Comparison of noninvasive cardiac output measured by use of partial carbon dioxide rebreathing or the lithium dilution method in anesthetized foals

Evaluation of Electrical Cardiometry for Measuring Cardiac Output and Derived Hemodynamic Variables in Comparison with Lithium Dilution in Anesthetized Dogs

Numerous cardiac output (CO) technologies were developed to replace the 'gold standard' pulmonary artery thermodilution due to its invasiveness and the risks associated with it. Minimally invasive lithium dilution (LiD) shows excellent agreement with thermodilution and can be used as a reference standard in animals. This study evaluated CO via noninvasive electrical cardiometry (EC) and acquired hemodynamic variables against CO measured using LiD in six healthy, anesthetized dogs administered different treatments (dobutamine, esmolol, phenylephrine, and high-dose isoflurane) impacting CO values. These treatments were chosen to cause drastic variations in CO, so that fair comparisons between EC and LiD across a wide range of CO values (low, intermediate, and high) could be made. Statistical analysis included linear regression, Bland-Altman plots, Lin's concordance correlation coefficient (ρ_c), and polar plots. Values of p < 0.05 represented significance. Good agreement was observed between EC and LiD, but consistent underestimation was noted when the CO values were high. The good trending ability, ρ_c of 0.88, and low percentage error of ±31% signified EC's favorable performance. Other EC-acquired variables successfully tracked changes in CO measured using LiD. EC may be a pivotal hemodynamic tool for continuously monitoring circulatory changes, as well as guiding and treating cardiovascular anesthetic complications in clinical settings.

Effects of 2 modes of positive pressure ventilation on respiratory mechanics and gas exchange in foals

BACKGROUND

Continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) can improve respiratory mechanics and gas exchange, but different airway pressures have not been compared in foals.

HYPOTHESIS/OBJECTIVES

Assess the effect of different airway pressures during CPAP and PSV have on respiratory function in healthy foals with pharmacologically induced respiratory insufficiency. We hypothesized that increased airway pressures would improve respiratory mechanics and increased positive end-expiratory pressure (PEEP) would be associated with hypercapnia.

ANIMALS

Six healthy foals from a university teaching herd.

METHODS

A prospective, 2-phase, 2-treatment, randomized cross-over study design was used to evaluate sequential interventions in sedated foals using 2 protocols (CPAP and PSV). Outcome measures included arterial blood gases, spirometry, volumetric capnography, lung volume and aeration assessed using computed tomography (CT).

RESULTS

Sedation and dorsal recumbency were associated with significant reductions in arterial oxygen pressure (PaO₂ ), respiratory rate, and tidal volume. Continuous positive airway pressure was associated with improved PaO₂ , without concurrent hypercapnia. Volumetric capnography identified improved ventilation:perfusion (V/Q) matching and increased carbon dioxide elimination during ventilation, and spirometry identified decreased respiratory rate and increased tidal volume. Peak inspiratory pressure was moderately associated with PaO₂ and lung volume. Improved pulmonary aeration was evident in CT images, and lung volume was increased, particularly during CPAP.

CONCLUSIONS AND CLINICAL IMPORTANCE

Both CPAP and PSV improved lung mechanics and gas exchange in healthy foals with induced respiratory insufficiency.

Ultrasound dilution cardiac output and echocardiography findings in anesthetized mature alpacas (Vicugna pacos) during normotension, hypotension and hypertension

