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Pulmonary capillary perfusion within a single alveolar wall continually switches among segments, even when large-vessel hemodynamics are constant. The mechanism is unknown. We hypothesize that the continually varying size of plasma gaps between individual red blood cells affects the likelihood of capillary segment closure and the probability of cells changing directions at the next capillary junction. We assumed that an increase in hematocrit would decrease the average distance between red blood cells, thereby decreasing the switching at each capillary junction. To test this idea, we observed 26 individual alveolar capillary networks by using videomicroscopy of excised canine lung lobes that were perfused first at normal hematocrit (31–43%) and then at increased hematocrit (51–62%). The number of switches decreased by 38% during increased hematocrit (P < 0.01). These results support the idea that a substantial part of flow switching among pulmonary capillaries is caused by the particulate nature of blood passing through a complex network of tubes with continuously varying hematocrit. [ABSTRACT FROM AUTHOR]

Objectives: To determine the incidence and to describe wound complications and associated risk factors of pediatric tracheotomy., Design: Retrospective case series., Setting: Freestanding tertiary care academic pediatric hospital., Patients: Sixty-five consecutive children undergoing tracheotomy over 15 months., Main Outcome Measures: Postoperative wound complications objectively and independently documented by an advanced practice nurse specializing in tracheotomy care. Secondary outcome measures included comorbidities, mortality rates, and wound status after subsequent examinations and management., Results: The mean (SEM) patient age at tracheotomy was 45 (8.7) months (median age, 9.1 months). The most common indication for tracheotomy was pulmonary disease (36.9%), followed by neurologic impairment and laryngeal abnormalities. There were 19 patients (29%) with and 46 patients (71%) without wound complications. There were no significant differences between the 2 groups in age (P = .68) or weight (P = .55); however, infants younger than 12 months had an increased complication rate (39% vs. 17%, P = .04). The type of tracheotomy tube was predictive of postoperative wound complications (P = .02). All patients with wounds received aggressive local wound care. Five of 13 patients had complete resolution of stomal wounds, whereas 8 patients had persistent wound issues. There were 5 non-wound-related mortalities., Conclusions: With attempts to classify tracheotomy wound breakdowns as reportable events, including never events, increasing emphasis is being placed on posttracheotomy care. This study demonstrates that wound breakdown in pediatric tracheotomy patients is common. These complications can be mitigated, although not prevented completely, with aggressive wound surveillance and specialized wound care.

Objective: To determine polysomnographic (PSG) variables that may potentially predict adverse respiratory events after pediatric adenotonsillectomy., Design: Retrospective, case-control study., Setting: Free-standing academic tertiary-care pediatric hospital., Patients: The study included 1131 patients undergoing adenotonsillectomy by 2 attending surgeons. There were no exclusion criteria., Main Outcome Measures: Variables from preoperative PSGs were analyzed to determine predictors of postoperative respiratory complications. Logistic regression analysis was performed., Results: A total of 151 patients (13.4%) underwent preoperative PSG. Twenty-three of these patients (15.2%) had adverse respiratory events. The primary adverse event was desaturation requiring supplemental oxygen therapy, with 1 case of postobstructive pulmonary edema. Patients with adverse events had a significantly higher apnea-hypopnea index) (31.8 vs 14.1; P = .001), higher hypopnea index (22.6 vs 8.9; P = .004), higher body mass index (z score, 1.43 vs 0.70; P = .02), and lower nadir oxygen saturation (72% vs 84%; P <.001). Patients with adverse events had a prolonged hospital course (odds ratio, 32.1; 95% confidence interval, 7.8-131.4). There were no differences in age or other PSG variables. There were no intubations or mortalities., Conclusions: Polysomnography may be used to predict which patients are at higher risk for adverse respiratory events after adenotonsillectomy. Such knowledge is valuable for planning optimal postoperative management and intraoperative anesthesia. Predictors of increased respiratory complications include apnea-hypopnea index, hypopnea index, body mass index, and nadir oxygen saturation.

Pulmonary capillary perfusion within a single alveolar wall continually switches among segments, even when large-vessel hemodynamics are constant. The mechanism is unknown. We hypothesize that the continually varying size of plasma gaps between individual red blood cells affects the likelihood of capillary segment closure and the probability of cells changing directions at the next capillary junction. We assumed that an increase in hematocrit would decrease the average distance between red blood cells, thereby decreasing the switching at each capillary junction. To test this idea, we observed 26 individual alveolar capillary networks by using videomicroscopy of excised canine lung lobes that were perfused first at normal hematocrit (31-43%) and then at increased hematocrit (51-62%). The number of switches decreased by 38% during increased hematocrit (P < 0.01). These results support the idea that a substantial part of flow switching among pulmonary capillaries is caused by the particulate nature of blood passing through a complex network of tubes with continuously varying hematocrit.