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Biomedical subjects

S Ramanathan

Publications and source records attributed to S Ramanathan.

171 records · Page 10Linked to original sources
PubMedDate not supplied

An infant circuit with a water vaporizer warmed by carbon dioxide neutralization.

A pediatric anesthesia system was constructed by connecting the machine end of a modified Mapleson D system to a soda lime canister containing a water vaporizer heated through the reaction of neutralization of the lime by the CO2 emerging from the breathing tube. The vaporizer was placed in line with the fresh-gas delivery tube of the circuit. The humidity output of the system varied from 15 +/- 1 mg H2O/L with a CO2 output of 15 ml/L to 27 +/- 1.5 mg H2O/L with a CO2 output of 60 ml/min. Rebreathing of CO2 was within acceptable limits as long as fresh-gas inflow remained at 5 L/min. The system compares favorably in respect to its humidity output with all other circuits availabe on the market for pediatric anesthesia.

Anesthesiology↗
PubMedDate not supplied

Systemic vascular uptake of epinephrine from the lumbar epidural space in parturients.

BACKGROUND AND OBJECTIVES: To assess the systemic vascular uptake of epinephrine from the lumbar epidural space in parturients during epidural anesthesia for cesarean delivery. METHODS: Thirty-eight healthy patients were randomly divided into two equal groups. In one group, bupivacaine-epinephrine (5 micrograms/mL) mixture was used to produce lumbar epidural anesthesia to a T6 level; in the other group, bupivacaine 0.5%. Maternal venous plasma epinephrine and norepinephrine concentrations were measured before anesthesia (baseline), at a T6 sensory level and at delivery; and 10, 20, 30, and 50 minutes after delivery. Statistical comparisons were made using nonparametric analysis of variance at P < .05. RESULTS: In the bupivacaine-epinephrine group, the plasma epinephrine concentration increased approximately fourfold at T6 sensory level compared to the baseline value or to the corresponding value in the bupivacaine group (P < .01), and it remained elevated significantly for 20 minutes after delivery. In the bupivacaine group, no significant changes occurred in the epinephrine concentrations. In both groups, plasma norepinephrine concentration increased at T6 level approximately 1.8-fold compared to the baseline value (P < .01), with no intergroup differences. CONCLUSIONS: Epinephrine is absorbed from the epidural space and raises the maternal circulating epinephrine concentration. Maternal plasma norepinephrine concentration rises during lumbar epidural anesthesia regardless of epinephrine use.

Adult↗
PubMedDate not supplied

Thoracic versus lumbar administration of epidural morphine for postoperative analgesia after thoracotomy.

BACKGROUND AND OBJECTIVES: The purpose of this study was to compare the effects of thoracic and lumbar epidural morphine on pulmonary function and analgesia after thoracotomy for pulmonary resection. METHODS: Twenty-seven patients were randomized into two groups to receive either thoracic or lumbar epidural morphine as needed for postoperative analgesia. Postoperative pain was assessed hourly on a 10-cm visual analog scale (VAS), and epidural morphine was administered in 3 mg doses for a VAS score > 2 cm. Patients underwent pulmonary function tests (forced vital capacity, forced expiratory volume at 1 second, peak expiratory flow) preoperatively, and 24 hours postoperatively. Results were expressed as mean +/- 1 SE and analyzed using Student's t-test and Student-Newman-Keuls test at p < 0.05. RESULTS: Twenty patients completed the study (n = 10 per group). Patients in the thoracic group required 3.1 +/- 0.4 injections to a total morphine dose of 11.9 +/- 1.4 mg during the first 24 hours postoperatively, and those in the lumbar group required 4.7 +/- 0.4 doses to a total 24-hour morphine dose of 16.4 +/- 1.2 mg (p < 0.05). Median hourly VAS scores were similar in both groups. Postoperative pulmonary function decreased in both groups without intergroup differences. CONCLUSIONS: The authors conclude that thoracic epidural morphine administration in patients after thoracotomy results in decreased morphine requirements and the same degree of analgesia as does lumbar administration.

Aged↗
PubMedDate not supplied

Hemodynamic effects of subarachnoid fentanyl in laboring parturients.

