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Biomedical subjects

A S Tonnesen

Publications and source records attributed to A S Tonnesen.

At least 19 recordsLinked to original sources
PubMed2001

Computerized decision support for mechanical ventilation of trauma induced ARDS: results of a randomized clinical trial.

BACKGROUND: Variability and logistic complexity of mechanical ventilatory support of acute respiratory distress syndrome, and need to standardize care among all clinicians and patients, led University of Utah/LDS Hospital physicians, nurses, and engineers to develop a comprehensive computerized protocol. This bedside decision support system was the basis of a multicenter clinical trial (1993-1998) that showed ability to export a computerized protocol to other sites and improved efficacy with computer- versus physician-directed ventilatory support. The Memorial Hermann Hospital Shock Trauma intensive care unit (ICU) (Houston, TX; a Level I trauma center and teaching affiliate of The University of Texas Houston Medical School) served as one of the 10 trial sites and recruited two thirds of the trauma patients. Results from the trauma patient subgroup at this site are reported to answer three questions: Can a computerized protocol be successfully exported to a trauma ICU? Was ventilator management different between study groups? Was patient outcome affected? METHODS: Sixty-seven trauma patients were randomized at the Memorial Hermann Shock Trauma ICU site. "Protocol" assigned patients had ventilatory support directed by the bedside respiratory therapist using the computerized protocol. "Nonprotocol" patients were managed by physician orders. RESULTS: Of the 67 trauma patients randomized, 33 were protocol (age 40 +/- 3; Injury Severity Score [ISS] 26 +/- 3; 73% blunt) and 34 were nonprotocol (age 38 +/- 2; ISS 25 +/- 2; 76% blunt). For the protocol group, the computerized protocol was used 96% of the time of ventilatory support and 95% of computer-generated instructions were followed by the bedside respiratory therapist. Outcome measures (i.e., survival, ICU length of stay, morbidity, and barotrauma) were not significantly different between groups. Fio2 > or = 0.6 and Pplateau > or = 35 cm H2O exposures were less for the protocol group. CONCLUSION: A computerized protocol for bedside decision support was successfully exported to a trauma center, and effectively standardized mechanical ventilatory support of trauma-induced acute respiratory distress syndrome without adverse effect on patient outcome.

Adult↗
PubMed1999

Electronic medical record implementation barriers encountered during implementation.

The authors were intimately involved in choosing and implementing a clinical information system for an integrated medical care delivery system. We will describe our experiences in implementing the first stages of an electronic medical record. We will consider the problems encountered, solutions that were found and continuing areas of sub-optimal performance.

Attitude to Computers↗
PubMed1997

Intratracheal pressure monitoring during synchronized intermittent mandatory ventilation and pressure controlled-inverse ratio ventilation.

OBJECTIVES: To directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator. DESIGN: Prospective, nonrandomized study. SETTING: Surgical intensive care unit at a trauma center. PATIENTS: Group 1: Eight intubated adult patients connected to mechanical ventilators in the SIMV mode were studied. All patients required mechanical ventilation following traumatic injuries. Group 2: Five intubated adult patients with adult respiratory distress syndrome connected to mechanical ventilators were studied. INTERVENTIONS: A small polyethylene catheter was threaded through each endotracheal tube such that it could be positioned to measure pressures proximal and distal to the tubes. MEASUREMENTS AND MAIN RESULTS: During SIMV, a significant pressure gradient exists across endotracheal tubes. In addition, although initiation of PC-IRV did lead to a lower peak airway pressure measured proximally, intratracheal peak airway pressure was unchanged. CONCLUSIONS: A pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.

Adult↗
PubMed1995

Transesophageal echocardiographic study of venous air embolism following pneumomediastinum in dogs.

