In this retrospective study, eighty-five of 160 enrolled patients developed postoperative hypokalemia within 5 days, and the rate of postoperative hypokalemia on the third day was the highest. Multivariate analysis showed that preoperative potassium, red blood cell count and diabetes were independent risk factors for hypokalemia. In the ROC analysis, the cut-off value of preoperative potassium was set at 4.0mmol/L, the sensitivity and specificity of postoperative hypokalemia were 78.8% and 48.0%, respectively.
Hypokalemia is not uncommon after surgery, accounting for 25% , but few studies have reported serum potassium abnormalities after TJA. Only one recent retrospective study reported the incidence of postoperative abnormalities of potassium, which was about 25.2% . However, the risk factors were not mentioned. Based on our study, 53.1% of patients developed serum hypokalemia within five days after surgery, with slight, moderate and severe hypokalemia accounting for 48.75%, 3.13% and 1.25%, respectively.
The level of serum potassium displayed a remarkable drop from pre-operational to the third day after surgery and then showed a slight increase. Thus, we proposed that the serum potassium should be checked on the third day after TJA for avoiding severe hypokalemia. However, the previous study has thought postoperative basic metabolic panel should not be routinely tested in patients unless they have medical comorbidities, and their potassium is below 4 mmol/L. Halawi et al. provided evidence that routine postoperative laboratory testing is not necessary in modern-day primary unilateral THA. Therefore, whether and when to detect serum potassium after joint replacement still needs further study. In addition, our study showed that there were two patients got severe hypokalemia after the operation. If we did not carry out serum potassium monitoring, serious complications may occur, and the previous study has thought early potassium monitoring can be helpful to correct hypokalemia, effective to recover trauma operation .
It is believed that the occurrence of postoperative hypokalemia is related to a variety of factors, including insufficient intake, excessive potassium loss and impaired potassium distribution mechanism . By multivariate regression analysis, we found that the independent risk factors for hypokalemia after TJA were diabetes, preoperative serum potassium level, which was similar to the report of Mohamad J et al. .
Kildow BJ  also regarded Diabetes as an important predictor. the feedback system regulates potassium and insulin levels. The increase of extracellular potassium concentration stimulates the release of insulin and causes cells to absorb potassium  . Normally, high extracellular potassium levels increase the release of endogenous insulin by inhibiting ATP-sensitive potassium channels in pancreatic B cells . In diabetics, however, low insulin levels lead to the elimination of glucose in the kidneys, which increases the delivery of sodium to the distal nephron and increases potassium excretion . Diabetes often requires oral glucose-lowering drugs or subcutaneous injections of insulin, compared with normal patients, diabetes tend to have larger fluctuation, which can cause abnormal potassium ion distribution, likely the cause of postoperative low potassium . Our study, patients with diabetes mellitus, also showed a significant increase in postoperative hypokalemia, confirming previous findings.
Our study also first found that preoperative red blood count is also a risk factor for postoperative hypokalemia, which may be related to intraoperative and postoperative loss of red blood cells and fluid in patients, and further prospective studies are needed to confirm this.
In addition, another study in a single institution with hip or knee primary total joint replacement showed that preoperative potassium levels below 4 mmol/L in 72% of patients had hypokalemia after surgery, while about 28% of the patients had anemia, heart disease, cardiovascular disease, or a history of chronic kidney disease . Similarly, In our study, patients with preoperative serum potassium lower than 4mmol/L should be treated with preoperative oral potassium supplementation, but a larger sample study is needed.