Pilot Study for the Tight K Study

Arrhythmias are common in critical care, with atrial tachyarrhythmias (and especially AF) being the most prevalent. This is especially true after cardiac surgery, with approximately 1 in 3 patients affected. The occurrence of new-onset post-operative AF is associated with increased short and long-term mortality, intensive care unit (ICU) and hospital stay and costs of care. This association appears causal, even after correction for confounding factors.

Potassium (K+) plays an important role in cardiac electrophysiology and abnormal levels may cause arrhythmias. Hypokalaemia, defined as a serum K+ <3.6 milliequivalents per litre (mEq/L) is thus associated with an increased incidence of ventricular arrhythmia after myocardial infarction. Low K+ levels are common following cardiac surgery, and appear marginally lower in those suffering atrial arrhythmias in this context. Despite an absence of proof that this association is causal, efforts to maintain serum \[K+\] in the 'high-normal' range (4.5 - 5.5 mEq/L) are considered 'routine practice' for AF prevention worldwide. The efficacy of such intervention remains unproven and data supporting this practice is extremely limited, being derived from observational rather than interventional studies. Indeed, no data exist to demonstrate that maintaining a high-normal potassium level is beneficial, or that aggressive replenishment of potassium in patients with heart disease necessarily leads to a better clinical outcome.

Furthermore, the method of potassium supplementation may be problematic. Oral replacement is not possible immediately post-operatively. Central venous administration is thus generally utilised in the early post-operative period. However, this practice is both time-consuming and costly: the intravenous administration of potassium carries recognised clinical risk, and is now prescribed in pre-diluted doses, stored securely for a safety purposes. Oral replacement is commonly associated with profound nausea, and is very poorly tolerated by patients. The investigators have estimated that the annual spending on potassium in cardiothoracic patients at Barts Health National Health Service (NHS) Trust is £100,000, compared to £16,500 for Milrinone (perceived as a high cost drug (2011-2012 prices). Additional costs relating to nursing time, drug checks, and intravenous connection and charting are also accrued. Central venous catheters may also be routinely left in situ solely for the purposes of parenteral potassium replacement; leading to an increased risk of line-related sepsis.

The routine maintenance of serum K+ in the high-normal range is thus a costly and unproven practice.

• Potassium (Drug): The trial treatment will start when patients are admitted to the intensive care unit after their surgery. The patient will undergo regular blood investigations, as per current practice. The frequency of K+ monitoring while on ICU will be according to clinician / nursing staff preference. Potassium supplementation will be according to local hospital protocols. This can be either via an intravenous infusion or as a tablet. Patients will otherwise be treated as per current hospital protocol.

Primary outcomes

• Total number of patients recruited over a 6 month period [6 months]: The pilot study is being conducted to assess if it is feasible to recruit the required patient population into the study. The aim of the pilot is to recruit 160 patients over 6 months from two different centres.
• Number of patients successfully randomised into the study to receive standard either usual care or control of potassium at the lower limit of the normal range [6 months]: The pilot study will investigate if it is feasible to randomised patients between the control and intervention arms of the study
• Protocol violation rate [6 months]: Feasibility of ensuring that protocol violation rate is no more than 10%
• Number of patient with outcome data at 28 days [6 months]: This is a feasibility and one of the main outcome will be to assess the number of participants with outcome data at 28 days. The study will aim to follow up 90% of the patients randomised.

Secondary outcomes

• Incidence of new onset atrial fibrillation [Maximum of 5 days]: Episode of AF lasting at least 30 seconds that is clinically detected and/or electrocardiographically confirmed post surgery until day 5
• Mean critical care length of stay [Maximum 28 days]: Average time patients are treated on critical care ward
• Mean hospital length of stay [Maximum 28 days]: Average time patients are inpatients in all hospital wards
• Incidence of all other arrhythmias, defined using standard diagnostic criteria [Maximum of 5 days]: All other arrhythmias detected clinically and/or review of holter monitor data
• Incidence of in-patient mortality [28 days from randomisation]: Number of patients deceased during their hospital stay
• Incidence of mortality [28 days from randomisation]: All incidence of mortality during hospital stay and follow up
• Cost-effectiveness [28 days from randomisation]

Sex: All, ages: 18 Years to any

Inclusion Criteria:

1\. All patients undergoing isolated elective coronary artery bypass graft (CABG)

Exclusion Criteria:

1. Age less than 18 years
2. Previous AF
3. Concurrent patient involvement in another clinical study assessing post-operative interventions
4. On-going infection/sepsis at the time of operation
5. Pre-op high-degree atrioventricular (AV) block
6. Pre-op serum K+ greater than 5.5 mEq/L
7. Current or previous use of medication for the purposes of cardiac rhythm management
8. Dialysis dependent end stage renal failure

• Results publication: Campbell NG, Allen E, Sanders J, Swinson R, Birch S, Sturgess J, Al-Subaie N, Elbourne D, Montgomery H, O'Brien B. The impact of maintaining serum potassium >/=3.6 mEq/L vs >/=4.5 mEq/L on the incidence of new-onset atrial fibrillation in the first 120 hours after isolated elective coronary artery bypass grafting - study protocol for a randomised feasibility trial for the proposed Tight K randomized non-inferiority trial. Trials. 2017 Dec 28;18(1):618. doi: 10.1186/s13063-017-2349-x. PMID 29282098