Ventilator Weaning and Terminal Extubation: Withdrawal of Life-Sustaining Therapy in Children. Secondary Analysis of the Death One Hour After Terminal Extubation Study

OBJECTIVE

Terminal extubation (TE) and terminal weaning (TW) during withdrawal of life-sustaining therapies (WLSTs) have been described and defined in adults. The recent Death One Hour After Terminal Extubation study aimed to validate a model developed to predict whether a child would die within 1 hour after discontinuation of mechanical ventilation for WLST. Although TW has not been described in children, pre-extubation weaning has been known to occur before WLST, though to what extent is unknown. In this preplanned secondary analysis, we aim to describe/define TE and pre-extubation weaning (PW) in children and compare characteristics of patients who had ventilatory support decreased before WLST with those who did not.

DESIGN

Secondary analysis of multicenter retrospective cohort study.

SETTING

Ten PICUs in the United States between 2009 and 2021.

PATIENTS

Nine hundred thirteen patients 0-21 years old who died after WLST.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

71.4% ( n = 652) had TE without decrease in ventilatory support in the 6 hours prior. TE without decrease in ventilatory support in the 6 hours prior = 71.4% ( n = 652) of our sample. Clinically relevant decrease in ventilatory support before WLST = 11% ( n = 100), and 17.6% ( n = 161) had likely incidental decrease in ventilatory support before WLST. Relevant ventilator parameters decreased were F io2 and/or ventilator set rates. There were no significant differences in any of the other evaluated patient characteristics between groups (weight, body mass index, unit type, primary diagnostic category, presence of coma, time to death after WLST, analgosedative requirements, postextubation respiratory support modality).

CONCLUSIONS

Decreasing ventilatory support before WLST with extubation in children does occur. This practice was not associated with significant differences in palliative analgosedation doses or time to death after extubation.

Effort and work-of-breathing parameters strongly correlate with increased resistance in an animal model

BACKGROUND

Effort of Breathing (EOB) calculations may be a reliable alternative to Work of Breathing (WOB) calculations in which Respiratory Inductance Plethysmography (RIP) replaces spirometry. We sought to compare EOB and WOB measurements in a nonhuman primate model of increasing extrathoracic inspiratory resistance simulating upper airway obstruction (UAO).

METHODS

RIP, spirometry, and esophageal manometry were measured in spontaneously breathing, intubated Rhesus monkeys utilizing 11 calibrated resistors randomly applied for 2-min. EOB was calculated breath-by-breath as Pressure Rate Product (PRP) and Pressure Time Product (PTP). WOB was calculated from the Pressure-Volume curve based on spirometry (WOBSPIR) or RIP flow (WOBRIP).

RESULTS

WOB, PRP and PTP showed similar linear increases when exposed to higher levels of resistive loads. When comparing WOBSPIR to WOBRIP, a similar strong correlation was seen for both signals as resistance increased and there were no statistically significant differences.

CONCLUSION

EOB and WOB parameters utilizing esophageal manometry and RIP, independent of spirometry, showed a strong correlation as a function of increasing inspiratory resistance in nonhuman primates. This allows several potential monitoring possibilities for non-invasively ventilated patients or situations where spirometry is not available.

IMPACT

EOB and WOB parameters showed a strong correlation as a function of increasing inspiratory resistance in nonhuman primates. There was a strong correlation between spirometry-based WOB versus RIP-based WOB. To date, it has remained untested as to whether EOB is a reliable alternative for WOB and if RIP can replace spirometry in these measurements. Our results enable additional potential monitoring possibilities for non-invasively ventilated patients or situations where spirometry is not available. Where spirometry is not available, there is no need to apply a facemask post extubation to a spontaneously breathing, non-intubated infant to make objective EOB measurements.

PICU admission and complications following adenotonsillectomies in pediatric patients: A retrospective cohort study

BACKGROUND

Children with obstructive sleep apnea (OSA) have higher risks of post-operative respiratory complication after adenotonsillectomy. However, there is no clinical standard criteria for pediatric intensive care unit (PICU) admission following adenotonsillectomy. The purpose of this study was to identify perioperative risk factors associated with the need for PICU level care after adenotonsillectomy.

METHODS

We performed a retrospective chart review of children with severe OSA (apnea hypopnea index on polysomnography; AHI ≥10) and/or post-operative PICU admission at a tertiary academic center from May 2010 to September 2018. We collected demographics, pre-existing comorbidities, perioperative medications, and post-operative complications. We defined a primary outcome as escalation of airway management while in the PICU or PICU stay >48 h. Airway escalation included the need for an invasive airway, new CPAP application, increased CPAP setting, or increased supplemental oxygen.

RESULTS

Analysis included 278 children with severe OSA and/or PICU admission. Median age was 6.6 years old; 181 (65%) were admitted to the PICU, and 60 (21.5%) had the composite outcome of escalation of airway management or prolonged stay. In patients with an escalation of airway management, 28 needed intubation or mechanical ventilation. Multivariable logistic regression showed intraoperative respiratory complications, polysomnography (PSG) peak end-tidal CO₂ (EtCO₂) reading >60 mmHg, and the presence of neuromuscular disease as significant associated factors for escalation of airway management or prolonged PICU stay (P values < 0.01; odd ratios 3.4, 5.3, and 5.4, respectively).

CONCLUSION

For children following adenotonsillectomy, PSG EtCO₂ ≥ 60%, preexisting neuromuscular disease, and intraoperative complications (hypoxia, difficult airway, etc.) were independently associated with escalation of airway management or prolonged stay. AHI was not an independent predictor for PICU complication. We concluded factors should be considered for PICU admission in addition to AHI.

