Venous Collapse Research Articles

Alternatives to the intravenous route in emergency situations

Patients in emergency situations or life distress most often need a intravenous line (IV) to give them the medications they need. The IV route is the preferred route to treat most of the patients in emergency situations out of hospital or in the emergency room but can be very tricky to obtain. Various alternatives have been developed, such as the intraosseous route, particularly useful in cases of venous collapse (shock, cardiorespiratory arrest), the intramuscular route (anaphylaxis, sedation) or the intranasal route (status epilepticus, analgesia). This article reviews the indications, contraindications and pharmacology of these different routes.

Recurrent reflex syncope in idiopathic intracranial hypertension patient resolved after lumbar puncture: pathogenetic implications

BackgroundIdiopathic intracranial hypertension is a disease characterized by increased intracranial cerebrospinal fluid volume and pressure without evidence of other intracranial pathology. Dural sinuses are rigid structures representing a privileged low-pressure intracranial compartment. Rigidity of dural sinus ensures that the large physiologic fluctuations of cerebrospinal fluid pressure associated with postural changes or to Valsalva effect cannot be transmitted to the sinus. An abnormal dural sinus collapsibility, especially when associated with various anatomical sinus narrowing, has been proposed as a key factor in the pathogenesis of idiopathic intracranial hypertension. This pathogenetic model is based on an excessive collapsibility of the dural sinuses that leads to the triggering of a self-limiting venous collapse positive feedback-loop between the cerebrospinal fluid pressure, that compresses the sinus, and the increased dural sinus pressure upstream, that reduces the cerebrospinal fluid reabsorption rate, increasing cerebrospinal fluid volume and pressure at the expense of intracranial compliance and promoting further sinus compression. Intracranial compliance is the ability of the craniospinal space to accept small volumetric increases of one of its compartments without appreciable intracranial pressure rise. In idiopathic intracranial hypertension, a condition associated with a reduced rate of CSF reabsorption leading to its volumetric expansion, a pathologically reduced IC precedes and accompanies the rise of ICP. Syncope is defined as a transient loss of consciousness due to a transient cerebral hypoperfusion characterized by rapid onset, short duration, and spontaneous complete recovery. A transient global cerebral hypoperfusion represents the final mechanism of syncope determined by cardiac output and/or total peripheral resistance decrease. There are many causes determining low cardiac output including reflex bradycardia, arrhythmias, cardiac structural disease, inadequate venous return, and chronotropic and inotropic incompetence. Typically, syncopal transient loss of consciousness is mainly referred to an extracranial mechanism triggering a decrease in cardiac output and/or total peripheral resistance. Conversely, the association of syncope with a deranged control of intracranial compliance related to cerebral venous outflow disorders has been only anecdotally reported.Case PresentationWe report on a 57-year-old woman with daily recurrent orthostatic hypotension syncope and idiopathic intracranial hypertension-related headaches, which resolved after lumbar puncture with cerebrospinal fluid subtraction.ConclusionsA novel mechanism underlying the triggering of orthostatic syncope in the presence of intracranial hypertension-dependent reduced intracranial compliance is discussed.

Comparison of ultrasound-guided internal jugular vein and supraclavicular subclavian vein catheterization in critically ill patients: a prospective, randomized clinical trial

BackgroundThe aim of this study was to compare the effectiveness and safety of ultrasound-guided out-of-plane internal jugular vein (OOP-IJV) and in-plane supraclavicular subclavian vein (IP-SSCV) catheterization in adult intensive care unit.MethodsA total of 250 consecutive patients requiring central venous catheterization, were randomly assigned to undergo either ultrasound-guided OOP-IJV or IP-SSCV cannulation. All catheterizations were carried out by three physicians. The primary outcome was the first attempt success rate. Ultrasound scanning time, venous puncture time, insertion time, overall access time, number of puncture attempts, number of needle redirections, success rate, guidewire advancing difficulties, venous collapse and adverse events were also documented.ResultsThe first attempt success rate was significantly higher in IP-SSCV group (83.2%) compared to OOP-IJV group (63.2%) (p = 0.001). The IP-SSCV group was associated with a longer ultrasound scanning time (16.54 ± 13.51 vs. 5.26 ± 4.05 s; p < 0.001) and a shorter insertion time (43.98 ± 26.77 vs. 53.12 ± 40.21 s; p = 0.038). In the IP-SCCV group, we recorded a fewer number of puncture attempts (1.16 ± 0.39 vs. 1.47 ± 0.71; p < 0.001), needle redirections (0.69 ± 0.58 vs. 1.17 ± 0.95; p < 0.001), difficulties in guidewire advancement (2.4% vs. 27.4%; p < 0.001), venous collapse (2.4%, vs. 18.4%; p < 0.001) and adverse events (8.8% vs. 13.6%; p = 0.22).ConclusionsThe IP-SSCV approach is an effective and a safe alternative to the classic OOP-IJV catheterization in critical adult patients.Trial registration: Clinicaltrials.gov, NCT03879954. Registered March 19, 2019—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03879954.

