Potassium concentrations and ventricular ectopy: a prospective, observational study in post-cardiac surgery patients

A Narrative Review for Anesthesiologists of the 2017 American Heart Association/American College of Cardiology/Heart Rhythm Society Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death

This is a review of the 2017 AHA/ACC/HRS Guidelines with guidance for intraoperative physicians. Ventricular arrhythmias occurring during the perioperative period have the potential for significant morbidity and mortality. Hence, an in-depth knowledge of VA mechanisms, prevention, and management is crucial for all clinicians caring for these at-risk patients in the perioperative period. Perioperative optimization of patients with a known or suspected VA should be tailored to the specific patient population and condition as outlined in this manuscript.

The Utility of Basic Metabolic Panel Tests After Total Joint Arthroplasty

INTRODUCTION

Routine laboratory studies are often obtained daily after total joint arthroplasty (TJA) regardless of medical management. The purpose of this study was to investigate the utility of routine basic metabolic panel (BMP) tests after TJA. Furthermore, the goal was to identify factors that may predispose patients to abnormal laboratory values that require medical intervention.

METHODS

A retrospective review was performed on 767 patients who underwent primary TJA at a single institution. Preoperative and postoperative potassium, sodium, creatinine, and glucose values were collected along with demographic data, comorbidities, and procedural characteristics. Multivariable logistic regression models were used to determine independent risk factors for abnormal postoperative laboratory values.

RESULTS

Diabetes was associated with abnormal glucose (odds ratio [OR] 23.4, 95% confidence interval [CI] 10.7-51.0, P < .001), while chronic kidney disease was associated with abnormal creatinine (OR 3.1, 95% CI 1.7-5.8, P < .001) and potassium (OR 1.8, 95% CI 1.1-2.8, P = .014) requiring medical intervention. An abnormal preoperative laboratory value was also associated with medical treatment for each of sodium, potassium, and creatinine (all P < .001). Average number of BMP tests collected for patients who did not receive medical intervention was 2.8. This equated to $472,372.56 in total hospital charges.

CONCLUSION

Cost containment while maintaining high-quality patient care is critical. Routine postoperative BMP tests in patients with normal preoperative values without major medical comorbidities do not contribute to actionable information. Patients with diabetes, chronic kidney disease, or with abnormal preoperative values should obtain a BMP after TJA.

Safety, Efficacy, and Timeliness of Intravenous Potassium Chloride Replacement Protocols in a Pediatric Cardiothoracic Intensive Care Unit

OBJECTIVE

Hypokalemia in children following cardiac surgery occurs frequently, placing them at risk of life-threatening arrhythmias. However, renal insufficiency after cardiopulmonary bypass warrants careful administration of potassium (K⁺). Two different nurse-driven protocols (high dose and tiered dosing) were implemented to identify an optimal K⁺ replacement regimen, compared to an historical low-dose protocol. Our objective was to evaluate the safety, efficacy, and timeliness of these protocols.

DESIGN

A retrospective cohort review of pediatric patients placed on intravenous K⁺ replacement protocols over 1 year was used to determine efficacy and safety of the protocols. A prospective single-blinded review of K⁺ repletion was used to determine timeliness.

PATIENTS

Pediatric patients with congenital or acquired cardiac disease.

SETTING

Twenty-four-bed cardiothoracic intensive care unit in a tertiary children's hospital.

INTERVENTIONS

Efficacy was defined as fewer supplemental potassium chloride (KCl) doses, as well as a higher protocol to total doses ratio per patient. Safety was defined as a lower percentage of serum K⁺ levels ≥4.8 mEq/L after a dose of KCl. Between-group differences were assessed by nonparametric univariate analysis.

RESULTS

There were 138 patients with a median age of 3.0 (interquartile range: 0.23-10.0) months. The incidence of K⁺ levels ≥4.8 mEq/L after a protocol dose was higher in the high-dose protocol versus the tiered-dosing protocol but not different between the low-dose and tiered-dosing protocols (high dose = 2.2% vs tiered dosing = 0.5%, P = .05). The ratio of protocol doses to total doses per patient was lower in the low-dose protocol compared to the tiered-dosing protocol (P < .05). Protocol doses were administered 45 minutes faster (P < .001).

