Cutoff Values for Providing the Ideal Intravenous Patient-Controlled Analgesia According to the Intensity of Postoperative Pain—A Retrospective Observational Study

Background and Objectives: The cutoff values were analyzed for providing the ideal intravenous patient-controlled analgesia (PCA) that could reduce rescue analgesics or antiemetics requirements, based on the grades of postoperative pain intensity (PPI). Materials and Methods: PCA regimens of 4106 patients were retrospectively analyzed, and they were allocated into three groups with low, moderate, and high PPI grades (groups L, M, and H, respectively) based on numeric rating scores obtained 6 h postoperatively. Opioid and non-opioid analgesic doses were converted into fentanyl-equivalent doses (DOSE-FEN-OP and DOSE-FEN-NONOP, respectively). The primary endpoint was the cutoff values of these parameters. Results: With respect to the PCA settings to reduce rescue analgesic and antiemetic requirements, group L required a background infusion rate (BIR) of 1.75–3 mL/h, bolus volume of 0.5–1.25 mL, and lockout interval of ≤12.5 min. Group M required a BIR of 1.75 mL/h, bolus volume of 0.5–1.75 mL, and lockout interval of ≤5 min. Group H required a BIR of 1.75 mL/h, bolus volume of 0.5 mL, and lockout interval of ≤5 min. In assessments of the analgesic doses to reduce rescue analgesic requirement, the DOSE-FEN-OP was at least 950 μg of fentanyl regardless of group, while the DOSE-FEN-NONOP was ≥250 μg, ≥550 μg, and ≥700 μg for the L, M, and H groups, respectively. In assessments of the analgesic doses to reduce rescue antiemetic requirement, DOSE-FEN-OP was ≤950 μg for groups L and M and ≤850 μg for Group H, while DOSE-FEN-NONOP was ≤50 μg, ≤450 μg, and ≤700 μg for groups L, M, and H, respectively. Conclusion: The ideal PCA for reduction in rescue analgesics or antiemetics can be achieved by adjustment of PCA settings and drug dosages carefully with these cutoff values depending on the expected grades of PPI. Especially, the ideal PCA can be provided by adjusting the lockout interval and bolus volume rather than BIR and by applying smaller bolus doses and shorter lockout intervals with an increasing PPI grade.

Predicting oxygen tension along the ureter

Continuous measurement of bladder urine oxygen tension (PO2) is a new method to potentially detect renal medullary hypoxia in patients at risk of acute kidney injury (AKI). To assess its practicality, we developed a computational model of the peristaltic movement of a urine bolus along the ureter and the oxygen exchange between the bolus and ureter wall. This model quantifies the changes in urine PO2 as it transits from the renal pelvis to the bladder. The model parameters were calibrated using experimental data in rabbits, such that most of the model predictions are within ± 1 standard error (SEM) of the reported mean in the experiment, with the average percentage difference being 7.0%. Based on parametric studies performed using a model scaled to the geometric dimensions of a human ureter, we found that bladder-urine PO2 is strongly dependent on the bolus volume (i.e. bolus volume-to-surface area ratio), especially at a volume less than its physiological (baseline) volume (<0.2 ml). For the model assumptions, changes in peristaltic frequency resulted in a minimal change in bladder-urine PO2 (< 1 mmHg). The model also predicted there exists a family of linear relationships of the bladder-urine PO2 and the pelvic-urine PO2 for different input conditions. We conclude that it may technically be possible to predict renal medullary PO2 based on the measurement of bladder-urine PO2, provided there are accurate real-time measurements of model input parameters.

Effects of remifentanil on pharyngeal swallowing and esophageal motility - no impact of different bolus volumes, and partial antagonism by methylnaltrexone

Background Remifentanil impairs swallowing, and disturbed accommodation to bolus volume may be one of the underlying causes. It is not fully understood whether remifentanil-induced swallowing dysfunction is mediated by peripheral or central mechanisms. Aims To investigate if remifentanil-induced swallowing dysfunction is dependent on the bolus volume and whether the effect of remifentanil could be counteracted by methylnaltrexone, a peripherally acting opioid antagonist. Methods Nineteen healthy volunteers were included in this double-blinded, randomized, placebo-controlled, crossover study. Study participants received target-controlled remifentanil infusions and placebo infusions in a randomized order. Methylnaltrexone was administered by intravenous injection of doses of 0.3 mg/kg. Recordings of pressure and impedance data were acquired using a combined manometry and impedance solid state catheter. Data was analyzed from three series of bolus swallows, baseline, during remifentanil exposure, and 15 min after methylnaltrexone. Results Remifentanil induced significant effects on multiple pharyngeal and esophageal function parameters. No significant differences in remifentanil-induced swallowing dysfunction related to different bolus volumes were found. Pharyngeal effects of remifentanil were not significantly counteracted by methylnaltrexone, whereas on the distal esophageal level, effects on distension pressures were counteracted. Conclusions Changes in pharyngeal and esophageal pressure flow variables were consistent with previous results on remifentanil-induced swallowing dysfunction, and uniform across all bolus volumes. The effects of remifentanil on the pharyngeal level and on the proximal esophagus appear to be predominantly centrally mediated, whereas the effects of remifentanil on the distal esophagus may be mediated by both central and peripheral mechanisms.

