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Biomedical subjects

A D Bersten

Publications and source records attributed to A D Bersten.

14 recordsLinked to original sources
PubMed1992

Prospective evaluation of residents and nurses as severity score data collectors.

OBJECTIVES: To determine the interobserver reliability of residents and nurses collecting Acute Physiology and Chronic Health Evaluation (APACHE II) data and the subsequent effect of these data collections on individual patient mortality prediction. DESIGN: In a prospective study, residents and nurses independently collected data to derive APACHE II scores. When their scores differed, a standard score was determined by one of the investigators. SETTING: A general medical and surgical ICU. PATIENTS: A total of 120 consecutive patients were included; of these patients, 79 had standard scores determined because resident and nurse scores differed. MAIN RESULTS: There was overall agreement between the residents and nurses with no significant difference between mean APACHE II scores or mean predicted mortality rates. Intraclass correlation coefficients confirmed good overall agreement between observer groups for predicted mortality rate: resident vs. nurse r2 = .94, resident vs. standard r2 = .94, and nurse vs. standard r2 = .90. However, clinically significant lack of agreement was demonstrated in 5% of the patients by the 95% confidence limits of agreement: resident vs. nurse -14 to +14%, resident vs. standard -10 to +14%, and nurse vs. standard -14 to +20%. CONCLUSIONS: While interobserver variability between resident and nurse data collection has minimal effect on derived predicted mortality rate with large patient groups, significant variability may occur in individual patients. Residents were more accurate data collectors than nurses.

Data Collection↗
PubMed1992

Interaction of sepsis and sepsis plus sympathomimetics on myocardial oxygen availability.

The ability to regulate myocardial blood flows (Q) in accord with changing myocardial O2 needs may be depressed in sepsis. This could be an important concern when sympathomimetics are used to augment systemic oxygen delivery (QO2) in this syndrome as increased myocardial O2 needs may accompany an infusion of this class of drugs. Therefore after measuring the effect of sepsis on myocardial O2 metabolism, we then infused various sympathomimetics to evaluate the sepsis+sympathomimetic interaction on myocardial QO2. We measured Q to the left (LV) and right (RV) ventricles by the radioactive microsphere technique in 36 unanesthetized mature sheep, before and during the infusion of dopamine, dobutamine, dopexamine, norepinephrine, salbutamol, or placebo. Randomly selected for infusion, these drugs were titrated to augment the thermodilution-derived cardiac index (CI) by greater than 20%. This study was repeated 24-48 h after cecal ligation and perforation had resulted in a hyperdynamic septic state [change (delta) in CI = sepsis - baseline = +54%; P less than 0.01]. During the septic study, both Q-LV (delta = +80%; P less than 0.01) and Q-RV (delta = +84%; P less than 0.01) were increased above baseline values; the augmented Q to both LV and RV was directly correlated with the arterial perfusion pressure (PA) x CI product and the mean pulmonary artery pressure (PPA) x CI product, respectively. Only 23% of study animals demonstrated net transmyocardial lactate production during the septic study. When the infusion of sympathomimetics was accompanied by an increase in the PPA x CI and PA x CI products, a further increase in both Q-RV and Q-LV, respectively, occurred. Also, neither the ventricular endocardial-to-epicardial flow ratios nor transmyocardial lactate extraction were modified by the sympathomimetics infusion. We conclude that the septic response to infection in this animal model was not accompanied by significant abnormalities in the metabolic regulation of myocardial QO2 (R. E. Cunnion, G. L. Scher, and M. M. Parker, Circulation 73: 637-644, 1986).

Animals↗
PubMed1992

Dopamine and renal salvage in the critically ill patient.

Dopamine is a catecholamine used widely in critically ill patients and those undergoing major surgery, often as a 'renal protective' agent. Direct renal vasodilatation with 'low-dose' dopamine is the widely accepted basis for its use--hence the term 'renal dose' dopamine. However, recent evidence has revealed that the renal effects of this agent are far more complex. Moreover, some of these effects may be undesirable in the 'at-risk' kidney. The increased renal blood flow (RBF) of dopamine may be largely attributable to its inotropic (myocardial) action, even with low doses (i.e. less than 5 micrograms/kg/min). Similar increases in RBF can also be demonstrated with other (non-dopaminergic) inotropes. The early evidence for direct renal vasodilatation in response to dopamine has been brought into question by more recent research. The diuresis and natriuresis commonly seen following dopamine administration is now known to be due to a direct renal tubular (or 'diuretic') action. Furthermore, increasing knowledge regarding the pathophysiology of acute (ischaemic) renal failure, including RBF and the concept of 'oxygen supply and demand' in relation to tubular function, suggests that dopamine may mask important signs of renal ischaemia. Whether or not dopamine is truly beneficial to renal function currently remains unanswered. As it stands however, there is sufficient evidence to question its routine use in the setting of renal dysfunction in the critically ill patient.