CONCLUSION

The tiered-dosed, nurse-driven K⁺ replacement protocol was associated with decreased supplemental K⁺ doses without increased risk of hyperkalemia, administering doses faster than individually ordered doses; the protocol was effective, safe, and timely in the treatment of hypokalemia in pediatric patients after cardiac surgery.

Potassium and Magnesium Supplementation Do Not Protect Against Atrial Fibrillation After Cardiac Operation: A Time-Matched Analysis

BACKGROUND

Despite a lack of demonstrated efficacy, potassium and magnesium supplementation are commonly thought to prevent postoperative atrial fibrillation (POAF) after cardiac operation. Our aim was to evaluate the natural time course of electrolyte level changes after cardiac operation and their relation to POAF occurrence.

METHODS

Data were reviewed from 2,041 adult patients without preoperative AF who underwent coronary artery bypass grafting, valve operation, or both between 2009 and 2013. In patients with POAF, the plasma potassium and magnesium levels nearest to the first AF onset time were compared with time-matched electrolyte levels in patients without AF.

RESULTS

POAF occurred in 752 patients (36.8%). At the time of AF onset or the matched time point, patients with POAF had higher potassium (4.30 versus 4.21 mmol/L, p < 0.001) and magnesium (2.33 versus 2.16 mg/dL, p < 0.001) levels than controls. A stepwise increase in AF risk occurred with increasing potassium or magnesium quintile (p < 0.001). On multivariate logistic regression analysis, magnesium level was an independent predictor of POAF (odds ratio 4.26, p < 0.001), in addition to age, Caucasian race, preoperative β-blocker use, valve operation, and postoperative pneumonia. Prophylactic potassium supplementation did not reduce the POAF rate (37% versus 37%, p = 0.813), whereas magnesium supplementation was associated with increased POAF (47% versus 36%, p = 0.005).

CONCLUSIONS

Higher serum potassium and magnesium levels were associated with increased risk of POAF after cardiac operation. Potassium supplementation was not protective against POAF, and magnesium supplementation was even associated with increased POAF risk. These findings help explain the poor efficacy of electrolyte supplementation in POAF prophylaxis.

Response to intravenous potassium chloride supplementation in pediatric cardiac intensive care patients

Potassium chloride (KCl) supplementation is common among critically ill children. Intravenous (IV) KCl supplementation for pediatric patients is poorly characterized. This study aimed to examine the efficacy and safety of IV KCL and to determine factors affecting patient responses to IV KCL in the pediatric cardiac intensive care unit (CICU). A retrospective review of 211 children (794 KCl doses) undergoing cardiac surgery or a hospital stay for heart failure in the CICU of a tertiary care teaching and referral children's hospital in 2011 was performed. Demographic data, weight, height, creatinine, and concomitant medications during each KCl dose were recorded and analyzed. Body surface area (BSA), creatinine clearance, and change in [K(+)] were calculated. The median age of the children was 4 months (range, 10 days-18 years). In this study, 151 KCl doses were administered to neonates (19 %), 307 doses (39 %) to females, and 510 doses (64 %) to patients with a BSA smaller than 0.33 m(2) (a group with relative renal insufficiency). The mean KCl dose was 0.97 ± 0.006 mEq/kg. No adverse events were associated with IV KCl administration. Blood/plasma [K(+)] increased 0.8 ± 0.02 mEq/L. The responses to KCl did not differ significantly between males and females, between neonates and children, or between patients with a BSA smaller than 0.33 m(2) and those with a BSA of 0.33 m(2) or larger. The responses to IV KCl were attenuated by concomitant furosemide (p = 0.01), amphotericin B (p < 0.01), and KCl in parenteral nutrition (p < 0.01). The responses were augmented by concomitant enalapril (p = 0.03), ethacrynic acid (p < 0.001), and hemodialysis (p < 0.01). Intravenous KCl can be administered safely for CICU patients. Responses to KCl are altered when it is given with certain medications. Intravenous KCl should be used cautiously in children receiving angiotensin-converting enzyme inhibitors. Future studies are needed for further characterization of factors affecting responses to IV KCl in children.

