The effect of pulsatile perfusion on cerebral blood flow during profound hypothermia with total circulatory arrest: A randomized, prospective, double-blind study

Strategies to improve outcomes for acute type A aortic dissection with cerebral malperfusion

OBJECTIVES

We aimed to identify predictors of postoperative permanent neurological deficits (PNDs) and evaluate the early management of cerebral perfusion in patients undergoing surgical repair of acute type A aortic dissection with cerebral malperfusion.

METHODS

Between October 2009 and September 2018, a total of 197 patients with acute type A aortic dissection underwent aortic replacement. Of these, 42 (21.3%) patients had an imaging cerebral malperfusion (ICM). ICM was assessed preoperatively, which also revealed whether dissected supra-aortic branch vessels were occluded or narrowed by a thrombosed false lumen. After September 2017, early reperfusion and extra-anatomic revascularization were performed in cases with ICM.

RESULTS

Hospital mortality rates for cases with ICM were 4.8% (2/42). Before September 2017, PND were observed in 6 patients (54.5%) with preoperative neurological symptoms (n = 11), and 7 patients (33.3%) without neurological symptoms (n = 21) in patients with ICM. Occlusion or severe stenosis of supra-aortic branch vessels (odds ratio, 7.66; P < 0.001), regardless of preoperative clinical neurological symptoms, was a risk factor for PND. After September 2017, 7 of 10 patients with ICM underwent early reperfusion and extra-anatomic revascularization. PND did not occur in any of these 7 patients.

CONCLUSIONS

Occlusion or severe stenosis of supra-aortic branch vessels is a predictor of PND risk in patients undergoing surgery for acute type A aortic dissection. Early reperfusion and extra-anatomic revascularization may reduce the risk of neurological complications in patients with ICM, with or without neurological symptoms.

Design of a Physiologic Pulsatile Flow Cardiopulmonary Bypass System for Neonates and Infants

Cardiopulmonary bypass surgical techniques that allow a surgeon to operate on the infant's heart use an extracorporeal circuit consisting of a pump, oxygenator, arterial and venous reservoirs, cannulae, an arterial filter, and tubing. The extracorporeal technique currently used in infants and neonates is sometimes associated with neurologic damage. We are developing a modified cardiopulmonary bypass system for neonates that has been tested in vitro and in one animal in vivo. Unlike other extracorporeal circuits which use steady flow, this system utilizes pulsatile flow, a low prime volume (500ml) and a closed circuit. During in vitro experiments, the pseudo patient's mean arterial pressure was kept constant at 40 mmHg and the extracorporeal circuit pressure did not exceed a mean pressure of 200 mmHg. In our single in vivo experiment, the primary objective was to determine whether physiologic pulsatility with a 10F (3.3 mm) aortic cannula could be achieved. The results suggest that this is possible.

A new rotary blood pump for versatile extracorporeal circulation: the DeltaStream™

Today, rotary pumps are routinely used for extracorporeal circulation in different clinical settings and applications. A review of these applications and specific limitations in extracorporeal perfusion was performed and served as a basis for the development of the DeltaStream®. The Delta- Stream® is a miniaturized rotary blood pump of a new and unique design with an integrated drive unit. Despite its small design, the pump maintains a sufficient hydraulic capacity, which makes the DeltaStream® very flexible for intra- and perioperative applications. It also opens the field for short-term ventricular assist devices (VAD) applications or use as a component in extracorporeal life support systems (ECLS). The DeltaStream® and, specifically, its impeller design have been optimized with respect to haemolysis and nonthrombogenicity. Also, the pump facilitates an effective pulse generation in VAD applications and simulates heart action in a more physiological way than other rotary pumps or roller pumps. Hydraulic and haematological properties have been tested in vitro and in vivo. In a series of seven animal experiments in two different setups, the pump demonstrated its biocompatibility and applicability. Basic aspects of the DeltaStream® pump concept as well as important console features are presented. A summary of the final investigation of this pump is given with focus on hydraulic capabilities and results from animal studies.

