Does hemodilution enhance coagulability?

Recent publications reported enhanced coagulability in hemodilution determined by TEG. In contrast, earlier reports have shown prolongation of in-vivo bleeding time in anemia. In order to take a closer look at this discrepancy undiluted and diluted anticoagulated blood samples (20 % with saline solution, hydroxyl-ethyl starch 6 % (HES), autologous platelet poor plasma (PPP)) were investigated by TEG (n = 10), ball (n = 10), and hook coagulometer (n = 15) as well as tests simulating primary hemostasis ex vivo (Platelet Function Analyzer PFA-100, n = 10). RESULTS: Dilution with plasma changed TEG parameters in a way, when started by recalcification of the blood sample, which is characteristic of enhanced coagulability (r decreased in all and k in 8 of 10 samples, maximal amplitude increased in 9 out of 10). With HES, changes in TEG parameters mainly indicated reduced coagulability (k increased in 7 out of 10, MA decreased in 10 out of 10). When the coagulation was additionally activated by PTT reagent (InTEG) the TEG parameters also mainly showed hypocoagulation with the three dilution solutions. Coagulation times with ball and hook coagulometers were significantly prolonged by dilution especially with saline (+ 25 % and + 17 %, p < 0.001). Dilution always significantly (often abnormally) prolonged closure time in PFA-100 (saline + 41 +/- 18 %, PPP + 37 +/- 20 %, HES + 69 +/- 24 %) demonstrating disturbance of primary hemostasis, particularly with HES. Conclusions: From the results obtained it can be concluded that the changes in the classical TEG (without addition of PTT-reagent), suggesting an enhanced coagulability, may be caused methodically as they are also found with autologous PPP. On the other hand, a disturbance of the primary hemostasis in hemodilution has to be taken into account from the results seen with the PFA-100 and a number of published data.     

Does alvimopan enhance return of bowel function in laparoscopic right colectomy?

Alvimopan, a peripherally acting Mu-opioid receptor antagonist, has been shown to enhance recovery of gastrointestinal (GI) function in open bowel resection. The aim of this study was to determine the effect of Alvimopan on patients undergoing laparoscopic right colectomies in preventing postoperative ileus (POI). A prospective, nonrandomized trial of laparoscopic right colectomies was carried out with and without perioperative Alvimopan. The length of stay (LOS), time to first flatus, bowel movement, and tolerance of solid foods were recorded. Additionally, any occurrences of POI defined as the need for insertion of a nasogastric tube (NGT) were also noted. Student t tests were used for statistical analysis. A total of 33 patients underwent laparoscopic right colectomies for both benign and malignant diseases from October 2008, to December 2009. Sixteen patients received Alvimopan, whereas 17 patients did not. The demographics of both patient groups were similar. Patients receiving Alvimopan had an accelerated return of bowel function in terms of first flatus (2.37 vs 3.34; P = 0.03), tolerance of solid food (2.75 vs 3.94; P = 0.03), and first stool (2.53 vs 3.80; P = 0.04). There was a trend toward shorter LOS in patients receiving Alvimopan (P = 0.07). Two patients with POI requiring NGT did not receive Alvimopan. Alvimopan was successful in enhancing return of GI function in laparoscopic right colectomies and avoiding POI. The decreased LOS trended but did not approach statistical significance. A large randomized prospective trial will be needed to determine the validity of this study.     

Does dexmedetomidine cause less airway collapse than propofol when used for deep sedation?

Study objectiveThe risk of airway collapse in patients undergoing deep sedation is a major concern. In this study, we compared the airway patency of deep sedation provided by propofol with the airway patency of deep sedation provided by dexmedetomidine in magnetic resonance imaging (MRI) procedures. This comparison was done using MRI static and dynamic images and comparing these images to baseline after sevoflurane induction.DesignAfter institutional review board approval, children who were scheduled for MRI procedures were given an inhalation induction, had intravenous access established, and were randomized to receive either dexmedetomidine 1-μg/kg load followed by 1-μg/(kg h) infusion or propofol infusion at 300 μg/(kg min) reduced to 250-μg/(kg min) infusion. MR images were then obtained. Airway patency and collapse were assessed at the level of the posterior midtongue in the axial and sagittal planes. The degree of airway collapse was assessed by determining the percent change in the airway caliber from its minimum to maximum value. After conclusion of the MRI procedure, the study patients were immediately observed by a blinded observer to determine their level of sedation according to the Ramsey sedation scale.SettingMRI scanner at Women and Children's Hospital of Buffalo.PatientsForty children between the ages of 3 and 7 years.InterventionComparison of the utilization of propofol against dexmedetomidine infusions for deep sedation to determine the degree of airway collapse.MeasurementsMagnetic resonance images were then obtained using a 1.5-T GE Excite 12.0 scanner. Airway patency and collapse were assessed at the level of the posterior midtongue in the axial and sagittal planes. The degree of airway collapse was assessed by determining the percent change in the airway caliber from its minimum to maximum value. After conclusion of the MRI procedure, the study patients were immediately observed by a blinded observer to determine their level of sedation according to the Ramsey sedation scale.Main resultsOur study demonstrated no difference in airway collapse between dexmedetomidine-based deep sedation and propofol-based deep sedation following sevoflurane induction.ConclusionIn deep sedation, which is commonly associated with a loss of airway tone, it may not matter which of these intravenous study agents are used. Intravenous sedation with propofol or dexmedetomidine appears to produce the same effect on the pediatric airway.     