BACKGROUND: Continuous venous air emboli have been detected in the inferior vena cava and smaller veins using transesophageal echocardiography in patients with positive pressure ventilation and associated pulmonary barotrauma. The authors hypothesized that gas entered the venous circulation, following dissection of small vessels at several sites in the subcutaneous or retro-peritoneal soft tissues. OBJECTIVE: The present study was designed to determine if a comparable venous gas embolism occurred in anesthetized dogs, after creation of a pneumomediastinum. DESIGN: Using transesophageal echocardiography, we observed 11 anesthetized dogs mechanically ventilated with positive end-expiratory pressure, while mediastinal air was introduced through a catheter at a rate of 0.5 ml/kg/min. RESULTS: A continuous stream of bubbles appeared in the inferior vena cava in 8/11 dogs (73%) after an infusion period of 280 +/- 81 min. A surge of bubbles was commonly observed following abdominal massage and was often associated with a transient decrease of end-tidal carbon dioxide tensions. In two dogs the air infusion rate was reduced to 0.25 mg/kg/min, and bubbles were detected in the inferior vena cava for as long as 16 consecutive hours. CONCLUSION: We conclude that in anesthetized dogs mechanically ventilated with positive end-expiratory pressure, unremitting pneumomediastinum is usually followed by continuous venous air embolism. A mechanism hypothesized for venous gas entry in the clinical condition of positive end-expiratory pressure ventilation with subcutaneous gas is suggested by this model.

Animals↗
PubMed1995

Hemodynamic management of brain-injured patients.

Head-injured patients require maintenance of systemic hemodynamics as well as attention to cerebral hemodynamics. Most head-injured patients have increased metabolic oxygen consumption, mild hypertension, and increased cardiac indices. Assessment of regional perfusion, difficult in many patients, includes monitoring of urinary output. In head-injured patients, especially those with multiple injuries, the two most important goals are preservation of cerebral perfusion pressure (mean arterial pressure minus intracranial pressure) and maintenance of systemic oxygen availability (cardiac index times arterial oxygen content).

Blood Gas Analysis↗
PubMed1994

Acute life-threatening intraoperative atelectasis.

A case is presented of acute intraoperative atelectasis causing profound hypoxaemia in a patient undergoing a combined epidural-general anaesthetic for hip surgery in the lateral position. The pathophysiology of the resultant ventilation-perfusion mismatch and the effects of applied positive end-expiratory pressure in the lateral position are explored. The emergency management is assessed, with emphasis on the role of bronchoscopy in diagnosis and treatment of this rare cause of life-threatening hypoxaemia in the operating room. This patient with risk factors for respiratory complications may have benefited from preoperative bronchoscopy to assist in lung expansion.

Acetabulum↗
PubMed1994

Tracheal compression caused by traumatic thoracic duct leak.

A man with traumatic thoracic duct injury developed a lymphocele causing upper airway obstruction. Despite drainage of the chylothorax, tracheal compression persisted due to a thoracic duct tear. Operative repair of the tear resulted in resolution of the airway obstruction.

Accidents, Traffic↗
PubMed1994

Immunoassays for serum and urine myoglobin: myoglobin clearance assessed as a risk factor for acute renal failure.

We compared four immunoassays for serum and urine myoglobin. Within-run CVs were 5-13%, with biases seen between assays. Myoglobin was stable for 1 month in serum and 12 days in urine when the pH was adjusted to between 8.0 and 9.5. Hemoglobin caused no interference. We assayed 91 pairs of serum and timed urine specimens from 41 patients admitted for acute trauma or rhabdomyolysis. Most were treated with mannitol and alkalinization. Upon initial presentations, 21 patients with either low serum myoglobin concentrations (< 400 micrograms/L) or high myoglobin clearances (> or = 4 mL/min) had normal creatinine clearances and no clinical evidence of renal disease. The remaining 20 had low myoglobin clearances. Seven were in rhabdomyolysis-induced acute renal failure, or subsequently developed this complication. We suggest that low myoglobin clearance may indicate a high risk for developing renal failure or may be an early marker for kidney dysfunction. Low myoglobin clearance may prove useful in indicating failure of prophylactic treatment to clear myoglobin.

Acute Kidney Injury↗
PubMed1993

Continuous venous air embolism in patients receiving positive end-expiratory pressure.

