Minimally Invasive Determination of Cardiac Output by Transthoracic Bioimpedance, Partial Carbon Dioxide Rebreathing, and Transesophageal Doppler Echocardiography in Beagle Dogs

Plethysmography variability index for prediction of fluid responsiveness during graded haemorrhage and transfusion in sevoflurane-anaesthetized mechanically ventilated dogs

OBJECTIVE

To examine the accuracy of plethysmography variability index (PVI) as a noninvasive indicator of fluid responsiveness in hypovolaemic dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Six adult healthy sevoflurane-anaesthetized Beagle dogs.

METHODS

Dogs were anaesthetized with 1.3-fold their individual minimum alveolar concentration of sevoflurane. The lungs were mechanically ventilated after neuromuscular blockade with vecuronium bromide. Cardiopulmonary variables including mean arterial blood pressure (MAP), central venous pressure (CVP), transpulmonary thermodilution cardiac output (TPTDCO), stroke volume (SV), perfusion index (PI), pulse pressure variation (PPV), stroke volume variation (SVV) and PVI were determined during six stages of graded venous blood withdrawal (5 mL kg^-1 increments) and six stages of graded blood infusion (5 mL kg^-1 increments). The cardiopulmonary variables were analysed using paired t test or Wilcoxon signed rank test. Correlations between PPV and SVV or PVI were analysed by linear regression. The accuracy of PPV, SVV and PVI for predicting fluid responsiveness was examined by using receiver operating characteristic curve analysis. A value of p < 0.05 was considered statistically significant.

RESULTS

Blood withdrawal resulted in significant increases in PPV and PVI and decreases in MAP, CVP, TPTDCO, SV and PI. Blood infusion resulted in significant increases in MAP, CVP, TPTDCO, SV and PI and decreases in PPV and PVI. PPV and PVI showed a relevant correlation (p < 0.001, r² = 0.62) and threshold values of PPV ≥ 16% (sensitivity 71%, specificity 82%) and PVI ≥ 12% (sensitivity 78%, specificity 72%) for identifying fluid responsiveness. SVV did not change.

CONCLUSIONS AND CLINICAL RELEVANCE

Noninvasive measurement of PVI predicted fluid responsiveness with moderate accuracy equal to PPV in sevoflurane-anaesthetized mechanically ventilated dogs. Provisional threshold values for identification of fluid responsiveness were PPV ≥ 16% and PVI ≥ 12%. Clinical trials are needed to confirm these threshold values in dogs.

Heartworm Removal Guided by Transesophageal Echocardiography in a Dog with Naturally Acquired Caval Syndrome

A 14 mo old shih tzu was referred for dyspnea, hemoptysis, and hematuria. Heartworm disease with caval syndrome was diagnosed by laboratory tests, thoracic radiography, and transthoracic echocardiography. The minimally invasive heartworm removal procedure was performed using flexible alligator forceps guided by transesophageal echocardiography. The procedure was successfully performed removing over 94% of heartworms displayed echocardiographically without any intraoperative complication.

Comparison of cardiac output measurements using transpulmonary thermodilution and conventional thermodilution techniques in anaesthetized dogs with fluid overload

OBJECTIVE

To evaluate the agreement between cardiac output (CO) values obtained using a transpulmonary thermodilution technique (TPTDCO) and conventional thermodilution technique (TDCO) in anaesthetized dogs with fluid overload.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Six healthy Beagle dogs aged 7-8 years.

METHODS

Dogs were anaesthetized with sevoflurane in oxygen, and catheters were inserted for TPTDCO and TDCO measurement. After instrumentation, baseline CO was measured using each technique at a central venous pressure (CVP) of 3-7 mmHg. Dogs were subsequently administered lactated Ringer's solution and 6% hydroxyethyl starch to induce fluid overload. CO measurements were obtained using each technique at CVP values of 8-12 mmHg, 13-17 mmHg, 18-22 mmHg and 23-27 mmHg. Agreements between CO measurements obtained with the respective techniques were analysed using Dunnett's test, Pearson's correlation coefficient and Bland-Altman analysis.

