NOREPINEPHRINE AND INTESTINAL MUCOSAL PERFUSION IN VASODILATORY SHOCK AFTER CARDIAC SURGERY

When can we start early enteral nutrition safely in patients with shock on vasopressors?

Shock is a common critical illness characterized by microcirculatory disorders and insufficient tissue perfusion. Patients with shock and hemodynamic instability generally require vasopressors to maintain the target mean arterial pressure. Enteral nutrition (EN) is an important therapeutic intervention in critically ill patients and has unique benefits for intestinal recovery. However, the initiation of early EN in patients with shock receiving vasopressors remains controversial. Current guidelines make conservative and vague recommendations regarding early EN support in patients with shock. Increasing studies demonstrates that early EN delivery is safe and feasible in patients with shock receiving vasopressors; however, this evidence is based on observational studies. Changes in gastrointestinal blood flow vary by vasopressor and inotrope and are complex. The risk of gastrointestinal complications, especially the life-threatening complications of non-occlusive mesenteric ischemia and non-occlusive bowel necrosis, cannot be ignored in patients with shock during early EN support. It remains a therapeutic challenge in critical care nutrition therapy to determine the initiation time of EN in patients with shock receiving vasopressors and the safe threshold region for initiating EN with vasopressors. Therefore, the current review aimed to summarize the evidence on the optimal and safe timing of early EN initiation in patients with shock receiving vasopressors to improve clinical practice.

Perioperative fluid management and outcomes in adult deceased donor liver transplantation - A systematic review of the literature and expert panel recommendations

BACKGROUND

Fluid management practices during and after liver transplantation vary widely among centers despite better understanding of the pathophysiology of end-stage liver disease and of the effects of commonly used fluids. This reflects a lack of high quality trials in this setting, but also provides a rationale for both systematic review of all relevant studies in liver recipients and evaluation of new evidence from closely related domains, including hepatology, non-transplant abdominal surgery, and critical care.

OBJECTIVES

To develop evidence-based recommendations for perioperative fluid management to optimize immediate and short-term outcomes following liver transplantation.

DATA SOURCES

Ovid MEDLINE, Embase, Scopus, Google Scholar, and Cochrane Central.

METHODS

Systematic review following PRISMA guidelines and recommendations using the GRADE approach derived from an international expert panel. Studies included those evaluating the following postoperative outcomes: acute kidney injury, respiratory complications, operative blood loss/red cell units required, and intensive care length of stay. PROSPERO protocol ID: CRD42021241392 RESULTS: Following expert panel review, 18 of 1624 screened studies met eligibility criteria for inclusion in the final quantitative synthesis. These included six single center RCTs, 11 single center observational studies, and one observational study comparing centers with different fluid management techniques. Definitions of interventions and outcomes varied between studies. Recommendations are therefore based substantially on expert opinion and evidence from other clinical settings.

CONCLUSIONS

A moderately restrictive or "replacement only" fluid regime is recommended, especially during the dissection phase of the transplant procedure. Sustained hypervolemia, based on absence of fluid responsiveness, elevated filling pressures and/or echocardiographic findings, should be avoided (Quality of Evidence: Moderate | Grade of Recommendation: Weak for restrictive fluid regime. Strong for avoidance of hypervolemia). Mean Arterial Pressure (MAP) should be maintained at >60-65 mmHg in all cases (Quality of Evidence: Low | Grade of Recommendation: Strong). There is insufficient evidence in this population to support preferential use of any specific colloid or crystalloid for routine volume replacement. However, we recommend against the use of 130/.4 HES given the high incidence of AKI in this population.

