Cardiopulmonary Bypass, Hemolysis, and Nitroprusside-Induced Cyanide Production

Neuron-specific enolase levels immediately following cardiovascular surgery is modulated by hemolysis due to cardiopulmonary bypass, making it unsuitable as a brain damage biomarker

Neuron-specific enolase (NSE) is one of the biomarkers used as an indicator of brain disorder, but since it is also found in blood cell components, there is a concern that a spurious increase in NSE may occur after cardiovascular surgery, where cardiopulmonary bypass (CPB) causes hemolysis. In the present study, we investigated the relationship between the degree of hemolysis and NSE after cardiovascular surgery and the usefulness of immediate postoperative NSE values in the diagnosis of brain disorder. A retrospective study of 198 patients who underwent surgery with CPB in the period from May 2019 to May 2021 was conducted. Postoperative NSE levels and Free hemoglobin (F-Hb) levels were compared in both groups. In addition, to verify the relationship between hemolysis and NSE, we examined the correlation between F-Hb levels and NSE levels. We also examined whether different surgical procedures could produce an association between hemolysis and NSE. Among 198 patients, 20 had postoperative stroke (Group S) and 178 had no postoperative stroke (Group U). There was no significant difference in postoperative NSE levels and F-Hb levels between Group S and Group U (p = 0.264, p = 0.064 respectively). F-Hb and NSE were weakly correlated (r = 0.29. p < 0.01). In conclusion, NSE level immediately after cardiac surgery with CPB is modified by hemolysis rather than brain injury, therefore it would be unreliable as a biomarker of brain disorder.

Nitric Oxide in Cardiac Surgery: A Review Article

Perioperative organ injury remains a medical, social and economic problem in cardiac surgery. Patients with postoperative organ dysfunction have increases in morbidity, length of stay, long-term mortality, treatment costs and rehabilitation time. Currently, there are no pharmaceutical technologies or non-pharmacological interventions that can mitigate the continuum of multiple organ dysfunction and improve the outcomes of cardiac surgery. It is essential to identify agents that trigger or mediate an organ-protective phenotype during cardiac surgery. The authors highlight nitric oxide (NO) ability to act as an agent for perioperative protection of organs and tissues, especially in the heart-kidney axis. NO has been delivered in clinical practice at an acceptable cost, and the side effects of its use are known, predictable, reversible and relatively rare. This review presents basic data, physiological research and literature on the clinical application of NO in cardiac surgery. Results support the use of NO as a safe and promising approach in perioperative patient management. Further clinical research is required to define the role of NO as an adjunct therapy that can improve outcomes in cardiac surgery. Clinicians also have to identify cohorts of responders for perioperative NO therapy and the optimal modes for this technology.

Postoperative Hepatic Dysfunction After Frozen Elephant Trunk for Type A Aortic Dissection

Background: This study was aimed to investigate the incidence, risk factors, and outcomes of patients with postoperative hepatic dysfunction (PHD) after frozen elephant trunk (FET) for type A aortic dissection (TAAD).

Method: A retrospective study was performed with 492 patients who underwent FET for TAAD between 2015 and 2019. Independent risk factors for PHD were determined by multivariate mixed-effect logistic analysis with surgeon-specific factor as a random effect.

Results: The incidence of PHD was 25.4% (n = 125) in our cohort. Patients with PHD presented higher early mortality (10.4 vs. 1.1%, p < 0.001), rates of acute kidney injury (42.4 vs. 12.8%, p < 0.001), and newly required dialysis (23.2 vs. 3.0%, p < 0.001) compared with those without PHD. Moreover, with the median follow-up period of 41.3 months, the survival curve was worse in patients with PHD compared with no PHD group (log-rank p < 0.001), whereas it was similar after excluding patients who died within 30 days (log-rank p = 0.761). Multivariable analyses suggested that PHD was predicted by preoperative aspartate transferase [odds ratio (OR), 1.057; 95% confidence intervals (CI), 1.036–1.079; p < 0.001], celiac trunk malperfusion (OR, 3.121; 95% CI, 1.008–9.662; p = 0.048), and cardiopulmonary bypass time (OR, 1.014; 95% CI, 1.005–1.023; p = 0.003). Retrograde perfusion (OR, 0.474; 95% CI, 0.268–0.837; p = 0.010) was associated with a reduced risk of PHD. Celiac trunk malperfusion was an independent predictor for PHD but not associated with early mortality and midterm survival.