Acute Kidney Injury↗
PubMed1992

The effect of various sympathomimetics on the regional circulations in hyperdynamic sepsis.

Because sepsis is characterized by a depression in vascular reactivity, we hypothesized that changes in organ blood flows (Q) would differ between the nonseptic and septic state during the infusion of sympathomimetics. Therefore we examined the (sepsis x organ Q) interaction during the infusion of five sympathomimetics in 36 mature, awake sheep before and after cecal ligation and perforation produced hyperdynamic sepsis. A 3-hour infusion of dobutamine, norepinephrine, dopamine, dopexamine, or salbutamol was compared with that of placebo during both nonseptic and septic studies; drug infusion was titrated to an increase in cardiac index of greater than 20%. Increased plateau infusion doses of norepinephrine (+305%), salbutamol (+275%), dopamine (+70%), and dobutamine (+49%) were required to achieve predefined treatment guidelines during the septic versus nonseptic study. Few differences in the regional effects of individual sympathomimetics were found in the nonseptic study, although infusion of sympathomimetics was accompanied by a redistribution of systemic Q toward the heart and away from the brain, kidney, small intestine, liver, and pancreas. In the septic study, however, the sympathomimetic infusions were not accompanied by the redistribution of Q away from small intestine and liver that was demonstrated in the nonseptic study. Therefore (1) the depressed vascular reactivity in hyperdynamic sepsis altered the dose profile of exogenous sympathomimetics required to augment systemic Q, and (2) the (sepsis x sympathomimetic) interaction was characterized by a depression in the anticipated redistribution of organ Q from "nonvital" to "vital" circulations.

Animals↗
PubMed1991

Treatment of severe cardiogenic pulmonary edema with continuous positive airway pressure delivered by face mask.

BACKGROUND: Severe cardiogenic pulmonary edema is a frequent cause of respiratory failure, and many patients with this condition require endotracheal intubation and mechanical ventilation. We investigated whether continuous positive airway pressure delivered by means of a face mask had physiologic benefit and would reduce the need for intubation and mechanical ventilation. METHODS: We randomly assigned 39 consecutive patients with respiratory failure due to severe cardiogenic pulmonary edema to receive either oxygen alone or oxygen plus continuous positive airway pressure delivered through a face mask. It was not possible to blind the investigators to the assigned treatment. Physiologic measurements were made over the subsequent 24 hours, and the patients were followed to hospital discharge. RESULTS: After 30 minutes, both respiratory rate and arterial carbon dioxide tension had decreased more in the patients who received oxygen plus continuous positive airway pressure. The mean (+/- SD) respiratory rate at 30 minutes decreased from 32 +/- 6 to 33 +/- 9 breaths per minute in the patients receiving oxygen alone and from 35 +/- 8 to 27 +/- 6 breaths per minute in those receiving oxygen plus continuous positive airway pressure (P = 0.008); the arterial carbon dioxide tension decreased from 64 +/- 17 to 62 +/- 14 mm Hg in those receiving oxygen alone and from 58 +/- 8 to 46 +/- 4 mm Hg in those receiving oxygen plus continuous positive airway pressure (P less than 0.001). The patients receiving continuous positive airway pressure also had a greater increase in the arterial pH (oxygen alone, from 7.15 +/- 0.11 to 7.18 +/- 0.18; oxygen plus continuous positive airway pressure, from 7.18 +/- 0.08 to 7.28 +/- 0.06; P less than 0.001) and in the ratio of arterial oxygen tension to the fraction of inspired oxygen (oxygen alone, from 136 +/- 44 to 126 +/- 47; oxygen plus continuous positive airway pressure, from 138 +/- 32 to 206 +/- 126; P = 0.01). After 24 hours, however, there were no significant differences between the two treatment groups in any of these respiratory indexes. Seven (35 percent) of the patients who received oxygen alone but none who received oxygen plus continuous positive airway pressure required intubation and mechanical ventilation (P = 0.005). However, no significant difference was found in in-hospital mortality (oxygen alone, 4 of 20 patients; oxygen plus continuous positive airway pressure, 2 of 19; P = 0.36) or the length of the hospital stay. CONCLUSIONS: Continuous positive airway pressure delivered by face mask in patients with severe cardiogenic pulmonary edema can result in early physiologic improvement and reduce the need for intubation and mechanical ventilation. This short-term study could not establish whether continuous positive airway pressure has any long-term benefit or whether a larger study would have shown a difference in mortality between the treatment groups.

