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Biomedical subjects

A J Layon

Publications and source records attributed to A J Layon.

At least 37 records · Page 2Linked to original sources
PubMed1995

Using tracheal pressure to trigger the ventilator and control airway pressure during continuous positive airway pressure decreases work of breathing.

STUDY OBJECTIVE: We evaluated the difference in work of breathing (WOB) during spontaneous ventilation with continuous positive airway pressure (CPAP) among three methods of triggering the ventilator: conventional pressure triggering, tracheal pressure triggering, and flow-by triggering. METHODS: In an in vitro model of the respiratory system consisting of a bellows (lungs) in a plastic canister (chest wall), spontaneous ventilation was simulated with a piston-driven pump (respiratory muscles). Data were recorded during CPAP of 5 cm H2O (model 7200ae ventilator, Puritan-Bennett, Overland Park, Kan) at peak sinusoidal inspiratory flow rate demands of 60 and 80 L/min and airway resistances of 5 and 20 cm H2O/L/s, with the demand flow system triggered by conventional pressure, tracheal pressure, or flow. Under each condition, tidal volume, pressure-time product (PTP), WOB, and changes in intrapleural pressure (Ppl) and airway pressure were recorded in real time by means of a computerized portable respiratory monitor (model CP-100, Bicore, Irvine, Calif). The Ppl was measured from within the canister, tidal volume by positioning a flow sensor between the Y-piece of the breathing circuit and the endotracheal tube (ETT), and airway pressure from a catheter attached to the flow sensor. The WOB was calculated by the monitor in real time. RESULTS: Changes in Ppl were greatest with conventional pressure triggering, less with flow-by triggering, and least with tracheal pressure triggering. The WOB was significantly lower (approximately 50%) with tracheal pressure triggering than with the other two methods. With tracheal pressure triggering only, an effect similar to that of pressure support ventilation (PSV) occurred, which accounted in part for the significant decrease in WOB. The PTP/breath ratio correlated strongly and was a good predictor of WOB (r2 = 0.95). CONCLUSIONS: Compared with conventional pressure and flow-by methods, triggering with tracheal pressure decreased WOB significantly. This method of triggering may improve patient-ventilator interaction.

Air Pressure↗
PubMed1994

Is radiation treatment volume a predictor for acute or late effect on pulmonary function? A prospective study of patients treated with breast-conserving surgery and postoperative irradiation.

BACKGROUND: When tangential radiation beams are used in patients with breast cancer after breast-conserving surgery, the amount of lung included in the radiation field varies because of patient anatomy and treatment technique. The question of how much lung tissue can be irradiated incidentally without acute or late complications requires quantitative study. METHODS: Thirty-four women were enrolled in a prospective study of pulmonary function after breast-conserving surgery and radiotherapy for early stage breast cancer. The percentage of lung volume irradiated was estimated from computed tomography scans. Pulmonary function tests including spirometrics, lung volume, and diffusing capacity of carbon monoxide (DLCO) were performed before, during, and at regular intervals after radiotherapy. Both acute and long term changes in pulmonary function were analyzed in 29 eligible patients. RESULTS: Acutely, DLCO values dropped, but they returned to normal levels by 24 months. At 5 years, pulmonary function did not vary significantly according to the percentage of lung irradiated, the use of regional lymphatic irradiation, or the addition of chemotherapy. Symptomatic pneumonitis occurred only in two women with baseline deficits in DLCO (P = 0.016), who had more than 10% of the total lung volume irradiated. Patients with a smoking history had a clinically significant baseline deficit of 32% in DLCO values (P = 0.0011) but showed a 21% improvement (P = 0.11), which probably correlated with quitting smoking. CONCLUSION: Within the range evaluated in this study, the volume of lung irradiated did not predict a late decrease in pulmonary function, although pneumonitis was observed only when more than 10% of the lung was irradiated.

Adult↗
PubMed1994

Partially and totally unloading respiratory muscles based on real-time measurements of work of breathing. A clinical approach.