Alpacas (Vicugna pacos) have physiologic adaptations to live at high altitude. These adaptations may result in unexpected responses to changes in cardiac performance and blood pressure during general anesthesia. There are few studies evaluating cardiovascular variables in anesthetized alpacas. The purpose of this study was to report cardiovascular performance in anesthetized mature alpacas during normotension, hypotension, and hypertension using ultrasound dilution and echocardiography. Six adult alpacas, 3 females and 3 castrated males, weighing 62.6 to 88.7 kg were anesthetized and maintained with isoflurane and placed in right lateral recumbency. Each alpaca underwent ultrasound dilution and echocardiography measurements during three cardiovascular phases, normotension, hypotension via increased isoflurane concentration, and hypertension via phenylephrine infusion. Variables were analyzed with a Friedman test and a post hoc Dunn's test when significant. A p < 0.05 was used for significance. Cardiac output, cardiac index, systemic vascular resistance, stroke volume, total ejection fraction, left ventricular internal diameter during diastole, and total stroke volume indexed to body weight were greater for hypertension compared to hypotension. Total ejection fraction, stroke volume, and left ventricular ejection time were greater for hypertions compared to normotension. There was no difference between ultrasound dilution and echocardiography determined cardiac output measurements within each cardiovascular phase. Phenylephrine appeared to have increased ventricular performance and/or increased preload in anesthetized, mature alpacas. For detecting change in cardiovascular status in anesthetized alpacas, ultrasound dilution and echocardiography may be useful.

Effects of two alveolar recruitment manoeuvres (sustained inflation and stepwise) followed by positive end-expiratory pressure on cardiac output (measured with lithium dilution), invasive blood pressure and arterial oxygen tension in isoflurane-anaesthetised goats

Alveolar recruitment manoeuvres (ARM) performed during general anaesthesia improve oxygenation; however cardiovascular depression may be observed. The aim of the study was to compare the effects of sustained inflation (SI) and stepwise ARMs on cardiac output (CO), mean arterial blood pressure and arterial oxygen tension (PaO2) in ten mechanically ventilated goats anaesthetised with isoflurane. In the SI ARM, peak inspiratory presure (PIP) was increased to 30 cmH2O and sustained for 20 s. In the stepwise ARM, the PIP was increased by 5 cmH2O each minute for three minutes from 10 to 25 cmH2O. Both ARMs were followed by positive end-expiratory pressure of 5 cmH2O. Paired lithium dilution CO measurements and arterial blood samples were obtained before and after each ARM. The order of the ARM was randomised and each goat was subjected to both techniques. Data was reported as median and interquartile range (IQR). Significance was set at 0.05. The median change in CO (measured by subtracting values after and before ARM) was -0.15 L min-1 (IQR -0.51; 0.03) and - 0.90 L min-1 (IQR -1.69; -0.58) for SI and stepwise ARM respectively (p = 0.04). The median change in PaO2 was 3 kPa (IQR -2.7; 7.6) and 0.4 kPa (IQR -3.4; 5.5) for SI and stepwise ARM respectively (p = 0.03). In conclusion, SI ARM causes less impact on CO and provides a better improvement in PaO2 compared to stepwise ARM in goats.

The effect of a ketamine constant rate infusion on cardiovascular variables in sheep anesthetized at the minimum alveolar concentration of sevoflurane that blunts adrenergic responses

OBJECTIVE

To evaluate the effect of a constant rate infusion of ketamine on cardiac index (CI) in sheep, as estimated using noninvasive cardiac output (NICO) monitoring by partial carbon dioxide rebreathing, when anesthetized with sevoflurane at the previously determined minimum alveolar concentration that blunts adrenergic responses (MACBAR).

ANIMALS

12 healthy Dorset-crossbred adult sheep.

PROCEDURES

Sheep were anesthetized 2 times in a balanced placebo-controlled crossover design. Anesthesia was induced with sevoflurane delivered via a tight-fitting face mask and maintained at MACBAR. Following induction, sheep received either ketamine (1.5 mg/kg IV, followed by a constant rate infusion of 1.5 mg/kg/h) or an equivalent volume of saline (0.9% NaCl) solution (placebo). After an 8-day washout period, each sheep received the alternate treatment. NICO measurements were performed in triplicate 20 minutes after treatment administration and were converted to CI. Blood samples were collected prior to the start of NICO measurements for analysis of ketamine plasma concentrations. The paired t test was used to compare CI values between groups and the ketamine plasma concentrations with those achieved during the previous study.

