Sébastien Tanaka

Microcirculatory alterations in traumatic hemorrhagic shock

Objectives:Microcirculatory dysfunction has been well reported in clinical studies in septic shock. However, no clinical studies have investigated microcirculatory blood flow behavior in hemorrhagic shock. The main objective of this study was to assess the time course of sublingual microcirculation in traumatic hemorrhagic shock during the first 4 days after trauma. DesignProspective observational study. SettingICU. PatientsEighteen traumatic hemorrhagic shock patients. InterventionsThe sublingual microcirculation was estimated at the study inclusion after surgical or angiographic embolization to control bleeding (D1), and then three times at 24-hour intervals (D2, D3, and D4). Measurements and Main Results:Sublingual microcirculation was impaired for 72 hours despite restoration of the macrovascular circulation after control of bleeding in traumatic hemorrhagic shock patients. Furthermore, we found significantly higher decreases in the microvascular flow index and proportion of perfused vessels in high Sequential Organ Failure Assessment score patients at D4 (Sequential Organ Failure Assessment score ≥ 6) compared to low Sequential Organ Failure Assessment score patients at D4 (Sequential Organ Failure Assessment score < 6) without any differences in global hemodynamics between these two groups. Finally, the initial proportion of perfused vessels at D1 appears to be a good predictor of high Sequential Organ Failure Assessment score at D4. Conclusions:Alterations of microcirculation in traumatic hemorrhagic shock patients result from the interplay among hemorrhage-induced tissue hypoperfusion, trauma injuries, inflammatory response, and subsequent resuscitation interventions. Despite restoration of the macrocirculation, the sublingual microcirculation was impaired for at least 72 hours. The initial proportion of perfused vessels appears to be a good predictor of high Sequential Organ Failure Assessment score at D4. Further studies are required to firmly establish the link between microvascular alterations and organ dysfunction in traumatic hemorrhagic shock patients.

Intra-aortic balloon pump effects on macrocirculation and microcirculation in cardiogenic shock patients supported by venoarterial extracorporeal membrane oxygenation

Objectives:This study was designed to assess the effects on macrocirculation and microcirculation of adding an intra-aortic balloon pump to peripheral venoarterial extracorporeal membrane oxygenation in patients with severe cardiogenic shock and little/no residual left ventricular ejection. Design:A prospective, single-center, observational study where macrocirculation and microcirculation were assessed with clinical-, Doppler echocardiography–, and pulmonary artery–derived hemodynamic variables and also cerebral and thenar eminence tissue oxygenation and side-stream dark-field imaging of sublingual microcirculation. Setting:A 26-bed tertiary ICU in a university hospital. Patients:We evaluated 12 consecutive patients before and 30 minutes after interrupting and restarting intra-aortic balloon pump. Interventions:Measurements were performed before, and 30 minutes after interrupting and restarting intra-aortic balloon pump. Measurements and Main Results:Stopping intra-aortic balloon pump was associated with higher pulmonary artery-occlusion pressure (19 ± 10 vs 15 ± 8 mm Hg, p = 0.01), increased left ventricular end-systolic (51 ± 13 vs 50 ± 14 mm, p = 0.05) and end-diastolic (55 ± 13 vs 52 ± 14 mm, p = 0.003) dimensions, and decreased pulse pressure (15 ± 13 vs 29 ± 22 mm Hg, p = 0.02). Maximum pulmonary artery-occlusion pressure reduction when the intra-aortic balloon pump was restarted was observed in the seven patients whose pulmonary artery-occlusion pressure was more than 15 mm Hg when intra-aortic balloon pump was off (–6.6 ± 4.3 vs –0.6 ± 3.4 mm Hg, respectively). Thenar eminence and brain tissue oxygenation and side-stream dark-field–assessed sublingual microcirculation were unchanged by stopping and restarting intra-aortic balloon pump. Conclusions:Restoring pulsatility and decreasing left ventricular afterload with intra-aortic balloon pump was associated with smaller left ventricular dimensions and lower pulmonary artery pressures but did not affect microcirculation variables in cardiogenic shock patients with little/no residual left ventricular ejection while on peripheral venoarterial extracorporeal membrane oxygenation.

