Combination of continuous pulse pressure variation monitoring and cardiac filling pressure to predict fluid responsiveness.

To assess if combining central venous pressure (CVP) and/or pulmonary capillary wedge pressure (PCWP) information with arterial pulse pressure variation can increase the ability to predict fluid responsiveness in patients under general anesthesia. This study is a retrospective analysis of patients scheduled for coronary artery bypass surgery and monitored with a pulmonary artery catheter who underwent a volume expansion after induction of general anesthesia. Among the 46 patients studied, 31 were responders to volume expansion. CVP similar to PCWP, was a poor predictor of fluid responsiveness, as indicated by low values of areas under the receiver operating characteristic curves [0.585 (95 % CI 0.389-0.780) and 0.563 (95 % CI 0.373-0.753) respectively, p = 0.76]. The area obtained for PPV was 0.897 (95 % CI 0.801-0.992) with a threshold value of 12 %. The sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio was 83.9 %, 86.7 %, 6.29 and 0.19 respectively. Combining information on right and/or left cardiac filling pressures with PPV did not increase the ability to predict whether a patient will be a responder or a non-responder to volume expansion. The ability to identify a potentially fluid responsive patient was no better using PPV plus cardiac filling pressures when compared to using PPV alone. Therefore, if PPV values are being monitored in a patient, CVP and PCWP values do not provide additional information to predict fluid responsiveness.

Application of pulsed radiofrequency currents to rat dorsal root ganglia modulates nerve injury-induced tactile allodynia.

BACKGROUND: Application of pulsed radiofrequency (PRF) currents to the dorsal root ganglia (DRG) has been reported to produce relief from certain pain states without causing thermal ablation. In this study, we examined the direct correlation between PRF application to DRG associated with spinal nerve injury and reversal of injury-induced behavioral hypersensitivity in a rat neuropathic pain model. METHODS: Neuropathic lesioning was performed via left L5 spinal nerve ligation on male adult Sprague-Dawley rats. Once the injured rats had developed tactile allodynia, one group was then assigned to PRF treatment of the L5 DRG and another group was assigned to the sham treatment to the DRG. Behavioral testing was performed on both the control and treated paws using the von Frey filament test before the surgery and at indicated days. The resulting data were analyzed using a linear mixed model to assess the overall difference between the treatment groups and the overall difference among the study days. Cohen's d statistic was computed from paired difference-from-baseline scores for each of the 14 study days after treatment and these measures of effect size were then used to descriptively compare the recovery patterns over time for each study group. RESULTS: Spinal nerve injury resulted in the development of behavioral hypersensitivity to von Frey filament stimulation (allodynia) in the hindpaw of the left (injury) side. Mixed linear modeling showed a significant difference between the treatment groups (P = 0.0079) and a significant change of paw withdrawal threshold means over time (P = 0.0006) for all 12 animals. Evaluation of Cohen's d (effect size) revealed that the PRF-treated animals exhibited better recovery and recorded larger effect sizes than the sham-treated animals on 10 of the 14 post-PRF treatment days and exhibited moderate-to-strong effects posttreatment at days 8 to 10 and at and beyond day 32. CONCLUSIONS: Findings from this study support that PRF of the DRG causes reversal of nerve injury (spinal nerve ligation)-induced tactile allodynia in rats. This allodynia reversal indicates that nonablative PRF acting via modulation of the DRG can speed recovery in nerve injury-induced pain.