 mm/mm², p = 0.009]. Total vessel density was similar between the measurement locations.

CONCLUSIONS

SDF imaging can identify changes of the bowel serosal microcirculation. Significantly lower serosal microcirculatory parameters of the vascular transected bowel was seen compared with the non-transected bowel. The ability of SDF imaging to detect subtle differences holds promise for future research on microvascular cut-off values leading to a non-viable bowel.

Circulating intestinal fatty acid-binding protein as an early marker of intestinal necrosis after aortic surgery: a prospective observational cohort study

OBJECTIVE

This study evaluated the usefulness of plasma intestinal fatty-acid binding protein (IFABP) levels in the early identification of intestinal necrosis (IN) in patients undergoing different types of aortic surgery.

BACKGROUND

Intestinal compromise greatly contributes to postoperative adverse outcome. IN is the most detrimental form of intestinal compromise and is notoriously difficult to diagnose. IFABP is a small protein exclusively expressed by mature enterocytes and a promising marker of intestinal damage.

METHODS

Plasma IFABP concentrations were measured in blood samples taken perioperatively from 55 patients undergoing open thoracic or thoracoabdominal aneurysm repair [OR-TAA(A)], 25 patients undergoing conventional open abdominal aneurysm repair (OR-abdominal aortic aneurysm [AAA]), and 16 patients undergoing endovascular aneurysm repair (EVAR). Data were compared with perioperative changes in arterial pH and serum lactate levels.

RESULTS

IFABP levels increased in all patients undergoing OR-TAA(A) and OR-AAA reaching peak levels shortly after surgery; 281 ± 33 to 2,298 ± 490 pg/mL (P < 0.001) and 187 ± 31 to 641 ± 176 pg/mL (P < 0.05) respectively. IFABP levels were significantly higher in patients undergoing OR-TAA(A) (P < 0.001). IFABP levels in EVAR patients remained at baseline concentrations throughout the study. Four patients [2 OR-AAA, 2 OR-TAA(A)] developed fatal postoperative intestinal ischemia on day 2 or 3. High levels of plasma IFABP at the end of surgery had 100% sensitivity and 98.1% specificity for the identification of patients developing IN. In OR-AAA patients, arterial pH and lactate levels were of additional discriminating value. Complete discrimination between patients with and without IN using plasma IFABP could be made on the first postoperative day.

CONCLUSIONS

Analysis of plasma IFABP levels is of additional value to other current plasma markers in the diagnosis of IN, and it enables early identification of patients with IN after aortic surgery days before clinical diagnosis.

Descending aortic blood flow during aortic cross-clamp indicates postoperative splanchnic perfusion and gastrointestinal function in patients undergoing aortic reconstruction

BACKGROUND

The purpose of this observational study was to investigate the relationship between splanchnic and renal blood flow during infrarenal aortic cross-clamp (XC) and postoperative gastrointestinal perfusion and function.

METHODS

Descending aortic blood flow (DABF) was continuously monitored with an oesophageal Doppler monitor (Cardio-Q, Deltex Ltd, Chichester, UK) in 31 patients undergoing elective abdominal aortic aneurysm repair. Cardiac output (CO) was determined by indocyanine green dilution before, during, and after XC. Perioperative gastrointestinal perfusion was assessed by gastric intramucosal pH (pHi, Tonocap, GE Healthcare, Helsinki, Finland). Postoperative gastrointestinal recovery was assessed by the number of postoperative days until the patient successfully resumed solid food intake. The relationship between the mean DABF during XC and gastric pHi after XC release and postoperative gastrointestinal recovery was analysed with Spearman's correlation coefficient.

RESULTS

accounted for ∼ 55% of CO during XC and significantly decreased during XC, despite arterial pressure remaining within an optimal range. There were two distinct relationships between DABF during XC and gastric pHi after XC release. Gastric pHi steeply and linearly declined when indexed DABF was below 0.82 litre min(-1) m(-2). Above this critical value, there was no linear relationship between them. The duration of postoperative gastrointestinal dysfunction was inversely correlated with the mean DABF during XC. The best cut-off value of the mean indexed DABF during XC to prevent prolonged gastrointestinal dysfunction was 1.2 litre min(-1) m(-2).