Arterial pressure and cerebral blood flow variability: friend or foe? A review

Variability in arterial pressure and cerebral blood flow has traditionally been interpreted as a marker of cardiovascular decompensation, and has been associated with negative clinical outcomes across varying time scales, from impending orthostatic syncope to an increased risk of stroke. Emerging evidence, however, suggests that increased hemodynamic variability may, in fact, be protective in the face of acute challenges to perfusion, including significant central hypovolemia and hypotension (including hemorrhage), and during cardiac bypass surgery. This review presents the dichotomous views on the role of hemodynamic variability on clinical outcome, including the physiological mechanisms underlying these patterns, and the potential impact of increased and decreased variability on cerebral perfusion and oxygenation. We suggest that reconciliation of these two apparently discrepant views may lie in the time scale of hemodynamic variability; short time scale variability appears to be cerebroprotective, while mid to longer term fluctuations are associated with primary and secondary end-organ dysfunction.

Choroidal Microcirculation in Patients With Rotary Cardiac Assist Device

BACKGROUND

In recent years, fully implanted rotary blood pumps have been used for long-term cardiac assist in patients with end-stage heart failure. With these pumps, the pulsatility of arterial blood flow and arterial pressure pulse is considerably reduced. Effects on end-organ perfusion, particularly microcirculation, have been assessed.

METHODS

The ocular choroid offers a unique opportunity to study the pulsatile component of blood flow by measurement of fundus pulsation amplitude (FPA) as well as the microcirculation by laser Doppler flowmetry. Both techniques were applied in three male patients with rotary pumps (MicroMed DeBakey VAD), in whom pump velocity was adjusted to four levels of flow between individual minimal need and maximal support. In addition, blood flow velocities in the ophthalmic artery (peak, end-diastolic and mean flow velocity--PSV, EDV and MFV, respectively) were measured using color Doppler imaging.

RESULTS

Systolic blood pressure increased by 6 to 22 mm Hg with increasing support. At maximal support FPA was reduced by -60% to -52% as compared with minimal pump support. Blood flow in the choroidal microvasculature, however, did not show relevant changes. A reduction in PSV (-31%, range -47% to -21%) and a pronounced rise in EDV (+93%, range +28% to +147%) was observed, whereas MFV was independent of pump flow.

CONCLUSIONS

Our data indicate that mean choroidal blood flow is maintained when pump support is varied within therapeutic values, whereas the ratio of pulsatile to non-pulsatile choroidal flow changes. This study shows that, in patients with ventricular assist devices, a normal perfusion rate in the ocular microcirculation is maintained over a wide range of support conditions.

An Evaluation of the Benefits of Pulsatile versus Nonpulsatile Perfusion during Cardiopulmonary Bypass Procedures in Pediatric and Adult Cardiac Patients

The controversy over the benefits of pulsatile and nonpulsatile flow during cardiopulmonary bypass procedures continues. The objective of this investigation was to review the literature in order to clarify the truths and dispel the myths regarding the mode of perfusion used during open-heart surgery in pediatric and adult patients. The Google and Medline databases were used to search all of the literature on pulsatile vs. nonpulsatile perfusion published between 1952 and 2006. We found 194 articles related to this topic in the literature. Based on our literature search, we determined that pulsatile flow significantly improved blood flow of the vital organs including brain, heart, liver, and pancreas; reduced the systemic inflammatory response syndrome; and decreased the incidence of postoperative deaths in pediatric and adult patients. We also found evidence that pulsatile flow significantly improved vital organ recovery in several types of animal models when compared with nonpulsatile perfusion. Several investigators have also shown that pulsatile flow generates more hemodynamic energy, which maintains better microcirculation compared with nonpulsatile flow. These results clearly suggest that pulsatile flow is superior to nonpulsatile flow during and after open-heart surgery in pediatric and adult patients.

Physiology of continuous blood flow in recipients of rotary cardiac assist devices

The beating heart and the resultant pulse wave have been a symbol of life for centuries. The development history of roller pumps for cardiopulmonary bypass shows that the human body tolerates non-pulsatile blood flow, at least for short-term support. Over the last few years, many types of rotary blood pumps have been developed for clinical use in patients requiring mid- to long-term support. Although early clinical experiences in patients with long-term support have been promising, the matter of whether pulsatile flow is needed or not remains controversial. Therefore, this review summarizes the observed clinical consequences of continuous blood flow in patients supported by rotary blood pumps and relates these consequences to underlying experimental studies.

