Biomedical subjects

J E Thompson

Publications and source records attributed to J E Thompson.

At least 109 records · Page 6Linked to original sources

PubMed1995

Bacteriology of skin and soft-tissue infections: comparison of infections in intravenous drug users and individuals with no history of intravenous drug use.

The bacteriology of cutaneous or subcutaneous abscesses (86 specimens) among intravenous drug users (IVDUs) was compared with the bacteriology of abscesses (74 specimens) in patients with no history of intravenous drug use (non-IVDUs). The IVDU abscesses yielded 173 aerobes and 131 anaerobes. Staphylococcus aureus was the most common aerobe isolated (50% of specimens yielded this isolate), followed by "Streptococcus milleri" (46%). The commonly encountered anaerobes were Fusobacterium nucleatum (17%), pigmented Prevotella species (22%), Peptostreptococcus micros (17%), Actinomyces odontolyticus (15%), and Veillonella species (13%). The non-IVDU isolates included 116 aerobes and 106 anaerobes. S. aureus was isolated from 53% of these specimens, followed by coagulase-negative staphylococci (19%), "S. milleri" (19%), and Streptococcus pyogenes (16%). The main groups of anaerobes were Peptostreptococcus species (35%), Bacteroides species (19%), and gram-positive bacilli (31%). Overall, 67% of the IVDU isolates were of oral origin, compared with 25% of the non-IVDU isolates. Of the specimens from IVDUs and non-IVDUs, 48% and 67%, respectively, yielded only aerobes, and 2% and 4%, respectively, yielded only anaerobes. Sixty-four percent of the patients had one or more beta-lactamase-producing organisms.

Abscess↗

PubMed1995

Respiratory deadspace measurements in neonates with congenital diaphragmatic hernia.

OBJECTIVE: To apply the technique of respiratory deadspace measurement to consecutive infants with congenital diaphragmatic hernia, who were referred to our institution, in order to assess the efficiency of gas exchange. DESIGN: A cohort study evaluating the utility of deadspace measurements in neonates with congenital diaphragmatic hernia. SETTING: Tertiary care pediatric intensive care unit in a university hospital. PATIENTS: Thirty infants with congenital diaphragmatic hernia were studied on presentation to our institution, either before the institution of extracorporeal membrane oxygenation (ECMO) or after stabilization on ECMO. METHODS: The CO2 concentration of expired gas sampled at the exhaust port of the test ventilator was continuously measured and transformed to mixed expired CO2 by the following formula that corrects for compressible volume measured by the ventilatory pneumotachometer: mixed expired CO2 = (PCO2 in exhaust gas) x (ventilatory pneumotachometer minute volume)/(minute volume at the proximal airway). We then utilized the Bohr-Enghoff method to calculate the deadspace/tidal volume ratio: deadspace/tidal volume ratio = (PaCO2 - mixed expired PCO2)/PaCO2. MEASUREMENTS AND MAIN RESULTS: Deadspace/tidal volume ratio was calculated either before the institution of ECMO or during temporary separation from ECMO support as the patients demonstrated improvements in gas exchange and lung compliance. One hundred two measurements were made in 30 patients, with a mean of four measurements per patient (range 1 to 10). There was a significant (p = .005) difference between the first deadspace/tidal volume ratio measured, in survivors vs. nonsurvivors. The mean of the highest deadspace/tidal volume ratio in survivors was 0.47 compared with 0.62 in nonsurvivors (p = .003). A deadspace/tidal volume ratio of > or = 0.60 predicted mortality, with a positive predictive value of 80%, a negative predictive value of 79%, and an odds ratio of 15. The mean pre-ECMO deadspace/tidal volume ratio in those infants who ultimately required ECMO was significantly greater than the mean value for infants not requiring ECMO (0.65 vs. 0.43; p = .004). In patients who were treated with ECMO, survivors demonstrated a significant decrease in deadspace/tidal volume ratio during the course of ECMO. This decrease was not seen in the ECMO-treated patients who did not survive. CONCLUSIONS: Predictors of outcome in infants with congenital diaphragmatic hernia have been complicated and contradictory, particularly in the ECMO era. We demonstrated that the respiratory deadspace can be easily quantified in these infants, and that a physiologic deadspace of > 0.60 is associated with a 15-fold increase in mortality rate. We also demonstrated that in those infants treated with ECMO, the survivors manifested a significant decrease in their deadspace/tidal volume ratio before ECMO decannulation.

