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Biomedical subjects

N L Pace

Publications and source records attributed to N L Pace.

At least 73 records · Page 4Linked to original sources
PubMed1987

Antagonism of postoperative opioid-induced respiratory depression: nalbuphine versus naloxone.

The authors compared naloxone and nalbuphine as antagonists of opioid-induced respiratory depression to determine the relative efficacies and safety of the two agents. In a double-blind, randomized fashion, 90 anesthetized patients received a mean dose of 25 micrograms/kg fentanyl during surgery. Inadequate spontaneous respirations at the end of anesthesia were treated with either naloxone 0.08 mg or nalbuphine 2.5 mg IV every 2 min while heart rate (HR), systolic and diastolic blood pressures (SBP, DBP), respiratory rate (RR), and tidal volume (TV) were measured at 2-min intervals. Arterial blood samples for analysis of PaCO2, PaO2, and pH were drawn when spontaneous ventilation resumed, and 30 and 60 min later. Narcotic antagonism and respiration were deemed adequate when TV was greater than or equal to 4 ml/kg and RR greater than or equal to 8 breaths/min. Heart rate, SBP, DBP, TV and RR were recorded, as were the occurrence of renarcotization (RR less than 8) and analgesic requirements every 5 min during the recovery room stay. Sixty of 90 patients required narcotic antagonism at the end of surgery. No patient required more than three doses (0.24 mg) of naloxone or four doses (10 mg) of nalbuphine. Both antagonists produced similar and moderate increases in SBP and HR while restoring adequate spontaneous ventilation. There were no significant differences in TV, RR, or arterial blood gases (ABGS) between the two groups after narcotic reversal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Evaluation of two adaptive sodium nitroprusside control algorithms.

Computer control of sodium nitroprusside infusion may be safer and provide better control of arterial blood pressure than is achieved with manual control. In a series of test maneuvers in 20 mongrel dogs, the performance of two adaptive control algorithms (controllers) was compared and their safety tested. The controllers were set to infuse sodium nitroprusside to decrease mean arterial pressure and maintain it 20 to 30 mm Hg below the control pressure. Then, sequentially, the right atrium was paced to simulate a supraventricular tachydysrhythmia, the right ventricle was intermittently paced to simulate ventricular extrasystoles, large tidal volumes were given to simulate a respiratory-therapy maneuver, the catheter was clamped to simulate clotting, an air bubble was introduced, and the infused sodium nitroprusside concentrations were either doubled or halved. Next, 500 ml of blood was drawn. Then, in sequence, positive end-expiratory pressure was applied, the right atrium was paced, and large tidal volume breaths were given to cause the blood pressure to fluctuate. When the controllers were turned on, mean arterial pressure reached the set point and remained within 5 mm Hg of the target pressure after 8.6 +/- 0.9 minutes (mean +/- SEM). The controllers properly handled the differences in sodium nitroprusside sensitivity and the catastrophic challenges presented in the experiments. When the animals were not being disturbed, stability was maintained and the blood pressure was kept well within 5 mm Hg of the desired pressure. The controllers rejected all invalid pressure signals during testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Learning statistical methods.

Since at least 1951 anesthesia journals have called for a more rigorous application of statistical methods in research reports. This appeal for statistical excellence actually applies to the researcher, to the clinician journal reader, and to the editor. Thirty five years ago the obligations of these three groups was made clear in an unsigned editorial in Anesthesiology; there is now a widespread consensus on these responsibilities. The researcher must create valid science. The clinician reader must bring sufficient intellectual skills to understand a journal article; using these skills the reader must critique the research report to judge its applicability to his patients. The editor must decline manuscripts showing poor or absent application of the scientific method, experimental design, and statistical analysis. Though the editors continue to exhort further improvements, even a casual perusal of their journals demonstrates a tremendous improvement in the handling of numeric data over the last four decades. With the increasing sophistication of statistical methods in journals, the reader must continue to expand his statistical understanding. In this short review, a few highlights of statistical methods useful either in planning and accomplishing a research project or in reading a research report will be discussed; these include the planning of a study design, data collection, data analysis, and interpretation of the research. Comments about using these concepts to better understand a research article will be included. Also included will be an annotated reading list for further study and reference. Mathematical formulas have been avoided as much as possible. Actual use of statistics requires use of equations which can be found in the books of the reading list.