Development of a Venous Collapse Prevention Device for Blood Draw

Abstract Blood sampling typically involves puncturing a superficial vein with a needle and then creating a vacuum (e. g., with a syringe) to transfer the blood from the venous system to the collection container. In some cases, the venous walls collapse due to excessive vacuum generated. In this work, a device is presented that prevents venous collapse and can be combined with any blood collection system available on the market. The mechanism of preventing venous collapse is based on a tubular segment interconnected between the needle and the syringe, which collapses at a lower vacuum pressure than the vein. The prototype was tested and evaluated using a test rig that simulates venous blood draw. The experiments proved the functionality of the device on a vein phantom.

A conceptual model for changes in finger photoplethysmograph signals caused by hand posture and isothermic regulation

Objective. To observe changes in baseline position and pulsatile light absorbance (photoplethysmograph, PPG) in the finger-tip, by raising the hand above the horizontal plane in recumbent subjects. We applied current knowledge of the circulation to the finger-tip, particularly arteriovenous anastomoses (AVAs), and the physiology of the venous circulation. Approach.We studied healthy young volunteers in a quiet thermoneutral environment. A finger plethysmograph on the non-dominant hand recorded transmission of red and infra-red light, with observations expressed as absorbance to allow comparisons within and between subjects. Breathing movements were recorded unobtrusively to assess any effect on absorbance and the pulse amplitude of the signals. All body movements were passive: the study arm was elevated in a trough to about 40° above the horizontal plane. The following conditions were studied, each for 15 min, using the last 10 min for analysis: recumbent, study arm elevated, study arm horizontal, and both legs elevated by 40°. Main results. We found a substantial time-related effect, and considerable variation between subjects. Arm elevation reduced red light absorbance and increased the range of amplitudes of the PPG waveform: only in subjects with large absorbances, did waveform amplitude increase. Spontaneous, thermoregulatory decreases in absorbance were large and associated with decreases in waveform amplitude. Significance. Finger-tip vessels distend with blood and light absorbance increases when AVAs open. The vessels pulsate more strongly when the hand is raised: venous collapse allows the vessels to become more compliant. The postcapillary circulation is likely to be an important source of pulsation.

ACUTE VARICOCELE THROMBOSIS AFTER VACCINATION WITH MRNA SARS-COV-2 VACCINE- A CASE REPORT

ObjectivesThe dilatation of the pampiniform plexus, the venous system that drains the testicle, causes varicocele. Varicocele thrombosis is rare, with few reported cases in the medical literature [1-6]. Patients may present with acute scrotal pain, mimicking a testicular torsion or strangulated hernia. Diagnosis is difficult, therefore, when based solely on clinical history and examination. Our objective is to present an unusual case of varicocele thrombosis, after Covid 19 vaccination.MaterialsUltrasonography (US) with Doppler interrogation is the first-line imaging choice for diagnosis [1]. The therapeutical management is primarily conservative; however, some cases might require surgery [1,6]. The Coronavirus 2019 pandemic stimulated the development of vaccines with unprecedented speed and employing novel technologies. Serious adverse effects remained low after worldwide vaccination [7,8].ResultsWe report the case of a 35-year-old male patient who presented in the Urology Department accusing intense, continuous scrotal pain and swelling, with onset the next day after receiving the second dose of an mRNA Covid-19 vaccine (BNT162b2, Cominarty, Pfizer/BioNTech). There were no associated urinary signs and no fever. The patient was a healthy young man, with no known malignancy or blood dyscrasia. He could not recall suffering any local trauma between the vaccination and the appearance of the symptoms.The clinical exam revealed a tender, scrotal swelling inferior to the left testicle.The ultrasound exam demonstrated homogenous, normal echogenic testicles without changes in vascularity on Doppler US. Multiple variceal dilatations with a spontaneous diameter of up to 5 mm were observed around the left testis. The lumen of several dilated veins appeared filled with echogenic debris. The blood flow was slow in the remaining veins, with a sluggish aspect. Continuous, progressive probe compression was applied, with no complete venous collapse observed. The greyscale aspect was consistent with partially obstructing thrombi. The venous filling defects were confirmed on Colour Doppler. No signs of thrombosis were present at the level of the spermatic cord or the inguinal canal.ConclusionsPampiniform plexus thrombosis should be considered in the differential diagnosis of acute testicular pain.This case report reveals an unprecedented etiology of varicocele thrombosis, as a side effect of an mRNA SARS-COV2 vaccine.