Hemodynamic Influences on Mesenteric Blood Flow in Shock Conditions

The gastrointestinal (GI) system, is most vulnerable to hypoperfusion among the splanchnic organs. Disturbed perfusion of the mesenteric area may lead to GI dysfunction, cause further injury to the patients and even vital outcomes. However, due to the limitation of detection methods, the hemodynamic influences on mesenteric blood flow in clinical practice are not fully understood. By elucidating the underlying mechanisms, we may be able to recognize disturbed GI perfusion and eventually GI dysfunction at an early phase. Thus, in this review, we will focus on situations where mesenteric blood flow is disturbed due to hemodynamic causes in shock conditions, and the present research status will be discussed. English language articles published before 2020 were identified through a computerized PubMed search using the terms "mesenteric, gastrointestinal, intestinal, splanchnic, blood flow, perfusion" and the cofactors. Relevant publications were retrieved and scanned for additional sources. There were few clinical trials focusing on mesenteric blood flow in shock patients. Most were animal experiments. Based on the best current evidence from these sources, we described the major influences on mesenteric blood flow in the context of physiologic accommodation, disease-related effects and the consequences of medical interventions related to shock conditions. During circulatory shock, sepsis, and medical interventions related to shock treatment, mesenteric blood flow changes and shows different features. We need to carefully consider these issues when making medical decisions, and more work needs to be done on early detection of GI hypoperfusion and its accurate correlation with GI dysfunction.

Renal effects of norepinephrine-induced variations in mean arterial pressure after liver transplantation: A randomized cross-over trial

BACKGROUND

Acute kidney injury is commonly seen after liver transplantation. The optimal perioperative target mean arterial pressure (MAP) for renal filtration, perfusion and oxygenation in liver recipients is not known. The effects of norepinephrine-induced changes in MAP on renal blood flow (RBF), oxygen delivery (RDO₂ ), glomerular filtration rate (GFR) and renal oxygenation (=renal oxygen extraction, RO₂ Ex) were therefore studied early after liver transplantation.

METHODS

Ten patients with an intra- and post-operative vasopressor-dependent systemic vasodilation were studied early after liver transplantation during sedation and mechanical ventilation. To achieve target MAP levels of 60, 75 and 90 mm Hg, the norepinephrine infusion rate was randomly and sequentially titrated. At each target MAP, data on cardiac index (CI), RBF and GFR were obtained by transpulmonary thermodilution (PiCCO), the renal vein thermodilution technique and renal extraction of chromium ethylenediaminetetraaceticacid (⁵¹ Cr-EDTA), respectively. Renal oxygen consumption (RVO₂ ) and extraction (RO₂ Ex) were calculated according to standard formulas.

RESULTS

At a target MAP of 75 mm Hg, CI (13%), RBF (18%), RDO₂ (24%), GFR (31%) and RVO₂ (20%) were higher while RO₂ Ex was unchanged compared to a target MAP of 60 mm Hg. Increasing MAP from 75 up to 90 mm Hg increased RVR by 38% but had no further effects on CI, RBF, RDO₂ or GFR.

CONCLUSIONS

In patients undergoing liver transplantation, RBF and GFR are pressure-dependent at MAP levels below 75 mm Hg. Our results suggest that MAP should probably be targeted to approximately 75 mm Hg for optimal perioperative renal filtration, perfusion and oxygenation in patients undergoing liver transplantation.

Abdominal obesity and prolonged prone positioning increase risk of developing sclerosing cholangitis in critically ill patients with influenza A-associated ARDS

Background

Secondary sclerosing cholangitis is a severe disease of the biliary tract. Over the last decade, several cases of sclerosing cholangitis in critically ill patients (SC-CIP) were reported. Reports in the literature so far are characterized by a wide variety of underlying causes of critical illness, thereby hindering a risk-factor analysis. We report on a homogenous cohort of critically ill patients with influenza A (H1N1) pneumonia and severe acute respiratory distress syndrome (ARDS), of whom a subgroup developed sclerosing cholangitis, allowing for probing of risk factors associated with SC-CIP.

Methods

Twenty-one patients (5 female, 16 male, 46.3 ± 10.8 years) with severe ARDS due to H1N1 pneumonia were retrospectively divided into two groups, characterized by the presence (n = 5) and absence of SC-CIP (n = 16). A large array of clinical data, laboratory parameters, and multi-detector computed tomography-derived measures were compared.