Conclusions: PHD was associated with increased early mortality and morbidity, but not with late death in midterm survival. PHD was predicted by preoperative aspartate transferase, celiac trunk malperfusion, and cardiopulmonary bypass (CPB) time, and retrograde perfusion was associated with a reduced risk of PHD.

Renal Toxicodynamic Effects of Extracellular Hemoglobin After Acute Exposure

Plasma hemoglobin (Hb) is elevated in some hematologic disease states, during exposures to certain toxicants, and with the use of some medical devices. Exposure to free Hb can precipitate oxidative reactions within tissues and alter the normal physiological function of critical organ systems. As kidney structures can be highly sensitive to Hb exposures, we evaluated the acute dose dependent renal toxicologic response to purified Hb isolated from RBCs. Male Hartley guinea pigs (n = 5 per group) were dosed with 0.9% saline (2 ml), 15, 75, 150, or 300 mg of purified Hb, infused over a 2-h period. The primary endpoints of this study were to define toxicokinetic parameters after increasing doses of purified Hb, identify clinically recognized and experimental markers of acute kidney injury (AKI), and determine relevant toxicological parameters and potential causes of renal toxicity in this model. Experimental findings demonstrated a dose dependent increase in Cmax after a 2-h infusion, which correlated with an elevation in serum creatinine, renal Kim-1 mRNA expression and increased urinary Kim-1. Renal NGAL mRNA expression and urinary NGAL excretion were also increased in several groups, but these parameters did not correlate with exposure. Iron increased in the renal cortex as Hb exposure increased and its deposition colocalized with 4-hydroxy-nonenal and 8-Oxo-2-deoxyguanosine immune reactivity, suggesting oxidative stressors may contribute to AKI in animals exposed to Hb. The results presented here suggest that Cmax may effectively predict the risk of AKI in normal healthy animals exposed to Hb.

Hyperinflation of Nitroprusside

Sodium nitroprusside (SNP) is a generically available and rapid-acting intravenous (IV) vasodilator that has been used clinically for decades. Prior to 2013, the cost of SNP was relatively low, and SNP was an affordable option for the treatment of acute hypertension. However, from 2013 to 2017, average wholesale prices for SNP rose to as high as $900 per vial, earning the drug its status as a "hyperinflation drug." Hyperinflation drugs such as SNP pose a significant challenge for pharmacy departments. A multidisciplinary effort involving stakeholders from many backgrounds, including pharmacists, physicians, and nurses, is key to developing an effective plan to address the problem. A therapeutic interchange, wherein a drug with similar efficacy is substituted for another, is often an appropriate strategy in this scenario. Fortunately, alternative drugs with a solid evidence base exist for the management of acute hypertension. The dihydropyridine calcium channel blockers, clevidipine and nicardipine, are IV titratable antihypertensive agents with favorable pharmacokinetic and safety profiles. Various studies indicate that clevidipine and nicardipine are effective alternatives to SNP for indications including hypertensive crisis and postoperative hypertension. Some hospitals have reported significant cost savings without adverse outcomes by substituting clevidipine or nicardipine for SNP. This article is intended to serve as a review of the evidence for clevidipine and nicardipine as potential substitutes for SNP and to provide strategies to successfully implement this therapeutic interchange.