Carbon Dioxide↗

PubMed1995

Estrogen receptors in gallbladder cancer: detection by an improved immunohistochemical assay.

Although gallbladder carcinoma is the most common malignancy of the extrahepatic biliary tract, patients with this disease have a very poor prognosis. Previous investigations have documented the presence of estrogen receptors (ER) in gallbladder cancers for possible therapeutic benefit; however, the methods used for detection were largely imprecise, which led to a wide range of results. In light of these unclear results obtained with inferior techniques, we have attempted to determine more accurately the prevalence of ER positivity in gallbladder cancer using an improved, more specific immunohistochemical assay (IHA) for estrogen receptors. The IHA, which used a pronase pretreatment and the H222 monoclonal antibody, was performed on archival tumor specimens of 25 patients. There were no strongly or moderately positive specimens. Three specimens stained weakly positive, and 22 specimens (88%) were negative. The three specimens that were weakly positive showed neither statistical significance nor any identifiable trends with respect to patient sex, tumor stage, or histologic type. We conclude that, contrary to previous reports, weak estrogen receptor staining occurs in a very small percentage of gallbladder carcinomas. Furthermore, although the minimum concentration of ER required for potential therapeutic benefit is unclear, the addition of hormonal therapy in patients with gallbladder cancer is not likely to alter the outcome of this malignancy.

Aged↗

PubMed1994

Energetics of catalysis by ribonucleases: fate of the 2',3'-cyclic phosphodiester intermediate.

Ribonucleases catalyze the hydrolysis of the P-O5' bond in RNA. This reaction occurs in two steps: transphosphorylation of RNA to a 2',3'-cyclic phosphodiester intermediate and hydrolysis of this intermediate to a 3'-phosphomonoester. 31P NMR spectroscopy was used to monitor the accumulation of the 2',3'-cyclic phosphodiester intermediate during the transphosphorylation and hydrolysis reactions catalyzed by various ribonucleases and by small molecules. The intermediate was found to accumulate during catalysis by monomeric bovine pancreatic ribonuclease A (RNase A), a dimer and a trimer of RNase A, bovine seminal ribonuclease, RNase T1, barnase, and RNase 1. These enzymes, which are of widely disparate phylogenetic origin, released rather than hydrolyzed most of the intermediate formed transphosphorylation of RNA. In contrast, the intermediate did not accumulate during catalysis by hydroxide ion or imidazole buffer. In the presence of these small molecules, hydrolysis is faster than transphosphorylation. A trapping experiment was used to assess the throughput of the reaction catalyzed by RNase A. [5,6-3H]Uridylyl-(3'-->5')adenosine was incubated with RNase A in the presence of excess unlabeled uridine 2',3'-cyclic phosphodiester, which dilutes the specific radioactivity of any released cyclic intermediate. Only 0.1% of the RNA substrate was found to be both transphosphorylated and hydrolyzed without dissociating from the enzyme. These results suggest that ribonucleases have evolved primarily to catalyze RNA transphosphorylation and not RNA hydrolysis.

Animals↗

PubMed1994

Inhaled nitric oxide in the treatment of postoperative graft dysfunction after lung transplantation.