RESULTS

Mean ± SD CI of the ketamine and placebo treatments were 2.69 ± 0.65 and 2.57 ± 0.53 L/min/m2, respectively. No significant difference was found between the 2 treatments. Mean ketamine plasma concentration achieved prior to the NICO measurement was 1.37 ± 0.58 µg/mL, with no significant difference observed between the current and prior study.

CLINICAL RELEVANCE

Ketamine, at the dose administered, did not significantly increase the CI in sheep when determined by partial carbon dioxide rebreathing.

Lithium dilution cardiac output measurements in isoflurane-anaesthetised goats: Jugular versus cephalic lithium chloride administration

The administration of lithium chloride (LiCl) for cardiac output (CO) measurement via a peripheral instead of a central vein has been described previously as a valid alternative route in pigs and dogs. The aim of the study was to compare CO measurements after administration of LiCl using two peripheral veins, cephalic or jugular, in goats. Ten adult, female, experimental goats undergoing bilateral stifle arthrotomy were recruited for the study. Paired CO measurements were taken two minutes apart during stable conditions in isoflurane-anaesthetised goats. Forty-two paired CO measurements were taken in total, and the median (range) of paired CO measurement per goat were 4.5 (3-6). The mean (SD) CO using the cephalic and jugular vein for injection of LiCl was 5.28 (1.29) L min^-1 and 5.20 (1.24) L min^-1 respectively. The Bland-Altman analysis showed an acceptable agreement with a mean bias of 1.33% with limits of agreement (LoA) of -18.43 to 21.09%. The percentage of error was 25%. The four-quadrant plot analysis showed a poor agreement (71%) between the two routes. The polar plot showed a poor trending ability. An 86% inclusion rate (18/21 points) was reached with a ± 35° radial sector size. The findings revealed that the agreement between the two routes is not as precise as the authors expected, however the results are comparable with studies published previously.

Comparison of thermodilution, lithium dilution, and pulse contour analysis for the measurement of cardiac output in 3 different hemodynamic states in dogs

OBJECTIVE

To (1) evaluate lithium dilution (LiDCO) and transpulmonary thermodilution (PiCCOTD ) in relation to traditional thermodilution (PAC-TD) for determining cardiac output (CO) in 3 different hemodynamic states in dogs and to (2) compare the continuous CO values obtained using power analysis (PulseCO) with continuous PiCCO (PiCCOc).

DESIGN

Prospective randomized study.

SETTING

University research laboratory.

ANIMALS

Fourteen healthy Beagles.

INTERVENTIONS

CO was measured using PAC-TD, LiDCO, and PiCCOTD in 3 different hemodynamic states induced in random order and defined on the basis of the mean arterial pressure (MAP). Normodynamic state was defined as the baseline MAP and 1 MAC sevoflurane. The hypodynamic state was induced with a deep level of sevoflurane anesthesia. The hyperdynamic state was induced with noradrenaline. After these measurements were obtained in each hemodynamic state, CO was monitored continuously for 30 min using PulseCO and PiCCOc. Agreement was assessed using Bland-Altman analysis and intraclass correlation coefficients, and a trend score was determined for the continuous CO measurements.

MEASUREMENTS AND MAIN RESULTS

There was good agreement among the 3 modalities of CO measurement in each hemodynamic state. The mean CIPAC-TD /CIPICCOTD bias was -0.04 ± 1.19 L/min/m(2) (limits of agreement, -2.37/1.93 L/min/m(2) ), and the mean CIPAC-TD /CILiDCO bias was -0.11 ± 1.55 L/min/m(2) (limits of agreement, -3.04/2.93 L/min/m(2) ). The mean CIPulseCO -CIPiCCOc bias was -0.04 ± 1.91 L/min/m(2) (limits of agreement, -1.95/1.87 L/min/m(2) ), which suggested good agreement. The CIPulseCO -CIPiCCOc trend score, calculated from 252 paired comparisons, was 93.3% positive after zone exclusion (∆CI < 15%).