Sodium Nitroprusside as a Hyperinflation Drug and Therapeutic Alternatives

Sodium nitroprusside (SNP) is a generically available and rapid-acting intravenous (IV) vasodilator that has been used clinically for decades. Prior to 2013, the cost of SNP was relatively low, and SNP was an affordable option for the treatment of acute hypertension. However, from 2013 to 2017, average wholesale prices for SNP rose to as high as US$900 per vial, earning the drug its status as a "hyperinflation drug." Hyperinflation drugs pose a significant challenge for pharmacy departments. A multidisciplinary effort involving stakeholders from many backgrounds, including pharmacists, physicians, and nurses, is key to developing an effective cost containment strategy. A therapeutic interchange, wherein a drug with similar efficacy is substituted for another, is often an appropriate strategy to address rising drug costs. Fortunately, alternative drugs with a solid evidence base exist for the management of acute hypertension. The dihydropyridine calcium channel blockers, clevidipine and nicardipine, are IV titratable antihypertensive agents with favorable pharmacokinetic and safety profiles. Various studies indicate that clevidipine and nicardipine are effective alternatives to SNP for indications including hypertensive crisis and postoperative hypertension. Some hospitals have reported significant cost savings without adverse outcomes by substituting clevidipine or nicardipine for SNP. This article is intended to serve as a review of the evidence for clevidipine and nicardipine as potential substitutes for SNP and to provide strategies to successfully implement this therapeutic interchange.

Thiocyanate Accumulation in Critically Ill Patients Receiving Nitroprusside Infusions

PURPOSE

This study evaluated thiocyanate concentrations and factors associated with thiocyanate accumulation in intensive care unit patients receiving nitroprusside with and without sodium thiosulfate coadministration.

MATERIALS AND METHODS

This retrospective study evaluated critically ill adults who received nitroprusside infusions and had at least one thiocyanate concentration. Patients with thiocyanate accumulation (concentrations ≥30 µg/mL) were compared to patients without accumulation. Factors associated with accumulation were determined by Spearman correlation and multivariate regression.

RESULTS

Thiocyanate concentrations (n = 192) were obtained from 87 patients. Fourteen of the 87 (16%) patients experienced thiocyanate accumulation with a mean (SD) thiocyanate concentration of 44 ± 11 µg/mL. Patients with accumulation had received greater cumulative nitroprusside doses (28 vs 8.2 mg/kg, P < .01), greater cumulative sodium thiosulfate doses (16.8 vs 10.1 mg/kg, P < .01), and longer infusion durations (10.9 vs 6.0 days, P < .01), compared to patients without accumulation. Sodium thiosulfate coadministration resulted in greater thiocyanate concentrations (22.8 ± 16.7 vs 16.8 ± 14.9 μg/mL, P = .01), despite utilization of lower cumulative nitroprusside doses (10.2 vs 14.6 mg/kg, P = .03). Cumulative nitroprusside dose ( r² .44, P < .001) and cumulative sodium thiosulfate dose ( r² .32, P < .001) demonstrated a significant correlation with measured thiocyanate concentrations. Thiocyanate accumulation was independently associated with cumulative nitroprusside dose in mg/kg (regression coefficient 0.75, 95% CI 0.63-0.89; P < .01). No clinically significant adverse effects of cyanide or thiocyanate toxicity were observed.

CONCLUSIONS

Cumulative nitroprusside dose was independently associated with thiocyanate accumulation. Despite elevated thiocyanate levels in 16% of patients, there was no clinical evidence of cyanide or thiocyanate toxicity. Routine monitoring of thiocyanate concentrations appears most warranted in patients receiving higher cumulative doses of nitroprusside.

Cyanide toxicity during cardiopulmonary bypass with small dose of nitroprusside: a case report

Sodium nitroprusside (SNP) is an anti-hypertensive drug, commonly used to decrease the systemic vascular resistance and lower the blood pressure. When the amount of cyanide generated by the SNP exceeds the metabolic capacity for detoxification, cyanide toxicity occurs. Under general anesthesia and cardiopulmonary bypass (CPB), it may be difficult to detect the development of cyanide toxicity. In cardiac surgical patients, hemolysis, hypothermia and decreased organ perfusion, which emphasize the risk of cyanide toxicity, may develop as a consequence of CPB. In particular, hemolysis during CPB may cause an unexpected overproduction of cyanide due to free hemoglobin release. We experienced a patient who demonstrated SNP tachyphylaxis and cyanide toxicity during CPB, even though the total amount of SNP administered was much lower than the recommended dose. We therefore report this case with a review of the relevant literature.