The occurrence of venous air embolism in critically ill patients can cause profound cardiopulmonary compromise. Recognized causes include aspiration through an indwelling catheter and pneumothorax. We report three patients in whom we found continuous air embolism in the inferior vena cava that persisted for days. The bubbles appeared to arise from splanchnic veins, and they were associated with barotrauma and positive airway pressure. In the two survivors, the bubbling ceased when the ARDS resolved and airway pressures were decreased. We suspect that venous air embolism is not an uncommon occurrence in critically ill patients receiving high positive airway pressure.

Adolescent↗
PubMed1993

Preliminary evaluation of an experimental clinical chemistry analyzer developed for space medicine.

An experimental clinical chemistry analyzer system was designed and built to demonstrate the feasibility of clinical chemistry as part of a medical-care system at NASA's planned space station Freedom. We report the performance of the experimental analyzer, called a medical development unit (MDU), for selected analytes in a laboratory setting in preparation for a preliminary clinical trial at patients' bedsides in an intensive-care unit. Within-run CVs ranged from 0.7% for sodium to 7.1% for phosphorus; day-to-day CVs ranged from 1.0% for chloride to 23.4% for calcium. Correlation of patients' blood sample analyses compared well with those by Ektachem E700 and other high-volume central laboratory analyzers (r ranged from 0.933 for creatine kinase MB isoenzyme to 0.997 for potassium), except for hemoglobin (r = 0.901) and calcium (r = 0.823). Although several CVs obtained in this study exceeded theoretical desired precision limits based on biological variations, performance was adequate for clinical laboratory diagnosis. We examined the effect of potentially interfering concentrations of hemoglobin, bilirubin, and lipids: the only effect was negative interference with calcium analyses by high concentrations of bilirubin. We also examined the effects of preanalytical variables and the performance of experimental sample-transfer cups designed to retain sample and reference liquid in microgravity. Continued development of the MDU system is recommended, especially automation of sample processing.

Aerospace Medicine↗
PubMed1991

Intensive, focused utilization management in a teaching hospital. An exploratory study.

A 3-month study was performed in a teaching hospital to determine the impact of intensive, focused utilization management on the average length of stay and average total charges in a carefully defined group of indigent patients. Prompt admission review was performed, the treatment plan ascertained, and a physician advisor notified. The attending physician was informed by a physician advisor of the patient's financial class, and assistance with expediting patient care and discharge planning was offered. Daily concurrent review monitored the treatment and discharge plans. The study compared 73 patients with a control group of 191 patients of similar financial class and diagnosis related groups (DRGs) for the immediately preceding 3 months. Compared with the control patients, the study patients experienced a 23% decrease in average length of stay and 16% decrease in average total charges. This study indicates that an intensive utilization management effort in a teaching hospital can be effective without compromising the quality of care.

Hospital Bed Capacity, 500 and over↗
PubMed1990

Hypophosphatemia--incidence, etiology, and prevention in the trauma patient.

Hypophosphatemia is associated with a number of undesirable physiologic consequences and has been reported to occur frequently in trauma patients. We studied patients in the immediate posttraumatic period to document a) the decrease in serum P, b) renal P excretion, and c) the response to prophylactic PO4 administration. In both group 1 (n = 12) and group 2 (n = 10) patients, we measured serum P, creatinine, ionized Ca, urinary P excretion, and creatinine clearance daily for the first 3 to 4 days postinjury. Patients in group 2 also received 0.5 mmol/kg.day of PO4 for the first 48 h after admission. Group 1 patients exhibited a significant (p less than .05) decrease in serum P over the first 24 h (1.00 +/- 0.30 to 0.75 +/- 0.23 mmol/L). In contrast, group 2 patients did not demonstrate a decrease in serum P. Urinary P excretion in group 1 accounts for the observed decrease in serum P. The results of our study show that the immediate posttraumatic period is associated with a decrease in serum P and massive urinary P excretion. We also showed that prophylactic administration of 0.5 mmol PO4/kg.day prevents serum P decrease.

Adult↗
PubMed1988

Effect of a rotating bed on the incidence of pulmonary complications in critically ill patients.

