Changes in resistances of endotracheal tubes with reductions in the cross-sectional area.

BACKGROUND AND OBJECTIVES: Partial obstruction of endotracheal tubes due to accumulation of secretions and mucus plugs can increase the tube resistance and subsequently impose increased resistive load on the patient. This study was performed to determine the changes in the resistance of endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm with different degrees and locations of endotracheal tube narrowing. METHODS: Reductions of 10%, 25%, 50% and 75% in the endotracheal tube's cross-sectional areas were created at different sites along the axes of the tube connected to an artificial lung. While ventilating with a constant inspiratory flow, a 1 s end-inspiratory occlusion manoeuvre was applied and the resulting plateau pressure was determined. The resistance was calculated as (peak airway pressure--plateau pressure)/peak inspiratory flow. RESULTS: Significant increases in the endotracheal tube's resistances were observed as the tube's cross-sectional area reduction was increased from 25% to 50% and from 50% to 75% for the 7.5 mm endotracheal tube, from 25% to 50% for the 8.0 mm endotracheal tube, and from 50% to 75% for the 8.5 mm endotracheal tube. Changes of the endotracheal tube resistances were not affected by the site of cross-sectional area reductions along the axes of the tubes. CONCLUSIONS: For endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm, significant changes in the tubes resistances are observed when the partial obstructions of the tubes exceed certain critical values. The location of the partial obstruction did not affect the changes in the endotracheal tube resistances.

Thromboembolism and toxic shock syndrome: a case presentation and literature update.

A case of progressive shock and multisystem organ failure is reported for an 18 year old Lebanese woman, clinically diagnosed as toxic shock syndrome (TSS). The patient developed cough and dyspnea during hospitalization; chest CT angiography revealed thromboembolism of the pulmonary artery. CBC analysis showed leukocytosis with a white cell count (WCC) with a marked increase in PT and PTT coupled with reduced protein S, antithrombin III, and protein C levels. The patient improved gradually and was discharged from the hospital 7 days later on oral anticoagulation, and was followed up for six months with no disease recurrence or complications. To our knowledge, this is the first reported case in the literature of toxic shock syndrome associated with pulmonary thromboembolism.

Thrombotic thrombocytopenic purpura in a case of scleroderma renal crisis treated with twice-daily therapeutic plasma exchange.

We report the rare complication of thrombotic thrombocytopenic purpura (TTP) in an elderly patient with the uncommon scleroderma renal crisis (SRC) at the advanced age of 85 years. Initially, she was treated by standard daily one and a half plasma volume therapeutic plasma exchange (TPE), in combination with steroid therapy. Due to an unsatisfactory clinical response, she was consequently, treated by an intensive twice-daily one and a half plasma volume TPE regimen. Although there was an increase in the platelet count, a 7-day course of the intensive regimen did not elicit further propitious laboratory test results or a clinical improvement and the patient expired secondary to the pulmonary and cardiac conditions related to SRC. Intensive TPE administration has been advocated in few specific patients who are refractory to standard daily treatment. The unfavorable outcome in this case may be attributed to the multiple complications associated with her primary disorder. In conclusion, we observed intensive twice-daily TPE to increase temporarily the platelet count, but not to be of benefit in a patient with SRC and multiple organ failure. The two TPE regimens and outcomes are compared and the pathogenesis of TTP and scleroderma are discussed.

Deterioration of gas exchange in patients with severe thrombotic thrombocytopenic purpura with respiratory failure during therapeutic plasma exchange.

Therapeutic plasma exchange (TPE) is a procedure performed on patients suffering from various disorders, including thrombotic thrombocytopenic purpura (TTP). As we noted a frequent transient deterioration in respiratory function when the procedure was performed on intensive care unit (ICU) patients, we studied retrospectively the incidence of respiratory deterioration during and shortly after TPE and looked for a probable correlation with a change in the white blood cell (WBC) counts. Over a period of 10 months six patients with TTP, five of whom had parenchymal lung disease due to different medical reasons, underwent TPE. The oxygen saturation was measured continuously before, during, and after TPE; additionally, the WBC and differential counts were measured pre- and post-TPE. The ratio of the oxygen saturation by pulse oxymetry (SpO2) to the fraction of inspired oxygen (FiO2) was calculated before, during and after TPE. In these five patients with lung disorders, there was a consistent trend of a decreasing SpO2/FiO2 quotient during and within 2 h post TPE compared to the pre-TPE value. The decrease in SpO2/FiO2 range was 0.20-0.89 with an average of 0.56. In the same 5 patients there was an increase in the WBC count in the range of 2.3-19.7 x 10(9)/L with an average increase of 9.3 x 10(9)/L. The percent neutrophils of the total WBC counts also increased following most of the sessions, this increase was in the range of 1-15 % with an average of 7%. The effect of TPE on the SpO2/FiO2 ratio and the correlation to the WBC count and to a possible neutrophil activation has not been previously reported. We postulate that TPE can accentuate respiratory deterioration in patients with TTP who already have acute lung injury. This may be due to the priming and activation of the leukocytes that could lead to the release of cytokines and inflammatory mediators during the procedure. Thus, it is important to be aware of the possible deterioration in respiratory function and gas exchange while administering TPE to patients with pre-existing parenchymal lung injury.

