Innate immunity mediating inflammation secondary to endotracheal intubation.

OBJECTIVE: To investigate the inflammatory markers associated with short-term endotracheal intubation in healthy surgical patients. DESIGN: An observational and prospective study of subjects scheduled for same-day surgery procedures. SETTING: Level I trauma center. PATIENTS: Fourteen healthy patients intubated for same-day surgery procedures. The median duration of surgery was 3 hours. INTERVENTIONS: Serial lavages above the tracheal cuff were obtained at the beginning of surgery, at 1 hour, and at the end of surgery; samples were assayed for cellular counts and levels of cytokines and complement 5a (C5a). RESULTS: The total number of polymorphonuclear cells (PMNs) increased almost 10-fold from intubation to extubation (P < .01). The levels of 3 of the cytokines measured in tracheal lavage supernatants were significantly elevated over the time of intubation: tumor necrosis factor (TNF) (P < .01), interleukin 6 (IL-6) (P < .01), and IL-1ß (P < .025). Levels of IL-8 showed an upward trend over time but were not significantly increased; C5a levels were significantly elevated over time (P < .05). CONCLUSIONS: Short-term intubation in healthy patients resulted in significant tracheal inflammation. Involvement of the innate immune system as documented in the present study provides information that may help to better understand the pathophysiologic characteristics of subglottic stenosis and other endotracheal injuries secondary to endotracheal intubation.

Cardiorespiratory and neural consequences of rats brought past their aerobic dive limit.

The mammalian diving response is a dramatic autonomic adjustment to underwater submersion affecting heart rate, arterial blood pressure, and ventilation. The bradycardia is known to be modulated by the parasympathetic nervous system, arterial blood pressure is modulated via the sympathetic system, and still other circuits modulate the respiratory changes. In the present study, we investigate the submergence of rats brought past their aerobic dive limit, defined as the diving duration beyond which blood lactate concentration increases above resting levels. Hemodynamic measurements were made during underwater submergence with biotelemetric transmitters, and blood was drawn from cannulas previously implanted in the rats' carotid arteries. Such prolonged submersion induces radical changes in blood chemistry; mean arterial PCO(2) rose to 62.4 Torr, while mean arterial PO(2) and pH reached nadirs of 21.8 Torr and 7.18, respectively. Despite these radical changes in blood chemistry, the rats neither attempted to gasp nor breathe while underwater. Immunohistochemistry for Fos protein done on their brains revealed numerous Fos-positive profiles. Especially noteworthy were the large number of immunopositive profiles in loci where presumptive chemoreceptors are found. Despite the activation of these presumptive chemoreceptors, the rats did not attempt to breathe. Injections of biotinylated dextran amine were made into ventral parts of the medullary dorsal horn, where central fibers of the anterior ethmoidal nerve terminate. Labeled fibers coursed caudal, ventral, and medial from the injection to neurons on the ventral surface of the medulla, where numerous Fos-labeled profiles were seen in the rats brought past their aerobic dive limit. We propose that this projection inhibits the homeostatic chemoreceptor reflex, despite the gross activation of chemoreceptors.

Early biochemical markers of inflammation in a swine model of endotracheal intubation.

BACKGROUND: A common complaint after endotracheal tube use is sore throat, which may be due to abrasion, ischemia-reperfusion injury, or an inflammatory reaction. Few studies have evaluated localized tracheal inflammation as part of the response to intubation. METHODS: Inflammation of the trachea due to intubation was assessed in a swine model by following indicators of inflammation over time in the tracheal lumen. Repeated tracheal lavages proximal to the endotracheal tube cuff were performed, and recovered lavage was analyzed for cells, protein, lactate dehydrogenase, and cytokines. RESULTS: The baseline tracheal lavage samples contained 18% polymorphonuclear cells. These cells increased rapidly to 43% by 1 h. The polymorphonuclear cell increase from baseline was significant at 1, 2, and 4 h (P < 0.01) after intubation. Tumor necrosis factor alpha, interleukin 1beta, interleukin 6, and interleukin 8 increased over time, but only interleukin 6 increased significantly (P < 0.01). Interleukin 6 was not detected at baseline or 1 h, but was detected at 2 h and increased significantly by 4 h. Neither lavage protein concentration nor lactate dehydrogenase activity increased over time. CONCLUSIONS: These results demonstrate that inflammation does occur during tracheal intubation, even when markers suggest minimal tracheal damage. The dramatic elevation in polymorphonuclear cells, along with the increase in interleukin 6, suggests an inflammatory response to the endotracheal tube itself or to some aspect of the intubation process. A more complete understanding of the response of the tracheal tissues is important in improving the treatment of intubated patients.