Results

Both patient groups showed severe pulmonary impairment. Severity of disease on admission day and during the first 14 days of treatment showed no difference. The patients developing SC-CIP had a higher body mass index (BMI) (37.4 ± 6.0 kg/m² vs. 29.3 ± 6.8 kg/m²; P = 0.029) and a higher volume of intraperitoneal fat (8273 ± 3659 cm³ vs. 5131 ± 2268 cm³; P = 0.033) and spent a longer cumulative period in the prone position during the first 14 days (165 ± 117 h vs. 78 ± 61 h; P = 0.038).

Conclusion

Our results suggest that obesity, intraperitoneal fat volume, and a longer cumulative duration spent in the prone position may put patients with ARDS at risk of developing SC-CIP. These results lead us to propose that the prone position should be carefully deployed, particularly in abdominally obese patients, and that frequent checks be made for early hepatic dysfunction.

Vasoplegic syndrome during liver transplantation

A 56-yr-old woman with chronic hepatitis B and decompensated hepatic cirrhosis was treated with liver transplantation. At the beginning of the neohepatic phase, her arterial blood pressure remained at 60/40 mm Hg for approximately 40 min and did not respond to vasoconstrictive drugs. Her other clinical and laboratory values remained normal, apart from a high cardiac output and low systemic vascular resistance. This patient was diagnosed with vasoplegic syndrome and was treated with i.v. infusion of methylene blue (0.5 mg/kg) and norepinephrine. This report has potential significance to treatment in patients who undergo orthotopic liver transplantation.

Vasopressin decreases intestinal mucosal perfusion: a clinical study on cardiac surgery patients in vasodilatory shock

BACKGROUND

Low to moderate doses of vasopressin have been used in the treatment of cathecholamine-dependent vasodilatory shock in sepsis or after cardiac surgery. We evaluated the effects of vasopressin on jejunal mucosal perfusion, gastric-arterial pCO2 gradient and the global splanchnic oxygen demand/supply relationship in patients with vasodilatory shock after cardiac surgery.

METHODS

Eight mechanically ventilated patients, dependent on norepinephrine to maintain mean arterial pressure (MAP) > or = 60 mmHg because of septic/post-cardiotomy vasodilatory shock and multiple organ failure after cardiac surgery, were included. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h for 30-min periods. Norepinephrine was simultaneously decreased to maintain MAP at 75 mmHg. At each infusion rate of vasopressin, data on systemic hemodynamics, jejunal mucosal perfusion, jejunal mucosal hematocrit and red blood cell velocity (laser Doppler flowmetry) as well as gastric-arterial pCO2 gradient (gastric tonometry) and splanchnic oxygen and lactate extraction (hepatic vein catheter) were obtained.

RESULTS

The cardiac index, stroke volume index and systemic oxygen delivery decreased and systemic vascular resistance and systemic oxygen extraction increased significantly, while the heart rate or global oxygen consumption did not change with increasing vasopressin dose. Jejunal mucosal perfusion decreased and the arterial-gastric-mucosal pCO2 gradient increased, while splanchnic oxygen or lactate extraction or mixed venous-hepatic venous oxygen saturation gradient were not affected by increasing infusion rates of vasopressin.

CONCLUSIONS

Infusion of low to moderate doses of vasopressin in patients with norepinephrine-dependent vasodilatory shock after cardiac surgery induces an intestinal and gastric mucosal vasoconstriction.

Enteral nutrition in the cardiothoracic intensive care unit: challenges and considerations

Cardiovascular disease is a common preexisting condition among hospitalized patients. Acute myocardial infarction and cardiac surgery account for 2 of the most common reasons patients are admitted to the intensive care unit. Determining how and when to feed these patients is a constant challenge presented to nutrition support practitioners. Enteral nutrition has emerged as the preferred route of feeding particularly in critical illness. By providing enteral nutrition instead of parenteral nutrition, the natural physiologic pathway is being followed and gut immunity preserved. However, obstacles such as upper gastrointestinal intolerance, hypoperfusion vasopressor support, and glycemic control make the task of initiating feeds a challenge. Once a patient has successfully tolerated feeds, the nutrition support clinician must still determine how much to feed and if specialty formulas such as those containing omega-3 fatty acids are beneficial for their patient. The purpose of this review is to present recent research on the feeding challenges in the critical care population with a focus on the cardiothoracic population and an emphasis on improving patient outcomes.