David L. Bowton

High tidal volume ventilation produces increased lung water in oleic acid-injured rabbit lungs.

Repeated lung inflation with very high tidal volumes (VT) is associated with the production of permeability pulmonary edema in animal models using previously normal lungs. We studied the effect of mechanical ventilation, at VT values approaching those used clinically, on lung weight gain (lung water) in salt-perfused rabbit lungs diffusely injured by the administration of oleic acid. Lungs ventilated at a VT of 18 ml/kg gained significantly more weight at 30 through 90 min than did lungs ventilated at 6 ml/kg. These differences in weight gain were not associated with differences in the evolution of thromboxane B2 in the perfusate. The impact of VT on lung water and outcome in patients with lung injury deserves further study.

Results of a survey of blood pressure monitoring by intensivists in critically ill patients: A preliminary study

Objectives:Maintenance of mean arterial pressure >65 mm Hg has been associated with improved clinical outcomes in many studies of critically ill patients. Current guidelines for the management of septic shock and guidelines for managing other critical illnesses suggest intra-arterial blood pressure measurement is preferred over automated oscillometric noninvasive blood pressure measurement. Despite these recommendations, anecdotal experience suggested that the use of noninvasive blood pressure measurement in our institution and others in preference to intra-arterial blood pressure measurement remained prevalent. Design:We designed an online survey and sent it by e-mail. Setting:Intensive care units. Patients and Subjects:A randomly selected group from the membership of the Society for Critical Care Medicine. Interventions:None. Measurements and Main Results:Use of non-invasive and invasive blood pressure devices. Eight hundred eighty individuals received an invitation to complete the survey and 149 responded. We found that 71% (105 of 149) of intensivists estimated the correct cuff size rather than measuring arm circumference directly. In hypotensive patients, 73% of respondents (108 of 149) reported using noninvasive blood pressure measurement measurements for patient management. In patients on a vasopressor medication, 47% (70 of 149) of respondents reported using noninvasive blood pressure measurement for management. Conclusions:The use of noninvasive blood pressure measurement measurements in critically ill patients is common despite the paucity of evidence validating its accuracy in critically ill patients. Given this widespread use, accuracy and precision validation studies comparing noninvasive blood pressure measurement with intra-arterial blood pressure measurement in critically ill patients should be performed.

The Impact of Hospital-Wide Use of a Tapered-Cuff Endotracheal Tube on the Incidence of Ventilator-Associated Pneumonia

BACKGROUND: Aspiration of colonized oropharyngeal secretions is a major factor in the pathogenesis of ventilator-associated pneumonia (VAP). A tapered-cuff endotracheal tube (ETT) has been demonstrated to reduce aspiration around the cuff. Whether these properties are efficacious in reducing VAP is not known. METHODS: This 2-period, investigator-initiated observational study was designed to assess the efficacy of a tapered-cuff ETT to reduce the VAP rate. All intubated, mechanically ventilated patients over the age of 18 were included. During the baseline period a standard, barrel-shaped-cuff ETT (Mallinckrodt Hi-Lo) was used. All ETTs throughout the hospital were then replaced with a tapered-cuff ETT (TaperGuard). The primary outcome variable was the incidence of VAP per 1,000 ventilator days. RESULTS: We included 2,849 subjects, encompassing 15,250 ventilator days. The mean ± SD monthly VAP rate was 3.29 ± 1.79/1,000 ventilator days in the standard-cuff group and 2.77 ± 2.00/1,000 ventilator days in the tapered-cuff group (P = .65). While adherence to the VAP prevention bundle was high throughout the study, bundle adherence was significantly higher during the standard-cuff period (96.5 ± 2.7%) than in the tapered-cuff period (90.3 ± 3.5%, P = .01). CONCLUSIONS: In the setting of a VAP rate very near the average of ICUs in the United States, and where there was high adherence to a VAP prevention bundle, the use of a tapered-cuff ETT was not associated with a reduction in the VAP rate.

