Myocardial contractile function and intradialytic hypotension

Dialysis‐induced hypotension remains a significant problem in hemodialysis (HD) patients. Numerous factors result in dysregulation of blood pressure control and impaired myocardial reserve in response to HD‐induced cardiovascular stress. Episodic intradialytic hypotension may be involved in the pathogenesis of evolving myocardial injury. We performed an initial pilot investigation of cardiovascular functional response to pharmacological cardiovascular stress in hypotension‐resistant (HR) and hypotension‐prone (HP) HD patients. We studied 10 matched chronic HD patients (5 HP, 5 HR). Dobutamine‐atropine stress (DAS) was performed on a nondialysis short interval day, with noninvasive pulse‐wave analysis using the Finometer^® to continuously measure hemodynamic variables. Baroreflex sensitivity was assessed at rest and during DAS. Baseline hemodynamic variables were not significantly different. The groups had differing hemodynamic responses to DAS. The Mean arterial pressure was unchanged in the HR group but decreased in HP patients (?13.6 ± 3.5 mmHg; P<0.001). This was associated with failure to significantly increase cardiac output in the HP group (cf. increase in cardiac output in the HR group of +33.4 ± 6%; P<0.05), and a reduced response in total peripheral resistance (HP ?10.3 ± 6.8%, HR ?22.7 ± 2.9%, P=NS). Baroreflex sensitivity was not significantly different between groups at baseline or within groups with increasing levels of DAS; however, the mean baroreflex sensitivity was higher in HR cf. HP subjects throughout pharmacological stress (P<0.05). Hypotension‐prone patients appear to have an impaired cardiovascular response to DAS. The most significant abnormality is an impaired myocardial contractile reserve. Early identification of these patients would allow utilization of therapeutic strategies to improve intradialytic tolerability, potentially abrogating aggravation of myocardial injury.     

Categorization of the hemodynamic response to hemodialysis: The importance of baroreflex sensitivity

Intradialytic hypotension (IDH) remains an important cause of morbidity and mortality in hemodialysis (HD) patients. The baroreflex arc is under autonomic control and regulates blood pressure. This study aimed to investigate the contribution of impaired baroreflex sensitivity (BRS) to the pathophysiology of IDH. Thirty-four chronic HD (12 IDH-prone, 22 IDH-resistant) patients underwent BRS measurement during HD with relative blood volume monitoring. During analysis, patients were separated into four age-matched groups according to resting BRS≥4.5 ms/mmHg and hemodynamic stability. Resting BRS was extremely heterogenous (geometric mean BRS 5.78±1.41 [range 1.76–41.41] ms/mmHg). Relative blood volume reduction was well matched in all groups (mean reduction in relative blood volume for all patients −6.74%±0.86%, P>0.05). Thirty-seven episodes of IDH occurred in the IDH prone, reduced BRS group. Patients with impaired resting BRS and prone to IDH had markedly different responses to HD as compared to the preserved BRS group, but the total peripheral resistance response was significantly lower than in the IDH-resistant patients (15.9%±2.1% vs. 42.4%±3.0%, respectively, P<0.001). In those patients prone to IDH and with impaired resting BRS, percentage reduction in cardiac output at the end of HD highly correlated with reduction in relative blood volume (r=0.94, P=0.006). Hypotension during dialysis may be an important source of recurrent cardiac injury and early recognition of those patients prone to relative symptomatic and asymptomatic hypotension remains important. Impaired resting BRS and recognition of a suboptimal peripheral pressor response, appear to predict those patients most likely to undergo hemodynamic instability and may assist in the pursuit of this elusive goal.     

A study of the extracorporeal rate of blood flow and blood pressure during hemodialysis

Hemodynamic instability is a common problem during hemodialysis (HD). The effect of blood flow rate (BFR) on blood pressure (BP) during HD has not been previously evaluated. Subjects receiving HD for the treatment of renal failure were enrolled (n=34). For each patient, during the last hour of 2 consecutive HD sessions the BFR was set at 200 mL/min for 30 min and at 400 mL/min for 30 min, during which period the fluid removal rate was kept constant. The order of the BFR alterations was randomized. The study procedure was repeated during the next HD session but with reversal of the order of the altered BFR. During each 30-min period, BP was recorded at baseline and subsequently every 10 min. During the BFR of 400 mL/min, subjects had a higher systolic BP by an average of 4.1 mmHg compared with the BFR of 200 mL/min (95% confidence interval [CI] 0.22-7.98; p=0.038). Similarly, during the BFR of 400 mL/min, subjects had a higher diastolic BP by an average of 3.04 mmHg compared with the BFR of 200 mL/min (95% CI 0.55-5.53; p=0.017). Likewise, during the BFR of 400 mL/min, subjects had a higher mean arterial pressure by an average of 3.44 mmHg (95% CI 0.77-6.11; p=0.012). The findings suggest that during HD, BPs are maintained higher at higher BFRs as compared with lower BFRs.     

煤层底板水害预测与超前预治理技术

煤矿水害防治工作是煤矿安全生产工作的重中之重。针对煤层底板水害防治问题,介绍了实际生产过程中针对掘进工作面和回采工作面突水危险性预测的常规方法,对其优缺点进行综合分析,从而进行煤层底板突水危险性的预测评价,进而制定工作面超前预治理的技术方案,主要包括应用煤层底板含水层注浆改造技术对煤层底板突水可能性大的区域进行注浆改造,或利用煤层底板含水层疏水降压技术对危险区域进行疏水降压。上述这些措施的使用,最大限度地避免了水害事故的发生,实现了安全开采。     

Does Blood Pressure Control by Gentle Ultrafiltration Improve Survival in Hemodialysis Patients?

