Development and application of a logistic-based systolic model for hemodynamic measurements using the esophageal Doppler monitor.

The esophageal Doppler monitor (EDM) is a clinically useful device for minimally invasive assessment of cardiac output, preload, afterload, and contractility. An empirical model, based upon the logistic function, has been developed. Use of this model illustrates how the EDM could estimate the net effect of aortic and non-aortic contributions to inertia, resistance, and elastance within real time.

Development of a recursive finite difference pharmacokinetic model from an exponential model: application to a propofol bolus.

Propofol is commonly administered, as a single bolus dose, for the induction of general anesthesia. The purpose of this study was to mathematically assess the ability to model propofol induction-dose serum levels with a recursive finite difference equation (RFDE). Using data obtained from a prior published study, propofol induction pharmacokinetics were accurately modeled, on a subject-specific basis, with a third-order homogeneous finite difference equation with constant coefficients: P((k + 3)) = AP((k + 2)) + BP((k + 1)) + CP((k)).

A mathematical model of differential tracheal tube cuff pressure: effects of diffusion and temperature.

The tracheal tube cuff performs an important function during anesthesia and critical care situations by allowing positive pressure ventilation and isolating the lungs from aspiration. Other maneuvers, such as pressure support ventilation and positive end-expiratory pressure, are also cuff-dependent. However, excessive cuff pressure, as well as long-term intubation without excessive cuff pressure, have been associated with significant morbidity and mortality.

A comparison of fiberoptic-compatible oral airways.

Fiberoptic-compatible oral airways (FCOAs) combine the simplicity and benefits that traditional oral airways provide, with the advantage of mechanically guiding fiberoptic intubation. This review examines and compares the salient properties of these devices. Of note, the clinician should pay particular attention to the location and depth of the channel.

Electrocautery-induced pacemaker malfunction during surgery.

We report a case of electrocautery-induced pacemaker failure that resulted in asystole in a 15-year-old girl scheduled for cardiac surgery. Her pacemaker was converted to the asynchronous mode the night before surgery. Electromagnetic interference from the unipolar electrocautery caused a reduction in the battery voltage, which allowed the digital circuitry, but not the voltage control oscillator (VCO), to work properly.