Faculty Bibliography

OBJECTIVE: To assess obstructive sleep apnea syndrome (OSAS) severity among pediatric patients. Design. A retrospective review of charts and polysomnography (PSG) results. MEASUREMENTS AND MAIN RESULTS: Apnea-hypopnea index (AHI) and the cumulative duration of sleep while O(2)SAT was <91% were determined in 389 patients with OSAS. Patients with AHI ranging <5, 5 to 15, 16 to 30, and >30, had mean lowest observed O(2)SAT values of 88% +/- 8%, 85% +/- 9%, 78% +/- 12%, and 69% +/- 13%, respectively. The patients spent a mean of 3.5% +/- 9.2 % of their sleep time with O(2)SAT < 91%. AHI values showed a poor linear correlation with the lowest measured O(2)SAT values. Body mass index percentiles showed no significant linear correlation with AHI values or with the lowest measured values of O(2)SAT. CONCLUSION: Values of AHI cannot accurately predict severity of oxyhemoglobin desaturation in pediatric OSAS and vice versa. No significant correlation between body mass index percentiles and severity of OSAS was established

OBJECTIVE: To compare pressure characteristics of mechanical ventilation and their impact on pediatric patients with severe ARDS in the pre-protective lung strategy (PLS) and post-PLS eras. METHODS: Medical records of 33 patients admitted to our pediatric ICU with ARDS from 1992 through 1994 (pre-PLS) and 52 patients with ARDS admitted from 2000 through 2003 (post-PLS) were retrospectively reviewed. RESULTS: Patient age and gender distribution were identical in both eras. Fifty-five percent of the patients in the pre-PLS era had pneumothorax, compared to 17% in the post-PLS era (p < 0.05). Overall mortality rates for patients in the pre-PLS and post-PLS eras were 42% and 25%, respectively (p = 0.09; not significant). Mean duration of exposure to peak inspiratory pressure (PIP) values > 40 cm H2O was significantly longer in the pre-PLS era than in the post-PLS era. Pre-PLS patients with pneumothorax received mean maximum PIP of 72 +/- 17 cm H2O, mean maximum positive end-expiratory pressure (PEEP) of 20 +/- 5 cm H2O, and maximum mean airway pressure (MAP) of 46 +/- 8 cm H2O, while patients in the post-PLS era required mean maximum PIP of 42 +/- 2 cm H2O, mean maximum PEEP of 14 +/- 2 cm H2O, and maximum MAP of 30 +/- 6 cm H2O, respectively (p < 0.05 for all pressure parameters). There were no significant differences in mechanical ventilation pressure characteristics among patients who did not have pneumothorax during their course of management in both eras. CONCLUSIONS: A significantly more aggressive use of ventilator pressure characteristics distinguished the pre-PLS era from the post-PLS era, and was found to be associated with a markedly higher incidence of pneumothorax. Outcome in both eras did not differ significantly, presumably due to insufficient statistical power

OBJECTIVE: We evaluated whether or not changes in bispectral index (BIS) are associated with concomitant changes in autonomic variables that are in agreement with the different level of sedation that the changes in BIS indicate. DESIGN: A retrospective chart review. SETTING: A pediatric ICU of a children's hospital. Methods and main results: Charts of patients who were receiving mechanical ventilation and IV sedation, neuromuscular blockade, and continuous BIS monitoring were enrolled in the study. Changes in BIS values > or = 30% from previous readings were evaluated to determine whether or not concomitant changes of > or = 10% in autonomic variables, in the same direction, coexisted. Forty-seven patients (35 male and 12 female) were enrolled in our study; ages ranged from 10 days to 18 years (mean, 4.2 +/- 6.2 years [+/- SD]). Twenty-five patients were < 1 year of age (53%). All patients were sedated and pharmacologically paralyzed. Overall, 387 BIS readings (15%) showed a > or = 30% change from the previously documented BIS number. These BIS changes were in agreement with heart rate (HR) changes, mean arterial pressure (MAP) changes, and both HR and MAP changes in 10.6%, 23.8%, and 5.7% of the time, respectively. The same analysis of agreement was done for patients < or = 1 year old, and results were no different from those of older patients. Among 21 patients who were not receiving any vasoactive drugs (alpha- and/or beta-adrenergic agonists) during the study period, 157 BIS recordings (15%) showed a > or = 30% change from the previously documented BIS number. The percents of agreement with HR, MAP, and HR and MAP for these patients were 14.6%, 17.2%, and 7.6%, respectively. In 26 patients who were receiving vasoactive medications during the study, 230 BIS recordings (15%) showed a > or = 30% change from the previously documented BIS number. For these patients, the percentages of agreement were 7.8%, 28.3%, and 4.3%, respectively. Agreement with MAP was significantly better than with HR for this group of patients (p < 0.05; Fisher Exact Test).Summary: While significant changes in BIS are thought to reflect significant changes in depth of sedation, they have a very low rate of agreement with changes in vital signs. In the absence of BIS, the level of sedation of chemically paralyzed pediatric patients can be better guided by changes in MAP than in HR, particularly in patients receiving vasoactive drug treatment

