Julia Fleming

Transesophageal Doppler cardiac output monitoring: performance during aortic reconstructive surgery.

Transesophageal Doppler (TED) monitoring provides continuous, noninvasive monitoring of cardiac output by measurement of aortic flow velocities. Because of the effects on aortic flow dynamics resulting from atherosclerosis, aortic cross-clamping, and wide variations in arterial blood pressure, the validity of TED monitoring during aortic surgery is unresolved. The authors prospectively evaluated a second-generation TED cardiac output monitor in 42 patients undergoing aortic reconstructive surgery. Four hundred eighty-nine simultaneous measurements of TED and thermodilution cardiac output were obtained. Transesophageal Doppler measurements were highly correlated to thermodilution measurements (R = 0.94); however, Bland-Altman analysis revealed a moderate error in the TED measurements (2 SD of the bias = 1.4 L/min). Trending analysis showed that TED monitoring accurately tracked changes in thermodilution cardiac output. Placement of an aortic cross-clamp resulted in significant reductions in the accuracy of Doppler measurements. Arterial blood pressure variations did not systematically affect the accuracy of the transesophageal technique. Limitations of TED monitoring, including a difficult calibration procedure, poor performance during aortic cross-clamping, and the need for probe repositioning, suggest further development is warranted.

Intravenous cocaine challenges during naltrexone maintenance: A preliminary study

In 1976 Byck hypothesized that opioid antagonists would block the euphoric effect of cocaine, and recent clinical observations have suggested lower rates of cocaine abuse by people receiving naltrexone (NTX) than by those receiving methadone (Kosten et al 1989). Although early workers found that both rodents and primates maintained on antagonists showed no attenuation of cocaine self-administration (Killian et al 1978; Carroll et al 1986), more recent studies have found attenuation with NTX administration (Mello et al 1990; DeVry et al 1989; Ramsey and van Ree 1991). Furthermom, Bain and Kornetsky (1987), using rewarding brain stimulation in rodents, showed that the antagonist naloxone can reverse cocaines potentiation of this stimulation. An early human study using cocaine administration found a potentiation rather than a reduction of cocaine effect after acute high-dose naloxcne (20 mg i.e.; Byck et al 1982), but this situation is clearly different from maintenance blocking with lower doses of NTX. We therefore undertook the current cocaine challenge study during chronic NTX.

Transesophageal doppler ultrasonography : evidence for improved cardiac output monitoring

Cardiac output monitoring by transesophageal Doppler ultrasound has not gained wide clinical acceptance. A recently developed transesophageal Doppler device, Accucom 2, features technological advances aimed to reduce the error of this approach to the monitoring of cardiac output. To determine if Accucom 2 enables more accurate cardiac output monitoring, a prospective investigation was undertaken. Analyses of 923 simultaneous measurements of transesophageal Doppler and thermodilution cardiac output in 47 anesthetized patients were compared. Results using Accucom 2 were highly correlated with the results obtained with thermodilution (R = 0.91) and provided significantly greater accuracy in comparison with a previously developed Doppler cardiac output monitor, Accucom 1. Technological advances in transesophageal Doppler ultrasound hold promise for clinically useful noninvasive monitoring of cardiac output.

Predictors of postoperative respiratory complications in premature infants after inguinal herniorrhaphy

There is a significant incidence of inguinal hernia in premature infants and the optimal timing of repair is controversial. A high rate of postoperative respiratory complications has been reported in this group. In this study, the records of 47 premature infants (mean gestational age, 30.3 weeks) who underwent herniorrhaphy while still in the neonatal intensive care unit were reviewed in an effort to define those conditions that are independent risk factors for complications. Forty-three percent of infants had complications, including postoperative assisted ventilation (34%), episodes of apnea and/or bradycardia (23%), emesis and cyanosis with first feeding (6%), and requirement for postoperative reintubation (4%). Although low gestational age and postconceptual age at operation, low birth weight for gestational age, and preoperative ventilatory assistance were significantly associated with postoperative complications, only a history of respiratory distress syndrome/bronchopulmonary dysplasia (odds ratio 2.3), a history of patent ductus arteriosus (odds ratio 2.5), and low absolute weight at operation (odds ratio 3.5 for 1,000-g decrease) were independent risk factors for postoperative complication. Despite previous reports citing postconceptual age as the factor having the greatest impact on postoperative complications, these results indicate that a history of respiratory dysfunction and size at operation may be more important predictors of postoperative respiratory dysfunction in preterm infants.

Decreased digital flow persists after the abatement of cocaine-induced hemodynamic stimulation.

This study determined whether the development of delayed ischemic sequelae due to cocaine use-after the return of arterial blood pressure (BP) and heart rate to near-baseline values-may be attributable to regional vasoconstriction which persists beyond the acute systemic hemodynamic response. Five cocaine-using volunteers received intravenous infusions of saline placebo and cocaine 0.50 mg/kg several days apart in a double-blinded cross-over design. The intensity and duration of the cocaine-induced decrease in peripheral blood flow (as documented by laser Doppler flowmetry of the finger) were compared to the increases in BP (obtained with a Dinamap [R]) and heart rate using paired t-test and repeated-measures analysis of variance. A significant increase in BP and a significant decrease in finger flow were noted by the first time point (5 min). Within 15 min, cocaine induced a 36% +/- 5% increase in BP and a 73% +/- 18% decline in finger flow (P < 0.05 for difference between percent change in BP and percent change in flow). Dinamapsystolic and Dinamapdiastolic returned to within 15% of baseline within 30 min, while finger flow remained more than 50% below baseline for the remainder of the 60-min study period (P < 0.05). Changes in heart rate paralleled those in BP. Except for isolated cases of documented coronary vasoconstriction in patients presenting with complications after cocaine use, this study is the first to document the persistence of cocaine-induced vasoconstriction of a sensitive vascular bed beyond the hypertensive response. It thus helps to explain the development of ischemic injury after cocaine use despite a stable rate-pressure product. (Anesth Analg 1997;84:46-50)

The effects of bupivacaine on the umbilical circulation and placental gas exchange in the fetal lamb

Seven chronically catheterized fetal sheep at 125–140 days gestation were studied in 12 experiments to determine the direct effects of the local anesthetic bupivacaine (infused intravenously to the fetus) on the umbilical circulation and placental gas exchange. Electrocortical activity, umbilical blood flow, heart rate, and umbilical arterial and venous pressures were continuously monitored in experiments comprising a baseline period, a drug infusion period and a recovery period, each of 2 hr duration. Samples of umbilical arterial and venous blood were taken for blood gas analysis, and for bupivacaine assay using high pressure liquid chromatography technique. Fetal plasma bupivacaine levels were 1.3 ± 0.3 μg/ml (mean ± SEM) between 60–120 min of infusion. Heart rate and umbilical blood flow decreased significantly to 89 and 94% of control, respectively, (P < 0.05) during the infusion and returned to control levels by 2 hr afterwards. Mean umbilical arterial and venous pressures were not significantly altered, and no significant rise in umbilical vascular resistance occurred. No changes occurred in umbilical arterial or venous pH, Po2, or Pco2. In summary, bupivacaine reversibly depressed fetal heart rate and umbilical blood flow without detrimental changes in fetal blood gas or acid-base status.