Biometry↗
PubMed1986

Variability of the respiratory response to diazepam.

The authors investigated the respiratory effects of diazepam in 24 healthy volunteers using a modified Read rebreathing circuit. Resting end-tidal CO2 (PETCO2) and the slopes of the ventilatory (VE/PETCO2) and occlusion pressure (P0.1/PETCO2) response to CO2 were measured just prior to and 5, 20, 40, and 60 min after diazepam, 0.1 mg/kg iv. The slope of VE/PETCO2 for all 24 subjects analyzed as a single group was never significantly depressed. The slope of P0.1/PETCO2 for all 24 subjects analyzed as a single group was significantly depressed only at 5 min after diazepam. The resting PETCO2, however, had small but statistically significant increases throughout the 1 h of study. Group or cluster analysis of the slope of P0.1/PETCO2 clearly divided subjects into one group of five subjects, whose P0.1/PETCO2 slope was significantly and consistently augmented for 1 h and a second group of 19 subjects whose P0.1/PETCO2 slope was always less than control for the entire hour. Diazepam may, through effects on pulmonary mechanics and/or the central nervous system, sometimes enhance respiratory responses to CO2 rebreathing. Failure to select for such group effects when studying drug effects by CO2 rebreathing may obscure the severity and duration of respiratory depression that occurs in the majority of individuals. Resting PETCO2 indicated consistent depression of resting minute ventilation by diazepam and may be a more appropriate or sensitive measure of mild or subtle drug-induced respiratory effects.

Adult↗
PubMed1986

Computer-controlled optimization of positive end-expiratory pressure.

Positive end-expiratory pressure (PEEP) is a standard treatment for patients with refractory hypoxemia due to an acute restrictive pathology. The therapeutic range of PEEP can be quite narrow. PEEP therapy has been optimized using invasive variables such as oxygen transport and pulmonary shunt, and noninvasive variables such as compliance; however, the measurements are complex. We constructed a computerized PEEP-optimization system consisting of a Siemens 900C ventilator, Siemens prototype sulfur hexafluoride analyzer, Siemens 940 lung mechanics analyzer, and a DEC 11/23 microcomputer. The user may choose from three different noninvasive PEEP titration algorithms: maximizing static total respiratory system compliance (CTR), maximizing functional residual capacity(FRC)-based compliance (CFRC), and normalizing FRC. The device was tested in six dogs with pulmonary injury induced by oleic acid. The system was constrained to 3-cm H2O PEEP steps at 20-min intervals. The algorithm normalizing FRC reached optimal PEEP levels in 40 min, with a mean difference from the desired FRC of 15 +/- 48 (SEM) ml. This corresponds to a mean percent error of 1.0% +/- 2.63%. The CFRC and CTR algorithms reached optimal PEEP levels in 60 and 40 min, respectively, and maintained a maximal compliance for 85% of the time. This system provides fully automated noninvasive PEEP titration and is flexible enough to incorporate easily any other PEEP titration algorithms. It should improve patient care by guaranteeing that PEEP therapy is truly optimized throughout the patient's recovery.

Animals↗
PubMed1986

Failure of nalbuphine to antagonize morphine: a double-blind comparison with naloxone.