Directing CAR NK Cells via the Metabolic Incorporation of CAR Ligands into Malignant Cell Glycans

The abundance of sialic acid-containing glycans in the glycocalyx of malignant cells enables immune evasion. Here, we leverage the biosynthetic pathways that permit pervasive sialylation to incorporate a chimeric antigen receptor (CAR) ligand into malignant cell glycans, and demonstrate that this increases the susceptibility of malignant cells to the cytolytic activity of CAR-expressing natural killer (NK) cells. Specifically, we applied a C-9-functionalized nonnatural sialic acid [i.e., fluorescein sialic acid (FL-SA)] to modify malignant cell glycans. We confirm the metabolic incorporation of FL-SA into plasma membrane-associated glycans. The preparation of anti-fluorescein CAR NK cells permitted studies demonstrating that treating malignant cells with FL-SA increased susceptibility to CAR NK cell-mediated cytolysis. Furthermore, we observed that the specificity of the anti-fluorescein CAR NK cells is enhanced for fluorescein-labeled cells, and an increased release of cytokines from the CAR NK cells upon incubation with FL-SA-treated cells. The results arising from this study demonstrate that CAR ligands can be metabolically incorporated into malignant cells, and we reason that such strategies could be leveraged to tackle the issue of antigen heterogeneity that limits the clinical efficacy of CAR T/NK cell therapies.

Subglottic Post-Extubation Upper Airway Obstruction Is Associated With Long-Term Airway Morbidity in Children

OBJECTIVES

Post-extubation upper airway obstruction is the most common cause of extubation failure in children, but there are few data regarding long-term morbidity. We aim to describe the frequency of long-term airway sequelae in intubated children and determine the association with post-extubation upper airway obstruction.

DESIGN

Retrospective, post hoc analysis of previously identified prospective cohort of children in the pediatric/cardiothoracic ICU at Children's Hospital Los Angeles from July 2012 to April 2015. A single provider blinded to the upper airway obstruction classification reviewed the electronic medical records of all patients in the parent study, before and after the index extubation (extubation during parent study), to identify pre-index and post-index upper airway disease. Primary outcomes were prevalence of newly diagnosed airway anomalies following index extubation.

SETTING

Single center, tertiary, 391-bed children's hospital.

PATIENTS

From the parent study, 327 children younger than 18 years (intubated for at least 12 hr) were included if they received subsequent care (regardless of specialty) after the index extubation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

New airway anomalies were identified in 40 of 327 children (12.2%). Patients labeled with subglottic upper airway obstruction at the index extubation were more likely to be diagnosed with new airway anomalies on subsequent follow-up, receive long-term Otolaryngology follow-up, or receive airway surgery (all p ≤ 0.006). In multivariable modeling, upper airway obstruction as the primary reason for initial intubation (odds ratio, 3.71; CI, 1.50-9.19), reintubation during the index ICU admission (odds ratio, 4.44; CI, 1.67-11.80), pre-index airway anomaly (odds ratio, 3.31; CI, 1.36-8.01), and post-extubation subglottic upper airway obstruction (odds ratio, 3.50; CI, 1.46-8.34) remained independently associated with the diagnosis of new airway anomalies.

CONCLUSIONS

Post-extubation subglottic upper airway obstruction is associated with a three-fold greater odds of long-term airway morbidity. These patients may represent an at-risk population that should be monitored closely after leaving the ICU.

Machine Learning to Predict Cardiac Death Within 1 Hour After Terminal Extubation

OBJECTIVES

Accurate prediction of time to death after withdrawal of life-sustaining therapies may improve counseling for families and help identify candidates for organ donation after cardiac death. The study objectives were to: 1) train a long short-term memory model to predict cardiac death within 1 hour after terminal extubation, 2) calculate the positive predictive value of the model and the number needed to alert among potential organ donors, and 3) examine associations between time to cardiac death and the patient's characteristics and physiologic variables using Cox regression.

DESIGN

Retrospective cohort study.

SETTING

PICU and cardiothoracic ICU in a tertiary-care academic children's hospital.

PATIENTS

Patients 0-21 years old who died after terminal extubation from 2011 to 2018 (n = 237).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The median time to death for the cohort was 0.3 hours after terminal extubation (interquartile range, 0.16-1.6 hr); 70% of patients died within 1 hour. The long short-term memory model had an area under the receiver operating characteristic curve of 0.85 and a positive predictive value of 0.81 at a sensitivity of 94% when predicting death within 1 hour of terminal extubation. About 39% of patients who died within 1 hour met organ procurement and transplantation network criteria for liver and kidney donors. The long short-term memory identified 93% of potential organ donors with a number needed to alert of 1.08, meaning that 13 of 14 prepared operating rooms would have yielded a viable organ. A Cox proportional hazard model identified independent predictors of shorter time to death including low Glasgow Coma Score, high Pao2-to-Fio2 ratio, low-pulse oximetry, and low serum bicarbonate.

CONCLUSIONS

Our long short-term memory model accurately predicted whether a child will die within 1 hour of terminal extubation and may improve counseling for families. Our model can identify potential candidates for donation after cardiac death while minimizing unnecessarily prepared operating rooms.

Engaging Parents in Analgesia Selection and Racial/Ethnic Differences in Analgesia Given to Pediatric Patients Undergoing Urologic Surgery

BACKGROUND

Family-centered care aims to consider family preferences and values in care delivery. Our study examines parent decisions regarding anesthesia type (caudal regional block or local anesthesia) among a diverse sample of children undergoing urologic surgeries. Differences in anesthesia type were examined by known predictors of health disparities, including child race/ethnicity, parental English proficiency, and a proxy for household income.

METHODS

A retrospective review of 4739 patients (including 25.4% non-Latino/a White, 8.7% non- Latino/a Asians, 7.3% non-Latino/a Black, 23.1% Latino/a, and 35.4% others) undergoing urologic surgeries from 2016 to 2020 using univariate and logistic regression analyses.