Comparison of Minimally Invasive Thrombectomy with Percutaneous Balloon Angioplasty for Organized Thrombi in Hemodialysis Access.

Thrombi are an important challenge when establishing hemodialysis access for hemodialysis. We developed a minimally invasive thrombectomy (MIT) salvage treatment to solve this problem when traditional percutaneous transluminal angioplasty (PTA) fails. The study aimed to investigate the safety and patency rate following MIT as a rescue procedure for traditional PTA with organized thrombi obstructing hemodialysis access. This was a prospective study of MIT as a rescue procedure for traditional PTA to remove organized thrombi and establish hemodialysis access. We included patients with (1) stenotic lesions, (2) vascular access thrombi, (3) high venous pressure, (4) vascular collapse and suction. Nephrologists evaluated hemodialysis access immediately post-thrombi removal and patency at 7, 30, 60, 120, and 180 days post-removal, in addition to complications. Kaplan-Meier survival analysis was performed to analyze the primary and secondary patency rates after clinical procedural success. From June 2014 to May 2015, 746 patients underwent PTA in our hospital, and 425 patients consented to participate in this study. Of these patients, we enrolled 46 who underwent simultaneous PTA and MIT. Immediate clinical success was achieved in 100% of the patients in the MIT group. No complications were observed in any of the 46 patients, including major bleeding, shock, or hospitalization. The primary and secondary patency rates did not differ between MIT and PTA alone (p = 0.93 and p = 0.28, respectively). MIT can be considered a safe rescue procedure for removing organized thrombi to establish vascular access for hemodialysis when initial and traditional PTA fails.

Fluid-structure Interaction in the Cerebral Venous Transverse Sinus.

The biomechanics of the cerebral venous system plays an important role in determining blood flow to the brain. Computational approaches to help elucidate the role of the cerebral venous system in health and disease have largely focused on lumped-parameter models and one-dimensional computational fluid dynamics simulations. To expand upon the prior work, and to investigate the possible role of cerebral venous collapse in normal physiology and pathological conditions, we developed a fluid-structure interaction (FSI) model of the cerebral venous transverse sinus (TS), coupled to a lumpedparameter representation of the upstream cerebral circulation to provide boundary conditions for the FSI simulation. We simulated the effects of local venous hemodynamics on the TS distention and investigated TS vascular collapse under increased intracranial pressure, as has been hypothesized in the pathogenesis of idiopathic intracranial hypertension. Our baseline simulations reproduced pressures and flows in the cerebral venous system that compared favorably with what has been reported in the literature. The FSI simulations under increased intracranial pressure showed a decreased venous flow through and progressive collapse of the TS veins. Our simulations captured the dynamic behavior of the vascular collapse and may help shed light on the interactions between the cerebrovascular and cerebrospinal fluid spaces in health and disease.

Starling resistors, autoregulation of cerebral perfusion and the pathogenesis of idiopathic intracranial hypertension.