OBJECTIVES: To evaluate changes in oxygenation index (OI) in pediatric patients with ARDS during the first 24 h of prone positioning (PP), and to determine whether or not longer periods of PP (> 12 h) result in a more pronounced improvement in oxygenation. DESIGN: A retrospective chart review of patients with ARDS who had been placed in PP for their management. SETTING: Pediatric ICU of a children's hospital. Measurements and main results: We retrieved the charts of patients with ARDS who had been admitted to our pediatric ICU over a 3-year period and placed in PP for their management. The patients received mechanical ventilation, were sedated and pharmacologically paralyzed, and underwent arterial blood gas analysis, with concomitant documentation of ventilator settings, at a frequency of once every 4 h or more often. We divided the first 24 h of PP into two periods, brief and prolonged. The brief period was defined as duration of PP between 6 h and 10 h, and the prolonged period was between 18 h and 24 h. We compared pre-PP OI values to values after brief periods and prolonged periods of PP. Values of the PaO(2)/fraction of inspired oxygen (P/F) ratio and the mean airway pressure (MAP) were similarly evaluated. We also evaluated the degree of OI fluctuations during 24 h of PP by identifying the time points at which the best OI and the worst OI were observed. Data from a total of 40 pediatric patients with ARDS were evaluated. Twenty-one of the patients were male, and 19 were female; their ages ranged from 1 month to 18 years (mean +/- SD, 6.22 +/- 6.27 years). Thirty-two patients received conventional mechanical ventilation, and 8 patients received high-frequency oscillatory ventilation. Thirty-three patients survived, and 7 patients (21%) died. The mean duration of PP was 67 +/- 64 h (2.8 +/- 2.7 days), the mean number of ventilator days was 32 +/- 32, and the mean interval between endotracheal intubation and placing the patients in PP was 107 +/- 108 h (4.5 +/- 4.5 days). Thirty-seven patients completed 20 h of PP or more. The mean post-PP time points at which OI values were actually evaluated for these patients were 8 +/- 2 h (brief) and 21 +/- 4 h (prolonged), respectively. Overall, the OI decreased from a pre-PP value of 24.8 +/- 13.0 to 16.7 +/- 13.7 after a brief period of PP (p < 0.05 when compared to baseline) and 11.4 +/- 6.3 after prolonged period (p < 0.05 when compared to baseline and brief period values). This improvement in OI followed the improvement seen in the P/F ratio, whereas the MAP remained unchanged. The best mean OI value, with patients in PP, was 11 +/- 9 (p < 0.05 when compared to baseline) that occurred at 16 +/- 6 h, and the worst was 22 +/- 15 (p = not significant when compared to baseline) that occurred at 9 +/- 7 h. CONCLUSIONS: PP of pediatric patients with ARDS for prolonged periods (18 to 24 h) results in a more pronounced and more stable reduction in their OI values than those observed after brief periods (6 to 10 h). This improvement in OI was not associated with changes in MAP during the first 24 h of mechanical ventilation. OI values tend to fluctuate more during the first 12 h of PP then they do during the subsequent 12 h

OBJECTIVE: To test the hypothesis that prone positioning of patients with acute respiratory distress syndrome results in significant cephalad movement of their endotracheal tubes (ETT). DESIGN: A retrospective review of chest radiographs and patient information. SETTING: Pediatric intensive care unit of a children's hospital. MEASUREMENTS AND MAIN RESULTS: Patients with acute respiratory distress syndrome had digital chest radiographs performed before and immediately after prone positioning as per our routine practice. Based on measurements of the length of the thoracic trachea and the length of the thoracic segment of the ETT, the movement of the ETT subsequent to prone positioning was calculated. Fifteen pairs of radiographs of 14 consecutive patients were evaluated. There were seven girls and seven boys, with ages ranging from 2 months to 18 yrs. All patients had a cephalad movement of their ETT ranging from 10% to 57% of their thoracic tracheal length (p < .001) associated with prone positioning. The mean amplitude of this movement was 34% +/- 16%, indicating that if the tip of the ETT is not deeper than one third of the thoracic tracheal length before prone positioning, it might slide into the cervical trachea as a result of this procedure. CONCLUSIONS: Prone positioning results in cephalad movement of ETT within the trachea. The tip of the ETT should be deeper than one third of the total length of the thoracic trachea before prone positioning to prevent it from moving into the cervical trachea. When prone positioning is done with an ETT originally not deeper than one third of the thoracic trachea, obtaining a chest radiograph immediately after prone positioning is important to determine whether the ETT remained safely situated in the trachea