RESULTS

62.1% of Latino/a parents and 60.8% of non-Latino/a Black parents did not agree to a regional block. 65.1% of Spanish-speaking parents with limited English Proficiency did not agree to a regional block. Of parents from households below poverty lines, 61.7% did not agree to a caudal regional block. In regression analysis, Latino/a and non- Latino/a Black youth were less likely to receive caudal regional block than non- Latino/a White patients.

CONCLUSIONS

We found disparities in the use of pediatric pain management techniques. Understanding mechanisms underlying Latino/a and non- Latino/a Black parental preferences may help providers reduce these disparities.

Thresholds for oximetry alarms and target range in the NICU: an observational assessment based on likely oxygen tension and maturity

BACKGROUND

Continuous monitoring of SpO₂ in the neonatal ICU is the standard of care. Changes in SpO₂ exposure have been shown to markedly impact outcome, but limiting extreme episodes is an arduous task. Much more complicated than setting alarm policy, it is fraught with balancing alarm fatigue and compliance. Information on optimum strategies is limited.

METHODS

This is a retrospective observational study intended to describe the relative chance of normoxemia, and risks of hypoxemia and hyperoxemia at relevant SpO₂ levels in the neonatal ICU. The data, paired SpO₂-PaO₂ and post-menstrual age, are from a single tertiary care unit. They reflect all infants receiving supplemental oxygen and mechanical ventilation during a 3-year period. The primary measures were the chance of normoxemia (PaO₂ 50-80 mmHg), risks of severe hypoxemia (PaO₂ ≤ 40 mmHg), and of severe hyperoxemia (PaO₂ ≥ 100 mmHg) at relevant SpO₂ levels.

RESULTS

Neonates were categorized by postmenstrual age: < 33 (n = 155), 33-36 (n = 192) and > 36 (n = 1031) weeks. From these infants, 26,162 SpO₂-PaO₂ pairs were evaluated. The post-menstrual weeks (median and IQR) of the three groups were: 26 (24-28) n = 2603; 34 (33-35) n = 2501; and 38 (37-39) n = 21,058. The chance of normoxemia (65, 95%-CI 64-67%) was similar across the SpO₂ range of 88-95%, and independent of PMA. The increasing risk of severe hypoxemia became marked at a SpO₂ of 85% (25, 95%-CI 21-29%), and was independent of PMA. The risk of severe hyperoxemia was dependent on PMA. For infants < 33 weeks it was marked at 98% SpO₂ (25, 95%-CI 18-33%), for infants 33-36 weeks at 97% SpO₂ (24, 95%-CI 14-25%) and for those > 36 weeks at 96% SpO₂ (20, 95%-CI 17-22%).

CONCLUSIONS

The risk of hyperoxemia and hypoxemia increases exponentially as SpO₂ moves towards extremes. Postmenstrual age influences the threshold at which the risk of hyperoxemia became pronounced, but not the thresholds of hypoxemia or normoxemia. The thresholds at which a marked change in the risk of hyperoxemia and hypoxemia occur can be used to guide the setting of alarm thresholds. Optimal management of neonatal oxygen saturation must take into account concerns of alarm fatigue, staffing levels, and FiO₂ titration practices.

Impact of Anesthetic and Ventilation Strategies on Invasive Hemodynamic Measurements in Pediatric Heart Transplant Recipients

BACKGROUND

Care of pediatric heart transplant recipients relies upon serial invasive hemodynamic evaluation, generally performed under the artificial conditions created by anesthesia and supportive ventilation.

OBJECTIVES

This study aimed to evaluate the hemodynamic impacts of different anesthetic and ventilatory strategies.

METHODS

We compared retrospectively the cardiac index, right- and left-sided filling pressures, and pulmonary and systemic vascular resistances of all clinically well and rejection-free heart transplant recipients catheterized from 2005 through 2017. Effects of spontaneous versus positive pressure ventilation and of sedation versus general anesthesia were tested with generalized linear mixed models for repeated measures using robust sandwich estimators of the covariance matrices. Least squared means showed adjusted mean outcome values, controlled for appropriate confounders.

RESULTS

720 catheterizations from 101 recipients met inclusion criteria. Adjusted cardiac index was 3.14 L/min/m² (95% CI 3.01-3.67) among spontaneously breathing and 2.71 L/min/m² (95% CI 2.56-2.86) among ventilated recipients (p < 0.0001). With spontaneous breathing, left filling pressures were lower (9.9 vs 11.0 mmHg, p = 0.030) and systemic vascular resistances were higher (24.0 vs 20.5 Woods units, p < 0.0001). After isolating sedated from anesthetized spontaneously breathing patients, the observed differences in filling pressures and resistances emerged as a function of sedation versus general anesthesia rather than of spontaneous versus positive pressure ventilation.

CONCLUSION

In pediatric heart transplant recipients, positive pressure ventilation reduces cardiac output but does not alter filling pressures or vascular resistances. Moderate sedation yields lower left filling pressures and higher systemic vascular resistances than does general anesthesia. Differences are quantitatively small.

A Phase II randomized controlled trial for lung and diaphragm protective ventilation (Real-time Effort Driven VENTilator management)

Lung Protective Mechanical Ventilation (MV) of critically ill adults and children is lifesaving but it may decrease diaphragm contraction and promote Ventilator Induced Diaphragm Dysfunction (VIDD). An ideal MV strategy would balance lung and diaphragm protection. Building off a Phase I pilot study, we are conducting a Phase II controlled clinical trial that seeks to understand the evolution of VIDD in critically ill children and test whether a novel computer-based approach (Real-time Effort Driven ventilator management (REDvent)) can balance lung and diaphragm protective ventilation to reduce time on MV. REDvent systematically adjusts PEEP, FiO₂, inspiratory pressure, tidal volume and rate, and uses real-time measures from esophageal manometry to target normal levels of patient effort of breathing. This trial targets 276 children with pulmonary parenchymal disease. Patients are randomized to REDvent vs. usual care for the acute phase of MV (intubation to first Spontaneous Breathing Trial (SBT)). Patients in either group who fail their first SBT will be randomized to REDvent vs usual care for weaning phase management (interval from first SBT to passing SBT). The primary clinical outcome is length of weaning, with several mechanistic outcomes. Upon completion, this study will provide important information on the pathogenesis and timing of VIDD during MV in children and whether this computerized protocol targeting lung and diaphragm protection can lead to improvement in intermediate clinical outcomes. This will form the basis for a larger, Phase III multi-center study, powered for key clinical outcomes such as 28-day ventilator free days. Clinical Trials Registration: NCT03266016.