Safely treating hypokalaemia in high dependency cardiac surgical patients

In Australia, there were national issues on the use of potassium ampoules (resulting in patient deaths), which led to the removal of the ampoules from clinical areas. A decision was made by the Medication Safety Committee at a metropolitan Melbourne hospital to remove potassium ampoules from ward areas as part of the establishment of a hospital-wide potassium guideline. As a result, the nurses in the cardiothoracic ward Practice Review Committee identified the need to review the proposed practice of treating hypokalaemia with 30 mmol of potassium chloride (KCL) in 1000 mL over an extended period in postoperative cardiothoracic patients. The challenge was to develop a practice to safely administer intravenous KCL in fluid restricted patients in addition to the hospital guidelines to prevent hypokalaemic-induced cardiac dysrhythmias. A literature search revealed there were no clear or uniform approaches to guide our practice in addressing this clinical problem. The Practice Review Committee developed a KCL administration guideline based on a review of the available literature. The Practice Review Committee developed a ward-based guideline that addressed infusion concentration, duration of administration, responsiveness of nurses to severity of hypokalaemia and the evaluation of treatment by measuring serum potassium after replacement. This ward-based guideline was based on benchmarking from similar institutions and relevant literature. The review process provided an opportunity for the staff to critique their practice to improve patient care and allowed regular evaluation of the implemented practice guideline. The ward-based guideline required a revision as patients' renal function was not being taken into consideration prior to potassium infusions being administered. The implementation of the ward-based guideline into practice has been well received by the staff as it has allowed consistent practice and timely treatment of hypokalaemia.

Isolated perfused and paced guinea pig heart to test for drug-induced changes of the QT interval

INTRODUCTION

One of the biomarkers for assessing the risk of a cardiac adverse event is drug-induced prolongation of the QT interval. A model is needed for evaluating the potential liability of test compounds on QT interval in vitro. Since QT intervals can be generated from paced or spontaneously beating hearts, data so generated can also be used for validating QT(c) correction equations.

METHODS

Isolated guinea pig hearts were perfused in Locke's solution according to the Langendorff method. QT intervals were routinely measured from Lead II ECG waveforms.

RESULTS

Compounds known to inhibit HERG channel, such as dofetilide, prolonged the QT interval in this model. (+/-)Bay K8644, a calcium channel activator, prolonged the QT interval, while verapamil, a calcium channel blocker, shortened it. Procainamide, a sodium channel blocker, also prolonged the QT interval. Many of the compounds, which prolonged the QT interval, also prolonged PR interval, suggesting dual inhibition of the Ikr channel, the rapid component of delayed rectifier potassium channel, and the calcium channel. The QT/RR intervals exhibited a curvilinear relationship, which could be corrected into nearly straight horizontal lines by using correction equations derived from linear, parabolic, and hyperbolic models. However, these correction equations yielded different results on the QT prolongation produced by sotalol, which also slowed down the heart rate. With the data set obtained in this investigation, correction equations derived from linear and parabolic models worked better than the equations derived from the hyperbolic model. The exponential model did not fit at all.

CONCLUSION

QT intervals obtained under paced conditions provide the most direct and reliable QT information for a drug. The isolated perfused and paced guinea pig heart is a convenient model for studying the effect of compounds on QT interval in vitro.

Supraventricular tachyarrhythmia as early indicator of a complicated course after esophagectomy

In a group of 89 consecutive patients with a standardized operative procedure, the incidence of supraventricular tachyarrhythmia (SVT), predisposing risk factors (preoperative and intraoperative factors and parameters of intensive care strategy) and therapeutic strategies were evaluated. Operative treatment consisted of transthoracic esophagectomy, gastric interposition and intrathoracic anastomosis. Overall hospital mortality was 6.7%. In 32 (37%) patients a new onset SVT occurred. Age and elevated body temperature were the only significant risk factor for SVT in the multivariate analysis, their odds ratios being 1.3 for each year above 58 and 5.6 for each degree above 37.8 degrees C, respectively. Secondary risk factors were history of hypertension and use of epinephrine, the corresponding odds ratios being 6.6 and 10.2. Digitalis (2/32) and calcium-antagonists (2/9) were unsatisfactory, while beta-blockers (13/20) and amiodarone (12/12) were efficient therapeutic agents. Incidence of SVT was significantly correlated with the development of postoperative septic complications.