Sodium nitroprusside in 2014: A clinical concepts review

Sodium nitroprusside has been used in clinical practice as an arterial and venous vasodilator for 40 years. This prodrug reacts with physiologic sulfhydryl groups to release nitric oxide, causing rapid vasodilation, and acutely lowering blood pressure. It is used clinically in cardiac surgery, hypertensive crises, heart failure, vascular surgery, pediatric surgery, and other acute hemodynamic applications. In some practices, newer agents have replaced nitroprusside, either because they are more effective or because they have a more favorable side-effect profile. However, valid and adequately-powered efficacy studies are sparse and do not identify a superior agent for all indications. The cyanide anion release concurrent with nitroprusside administration is associated with potential cyanide accumulation and severe toxicity. Agents to ameliorate the untoward effects of cyanide are limited by various problems in their practicality and effectiveness. A new orally bioavailable antidote is sodium sulfanegen, which shows promise in reversing this toxicity. The unique effectiveness of nitroprusside as a titratable agent capable of rapid blood pressure control will likely maintain its utilization in clinical practice for the foreseeable future. Additional research will refine and perhaps expand indications for nitroprusside, while parallel investigation continues to develop effective antidotes for cyanide poisoning.

Hemolysis during cardiac surgery is associated with increased intravascular nitric oxide consumption and perioperative kidney and intestinal tissue damage

Introduction: Acute kidney injury (AKI) and intestinal injury negatively impact patient outcome after cardiac surgery. Enhanced nitric oxide (NO) consumption due to intraoperative intravascular hemolysis, may play an important role in this setting. This study investigated the impact of hemolysis on plasma NO consumption, AKI, and intestinal tissue damage, after cardiac surgery.

Methods: Hemolysis (by plasma extracellular (free) hemoglobin; fHb), plasma NO-consumption, plasma fHb-binding capacity by haptoglobin (Hp), renal tubular injury (using urinary N-Acetyl-β-D-glucosaminidase; NAG), intestinal mucosal injury (through plasma intestinal fatty acid binding protein; IFABP), and AKI were studied in patients undergoing off-pump cardiac surgery (OPCAB, N = 7), on-pump coronary artery bypass grafting (CABG, N = 30), or combined CABG and valve surgery (CABG+Valve, N = 30).

Results: FHb plasma levels and NO-consumption significantly increased, while plasma Hp concentrations significantly decreased in CABG and CABG+Valve patients (p < 0.0001) during surgery. The extent of hemolysis and NO-consumption correlated significantly (r² = 0.75, p < 0.0001). Also, NAG and IFABP increased in both groups (p < 0.0001, and p < 0.001, respectively), and both were significantly associated with hemolysis (R_s = 0.70, p < 0.0001, and R_s = 0.26, p = 0.04, respectively) and NO-consumption (R_s = 0.55, p = 0.002, and R_s = 0.41, p = 0.03, respectively), also after multivariable logistic regression analysis. OPCAB patients did not show increased fHb, NO-consumption, NAG, or IFABP levels. Patients suffering from AKI (N = 9, 13.4%) displayed significantly higher fHb and NAG levels already during surgery compared to non-AKI patients.

Conclusions: Hemolysis appears to be an important contributor to postoperative kidney injury and intestinal mucosal damage, potentially by limiting NO-bioavailability. This observation offers a novel diagnostic and therapeutic target to improve patient outcome after cardiothoracic surgery.