Coronary artery bypass grafting after pneumonectomy.

The need to perform coronary artery bypass grafting in patients who have a single lung is not uncommon. To date, the safety of such procedures has not been well documented. In this article, we review the literature using the Medline 1966 to September 2000 database to identify patients with pneumonectomy who underwent coronary artery grafting and we provide a compilation of all reported cases. We also present an additional case in whom the use of nasal bilevel positive airway pressure was beneficial in preventing postoperative pulmonary complications.

Comparative performance of PCR-based assay versus microscopy and culture for the direct detection of Mycobacterium tuberculosis in clinical respiratory specimens in Lebanon.

SETTING: American University of Beirut Medical Center, Lebanon. OBJECTIVE: To assess the performance of a polymerase chain reaction (PCR) using primers that flank 542 bp within IS6110 in Mycobacterium tuberculosis (TB) vs. microscopy and BACTEC culture, in the diagnosis of tuberculosis. DESIGN: A total of 82 clinical respiratory pulmonary specimens and 73 samples from BACTEC vials were tested by the three methods. RESULTS: Of 24 smear-positive culture-positive (SP-CP) and 11 smear-negative culture-positive (SN-CP) TB specimens, PCR detected 83% and 64%, respectively. Among 17 specimens yielding mycobacteria other than tuberculosis (MOTT), the PCR was positive in 33% SP-CP and 14% SN-CP specimens. Among the 73 BACTEC vials, PCR was positive in 36 of 38 (95%) yielding culture-positive TB, and in one of 20 (5%) yielding culture positive MOTT. None of the 30 smear-negative culture-negative (SN-CN) clinical specimens and 15 of the CN vials were positive by PCR. The overall sensitivity of PCR was 77% and 95% for TB detection in respiratory specimens and BACTEC vials, respectively, and the specificity was 94% in both. CONCLUSIONS: Because a substantial number of TB cases are missed, especially in SN-CP specimens, a PCR-based assay utilizing these primers cannot be used reliably, alone, in clinical laboratory diagnosis of mycobacterial respiratory infections.

Comparative study of antituberculous drug resistance among Mycobacterium tuberculosis isolates recovered at the American University of Beirut Medical Center: 1996-1998 vs 1994-1995.

PURPOSE: To study the overall current prevalence of antituberculous drug resistance among M. tuberculosis isolates recovered at the American University of Beirut Medical Center (AUBMC) between 1996-1998 in comparison to those reported on isolates recovered in 1994-1995. MATERIALS AND METHODS: Seventy-four consecutive M. tuberculosis isolates recovered from the same number of newly diagnosed cases of tuberculosis (TB), between January 1996 and December 1998 (referred to as 1998), were tested against isoniazid (INH), rifampicin (RIF), streptomycin (STM) and ethambutol (ETH), using the BACTEC-TB susceptibility procedure and system. The results were compared to those reported on the isolates recovered in 1994-1995 (referred to as 1995). RESULTS: A comparison between the results obtained in 1998 vs 1995 showed the following, respectively: The male to female ratio was 3.1:1 vs 2:1 and the mean ages were almost similar in males, 33.4 vs 34.1 years but were slightly higher in females 38.2 vs 32.7 years. Children (< or = 15 yrs) represented 10.8% vs 8.3% of the study population. The prevalence of resistance, to one or more drugs, was almost the same, 24% vs 26% but the overall percentages of single drug resistance were generally higher in 1998 vs 1995 against all the tested drugs except INH: INH (20.2% vs 23.9%), RIF (16.2% vs 12.5%), STM (13.5% vs 7.3%) and ETH (8.1% vs 3%). Among the resistant isolates, the profiles of resistance indicated decrease in resistance to one and two drugs, 6.7% vs 11.5% and 5.4% vs 10.4%, respectively, but showed increase in resistance to three and four drugs, 8.1% vs 2.1% and 4% vs 2.1%, respectively. Increase in resistance to two or more drugs was also observed, 17.6% vs 14.6%, and the prevalence of multidrug resistance, defined as resistance to at least both INH and RIF, was also increased, 14.7% vs 11.4%. CONCLUSIONS: This study shows a high prevalence and persistence of TB drug resistance tested in our Medical Center in Lebanon. In addition, the shift in the increase of resistance from one and two drugs to three and four drugs are very ominous and should be considered when treating patients in this country. Moreover, such information calls for scrutinizing the existing local TB control programs as part of the global efforts to minimize the incidence of this highly morbid infectious disease.