The authors describe a radiographic method to quantify a surgical procedure of thoracic expansion in a 2-year-old patient with achondroplasia, small chest cage, and severe restrictive lung disease. The patient had undergone three surgical procedures of thoracic expansion since birth. The authors utilized computer-generated lung volume histograms after spiral computed tomographic scanning and three-dimensional imaging of the lungs to calculate his lung volumes before and after the third surgical thoracic expansion. The lung volumes, calculated by the histograms, were 363 mL and 406 mL before and after surgery, respectively. This 40-mL difference in the patient's lung volumes (4 mL/kg) accounted for a significant clinical improvement. Lung volume histograms obtained by this radiographic method are very helpful in substantiating a successful surgical chest expansion or provide an explanation for an unsuccessful repair

OBJECTIVE: To determine whether ketamine infusion to mechanically ventilated children with refractory bronchospasm is beneficial. DESIGN: Retrospective chart review. SETTING: Pediatric intensive care unit (PICU) of a children's hospital. PATIENTS: Seventeen patients, ages ranging from 5 months to 17 years (mean 6 +/- 5.7 years), were admitted to our PICU over a 3-year period and received ketamine infusion during a course of mechanical ventilation. The patients had acute respiratory failure associated with severe bronchospasm due to status asthmaticus (n = 11), bronchiolitis caused by respiratory syncytial virus (n = 4), and bacterial pneumonia (n = 2). INTERVENTIONS: All patients had been mechanically ventilated for 1-5 days (2.2 +/- 1.5 days) and received conventional treatment to relieve bronchospasm for more than 24 h prior to the initiation of ketamine treatment. An intravenous bolus of ketamine of 2 mg/kg, followed by continuous infusions of 20-60 micrograms/kg per minute (32 +/- 10 micrograms/kg per minute) was administered to all patients without changing their preexisting bronchodilatory regimen. Benzodiazepines were also given intravenously to all patients during the ketamine treatment. MEASUREMENTS AND MAIN RESULTS: The PaO2/FIO2 ratio in all patients (n = 17) and the dynamic compliance in the volume-preset mechanically ventilated patients (n = 12) were calculated. The PaO2/FIO2 ratio increased significantly from 116 +/- 55 before ketamine, to 174 +/- 82, 269 +/- 151, and 248 +/- 124 at 1, 8, and 24 h respectively, after the initiation of the ketamine infusion (p < 0.0001). Dynamic compliance increased from 5.78 +/- 2.8 cm3/cmH2O to 7.05 +/- 3.39, 7.29 +/- 3.37, and 8.58 +/- 3.69, respectively (p < 0.0001). PaCO2 and peak inspiratory pressure followed a similar trend of improvement with ketamine administration. The mean duration of the ketamine infusion was 40 +/- 31 h. One patient required glycopyrrolate 0.4 mg/day to control excessive airway secretions and one patient required an additional dose of diazepam to control hallucinations while emerging from ketamine. All patients were successfully weaned from mechanical ventilation and discharged from the PICU. CONCLUSION: Continuous infusion of ketamine to mechanically ventilated patients with refractory bronchospasm significantly improves gas exchange and dynamic compliance of the chest.

To test the hypothesis that naloxone exerts a direct positive inotropic effect on the cardiac muscle, we employed two in vitro models. In one set of experiments we demonstrated that injection of 1 mg naloxone into an isolated perfused rat heart produced a significant increase in the amplitude of contraction. In another set of experiments we exposed an isolated and spontaneously contracting rat right atrium in a tissue bath to naloxone, and demonstrated that the amplitude of contraction increased significantly within a few minutes of naloxone administration. We showed that this effect of naloxone was not related to opiate receptors, since a similar effect was obtained with d-naloxone (the stereoisomer that is inactive as an opiate antagonist) and it was not affected by pretreatment with morphine. We also demonstrated that addition of alpha- and beta-adrenergic antagonists phentolamine and propranolol, in doses that effectively block alpha- and beta-adrenergic agonists, did not have any effect on naloxone's inotropic action. We validated our results in two electrically driven strips of human atrial myocardium in the tissue bath. A positive inotropic response to naloxone, measured as an increase of 80 and 50% in the amplitude of contraction, was noted. We postulate that naloxone's previously described cardiovascular pressor effect in states of shock may not only be related to reversal of the effects of endorphins but also to its direct inotropic action.