We tested the hypotheses that continuous total peripheral resistance (TPR) measurements are superior to intermittent data collection and that variables related to TPR can be used to distinguish between survivors and nonsurvivors of prolonged hemorrhagic hypotension (HH). One week after implanting a transit time ultrasound (TTU) probe on the ascending aorta, 21 rats were subjected to a 4-hour HH at 40 mmHg. Measurements were made before and up to 4 h after HH was initiated. Additional bleeding or Ringer's lactate (RL) infusion were used to maintain HH. TPR was continuously measured on-line using blood flow and arterial pressure recordings. About 67% of the rats survived 3 h (S); others were considered non-survivors (NS). Data collected at 30-min intervals failed to detect the maximum value of TPR (TPR_max). Time to reach TPR_max was similar for S and NS and was strongly correlated with the bleeding endpoint and with the RL infusion onset. However, S showed higher TPR_max than NS (p<0.005) and had a significantly longer period (116 ± 20 min) with the TPR above baseline level than NS (51 ± 10 min). In conclusion, (1) the TTU technique at high sampling rate allowed continuous and accurate real-time monitoring of TPR; (2) the bleeding endpoint and RL infusion onset may be used as surrogates of the time to TPR_max ; (3) TPR_max of S and NS could be detected only using a continuous TPR measurement; and (4) differences between S and NS could be revealed by the continuous TPR curve.