CONCLUSIONS

Both LiDCO and PiCCOTD agreed well with PAC-TD for the measurement of CO under different hemodynamic conditions. Moreover, PiCCOc appears to be an accurate method for monitoring continuous CO in dogs as its performance for measurement was similar to that of PulseCO.

A history of pediatric anesthesia: a tale of pioneers and equipment

The history of pediatric anesthesia is fascinating in terms of how inventive anesthesiologists became over time to address the needs for advances in surgery. We have many pioneers and heroes. We hope you will enjoy this brief overview and that we have not left out any of the early contributors to our speciality. Obviously there is insufficient space to include everyone.

Intravenous fluids cause systemic bias in a conductivity-based point-of-care hematocrit meter

BACKGROUND

Point-of-care (POC) devices measuring hematocrit rely on determination of electrical conductivity of whole blood. We hypothesized that some frequently administered IV fluids independently alter blood conductivity and confound hematocrit determination.

METHODS

Whole human blood was diluted to predetermined hematocrit values with normal saline, lactated Ringer solution, hetastarch, or plasma. Electrical conductivity and hematocrit (i-STAT® and spun methods) were measured at each dilution. In separate experiments, the effects of propofol and heparin were noted on these variables.

RESULTS

Greater dilution significantly increased conductivity irrespective of diluent type. The magnitude of the conductivity slopes increased in order for plasma, hetastarch, lactated Ringer solution, and normal saline dilution. Moreover, each slope varied from every other slope (all P < 0.0001), and 94.2% of hematocrit values measured by i-STAT (n = 211 of 224) were less than those for the spun method. Dilution with plasma, normal saline, lactated Ringer solution, and hetastarch caused bias (Bland-Altman limits of agreement) of -2.7% (-6.9/1.4), -4.6% (-7.3/-2.0), -4.8% (-7.8/-1.7), and -2.0% (-5.6/1.9), respectively. The Cohen κ agreement values (5th-95th confidence interval) for a transfusion trigger of 30% were 0.90 (all values, 0.85-0.95), 0.25 (hematocrit <30%, 0.02-0.48), and 0.21 (hematocrit 18%-30%, 0.01-0.42). Clinically relevant concentrations of propofol and heparin had minimal effects on electrical conductivity or hematocrit determination.

CONCLUSIONS

Dilution of blood with frequently used IV solutions affects whole blood conductivity determinations and thereby decreases hematocrits measured by a POC device relying on this method as compared with spun hematocrit. Conductivity-based hematocrit POC devices should be cautiously interpreted when hemodilution is present.

Comparison of Fick and thermodilution cardiac output determinations in standing horses

The Fick and thermodilution (TD) methods are two currently popular techniques for determination of cardiac output (CO) in adult horses. To our knowledge, a comparison of these two techniques has not been reported. Six healthy, resting, fit, adult horses of either sex and weighing 516.5+/-33.2 kg (mean+/-SD) were instrumented to enable measurement of cardiac output. Resting CO was determined by the Fick method and by thermodilution while the horses stood quietly in the stocks. Fick and thermodilution CO measurements were repeated under conditions of increased cardiac output achieved with the use of a dobutamine infusion (5 microg kg(-1) min(-1), IV), and again under conditions of decreased CO induced by administration of xylazine (0.5 mg/kg, IV). Fick and thermodilution cardiac outputs were compared using Bland-Altman analysis for repeated measures. The mean of the differences+/-1.96SD (bias and precision) between the two techniques was 1.88+/-24.17 L/min. Variability between measurements with the two techniques was decreased to 3.41+/-46.78 mL kg(-1) min(-1) when CO was normalized for body size by calculation of cardiac index.