Hans Knotzer

Microcirculatory function monitoring at the bedside—a view from the intensive care

Microcirculatory dysfunction plays a key role in the pathophysiology of various disease states and may consequently impact patient outcome. Until recently, the evaluation of the microcirculation using different measurement techniques has been mostly limited to animal and human research. With technical advances, microcirculatory monitoring nowadays becomes more and more available for application in clinical praxis. Unfortunately, measurements within the microcirculation are mostly limited to easily accessible surfaces, such as skin, muscle and tongue. Due to major differences in the physiologic regulation of microcirculatory blood flow and in metabolism between organs and even within different tissues in one organ, the clinical importance of regional microcirculatory measurements remains to be determined. In addition, technical methods available demonstrate large differences in the measured parameters and sampling volume, making interpretation of data even more difficult. Nonetheless, the monitoring of the microcirculation may, ahead of time, alert physicians that tissue oxygen supply becomes compromised and it may lead to a better understanding of basic pathophysiological aspects of disease. In the present review, we describe available non-invasive microcirculatory measurement techniques which can be applied clinically at the bedside. After a short discussion of physiologic and pathophysiologic basics related to microcirculatory monitoring, the measuring principles, applications, strengths and limitations of different monitoring systems are discussed.

Effects of phenylephrine on the sublingual microcirculation during cardiopulmonary bypass

BACKGROUND The objective of the present study was to investigate sublingual microvascular blood flow and microcirculatory haemoglobin oxygen saturation (Smc(O(2))) during cardiopulmonary bypass (CPB) using constant systemic blood flow but different perfusion pressures achieved by phenylephrine administration. METHODS Fifteen patients undergoing coronary artery bypass grafting were enrolled in this pilot study. Systemic haemodynamics, oxygen transport variables, arterial and mixed venous blood gas analysis, and microcirculatory variables were determined after initiation of general anaesthesia, during CPB (systemic blood flow=2.4 litre m(-2)), after increasing perfusion pressure by 20 mm Hg with a continuous infusion of phenylephrine, and after termination of phenylephrine infusion. RESULTS CPB immediately resulted in a significant (P<0.05) decrease in systemic oxygen transport without alterations in sublingual microcirculatory blood flow and Smc(O(2)). Increasing perfusion pressure from 47 (SD 9) to 68 (7) mm Hg using phenylephrine=1.4 (1.0) microg kg(-1) min(-1) resulted in a significant decrease in sublingual small vessel blood flow (from median 2.5 to 1.8 arbitrary units) representing mostly capillary blood flow, but not in medium-sized vessels (median 3 to 2.8 arbitrary units). Concurrently, global tissue blood flow from 110 (54) to 197 (100) perfusion units and Smc(O(2)) increased from 72 (11)% to 84 (7)%, suggesting significant microcirculatory blood flow shunting in vessels with diameters >25 microm. CONCLUSIONS Our data demonstrate that an increased perfusion pressure produced by phenylephrine at constant CPB flow may decrease microcirculatory blood flow in the sublingual mucosal microcirculation due to microvascular blood flow shunting.

Cutaneous vascular reactivity and flow motion response to vasopressin in advanced vasodilatory shock and severe postoperative multiple organ dysfunction syndrome

IntroductionDisturbances in microcirculatory homeostasis have been hypothesized to play a key role in the pathophysiology of multiple organ dysfunction syndrome and vasopressor-associated ischemic skin lesions. The effects of a supplementary arginine vasopressin (AVP) infusion on microcirculation in vasodilatory shock and postoperative multiple organ dysfunction syndrome are unknown.MethodIncluded in the study were 18 patients who had undergone cardiac or major surgery and had a mean arterial blood pressure below 65 mmHg, despite infusion of more than 0.5 μg/kg per min norepinephrine. Patients were randomly assigned to receive a combined infusion of AVP/norepinephrine or norepinephrine alone. Demographic and clinical data were recorded at study entry and after 1 hour. A laser Doppler flowmeter was used to measure the cutaneous microcirculatory response at randomization and after 1 hour. Reactive hyperaemia and oscillatory changes in the Doppler signal were measured during the 3 minutes before and after a 5-minute period of forearm ischaemia.ResultsPatients receiving AVP/norepinephrine had a significantly higher mean arterial pressure (P = 0.047) and higher milrinone requirements (P = 0.025) than did the patients who received norepinephrine only at baseline. Mean arterial blood pressure significantly increased (P < 0.001) and norepinephrine requirements significantly decreased (P < 0.001) in the AVP/norepinephrine group. Patients in the AVP/norepinephrine group exhibited a significantly higher oscillation frequency of the Doppler signal before ischaemia and during reperfusion at randomization. During the study period, there were no differences in either cutaneous reactive hyperaemia or the oscillatory pattern of vascular tone between groups.ConclusionSupplementary AVP infusion in patients with advanced vasodilatory shock and severe postoperative multiple organ dysfunction syndrome did not compromise cutaneous reactive hyperaemia and flowmotion when compared with norepinephrine infusion alone.