Early Recruitment of Cerebral Microcirculation by Neuronal Nitric Oxide Synthase Inhibition in a Juvenile Ischemic Rat Model

Background: The development of collateral circulation is proposed as an inherent compensatory mechanism to restore impaired blood perfusion after ischemia, at least in the penumbra. We have studied the dynamic macro- and microcirculation after ischemia-reperfusion in the juvenile rat brain and evaluated the impact of neuronal nitric oxide synthase (nNOS) inhibition on the collateral flow. Methods: Fourteen-day-old (P14) rats were subjected to ischemia-reperfusion and treated with either PBS or 7-nitroindazole (7-NI, an nNOS inhibitor, 25 mg/kg). Arterial blood flow (BF) was measured using 2D-color-coded pulsed ultrasound imaging. Laser speckle contrast (LSC) imaging and sidestream dark-field videomicroscopy were used to measure cortical and microvascular BF, respectively. Results: In basal conditions, 7-NI reduced BF in the internal carotids (by ∼25%) and cortical (by ∼30%) BF, as compared to PBS. During ischemia, the increased mean BF velocity in the basilar trunk after both PBS and 7-NI demonstrated the establishment of collateral support and patency. Upon re-flow, BF immediately recovered to basal values in the internal carotid arteries under both conditions. The 7-NI group showed increased collateral flow in the penumbral tissue during early re-flow compared to PBS, as shown with both LSC imaging and side-stream dark-field videomicroscopy. The proportion of perfused capillaries was significantly increased under 7-NI as compared to PBS when given before ischemia (67.0 ± 3.9 vs. 46.8 ± 8.8, p < 0.01). Perfused capillaries (63.1 ± 17.7 vs. 81.1 ± 20.7, p < 0.001) and the BF index (2.4 ± 0.6 vs. 1.3 ± 0.1, p < 0.001) significantly increased under 7-NI given at the re-flow onset. Conclusions: Collateral support in the penumbra is initiated during ischemia, and may be increased during early re-flow by neuronal NOS inhibition (given in pre- and post-treatment), which may preserve brain tissue in juvenile rats.

Effect of Rbc Transfusion on Sublingual Microcirculation in Hemorrhagic Shock Patients: A Pilot Study

Objectives: The effects of RBC transfusion on microvascular perfusion are not well documented. We investigated the effect of RBC transfusion on sublingual microcirculation in hemorrhagic shock patients. Design: Prospective, preliminary observational study. Settings: A 28-bed, surgical ICU in a university hospital. Patients: Fifteen hemorrhagic shock patients requiring RBC transfusion. Intervention: Transfusion of one unit of RBCs. Measurements and Main Results: The sublingual microcirculation was assessed with a Sidestream Dark Field imaging device before and after RBC transfusion. After transfusion of one unit of RBC, hemoglobin concentration increased from 8.5 g/dL (7.6–9.5 g/dL) to 9.6 g/dL (9.1–10.3 g/dL) g/dL (p = 0.02) but no effect on macrocirculatory parameters (arterial pressure, cardiac index, heart rate, and pulse pressure variations) was observed. Transfusion of RBC significantly increased microcirculatory flow index (from 2.3 [1.6–2.5] to 2.7 [2.6–2.9]; p < 0.003), the proportion of perfused vessels (from 79% [57–88%] to 92% [88–97%]; p < 0.004), and the functional capillary density (from 21 [19–22] to 24 [22–26] mm/mm2; p = 0.003). Transfusion of RBC significantly decreased the flow heterogeneity index (from 0.51 [0.34–0.62] to 0.16 [0.04–0.29]; p < 0.001). No correlations were observed between other macrovascular parameters and microvascular changes after transfusion. The change in microvascular perfusion after transfusion correlated negatively with baseline microvascular perfusion. Conclusions: RBC transfusion improves sublingual microcirculation independently of macrocirculation and the hemoglobin level in hemorrhagic shock patients. The change in microvascular perfusion after transfusion correlated negatively with baseline microvascular perfusion. Evaluation of microcirculation perfusion is critical for optimization of microvascular perfusion and to define which patients can benefit from RBC transfusion during cardiovascular resuscitation.

