Influence Of Serum Phosphorus Change Trend On Prognosis Of Critically Ill Patients During Continuous Renal Replacement Therapy

Background:At present,continuous renal replacement therapy（CRRT）is one of the most common important organ support methods in intensive care unit（ICU）.It can achieve solute clearance and volume control without affecting hemodynamics,maintain acid-base and electrolyte balance of the body.In addition to maintaining the balance of the patient’s internal environment,long-term bedside CRRT often brings corresponding complications to the patient,such as hypophosphatemia.Severe hypophosphatemia can cause energy metabolism disorder,resulting in muscle weakness,hemolysis,hyporeflexia,convulsion and even coma,which is a serious blow to critically ill patients.In addition,few studies have reported and little clinical attentions have been drew that the tendency of phosphate changes and its impact on patients during CRRT treatment.Therefore,this study discusses the risk factors of severe hypophosphatemia during CRRT and its impact on prognosis,then analyzes the relationship between the change tendency of blood phosphate and the prognosis of patients,thus providing references for clinical CRRT treatment.Methods:A retrospective study was conducted on 295 patients who were treated with CRRT in the Department of Critical Care from December 2019 to September 2022 in the Affiliated Hospital of Yangzhou University.The final 151 patients met the inclusion and exclusion criteria of this study,and the discharge or death record of the patients were regarded as the end point.1.Baseline data of all patients were collected,and all serum phosphate level indicators during CRRT were counted.Patients were divided into severe hypophosphatemia group and non-severe hypophosphatemia group according to whether the minimum serum phosphate level during CRRT was less than 0.65 mmol/L,and the differences between two groups were compared.The duration of CRRT,fasting time,dietary pattern,and baseline serum phosphorus level before CRRT,laboratory parameters at ICU admission,mechanical ventilation and recent surgery were collected.The risk factors of severe hypophosphatemia during CRRT were analyzed by univariate analysis and Logistic regression analysis.The duration of ICU,duration of hospitalization,duration of mechanical ventilation,tracheotomy rate and all-cause mortality were analyzed.2.Patients were divided into death group and survival group according to the outcome,and the baseline differences between groups were analyzed.The mean value P_{i mean} of serum phosphorus during CRRT,the maximum difference△P_i,the ratio P_i1 of serum phosphorus level after 24 hours of CRRT to the baseline serum phosphorus level before CRRT,the ratio P_i2 of serum phosphorus level after 72 hours of CRRT to the serum phosphorus level after 24 hours were recorded and the differences between two groups were calculated and analyzed.The cut-off value of P_i1 was calculated as 0.7,and the patients were divided into high and low rate groups according to whether P_i1 was greater than 0.7 or not.The variables with P<0.05 in univariate analysis were included in multivariate COX survival analysis.P<0.05 was considered to be statistically significant.Results:1.General clinical characteristics:A total of 151 patients were included,among which women and patients with severe pancreatitis were more likely to develop severe hypophosphatemia during CRRT.2.Risk factors for severe hypophosphatemia:Logistic regression analysis showed that duration of CRRT,long fasting during ICU,and enteral nutrition support were all risk factors for severe hypophosphatemia.Logistic multivariate regression analysis including CRRT time,fasting time and diet pattern showed that the duration of CRRT was statistically significantly associated with severe hypophosphatemia during CRRT（OR=1.006,95%CI 1.001-1.011,P=0.015）.3.Prognostic analysis of patients with severe hypophosphatemia:Patients with severe hypophosphatemia during CRRT treatment had longer mechanical ventilation time,longer ICU stay and total hospital stay,and higher hospitalization costs.No effect of severe hypophosphatemia during CRRT on all-cause mortality during hospitalization was observed.4.To study the relationships between the trend of serum phosphorus changes during CRRT and prognosis,patients were divided into survival group and death group according to the outcome.Univariate analysis showed that the ratio of serum phosphorus level 24hours after CRRT to the basal serum phosphorus level before CRRT,P_i1,had statistical differences between the two groups.The increase and decrease of serum phosphorus after CRRT treatment were distinguished according to whether the P_i1 ratio was greater than1,and the mortality rate was higher in patients with P_i1>1.Among patients with P_i1<1,the death group had higher P_i1.5.Correlation analysis of serum phosphorus change trend in the early stage of CRRT treatment:The proportion of male patients in the high ratio group（Pi1≥0.7）was higher than that in the low ratio group,the hemoglobin content was higher,the serum creatinine level and the serum BNP level were lower,and the serum potassium level was closer to normal.The mortality was independently associated with Pi1.The 28-day mortality of patients with high ratio was about 1.45 times higher than that of patients with low ratio（Pi1<0.7）（HR=2.449,95%CI1.141-5.254,P=0.021）.Conclusion:1.Duration of CRRT treatment is an independent risk factor for severe hypophosphatemia during CRRT;2.Patients with severe hypophosphatemia during CRRT treatment will lead to prolonged mechanical ventilation;3.The trend of serum phosphate at the beginning of CRRT was independently associated with 28-day in-hospital mortality.