Predicting Acute Pain After Surgery: A Multivariate Analysis.

OBJECTIVES: To identify perioperative practice patterns that predictably impact postoperative pain. BACKGROUND: Despite significant advances in perioperative medicine, a significant portion of patients still experience severe pain after major surgery. Postoperative pain is associated with serious adverse outcomes that are costly to patients and society. METHODS: The presented analysis took advantage of a unique observational data set providing unprecedented detailed pharmacological information. The data were collected by PAIN OUT, a multinational registry project established by the European Commission to improve postoperative pain outcomes. A multivariate approach was used to derive and validate a model predictive of pain on postoperative day 1 (POD1) in 1008 patients undergoing back surgery. RESULTS: The predictive and validated model was highly significant (P = 8.9E-15) and identified modifiable practice patterns. Importantly, the number of nonopioid analgesic drug classes administered during surgery predicted decreased pain on POD1. At least 2 different nonopioid analgesic drug classes (cyclooxygenase inhibitors, acetaminophen, nefopam, or metamizol) were required to provide meaningful pain relief (>30%). However, only a quarter of patients received at least 2 nonanalgesic drug classes during surgery. In addition, the use of very short-acting opioids predicted increased pain on POD1, suggesting room for improvement in the perioperative management of these patients. Although the model was highly significant, it only accounted for a relatively small fraction of the observed variance. CONCLUSION: The presented analysis offers detailed insight into current practice patterns and reveals modifications that can be implemented in today's clinical practice. Our results also suggest that parameters other than those currently studied are relevant for postoperative pain including biological and psychological variables.

Effect of acceleration forces during transport through a pneumatic tube system on ROTEM® analysis.

BACKGROUND: ROTEM® is considered a helpful point-of-care device to monitor blood coagulation in emergency situations. Centrally performed analysis is desirable but rapid transport of blood samples is an important prerequisite. The effect of acceleration forces on sample transport through a pneumatic tube system on ROTEM® should be tested at each institution to exclude a pre-analytical influence. The aims of the present work were: (i) to investigate the effect of pneumatic tube transport on ROTEM® parameters; (ii) to compare blood sample transport via pneumatic tube vs. manual transportation; and (iii) to determine the effect of acceleration forces on ROTEM® parameters. METHODS: This is a single centre study with 20 healthy volunteers. Five whole blood samples were transferred to the central haematology laboratory by either normal transport or pneumatic delivery with different speed and acceleration forces. EXTEM, INTEM, FIBTEM and APTEM were analysed in parallel with two ROTEM® devices and compared. Acceleration forces were measured during transport with two different instruments. RESULTS: Increment of transport time, speed and distance resulted in an augmentation of acceleration forces and peaks. All results of the ROTEM® analysis after manual transport or pneumatic delivery were within normal range. However, increase in acceleration forces resulted in minimally but statistically significant changes in multiple ROTEM® parameters. The higher the acceleration forces, the more ROTEM® parameters are influenced. CONCLUSIONS: Acceleration forces during transport through a pneumatic tube system have an influence on ROTEM® parameters. Prior to transfer blood samples via pneumatic tube system these influences should be tested to exclude clinically relevant blood coagulation activation in vitro.

Simulation of stress urinary incontinence for in-vitro studies.

A simulation system that generates dynamic bladder pressures for the use of testing and examining artificial urinary sphincters is designed, implemented, and compared to in-vivo measurements of Valsalva and coughing profiles. Cylinder and piston, which are integrated into the universal testing machine, simulating the bladder are connected with explanted sow urethras. The AMS 800 artificial urinary sphincter closes the urethra with well-defined external pressures. In order to select appropriate profiles for the bladder pressure, 34 Valsalva and coughing profiles of 6 patients were evaluated with respect to amplitude, pressure raise, dwell time, and half width.

Optimization of the artificial urinary sphincter: modelling and experimental validation.

The artificial urinary sphincter should be long enough to prevent strangulation effects of the urethral tissue and short enough to avoid the improper dissection of the surrounding tissue. To optimize the sphincter length, the empirical three-parameter urethra compression model is proposed based on the mechanical properties of the urethra: wall pressure, tissue response rim force and sphincter periphery length. In vitro studies using explanted animal or human urethras and different artificial sphincters demonstrate its applicability. The pressure of the sphincter to close the urethra is shown to be a linear function of the bladder pressure. The force to close the urethra depends on the sphincter length linearly. Human urethras display the same dependences as the urethras of pig, dog, sheep and calf. Quantitatively, however, sow urethras resemble best the human ones. For the human urethras, the mean wall pressure corresponds to (-12.6 +/- 0.9) cmH2O and (-8.7 +/- 1.1) cmH2O, the rim length to (3.0 +/- 0.3) mm and (5.1 +/- 0.3) mm and the rim force to (60 +/- 20) mN and (100 +/- 20) mN for urethra opening and closing, respectively. Assuming an intravesical pressure of 40 cmH2O, and an external pressure on the urethra of 60 cmH2O, the model leads to the optimized sphincter length of (17.3 +/- 3.8) mm.

Minipig urethra: a suitable animal model in vitro.

The study demonstrates that the minipig urethra is an appropriate animal model for in vitro experiments and therefore promising for long-term animal tests of artificial urinary sphincter systems in vivo. Freshly explanted porcine and minipig urethras were connected to a fluid reservoir that simulated the bladder pressure. This bladder pressure was adjusted by changing the water level (hydrostatic pressure). Specially designed aluminum sphincters loaded with a fluid-filled container were used to close/open the urethras. Results from minipigs and domestic pigs were compared to data published for human urethras. We measured the leak-point pressures (LPP) by adjusting the bladder pressure at a constant sphincter length and by changing the sphincter length at a constant bladder pressure. Because the urethral tissue shows visco-elastic behavior, LPPs for both opening and closing were measured. By fitting the in vitro data, we evaluated the three characteristic parameters from the empirical urethra compression model, i.e. wall pressure < pW >opening = −(12.9 ± 0.9) cmH2O, < pW >closing = (8.6 ± 1.1) cmH2O, < FR >opening = (0.06 ± 0.02) N, < FR >closing = (0.10 ± 0.02) N, < LR >opening = (3.0 ± 0.3) mm, < LR >closing = (5.1 ± 0.3) mm,and (male) minipig urethras:< pW >opening = −(13.4 ± 0.3) cmH2O, < pW >closing = −(8.6 ± 0.4) cmH2O,< FR >opening = (0.19 ± 0.01) N, < FR >closing = (0.21 ± 0.02) N,< LR >opening = (2.4 ± 0.1) mm, < LR >closing = (3.3 ± 1.0) mm. These {\it in vitro} tests quantified by means of the urethra compression model demonstrate that the minipig (especially the male one) represents a suitable animal model for testing artificial urinary sphincters.