Pulmonary hypertension and transient graft dysfunction may complicate the postoperative course of patients undergoing lung transplantation. We report the acute effect of inhaled nitric oxide (80 ppm) on hemodynamics and gas exchange in 6 patients (median age, 14 years; range, 5 to 21 years) after lung transplantation as well as the effect of extended treatment over 40 to 69 hours in 2 patients. In 5 patients with pulmonary hypertension nitric oxide lowered mean pulmonary artery pressure (from 38.4 +/- 1.6 to 29.4 +/- 3.1 mm Hg; p < 0.05), pulmonary vascular resistance index (from 9.3 +/- 1.4 to 6.4 +/- 1.3 Um2; p < 0.05), and intrapulmonary shunt fraction (from 28.6% +/- 8.3% to 21.0% +/- 5.7%; p < 0.05). There was a 28.4% +/- 7.2% reduction in transpulmonary pressure gradient with only minor accompanying effects on the systemic circulation. Mean arterial pressure decreased only 2.7% +/- 5% (from 76.4 +/- 2.2 to 74 +/- 2.3 mm Hg; p = not significant), and systemic vascular resistance index by 4.2% +/- 9.7% (from 21.7 +/- 3.1 to 20.6 +/- 3.6 Um2; p = not significant). Cardiac index was unchanged (from 3.5 +/- 0.8 to 3.6 +/- 0.7 L.min-1.m-2; p = not significant). Nitric oxide caused a sustained improvement in oxygenation and pulmonary artery pressure during extended therapy at doses of 10 ppm. There were no major side effects. However, transient methemoglobinemia (9%) developed in 1 patient after 10 hours of nitric oxide treatment. Nitric oxide may be useful in the treatment of pulmonary hypertension and the impaired gas exchange that occurs after lung transplantation.

Acetylcholine↗

PubMed1994

Biliary disease during pregnancy.

BACKGROUND: Biliary disease during pregnancy is rare and the need for surgery in these cases is controversial. We evaluated our experience with biliary disease during pregnancy with regard to outcome and cost containment. PATIENTS AND METHODS: We reviewed the clinical course of pregnant women with biliary disease at the University of California at Los Angeles and Olive View-UCLA Medical Centers from 1988 to 1993. RESULTS: Seventy-two of 46,075 pregnant women presented with biliary disease (incidence 0.16%). Sixteen underwent surgery while pregnant, 5 in the first and 11 in the second trimester. No maternal or fetal deaths occurred secondary to medical or surgical management of biliary disease. Patients who were treated medically at initial presentation had a 69% rate of relapse prior to delivery, compared to no relapses in those treated surgically (P < 0.01). Patients who experienced relapse spent an average of 3.0 additional days in hospital. CONCLUSION: Surgical therapy for biliary disease performed in the second trimester of pregnancy does not increase morbidity and may help reduce relapses and additional days in hospital.

Acute Disease↗

PubMed1994

Delivery and monitoring of inhaled nitric oxide in patients with pulmonary hypertension.

OBJECTIVE: The development of a safe, portable, accurate, and adaptable system to deliver nitric oxide to patients with pulmonary hypertension. DESIGN: A prospective, clinical study. SETTING: Tertiary care pediatric intensive care unit and cardiac catheterization laboratory. PATIENTS: One hundred twenty-three patients (median age 11 months, range 1 day to 72 yrs) with pulmonary hypertension who were administered nitric oxide between November 1991 and July 1993. Ninety-one patients were mechanically ventilated (volume-controlled ventilator, n = 53; pressure-controlled ventilator, n = 5; and a pressure-limited, time-cycled infant ventilator, n = 25). The system was adapted to allow high-frequency oscillator (n = 2) or hand ventilation, and for intraoperative use with an anesthesia machine (n = 6). Thirty-two patients were breathing spontaneously through a mask without assistance. INTERVENTIONS: Nitric oxide was delivered at 10 to 80 parts per million (ppm); the dose was adjusted independently of the FIO2 without altering minute ventilation or tidal volume. MEASUREMENTS AND MAIN RESULTS: Nitrogen dioxide was continuously monitored and exceeded 3 ppm in only four patients. Methemoglobin concentrations were < 5% in all but four patients. Nitric oxide doses remained stable, independent of minute ventilation and could be changed easily and quickly. CONCLUSIONS: Inhaled nitric oxide can be administered precisely and reliably through a variety of delivery systems which can be used in patients of any size. Potential toxicity requires careful monitoring and continued improvement on apparatus design.