Verification of inefficacy of the glucose method in detecting aspiration associated with tube feedings.

While some authors believe that testing for glucose in suctioned tracheal secretions can be used to detect aspiration of glucose-containing formula, others disagree. Previous evaluative studies of the glucose method's efficacy have lacked adequate statistical power and a gold standard for aspiration. In this animal study, a gold standard for aspiration was used and possessed sufficient statistical power to address the glucose method's sensitivity and specificity. As such, the results from the study provide the clinician with useful data to decide if the glucose method is appropriate for use in clinical settings.

Detection of pepsin in tracheal secretions after forced small-volume aspirations of gastric juice.

BACKGROUND: Detecting small-volume aspirations of gastric contents is an important but difficult task. A potentially useful method for this purpose is assaying tracheal secretions for pepsin, an expected constituent of gastric juice. METHODS: A 2-group experimental design was used. The primary subjects were 161 experimental and 21 control New Zealand white rabbits; 161 acutely ill humans provided the gastric juice used in the project. The animals were anesthetized before being intubated and mechanically ventilated. Three separate boluses of human gastric juice mixed with dye-stained enteral formula were instilled into the experimental animals' tracheas; the 21 control animals received only 0.9% sodium chloride solution. At the beginning of each experiment, 0.4 mL/kg of the substance was infused over a 30-minute period; the infusion was then stopped and 90 minutes were allowed to elapse before endotracheal suctioning was performed. This procedure was repeated at hour 2 and hour 4. After completion of the multiple aspiration portion of the study, 23 additional animals were subjected to a single aspiration of 0.4 mL/kg of a mixture of human gastric juice and dye-stained enteral formula; secretions were obtained at 2 hours, 4 hours, and 6 hours. An immunoassay was used to test for pepsin in all of the tracheal secretions. RESULTS: In the 3-aspiration group, pepsin was found in all of the secretions from 92.5% (149/161) of the experimental animals; in contrast, no pepsin was found in any of the secretions from the 20 control animals. In the single-aspiration group, pepsin was found in all of the tracheal secretions from the 23 animals at 2 hours and 4 hours and 21 of the 23 animals at 6 hours. CONCLUSIONS: The immunoassay used in this animal model study was able to detect pepsin in >90% of the experimental animals' tracheal secretions after multiple or single forced aspirations of gastric juice. The extent to which pepsin can be detected in the tracheal secretions of acutely ill tube-fed humans requires investigation, as does the extent to which clinical outcomes are affected by pepsin-positive tracheal secretions.

C-reactive protein increases F-actin assembly and cortical distribution with resultant loss of lamellipod formation in human neutrophils.

C-reactive protein (CRP) inhibits neutrophil movement through a p38 MAP kinase pathway. We hypothesized that CRP altered F-actin content and distribution on human neutrophils as a means of inhibiting movement. CRP produced simultaneous increased F-actin and decreased G-actin levels. CRP increased F-actin levels in a concentration-dependent manner once a threshold (>100 microg/ml) was reached, and transiently increased F-actin (peak levels at 2.5 and 10 min) that returned to baseline by 30 min. Confocal microscopy of neutrophils revealed that fMLP provoked acquisition of a migratory phenotype as evidenced by the appearance of F-actin rich lamellipods. In contrast, CRP caused neutrophil rounding, prevented lamellipod formation and shifted F-actin from the cytoskeleton to the cortex. The p38 MAP kinase inhibitor, SB203580, produced a similar effect on neutrophil shape. Concentrations of SB203580 that dramatically decreased p38 activity in neutrophils also caused round cell morphology and cortical F-actin distribution. Since CRP inhibits p38 MAP kinase and p38 blockade leads to actin polymerization and prevention of lamellipod formation, it is concluded that round morphology and loss of lamellipod formation result from CRP inhibition of p38 MAP kinase. Understanding the signal transduction of CRP prevention of lamellipod formation will aid in the development of therapeutic agents against neutrophil-associated inflammatory disease.

Efficacy of dye-stained enteral formula in detecting pulmonary aspiration.