The risk of nosocomial pneumonia and atelectasis is high among critically ill immobilized patients. We hypothesized that continuous turning on the kinetic treatment table would reduce their incidence. Sixty-five critically ill patients, immobilized because of head injury or traction, were prospectively randomized for treatment in a conventional bed (n = 38) or the kinetic treatment table (n = 27). Patients were well matched for baseline demographic and pulmonary risk factors. Patients in the conventional bed group had a higher incidence of cigarette smoking. The combined incidence of significant atelectasis or pneumonia was higher (66%) in the conventional vs. kinetic treatment table (33%) groups (p less than .01). Atelectasis, pneumonia, adult respiratory distress syndrome, requirements for ventilator treatment, for PEEP, and for an FIO2 greater than 0.50 were not significantly different, but tended to be higher in the control group. Survival and the incidence of decubitus ulcers were similar.

Adult↗
PubMed1988

The abdomen as a source of occult sepsis.

When a patient presents with sepsis and no clear etiology, the abdomen can hide a focus of infection and must be considered in the course of the evaluation (Fig. 1). There are certain groups of patients who do not exhibit the usual signs and symptoms of intra-abdominal infection and therefore constitute the population at risk for occult abdominal sepsis. These patients, for one reason or another, have an unreliable history or physical exam. Once intra-abdominal infection is suspected, certain basic laboratory and radiographic evaluations should be undertaken. Treatment delays are not tolerated and the performance of diagnostic tests when a laparotomy appears inevitable is not indicated. CT of the abdomen should not be used as a screening exam and should be reserved for those cases potentially having an infected fluid collection. If a thorough evaluation of the abdomen reveals a possible source, a measured medical and surgical approach can be undertaken, depending on the etiology. If no source is found, the question of a diagnostic laparotomy arises in certain cases (Fig. 2). This procedure should be reserved for those patients having some type of underlying abdominal surgery or pathology. Without a previous history of abdominal surgery or pathology, and with no other clinical evidence of intra-abdominal infection, a nondirected laparotomy can be safely performed when organ failure is not present but usually will not reveal a treatable lesion. Multiple organ failure may indicate the presence of a hidden abdominal source of infection; however, the window for successful surgical intervention may have already passed. Multiple organ failure does not mandate laparotomy when there is no clinical or radiographic basis for suspecting an abdominal source of infection. This is especially true if an alternative source of sepsis has been defined.

Abdomen↗
PubMed1987

Sweating, hemodynamic responses, and thermal equilibration during hyperthermia in humans.

Hyperthermia, to 42 degrees C, for treatment of cancer, was induced 23 times in 13 anesthetized patients utilizing an extracorporeal heat-exchange circuit. Sweating rate over the chest, abdomen, arm and forearm ranged from 0.2 to 0.9 mg sweat X min-1 X cm-2. Cardiac index (CI), stroke volume index (SVI), left ventricular stroke work index, and right ventricular stroke work index initially increased to 221 +/- 12.5, 162 +/- 9.6, 142 +/- 11, and 203 +/- 29% but later fell to 169-173, 113-120, 69, and 148-117% of control, respectively. Heart rate initially rose to 145 +/- 5.9% and then stabilized at 160-162% of control. Pulmonary arterial occlusion pressure and central venous pressure initially fell to 82 +/- 8 and 93 +/- 9% but later rose to 87-102 and 105-120% of control levels, respectively. The hemodynamic response to severe heat stress in anesthetized humans was characterized by peripheral vasodilation accompanied by compensatory increases in heart rate and CI. Ventricular function, as reflected by SVI and CI, declined with continued heat stress, despite reduced afterload and stable or increased filling pressures. Pulmonary arterial temperature rose fastest, followed by the esophageal, rectal, and bladder temperatures, respectively. Jugular bulb temperature also rose rapidly.

Analysis of Variance↗
PubMed1985

Intracranial hypertension secondary to tension subcutaneous emphysema.

A patient with severe closed head injury and tension subcutaneous emphysema developed intracranial hypertension unresponsive to conventional treatment. Subcutaneous air drainage controlled the intracranial pressure. The subcutaneous pressure was directly correlated with intracranial pressure.

Adolescent↗