CONCLUSIONS

Decreased DABF during XC associates splanchnic hypoperfusion after XC release and delayed recovery of gastrointestinal function.

How to assess intestinal viability during surgery: A review of techniques

Objective and quantitative intraoperative methods of bowel viability assessment are essential in gastrointestinal surgery. Exact determination of the borderline of the viable bowel with the help of an objective test could result in a decrease of postoperative ischemic complications. An accurate, reproducible and cost effective method is desirable in every operating theater dealing with abdominal operations. Numerous techniques assessing various parameters of intestinal viability are described by the studies. However, there is no consensus about their clinical use. To evaluate the available methods, a systematic search of the English literature was performed. Virtues and drawbacks of the techniques and possibilities of clinical application are reviewed. Valuable parameters related to postoperative intestinal anastomotic or stoma complications are analyzed. Important issues in the measurement and interpretation of bowel viability are discussed. To date, only a few methods are applicable in surgical practice. Further studies are needed to determine the limiting values of intestinal tissue oxygenation and flow indicative of ischemic complications and to standardize the methods.

Retroperitoneal approach to abdominal aortic aneurysm repair preserves splanchnic perfusion as measured by gastric tonometry

BACKGROUND

We investigated if minimizing bowel manipulation and mesenteric traction using the retroperitoneal approach in open abdominal aortic aneurysm (AAA) repair preserves splanchnic perfusion, as measured by gastric tonometry, and reduces the systemic inflammatory response and dysfunction of the various organs.

METHODS

Patients undergoing elective AAA repair were randomized into three groups. Group I had repair via the retroperitoneal approach, while groups II and III were repaired via the transperitoneal approach with the bowel packed within the peritoneal cavity or exteriorized in a bowel bag, respectively. A tonometer was used to measure gastric intramucosal pH (pHi), as an indicator of splanchnic perfusion, just prior to aortic clamping, during clamping, and at 0.5, 1, 2, 4, 6, and 12 hr after clamp release. Multiorgan dysfunction syndrome (MODS) and systemic inflammatory response syndrome (SIRS) scores were calculated and systemic interleukins (IL-6 and IL-10) measured at predetermined intervals.

RESULTS

Thirty-four patients were successfully randomized. The gastric pHi was significantly lower in group II (n=12) and group III (n=11) compared to group I (n=11) during aortic clamping and immediately after clamp release (p<0.05). The aortic clamp time, blood loss, MODS and SIRS scores, and systemic cytokine response were similar in all three groups. When the three groups were combined, there were significant positive correlations between the operation time, aortic clamp time, and amount of blood lost and transfused with plasma IL-6 levels and MODS score on the first postoperative day.

CONCLUSION

The retroperitoneal approach for open AAA repair is associated with gastric tonometric evidence of better splanchnic perfusion compared to the transperitoneal approach.

Effects of levosimendan on indocyanine green plasma disappearance rate and the gastric mucosal-arterial pCO2 gradient in abdominal aortic aneurysm surgery

BACKGROUND

Levosimendan has a dual mechanism of action: it improves myocardial contractility and causes vasodilatation without increasing myocardial oxygen demand. In a laboratory setting, it selectively increases gastric mucosal oxygenation in particular and splanchnic perfusion in general. The aim of our study was to describe the effects of levosimendan on systemic and splanchnic circulation during and after abdominal aortic surgery.

METHODS

Twenty abdominal aortic aneurysm surgery patients were randomized to receive either levosimendan (n=10) or placebo (n=10) in a double-blinded manner. Both the mode of anaesthesia and the surgical procedures were performed according to the local guidelines. Automatic gas tonometry was used to measure the gastric mucosal partial pressure of carbon dioxide. Systemic indocyanine green clearance plasma disappearance rate (ICG-PDR) was used to estimate the total splanchnic blood flow.