Two critical functions for the control of intracranial fluids dynamics are carried on the venous side of the perfusion circuit: the first is the avoidance of cortical veins collapse during the physiological increases of cerebrospinal fluid (CSF) pressure in which they are immersed. The second, is the generation of an abrupt venous pressure drop at the confluence of the cortical veins with the dural sinuses that is required to allow a CSF outflow rate balanced with its production. There is evidence that both of these effects are ensured by a Starling resistor mechanism (a fluid dynamic construct that governs the flow in collapsible tubes exposed to variable external pressure) acting at the confluence of cortical veins in the dural sinus. This implies that, in normal circumstances of perfusion balance, a certain degree of venous collapse physiologically occurs at the distal end of the cortical vein. This is passively modulated by the transmural pressure of the venous wall (i.e. the difference between internal blood pressure and external CSF pressure). The mechanism provides that the blood pressure of the cortical vein upstream the collapsed segment is dynamically maintained a few mmHg higher than the CSF pressure, so as to prevent their collapse during the large physiological fluctuations of the intracranial pressure. Moreover, the partial collapse of the vein confluence also generates a sharp pressure drop of the blood entering into the sinus. The CSF is drained in dural sinus through arachnoid villi proportionally to its pressure gradient with the sinus blood. The venous pressure drop between cortical veins and dural sinus is therefore needed to ensure that the CSF can leave the cranio-spinal space with the same speed with which it is produced, without having to reach a too high pressure, which would compress the cortical veins. Notably, the mechanism requires that the walls of the dural sinuses are rigid enough to avoid the collapse under the external cerebrospinal fluid pressure, and predicts that in the presence of excessively flexible dural sinuses, the system admits a second point of balance between cerebral fluid pressure and dural sinus pressure, at higher values. The second balance state is due to the triggering of a self-limiting venous collapse feedback loop between the CSF pressure, that compresses the sinus, and the subsequent increase of the dural sinus pressure, that further raises the intracranial pressure. The loop may stabilize only when the maximum stretching allowed by the venous wall is reached. Then, a new relatively stable and self-sustaining balance state is achieved, at the price of a higher CSF and dural sinus pressure values. We propose that this model is crucially involved in Idiopatic Intracranial Hypertension pathogenesis with and without papilledema, a condition that could be described as a pathological new balance state, relatively stable, between intracranial and dural venous pressure, at higher absolute values.

Retinal venous pulsation: Expanding our understanding and use of this enigmatic phenomenon.

Retinal vein pulsation was first noted soon after the invention of the ophthalmoscope 170 years ago and was seen to change with cerebrospinal fluid pressure (CSFP) variation in the 1920s. The classical explanation for vein pulsation was that the cardiac cycle induced systolic peak in intraocular pressure (IOP) tended to intermittently collapse the retinal vein close to its exit in the central optic disk, causing pulsation to be counter-phase to IOP. Recently, improved ophthalmodynamometry and video recording techniques have allowed us to explore the fundamentals of retinal vein pulsation. This demonstrates that retinal venous collapse is in phase with both IOP and CSFP diastole, indicating the dependence upon CSFP pulse. We describe in some detail the mathematical and physical models of Starling resistors and how their results can be applied to understand the physiology of retinal vein pulsation. We discuss various techniques for measuring retinal venous pulsation, including a novel modified photo-plethysmographic technique developed in our laboratory. With these techniques, non-invasive measurement of CSFP is beginning to look feasible. Venous pulsation properties also have significant prognostic value in predicting long-term outcomes for both glaucoma and central retinal vein occlusion, as well as utility in other retinal vasculopathies and orbital disease. We demonstrate the potential use of modified photo-plethysmographic images in assessing these various disorders. A revised understanding of retinal vein pulse wave transmission along with improved measurement techniques may generate useful clinical tools for assessing these disorders.

Idiopathic intracranial hypertension: ongoing clinical challenges and future prospects.

Idiopathic intracranial hypertension (IIH) is an uncommon disorder characterized by increased intracranial pressure without radiological or laboratory evidence of intracranial pathology except empty sella turcica, optic nerve sheath with filled out cerebrospinal fluid spaces, and smooth-walled nonflow-related venous sinus stenosis or collapse. This condition typically affects obese women. The incidence of IIH is increasing with the rising prevalence of obesity. Persistent headache is the most common symptom. Visual impairment is a serious complication that may not be recognized by the patients. This paper reviews clinical manifestations, diagnostic challenges, and current treatments of IIH in adults. Various imaging modalities have been studied on their validity for detection of IIH and papilledema. This review also includes new studies on medical, surgical, and interventional management of this condition. Acetazolamide and topiramate are the only two medications that have been studied in randomized controlled trials about their efficacy in treatment of IIH. In patients who have severe visual impairment or progressive visual deterioration despite medical management, surgical or interventional treatment may be considered. The efficacy and complications of cerebrospinal fluid diversion, optic nerve sheath fenestration, and endovascular venous stenting reported in the last 3 decades have been summarized in this review. Finally, the prospective aspects of biomarkers and treatments are proposed for future research.