OBJECTIVE: To evaluate the clinical feasibility of using real-time measurements of work of breathing obtained at the bedside with a portable, commercially available respiratory monitor as an objective and quantifiable guideline for appropriately setting pressure support ventilation (PSV) to partially and totally unload the respiratory muscles in patients with respiratory failure. DESIGN: In vivo measurements of work of breathing were performed on a consecutive series of patients after applying incremental levels of PSV. SETTING: University teaching hospital in a surgical ICU. PATIENTS: Thirty adults (18 men and 12 women, ages 20 to 77 years) who had acute respiratory failure were studied. All patients had an endotracheal or a tracheostomy tube in place and were breathing spontaneously, receiving continuous positive airway pressure and PSV. INTERVENTIONS: Intraesophageal pressure (indirect measurement of intrapleural pressure) was measured with an esophageal balloon catheter positioned in the mid- to lower-third of the esophagus. Tidal volume was obtained by positioning a flow sensor between the "Y" piece of the breathing circuit and the endotracheal or tracheostomy tube. Airway pressure was measured from a catheter attached to the flow sensor. Data from these measurements were directed to the respiratory monitor (CP-100, Bicore Monitoring Systems) which calculates work of breathing performed by the patient using the Campbell diagram. Work of breathing performed by the ventilator to inflate the respiratory system was calculated by the monitor by integrating the change in airway pressure and tidal volume. Initially, the level of PSV was set to 0 cm H2O and work measurements were obtained. Pressure support ventilation was then increased until the work performed by the patient decreased to a range of 0.3 to 0.6 J/L, which corresponds to a normal range for physiologic work of breathing (ie, partial respiratory muscle unloading), and then until the work decreased to 0 J/L (ie, total respiratory muscle unloading). RESULTS: Work performed by the patient varied inversely (r = -0.83; p < 0.001) and work performed by the ventilator varied directly with the level of PSV (r = 0.94; p < 0.001). Work performed by the patient was 1.5 +/- 0.3 J/L at zero pressure support ventilation and decreased significantly to 0.50 +/- 0.1 J/L (p < 0.05) as the level of PSV was increased to 18 +/- 7 cm H2O. The respiratory muscles were partially unloaded under these conditions. Patient work decreased to 0 J/L and ventilator work increased when the muscles were totally unloaded at a PSV level of 31 +/- 8 cm H2O. CONCLUSION: We propose an objective and goal-oriented clinical approach for using PSV by directly measuring the work of breathing performed by the patient with an easy to operate, bedside respiratory monitor and then applying pressure support ventilation to decrease the work to appropriate levels. Partially or totally shifting the workload from the respiratory muscles to the ventilator is appropriate under specific clinical conditions.

Acute Disease↗
PubMed1993

Decreasing imposed work of the breathing apparatus to zero using pressure-support ventilation.

OBJECTIVES: To apply pressure-support ventilation with the goal of decreasing the imposed work of the breathing apparatus (endotracheal tube, breathing circuit tubing, and the ventilator's demand-flow system) to zero and to evaluate a clinical method of measuring the imposed work of breathing. DESIGN: A prospective evaluation of adult and pediatric patients receiving mechanical ventilatory support. SETTING: A surgical and a pediatric intensive care unit in a university hospital. PATIENTS: Fifteen patients (11 adult and four pediatric), who were diagnosed with acute respiratory failure from various etiologies, and who were intubated and spontaneously breathing, received continuous positive airway pressure and pressure-support ventilation. MEASUREMENTS AND MAIN RESULTS: Imposed work of the breathing apparatus was calculated by integrating pressure measured at the tracheal end of the endotracheal tube from a narrow air-filled catheter and the change in volume from a miniature pneumotachograph (flow sensor) positioned between the "Y" piece of the breathing circuit and the endotracheal tube. Pressure and volume signals were directed to a computerized, portable respiratory monitor (Bicore Monitoring Systems) that provides real-time display of the pressure-volume (work) loops and calculation of the imposed work. Imposed work was measured at 0 cm H2O pressure-support ventilation, and then incremental levels of pressure-support ventilation were applied until the imposed work decreased to zero. Imposed work decreased in a quadratic fashion after incremental levels of pressure-support ventilation (r = -.83 [r2 = .69]; p < .001). At pressure-support ventilation level of 0 cm H2O, the imposed work was 0.60 +/- 0.17 joule/L. At mean pressure-support ventilation levels of 13.5 +/- 4.8 cm H2O, imposed work decreased to 0 joule/L. CONCLUSIONS: Ideally, the imposed work of the breathing apparatus should be zero to decrease the afterload on the ventilatory muscles and, thus, the patient's work of breathing. Eliminating the imposed work is achieved using appropriate levels of pressure-support ventilation. We describe an easily applied, practical method of measuring imposed work using a commercially available, portable, bedside respiratory monitor. We recommend that all patients diagnosed with respiratory failure and compromised pulmonary mechanics and who are intubated and breathing spontaneously, receive at least a minimal level of pressure-support ventilation that results in zero breathing apparatus-imposed work of breathing.

Acute Disease↗
PubMed1993

Postoperative complications in patients with human immunodeficiency virus disease. Clinical data and a literature review.