A Laboratory Comparison of Three Pulmonary Artery Oximetry Catheters

BackgroundMeasurement of mixed venous hemoglobin oxygen saturation via catheters employing reflectance spectrophotometry has been available for more than 10 yr. Despite numerous clinical reports that have presented data showing the poor accuracy of these devices when used clinically, they are still widely used in clinical care. The reason for lack of agreement with measurements made using bench spectrophotometry is unclear. The purpose of this study is to define the performance limitations of three hemoglobin oxygen saturation catheters (Oximetrix 3, SAT-2, and HEMOPRO2) in a controlled laboratory environment using a blood flow loop primed with fresh whole human blood as a model. Our hypothesis is that the performance limitations of these devices represent inherent limitations in the technology, not error introduced by patient anatomy and physiology. MethodsBlood was equilibrated in a flow loop to four analytic gas mixtures designed to achieve oxygen saturation of approximately 50%, 60%, 70%, and 80%, respectively, with carbon dioxide tension, pH, and temperature held constant. Saturation readings from the catheters were collected on-line by microcomputer. Periodic blood samples were withdrawn from the flow loop for analysis on a bench spectrophotometer and subsequent comparison with catheter-derived values. ResultsBy all measures, performances of the Oximetrix 3 and SAT-2 systems were comparable (all data are presented as percent saturation unless otherwise noted); bias ± precision was 3.20 ± 2.47 and −1.25 ± 3.36, respectively, versus −9.97 ± 7.05 for the HEMOPRO2. The 95% confidence limits based on intracatheter variability were ±3.49, ±2.90, and ±9.13 for the Oximetrix 3, SAT-2, and HEMOPRO2, respectively. The 95% confidence limits based on total variability, although similar for Oximetrix 3 (±4.83) and SAT-2 (±6.59), were larger for the HEMOPRO2 (±13.82). The 95% confidence Intervals for agreement between catheter brands were −2.14, 11.04 (Oximetrix 3 – SAT-2); −0.18, 26.52 (Oximetrix 3 – HEMOPRO2) and −5.24, 22.68 (SAT-2 – HEMOPRO2). ConclusionsWhile the Oximetrix 3 and SAT-2 may be acceptable as continuous monitors used to detect changes or trends, none of the three systems is equivalent to conventional bench oximetry for the measurement of hemoglobin oxygen saturation.

Community-acquired pneumonia : the clinical dilemma

Community-acquired pneumonia (CAP) is the sixth most common cause of death in the United States. Despite its frequency and mortality, specific etiologic diagnosis remains a major clinical challenge. The organisms most commonly implicated in CAP are Streptococcus pneumoniae, Mycoplasma pneumoniae, Legionella pneumophila, Haemophilus influenzae, Chlamydia pneumoniae (TWAR), and viruses. Clinical and radiographic criteria have proven to be of little value in determining the etiology of CAP. Laboratory studies, including Grams stain and culture of sputum, have also been shown to be of severely limited value to the clinician faced with the patient with CAP. Antibiotic therapy must, therefore, generally be empiric. Regimens including erythromycin either as a single agent or coupled with an aminoglycoside or cephalosporin appear to be most efficacious.

Skin sensitivity to allergen does not accurately predict airway response to allergen

BACKGROUND Allergen challenge of the asthmatic airway has become widely applied in the study of allergic asthma in humans. Skin sensitivity correlates with inhaled sensitivity in some populations. Skin test titration has been proposed as a useful tool to guide the selection of initial allergen concentration. OBJECTIVE To determine the relationship between skin test sensitivity and inhaled reactivity to allergen. METHODS We examined the relationship between skin test and inhaled reactivity in 22 allergic asthmatic subjects. Methacholine bronchoprovocation was performed using a standardized tidal breathing technique. Prick skin test titrations were done using serially diluted lyophilized antigen extracts reconstituted in normal saline from 1:100,000 to 1:10. Inhaled allergen challenge was routinely performed in the morning using the same allergen employed in skin test titration. RESULTS There was no correlation between skin test threshold and the inhaled concentration required to produce a 20% fall in FEV1 (r = 0.07; P = .78). If subjects who manifested marked cutaneous reactivity (i.e., skin reactivity at dilutions greater than 1:10,000) were excluded from analysis, there was a significant correlation between cutaneous and inhaled reactivity (r = 0.84; P < .001). CONCLUSION While a correlation between skin test threshold and inhaled reactivity is present in some subjects with allergic asthma, the relationship is inconsistent.

VARIABILITY IN CENTRAL VENOUS PRESSURE MEASUREMENTS AND THE POTENTIAL IMPACT ON FLUID MANAGEMENT

In the intensive care unit (ICU) of our tertiary care university medical center, central venous pressure (CVP) measurements derived from bedside monitors differ considerably from measurements by trained intensivists using paper tracings. To quantify these differences, printed CVP tracings and concurrent respiratory waveforms were collected from 100 consecutive critically ill patients along with the corresponding monitor-displayed CVP. Four blinded intensivists interpreted the tracings. The mean difference between the intensivists and the monitor was −0.26 mmHg (95% confidence interval, +7.19 to −7.71 mmHg). Seventy-six percent of the paired measurements were within 2 mmHg, whereas 7% differed by more than 5 mmHg. To determine the potential clinical impact of these differences, we used the original Surviving Sepsis Campaign Guidelines for fluid administration based upon the measurement of CVP. For individual physicians, protocol-driven fluid management strategy would have differed in 19.2% to 25.3% of cases, dependent upon which measured value was chosen. Although protocol-driven strategies to direct fluid infusion therapy may improve outcomes, these interventions in a specific patient are dependent upon the method by which the CVP is measured.