Effects of stomach inflation on haemodynamic and pulmonary function during spontaneous circulation in pigs

AIM Stomach inflation during mask ventilation is frequent, but the effects on haemodynamic and pulmonary function are unclear. We evaluated the effects of stomach inflation on haemodynamic and pulmonary function during spontaneous circulation in a porcine model. METHODS Randomised prospective animal study. After randomisation, in 23 domestic pigs the stomach was inflated every 90s with 0L (control; n=8), 0.5L (n=7) or 1L (n=8) ambient air. RESULTS After 22.5min, i.e. 8.5L in the 0.5L and 17L in the 1L stomach inflation group, stomach inflation increased central venous pressure (median) (control: 10mmHg vs. 1L: 23mmHg, P<0.05) and mean pulmonary artery pressure (control: 24mmHg vs. 1L: 45mmHg, P<0.05). As a result stroke volume index decreased (control: 135mL/kg vs. 0.5L: 90mL/kg, P<0.05; vs. 1L: 72mL/kg, P<0.05). Stomach inflation also decreased static pulmonary compliance (control: 24mL/cmH(2)O vs. 0.5L: 8mL/cmH(2)O, P<0.05; vs. 1L: 3mL/cmH(2)O, P<0.05), which increased peak airway pressure (control: 28cmH(2)O vs. 0.5L: 69cmH(2)O, P<0.05; vs. 1L: 73cmH(2)O, P<0.05). Additionally, arterial oxygen partial pressure (control: 305mmHg vs. 0.5L: 140mmHg, P<0.05; vs. 1L: 21mmHg, P<0.05) and systemic oxygen delivery (control: 53mLO(2)/min vs. 1L: 19mLO(2)/min, P<0.05) decreased. Stomach inflation increased mortality (control: 0/8 vs. 1L: 5/8, P<0.05). CONCLUSIONS Stomach inflation with 1L when compared to 0.5L increments resulted in faster haemodynamic and pulmonary failure and increased mortality. Stomach inflation may cause a hyper-acute abdominal compartment syndrome.

Arginine-vasopressin attenuates beneficial norepinephrine effect on jejunal mucosal tissue oxygenation during endotoxinaemia

BACKGROUND The objective of the present study was to investigate the effects of increasing doses of norepinephrine (NE) with or without arginine-vasopressin (AVP) on intestinal oxygen supply and jejunal mucosal tissue oxygen tension in an acute endotoxic pig model. METHODS In this prospective, randomized, experimental study on 24 domestic pigs, jejunal mucosal tissue PO2 (PO2muc) was measured using two Clark-type surface oxygen electrodes. Oxygen saturation of jejunal microvascular haemoglobin (HbO2j) was determined by tissue reflectance spectrophotometry. Systemic haemodynamic variables, mesenteric-venous and systemic acid-base and blood gas variables, and lactate measurements were recorded. Measurements were performed at baseline, after Escherichia coli lipopolysaccharide (LPS) administration, and at 20 min intervals during incremental NE infusion (0.05, 0.1, 0.5, 1.0, and 2 microg kg(-1) min(-1), respectively) with 57 mU kg(-1) h(-1) AVP (n=8; NE+AVP group) or without (n=8; NE group); or infusion of an equal amount of normal saline (n=8; CON group). RESULTS LPS infusion led to a significant (P<0.05) decrease of PO2muc and HbO2j. Both NE and NE+AVP increased arterial pressure, cardiac output, and mesenteric artery blood flow. Concomitant to an increase in systemic oxygen delivery, NE improved PO2muc and HbO2j. NE alone was superior in restoration of PO2muc when compared with NE+AVP. CONCLUSIONS Both NE and NE+AVP improved global haemodynamics and systemic oxygen transport variables when compared with control animals in an acute endotoxic pig model. NE improved jejunal PO2muc at all dosages. NE effects were significantly blunted by simultaneous administration of AVP.