OBJECTIVE: To compare complications after and outcome from surgical procedures between patients with human immunodeficiency virus (HIV) disease and a matched control population. DESIGN: Retrospective case review. SETTING: 476-bed university tertiary care center. PATIENTS: Of 343 patients diagnosed as having HIV disease between 1981 and September 1991, 26 (7.6 percent) were Walter Reed classifications system 3B or greater and underwent a surgical procedure with general anesthesia or, in the case of 2 patients, regional anesthesia, at the study hospital. These patients were matched to 26 control patients by severity of illness according to APACHE II severity of illness score and by age, sex, race, and anesthetic regimen. MEASUREMENTS AND RESULTS: The postoperative occurrence of dysrhythmia, hypotension, hypoxia, hemorrhage, renal insufficiency, or infection was evaluated in the study and control groups. Deaths within 3 and 30 days of the procedure and duration of survival after discharge from the hospital were recorded. Frequency of complications and 3- and 30-day mortality did not differ between the 2 groups. Duration of survival after discharge from the hospital in patients with HIV disease (7.4 +/- 9.7 months) was approximately 25 percent that in control patients (30.6 +/- 35.9 months) (p = 0.02). CONCLUSIONS: HIV disease does not increase the risk of postprocedural complications, including death, up to 30 days postprocedure. Thereafter, patients with HIV disease classified by the Walter Reed System as > or = 3B may survive for a shorter time than do equally ill patients who do not have HIV disease. Thus, needed surgical intervention should not be limited based on HIV status and concern for subsequent complications.

Adult↗
PubMed1991

The effect of duodenojejunal alimentation on gastric pH and hormones in intensive care unit patients.

We evaluated effects of duodenojejunal (DJ) feeding on gastric pH and selected gastrointestinal hormones in 13 randomly selected patients in an intensive care unit (ICU). To obtain baseline values for gastric pH, a nasogastric (NG) tube was placed in each patient and gastric pH was measured every 30 minutes for 2 hours. To obtain control values, a Dobbhoff tube was placed fluoroscopically and 0.45 percent saline solution (NaCl), 75 ml, was infused for 1 hour and gastric pH was measured again; the previously placed NG tube was left in position. Then, by randomization, either 0.45 percent NaCl (pH = 5) was continued (n = 6) or a high-nitrogen, isotonic, enteral feeding solution (Osmolite HN, pH = 6.4) (n = 7) was infused, both at 75 ml/h. Gastric pH was noted hourly for 96 hours; antacid (Maalox TC, 15-ml aliquots) was given by NG tube when the pH was 4 or less. After 96 hours, the infusion was stopped and gastric pH was noted for 4 additional hours. Before and during initial saline solution infusion; after 24, 48, 72, and 96 hours of continuous infusion; and 4 hours after stopping the infusion, peripheral venous blood was obtained for measurement of plasma gastric inhibitory polypeptide (GIP) and serum gastrin. Data were analyzed by ANOVA (RMD), Fishers' exact test, and the unpaired t-test. Groups did not differ demographically. Throughout the infusion, gastric pH tended to be higher with the enteral feeding solution than with saline solution, but this was significant only at 24 hours. Less antacid was required with the enteral feeding solution at 24 and 48 hours than with saline solution. Plasma GIP levels were significantly higher with the enteral feeding solution than with saline solution during most of the infusion. Serum gastrin levels did not differ between the groups. In this cohort, infusion of the enteral feeding solution tended to maintain a gastric pH of more than 4 and was associated with increased plasma GIP levels, which may inhibit gastric acid secretion. Early enteral feeding may benefit certain ICU patients.

Antacids↗
PubMed1990

Five percent human albumin in lactated Ringer's solution for resuscitation from hemorrhagic shock: efficacy and cardiopulmonary consequences.

Using an ovine model of acute hemorrhagic shock, we evaluated the utility of 5% albumin in lactated Ringer's (5% ALR) solution as a resuscitation solution. After instrumentation and obtaining baseline values for BP, mean arterial pressure (MAP), pulmonary capillary wedge pressure (WP), CVP, cardiac output, extravascular lung water (EVLW), and blood gases (mixed venous and arterial), animals were rapidly exsanguinated to an MAP of 50 mm Hg. After 30 min at this pressure, measurements were repeated and 5% ALR was administered until two of three variables (WP, MAP, cardiac output) were restored to baseline values. The administration of 5% ALR was continued as needed to maintain baseline values of these variables. Sixty minutes later, data were again recorded. For induction of shock, 15.7 +/- 5.2 ml of blood/kg body weight was removed. Pulmonary artery pressure, WP, MAP, and cardiac output all significantly decreased with shock. After resuscitation, all values except MAP returned to baseline. The resuscitation volume of 5% ALR was 25.2 +/- 18.4 ml/kg. There were no changes in EVLW or intrapulmonary shunt. Oxygen delivery was significantly compromised during shock but returned to baseline after resuscitation. We conclude that in a model such as ours, 5% ALR can reverse the hemodynamic effects of acute hemorrhagic shock.

