Robert F. Bedford

A clinical evaluation of pulse oximetry during thoracic surgery

To evaluate the utility of pulse oximetry for monitoring oxygenation during thoracic surgery, pulse oximeter oxygen saturation (SpO2) values from the Nellcor N-100 (Nellcor Inc, Haywood, CA) and Novametrix model 500 (Medical Systems Inc, Wallingford, CT) were compared with simultaneous arterial saturation values (SaO2) in 20 patients. A total of 255 matched observations were recorded, and the data were divided for statistical analysis into preinduction of anesthesia and postinduction groups. The preinduction group showed a good correlation between SpO2 and SaO2 values, with both pulse oximeters consistently overestimating the SaO2. However, once anesthesia was induced, there was no longer any correlation for either of the pulse oximeters versus simultaneous SaO2 values, although on average, the SpO2 values were significantly higher than the corresponding SaO2 values. It was concluded that pulse oximetry is useful in following trends of oxygenation in patients with preexisting lung pathology undergoing thoracic surgery, but it cannot replace arterial blood gas sampling for the intraoperative management of respiratory function.

Isoflurane versus fentanyl: hemodynamic effects in cancer patients treated with anthracyclines.

Cancer patients treated with anthracycline derivatives are at risk for perioperative cardiovascular decompensation. The authors studied hemodynamic performance before, during, and after laparotomy in 14 anthracycline-treated patients with ovarian carcinoma. General anesthesia was maintained with 70% N2O in O2, and patients were randomized to receive supplementation with either isoflurane, 0.59% end-tidal +/- 0.04 (mean +/- SE), or fentanyl, 2.67 micrograms/kg +/- 0.49 as a loading dose, and a total dose of 7.16 micrograms/kg +/- 0.71. The degree of hemodynamic stability relative to the baseline was assessed. There was no obvious superiority of either technique prior to the skin incision. However, during and immediately after surgery, a clearer tendency for isoflurane-N2O to result in better hemodynamic stability was found. Isoflurane-N2O demonstrated significantly smaller change scores in systemic vascular resistance (SVR) and cardiac index (CI). At the start of surgery, the isoflurane-N2O change in SVR was 228.08 dyne.sec.cm-5 compared to 479.58 for the fentanyl patients, (P = 0.002); at the end of surgery the corresponding means were -12.09 and 703.14 dyne.sec.cm-5, respectively, (P = 0.002). Isoflurane-N2O was associated with significantly greater CI stability in the early postoperative period: the isoflurane-N2O mean change was -0.081 L/min/m2, versus -0.993 for the fentanyl-N2O patients, (P = 0.005). The authors conclude that anthracycline-treated patients who do not have overt evidence of cardiomyopathy can be safely anesthetized with either anesthetic technique. However, during surgery and in the early postoperative period, an isoflurane-N2O technique appears to offer better hemodynamic stability.

Esmolol infusion during nitroprusside-induced hypotension: Impact on hemodynamics, ventricular performance, and venous admixture

The impact of esmolol infusion on hemodynamics, ventricular performance, venous admixture, sympathoadrenal, and renin-angiotensin system responses during sodium nitroprusside (SNP)-induced hypotension was studied in 11 patients undergoing lymph node dissection during general anesthesia with 60% nitrous oxide and fentanyl. Radial arterial and thermistor-tipped pulmonary catheters were employed for hemodynamic monitoring. Arterial and mixed venous blood gas tensions, arterial plasma renin activity (PRA), and plasma catecholamine levels were measured. Derived hemodynamic parameters and venous admixture (Qs/Qt) data were obtained from standard equations. Transesophageal echocardiography (6 patients) was used to assess left ventricular performance using the relationship between end-systolic wall stress (ESWS) and velocity of circumferential shortening (VCFC). After surgical incision, arterial hypotension was induced with SNP alone. Esmolol was infused at each of the following rates in sequence: 200, 300, and 400 micrograms/kg/min. Each esmolol infusion lasted 20 minutes and the SNP dose was adjusted to maintain MAP at 55 to 60 mm Hg. The mean dose of SNP required to induce hypotension was 5.5 micrograms/kg/min +/- 0.5 SE. Compared to prehypotension values, SNP induced significant increases in Qs/Qt and reductions in PaO2, systemic vascular resistance (SVR), and stroke volume index (SVI). Esmolol infusion caused dose-dependent (highest with 400 micrograms/kg/min) reductions in the SNP requirement, heart rate (HR), SVI, Qs/Qt, and PRA, and also led to significant increases in SVR and left ventricular (LV) internal diameter in diastole as well as systole. Furthermore, esmolol infusion was associated with a dose-dependent downward and leftward shift of the ESWS versus VCFC relationship, implying diminished contractility.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved detection of hypotension by automated noninvasive blood pressure monitoring

This study was undertaken to determine whether the use of automated noninvasive blood pressure monitoring altered the frequency of detection of intraoperative hypotension. We retrospectively reviewed 1,861 anesthetic records from a period in 1987, when blood pressure was obtained manually by auscultation. We compared the records from 1987 with 1,716 anesthetic records from 1989, when automated blood pressure monitors were used universally. The incidences of hypotension requiring vasopressor therapy were determined during the two periods and compared using Students two-tailedt test. The data revealed that the incidence of detected hypotension increased from 2.4 to 5.2% with the use of automated blood pressure monitors (P<0.00002). We conclude that at our hospital the use of automated noninvasive blood pressure monitors increases the incidence of detection of intraoperative hypotension as compared with the use of manual blood pressure measurement.

Blood pressure monitoring

High blood pressure (hypertension) affects 20% of the general population and up to half of all individuals 70 years of age and older. Approximately one billion people currently have high blood pressure, and this number is expected to increase by more than fifty percent by the year 2025. Worldwide hypertension is the third leading cause of death and hypertension-related deaths are expected to rise drastically in the coming decades. Because hypertension is a major risk factor for developing cardiovascular disease, in 2002 it was named “the number one killer” by the World Health Organization (WHO), who also stated that the global disease burden attributable to hypertension causes: • 20% of all deaths in men and 24% of all deaths in women • 62% of strokes and 49% of coronary heart disease • 11% of disability adjusted life years (DALYs)