Leukodepleted versus nonleukodepleted red blood cell transfusion in septic patients: a microcirculatory vision

Storage time and residual leukocytes in red blood cell (RBC) units may be deleterious by increasing the accumulation of leukocyte-derived cytokines and by raising the adhesion of RBCs to endothelium. Leukodepleted RBC transfusion may reduce the incidence of infection and organ dysfunction. However, the influence of leukodepletion on microcirculation remains not well defined in ICU patients. In this context, an original study in a previous issue of Critical Care emphasizes the microcirculatory effects of transfusion of leukodepleted RBCs (post-storage leukoreduction) or nonleukodepleted RBCs in septic patients. This study suggests a positive rheological impact of leukodepleted RBCs in septic patients with an increase in sublingual microvascular flow and perfused vessel density. Given the variability in the microvascular response to RBC transfusion in individual patients, there is a need for monitoring the microcirculation to guide transfusion in patients with sepsis rather than deciding to transfuse RBCs according to an arbitrary hemoglobin level. Further studies to identify the microvascular response to RBC transfusion in ICU patients are warranted.

An Alternative Ultrasonographic Approach to Assess Basilar Artery Flow

BACKGROUND: Assessment of basilar artery blood flow is of interest in many neurosurgical situations. With use of ultrasonography, the standard posterior approach is difficult in neurointensive care. OBJECTIVE: To evaluate the accuracy of an alternative submandibular approach for the assessment of blood flow in the basilar artery. METHOD: Fifty adult trauma patients without cervical spine injury were included in a prospective, comparative study. Doppler color-coded sonography of the basilar artery was performed using a 2-MHz pulsed probe. Blood flow velocities and pulsatility indexes obtained from the new submandibular approach and the standard suboccipital approach were compared. RESULTS: There were no significant differences in systolic, mean, and end-diastolic velocities between both approaches. Strong relationships were found between suboccipital and submandibular approaches for systolic, mean, end-diastolic velocities, and pulsatility indexes (r2 = 0.94, 0.95, 0.95, and 0.91, respectively; P < .001 for all). The mean bias between suboccipital and submandibular approaches was 1.1 cm/s for systolic velocity, 0.4 cm/s for mean velocity, −1.2 cm/s for end-diastolic velocity, and 0.0 for pulsatility index. CONCLUSION: This alternative submandibular approach appears to be accurate in measuring blood flow velocity and pulsatility index in the basilar artery. The main advantage of this approach is to facilitate monitoring of brainstem perfusion by avoiding neck flexion. This can be very helpful in intensive care settings.

The Microcirculation in Hemorrhagic Shock

Hemorrhagic shock is characterized by both macrovascular hemodynamic abnormalities (decreased venous return, decreased cardiac output and systemic hypotension) and alterations of the microcirculation. The microcirculation is a critical component of the cardiovascular system, which regulates flow to the tissues. Several studies have shown a significant decrease in microvascular blood flow in various organs during the acute phase of hemorrhagic shock and resuscitation [1–4]. Persistence of these microvascular alterations is believed to be a contributing factor to the development of organ dysfunction. The pathogenesis of the microvascular alterations involves both vascular and cellular components. In current clinical practice, guidelines for resuscitation are provided by monitoring macrocirculatory variables, such as arterial blood pressure, heart rate, and cardiac output.