Aged↗
PubMed1991

Optimizing fresh gas flow and circuit design for the delivery of continuous positive airway pressure.

OBJECTIVE: To examine the effect of varying circuit design and the fresh gas flow rate on the circuit work imposed by a continuous positive airway pressure (CPAP) circuit. DESIGN: Circuit work was measured during simulated inspiration (500 mL) with a lung model at inspiratory flow rates (V) of 40, 60, and 80 L/min during the administration of 10 cm H2O CPAP through either a modified Mapleson-A or modified Mapleson-D circuit, both alone and when connected to a face mask (i.e., simulating an intubated and nonintubated patient). Fresh gas flow was varied from 10 to 250 L/min. RESULTS: The minimum circuit work occurred at a fresh gas flow rate approximating V; however, circuit work was consistently lower for the modified Mapleson-A circuit compared with the modified Mapleson-D circuit. As the fresh gas flow rate was increased sequentially to 250 L/min, circuit work remained close to the minimum value for the modified Mapleson-A, but increased gradually with the modified Mapleson-D, e.g., from 0.017 kg.m/L at a fresh gas flow rate and V of 80 L/min to 0.035 kg.m/L at a fresh gas flow rate of 250 L/min and a V of 80 L/min. Rotation of the fresh gas flow inlet did not change the circuit work vs. fresh gas flow rate relationship. Addition of a face mask resulted in a smaller increase in circuit work for the modified Mapleson-D with increasing fresh gas flow rate. However, unlike the modified Mapleson-A circuit alone, the addition of a mask caused circuit work to increase with increasing fresh gas flow rate. CONCLUSIONS: The modified Mapleson-A circuit at a fresh gas flow rate equal to V minimizes circuit work, and hence represents an optimal CPAP circuit. The increases in circuit work at fresh gas flow rates above V that were found with the modified Mapleson-D circuit are not due to inertial differences, and are likely due to turbulent gas flow.

Humans↗
PubMed1990

Hyperdynamic sepsis modifies a PEEP-mediated redistribution in organ blood flows.

Changes in organ blood flow (Q) produced by 20 cm H2O positive end-expiratory pressure (PEEP) were measured before and after the induction of hyperdynamic sepsis in nine unanesthetized sheep. During the baseline nonseptic study, PEEP was associated with a 9% fall in thermodilution-measured systemic Q, although arterial perfusing pressures were unaffected. Concurrently, microsphere-derived Q was maintained to the brain and heart, but fell to liver, spleen, pancreas, kidney, large intestine, and gastrocnemius. Twenty-four to 36 h after cecal ligation and perforation, a pre-PEEP septic study demonstrated an increase in all of the cardiac index (CI) (+43%) and systemic O2 delivery (+54%) when compared with the nonseptic study, whereas whole-body O2 extraction (-30%) was depressed. Although PEEP depressed systemic Q (-17%) during the septic study to a greater extent than during the nonseptic study (p less than 0.02), absolute organ Q fell only to pancreas, liver, and spleen. Relative to the simultaneous fall in the CI, Q to some splanchnic organs was not depressed by PEEP to the same magnitude in the septic as in the nonseptic study. When an infusion of Ringer's lactate (993 +/- 295 ml) subsequently restored systemic Q to pre-PEEP septic levels, individual flows that had been depressed by PEEP were not restored. Furthermore, Q-kidney continued to fall, such that the postfluid Q-kidney (-19%) was significantly less than was demonstrated in the pre-PEEP septic study. We postulate that differences noted in the distribution of organ Q between the nonseptic and hyperdynamic septic studies after the application of PEEP were secondary to the vasculopathy of sepsis and/or an alteration in the function of specific organ microcirculations. However, these data do not address whether the changes in organ Q distribution after a PEEP-mediated depression in systemic Q during sepsis significantly restricted tissue DO2. The inability to acutely reverse the PEEP-mediated changes in organ Q after restoring systemic Q by a fluid infusion also suggests the need to evaluate alternative methods of support to organ Q in acute respiratory failure secondary to sepsis when the addition of PEEP acutely depresses systemic DO2.

Animals↗
PubMed1990

Histologic and ultrastructural changes in nonpulmonary organs during early hyperdynamic sepsis.