The authors studied the respiratory and analgesic effects of nalbuphine (0.21 mg/kg, intravenous), naloxone (0.014 mg/kg, intravenous), and placebo (normal saline) when given after morphine (0.21 mg/kg, intravenous) in a double-blind, randomized fashion. Resting end-tidal CO2 (PETCO2), ventilatory and occlusion pressure responses to CO2 rebreathing, and pain threshold were measured in 12 healthy adult volunteers before, 5 min, and 30 min after morphine. Nalbuphine, naloxone, or saline were administered 55 min after morphine, and the above measurements were repeated 5 min later (60 min after morphine) as well as 90, 120, 180, and 240 min after morphine. Whereas naloxone reversed respiratory depression as measured by all three respiratory parameters, nalbuphine either further depressed (resting PETCO2) or did not affect (ventilatory and occlusion pressure responses to CO2 rebreathing) respiratory drive. Morphine produced a significant elevation of the pain threshold. Significant decreases in the pain threshold were seen only after naloxone. Saline and nalbuphine did not significantly alter the pain threshold. The data indicate that nalbuphine may not reliably antagonize moderate doses of morphine.

Adult↗
PubMed1985

Transcutaneous PO2 poorly estimates arterial PO2 in adults during anesthesia.

We compared values of PaO2 and transcutaneous PO2 in 21 adult patients during anesthesia. In 282 simultaneous determinations during anesthetic periods of 3-10 h, transcutaneous PO2 was a poor predictor of absolute PaO2 and changes in PaO2. Transcutaneous PO2 monitoring in adults during anesthesia is of unproven value.

Adult↗
PubMed1985

Pulmonary arterial catheterization before anesthesia in patients undergoing cardiac surgery. Placement of the pulmonary arterial catheter before anesthesia for cardiac surgery: safe, intelligent, and appropriate use of invasive hemodynamic monitoring.

Should one catheterize the pulmonary artery (PA) for cardiac surgery before or after induction of anesthesia? Issues of central importance to this question include (1) the patient's preexisting hemodynamic abnormalities, (2) cardiovascular effects of anesthetic induction drugs, and (3) hemodynamic stress caused by laryngoscopy, endotracheal intubation, and PA catheter insertion. Some clinicians use the PA catheter immediately before anesthetic induction to detect and correct acute abnormalities in preload and ventricular function. This approach has been described as being partially responsible for decreased morbidity and mortality in patients with cardiovascular disease. Hemodynamic instability during induction has been reported with many of the common anesthetic induction agents, especially in patients with poor ventricular function. Since blood pressure is the product of cardiac output and systemic vascular resistance, accurate interpretation and treatment of hypotension are possible only when these variables are provided by vigorous use of the PA catheter. Early detection of myocardial ischemia is possible with examination of acute changes in the pulmonary capillary wedge pressure tracing. However, the lack of such information can restrict even the best anesthetist. Insertion of the PA catheter in the awake patient can be accomplished effectively and with minimal risk, so long as good patient rapport, adequate premedication, and continuation of antianginal medication until the time of surgery are assured. Preinduction placement of the PA catheter provides valuable, objective information for the cardiac anesthesiologist without incurring significant risk to the patient.

Anesthesia↗
PubMed1985

Anesthetic induction with fentanyl.

The efficacy of fentanyl, 30 micrograms/kg, was evaluated as an anesthetic induction agent in 72 ASA I-III patients scheduled for 2-4-hr operations. The effect of preinduction pretreatment with pancuronium and/or diazepam and the incidence of loss of consciousness (anesthesia), recall, rigidity, abnormal muscle movements, and hemodynamic changes were documented. Seventy-four percent of all patients became anesthetized. Diazepam pretreatment enhanced but did not ensure success of anesthetic induction. There was a significant correlation between age and the incidence of unconsciousness (P = 0.0287) and all patients over 60 yr old were anesthetized with 30 micrograms/kg of fentanyl. The incidence and severity of rigidity was reduced by pancuronium (P = 0.0002) but not by diazepam pretreatment. However, pancuronium plus diazepam produced a significant reduction in the incidence of rigidity when compared to pancuronium alone (P = 0.031). A significant positive correlation between age and the incidence of rigidity (P = 0.003) was found. Six patients had focal and one patient global tonic-clonic abnormal muscle movements. Diazepam but not pancuronium significantly decreased both heart rate (P = 0.05) and blood pressure (P = 0.04). Seventeen patients required reversal of narcotic effect to restore adequate spontaneous respiration after surgery. No patient required postoperative mechanical ventilatory assistance. The results of this study demonstrate that 30 micrograms/kg of fentanyl is not a reliable anesthetic induction dose in patients less than 60 yr old. Both age and premedication enhance the anesthetic capabilities of induction with fentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Computer-controlled regulation of sodium nitroprusside infusion.

