Background The cardiovascular characteristics during septic shock in premature neonates are characterized by elevated ventricular output and normal ejection fraction.However,there is little knowledge about other vari-ables in premature infants with Klebsiella Pneumoniae(KPN)septicemia and shock.This study aimed to investi-gate the characteristics of cardiovascular changes in premature infants diagnosed with Klebsiella pneumonia(KPN)septicemia and shock.Methods Our study included premature infants(gestational age ≤34 weeks)in the neonatal intensive care unit(NICU)of Guangdong Provincial People's Hospital from November 1st,2013 to November 31st,2016.17 participants diagnosed with KPN septicemia complicated with shock and 17 healthy pre-mature infants were respectively enrolled in study group and control group for analysis.All the infants underwent non-invasive ultrasound cardiac output monitor examinations in normal time,early stage of shock and cured time.Results Compared with the control group,higher values of heart rate(HR)(P＜0.001),cardiac output index(CI)(P＜0.001),Smith-Madigan inotropy index(SMII)(P＜0.001)and oxygen delivery(DO2)(P＜0.001),and lower levels of systemic vascular resistance index(SVRI)(P＜0.00l)were observed in the study group.The difference of mean blood pressure(MBP)was not statistically significant(P=0.943).In the study group,the values of HR(P=0.004),CI(P=0.004),SMII(P=0.004)and DO2(P=0.004)in the early stage of septic shock were significantly higher when compared with the values in the normal time,while the value of SVRI(P＜0.001)was significantly lower.HR(P＜0.001)and DO2(P=0.009)decreased from the early stage of septic shock to the cured time,while SVRI(P＜0.001)increased.There were no significant changes in CI(P＞0.999)and SMII(P=0.646)from early stage of septic shock to improvement in the study group.Conclusions Systemic vascular resistance index de-creased and oxygen deliver elevated in preterm infants with gestational age less than 34 weeks with Klebsiella Pneumoniae septicemia and shock.Vasoregulatory failure may be the main cause of Klebsiella Pneumoniae septi-cemia and shock.Vasoactive drugs may be needed during shock.The increase of oxygen deliver level in the early stage of shock indicates that timely and effective vasoactive infusion can prevent the deterioration of the disease.