Previous studies describing the histologic elements of multi-system organ failure caused by bacterial sepsis may have been complicated by a significant interaction on tissue injury from either a preterminal low-flow state or the effects of therapy immediately before death. Therefore we evaluated the nonpulmonary histologic findings of sepsis during a 3-day period that followed cecal ligation and perforation. In this septic model, mean arterial perfusion pressures remained unchanged from baseline, systemic flows rose by 54%, and laboratory evidence of organ dysfunction including an elevation of the serum bilirubin levels and a depression of the serum total protein values was considered mild. Concurrently, development of the hyperdynamic central circulatory septic state was associated with widespread histologic changes in myocardium, striated muscle, liver, gut, and pancreas. Lesions common to these organs included high-protein interstitial and intracellular edema, mitochondrial destruction, and patchy cell necrosis. Lesions within the pancreas were exaggerated over those noted in other organs. Of all organs examined, only the liver demonstrated microvascular neutrophil accumulation. Unlike models of shock caused by sepsis, fibrin thrombi were not seen in the microvasculature of any organ. We conclude that tissue injury characterized by the accumulation of protein-rich extravascular fluid and the development of reversible and irreversible cell injury antedated significant multiple-system organ failure in this animal model of normotensive sepsis.

Animals↗
PubMed1989

Additional work of breathing imposed by endotracheal tubes, breathing circuits, and intensive care ventilators.

A disadvantage of spontaneous breathing through an endotracheal tube (ETT) and connector attached to a breathing circuit and/or ventilator (breathing device) is an increase in the work of breathing. The work of breathing associated with ETT of 6 to 9-mm diameter and eight breathing devices was determined, using a lung simulator to mimic spontaneous inspiration at flow rates of 20 to 100 L/min and a tidal volume of 500 ml, at both zero end-expiratory pressure (ZEEP) and 10 cm H2O continuous positive airway pressure (CPAP). Work associated with the breathing devices alone (WCIR) ranged from -0.002 kg.m/L (Servo 900-C ventilator, 7-mm ETT, 20 L/min, ZEEP) to 0.1 kg.m/L (continuous flow circuit, 7-mm ETT, 100 L/min, CPAP), the latter representing 196% of the work of normal breathing. When the devices were attached to ETT, total apparatus work (WAPP) ranged from 0.009 kg.m/L (Mapleson-D circuit, 9-mm ETT, 20 L/min, ZEEP) to 0.25 kg.m/L (Drager EV-A, 6-mm ETT, 100 L/min, ZEEP), the latter representing 490% of the work of normal breathing. This additional work imposed by the ETT varied considerably among devices. Spontaneous breathing through modern ventilators, circuits and ETT imposes a burden of increased work, most of which is associated with the presence of the ETT and connector. Whether this burden represents an impediment to the weaning patient, or has training value for the ultimate resumption of unassisted spontaneous ventilation, remains to be determined.

Female↗
PubMed1988

Central venous catheter stiffness and its relation to vascular perforation.

Delayed central venous perforation is an uncommon but serious complication of central venous catheter insertion. An increase in catheter stiffness may have been responsible for our association of venous perforation with use of a guidewire insertion technique. A bench model was used to investigate the stiffness characteristics of thirty-four different types of catheters. The initial stiffness is poorly described by material or catheter gauge. A large range of values is seen between apparently similar catheters--the 16 gauge polyethylene catheter associated with two perforations at our institution had an initial stiffness value 7.5 Nm2 X 10(-5) at 37 degrees C in comparison with our previous standard--the 16 gauge Deseret Intracath with an initial stiffness of 2 Nm2 X 10(-5). Multilumen catheters had a similar range of stiffness to single lumen catheters, while paediatric catheters in general were less stiff. Dialysis catheters were up to five times as stiff as the stiffest central venous catheter. Stiffness decayed at a rate and to an extent which differed from catheter to catheter. Absorption of water by the catheter appears to be one factor involved in stress relaxation.

Aged↗
PubMed1986

New generation ventilators.

Desirable features of new generation intensive care ventilators include the ability to ventilate a wide range of patient sizes, an uncomplicated control panel, an appropriate but not excessive variety of ventilatory patterns, adequate patient monitoring and alarm functions, and simplicity of cleaning and routine maintenance. Examples of currently available ventilators include the Servo 900-C, CPU-1, Engstrom Erica, Bear 5, Drager EV-A and Hamilton Veolar. The incorporation of microcomputer control into some of these ventilators has resulted in improved flexibility and a limited number of automatic responses to detected patient changes. However, the function of components provided to allow spontaneous ventilation, such as demand valves, requires considerable improvement. Current trends in ventilator design include further refinement of computer control and the provision of graphic displays showing the results of continuous sophisticated analysis of respiratory function. The extent to which these developments will prove clinically useful will require careful evaluation.

Critical Care↗