Adolescent↗

PubMed1994

A multicentre comparison of the efficacy of terbutaline Turbuhaler and salbutamol pressurized metered dose inhaler in hot, humid regions.

Twenty seven adults and 20 children with previously diagnosed stable asthma, using a salbutamol pressurized metered dose inhaler (P-MDI) and living in Cairns, Townsville and Southport, Queensland, Australia participated in a randomized, open-label cross-over comparison of terbutaline administered via Turbuhaler and salbutamol administered via P-MDI. The aim of the study was to compare the clinical effectiveness and patient acceptance of the two treatments in hot, humid regions. Terbutaline was administered via Turbuhaler and salbutamol via P-MDI on at least two occasions per day during each four week treatment period. Spirometry was performed at the start of the study, after the two week run-in and at the end of each treatment period. Patients used diary cards to record morning and evening peak expiratory flows, daily symptom scores and daily intake of beta 2 agonist medication. At the end of the study, patients answered a treatment preference question. Forty six patients completed the study. No statistically significant differences were observed between the two treatments in peak expiratory flow, change in morning peak expiratory flow pre- and post-beta-agonist, daily symptom scores, diurnal variability and spirometry. Forty four percent of patients preferred the terbutaline Turbuhaler and 39% preferred salbutamol P-MDI. Both agents were similarly tolerated. Terbutaline delivered by Turbuhaler is as clinically effective as salbutamol delivered by P-MDI in patients with asthma living in hot, humid regions.

Aerosols↗

PubMed1994

Pancreatitis associated with adult choledochal cysts.

We reviewed the records of 32 adult patients with choledochal cysts (CDC) to determine the characteristics of the associated pancreatic disease. Eighteen patients (56%) had 30 documented episodes of pancreatitis with epigastric pain and elevated serum amylase levels. Three patients developed a prolonged course with a pancreatic phlegmon and one patient died secondary to a pancreatic abscess after endoscopic retrograde cholangiopancreatography (ERCP). Pancreatitis occurred in all types of CDC and was not related to the age, gender or race of the patient. There was an association with the size of the CDC: 90% of patients with CDC > or = 5 cm developed pancreatitis compared with only 9% of patients with CDC < 5 cm (p < 0.0004). In addition, ERCP was performed in 14 patients and demonstrated an abnormal pancreaticobiliary duct junction in eight (57%). All eight patients with an abnormal pancreaticobiliary junction developed pancreatitis compared with only 2 out of 6 patients with normal pancreatic duct anatomy (p < 0.006). Patients undergoing surgical bypass rather than resection also tended to have higher rates of pancreatitis (80 vs. 50%). One patient with a Type I CDC and chronic pancreatitis was treated with surgical resection of the CDC and pancreatic head; this combined procedure relieved the pain. Microscopic examination of the CDC and the abnormal "common channel" within the pancreas revealed identical fibrous thickening of the duct walls with focal chronic inflammation and loss of surface epithelium. In conclusion, these data stress the previously unrecognized high incidence of symptomatic pancreatic inflammatory disease that accompanies adult CDC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

Management of pancreatitis complicating pregnancy.