RESULTS

The immediate post-operative recovery was uneventful in the two groups with a comparable, overnight length of stay in the intensive care unit. Cumulative doses of additional vasoactive drugs were comparable between the groups, with a tendency towards a higher cumulative dose of noradrenaline in the levosimendan group. After aortic clamping, the cardiac index was higher [4(3.8-4.7) l/min/m(2) vs. 2.6(2.3-3.6) l/min/m(2); P<0.05] and the gastric mucosal-arterial pCO(2) gradient was lower in levosimendan-treated patients [0.9(0.6-1.2) kPa vs. 1.7(1.2-2.1) kPa; (P<0.05)]. However, the total splanchnic blood flow, estimated by ICG-PDR, was comparable [29(21-29)% vs. 20(19-25)%; NS]. Organ dysfunction scores (sequential organ dysfunction assessment) were similar between the groups on the fifth post-operative day.

CONCLUSION

Levosimendan favours gastric perfusion but appears not to have a major effect on total splanchnic perfusion in patients undergoing an elective aortic aneurysm operation.

An evaluation of the effect of a gastric ischemia-reperfusion model with laser Doppler blood perfusion imaging

The objectives of this study are to establish a gastric ischemia-reperfusion model and test it using the laser Doppler blood perfusion imaging (LDPI) method and to evaluate the role of the LDPI technique in the measure of gastric blood circulation. The right gastric artery of the rat was clamped for 30 min and then reperfused. The LDPI was used to display the blood circulation of the whole gastric surface during this process. The blood flow perfusion image of the gastric surface was displayed clearly. After the right gastric artery was clamped, the blood flow perfusion on the gastric surface decreased very significantly until the clamp was loosened. Following reperfusion, the blood flow suddenly increased. Within the first 10 min, the blood-flow perfusion exceeded the level before the clamping and then gradually became smooth and steady. The right gastric artery is a main pathway for gastric blood supply. LDPI can display successfully the blood circulation state of the stomach and the course of ischemia-reperfusion of a large area with an image.

Effect of Dansen on gastric mucosal Na+-K+-ATPase activity and gastric transmucosal potential difference during severe intraperitoneal infection in rats

AIM: To investigate the effect of Dansen on gastric mucosal Na⁺-K⁺-ATPase activity and gastric transmucosal potential difference during severe intraperitoneal infection in rats.

METHODS: The intraperitoneal infection rat model was established by cecal ligation and puncture (CLP). Assay of Na⁺-K⁺-ATPase activity in gastric mucosal tissue was conducted by biochemical method. The electric-physiological recorder was used to measure gastric mucosal potential difference.

RESULTS: The activity of Na⁺-K⁺-ATPase was markedly decreased in infected group at 3h after perforation, compared with the control group (P = 0.0 271 < 0.05). There was a minimum of Na⁺-K⁺-ATPase activity at 12h post-perforation in infected group (P = 0.0 062 < 0.01), only about 48.5% matched to the control group. Gastric transmucosal potential difference (GTPD) of infected group decreased significantly as compared with the control group (P = 0.0 253 < 0.05) at 6h after perforation, and rapidly dropped to the lowest at 12 h post-perforation (P = 0.0 025 < 0.01). At 12 h and 24 h after perforation, GTPD was lower in infected group than that in the control group (P = 0.0 293 < 0.05).

CONCLUSION: The reduce of Na⁺-K⁺-ATPase activity may play an important role in gastric mucosal barrier damage following severe abdominal infection induced by CLP, and the application of Dansen in earlier period can prevent the occurrence of stress ulcer.

Renal dysfunction after vascular surgery

PURPOSE OF REVIEW

The purpose of this review is to focus on the static incidence of renal dysfunction, the lack of evidence of benefit of traditional renoprotective strategies, and newer techniques that may provide an insight into the mechanisms of acute perioperative renal injury associated with vascular surgery.

RECENT FINDINGS

Recent studies that have investigated the long-term results of aortic surgery still report a significant incidence of postoperative renal dysfunction. This finding remains consistent in several reports. However, less invasive techniques such as endovascular repair seem to be associated with reduced inflammation and postoperative renal dysfunction. The possible association between genetic heterogeneity and renal dysfunction in vascular surgical patients is an exciting new area of research.

SUMMARY

Renal dysfunction after major vascular surgery remains a significant problem. New insights into the mechanisms of acute renal injury and less invasive techniques of vascular repair may help reduce the incidence of renal dysfunction in this patient population. The lack of a truly 'renoprotective' agent has hampered our efforts in preventing this major complication of vascular surgery.