How do changes in exhaled CO₂ measure changes in cardiac output? A numerical analysis model.

Objective: In a previous study in anesthetized animals, the slope of percent decreases in exhaled CO₂ versus percent decreases in cardiac output (Q(T) inflation of vena cava balloons) was 0.73. To examine the mechanisms underlying this exhaled CO₂-Q(T) relationship, an iterative numerical analysis computer model of non-steady state CO(2) kinetics was developed.

Novel portable device measures preoperative patient metabolic gas exchange.

Background: Indirect calorimetry (IC), the measurement of airway CO2 elimination (VCO2), O2 [corrected] uptake (VO2) [corrected], and respiratory exchange ratio (RER = VCO2/VO2), is a noninvasive modality for the assessment of body metabolism. In anesthesia, IC can signal critical events and onset of acute metabolic derangements. We have previously demonstrated the accuracy and precision of a new IC measurement system designed for mechanically ventilated patients, comprised of a new clinical bymixer, fast response humidity and temperature sensor, and a flowmeter.

Bymixer system can measure O2 uptake and CO2 elimination in the anesthesia circle circuit.

Background: The ability to measure carbon dioxide elimination (Vco(2)), oxygen uptake (Vo(2)), and R (respiratory exchange ratio, Vco(2)/Vo(2)) during anesthesia may help the non-invasive detection of critical events (e.g., abrupt decrease in cardiac output) and metabolic upset (e.

Importance and interpretation of fast-response airway hygrometry during ventilation of anesthetized patients.

Background: Measurement of oxygen uptake (Vo2) should help detect non-steady state critical events and metabolic derangement during anesthesia. Vo2 requires measurement of respiratory relative humidity (RH) and temperature (T). We have developed a fast response T and humidity sensor (HS), which uses tiny wet and dry thermometers to determine RH by psychrometry, where low RH causes evaporation to decrease wet T below dry T.

New metabolic lung simulator: development, description, and validation.

Objective: Indirect calorimetry, the determination of airway carbon dioxide elimination (V(CO2),and oxygen uptake (V(O2)), can be used to non-invasively detect non-steady state perturbations of gas kinetics and mirror tissue metabolism. Validation of monitoring instruments in patients is difficult because there is no standard reference measurement, a wide range of physiologic values is required, and steady state is difficult to achieve and confirm. We present the development, critical details, and validation of a practical bench setup of a metabolic lung simulator, to generate a wide range of accurate, adjustable, and stable reference values of V(CO2) and V(O2), for development, calibration, and validation of indirect calorimetry methodology and clinical monitors.

Infusion pump delivers over-dosage of propofol as a result of missing syringe support.

We describe the malfunction of a common drug infusion pump. The syringe saddle was missing and allowed the syringe barrel to contact the pump case, which decreased the outward displacement of the syringe clamp. Then, the infusion pump falsely detected a smaller syringe size and consequently delivered an increased infusion rate and overdose of propofol to the patient.

Measurement of oxygen uptake and carbon dioxide elimination using the bymixer: validation in a metabolic lung simulator.

Background: The authors have developed a new clinical bymixer that bypasses a constant fraction of gas flow through a mixing arm. A separate bymixer was interposed in the expiratory and inspiratory limbs of the ventilation circuit to measure mixed gas fractions. By utilizing nitrogen conservation, the clinical bymixer allows the determination of airway carbon dioxide elimination (VCO2) and oxygen uptake (VO2), whenever basic expired flow and gas monitoring measurements are used for the patient.

Novel, adjustable, clinical bymixer measures mixed expired gas concentrations in anesthesia circle circuit.

Unlabelled: We have introduced a novel, parallel design into a new clinical bymixer (patent pending), named for the bypass of a constant fraction of total flow through a mixing chamber. Over a wide range of tidal volumes (300-1200 mL), frequency (6-20 breaths/min), and PCO(2) (6-50 mm Hg), the bymixer provided accurate measurement of mixed expired gas fractions in the ventilation circuit compared with an expired gas collection in a metabolic lung bench setup (average slope, 1.00; average y intercept, -0.