We built and tested a combined proportional/derivative and minimum variance adaptive control algorithm for the regulation of blood pressure using sodium nitroprusside (SNP). In ten dogs the pressure was reduced by 30 mm Hg for 1 hr. The blood pressure came to within 5 mm Hg of the desired pressure in 1.7 +/- 4 min and after 3.4 +/- 0.3 min it remained within +/- 5 mm Hg of the desired value. During the nitroprusside infusion, bolus doses of epinephrine and SNP as well as phlebotomy were used to challenge the controller. The controller responded rapidly and effectively so that blood pressure remained stable throughout each challenge. Control was achieved in ten dogs with very different sensitivities to SNP. After 1 hr of SNP infusion, the rate of SNP infusion required to maintain a 30 mm Hg reduction in pressure averaged 112 ml/hr with a standard deviation of 108 ml/hr. Adaptive control met the challenge of large differences in sensitivity and maintained the desired blood pressure.

Animals↗
PubMed1985

Etomidate versus thiopental for induction of anesthesia.

Hemodynamic changes and side effects of anesthesia induction with etomidate or thiopental were evaluated in 83 ASA class I or II patients. Patients were randomly assigned to one of 12 groups according to pretreatment drug (fentanyl, 100 micrograms, or normal saline intravenously), induction agent (etomidate, 0.4 mg/kg, or thiopental, 4 mg/kg), and maintenance anesthetic technique (isoflurane-oxygen, isoflurane-nitrous oxide-oxygen, or fentanyl-nitrous oxide-oxygen). The purpose of this experiment, of factorial design, was to evaluate the combined effects of two or more experimental variables used simultaneously and to observe interaction effects. There were significant increases in heart rate in all groups, especially after tracheal intubation. These increases were attenuated but not eliminated by fentanyl pretreatment. Systolic arterial blood pressure increased significantly after intubation and was not affected either by fentanyl pretreatment or by the induction agent. Patients in whom anesthesia was induced with etomidate had a greater incidence of pain on injection and myoclonus and a lesser incidence of apnea than patients in whom anesthesia was induced with thiopental. Fentanyl pretreatment significantly decreased the incidence of pain on injection and myoclonus, but it increased the incidence of apnea when anesthesia was induced with etomidate. The incidence of postoperative nausea and vomiting was similar after thiopental and etomidate and was unaffected by fentanyl pretreatment. (ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Lateral positioning with differential lung ventilation and unilateral PEEP following unilateral acid aspiration in the dog.

Body position can significantly alter the efficiency of gas exchange following unilateral lung injury. We systematically examined three positions during differential lung ventilation with unilateral positive end-expiratory pressure (PEEP) following unilateral hydrochloric acid aspiration in the dog. Twelve mongrel dogs were intubated with a double-lumen endobronchial tube and mechanically ventilated with a microcomputer-controlled pair of ventilators. A tidal volume of 7.5 ml/kg was delivered to each lung. The PaCO2 was maintained at 4.67 kPa. A unilateral injury was induced with an injection of 0.1 N hydrochloric acid (2.5 ml/kg) into one lumen of the endobronchial tube. 0.984 kPa PEEP was applied to the injured lung and the dogs were placed sequentially in one of three positions (supine, lateral decubitus with injured lung non-dependent, and lateral decubitus with injured lung dependent) for 1 h apiece. There was no significant difference between the three positions with regard to PaO2 (F (2, 10) = 1.60, P = 0.25) of venous admixture (F (2, 10) = 0.49, P = 0.63). Our data indicated that position did not alter oxygenation. This was probably due to the use of differential ventilation with unilateral PEEP which eliminated redistribution of ventilation between the two lungs and minimized position-dependent changes in pulmonary blood flow.

Animals↗