Mechanically Assisted Total Cavopulmonary Connection With an Axial Flow Pump: Computational and In Vivo Study.

A relevant number of patients undergoing total cavopulmonary connection (TCPC) experience heart failure (HF). Heart transplant is then the final option when all other treatments fail. The axial flow blood pumps are now the state of the art; however, there is little experience in low-pressure circuits, such as support of the right ventricle or even a TCPC circulation. A new T-shaped model of mechanically assisted TCPC using the "Jarvik Child 2000" axial pump, (flow rates between 1 and 3 L/m in a range of 5000-9000 rpm) was designed, simulated numerically, and then tested in animals. Eight sheep (42-45 kg) were studied: two pilot studies, four pump-supported (PS) TCPC for 3 h, and two not pump-supported (NPS) TCPC. In the PS, the axial pump was set to maintain the baseline cardiac output (CO). Pressures, CO, systemic and pulmonary vascular resistance, lactate levels, and blood gases were recorded for 3 h. Computational fluid dynamics (CFD) study allows us to set the feasible operating condition and the safety margins to minimize the venous collapse risk. In the NPS animals, a circulatory deterioration, with increasing lactate level, occurred rapidly. In the PS animals, there was a stable cardiac index of 2.7 ± 1.4 L/min/m(2), central venous pressure of 12.3 ± 1 mm Hg, and a mean pulmonary artery pressure (PAP) of 18.1 ± 6 after 3 h of support up to 9000 rpm. systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), blood gasses, and arterial lactate levels remained stable to baseline values. No caval collapse occurred. A new pediatric axial flow pump provides normal CO and physiologic stability in a new T-shaped model of TCPC in sheep, in vivo. CFD and in vivo data showed that this experimental arrangement will allow us to evaluate the potential for mechanical support in patients with Fontan failure avoiding major adverse events.

Flow and oscillations in collapsible tubes: Physiological applications and low-dimensional models

The motivation for this subject comes from physiology: Air-flow in the lungs, where flow limitation during forced expiration is a consequence of large-airway collapse, and wheezing, which is a manifestation of self-excited mechanical oscillations; Blood flow in veins, such as those of giraffes, in which the return of blood to the heart from the head must be accompanied by partial venous collapse, and in arteries, which exhibit self-excited oscillations (Korotkov sounds) when compressed by a blood-pressure cuff. Laboratory experiments are frequently conducted in a Starling resistor, a finite length of flexible tube, mounted between two rigid tubes and contained in a pressurised chamber. Steady conditions upstream and downstream give rise not only to steady flows, but also to a rich variety of self-excited oscillations, which theoreticians have been seeking to understand for at least five decades. Some of the observations have been reproduced in full Navier–Stokes computations for a two-dimensional model, but these do not provide physical understanding. We seek a self-consistent mathematical model for the oscillations. We concentrate first on 1D models, in which the key dependent variables are the cross-sectional area A and the cross-sectionally averaged velocity u and pressure p, all taken to be functions of longitudinal coordinate x and time t. The governing equations are those of conservation of mass and momentum and a tube law representing the elastic properties of the vessel. In the momentum equation, the viscous resistance term is conventionally modelled either as a linear function of fluid velocity, accurate at low Reynolds number, or with an ad hoc representation of the energy loss at flow separation. Even with such crude approximations, the predictions of 1D models agree quite well both with observations in the giraffe and with some of the 2D computations and 3D experiments. For a more rational model, we examine a 2D model problem, in which part of one wall of a parallel sided channel is replaced by a membrane under tension. One approach, for large Reynolds-number flow, and a long membrane, is to consider small deflections of the membrane and use interactive boundary-layer theory. This leads to interesting predictions, such as the impossibility of simultaneously prescribing the flow rate and the upstream pressure, but not to oscillations, except in cases where wall inertia is important (flutter). Another approach is to assume a parabolic velocity profile everywhere, leading to a rational choice for the inertia and viscous terms in the 1D momentum equation. If, further, the undisturbed membrane is taken to be flat, by a suitable choice of external pressure distribution, the system leads to an oscillatory instability even without wall inertia. Whether these oscillations have the same physics as those computed numerically at lower Reynolds number remains to be seen.

How to prevent venous cannula orifice obstruction during extracorporeal circulation.