BACKGROUND AND OBJECTIVES: The subarachnoid administration of fentanyl to laboring parturients may decrease maternal blood pressure. The hemodynamic effects of subarachnoid fentanyl (SAF) in laboring women was studied by impedance cardiography. METHODS: Following a 500 mL fluid bolus, 15 healthy women received 25 micrograms of SAF for labor analgesia by a combined spinal-epidural technique. Maternal systolic, mean, and diastolic blood pressure, heart rate, cardiac index, stroke index, and end-diastolic index were measured before SAF administration (baseline) and every 5 minutes for 30 minutes after administration. Prelabor blood pressure values were obtained from the patient's last office visit. Data were analyzed by analysis of variance at P < .05. RESULTS: Following SAF administration, pain scores decreased and pruritus scores increased (based on 100-mm visual analog scales). Maternal systolic, diastolic, and mean blood pressures, heart rate, and cardiac index decreased significantly by 12, 18, 17, 12, and 14%, respectively, as compared with baseline values, with no significant change in stroke index. Cardiac preload (end-diastolic index) decreased by 10% 25 minutes following SAF administration but otherwise did not significantly change. Compared with prelabor blood pressure values, the diastolic pressure decreased significantly only 9% at 20 minutes and the mean arterial pressure decreased only 7 and 8% at 20 and 25 minutes, respectively; the systolic pressure did not change. In 53% of patients, at least one hypotensive episode (systolic pressure of < or = 100 mm Hg or a > 30% decrease in systolic pressure) occurred, following SAF administration. However, only two of these episodes (systolic pressures of 93 and 96 mm Hg) lasted longer than 1 minute, and these were easily treated with intravenous ephedrine. CONCLUSIONS: Vasodilation due to sympathectomy causes a decrease in preload (end-diastolic index) and in stroke index and an increase in heart rate. Since the end-diastolic index and stroke index remained relatively stable and the heart rate decreased, it was concluded that the observed decrease in blood pressure was not due to vasodilation.

Adult↗
PubMedDate not supplied

Detecting vascular access dysfunction.

Access flow (QACC) is a major determinant of patency. Access recirculation (AR > 2%), normalized venous intra-access pressure (vPIA/MAP), and QACC are used to detect access dysfunction. We compared these three measures of access function (ultrasound dilution to measure AR and QACC). A total of 779 measurements were performed on 58 arteriovenous fistulas (AVFs) and 114 polytetrafluoroethylene (PTFE) grafts (1-8/access) over 13 months, and the access parameters at the beginning of each period were related to access events within that period. Pump blood flow averaged > 420 ml/min. AR occurred uncommonly (3.8%), and in half the cases, resulted from technical error by staff. In accesses that thrombosed or underwent intervention for stenosis, AR was present in only 3 of 11 AVFs and 8 of 57 PTFE accesses. When AR was present in grafts, QACC averaged 270 +/- 23, and access thrombosis followed unless intervention occurred. In grafts, vPIA/MAP averaged 0.34 +/- 0.01 in those remaining patent, 0.52 +/- 0.08 in those that had undergone intervention, and 0.54 +/- 0.04 in those that had thrombosed. QACC averaged 1,121 +/- 26, 605 +/- 45, and 550 +/- 65 ml/min, respectively, in the three groups. By contrast, QACC differed significantly in patent AVFs (1,053 +/- 35) compared with failing AVFs (363 +/- 48), but vPIA/MAP did not. AR is thus a late manifestation of access failure. QACC is the best diagnostic test of access dysfunction in AVFs. Interpretation of vPIA/MAP in grafts is enhanced by periodic QACC measurements.

Arteriovenous Shunt, Surgical↗
PubMedDate not supplied

Detection of access strictures and outlet stenoses in vascular accesses. Which test is best?

The location of stenoses within an access may influence the diagnostic value of access monitoring tests. Whereas decreasing access flow (QACC) should occur with both venous outlet stenoses and strictures within the body of the access, normalized intra-access venous pressure (vPIA/MAP) depends on location of the venous needle relative to the lesion. The authors determined the value of vPIA/MAP and direct measurement of percent access recirculation (AR) and QACC in detecting venous outlet stenoses and strictures. Abnormal access studies were evaluated by Doppler ultrasound and fistulography. Well functioning grafts and arteriovenous fistulas (AVFs) have no AR; QACC averages 1,101 +/- 26 and 1,073 +/- 35 mL/min, and vPIA/MAP ratios are 0.34 and 0.16, respectively. Venous outlet stenoses (n = 36) or strictures (n = 32) were detected before thrombosis or intervention in 172 vascular accesses at risk. QACC in accesses with stricture was significantly lower than in those with venous outlet stenosis (361 +/- 11 vs 526 +/- 43 ml/min), as was less than prescribed blood flow (423 +/- 7 ml/min). AR was not detected in any access with stricture and in only 4 of 36 accesses with outlet stenosis. vPIA/MAP was elevated with venous outlet stenosis but not with strictures. The findings of QACC being less than blood pump flow without AR by dilution methods differentiated strictures from venous outlet stenoses.

Arteriovenous Shunt, Surgical↗