Acute Disease↗
PubMed1990

A new device that allows synchronous intermittent inspiratory chest tube occlusion with any mechanical ventilator.

Controlling a massively leaking bronchopleural fistula (BPF) can prove difficult. In combination with acute respiratory failure (ARF), BPF results in a mortality of 81 percent. Intermittent inspiratory chest tube occlusion (IICTO) is recognized as effective in controlling even the largest BPF; however, IICTO, as previously described, is difficult to use for a variety of reasons. We report two cases of BPF in association with ARF managed with a simple new device that allows the application of IICTO with virtually any mechanical ventilator. The effectiveness of the device and associated technique in controlling BPF leaks is clearly demonstrated and may have played a role in the eventual recovery of a patient with BPF. Further study of the technique is warranted.

Adult↗
PubMed1987

Effects of hetastarch resuscitation on extravascular lung water and cardiopulmonary parameters in a sheep model of hemorrhagic shock.

Eight sheep, weighing 29-71 kg, were used to evaluate the cardiopulmonary response to Hespan infusion following shock. Before shock was induced, mean arterial pressure (MAP), pulmonary capillary wedge pressure (PCWP), pulmonary artery pressure (PAP), cardiac output (CO), extravascular lung water (EVLW), colloid oncotic pressure (COP), and hemoglobin were measured and shunt, arteriovenous oxygen content difference (C[a - v]O2) and COP-PCWP gradient were calculated. The animals were bled to a MAP of 50 mmHg and that level was maintained for 30 min. At the end of that time, the data were collected again. The animals were resuscitated back to baseline values of PCWP, MAP, and CO with a 6% hydroxyethylstarch solution. With shock, PCWP, MAP, CO, and arterial pH decreased and C(a - v)O2 increased significantly (P less than 0.05). With resuscitation, PAP, PCWP and CO were significantly greater than baseline. Arterial pH was less than the baseline value but was within normal range. MAP did not return to preshock levels. EVLW and venous admixture did not change at any time. C(a - v)O2 returned to baseline with resuscitation. Volume of hetastarch infused was 29.1 +/- 10 cm3/kg. We conclude that hetastarch is an effective resuscitation solution in a model of hemorrhagic shock and appears to have no adverse cardiopulmonary effects.

Animals↗
PubMed1987

Influence of sterile protective sleeves on the sterility of pulmonary artery catheters.

Eighty-seven pulmonary artery catheters (PACs) with sterile protective sleeves were placed into 69 surgical ICU patients by one of the following two methods: through an introducer placed in a new, percutaneous site or by exchanging an indwelling catheter for an introducer. On removal, 5-cm catheter segments from the catheter tip and from within the introducer and sleeve, peripheral blood, and blood drawn from the PAC distal port were cultured quantitatively. Sleeve segment cultures were sterile if catheterization was less than 48 h and had been accomplished through a new percutaneous site. The risk of growing greater than 10(3) colonies on the tip and introducer segment increased to greater than 30% when PACs were left in over 96 h. The incidence of catheter-related bacteremia (CRB), defined as the simultaneous growth of identical organisms from the blood and the PAC tip, was 5.3% but may have been underestimated. CRB was associated with the use of corticosteroids (p = .009) and with cultures from any PAC segment growing more than 10(3) colonies (p less than .01). Although our data suggest that the use of the sterile protective sleeve is associated with a low risk of colonization, further study will be required to delineate the relationship between the use of protective sleeves and CRB.

Bacterial Infections↗
PubMedDate not supplied

Pneumonitis of unclear etiology in the surgical intensive care unit leading to the demise of an elderly, immunocompromised woman.

Multiple system organ failure, likely an expression of a dysregulated immune system, is a common cause of death in the surgical intensive care unit (ICU). While investigational modalities of therapy are on the horizon, current treatment primarily consists of supportive care. The case of an elderly woman who was admitted to the surgical ICU after a celiac axis-superior mesenteric artery bypass, is presented. Her course was complicated by Influenza-B pneumonitis, multiple system organ failure, and, ultimately, death. The course, pathophysiology, and therapeutic modalities involved in this syndrome are discussed. Additionally, the natural history of influenza infection is reviewed.

Aged↗