Does propofol anesthesia affect intraoperative parathyroid hormone levels? A randomized, prospective trial

BACKGROUND: Intravenous propofol (2,6-diisopropylphenol) infusion is used commonly for sedation/anesthesia during operations. Several authors have reported that propofol can interfere with intact parathyroid hormone (PTH) testing in vitro. Therefore, many surgeons avoid propofol during parathyroidectomy. METHODS: To determine whether propofol affects intraoperative PTH levels in vivo, we randomly assigned 34 patients (80% power; alpha < .05) with secondary hyperparathyroidism to undergo surgery for dialysis access. Patients were assigned randomly to local anesthesia with either propofol (n = 17 patients) or midazolam (n = 17 patients) sedation. PTH values were obtained before the procedure and at 10 minutes and 30 minutes after the start of the propofol or midazolam. RESULTS: Median preoperative serum PTH and calcium levels were 175 pg/mL (range, 27-2646 pg/mL) and 9.2 mg/dL (range, 8.1-10.8 mg/dL), respectively. There was no statistically significant difference between the PTH levels in the 2 groups at each of our time points. There was also no difference in the percentage of change from baseline in the PTH values between our 2 groups. No patient in either group had a sustained drop in their PTH level of greater than 50%. CONCLUSIONS: Intravenous propofol infusion does not alter PTH levels significantly during the operation. Therefore, we believe the intraoperative PTH assay can be used safely during propofol sedation when parathyroid surgical procedures are being performed.     

Does sevoflurane preserve regional cerebral oxygen saturation measured by near-infrared spectroscopy better than propofol?

Objective

The aim of this study was to compare the effect of sevoflurane and propofol on cerebral oxygenation, using regional cerebral oxygen saturation (SrO₂) measured by near-infrared spectroscopy (NIRS).

Study design

Prospective, randomized, controlled study.

Patients and methods

Fifty-four patients aged between 18 and 65 years who underwent elective minor surgery (tumorectomy for breast cancer or inguinal hernia repair) were randomly assigned to receive sevoflurane or propofol anaesthesia. Exclusion criteria included pre-existing cerebrovascular diseases, anaemia, ASA >III, blood loss ≥200 mL, arterial hypotension, baseline pulse oximetry <97%, sign of sensor low quality of SrO₂ or bispectral index, and patients with a forehead area <6.5 cm. SrO₂, bispectral index, haemodynamic data and anaesthetic doses were recorded during surgery.

Results

A total of 48 patients were included in the final analysis (24 in each group). There were no significant differences in mean, minimum and maximum SrO₂ between sevoflurane and propofol groups. The relative maximum decrease was higher in propofol anaesthesia than sevoflurane anaesthesia (9.6 ± 10.7 versus 4.2 ± 7.2%; P = 0.048). Cerebral desaturation (20% reduction from SrO₂ baseline during 15 seconds) occurred in 4 patients in propofol group exclusively (P = 0.109). SrO₂ adjusted for baseline was higher in the sevoflurane group than in the propofol group (67.3 ± 1.8% versus 64.2 ± 1.7%; P = 0.018). There were no significant differences in haemodynamic parameters between the two groups.

Conclusions

Cerebral cortical oxygenation measured by NIRS may be better preserved with sevoflurane than with propofol. These findings suggest that sevoflurane anaesthesia could be a good option in patients with compromised cerebral oxygenation, given the absence of intracranial hypertension. Further studies with larger sample sizes are required to support our results.     

Does blood pressure enhance solute transport in the bone lacunar–canalicular system?

Solute transport through bone plays an important role in tissue metabolism and cellular mechanotransduction. Due to limited diffusion within the mineralized bone matrix, both mechanical loading and vascular pressure have been proposed to drive interstitial fluid flow within the lacunar–canalicular system (LCS); thereby augmenting solute diffusion in bone. Although blood supply is critical for bone nutrition, growth, and fracture healing, whether physiological blood pressures can drive significant fluid and solute convection remains controversial within the literature. The goal of this study was to directly test the hypothesis that in vivo blood pressures enhance solute transport in the bone LCS. Using a newly developed imaging approach based on fluorescence recovery after photobleaching (FRAP), we first measured the transport rate of sodium fluorescein (M.W. 376 Da) through the tibial LCS in four anesthetized mice (in the presence of vascular pressure). These data were then compared with the tracer transport rates at the same locations/lacunae after sacrifice (in the absence of vascular pressure). Using paired FRAP experiments we did not detect differences in tracer transport rates between bones from live anesthetized animals versus those in postmortem bodies (p > 0.05, N=18). In a separate cohort of four anesthetized mice a mean jugular pulse pressure of ～ 10 mmHg at ～ 10 Hz was measured. Further theoretical analysis showed that for bones from both small and large animal species the blood pressure-driven convection of either small (376 Da) or large (43,000 Da) molecules was at least one order of magnitude smaller than diffusion under either normal or elevated pressure conditions. We conclude that despite the extreme importance of vasculature in bone physiology, vascular pressure itself does not enhance acute solute transport within the bone LCS. Therefore, mechanisms other than the vascular pressure-induced fluid flow such as altered biochemical factors may account for the bone adaptation associated with altered circulation. The present study helped clarify a long-standing controversy regarding vascular pressure-induced bone fluid flow and provided a better understanding of bone adaptation in both physiological and pathological conditions.