Harmonic analysis of perfusion pumps

The controversy over the use of nonpulsatile versus pulsatile pumps for maintenance of normal organ function during ex vivo perfusion has continued for many years, but resolution has been limited by lack of a congruent mathematical definition of pulsatility. We hypothesized that the waveform frequency and amplitude, as well as the underlying mean distending pressure are all key parameters controlling vascular function. Using discrete Fourier Analysis, our data demonstrate the complexity of the pulmonary arterial pressure waveform in vivo and the failure of commonly available perfusion pumps to mimic in vivo dynamics. In addition, our data show that the key harmonic signatures are intrinsic to the perfusion pumps, are similar for flow and pressure waveforms, and are unchanged by characteristics of the downstream perfusion circuit or perfusate viscosity.

Effects of reduced pulse pressure to the cerebral metabolism during prolonged nonpulsatile left heart bypass

We investigated changes in the cerebral metabolism with long-term reduced pulse pressure. Nine goats underwent pulsatile left heart bypass (LHB) for 2 weeks while awake, and nonpulsatile LHB was subsequently conducted for 4 weeks. The average pulse pressure during nonpulsatile LHB (13, 10, 11, and 11 mm Hg at the 1st, 2nd, 3rd, and 4th nonpulsatile LHB week, respectively) was significantly lower than that during pulsatile LHB (36 mm Hg). There were no significant differences in either arterio-jugular venous oxygen differences (AJDO2) and cerebral oxygen extraction ratio between the 2nd pulsatile LHB week and the 1st, 2nd, 3rd, and 4th nonpulsatile LHB weeks. The arterio-jugular venous glucose differences, jugular venous-arterial lactate differences (JAD Lactate), and lactate oxygen indexes (JAD Lactate/AJDO2) also remained unchanged during the entire course of the experiments. In conclusion, the cerebral metabolism during nonpulsatile LHB did not change compared to that during pulsatile LHB.

Influence of biopump with and without intraaortic balloon on the coronary and carotid flow

BACKGROUND

The objective of this study was to evaluate the influence of biopump used for left ventricular assistance on the coronary and carotid flows in dogs with normal heart. The efficacy of the simultaneous use of an intraaortic balloon pump to compensate the possible deleterious effects of the circulatory assistance with continuous flow was also analyzed.

METHODS

Fifteen dogs were studied. The hemodynamic evaluation included serial measurements of the classic parameters. Carotid and coronary blood flows were obtained by electromagnetic transducers.

RESULTS

The hemodynamic evaluation did not show significant statistical changes. The use of circulatory-isolated assistance with biopump shows reduction (24.6% +/- 6.1%) in coronary flow, in relation to the control situation and the concomitant use of biopump and intraaortic balloon pump showed similar coronary flow. Regarding carotid flow, a similar trend was observed in relation to the positive influence of the pulsatile flow with an intraaortic balloon pump without statistical significance (p = 0.0582).

CONCLUSIONS

The biopump reduces the coronary flow in dogs. The use of intraaortic balloon pump with the biopump increases the coronary flow significantly, reaching similar values to those observed without the circulatory assistance.

Testing neonate-infant membrane oxygenators with the University of Texas neonatal pulsatile cardiopulmonary bypass system in vitro

Neurologic complications are already well documented after cardiopulmonary bypass (CPB) procedures in neonates and infants. Physiologic pulsatile flow CPB systems may be the alternative to the currently used steady-flow CPB circuits. In addition to the pulsatile pump, a membrane oxygenator should be chosen carefully, because only a few membrane oxygenators are suitable for physiologic pulsatile flow. We have tested four different types of neonate-infant membrane oxygenators for physiologic pulsatility with The University of Texas neonate-infant pulsatile CPB system in vitro. Evaluation criteria were based on mean ejection time, extracorporeal circuit (ECC) pressure, and upstroke of dp/dt. The results suggested that the Capiox 308 hollow-fibre membrane oxygenator produced the best physiologic pulsatile waveform according to the ejection time, ECC pressure, and the upstroke of dp/dt. The Minimax Plus and Masterflo Infant hollow-fibre membrane oxygenators also produced adequate pulsatile flow. Only the Variable Prime Cobe Membrane Lung (VPCML) Plus flat-sheet membrane oxygenator failed to reach the criteria for physiologic pulsatility. Depending on the oxygenator used, the lowest priming volume of the infant CPB circuit was 415 ml and the highest 520 ml.

