Reduction in tracheal lumen due to endotracheal intubation and its calculated clinical significance.

BACKGROUND: The flow in the human trachea is turbulent. Thus, the tracheal resistance (R) and the pressure gradient (DeltaP) required to maintain a given flow across the trachea is inversely related to its radius raised to the fifth power. If the caliber reduction ratio (X) after endotracheal intubation is calculated as X = radius of the endotracheal tube (rETT)/radius of the trachea (rT), then DeltaP and/or R will be increased by (1/X)(5). STUDY OBJECTIVES: To measure the actual ratio between rETT and rT following endotracheal intubation of pediatric patients with respiratory failure and to calculate the resulting increase in the tracheal R and DeltaP for a given inspiratory flow rate. DESIGN: Retrospective chart review. SETTING: Pediatric ICU in a tertiary-care teaching children's medical center. PATIENT ENROLLMENT: Twenty consecutive pediatric patients (mean [+/- SD] age, 6.4 +/- 7.2 years) whose tracheas had been intubated for various causes of respiratory failure, and who had received a CT scan, were included in our study. All patients received an endotracheal tube the size of which was derived from the following formula: (age in years/4) + 4. MEASUREMENTS AND MAIN RESULTS: rT and rETT were measured from CT scan sections at and around the level of the thoracic inlet, and the average values were used to calculate X. These values ranged from 0.33 to 0.65 (mean, 0. 55 +/- 0.8). The factor (1/X)(5) was calculated for each patient and then was multiplied by the known normal value for tracheal R for adolescents and adults (0.07 cm H(2)O/L/s) to obtain the value of R resulting from the artificial airway, (1/X)(5) x 0.07. Our results showed that tracheal R increased due to caliber reduction of the trachea after endotracheal intubation by 33.9 +/- 52.5-fold (range, 8.6- to 255.5-fold). In order to maintain an inspiratory flow of 1 L/s, the value of P for the intubated trachea would increase from 0. 07 cm H(2)O to a mean of 2.4 +/- 3.7 cm H(2)O (range, 0.6 to 18 cm H(2)O). In two of our patients, the rT/rETT ratios were < 0.5 (0.33 and 0.44, respectively); this translated into a more significant increase in the calculated DeltaPs, 18 and 4.2 cm H(2)O, respectively. CONCLUSIONS: : The common value of X due to endotracheal intubation is between 0.5 and 0.6, which in and of itself results in an increase in R across the intubated trachea up to 32-fold. The calculated increase in P as a result of this is between 2 and 3 cm H(2)O for adolescents or young adults. The addition of pressure support of at least 3 cm H(2)O during spontaneous ventilation via an endotracheal tube, which is common practice in pediatric critical care, should alleviate any respiratory distress emanating from the increased R. However, a value for X < 0.5, which was found in 10% of our patients (2 of 20 patients), results in a much higher calculated increase in the pressure gradient and, therefore, a higher level of pressure support is required to overcome this increase.

Economic implications of the timing of do-not-resuscitate orders for ICU patients.

Healthcare reform continues to move forward, with the influence of managed care increasing in most areas of the United States. Strategies for cost containment are being considered to limit marginally beneficial health care, including futile-care policies, capitation, preset limits on health care, and guidelines for writing do-not-resuscitate (DNR) orders. Recent studies which attempted to improve communication between patients and physicians have failed to improve the quality of end-of-life care offered by healthcare providers. In other recent works, the timing of when DNR orders are written has been associated with shortening needed hospital and ICU care, as well as effecting significant reductions in resources utilized. This study reviews the current literature with respect to the timing of when DNR orders are written. We present a conservative estimate that for each ICU patient moved from late DNR to early DNR status, approximately $10,000 per patient could be saved. Moreover, approximately 0.5% of all ICU care could be limited should DNR orders be written earlier in a patient's hospital or ICU stay. In addition, a shift from open-format ICUs to semiclosed units managed by qualified critical care physician directors would reduce the number of patients with futile or failed cardiopulmonary resuscitation, and increase the number of patients having care withheld or withdrawn after failed ICU therapy. Such a change would result in more substantial savings.

The safety and diagnostic accuracy of minibronchoalveolar lavage in patients with suspected ventilator-associated pneumonia.

OBJECTIVES: To assess the safety of minibronchoalveolar lavage done by respiratory therapists for the evaluation of suspected ventilator-associated pneumonia and to determine the diagnostic agreement between quantitative lower airway cultures obtained by the minibronchoalveolar lavage and protected specimen brush techniques. DESIGN: A prospective direct comparison of two diagnostic techniques. SETTING: An academic tertiary care center in St. Louis, Missouri. PATIENTS: 72 consecutive patients suspected of having ventilator-associated pneumonia on the basis of clinical evidence. INTERVENTIONS: Sampling of lower airway secretions using the protected specimen brush and minibronchoalveolar lavage techniques. MAIN OUTCOME MEASURES: Clinical complications and quantitative cultures of respiratory secretions. RESULTS: 72 patients suspected of having ventilator-associated pneumonia (first episode) were evaluated using minibronchoalveolar lavage. In 42 patients, lower airway secretions were also obtained using the protected specimen brush technique. No change in arterial blood oxygen saturation or heart rate occurred after minibronchoalveolar lavage (P > 0.2). Mean arterial pressure slightly increased with minibronchoalveolar lavage (baseline mean pressure, 90.1 mm Hg [CI, 88.4 to 91.7 mm Hg]; average within-person change, 2.6 mm Hg; P = 0.024). Good diagnostic agreement was shown for quantitative cultures obtained with the protected specimen brush and minibronchoalveolar lavage techniques (kappa statistic, 0.63; concordance, 83.3%); 10(3) colony forming units/mL was used as the threshold for a clinically significant culture result. CONCLUSIONS: Minibronchoalveolar lavage is a safe and technically simple procedure for obtaining quantitative lower airway cultures in patients requiring mechanical ventilation. Quantitative culture results obtained by minibronchoalveolar lavage are similar to those obtained by the protected specimen brush technique.

RNA and protein components of maize streak and cassava latent viruses.

Polyacrylamide gel electrophoresis indicated that maize streak (MSV) and cassava latent (CLV) viruses each contain one species of protein and two of RNA. The estimated protein mol. wt is 28000 for MSV and 34000 for CLV. The mol. wts obtained for the two RNA species using formamide-containing gels were the same for the two viruses: 1-7 X 10(6) and 1-3 X 10(6). It is suggested that the viruses have a two-part genome and that the tendency of their nucleoprotein particles to form pairs favours the delivery of complete genomes to sites of infection.