Venous cannula orifice obstruction is an underestimated problem during augmented cardiopulmonary bypass (CPB), which can potentially be reduced with redesigned, virtually wall-less cannula designs versus traditional percutaneous control venous cannulas. A bench model, allowing for simulation of the vena cava with various affluent orifices, venous collapse and a worst case scenario with regard to cannula position, was developed. Flow (Q) was measured sequentially for right atrial+hepatic+renal+iliac drainage scenarios, using a centrifugal pump and an experimental bench set-up (afterload 60 mmHg). At 1500, 2000 and 2500 RPM and atrial position, the Q values were 3.4, 6.03 and 8.01 versus 0.77*, 0.43* and 0.58* l/min: p<0.05* for wall-less and the Biomedicus® cannula, respectively. The corresponding pressure values were -15.18, -31.62 and -74.53 versus -46.0*, -119.94* and -228.13* mmHg. At the hepatic position, the Q values were 3.34, 6.67 and 9.26 versus 2.3*, 0.42* and 0.18* l/min; and the pressure values were -10.32, -20.25 and -42.83 versus -23.35*, -119.09* and -239.38* mmHg. At the renal position, the Q values were 3.43, 6.56 and 8.64 versus 2.48*, 0.41* and 0.22* l/min and the pressure values were -9.64, -20.98 and -63.41 versus -20.87 -127.68* and -239* mmHg, respectively. At the iliac position, the Q values were 3.43, 6.01 and 9.25 versus 1.62*, 0.55* and 0.58* l/min; the pressure values were -9.36, -33.57 and -44.18 versus -30.6*, -120.27* and -228* mmHg, respectivly. Our experimental evaluation demonstrates that the redesigned, virtually wall-less cannulas, allowing for direct venous drainage at practically all intra-venous orifices, outperform the commercially available control cannula, with superior flow at reduced suction levels for all scenarios tested.

Venous cannula performance assessment in a realistic caval tree model.

A new caval tree system was designed for realistic in vitro simulation. The objective of our study was to assess cannula performance for virtually wall-less versus standard percutaneous thin-walled venous cannulas in a setting of venous collapse in case of negative pressure. For a collapsible caval model, a very flexible plastic material was selected, and a model with nine afferent veins was designed according to the anatomy of the vena cava. A flow bench was built including a lower reservoir holding the caval tree, built by taking into account the main afferent vessels and their flow provided by a reservoir 6 cm above. A cannula was inserted in this caval tree and connected to a centrifugal pump that, in turn, was connected to a reservoir positioned 83 cm above the second lower reservoir (after-load = 60 mmHg). Using the same pre-load, the simulated venous drainage for cardiopulmonary bypass was realized using a 24 F wall-less cannula (Smartcanula) and 25 F percutaneous cannula (Biomedicus), and stepwise increased augmentation (1500 RPM, 2000 and 2500 RPM) of venous drainage. For the thin wall and the wall-less cannulas, 36 pairs of flow and pressure measurements were realized for three different RPM values. The mean Q-values at 1500, 2000 and 2500 RPM were: 3.98 ± 0.01, 6.27 ± 0.02 and 9.81 ± 0.02 l/min for the wall-less cannula (P <0.0001), versus 2.74 ± 0.02, 3.06 ± 0.05, 6.78 ± 0.02 l/min for the thin-wall cannula (P <0.0001). The corresponding inlet pressure values were: -8.88 ± 0.01, -23.69 ± 0.81 and -70.22 ± 0.18 mmHg for the wall-less cannula (P <0.0001), versus -36.69 ± 1.88, -80.85 ± 1.71 and -101.83 ± 0.45 mmHg for the thin-wall cannula (P <0.0001). The thin-wall cannula showed mean Q-values 37% less and mean P values 26% more when compared with the wall-less cannula (P <0.0001). Our in vitro water test was able to mimic a negative pressure situation, where the wall-less cannula design performs better compared with the traditional thin-wall cannula.

Non-invasive bedside assessment of central venous pressure: scanning into the future.