The relation between pump flow rate and pulsatility on cerebral hemodynamics during pediatric cardiopulmonary bypass

OBJECTIVES

Neurologic impairment, at least partly ischemic in origin, has been reported in up to 25% of infants undergoing cardiopulmonary bypass, with or without circulatory arrest. Controversy continues about the effect of pump flow, pulsatile or nonpulsatile, on the brain and in particular on cerebral blood flow. This study examines the relationship between pump flow rate and cerebral hemodynamics during pulsatile and nonpulsatile cardiopulmonary bypass.

METHOD

Near-infrared spectroscopy was used to determine cerebral blood flow and cerebral blood volume (measured as concentration change) in a randomized crossover study. Pulsatile and nonpulsatile flow were used for six 5-minute intervals at each of three different pump flow rates (0.6, 1.2, and 2.4 L x m2 x min(-1)) in 40 patients, median age 2 months (range 2 weeks to 20 years 5 months). The relations between pulsatile flow, pump flow rate, cerebral blood flow, hemoglobin concentration change (cerebral blood volume), mean arterial pressure, arterial carbon dioxide tension, and hematocrit value were prospectively examined by means of multivariate analysis.

RESULTS

Cerebral blood flow decreased 36% per L x m(-2) x min(-1) decrease in pump flow rate and was associated with changes in mean arterial pressure but did not differ according to pulsatility. Change in hemoglobin concentration was unrelated to changes in pulsatility of pump flow.

CONCLUSION

Cerebral blood flow is related to pump flow rate. Pulsatile flow delivered with a Stöckert pump does not increase cerebral blood flow or alter hemoglobin concentration during cardiopulmonary bypass in children.

Pulsatile and nonpulsatile perfusion: the continuing controversy

This report discusses pulsatile and nonpulsatile perfusion with regard to hemodynamics, cell metabolism, and the visceral consequences of these forms of cardiopulmonary bypass. It argues that differences between the two modes and a benefit for pulsatile perfusion, are most clearly manifested in identifiable high-risk patient groups.

Determinants of cerebral perfusion during cardiopulmonary bypass

The risk of postoperative neurologic dysfunction in patients undergoing cardiac surgery remains high despite continued improvements in myocardial protective strategies. Part of this neurologic morbidity can be attributed to patients' increased age and underlying pathology, but other factors adversely affecting cerebral blood flow and cerebral metabolism during cardiopulmonary bypass may also contribute. Particulate microembolization during cardiopulmonary bypass appears to be a major cause of postoperative neurologic dysfunction and the pH-stat method of carbon dioxide management during hypothermia may potentiate neurologic damage by allowing a greater embolic load to be delivered to the brain. Echocardiography and transcranial Doppler methods may contribute to reducing the incidence of cerebral embolization by recognizing the timing and number of microemboli. Although hypothermia confers cerebral protection, rewarming may unmask and perhaps potentiate any ischemic damage that occurred with embolization during hypothermia. Both the degree and speed of rewarming may be important factors contributing to the extent of ischemic damage and ultimately neurologic function. In addition, many other factors related to cardiopulmonary bypass can alter cerebral perfusion and metabolism, such as nonpulsatile flow, hemodilution, pressure autoregulation, anesthetic and cerebroprotective drugs, and the neuroimmune response to bypass. In this review, the major factors affecting cerebral blood flow during cardiopulmonary bypass are discussed and their relative importance evaluated with regard to postoperative neurologic function.

Cerebral hemodynamics after low-flow versus no-flow procedures

Temperature induces depression of cerebral perfusion and cerebral oxygen metabolism in particular, and this seems to explain why a reduced pump flow above a critical level is well tolerated during hypothermic cardiopulmonary bypass with apparent full metabolic recovery afterward. It only partly explains why a longer period of hypothermic circulatory arrest leads to a protracted recovery of cerebral perfusion and cerebral metabolism. This review suggests there is evidence that energy metabolism can easily be compromised during and after rewarming after hypothermic cardiopulmonary bypass with low flow and with circulatory arrest. Although data indicate that cerebral metabolism and cerebral energy state are better after low flow than after circulatory arrest, the risk of energy crises appears imminent with both techniques.