Body Habitus and Risk of Mortality in Pediatric Sepsis and Septic Shock: A Retrospective Cohort Study

OBJECTIVE

To investigate the association between body habitus and mortality in critically ill children with sepsis or septic shock.

STUDY DESIGN

This was a retrospective cohort study of prospectively collected data of children admitted to US pediatric intensive care units (PICUs) with a primary or secondary diagnosis of sepsis or septic shock. We separated body habitus into underweight, normal weight, overweight, and obese. Outcomes were mortality (primary), treatment with invasive mechanical ventilation (secondary), and time to PICU discharge for survivors (secondary). Multivariable analyses using mixed-effects logistic regression and shared frailty models clustered by unit and adjusted for confounding variables were used to assess the association between body habitus and outcomes.

RESULTS

There were 7038 children with sepsis or septic shock. Mortality was 10.1% (n = 714) and 52.9% (n = 3720) required invasive mechanical ventilation. Body habitus was not associated with mortality after controlling for hospital level effects and confounding variables. Children who were overweight and obese had greater odds of invasive mechanical ventilation (overweight OR 1.23 [95% CI 1.05-1.45], P = .011 and obese OR 1.57 [95% CI 1.37-1.80], P < .001) compared with children of normal weight. In survivors treated with invasive mechanical ventilation, children who were obese had a longer time to PICU discharge than children of normal weight (obese hazard ratio for discharge 0.84 [95% CI, 0.77-0.92], P < .0001).

CONCLUSIONS

There was no association between body habitus and mortality in critically ill children with sepsis. Children who were overweight and obese were more likely to receive invasive mechanical ventilation and mechanically ventilated survivors who were obsese had a longer time to PICU discharge.

Hypoxemic and hyperoxemic likelihood in pulse oximetry ranges: NICU observational study

OBJECTIVE

Describe the likelihood of hypoxemia and hyperoxemia across ranges of oxygen saturation (SpO₂), during mechanical ventilation with supplemental oxygenation.

DESIGN

Retrospective observational study.

SETTING

University affiliated tertiary care neonatal intensive care unit.

PATIENTS

Two groups of neonates based on postmenstrual age (PMA): <32 weeks (n=104) and >36 weeks (n=709).

MAIN MEASURES

Hypoxemia was defined as a PaO₂ <40 mm Hg, hyperoxemia as a PaO₂ of >99 mm Hg and normoxemia as a PaO₂ of 50-80 mm Hg. Twenty-five per cent was defined as marked likelihood of hypoxemia or hyperoxemia.

RESULTS

From these infants, 18 034 SpO₂-PaO₂ pairs were evaluated of which 10% were preterm. The PMA (median and IQR) of the two groups were: 28 weeks (27-30) and 40 weeks (38-41). With SpO₂ levels between 90% and 95%, the likelihoods of hypoxemia and hyperoxemia were low and balanced. With increasing levels of SpO₂, the likelihood of hyperoxemia increased. It became marked in the preterm group when SpO₂ was 99%-100% (95% CI 29% to 41%) and in the term group with SpO₂ levels of 96%-98% (95% CI 29% to 32%). The likelihood of hypoxemia increased as SpO₂ decreased. It became marked in both with SpO₂ levels of 80%-85% (95% CI 20% to 31%, 24% to 28%, respectively).

CONCLUSIONS

The likelihood of a PaO₂ <40 mm Hg is marked with SpO₂ below 86%. The likelihood of a PaO₂ >99 mm Hg is marked in term infants with SpO₂ above 95% and above 98% in preterm infants. SpO₂ levels between 90% and 95% are appropriate targets for term and preterm infants.

Minimal Change in Cardiac Index With Increasing PEEP in Pediatric Acute Respiratory Distress Syndrome

Objective: To determine if increasing positive end expiratory pressure (PEEP) leads to a change in cardiac index in children with Pediatric Acute Respiratory Distress Syndrome ranging from mild to severe. Design: Prospective interventional study. Setting: Multidisciplinary Pediatric Intensive Care Unit in a University teaching hospital. Patients: Fifteen intubated children (5 females, 10 males) with a median age of 72 months (IQR 11, 132) and a median weight of 19.3 kg (IQR 7.5, 53.6) with a severity of Pediatric Acute Respiratory Distress Syndrome that ranged from mild to severe with a median lung injury score of 2.3 (IQR 2.0, 2.7). Measurements: Cardiac index (CI) and stroke volume (SV) were measured on baseline ventilator settings and subsequently with a PEEP 4 cmH₂O higher than baseline. Change in CI and SV from baseline values was evaluated using Wilcoxon signed rank test. Results: A total of 19 paired measurements obtained. The median baseline PEEP was 8 cmH₂O (IQR 8, 10) Range 6-14 cmH₂O. There was no significant change in cardiac index or stroke volume with change in PEEP. Baseline median CI 4.4 L/min/m² (IQR 3.4, 4.8) and PEEP 4 higher median CI of 4.3 L/min/m² (IQR 3.6, 4.8), p = 0.65. Baseline median SV 26 ml (IQR 13, 44) and at PEEP 4 higher median SV 34 ml (IQR 12, 44) p = 0.63. Conclusion: There is no significant change in cardiac index or stroke volume with increasing PEEP by 4 cmH₂O in a population of children with mild to severe PARDS. Clinical Trial Registration: The study is registered on Clinical trails.gov under the Identifier: NCT02354365.