BackgroundNoninvasive evaluation of central venous pressure (CVP) can be achieved by assessing the Jugular Venous Pressure (JVP), Peripheral Venous Collapse (PVC), and ultrasound visualization of the inferior vena cava. The relative accuracy of these techniques compared to one another and their application by trainees of varying experience remains uncertain. We compare the application and utility of the JVP, PVC, and handheld Mini Echo amongst trainees of varying experience including a medical student, internal medicine resident, and cardiology fellow. We also introduce and validate a new physical exam technique to assess central venous pressures, the Anthem sign.MethodsPatients presenting for their regularly scheduled echocardiograms at the hospital echo department had clinical evaluations of their CVP using these non-invasive bedside techniques. The examiners were blinded to the echo results, each other's assessments, and patient history; their CVP estimates were compared to the gold standard level 3 echo-cardiographer's estimates at the completion of the study.Results325 patients combined were examined (mean age 65, s.d. 16 years). When compared to the gold standard of central venous pressure by a level 3 echocardiographer, the JVP was the most sensitive at 86%, improving with clinical experience (p<0.01). The classic PVC technique and Anthem sign had better specificity compared to the JVP. Mini Echo estimates were comparable to physical exam assessments.ConclusionsJVP evaluation is the most sensitive physical examination technique in CVP assessments. The PVC techniques along with the newly described Anthem sign may be of value for the early learner who still has not mastered the art of JVP assessment and in obese patients in whom JVP evaluation is problematic. Mini Echo estimates of CVPs are comparable to physical examination by trained clinicians and require less instruction. The use of Mini Echo in medical training should be further evaluated and encouraged.

Case report: (Pre)syncopal symptoms associated with a negative internal jugular venous pressure.

A siphon is suggested to support cerebral blood flow but appears not to be established because internal jugular venous (IJV) pressure is close to zero in upright humans. Thus, in eleven young healthy males, IJV pressure was 9 ± 1 mmHg (mean ± SE) when supine and fell to 3 ± 1 mmHg when seated, and middle cerebral artery mean blood velocity (MCA Vmean; P < 0.007) and the near-infrared spectroscopy-determined frontal lobe oxygenation (ScO2; P = 0.028) also decreased. Another subject, however, developed (pre)syncopal symptoms while seated and his IJV pressure decreased to −17 mmHg. Furthermore, his MCA Vmean decreased and yet within the time of observation ScO2 was not necessarily affected. These findings support the hypothesis that a negative IJV pressure that is a prerequisite for creation of a siphon provokes venous collapse inside the dura, and thereby limits rather than supports CBF.

Caval collapse during cardiopulmonary bypass: a reproducible bench model

During open heart surgery, so-called atrial chatter, a phenomenon due to right atria and/or caval collapse, is frequently observed. Collapse of the cava axis during cardiopulmonary bypass (CPB) limits venous drainage and may result downstream in reduced pump flow on (lack of volume) and upstream in increased after-load (stagnation), which in turn may both result in reduced or even inadequate end-organ perfusion. The goal of this study was to reproduce venous collapse in the flow bench. In accordance with literature for venous anatomy, a caval tree system is designed (polyethylene, thickness 0.061 mm), which receives venous inflow from nine afferent veins. With water as medium and a preload of 4.4 mmHg, the system has an outflow of 4500 ml/min (Scenario A). After the insertion of a percutaneous venous cannula (23-Fr), the venous model is continuously served by the afferent branches in a venous test bench and venous drainage is augmented with a centrifugal pump (Scenario B). With gravity drainage (siphon: A), spontaneously reversible atrial chatter can be generated in reproducible fashion. Slight reduction in the outflow diameter allows for generation of continuous flow. With augmentation (B), irreversible collapse of the artificial vena cava occurs in reproducible fashion at a given pump speed of 2300 ± 50 RPM and a pump inlet pressure of -112 mmHg. Furthermore, bubbles form at the cannula tip despite the fact that the entire system is immersed in water and air from the environment cannot enter the system. This phenomenon is also known as cavitation and should be avoided because of local damage of both formed blood elements and endothelium, as well embolization. This caval model provides a realistic picture for the limitations of flow due to spontaneously reversible atrial chatter vs irreversible venous collapse for a given negative pressure during CPB. Temporary interruption of negative pressure in the venous line can allow for recovery of venous drainage. This know-how can be used not only for testing different cannula designs, but also for further optimizing perfusion strategies.