Pregnancy complicated by pancreatitis may lead to significant fetal and maternal morbidity and mortality. We reviewed the clinical course of 30 women who developed pancreatitis in our institution during pregnancy from 1988 to 1992. Pancreatitis complicated 0.07 per cent of pregnancies (n = 46,075) during this time period. The etiology was gallstones in 22 patients, alcohol in 2 patients, and idiopathic in 6 patients. Average age, multiparity, and symptoms at presentation were similar between patients with gallstone (GSP) or non-gallstone pancreatitis (NGSP). All patients were initially treated medically. GSP patients had significantly lower Ranson criteria than NGSP (0.7 vs. 1.9, P < 0.01), but response to initial therapy, need for emergency surgery, fetal outcome, and fetal and maternal mortality (0 per cent) were the same. Twenty-six of 30 patients were successfully treated with conservative management. A significantly higher relapse rate was seen in GSP than NGSP patients before delivery (72% vs. 0%, P < 0.05). These relapses required hospitalization 90 per cent of the time and resulted in 3.9 additional days per patient. Six patients underwent surgery during pregnancy (two in the first trimester and four in the second trimester) without fetal or maternal mortality and with normal birthweights and Apgar scores. No relapses or additional days in hospital were noted in GSP patients following surgery. We recommend that GSP patients presenting in the first or second trimester should, if possible, undergo cholecystectomy in the second trimester when the risk of anesthesia and premature labor are the lowest. Patients presenting in the third trimester should undergo surgery immediately post-partum.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1994

Analysis of risk factors of postappendectomy intra-abdominal abscess.

BACKGROUND: Postappendectomy intra-abdominal abscesses (PAIAA) complicate the recovery of a small but significant fraction of patients with advanced appendicitis. STUDY DESIGN: A retrospective review of 1,184 patients with appendicitis was undertaken to define the clinical characteristics and risk factors associated with PAIAA. RESULTS: Thirty-three patients with 36 PAIAAs were found, an incidence of 2.8 percent. The mean age of patients with PAIAA was less than the overall group (16.9 versus 23.1 years, p = 0.002), and the mean core temperature of the PAIAA group was significantly higher (38.5 versus 38.2 degrees C). The incidence of PAIAA increased as the degree of appendiceal pathology worsened. The incidence of PAIAA was six (3.2 percent) of 190 in patients with gangrenous appendicitis and was 27 (8.7 percent) of 309 among patients with perforated appendicitis. Logistic regression analysis showed that independent predictors for the occurrence of PAIAA were young age and perforation. Although children presented with a higher rate of perforated appendicitis, this did not account for the younger age of the patients with PAIAA. Children (less than ten years of age) with perforation had PAIAA in ten (14 percent) of 69 cases compared with the incidence in the older patients with perforation of 17 (7.1 percent) of 240. CONCLUSIONS: These findings improve the surgeon's ability to identify patients at risk for PAIAA. Alterations in the perioperative management of perforated appendicitis, particularly in the pediatric patient, may reduce the occurrence of PAIAA.

Abdominal Abscess↗

PubMed1994

Cecectomy for complicated appendicitis.

BACKGROUND: Cecal leak or disruption after appendectomy for complicated appendicitis is a consequence of severity of disease and is related to residual abscess cavity, inflammation, phlegmon, and nonviable intestine. In an attempt to improve results, we have begun to resect the cecum and other localized infected tissue in instances of complicated appendicitis in which the viability of the appendiceal base and adjacent cecum is questionable. STUDY DESIGN: This is a prospective series of all patients who have undergone resectional therapy for complicated appendicitis in the last four years. Patients with other inflammatory conditions of the right colon have been specifically excluded. RESULTS: Seventeen patients have undergone resectional therapy for complicated appendicitis. Thirteen (76.5 percent) were men; the mean age was 42.4 years. The mean temperature and leukocyte count were 37.8 degrees C and 16.1 x 10(9) per L, respectively. These patients presented with a mean of 6.8 days of abdominal pain. Nine had a palpable abdominal mass, and all had tenderness in the right lower quadrant. In ten patients an abscess was encountered at operation. While the extent of the resection varied, it generally included the cecum, part of the right colon, and 5 to 7 cm of terminal ileum. Fourteen patients had a primary anastomosis, while the other three had the creation of an ileostomy. Complications were encountered in only two patients: one wound infection and one pulmonary embolus. There were no instances of postoperative intra-abdominal abscess, intestinal obstruction, or fecal fistula. All patients had a benign postoperative course and were discharged on the average of 9.9 days postoperatively. The ileostomies in three patients have been closed and no complications have occurred on follow-up examination. CONCLUSIONS: We conclude that aggressive resectional therapy of the cecum during appendectomy in selected patients with complicated appendicitis is effective therapy and can be performed safely.

