Agreement Between Transesophageal Echocardiographic Tricuspid Annular Plane Systolic Excursion Measurement Methods in Cardiac Surgery Patients.

OBJECTIVE: To assess the agreement between 2-dimensional tricuspid annular plane systolic excursion (2D-TAPSE), 2D-TAPSE-apex, and 2D speckle tracking echocardiography (STE-TAPSE) in a cross-section of routine cardiac surgery patients. DESIGN: Retrospective, observational study. SETTING: Tertiary, academic referral hospital. PARTICIPANTS: Patients undergoing elective cardiac surgery with intraoperative transesophageal echocardiography (TEE) imaging. INTERVENTIONS: TEE imaging was reviewed and evaluated for the following three different measurements of transthoracic echocardiography-TAPSE surrogates: 2D-TAPSE, 2D-TAPSE-apex, and STE-TAPSE. Statistical analyses, including 2-sample t tests, linear regression, and agreement using the Bland-Altman methods, were performed. MEASUREMENTS AND MAIN RESULTS: Modest correlation was demonstrated between STE-TAPSE and 2D-TAPSE (R2 = 0.37; p < 0.001) and between STE-TAPSE and 2D-TAPSE-apex (R2 = 0.34; p < 0.001). There was good correlation between 2D-TAPSE and 2D-TAPSE-apex (R2 = 0.77, p < 0.001). The Bland-Altman analysis between these methods showed minimal bias: STE-TAPSE and 2D-TAPSE 0.84 mm, STE-TAPSE and 2D-TAPSE-apex 0.14 mm, and 2D-TAPSE and 2D-TAPSE-apex 0.98 mm. However, the agreement was poor, with 95% limits of agreement of -10.67 to 8.99 mm, -10.67 to 10.96 mm, and -4.91 to 6.88 mm, respectively. CONCLUSIONS: Correlation and minimal bias were found between the several proposed TEE surrogates of transthoracic echocardiography-TAPSE; however, there was poor agreement. Therefore, these surrogates are not interchangeable, and each method needs to be separately validated for clinical use to relevant perioperative outcomes.

Incomplete Spontaneous Recovery from Airway Obstruction During Inhaled Anesthesia Induction: A Computational Simulation.

BACKGROUND: Inhaled induction with spontaneous respiration is a technique used for difficult airways. One of the proposed advantages is if airway patency is lost, the anesthetic agent will spontaneously redistribute until anesthetic depth is reduced and airway patency can be recovered. There are little and conflicting clinical or experimental data regarding the kinetics of this anesthetic technique. We used computer simulation to investigate this situation. METHODS: We used GasMan, a computer simulation of inhaled anesthetic kinetics. For each simulation, alveolar ventilation was initiated with a set anesthetic induction concentration. When the vessel-rich group level reached the simulation specified airway obstruction threshold, alveolar ventilation was set at 0 to simulate complete airway obstruction. The time until the vessel-rich group anesthetic level decreased below the airway obstruction threshold was designated time to spontaneous recovery. We varied the parameters for each simulation, exploring the use of sevoflurane and halothane, airway obstruction threshold from 0.5 to 2 minimum alveolar concentration (MAC), anesthetic induction concentration 2 to 4 MAC sevoflurane and 4 to 6 MAC halothane, cardiac output 2.5 to 10 L/min, functional residual capacity 1.5 to 3.5 L, and relative vessel-rich group perfusion 67% to 85%. RESULTS: In each simulation, there were 3 general phases: anesthetic wash-in, obstruction and overshoot, and then slow redistribution. During the first 2 phases, there was a large gradient between the alveolar and vessel-rich group. Alveolar do not reflect vessel-rich group anesthetic levels until the late third phase. Time to spontaneous recovery varied between 35 and 749 seconds for sevoflurane and 13 and 222 seconds for halothane depending on the simulation parameters. Halothane had a faster time to spontaneous recovery because of the lower alveolar gradient and less overshoot of the vessel-rich group, not faster redistribution. Higher airway obstruction thresholds, decreased anesthetic induction, and higher cardiac output reduced time to spontaneous recovery. To a lesser effect, decreased functional residual capacity and the decreased relative vessel-rich groups' perfusion also reduced the time to spontaneous recovery. CONCLUSIONS: Spontaneous recovery after complete airway obstruction during inhaled induction is plausible, but the recovery time is highly variable and depends on the clinical and physiologic situation. These results emphasize that induction is a non-steady-state situation, thus effect-site anesthetic levels should be modeled in future research, not alveolar concentration. Finally, this study provides an example of using computer simulation to explore situations that are difficult to investigate clinically.

Airway ventilation pressures during bronchoscopy, bronchial blocker, and double-lumen endotracheal tube use: an in vitro study.