Does Size Matter When Calculating the "Correct" Tidal Volume for Pediatric Mechanical Ventilation?: A Hypothesis Based on FVC

BACKGROUND

Tidal volumes standardized to predicted body weight are recommended for adult mechanical ventilation, but children are frequently ventilated by using measured body weight. The goal of this study was to examine the difference in FVC (in milliliters per kilogram [mL/kg]) by using measured body weight compared with predicted body weight in children.

METHODS

This retrospective analysis included outpatient pulmonary function tests (PFTs) from two datasets. Dataset one included 6- to 19-year-old patients undergoing PFTs from the nationally representative Canadian Health Measures Survey. Dataset two included 6- to 20-year-old patients undergoing PFTs at a freestanding children's hospital. FVC mL/kg values were analyzed against BMI z scores to show changes in FVC vs BMI between measured and predicted weight.

RESULTS

Dataset one included 5,394 PFTs from the Canadian survey. FVC from measured weight decreased as the BMI z score group increased. The median FVC from measured weight was 81.4 mL/kg in the lowest BMI z score group and 51.7 mL/kg in the highest BMI z score group. FVC from predicted weight increased slightly with increasing BMI z score group. Dataset two included 8,472 patient PFTs from clinical measurement. A decline in median FVC from measured weight (from 69.4 to 37.6 mL/kg) as BMI z score group increased was also seen.

CONCLUSIONS

FVC differs significantly when standardizing to measured weight vs predicted weight. Obese children have lung volumes reflecting their predicted body weight from height. Children with low or normal BMI have lung volumes reflecting measured body weight. These findings suggest that targeting tidal volume by using the lower of measured and predicted body weights would be the most lung-protective strategy.

Declining Procedures by Pediatric Critical Care Medicine Fellowship Trainees

Background: Pediatric Critical Care Medicine Fellowship trainees need to acquire skills to perform procedures. Over the last several years there have been advances that allowed for less invasive forms of interventions. Objective: Our hypothesis was that over the past decade the rate of procedures performed by Pediatric Critical Care Medicine Fellowship trainees decreased. Methods: Retrospective review at a single institution, tertiary, academic, children's hospital of patients admitted from July 1, 2007-June 30, 2017 to the Pediatric Intensive Care Unit and Cardiothoracic Intensive Care Unit. A Poisson regression model with a scale adjustment for over-dispersion estimated by the square root of Pearson's Chi-Square/DOF was applied. Results: There has been a statistically significant decrease in the average rate of central venous lines (p = 0.004; -5.72; 95% CI: -9.45, -1.82) and arterial lines (p = 0.02; -7.8; 95% CI: -13.90, -1.25) per Fellow per years in Fellowship over the last 10 years. There was no difference in the rate of intubations per Fellow per years in Fellowship (p = 0.27; 1.86; 95% CI:-1.38, 5.24). Conclusions: There has been a statistically significant decrease in the rate of central venous lines and arterial lines performed by Pediatric Critical Care Medicine Fellowship trainees per number of years in Fellowship over the last 10 years. Educators need to be constantly reassessing the clinical landscape in an effort to make sure that trainees are receiving adequate educational experiences as this has the potential for an impact on the education of trainees and the safety of the patients that they care for.

Predicting Body Height in a Pediatric Intensive Care Unit Using Ulnar Length

Objective: To determine if ulnar length obtained by the bedside nurse can be used to estimate patient length. To compare our findings to previous predictive equations of height and ulnar length. To evaluate the performance of predictive equations for height and ulnar length on patients with syndromes that affect height. Design: Retrospective observational study of prospectively collected data. Settings: Multidisciplinary Pediatric Intensive Care Unit in a university teaching hospital. Patients: 1,177 patients, ages 1 month to 23 years. Mean age was 79.7 months (1,3 IQR 19.5, 164.5 months) and 55.4% male. Measurements: Ulnar length was obtained using digital calipers by bedside nurses in PICU as well as height and weight. The electronic health care record was used to extract patient information. Main Results: The predictive equation for height for the entire group is: height (cm) = 0.59^*ulnar length (mm) + 13.1 (r² = 0.93). Bland Altman analysis of the derivation formula applied to the testing group did not show any systematic bias. Conclusions: Our study shows that ulnar length measurements can be used to predict height with a simple linear formula in a PICU setting. Not having specific individuals or specific training for ulnar measurement did not seem to alter the accuracy (r² = 0.93). The robust nature of the measurement and ease of use may make this an unconventional but reasonable alternative to obtaining height when that cannot be measured directly.

The Relationship between High Flow Nasal Cannula Flow Rate and Effort of Breathing in Children

OBJECTIVE

To use an objective metric of effort of breathing to determine optimal high flow nasal cannula (HFNC) flow rates in children <3 years of age.

STUDY DESIGN

Single-center prospective trial in a 24-bed pediatric intensive care unit of children <3 years of age on HFNC. We measured the percent change in pressure∙rate product (PRP) (an objective measure of effort of breathing) as a function of weight-indexed flow rates of 0.5, 1.0, 1.5, and 2.0 L/kg/minute. For a subgroup of patients, 2 different HFNC delivery systems (Fisher & Paykel [Auckland, New Zealand] and Vapotherm [Exeter, New Hampshire]) were compared.

