Objective To investigate the effect of prophylaxis against respiratory and circulation depression caused by propofol during painless colonoscopy by intravenous doxpram with small dose.Methods 80 patients undergoing painless colonoscopy were randomly divided into the control group(A group) and the doxpram group(B group).All patients used propofol,and then used propofol after induction.In group B,doxpram was injected before anesthesia.The degree and incidence rate of respiratory and circulotion depression,the dose of propofol,the awake time,the examination time,the complication during anesthesia and awake were monitored.Results The SBP,DBP,SpO2,RR during anesthesia were obviously lower in group A than in group B(P