OBJECTIVE: To quantify inspiratory flow resistance of instrumented single-lumen and double-lumen endotracheal tubes. DESIGN: Bench-top in vitro experiments. SETTING: Laboratory of a university hospital. PARTICIPANTS: In vitro lung simulator. INTERVENTIONS: A lung simulator was ventilated mechanically via several single- and double-lumen endotracheal tubes (ETT) that were instrumented with adult and pediatric bronchoscopes as well as bronchial blockers. While ventilating with a square-flow wave and increasing peak inspiratory flow from 10-100 L/min, the pressures proximal and distal to the instrumented ETT were measured. Flow (Q) and the pressure loss (∆P) were related with regression of the quadratic equation: ∆P=k1Q+k2Q2. MEASUREMENTS AND MAIN RESULTS: With all combinations of single-lumen endotracheal tubes, double-lumen endotracheal tubes, bronchial blockers, and adult and pediatric bronchoscopes, ∆P was accurately related to Q using the quadratic equation with excellent fit, R2>0.99 for all combinations. The regression parameters k1 and k2 were statistically significant for all combinations except k1 with a bronchoscope through 37-Fr double-lumen endotracheal tube. Parameter k2 was dominant at flows above 10 L/min for uninstrumented airways and 20 L/min for instrumented airways. ∆P increased dramatically with flow, and increased with decreasing endotracheal tube size or addition of instrumentation in a quantitatively predictable manner. CONCLUSIONS: Pressure loss across instrumented endotracheal tubes follows a predictable flow-dependant quadratic pattern. Using the quantitative in vitro results of this study, a clinician can maximize inspiratory ventilation pressures during these situations without delivering excessive airway pressures to the patient.

The relationship between pulmonary system impedance and right ventricular function in normal sheep.

Right ventricular (RV) afterload is a key determinant of RV function and is increased in many cardiopulmonary pathologies. Pulmonary circulation input impedance has been used to quantify afterload previously but due to its complexity has not been widely applied. This study examines the effect of a subset of the impedance spectrum, the zeroth and first harmonic impedance moduli (Z (0), Z (1)), on RV performance in large animals. An artificial circuit with adjustable resistance and compliance (C) was implanted into the pulmonary circulation of five sheep. Resistance was varied to increase Z (0) in increments of 2 mmHg/(L/min) until Z (0) was 8 mmHg/(L/min) above baseline. At each Z (0), C was adjusted between 0, 0.5 and 2 mL/mmHg or 0, 1, and 5 mL/mmHg. Fourier transforms of the pulmonary artery pressure and flow in each situation were used to calculate the pulmonary impedance. Results show that the percent change in cardiac output (%DeltaCO) is linearly related to the change in Z (0) (DeltaZ (0)). Increases in Z (1) (DeltaZ (1)) decreased %DeltaCO but to a much smaller degree, with the effect of DeltaZ (1) increasing with DeltaZ (0). Regression of these results produce the equation: %DeltaCO = (-0.0829DeltaZ (1) - 3.65)DeltaZ (0) - 9.02 (R (2) = 0.69). Blood flow and pressure moduli are small at harmonics higher than the first and are unlikely to affect RV function. Therefore, during acute, high afterload states, Z (0) is the primary determinant of CO, while the effect of Z (1) is minor.

Pulmonic valve function during thoracic artificial lung attachment.

Pulmonic valve incompetence has been observed during implantation of total artificial lungs (TAL) and may contribute to right ventricular dysfunction in certain attachment modes. The roles of pulmonary system resistance and inertia on valve function were examined retrospectively using data from attachments of a prototype TAL in six pigs. The TAL was attached in parallel and in series with the natural lungs and a hybrid of parallel and series. These conditions lead to varying conditions of resistance and inertia in each animal. The periods of ejection (TE), regurgitation (TR), and sealed valve (TSV), and the regurgitant fraction (Fr) were determined at each condition. The relationships between these variables and the effective pulmonary system resistance (R) and the calculated inertial pressure drop during flow deceleration (DeltaPI) were determined. A large R created pulmonic valve incompetence and increased regurgitation, as evidenced by a decreased TSV. A highly negative DeltaPI decreased regurgitation by increasing TE. When R <5 mm Hg/(L/min), Fr remained at baseline levels, regardless of other conditions. When R >5 mm Hg/(L/min), the relationship between Fr, R, and DeltaPI was found to be Fr = 0.014R + 0.011DeltaPI + 0.15 (R = 0.82). Thus, pulmonary system resistance should be maintained <5 mm Hg/(L/min) to avoid pulmonic valve incompetence. High device inertance reduced regurgitation but also lead to increased pulmonary system impedances and ventricular work. The design and implementation of a TAL, thus, should focus on having a small effective pulmonary system resistance.