RESULTS

Twenty-one patients (49 titration episodes) were studied. The most common diagnoses were bronchiolitis and pneumonia. Overall, there was a significant difference in the percent change in PRP from baseline (of 0.5 L/kg/minute) with increasing flow rates for the entire cohort (P < .001) with largest change at 2.0 L/kg/min (-21%). Subgroup analyses showed no significant difference in percent change in PRP from baseline when comparing the 2 different HFNC delivery systems (P = .12). Patients ≤8 kg experienced a larger percent change in PRP as HFNC flow rates were increased (P = .001) than patients >8 kg.

CONCLUSIONS

The optimal HFNC flow rate to reduce effort of breathing in infants and young children is approximately 1.5-2.0 L/kg/minute with more benefit seen in children ≤8 kg.

Comparison of Effort of Breathing for Infants on Nasal Modes of Respiratory Support

OBJECTIVE

To directly compare effort of breathing between high flow nasal cannula (HFNC), nasal intermittent mechanical ventilation (NIMV), and nasal continuous positive airway pressure (NCPAP).

STUDY DESIGN

This was a single center prospective cross-over study for patients <6 months in the cardiothoracic or pediatric intensive care unit receiving nasal noninvasive respiratory support after extubation. We measured effort of breathing using esophageal manometry with pressure-rate product (PRP) on all 3 modes. NIMV synchrony was determined by comparing patient efforts (esophageal manometry) with mechanically delivered breaths (spirometry in ventilator circuit). On NIMV, PRP and synchrony was also measured after adding a nasal clip on 26 patients.

RESULTS

Forty-two children were included. Median (IQR) age was 2 (0.5, 4) months. There was no difference in median PRP between HFNC 6 liters per minute, 355 (270,550), NIMV 12/5 cm H₂O, 341 (235, 472), and NCPAP 5 cm H₂O, 340 (245,506) (P?=?.33). Results were similar regardless of HFNC flow rate or NIMV inspiratory pressure. Median PRP on CPAP of 5 cm H₂O prior to extubation 255 (176, 375) was significantly lower than all postextubation values (P?<?.002). On NIMV, less than 50% of patient efforts resulted in a ventilator breath, which was not improved with a nasal clip (P?>?.07)). However, as NIMV synchrony improved (>60%), PRP on NIMV was lower than on HFNC.

CONCLUSIONS

For infants, effort of breathing is similar on HFNC, NIMV, and NCPAP after extubation, regardless of flow rate or inspiratory pressure. We speculate that bi-level NIMV may be superior if high levels of synchrony can be achieved.

Change in Oxygen Consumption Following Inhalation of Albuterol in Comparison with Levalbuterol in Healthy Adult Volunteers

BACKGROUND

Albuterol is the most commonly used β agonist to treat reversible lower airway obstruction. Albuterol contains a racemic mixture of two enantiomers. Levalbuterol contains the single R form enantiomer. Levalbuterol is frequently prescribed to limit cardiovascular toxicity.

OBJECTIVE

We examined changes in oxygen consumption (V'O₂) and heart rate (HR) following administration of albuterol and levalbuterol.

METHODS

This is a prospective, randomized, single-blinded, controlled study of healthy adult volunteers. Subjects separately received albuterol (5 mg) and levalbuterol (2.5 mg) aerosolized over 15 min. V'O₂ and vital signs were measured before the medications and 5, 10, 20, 40, and 60 min after.

RESULTS

We enrolled 24 volunteers with a median age of 32 years. Compared to baseline, there was a significant maximum increase in V'O₂ following administration of both albuterol (median 17% (1, 3 IQR 9, 43%) p < 0.001) and levalbuterol (median 23% (1, 3 IQR 10, 32%) p < 0.001). There was no significant difference between the maximum increase in V'O₂ following administration of albuterol compared to levalbuterol (p = 0.57). Compared to baseline, there was a significant maximal increase in HR with both albuterol (median 30% (1, 3 IQR 19, 43%) p < 0.001) and levalbuterol (median 23% (1, 3 IQR 19, 31%) p < 0.001). There was a statistically significant greater increase in maximal HR following administration of albuterol as compared to levalbuterol (p = 0.009).

CONCLUSION

Albuterol and levalbuterol both cause a significant increase in V'O₂ and HR. There was no significant difference between albuterol and levalbuterol regarding the maximum increase in V'O₂. There was a statistically significant but likely clinically insignificant difference in maximum increase in HR in patients with adequate oxygen delivery when comparing albuterol to levalbuterol.

Evaluating Risk Factors for Pediatric Post-extubation Upper Airway Obstruction Using a Physiology-based Tool

RATIONALE

Subglottic edema is the most common cause of pediatric extubation failure, but few studies have confirmed risk factors or prevention strategies. This may be due to subjective assessment of stridor or inability to differentiate supraglottic from subglottic disease.

OBJECTIVES

Objective 1 was to assess the utility of calibrated respiratory inductance plethysmography (RIP) and esophageal manometry to identify clinically significant post-extubation upper airway obstruction (UAO) and differentiate subglottic from supraglottic UAO. Objective 2 was to identify risk factors for subglottic UAO, stratified by cuffed versus uncuffed endotracheal tubes (ETTs).

METHODS

We conducted a single-center prospective study of children receiving mechanical ventilation. UAO was defined by inspiratory flow limitation (measured by RIP and esophageal manometry) and classified as subglottic or supraglottic based on airway maneuver response. Clinicians performed simultaneous blinded clinical UAO assessment at the bedside.

MEASUREMENTS AND MAIN RESULTS

A total of 409 children were included, 98 of whom had post-extubation UAO and 49 (12%) of whom were subglottic. The reintubation rate was 34 (8.3%) of 409, with 14 (41%) of these 34 attributable to subglottic UAO. Five minutes after extubation, RIP and esophageal manometry better identified patients who subsequently received UAO treatment than clinical UAO assessment (P < 0.006). Risk factors independently associated with subglottic UAO included low cuff leak volume or high preextubation leak pressure, poor sedation, and preexisting UAO (P < 0.04) for cuffed ETTs; and age (range, 1 mo to 5 yr) for uncuffed ETTs (P < 0.04). For uncuffed ETTs, the presence or absence of preextubation leak was not associated with subglottic UAO.