Editorial Comment: Miniaturized cardiopulmonary bypass: the importance of controlling the controllable

Despite some demonstrable advantages, miniaturized cardiopulmonary bypass (mCPB) remains on the edge of clinical practice. Our team at the Hammersmith Hospital in London have deliberated at length on why its widespread adoption has not occurred. The evolution from conventional to mCPB involved significant modifications that were all made simultaneously. This accelerated transition has been a key contributor in obstructing wider clinical acceptance. The risk is that these multiple changes can create an uncomfortable clinical environment for the cardiac team. For some users, this exposure has diminished the ability to embrace the advantages and the ambition to advance the technique. Implementing change presents both advantages and disadvantages. It is our responsibility as a cardiac team, specifically the Perfusion profession, to balance the advantages against the disadvantages and deliver a technique that improves extracorporeal support. On the surface, current mCPB research may be perceived as merely revisiting the same findings. This is not the case. We must consider publications in the context of guiding us to where mCPB needs to be, rather than presuming that it describes the finished article. The publication in this issue by Aboud et al .[ 1] is a prime example. The advantages of the technique are eloquently demonstrated, which are reduced haemodilution, reduced inflammatory markers, reduced haemolysis and reduced cardiac damage. Two significant disadvantages are also identified: excessive negative venous pressure and increased arterial air. Importantly, these disadvantages are described and quantified. If we consider venous pressure, this is an important and underappreciated quality indicator for cCPB as well as mCPB. De Somer [2] makes the point that an increase in venous negative pressure will coincide with vein collapse when the negative pressure at the tip of the venous cannula exceeds −4 mmHg. The relationship between the pressure at the tip of the cannula and the pressure in the venous line is patient specific. At the Hammersmith, we refer to this as the Patient Specific Venous Collapse Pressure (PSVCP). We have in vivo data to show that this threshold varies from −5 mmHg to −60 mmHg, depending on the IVC size, RA size, cannula size, cannula type, cannula position and patient circulating volume. By considering this information alongside the results published in Table 2 by Aboud et al. ,i t is confirmed that for some patients, even gravity drainage is excessive. We have all experienced the visual consequence of this phenomenon in the form of venous line judder when using gravity venous drainage. Venous line pressure is not a routinely measured CPB parameter. Aboud’s research and our experience at the Hammersmith suggest it is a robust quality indicator and therefore should be monitored during all cases. Without a doubt, monitoring this parameter should be a minimum requirement for all mCPB. The problem with excessive negative venous line pressure is 2-fold. First, it creates venous congestion. When the PSVCP is exceeded, it is equivalent to placing a clamp across the IVC. This will have an impact on end-organ perfusion and potentially, clinical outcome. The second consequence of excessive negative venous line pressure is the generation of gaseous micro-emboli. This problem is compounded when using a closed system as is the case with mCPB. This is confirmed by Aboud’s paper as significantly more air was detected in the arterial line of the mCPB group. As stakeholders in delivering better cardiopulmonary bypass, the question for all of us is ‘what do we do with the findings in Aboud’s research?’ The starting point should be to identify and control the controllable.

Miniaturized cardiopulmonary bypass: the Hammersmith technique

BackgroundConventional Cardiopulmonary Bypass (cCPB) is a trigger of systemic inflammatory reactions, hemodilution, coagulopathy, and organ failure. Miniaturised Cardiopulmonary Bypass (mCPB) has the potential to reduce these deleterious effects. Here, we describe our standardised ‘Hammersmith’ mCPB technique, used in all types of adult cardiac operations including major aortic surgery.MethodsThe use of mCPB remains limited by the diversity of technologies which range from extremely complex, micro systems to ones very similar to cCPB. Our approach is designed around the principle of balancing the benefits of miniaturisation; reducing foreign surface area while maintaining patient safety.ResultsFrom January 2010 to March 2011, a single surgeon performed 184 consecutive operations (Euro score Logistic 8.4+/-9.9): 61 aortic valve replacements, 78 CABGs, 25 aortic valve replacement and CABG and 17 other procedures (major aortic surgery, re-do operations or double/triple valve replacements).Our clinical experience suggests that:i. Venous drainage is optimally maintained using kinetic energy.ii. Venous collapse pressure depends on the patient’s anatomy and cannula size, but most importantly on the negative pressure generated by venous drainage.iii. The patient-prime interaction is optimised with antegrade and retrograde autologous priming, which mixes the blood and prime away from the tissues and results in a reduced oncotic destabilization.iv. mCPB is a safe and reproducible techniqueConclusionThe Hammersmith mCPB is a “next generation” system which uses standard commercially available components. It aims to maintain safety margin and the benefit of miniaturised system whilst reducing the human factor demands.