Factors influencing blood transfusion requirements in robotic totally endoscopic coronary artery bypass grafting on the arrested heart

OBJECTIVE Robotic technology enables totally endoscopic coronary artery bypass grafting (TECAB) procedures. These operations can be performed on either the beating or arrested heart. One challenge of the latter version is a potentially increased need for blood transfusions. We investigated factors associated with transfusion requirements in totally endoscopic coronary artery bypass on the arrested heart (AH-TECAB). PATIENTS AND METHODS A total of 161 patients, 124 males and 37 females, aged 59 (31-77 years) years, with European System for Cardiac Operative Risk Evaluation (EuroSCORE) 1 (0-7) underwent AH-TECAB using the daVinci telemanipulation system. The Heartport/Cardiovations™ or ESTECH-RAP™ systems were applied for remote access perfusion and aortic endoocclusion. In all cases, the operation was carried out in moderate hypothermia and cardiac arrest using cold crystalloid cardioplegia mixed with blood. RESULTS After 20 cases, the blood-transfusion rate dropped from 69% to 44%. The overall median number of transfusions was 1 (0-21). The following pre- and intra-operative factors showed a strong association with the application of packed red blood cells (PRBCs): preoperative haemoglobin level (p < 0.001), female gender (p < 0.001), shorter height (p < 0.001), lower weight (p < 0.001), long operative time (p < 0.001) and long cardiopulmonary bypass time (p = 0.001), intra-operative surgical problem (p < 0.001) and conversion to a larger thoracic incision (p < 0.001). Postoperatively, patients with longer ventilation time (p < 0.001) and those needing revision for bleeding (p < 0.001) also received significantly more PRBCs. CONCLUSION We conclude that multiple factors are associated with increased blood transfusion requirements in AH-TECAB. However, the transfusion rate can be reduced with experience. Identification of these factors may help in avoiding the application of blood products in the next generation of AH-TECAB procedures.

Oscillation frequency of skin microvascular blood flow is associated with mortality in critically ill patients

Background:  Microcirculatory dysfunction has been hypothesized to play a key role in the pathophysiology of multiple organ failure and, consequently, patient outcome. The objective of this study was to investigate the differences in reactive hyperemia response and oscillation frequency in surviving and non‐surviving patients with multiple organ dysfunction syndrome.

The Physiologic Perspective in Fluid Management in Vascular Anesthesiology

Vascular surgery patients frequently suffer from atherosclerosis and peripheral arterial occlusive disease generating endothelial dysfunction. Furthermore, ischemia and reperfusion during surgery damage endothelial cells and, especially, the endothelial glycocalix. The damage of the glycocalix promotes an increase in permeability. Not only crystalloids, which freely diffuse between the intravascular and the interstitial compartment, but also colloidal fluids cross from the intravascular space in the interstitial space with the consequence of edema formation. Possible tissue edema may result in an impairment of tissue oxygenation, leading to wound healing disturbances and initiation of inflammatory responses up to tissue apoptosis. Particularly in vascular anesthesia, this possibly means that colloids only should be administered in acute volume resuscitation immediately after unclamping a big vessel for immediate volume restoration. Which colloidal fluid should be administered is still under intense discussion. From a theoretical physiologic point of view, iso-osmolar albumin is the best choice regarding volume effect, antioxidative properties, and protection against destruction of the glycocalix. Nonetheless, albumin experimentally has not lived up to its promise in the clinical setting. Thus, further well-conducted large randomized clinical trials are necessary to ascertain the optimal fluid therapy in vascular surgery patients.

The Eustachian Valve as a Pitfall in Persistent Foramen Ovale and Atrial Septum Defect Closure

a A b a n t i c r e b T s t r a A b c w THE EUSTACHIAN VALVE plays an important role during fetal life by directing oxygen-rich blood from the inferior vena cava (IVC) through the foramen ovale into the left atrium (LA) and the systemic circulation. After birth, the eustachian valve disappears or is reduced to a thin, nonfunctional ridge. Occasionally, it remains as an elongated and prominent structure within the right atrium (RA). If the eustachian valve is very prominent with undulating motion, it is called a giant eustachian valve.1 Otherwise, if t is very thin and small, it is called a Chiari network.2 Occasionally, it can be elongated and appears prominent with an undulating motion in echocardiography.1 It is best visualized by transesophageal echocardiography (TEE) in the midesophageal bicaval view, where it can be seen to originate from the junction of the RA and the IVC.2 A patent eustachian valve is not only a possible pitfall in echocardiography but also for the cardiac surgeon closing an atrial septum defect (ASD). There are several reports of the eustachian valve being mistaken for the lower rim of the ASD, thus causing inadvertent diversion of the IVC blood flow into the left atrium.3 Moreover, inflow obstruction of the IVC is reported to cause Budd-Chiari–like symptoms.4 TEE is superior to transthoracic echocardiography for the identification and characterization of ASDs in adults.5 Consequently, the authors resent 2 patients showing intraoperative TEE evidence of nintentional sewing of the eustachian valve into a surgical SD/PFO closure.