RESULTS

Thirty pairs of CO values were obtained, ranging from 1.45 L minute(-1) to 4.69 L minute(-1) for TPTDCO and from 1.30 L minute(-1) to 4.61 L minute(-1) for TDCO. TPTDCO and TDCO values correlated strongly (r(2)  = 0.915, p < 0.001). The bias and mean relative bias between TPTDCO and TDCO were 0.26 ± 0.30 L minute(-1) (limits of agreement - 0.29 to 0.81 L minute(-1) ) and 9.7%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

TPTDCO and TDCO measurements obtained in anaesthetized dogs during fluid overload exhibited good agreement. Accordingly, transpulmonary thermodilution provides an accurate measurement of CO in dogs with fluid overload.

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.

Cardiovascular effects of tramadol in dogs anesthetized with sevoflurane

Cardiovascular effects of tramadol were evaluated in dogs anesthetized with sevoflurane. Six beagle dogs were anesthetized twice at 7 days interval. The minimum alveolar concentration (MAC) of sevoflurane was earlier determined in each dog. The dogs were then anesthetized with sevoflurane at 1.3 times of predetermined individual MAC and cardiovascular parameters were evaluated before (baseline) and after an intravenous injection of tramadol (4 mg/kg). The administration of tramadol produced a transient and mild increase in arterial blood pressure (ABP) (P=0.004) with prolonged increase in systemic vascular resistance (SVR) (P<0.0001). Compared with baseline value, mean ABP increased significantly at 5 min (119% of baseline value, P=0.003), 10 min (113%, P=0.027), and 15 min (111%, P=0.022). SVR also increased significantly at 5 min (128%, P<0.0001), 10 min (121%, P=0.026), 30 min (114%, P=0.025), 45 min (113%, P=0.025) and 60 min (112%, P=0.048). Plasma concentrations of tramadol were weakly correlated with the percentage changes in mean ABP (r=0.642, P<0.0001) and SVR (r=0.646, P<0.0001). There was no significant change in heart rate, cardiac output, cardiac index, stroke volume, pulmonary arterial pressure, right atrial pressure and pulmonary capillary wedge pressure. In conclusion, the administration of tramadol produces a prolonged peripheral vascular constriction in dogs anesthetized with sevoflurane, which is accompanied with a transient and mild increase in arterial blood pressure. It also indicated that the degree of vasoconstriction might depend on the plasma concentration of tramadol.

Evaluation of a commercial ultrasonographic hemodynamic recording system for the measurement of cardiac output in dogs

OBJECTIVE

To evaluate the accuracy of a commercial ultrasonographic cardiac output (CO) monitoring system (UCOMS) in anesthetized Beagles as assessed by comparison with thermodilution CO (TDCO).

ANIMALS

8 healthy anesthetized Beagles.

PROCEDURES

Simultaneous UCOMS and TDCO measurements of CO were obtained during 4 hemodynamic states: baseline anesthesia (0.5% to 1.5% isoflurane), a higher depth of anesthesia (2% to 3.5% isoflurane) to yield a >or= 15% reduction in systolic arterial blood pressure, IV infusion of colloidal solution to a mean right atrial pressure of >or= 15 mm Hg, and IV infusion of dobutamine at 5 microg/kg/min. Measurements were obtained at 2 probe positions: the subxiphoid region and the right thoracic inlet. Correlation and agreement of results between methods were determined via linear regression analysis and Bland-Altman plots.

RESULTS

A significant positive correlation was detected between UCOMS andTDCO measurements obtained at the subxiphoid (R = 0.86) and thoracic inlet (R = 0.83) positions. Bland-Altman plots revealed minimal bias between methods (bias +/- SD, -0.03 +/- 0.73 L/min and -0.20 +/- 0.80 L/min for subxiphoid and thoracic inlet measurements, respectively). However, the percentage error associated with UCOMS measurements made at the 2 positions was > 45%.

CONCLUSIONS AND CLINICAL RELEVANCE

When compared with the results of TDCO, CO measured with the UCOMS exceeded commonly accepted limits of error in healthy dogs. The UCOMS was, however, able to track changes in CO across hemodynamic states. Additional research is needed to assess the usefulness of the UCOMS for monitoring CO in critically ill dogs.