Agentle ultrafiltration can be achieved using a long and slow hemodialysis. It is easier to achieve gentle ultrafiltration if the interdialytic weight intake is moderate ( i.e., if the patient maintains a low sodium diet) and if diffusion allows for a negative or nil sodium balance during the session ( i.e., dialysate sodium < 140 mmol/L). A gentle ultrafiltration allows control of blood pressure by reducing the extracellular volume to its ideal level, the “dry weight,” at the end of the session. Controlling blood pressure reduces cardiovascular mortality, which is by far the foremost cause of death in hemodialysis. Controlling blood pressure means reducing the occurrence of both hypertension and hypotension. Hypotension has been reported to correlate with mortality in hemodialysis as much as or more than hypertension itself. This “U‐curve” phenomenon is not paradoxical. It displays two distinct facts on the same figure: an increased early mortality in hypotensive patients (hypotension is a marker of frailty or congestive heart failure, both of which cause increased mortality) and, on the other hand, the well‐established, long‐term increased mortality in hypertensive patients. Hypotension is not a mandate to undertreat hypertension.     

Fallacies of High‐Speed Hemodialysis

Chronic hemodialysis sessions, as developed in Seattle in the 1960s, were long procedures with minimal intra‐ and interdialytic symptoms. Financial and logistical pressures related to the overwhelming number of patients requiring hemodialysis created an incentive to shorten dialysis time to four, three, and even two hours per session in a thrice weekly schedule. This method spread rapidly, particularly in the United States, after the National Cooperative Dialysis Study suggested that time of dialysis is of minor importance as long as urea clearance multiplied by dialysis time and scaled to total body water (Kt/V_urea) equals 0.95–1.0. This number was later increased to 1.3, but the assumption remained unchanged that hemodialysis time is of minimal importance as long as it is compensated by increased urea clearance. Patients accepted short dialysis as a godsend, believing that it would not be detrimental to their well‐being and longevity. However, Kt/V_urea measures only removal of low molecular weight substances and does not consider removal of larger molecules. Besides, it does not correlate with the other important function of hemodialysis, namely ultrafiltration. Whereas patients with substantial residual renal function may tolerate short dialysis sessions, the patients with little or no urine output tolerate short dialyses poorly because the ultrafiltration rate at the same interdialytic weight gain is inversely proportional to dialysis time. Rapid ultrafiltration is associated with cramps, nausea, vomiting, headache, fatigue, hypotensive episodes during dialysis, and hangover after dialysis; patients remain fluid overloaded with subsequent poor blood pressure control, left ventricular hypertrophy, diastolic dysfunction, and high cardiovascular mortality. Short, high‐efficiency dialysis requires high blood flow, which increases demands on blood access. The classic wrist arteriovenous fistula, the access with the best longevity and lowest complication rates, provides “insufficient” blood flow and is replaced with an arteriovenous graft fistula or an intravenous catheter. Moreover, to achieve high blood flows, large diameter intravenous catheters are used; these fit veins “too tightly,” so predispose the patient to central‐vein thrombosis. Longer hemodialysis sessions (5–8 hrs, thrice weekly), as practiced in some centers, are associated with lower complication rates and better outcomes. Frequent dialyses (four or more sessions per week) provide better clinical results, but are associated with increased cost. It is my strong belief that a wide acceptance of longer, gentler dialysis sessions, even in a thrice weekly schedule, would improve overall hemodialysis results and decrease access complications, hospitalizations, and mortality, particularly in anuric patients.     

Intradialytic complications during hemodialysis

With the advent of developments and advances in hemodialysis machine technology, dialysate water purification, and dialyzers, the clinical spectrum of intradialytic complications has changed over the decades. In the pioneering days of hemodialysis, patients could develop allergic reactions to dialyzer membranes, sterilizing and reprocessing agents, coupled with machines that could not accurately control ultrafiltration rates, and chemically and bacterially contaminated dialysate. Whereas today, although cardiovascular problems remain the most common intradialytic complication, these are mainly due to the time restraints of trying to cope with excessive dialytic weight gains and achieve target dry weight on a thrice weekly schedule, coupled with an aging elderly dialysis population with increasing co-morbidity.     

Effects of secondary amyloidosis on arteriovenous hemodialysis fistula outcomes and intradialytic hypotension: a case-control study

Amyloid fibrils can affect vascular structure through deposition and by causing nitric oxide depletion and increase of asymmetric dimethyl arginine. Patients with amyloidosis are prone to development of hypotension. Hypotension may also affect the maturation of arteriovenous fistula (AVF) and may set the stage for formation of thrombosis and fistula failure. Thus, we aimed to evaluate effects of secondary amyloidosis on AVF outcomes and intradialytic hypotension. This is a case‐control study which included 20 hemodialysis patients with amyloidosis and 20 hemodialysis patients without amyloidosis as control group. All patients underwent Doppler ultrasound of AVF. A thorough fistula history and baseline laboratory values along with episodes of intradialytic hypotension and blood pressure measurements were recorded. There was no difference between the groups regarding age, gender, body mass index, presence of comorbidities, hypertension, and drug use. Systolic and diastolic blood pressures were similar (119 ± 28/75 ± 17 and 120 ± 14/75 ± 10 mmHg for patients with and without amyloidosis, respectively). Intradialytic hypotension episodes were also similar. Patients with amyloidosis had significantly lower serum albumin and higher C‐reactive protein values compared to control hemodialysis patients. AVF sites and total number of created fistulas were similar in both groups. Flow rates of current functional AVFs were not different between the groups (1084 ± 875 and 845 ± 466 mL/minute for patients with and without amyloidosis, respectively, p:0.67). Patency duration of first AVF was not different between the groups. Clinical fistula outcomes and rate of intradialytic hypotension episodes were not significantly different between patients with and without secondary systemic amyloidosis.