Abscess↗

PubMed1993

Enrichment of proteinase activity in deteriosomes, a new class of microvesicles.

Non-sedimentable microvesicles, termed deteriosomes, have been isolated from the cytosol of bean cotyledons by ultrafiltration, and found to be enzymatically active. Specifically, they possess proteinase activity that is able to catabolize exogenous proteins as well as deteriosome proteins. The proteolytic activity is inhibited by heat-denaturation and known proteinase inhibitors (iodoacetate and phenylmethylsulfonyl fluoride), and the pattern of deteriosome-associated proteinase activity changes with advancing senescence of the cotyledon tissue. Deteriosomes are formed by blebbing from membranes. The finding that they possess proteinase activity is consistent with an earlier proposal [(1991) Proc. Natl. Acad. Sci. USA 88, 2269-2273] that they are involved in membrane turnover and serve as a vehicle for moving bilayer-destabilizing phospholipid and protein catabolites out of membranes into the cytosol for further processing. The data also indicate that a significant proportion of the proteinase activity traditionally considered to be cytosolic is associated with deteriosomes.

Cell Membrane↗

PubMed1993

Isolation and characterization of deteriosomes from rat liver.

Deteriosomes, a new class of microvesicles, have been isolated from rat liver tissue. These microvesicles are similar to those isolated previously from plant tissue [Yao et al., Proc Natl Acad Sci USA 88:2269-2273, 1991] in that they are nonsedimentable and enriched in membrane catabolites, particularly products of phospholipid degradation. Liver deteriosomes range in size from 0.05 microns to 0.11 microns in radius. They are also much more permeable than microsomal membrane vesicles indicating that the deteriosome bilayer is perturbed. The data are consistent with the proposal that deteriosomes are formed from membranes by microvesiculation and that they represent an intermediate stage of membrane deterioration. Furthermore, liver deteriosomes were found to contain phospholipase A2 activity. This suggests that they not only serve as a means of moving destabilizing macromolecular catabolites out of membranes into the cytosol but also possess enzymatic activity. The fact that the specific activity of phospholipase A2 is higher in deteriosomes than in deteriosome-free cytosol suggests that some of the enzymatic activity traditionally assumed to be cytosolic may in fact be associated with deteriosomes.

Animals↗

PubMed1993

High-frequency oscillatory ventilation in pediatric respiratory failure.

OBJECTIVE: To evaluate the safety and effectiveness of high-frequency oscillatory ventilation using a protocol designed to achieve and maintain optimal lung volume in pediatric patients with respiratory failure. SETTING: Tertiary care pediatric ICU in a university hospital. DESIGN: A prospective, clinical study. PATIENTS: Seven patients aged 1 month to 15 yrs with diffuse alveolar disease and airleak with a variety of primary diagnoses, including pneumonia, adult respiratory distress syndrome, and pulmonary hemorrhage. INTERVENTIONS: After varying periods of conventional mechanical ventilation (16 to 216 hrs), patients were managed with high-frequency oscillatory ventilation using a "high-volume" strategy that consisted of incremental increases in mean airway pressure and lung volume to achieve an arterial oxygen saturation of > or = 90%, with an FIO2 of < or = 0.6. MEASUREMENTS AND MAIN RESULTS: Ventilatory settings, including FIO2 and mean airway pressure, hemodynamic parameters (cardiac index, systemic and pulmonary vascular resistance indices, oxygen delivery [DO2] and oxygen extraction ratio) and the oxygenation index (oxygenation index = [FIO2 x mean airway pressure x 100]/PaO2) were monitored during the transition to high-frequency oscillation and throughout the course of the high-frequency oscillatory ventilation with rapid and sustained reductions in mean airway pressure (p = .0001, repeated-measures analysis of variance [ANOVA]) and a trend toward decreasing oxygenation index (p = .08, repeated-measures ANOVA). In the four patients from whom hemodynamic data were obtained, there were no compromises of cardiac index or DO2 despite a significant increase in mean airway pressure (26 +/- 2 to 35 +/- 2 cm H2O) during conversion from conventional ventilation to high-frequency oscillation. CONCLUSIONS: High-frequency oscillatory ventilation, using a high-volume strategy, may be used safely and effectively in pediatric patients with respiratory failure and with high predicted mortality rates. High mean airway pressure during oscillatory ventilation does not appear to compromise DO2. Whether this technique can alter morbidity or mortality rates in this population awaits prospective randomized study.