STUDY OBJECTIVE: To determine the extent to which a mixture of human gastric juice and enteral formula stained with two concentrations of FD&C Blue No. 1 food dye (0.8 and 1.5 mL/L) is visible in suctioned tracheobronchial secretions following three forced small-volume pulmonary aspirations over a 6-h period in an animal model. DESIGN: Experimental 2 x 3 repeated measures. SETTING: Animal laboratory and an acute care hospital. PARTICIPANTS: Ninety New Zealand white rabbits weighing approximately 3 kg each, and 90 acutely ill adults who furnished gastric juice. INTERVENTIONS: A mixture of human gastric juice and enteral formula stained with 0.8 or 1.5 mL of dye per liter was instilled intratracheally over a 30-min period into anesthetized intubated animals at baseline, 2 h, and 4 h. A total of 0.4 mL/kg of the mixture was instilled at each session. Ninety minutes after each instillation, suctioned secretions were examined for visible dye and blood. MEASUREMENTS AND RESULTS: Dye was visible in 46.3% of the secretions (125 of 270). The concentration of dye had no significant effect on dye visibility. Blood that was present in 114 of 270 of the secretions (42.2%) interfered with dye visibility in all but two secretions. For reasons unknown, even in the absence of blood, dye visibility decreased from 90.2% (55 of 61 secretions) after the first aspiration event to only 61% (25 of 41 secretions) after the third aspiration event. CONCLUSIONS: Findings from this animal model study do not support the use of the dye method to detect repeated small-volume aspirations. For clinicians who choose to use the dye method in selected situations, it appears that a dye concentration of 0.8 mL/L may be as effective in detecting aspiration as a 1.5 mL/L concentration.

Pepsin as a marker for pulmonary aspiration.

BACKGROUND: Although assessment for aspiration of small volumes of gastric contents in tube-fed patients receiving mechanical ventilation is important, available methods for this purpose are not wholly satisfactory. A potential method is immunoassay of tracheal secretions for the gastric enzyme pepsin. OBJECTIVES: To determine the frequency with which pepsin in suctioned tracheal secretions from acutely ill, tube-fed patients receiving mechanical ventilation could be detected via an immunoassay. METHODS: A convenience sample of 136 specimens of suctioned tracheal secretions was collected from 30 acutely ill, tube-fed adults receiving mechanical ventilation. Multiple samples were obtained from 26 of the 30 patients (range, 2-11 per subject). An immunoassay with rooster polyclonal antibodies to purified human pepsin was used to detect pepsin in the secretions. RESULTS: Fourteen specimens tested positive for pepsin. Secretions from 5 patients accounted for the 14 pepsin-positive results. A significant relationship was found between the position of the head of the bed and the presence of pepsin in tracheal secretions (P<.001). Of the 14 pepsin-positive specimens, 13 (92.9%) were obtained from subjects in a flat position. CONCLUSIONS: A pepsin immunoassay can be used to detect pepsin in human tracheal secretions. If pepsin in tracheal secretions is considered an indicator of aspiration of gastric contents, aspiration occurred in 5 of the 30 subjects. A flat position is strongly associated with the presence of pepsin in tracheal secretions.

Physiologic responses to small emboli and hemodynamic effects of changes in deformability of polymorphonuclear leukocytes in isolated rabbit lung.

We hypothesized that polymorphonuclear leukocytes (PMNs) exposed to lipopolysaccharide (LPS) or chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) would alter the pulmonary hemodynamics of buffer-perfused rabbit lung. Pulmonary arterial pressure (Ppa) was measured at baseline, at peak response, and at 30 min after PMN infusion in the perfusate (Ppa x time, PT product). Infusion of peritoneal-harvested PMNs resulted in a transient increase in both pulmonary vascular resistance (PVR) and lung weight. PVR also increased when glutaraldehyde-treated rabbit PMNs (GPMNs) or beads were infused. Upstream PVR (Pao-Pdo) remained high with the infusion of GPMNs and beads and returned to baseline only when PMNs were infused 30 min thereafter. FMLP-exposed PMNs increased the peak Ppa and PT product. Pretreatment with 3-isobutyl-1-methylxanthine (IBMX) blocked this increase in pressure, suggesting the release of vasoconstrictor(s) or a direct effect of FMLP. PMNs exposed to LPS increased peak Ppa and PT product with and without the addition of IBMX. Cytochalasin D treatment of PMNs prevented the increase in PT product, suggesting that actin polymerization of PMNs is involved. The effects of these agents on PMN rigidity were verified by means of 6.5-microm polycarbonate filters. PMN suspension treated with FMLP or LPS increased filter perfusion pressure and PT product. Cytochalasin D prevented these increases. These results suggest that, initially after injection, PMNs behave like small beads embolizing primarily the small arteries in the lung and that they then move distally through the vasculature. Exposure to FMLP or LPS alters PMN deformability and the ability of PMNs to pass through the pulmonary vasculature, resulting in increased pulmonary vascular resistance.