Modulation of pharyngeal swallowing by bolus volume and viscosity

The neuromodulation of the healthy oropharyngeal swallow response was described in relation to bolus volume and viscosity challenges, using intraluminal pressure and impedance topography methods. Among a wide range of physiological measures, those indicative of distension pressure, luminal opening, and flow timing were most significantly altered by bolus condition and therefore considered potential markers of swallow neuromodulation. The study methods and associated findings inform a diagnostic framework for swallow assessment in patients with oropharyngeal dysphagia.

Relationship between distension-contraction waveforms during esophageal peristalsis: effect of bolus volume, viscosity, and posture

We studied esophageal distension (surrogate of inhibition) ahead of contraction during peristalsis from intraluminal esophageal impedance measurements. Esophageal distension, similarly to contraction, travels the esophagus in a sequential manner, and the amplitude of esophageal distension increases from proximal to distal direction in the esophagus. Bolus volume, viscosity, and posture have significant effects on the amplitude of distension and its temporal relationship with contraction.

Influence of variable viscosity and wall properties on the peristalsis of Jeffrey fluid in a curved channel with radial magnetic field

The current investigation attempts to address the peristalsis exhibited by a Jeffrey fluid through channels with curvature and compliant walls. The flow of fluid is exposed to an external magnetic field. Moreover, variation of the viscosity of the fluid with the spatial coordinate is considered. Long wavelength and small values of Reynolds number are considered for the mathematical modeling of the problem under scope. The system of differential equations thus obtained is non-linear, the solution for which is obtained by the method of perturbation for small values of variable viscosity. The authors have provided special emphasis on the influence of pertinent parameters on velocity and trapping phenomenon. The results obtained suggest that as the channel changes from straight to curved, the velocity profile bends away from the center of the channel. Further, the trapped bolus volume is seen to be reducing with decrease in the Hartmann number.

P1090DETERMINATION OF ABSOLUTE BLOOD VOLUME USING ONLINE DIALYSATE DILUTION: WHEN SHOULD BE MEASURED?

Background and Aims Current on-line haemodiafiltration (HDF) machines equipped with a blood volume monitor (BVM) and an on-line bolus function have the potential for measuring absolute blood volume (aBV). Recently, we developed a simple method to determine absolute BV in everyday dialysis sessions. The aim of the present study was to evaluate the reproducibility of measurements. Method Intra-individual reproducibility was studied in 10 patients during a single dialysis session by 4 measurements of absolute BV: immediately after beginning before ultrafiltration (UF) was started, and after one, two and three hours. ABV was determined by indicator dilution. A defined volume bolus of 240 mL dialysate was infused into the venous blood line by pressing the emergency button of the HDF machine 5008 (FMC). For this reason, total UF volume was increased by 1L. UF was automatically stopped during and after the infusion. The resulting increase in relative blood volume (RBVpost-RBVpre) was measured by the ultrasonic relative BVM incorporated in the dialysis machine. ABV was measured in hourly intervals and for assessment of reproducibility the volume at treatment start (t=0) where RBV is 100% was calculated for all measurements as: aBV in mL = bolus volume 240 mL x 100% / increase RBV in % ABV data were normalized for body mass at dry weight (in mL/kg). Additionally, in 5 patients the RBV graph was monitored immediately at the beginning of dialysis without UF in a separate dialysis session. Results ABV at t=0 were consistently larger when calculated from measurements done immediately after the beginning compared to measurements obtained after 1 h (6.52 ± 1.40 L or 80.6 ± 14.5 mL/kg vs. 5.16 ± 1.40 L or 63.9 ± 14.3 mL/kg). Specific BV derived from 2 and 3 h measurements did not significantly differ from the measured volumes after 1 hour (61.4 ± 13.8 mL/kg, and 60.9 ± 13.9 mL/kg). The standard deviations of the 3 examinations in the same study patient during a further course of dialysis were between 0.6 and 5.3 ml/kg (ø 2.6 ml/kg). In a separate session, RBV decreases without UF at the beginning of dialysis in the first 3 minutes by 0.5 % and in 5 minutes by 0.6 %. Conclusion If BV is diluted by additional priming volume and bolus volume, a part of this volume will leave the circulation. This represented the time frame where the bolus was initially infused and the measurements were carried out. This loss is caused by the reduction in plasma colloid osmotic pressure induced by the dilution thereby changing the microvascular filtration equilibrium. The increase in RBV display is not solely caused by the bolus volume in this time and, and therefore, calculated BV would be overestimated by about 17 mL/kg. If measurement is performed at a later time, UF will take place and, consequently, refilling. This inward drive matches the outward bolus escape as a counterforce. BV measurement during a further course of dialysis is well reproducible with a deviation of only ± 2.6 ml/kg. The method would therefore be sufficiently precise in clinical practice. Therefore, we propose the determination of aBV only after 1 hour dialysis when a sufficient refilling takes place. With a software modification, the BV measurement could be routinely automated during each dialysis treatment. Manufacturers are asked to implement this technology in their devices.