Preoperative serum potassium changes in patients undergoing Open Heart Surgery under Cardiopulmonary Bypass: A Comparative study between two group of patients- one group of patients on long term preoperative diuretics and the other group not on diuretics

Abstract

INTRODUCTION: The patients who undergo cardiac surgery in our hospital can be mainly divided into two groups. The first group of patients are who have coronary artery disease and the second group of patients are those with valvular heart disease. The first group of patients undergo coronary artery bypass grafting and the second group undergo valve repair or replacement. These patients will undergo these surgeries under cardiopulmonary bypass. They are in different class on the New York Heart Association’s physical status classification. Based on the severity of the disease and the symptoms, these patients are treated with different group of medications. As the disease advances these patients develop cardiac failure. When systolic heart failure occur, the heart can no more pump adequate amount of blood into the systemic circulation leading to symptoms of low cardic output or of the fluid overload to the heart . When diastolic dysfunction occur, the patients develop heart failure due to atrial hypertension. Congestive cardiac failure leads to the symptoms like easy fatiguability, dyspnea and congestion. The medical management of heart failure includes angiotensin converting enzyme inhibitors, diuretics, vasodilators and digitalis. Diuretics are used to relieve circulatory congestion. Symptoms improve as the pulmonary and peripheral edema are relieved. Diuretics reduce atrial and ventricular diastolic pressures thereby reducing the diastolic stress on the ventricular wall. This will help in preventing persistent cardiac distension and improve subendocardial perfusion. Chronic use of diuretics will lead to hypokalemia. So potassium supplementation is given in patients on chronic diuretics use. Potassium sparing diuretics helps in avoiding hypokalemia but they will not cause adequate natriuresis. Hypokalemia or hyperkalemia in the perioperative period cause cardiac conduction disturbances and they are not desirable. There are various factors in the perioperative period which can alter potassium homeostasis like the prescence of diabetic mellitus, hypertension, chronic renal failure, ischemic and valvular heart diseases, respiratory and metabolic acid-base disturbances, hypothermia, blood transfusion, dose and duration of the use of cardioplegia. The potassium homeostasis is maintained by giving potassium correction in the form of intravenous potassium in hypokalemia and by giving calcium, sodium bicarbonate, glucose-insulin infusion, nebulization with beta 2 agonists when hyperkalemia occurs. This is an observational study to study the role of preoperative use of diuretics in the incidence of altered serum potassium levels in the perioperative period. We compared two group of patients with one group on long term preoperative diuretic and the other group not on diuretics. This study helped us to understand whether diuretics played a role in the perioperative potassium homeostasis. AIMS AND OBJECTIVES: 1. To study the differences in the perioperative serum potassium changes between one group of patients on long term preoperative diuretics and the second group of patientswho were not on preoperative diuretics who underwent openheart surgery under cardiopulmonary bypass. 2. To compare the interventions needed to keep potassium homeostasis between the two groups. METHODOLOGY: Study Setting: The study was conducted in the Cardiothoracic operating suites and in the cardiothoracic intensive care units in Christian Medical College Hospital, Vellore. Study Population: 100 consecutive patients between 14 – 75 years who underwent cardiac surgeries during the 6 months study period in Christian Medical College Hospital, Vellore. Inclusion criteria: • Age < 14 years, • Chronic renal failure with serum creatinine > 1.6 mgms%. STUDY PERIOD: The study was conducted over a period of 6 months between July to December 2012. A pilot study was conducted prior to the commencement of the study. SAMPLE SIZE: 46. STUDY METHOD: The patients who fulfilled the inclusion criteria and gave consent were enrolled in the study. All medications that the patient was taking preoperatively were continued as per the routine schedule except ACE inhibitors. Tablet lorazepam and tablet omeprazole were given as premedication the night before and on the day of surgery. The preoperative comorbid conditions like diabetic mellitus, chronic renal failure, the medication taken like diuretics, ACE inhibitors, digoxin, Potassium supplements are all noted in the proforma. A baseline arterial blood gas (ABG) is done and the values entered in the proforma. The ABG is repeated once the patient is on the cardiopulmonary bypass circuit, before coming out of bypass circuit and after coming out of the bypass circuit. Any incidence of hypokalemia or hyperkalemia in noted along with the interventions made to keep the potassium levels normal. In hypokalemia, potassium chloride (kcl) is given and in hyperkalemia the treatment includes calcium, sodium bicarbonate, glucose insulin infusion. Any need for blood transfusion is noted as it may have an influence on serum potassium levels. The potassium rich cardioplegia is used to arrest the heart during cardiac surgery. The dose and the duration of cardioplegia is also noted. These patients are not extubated in the operation suite. They are shifted to the cardiothoracic intensive care unit (I C U)with endotracheal tube and electively ventilated for a day. The patient is followed in the for first two postoperative days in the ICU. In the ICU, arterial blood gas (ABG) is repeated every four to six hourly. Any event of hypokalemia or hyperkalemia along with the interventions needed to keep the the potassium level normal in noted. All patients received nebulizations with salbutamol and ipratropium bromide after extubation .We could enroll 100 patients in this study with 50 patients in the diuretic group and fifty I n the non-diuretic group. Once the adequate sample size has been achieved, all these datas were entered in the Epidata soft ware and exported into the Excel spreadsheet. STATISTICAL METHODS: 47. All the datas collected were analyzed using Generalized Estimating Equations. CONCLUSIONS: The observations of the study on ‘perioperative serum potassium changes in patients undergoing open heart surgery under cardiopulmonary bypass: A comparative study between two group of patients – one group of patients on long term preoperative diuretics and the other group not on diuretics’ are: 1. There is no significant statistical difference in the incidence of hypokalemia or hyperkalemia between the two group of patients. 2. A subgroup of patients who received preoperative oral potassium supplementation were found to be requiring 2 gms lesser potassium correction than in those who never received oral potassium in the preoperative period which is statistically significant with the p value of 0.000. 3. The patients who were diabetic and also on long term diuretic therapy required 1.3 gms lesser kcl to keep their potassium above 4 mEq/L than those who were not diabetic. This was found to be statistically significant with a p value of 0.010. 4. The role of other preoperative medications like ACE inhibitors, digoxin, did not have any statistical significance in causing a difference in serum potassium levels in both the groups. 5. The effects of parameters like haemoglobin, serum creatinine, serum bicarbonate, base excess, pH, Pco2 were all found to be clinically insignificant in affecting the perioperative potassium requirements in both the groups with the p values more than 0.7. 6. This study did not show any significant statistical difference in the perioperative requirement of sodium bicarbonate, calcium, magnesium ,glucose-insulin infusion and frusemide. 7. The role of cardioplegia and blood transfusion were also found to be statistically not significant in causing a change in serum potassium levels between both the groups