Acute kidney injury following cardiac surgery: role of perioperative blood pressure control

BACKGROUND/AIMS

Patients who develop acute kidney injury (AKI) after cardiac surgery continue to have a high mortality rate. Although factors that predispose to postoperative renal dysfunction have been identified, this knowledge has not been associated with a substantial reduction in the incidence of this serious adverse event.

METHODS

This review uses the existing literature to explore the relationship between AKI and perioperative blood pressure (BP) control in cardiac surgery patients. The results of recent novel analyses are introduced, and the implications of these studies for the management of cardiac surgery patients in the perioperative period are discussed.

RESULTS

Preexisting isolated systolic hypertension and wide pulse pressure increase the risk of postoperative renal dysfunction in the cardiac surgery population. New data suggest that BP lability (i.e., BP excursions outside an acceptable physiologic range) during cardiac surgery may also be an important predictor of subsequent renal dysfunction.

CONCLUSION

Recently published data suggest that perioperative BP lability influences both the risk of postoperative renal dysfunction and 30-day mortality. Future studies will determine whether the use of agents that allow improved BP control within a desirable range will reduce the incidence of postoperative AKI in cardiac surgery patients.

Strategies for managing perioperative hypertension

Acute perioperative hypertension is associated with a higher risk of perioperative myocardial ischemia, bleeding, stroke, and renal failure. The immediate concern of short-term antihypertensive therapy is to prevent excessive surgical bleeding from arterial anastomoses, myocardial ischemia, and neurologic complications while causing minimal adverse effects until oral therapy can be resumed. This article reviews perioperative hypertension emergencies/urgencies and various approaches for management.

Perioperative hypertension: a review of current and emerging therapeutic agents

Perioperative hypertension is a common problem encountered by anesthesiologists, surgeons, internists, and intensivists. Surprisingly, no randomized, placebo-controlled studies exist that show that the treatment of perioperative hypertension reduces morbidity or mortality. Nevertheless, perioperative hypertension requires careful management. While sodium nitroprusside and nitroglycerin are commonly used to treat these conditions, these agents are less than ideal. Intravenous beta blockers and calcium channel blockers have particular appeal in this setting.

Evaluation of Sodium Nitroprusside Toxicity in Pediatric Cardiac Surgical Patients

Background:

Sodium nitroprusside (SNP) is often used in postoperative pediatric cardiac surgical patients. Cyanide toxicity may occur with the use of SNP. There is a paucity of literature describing dosing parameters or physical signs and symptoms of toxicity with SNP.

Objective:

To determine the incidence of cyanide toxicity in postoperative pediatric cardiac surgical patients treated with SNP and identify dosing parameters and physical signs and symptoms that may predict elevated cyanide concentrations.

Methods:

Medical records of patients who received SNP in the pediatric cardiac intensive care unit from January 2002 through December 2002 were identified and evaluated for cyanide and thiocyanate levels, dosing, and signs and symptoms of toxicity. Patients were included if they had received SNP after cardiac surgery, were 18 years of age or less, and had at least one cyanide or thiocyanate level determined while receiving therapy. Patients were excluded if they had received sodium thiosulfate. The Mann-Whitney U test was used to determine significant differences in mean dose, duration of infusion, renal function, serum lactate, and acid-base status between groups with elevated or nonelevated levels. Logistic regression and receiver operator curve were used to determine variables associated with elevated levels. Relationships between signs and symptoms of toxicity and elevated levels were evaluated with Fisher's exact test.

Results:

Cyanide concentrations were in the toxic range in 7 of 63 (11%) patients. Patients with elevated concentrations had significantly higher mean dose, cumulative dose, and acid-base excess values. Elevated cyanide levels were independently predicted by mean dose, cumulative dose, and acid-base excess values, and a dose of 1.8 μg/kg/min predicted an elevated cyanide concentration with 89% sensitivity and 88% specificity. Adverse events were not reliable predictors of elevated cyanide levels.

Conclusions:

Mean dose of SNP is the best predictor of elevated cyanide levels. Adverse events commonly associated with cyanide toxicity may not be reliable indicators of elevated cyanide concentrations.