Wilhelm K. Schwab

Effects of elevating the head of bed on interface pressure in volunteers.

Objective:Intensive care unit patients are at particular risk for pressure ulcers and ventilator-associated pneumonia. Current guidelines recommend that mechanically ventilated patients be kept in a semirecumbent position with the head of bed elevated 30°–45° to prevent aspiration and ventilator-associated pneumonia. We tested the effects of elevating the head of bed on the interface pressure between the skin of the sacral area and the bed with healthy volunteers. Interventions:Interface pressure profiles of the sacral area were obtained for the 0°, 10°, 20°, 30°, 45°, 60°, and 75° head of bed elevated positions from 15 subjects (14 men, one woman). Measurements and Main Results:Peak sacral interface pressures increased with large increases in head of bed elevation. The 30°, 45°, 60°, and 75° head of bed positions all had peak interface pressures that were significantly (p < 0.02) greater than the supine measurement and also were different from all other head of bed positions. Affected areas, defined as areas over which an interface pressure ≥32 mm Hg was obtained, increased with large elevation of the head of bed. The affected areas of the 45°, 60°, and 75° head of bed positions were significantly greater than the supine position and were also significantly different from all other head of bed positions. Conclusions:Raising the head of bed to 30° or higher on a intensive care unit bed increases the peak interface pressure between the skin at the sacral area and support surface in healthy volunteers. At 45° head of bed elevation or higher, the affected area attributed to a skin–intensive care unit bed interface pressure ≥32 mm Hg increased as well. Further study is needed to determine whether the increased peak interface pressures and affected areas that result from raising the head of bed actually increase the incidence of pressure ulcer formation.

Patient repositioning and pressure ulcer risk—Monitoring interface pressures of at-risk patients

Repositioning patients regularly to prevent pressure ulcers and reduce interface pressures is the standard of care, yet prior work has found that standard repositioning does not relieve all areas of at-risk tissue in nondisabled subjects. To determine whether this holds true for high-risk patients, we assessed the effectiveness of routine repositioning in relieving at-risk tissue of the perisacral area using interface pressure mapping. Bedridden patients at risk for pressure ulcer formation (n = 23, Braden score <18) had their perisacral skin-bed interface pressures recorded every 30 s while they received routine repositioning care for 4-6 h. All participants had specific skin areas (206 +/- 182 cm(2)) that exceeded elevated pressure thresholds for >95% of the observation period. Thirteen participants were observed in three distinct positions (supine, turned left, turned right), and all had specific skin areas (166 +/- 184 cm(2)) that exceeded pressure thresholds for >95% of the observation period. At-risk patients have skin areas that are likely always at risk throughout their hospital stay despite repositioning. Healthcare providers are unaware of the actual tissue-relieving effectiveness (or lack thereof) of their repositioning interventions, which may partially explain why pressure ulcer mitigation strategies are not always successful. Relieving at-risk tissue is a necessary part of pressure ulcer prevention, but the repositioning practice itself needs improvement.

Mixed simulators: Augmented physical simulators with virtual underlays

We introduce a taxonomy for mixed simulation focusing on mixed simulators with physical exteriors augmented with virtual underlays for practicing medical procedures such as central venous access (CVA). We used CT and MRI imaging and 3D printing to develop anatomically authentic mixed simulators, i.e., exact physical and/or virtual replicas of their human models. Embedded 6 DOF magnetic sensors monitor tracked instruments during simulated procedures, facilitating after action review or self-debriefing. We implemented automated scoring algorithms that include tracking and grading of near misses. After 28 anesthesia residents trained with the CVA simulator, incidence of pneumothorax and arterial puncture in the simulated environment dropped from 11 % to 7% and 13% to 7%, respectively.

Automated, real-time fresh gas flow recommendations alter isoflurane consumption during the maintenance phase of anesthesia in a simulator-based study.

BACKGROUND: The Low Flow Wizard (LFW) provides real-time guidance for user optimization of fresh gas flow (FGF) settings during general inhaled anesthesia. The LFW can continuously inform users whether it determines their FGF to be too little, efficient, or too much, and its color-coded recommendations respond in real time to changes in FGF performed by users. Our study objective was to determine whether the LFW feature, as implemented in the Dräger Apollo workstation, alters FGF selection and thereby volatile anesthetic consumption without affecting patient care. METHODS: To reduce potentially confounding variables, we used a human patient simulator that consumes and exhales volatile anesthetics. Standard monitoring was provided for the patient initially with invasive arterial blood pressure added after anesthetic induction. In this within-group study, each of 17 participants acted as his or her own control. Each participant was asked to anesthetize an identical simulated patient twice using a Dräger Apollo workstation, first with the LFW feature disabled and subsequently enabled. The volatile anesthetic was isoflurane. Both simulation runs were set up to have similar time durations for the different phases of anesthesia: induction, incision, and maintenance. Emergence was not simulated. The isoflurane vaporizer was weighed before and after each simulation run on a digital scale to verify total computed volatile liquid anesthetic consumption. In addition, the product of FGF (reported by the Apollo) times the isoflurane volumetric concentration (sampled by a multigas analyzer at the equivalent of the FGF hose for the Apollo) was integrated over time to obtain isoflurane consumption rate (on-the-fly anesthetic consumption rate measurement). RESULTS: The maintenance isoflurane consumption rate and FGF were significantly lower with the LFW display enabled than without (P = 0.005). The mean reduction in FGF was 53.6% (95% confidence interval, 39.2%–67.9%). There was no significant difference in alveolar isoflurane concentration (P = 0.13 for differences <0.1%). The isoflurane consumption measurement closely matched the consumption measured via the digital scale. CONCLUSIONS: Our data in a simulated anesthetic suggest that enabling the display of FGF efficiency data by the LFW results in a median percent reduction in volatile liquid anesthetic consumption rate of 53.2%. Since the lower limit of the 95% confidence interval for the median is 39.4%, this finding is likely to translate into cost savings and less waste anesthetic gas generated in the clinical setting and released into the atmosphere.

Transfusion has no effect on recurrence in hepatitis C after liver transplantation.

Background: The literature suggests that blood product transfusions have a negative impact on the survival of liver transplant patients. We investigated the impact of intraoperative blood product usage on the survival of liver transplantation patients being transplanted for hepatitis C‐related end‐stage liver disease. In addition, we analyzed a potentially more sensitive metric, namely disease recurrence and fibrosis progression, obtained from follow‐up liver biopsies.

Interfacing existing medical monitoring equipment: a device driver approach

A method to interface with different physiological monitors is presented. Device-specific characteristics are implemented in device drivers in the form of Microsoft Windows DLLs (dynamic link libraries). A unified data representation is defined to make the application independent of the monitor providing the data.