Adolescent↗

PubMed1993

Respiratory deadspace measurements in neonates during extracorporeal membrane oxygenation.

OBJECTIVES: To evaluate the bias and precision of a simple, bedside method of quantification of minute CO2 production (study 1) and then apply the technique to measure physiologic deadspace in a group of neonates undergoing extracorporeal membrane oxygenation (ECMO) (study 2). DESIGN: A prospective, clinical study comparing a simple method of quantifying minute CO2 production with a criterion standard (study 1); a cohort study evaluating the utility of deadspace measurements in neonates undergoing extracorporeal membrane oxygenation (study 2). SETTING: Tertiary care pediatric intensive care unit (ICU) in a university hospital. PATIENTS: Study 1: Thirteen neonates (weighing from 2.5 to 6.2 kg) were studied during mechanical ventilation being administered for a variety of respiratory diseases. Study 2: Fifteen neonates with respiratory failure were examined during the course of ECMO. INTERVENTIONS (METHODS): Study 1: The CO2 concentration of expired gas sampled at the exhaust port of the test ventilator was continuously measured and transformed to minute CO2 production by the following formula: (calculated minute CO2 production) = (tension of CO2 in exhaust gas) x 0.0013 x (ventilator pneumotachometer minute volume), where 0.0013 is the conversion factor to express gas tension as fractional volume at standard conditions. Minute CO2 production was measured independently with a previously validated bedside calorimeter and the calculated and measured values were compared. Study 2: The CO2 concentration of expired gas sampled at the exhaust port of the test ventilator was continuously measured and transformed to mixed expired CO2 by the following formula, which corrects for compressible volume measured by the ventilator pneumotachometer: mixed expired CO2 = (tension of CO2 in exhaust gas) x (ventilator pneumotachometer minute volume)/(minute volume at proximal airway). We then utilized the Bohr-Enghoff method to calculate the deadspace/tidal volume ratio: deadspace/tidal volume ratio = (PaCO2--mixed expired CO2 tension)/PaCO2. MEASUREMENTS AND MAIN RESULTS: Study 1: Calculated minute CO2 production ranged between 11.8 and 38.9 mL/min. When compared with measured minute CO2 production, the bias and precision were -0.8 and 1.7 mL/min, respectively. The mean percent difference for calculated minute CO2 production was 3.7%. Study 2: Deadspace/tidal volume ratio was calculated during temporary separation from ECMO support as the patients demonstrated improvements in gas exchange and lung compliance. Fifty-two measurements were made in 15 patients, and 13 of 15 patients demonstrated a decrease in deadspace/tidal volume ratio during the course of ECMO. The mean decrease was 21% and the decrease was statistically significant. CONCLUSIONS: Minute CO2 production can be measured simply and accurately, using equipment readily available in most ICU settings. The same method can be utilized to calculate the deadspace/tidal volume ratio, which provides valuable information regarding the gas exchanging efficiency of the neonatal lung during ECMO.