CONCLUSIONS

RIP and esophageal manometry can objectively identify subglottic UAO after extubation. Using this technique, preextubation leak pressures or cuff leak volumes predict subglottic UAO in children, but only if the ETT is cuffed.

Obesity and Mortality Risk in Critically Ill Children

BACKGROUND AND OBJECTIVES

Childhood obesity is epidemic and may be associated with PICU mortality. Using a large multicenter PICU database, we investigated the association between obesity and PICU mortality, adjusting for initial severity of illness. We further investigated whether height- and weight-based classifications of obesity compared with a weight-based classification alone alter the mortality distribution.

METHODS

This retrospective analysis used prospectively collected data from the Virtual PICU Systems database. Height, weight, age, and gender were used to calculate z score groups based on Centers for Disease Control and Prevention and World Health Organization growth curves. A random effects mixed logistic regression model was used to evaluate the association between obesity and PICU mortality, controlling for hospital, initial severity of illness, and comorbidities.

RESULTS

A total of 127,607 patients were included; the mortality rate was 2.48%. Being overweight was independently associated with increased PICU mortality after controlling for severity of illness with the Pediatric Index of Mortality 2 score and preexisting comorbidities. Mortality had a U-shaped distribution when classified according to weight-for-age or weight-for-height/BMI. When classifying patients using weight-for-age without respect to height, the nadir of the mortality curve was shifted, potentially falsely implying a benefit to mild obesity.

CONCLUSIONS

Risk-adjusted PICU mortality significantly increases as weight-for-height/BMI increases into the overweight and obese ranges. We believe that height data are necessary to correctly classify body habitus; without such information, a protective benefit from mild obesity may be incorrectly concluded.

Validation of an Ultrasound Cardiac Output Monitor as a Bedside Tool for Pediatric Patients

The aim of our study was to determine the validity of cardiac output (CO) measurements taken with the ultrasonic cardiac output monitor (USCOM) by comparing to CO measured by pulmonary arterial catheter (PAC) thermodilution during cardiac catheterization. We enrolled thirty-one children (<18 years) undergoing cardiac catheterization in this double-blinded, prospective, observational study. The median CO measured by USCOM was 4.37 L/min (IQR 3.73, 5.60 L/min) compared to 4.28 L/min (IQR 3.52, 5.26 L/min) by PAC thermodilution. The bias (mean difference) between the two methods was 0.2 L/min, and the 95% limits of agreement were -1.2 to 1.6 L/min. The mean percentage error of CO between USCOM and PAC thermodilution was 11%. When excluding a sole outlier, the bias between the two measures decreased to 0.1 L/min (95% limits of agreement -0.6 to 0.9 L/min), and the percentage error was reduced to 8%. The median SVRI measured by USCOM was 22.0 Wood Units (IQR 17.0, 26.8 Wood Units) compared to 22.1 Wood Units (IQR 17.6, 27.4 Wood Units) by PAC thermodilution. Bias (mean difference) between the two methods was -0.6 Wood Units, and the 95% limits of agreement were -8.2 to 6.9 Wood Units. We found that the estimation of CO and by extension SVRI with USCOM is reliable against pulmonary artery catheter thermodilution in children with normal cardiac anatomy. Given the noninvasive nature of USCOM, speed of measurement, and relative ease of use, it may be useful as a bedside tool for pediatric patients.

Pulmonary function testing in infants with tetralogy of Fallot and absent pulmonary valve syndrome

Aim:

Absent pulmonary valve syndrome (APVS) is found in 3-6% of patients with Tetralogy of Fallot (TOF). Along with findings of TOF, absence of pulmonary valve tissue results in aneurysmal dilatation of the main and branch pulmonary arteries compressing the trachea, main-stem, and intrapulmonary bronchi leading to obstructive airways disease. Our objective was to review pulmonary function tests (PFT) in TOF-APVS patients.

Materials and Methods:

Eight PFT were performed on five mechanically ventilated TOF-APVS patients in the intensive care unit. Tidal volume, forced vital capacity (FVC), maximal expiratory flow 25%, resistance and compliance of the respiratory system were measured.

Results:

Pre-operative PFTs showed markedly elevated airways resistance (R_RS) (median 0.45 cmH₂O/mL/sec, range 0.17-0.66) and marked variability of the static compliance of the respiratory system (C_RS) (median 0.6 mL/cmH₂O/kg, range 0.25-2.6). Flow-volume loops measured by forced deflation showed flow limitation within the medium to small airways. Post-operative FVC was reduced in four of the five patients (median 46 mL/kg, IQR 42.9 - 48.8 mL/kg). Patients studied with various levels of positive end expiratory pressure (PEEP) showed improvement in tidal volume and reduced obstruction with PEEP greater than 10 cmH₂O. For three patients with pre-operative data available, surgical correction resulted in near-normal post-operative C_RS and improved, but still elevated R_RS (median 0.14 cmH₂O/mL/sec, interquartile range [IQR] 0.11-0.31).

Conclusion:

For our patients with TOF-APVS, airway resistance was elevated. Flow limitation was seen in the medium to small airways with a mild reduction of FVC. PFTs may help guide management of mechanical ventilation for TOF-APVS patients.

Fever is common postoperatively following posterior spinal fusion: infection is an uncommon cause

OBJECTIVE

To determine the frequency and clinical significance of postoperative fever in pediatric patients undergoing posterior spinal fusion (PSF).

STUDY DESIGN

A retrospective chart review was performed for consecutive patients undergoing PSF at a single institution between June 2005 and April 2011, with a minimum of 2-year follow up. Exclusion criteria were previous spine surgery, a combined anterior-posterior approach, and delayed wound closure at the time of surgery.

