Intra-Abdominal Hypertension Is Responsible for False Negatives to the Passive Leg Raising Test.

OBJECTIVES: To compare the passive leg raising test ability to predict fluid responsiveness in patients with and without intra-abdominal hypertension. DESIGN: Observational study. SETTING: Medical ICU. PATIENTS: Mechanically ventilated patients monitored with a PiCCO2 device (Pulsion Medical Systems, Feldkirchen, Germany) in whom fluid expansion was planned, with (intra-abdominal hypertension+) and without (intra-abdominal hypertension-) intra-abdominal hypertension, defined by an intra-abdominal pressure greater than or equal to 12 mm Hg (bladder pressure). INTERVENTIONS: We measured the changes in cardiac index during passive leg raising and after volume expansion. The passive leg raising test was defined as positive if it increased cardiac index greater than or equal to 10%. Fluid responsiveness was defined by a fluid-induced increase in cardiac index greater than or equal to 15%. MEASUREMENTS AND MAIN RESULTS: We included 60 patients, 30 without intra-abdominal hypertension (15 fluid responders and 15 fluid nonresponders) and 30 with intra-abdominal hypertension (21 fluid responders and nine fluid nonresponders). The intra-abdominal pressure at baseline was 4 ± 3 mm Hg in intra-abdominal hypertension- and 20 ± 6 mm Hg in intra-abdominal hypertension+ patients (p < 0.01). In intra-abdominal hypertension- patients with fluid responsiveness, cardiac index increased by 25% ± 19% during passive leg raising and by 35% ± 14% after volume expansion. The passive leg raising test was positive in 14 patients. The passive leg raising test was negative in all intra-abdominal hypertension- patients without fluid responsiveness. In intra-abdominal hypertension+ patients with fluid responsiveness, cardiac index increased by 10% ± 14% during passive leg raising (p = 0.01 vs intra-abdominal hypertension- patients) and by 32% ± 18% during volume expansion (p = 0.72 vs intra-abdominal hypertension- patients). Among these patients, the passive leg raising test was negative in 15 patients (false negatives) and positive in six patients (true positives). Among the nine intra-abdominal hypertension+ patients without fluid responsiveness, the passive leg raising test was negative in all but one patient. The area under the receiver operating characteristic curve of the passive leg raising test for detecting fluid responsiveness was 0.98 ± 0.02 (p < 0.001 vs 0.5) in intra-abdominal hypertension- patients and 0.60 ± 0.11 in intra-abdominal hypertension+ patients (p = 0.37 vs 0.5). CONCLUSIONS: Intra-abdominal hypertension is responsible for some false negatives to the passive leg raising test.

The effects of passive leg raising may be detected by the plethysmographic oxygen saturation signal in critically ill patients.

BACKGROUND: A passive leg raising (PLR) test is positive if the cardiac index (CI) increased by > 10%, but it requires a direct measurement of CI. On the oxygen saturation plethysmographic signal, the perfusion index (PI) is the ratio between the pulsatile and the non-pulsatile portions. We hypothesised that the changes in PI could predict a positive PLR test and thus preload responsiveness in a totally non-invasive way. METHODS: In patients with acute circulatory failure, we measured PI (Radical-7) and CI (PiCCO2) before and during a PLR test and, if decided, before and after volume expansion (500-mL saline). RESULTS: Three patients were excluded because the plethysmography signal was absent and 3 other ones because it was unstable. Eventually, 72 patients were analysed. In 34 patients with a positive PLR test (increase in CI ≥ 10%), CI and PI increased during PLR by 21 ± 10% and 54 ± 53%, respectively. In the 38 patients with a negative PLR test, PI did not significantly change during PLR. In 26 patients in whom volume expansion was performed, CI and PI increased by 28 ± 14% and 53 ± 63%, respectively. The correlation between the PI and CI changes for all interventions was significant (r = 0.64, p < 0.001). During the PLR test, if PI increased by > 9%, a positive response of CI (≥ 10%) was diagnosed with a sensitivity of 91 (76-98%) and a specificity of 79 (63-90%) (area under the receiver operating characteristics curve 0.89 (0.80-0.95), p < 0.0001). CONCLUSION: An increase in PI during PLR by 9% accurately detects a positive response of the PLR test. TRIAL REGISTRATION: ID RCB 2016-A00959-42. Registered 27 June 2016.

Carotid and femoral Doppler do not allow the assessment of passive leg raising effects.

BACKGROUND: The hemodynamic effects of the passive leg raising (PLR) test must be assessed through a direct measurement of cardiac index (CI). We tested whether changes in Doppler common carotid blood flow (CBF) and common femoral artery blood flow (FBF) could detect a positive PLR test (increase in CI ≥ 10%). We also tested whether CBF and FBF changes could track simultaneous changes in CI during PLR and volume expansion. In 51 cases, we measured CI (PiCCO2), CBF and FBF before and during a PLR test (one performed for CBF and another for FBF measurements) and before and after volume expansion, which was performed if PLR was positive. RESULTS: Due to poor echogenicity or insufficient Doppler signal quality, CBF could be measured in 39 cases and FBF in only 14 cases. A positive PLR response could not be detected by changes in CBF, FBF, carotid nor by femoral peak systolic velocities (areas under the receiver operating characteristic curves: 0.58 ± 0.10, 0.57 ± 0.16, 0.56 ± 0.09 and 0.64 ± 10, respectively, all not different from 0.50). The correlations between simultaneous changes in CI and CBF and in CI and FBF during PLR and volume expansion were not significant (p = 0.41 and p = 0.27, respectively). CONCLUSION: Doppler measurements of CBF and of FBF, as well as measurements of their peak velocities, are not reliable to assess cardiac output and its changes.

Validation of the Norwegian Pain Sensitivity Questionnaire.

BACKGROUND AND PURPOSE: There is a large variation in people's reactions to painful stimuli. Although some conditions are more painful, the variation between people is larger than the reaction to pain across conditions. Induced experimental pain is one way to assess some aspects of these differences in pain perception. Experimental nociceptive testing is time consuming and not always feasible in a clinical setting. In order to overcome the obstacles of assessing pain sensitivity using experimental stimulation, the Pain Sensitivity Questionnaire (PSQ) was developed. The purpose of this study is to validate the Norwegian version of the PSQ. METHODS: Construct validity was examined through an exploratory principal component factor analysis with varimax rotation. Internal consistency was measured by Cronbach's alpha reliability for subscales and the total PSQ. As confounding variables such as age and gender may contribute to the experience of pain, a regression analysis was performed with demographic variables and PSQ scores as independent variables and the experimental measures of pain as the dependent variable. RESULTS: The factor analysis yielded at two factor solution, with an eigenvalue greater than one, explain 58% of the variance. Cronbach's alpha for the PSQ was 0.92. In the regression analysis, only PSQ scores contributed to explain the experimental pain intensity and tolerance. Gender only influenced the experimental pain threshold, as men had statistically significant higher heat pain threshold than women. CONCLUSION: This study shows that PSQ is a valid and reliable questionnaire and might be a promising instrument for assessing pain sensitivity in Norwegian clinical settings. Further studies are needed to examine whether the PSQ can be used in clinical settings to predict postoperative pain and the development of chronic pain.