Bias↗

PubMed1993

Use of inhaled nitric oxide and acetylcholine in the evaluation of pulmonary hypertension and endothelial function after cardiopulmonary bypass.

BACKGROUND: Increased pulmonary vascular resistance is common in congenital heart disease and is exacerbated by cardiopulmonary bypass (CPB). We investigated whether CPB is responsible for pulmonary endothelial dysfunction and contributes to postoperative pulmonary hypertension. METHODS AND RESULTS: We infused the endothelium-dependent vasodilator acetylcholine (ACH) into the pulmonary circulation of pulmonary hypertensive children with congenital heart disease either before (n = 12) or after (n = 22) surgical repair on CPB. The dose response to ACH (10(-9) to 10(-6) M) was recorded for all hemodynamic variables. Nine additional postoperative patients were studied with ACH followed by inhalation of 80 ppm nitric oxide, an endothelium-independent smooth muscle relaxant. Plasma levels of cyclic GMP (cGMP) were measured before and after ACH and nitric oxide administration. Pulmonary vasodilation with 10(-6) M ACH was seen in all preoperative patients but was markedly attenuated in postoperative patients. Baseline pulmonary vascular resistance (5.6 +/- 1.0 U x m2) fell 46 +/- 5% in preoperative patients but declined only 11 +/- 4% from baseline (5.8 +/- 0.9 U x m2) in postoperative patients (P < .002). However, inhalation of 80 ppm nitric oxide after ACH infusion in postoperative patients lowered pulmonary vascular resistance by 33 +/- 4% (P < .0002 compared with postoperative ACH response) with minimal effects on the systemic circulation. This finding suggests that the capacity for smooth muscle relaxation and pulmonary vasodilation was present in postoperative patients but could not be induced by ACH. Plasma levels of cGMP in postoperative patients were unchanged after acetylcholine infusion but rose more than threefold during pulmonary vasodilation with nitric oxide (P < .0001). This finding is consistent with the purported role of cGMP as the second messenger effecting smooth muscle relaxation in this process. CONCLUSIONS: CPB may be responsible for postoperative dysfunction of the pulmonary endothelial cell and may contribute to postoperative pulmonary hypertension in children. Inhaled nitric oxide is a potent pulmonary vasodilator after CPB with minimal systemic circulatory effects. It may have important diagnostic and therapeutic applications in patients with congenital heart disease.

Acetylcholine↗

PubMed1993

Performance of pediatric resuscitation bags assessed with an infant lung simulator.

Many pediatric self-inflating bags are equipped with pressure relief (pop-off) valves to prevent barotrauma. We participated in a resuscitation in which a valve malfunction briefly caused inadequate ventilation. The pop-off valve was seated in an intermediate position between open and closed settings. To investigate this problem, we assessed the performance of several commonly used pediatric self-inflating bags using an infant lung simulator (D, B & M, Redlands, CA). Bags were deflated using a range of inspiratory times (TI), delivered tidal volumes, peak proximal airway pressure (Pp), and peak distal pressure (lung pressure, Pd). When the pop-off valve was set in the open position, Pp ranged from 42 cm to 105 cm H2O, although P(d) never exceeded 45 cm H2O. The mean difference between Pp and P(d) decreased from 14.2 +/- 1.1 cm H2O at TI = 0.2 s to 6.1 +/- 0.5 cm H2O at TI = 1 s. Inflation of all DMR (disposable) and PMR (nondisposable) bags in the intermediate valve position produced marked air leakage through the valve, with delivered tidal volumes of only 92 +/- 13 mL (DMR) for TI < 0.5 s, and unrecordable tidal volumes (< 50 mL) for both DMR and PMR self-inflating bags for TI > 0.6 s. A wide range of delivered tidal volumes was observed among all bags examined. We conclude that both DMR and PMR bags can be placed inadvertently in an intermediate valve position that can produce disastrous hypoventilation during resuscitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Failure↗