Ventilatory Management of the Noninjured Lung

This article reviews aspects of mechanical ventilation in patients without lung injury, patients in the perioperative period, and those with neurologic injury or disease including spinal cord injury. Specific emphasis is placed on ventilator strategies, including timing and indications for tracheostomy. Lung protective ventilation, using low tidal volumes and modest levels of positive end-expiratory pressure, should be the default consideration in all patients requiring mechanical ventilatory support. The exception may be the patient with high cervical spinal cord injuries who requires mechanical ventilatory support. There is no consensus on the timing of tracheostomy in patients with neurologic diseases.

Comparison of two formulas to calculate alveolar oxygen tension in canine oleic acid pulmonary edema

Alveolar oxygen tension (PAO2) is calculated by either of two mathematical formulas incorporating various respiratory variables. The first formula, Equation 1, assumes a constant RQ of 0.8; the second formula, Equation 2, uses the mixing equation and requires analysis of inspired, mixed expired, and end-tidal gas samples. We tested the consistency of these formulas before and after asymmetric oleic acid pulmonary edema, then calculated and compared venous admixture values using the PAO2 value derived from each formula. Before oleic acid, Equations 1 and 2 were similar (213 +/- 22 vs. 211 +/- 22 [SD] torr, respectively), as were venous admixture values (8.7 +/- 2.9% vs. 8.5 +/- 2.9%, respectively). After oleic acid injury, Equation 1 was significantly lower than Equation 2, thus slightly but consistently underestimating venous admixture (29.9 +/- 12.2% vs. 30.2 +/- 12.3%; p less than .01). However, the venous admixture values obtained after oleic acid injury calculated from Equations 1 and 2 correlated closely (r2 = .998; p less than .001), and the clinical differences yielded by the two formulas would be minimal. We recommend using the simpler formula (Eq. 1) when calculating PAO2.

Haloperidol and Ziprasidone for Treatment of Delirium in Critical Illness

BACKGROUND There are conflicting data on the effects of antipsychotic medications on delirium in patients in the intensive care unit (ICU). METHODS In a randomized, double‐blind, placebo‐controlled trial, we assigned patients with acute respiratory failure or shock and hypoactive or hyperactive delirium to receive intravenous boluses of haloperidol (maximum dose, 20 mg daily), ziprasidone (maximum dose, 40 mg daily), or placebo. The volume and dose of a trial drug or placebo was halved or doubled at 12‐hour intervals on the basis of the presence or absence of delirium, as detected with the use of the Confusion Assessment Method for the ICU, and of side effects of the intervention. The primary end point was the number of days alive without delirium or coma during the 14‐day intervention period. Secondary end points included 30‐day and 90‐day survival, time to freedom from mechanical ventilation, and time to ICU and hospital discharge. Safety end points included extrapyramidal symptoms and excessive sedation. RESULTS Written informed consent was obtained from 1183 patients or their authorized representatives. Delirium developed in 566 patients (48%), of whom 89% had hypoactive delirium and 11% had hyperactive delirium. Of the 566 patients, 184 were randomly assigned to receive placebo, 192 to receive haloperidol, and 190 to receive ziprasidone. The median duration of exposure to a trial drug or placebo was 4 days (interquartile range, 3 to 7). The median number of days alive without delirium or coma was 8.5 (95% confidence interval [CI], 5.6 to 9.9) in the placebo group, 7.9 (95% CI, 4.4 to 9.6) in the haloperidol group, and 8.7 (95% CI, 5.9 to 10.0) in the ziprasidone group (P=0.26 for overall effect across trial groups). The use of haloperidol or ziprasidone, as compared with placebo, had no significant effect on the primary end point (odds ratios, 0.88 [95% CI, 0.64 to 1.21] and 1.04 [95% CI, 0.73 to 1.48], respectively). There were no significant between‐group differences with respect to the secondary end points or the frequency of extrapyramidal symptoms. CONCLUSIONS The use of haloperidol or ziprasidone, as compared with placebo, in patients with acute respiratory failure or shock and hypoactive or hyperactive delirium in the ICU did not significantly alter the duration of delirium. (Funded by the National Institutes of Health and the VA Geriatric Research Education and Clinical Center; MIND‐USA ClinicalTrials.gov number, NCT01211522.)