RESULTS

Two hundred and seventy-eight patients with an average age of 13 years (1-22 years) met inclusion criteria, with the following diagnoses: adolescent idiopathic scoliosis 43%, neuromuscular/syndromic scoliosis 39%, congenital scoliosis 11%, spondylolisthesis 4%, and Scheuermann kyphosis 3%. Seventy-two percent (201/278) of patients had a maximum temperature (Tmax) >38(°) postoperatively, and 9% (27/278) Tmax >39(°). The percentage of febrile patients trended down following the first postoperative day. Infection rate was 4% (12/278). There was no correlation between Tmax >38(°) or Tmax >39(°), and timing of fever, positive blood or urine cultures, pneumonia, or surgical site infection.

CONCLUSION

Seventy-two percent of pediatric patients undergoing PSF experienced postoperative fever, and 9% of patients had Tmax>39(°). There was no significant correlation between fever and positive blood culture, urine culture, pneumonia, or surgical site infection. This information may help relieve stress for families and healthcare providers, and obviate routine laboratory evaluation for fever alone.

Respiratory inductance plethysmography calibration for pediatric upper airway obstruction: an animal model

BACKGROUND

We sought to determine optimal methods of respiratory inductance plethysmography (RIP) flow calibration for application to pediatric postextubation upper airway obstruction.

METHODS

We measured RIP, spirometry, and esophageal manometry in spontaneously breathing, intubated Rhesus monkeys with increasing inspiratory resistance. RIP calibration was based on: ΔµV(ao) ≈ M[ΔµV(RC) + K(ΔµV(AB))] where K establishes the relationship between the uncalibrated rib cage (ΔµV(RC)) and abdominal (ΔµV(AB)) RIP signals. We calculated K during (i) isovolume maneuvers during a negative inspiratory force (NIF), (ii) quantitative diagnostic calibration (QDC) during (a) tidal breathing, (b) continuous positive airway pressure (CPAP), and (c) increasing degrees of upper airway obstruction (UAO). We compared the calibrated RIP flow waveform to spirometry quantitatively and qualitatively.

RESULTS

Isovolume calibrated RIP flow tracings were more accurate (against spirometry) both quantitatively and qualitatively than those from QDC (P < 0.0001), with bigger differences as UAO worsened. Isovolume calibration yielded nearly identical clinical interpretation of inspiratory flow limitation as spirometry.

CONCLUSION

In an animal model of pediatric UAO, isovolume calibrated RIP flow tracings are accurate against spirometry. QDC during tidal breathing yields poor RIP flow calibration, particularly as UAO worsens. Routine use of a NIF maneuver before extubation affords the opportunity to use RIP to study postextubation UAO in children.

Accuracy of pulse oximetry in children

OBJECTIVE

For children with cyanotic congenital heart disease or acute hypoxemic respiratory failure, providers frequently make decisions based on pulse oximetry, in the absence of an arterial blood gas. The study objective was to measure the accuracy of pulse oximetry in the saturations from pulse oximetry (SpO2) range of 65% to 97%.

METHODS

This institutional review board-approved prospective, multicenter observational study in 5 PICUs included 225 mechanically ventilated children with an arterial catheter. With each arterial blood gas sample, SpO2 from pulse oximetry and arterial oxygen saturations from CO-oximetry (SaO2) were simultaneously obtained if the SpO2 was ≤ 97%.

RESULTS

The lowest SpO2 obtained in the study was 65%. In the range of SpO2 65% to 97%, 1980 simultaneous values for SpO2 and SaO2 were obtained. The bias (SpO2 - SaO2) varied through the range of SpO2 values. The bias was greatest in the SpO2 range 81% to 85% (336 samples, median 6%, mean 6.6%, accuracy root mean squared 9.1%). SpO2 measurements were close to SaO2 in the SpO2 range 91% to 97% (901 samples, median 1%, mean 1.5%, accuracy root mean squared 4.2%).

CONCLUSIONS

Previous studies on pulse oximeter accuracy in children present a single number for bias. This study identified that the accuracy of pulse oximetry varies significantly as a function of the SpO2 range. Saturations measured by pulse oximetry on average overestimate SaO2 from CO-oximetry in the SpO2 range of 76% to 90%. Better pulse oximetry algorithms are needed for accurate assessment of children with saturations in the hypoxemic range.

Elevated positive end-expiratory pressure decreases cardiac index in a rhesus monkey model

RATIONALE

Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) will decrease cardiac index (CI). PEEP affects CI through multiple inter-related mechanisms. The adult Rhesus monkey is an excellent model to study cardiopulmonary interaction due to similar pulmonary and chest wall compliances to human infants.

OBJECTIVE

Our goal was to examine the impact of increasing PEEP on CI in Rhesus monkeys as a model for critically ill children.

METHODS

Prospective, experimental animal study. Nine healthy anesthetized, intubated Rhesus monkeys were allowed to breathe spontaneously at a PEEP of 0, 5, 10, and 15 cm H2O while CI was measured with an ultrasonic Doppler (USCOM).

MEASUREMENTS AND MAIN RESULTS

Cardiac index decreased between PEEP levels of 5 and 15 cm H2O. The mean decrease in CI for the entire cohort of monkeys was 18% (p < 0.01) with a range of -11 to 49%. Stroke volume and oxygen delivery also decreased between PEEP levels of 5 and 15 cm H2O (p < 0.01).

CONCLUSION

Between PEEP levels of 5 and 15 cm H2O, there was a decrease in CI, stroke volume, and oxygen delivery in intubated Rhesus monkeys. A plausible mechanism is that over-distention of normally compliant lungs at increased PEEP resulted in decreased preload to the right ventricle, outweighing the potentially beneficial decrease in left ventricular afterload or pulmonary vascular resistance. Further investigation is warranted, particularly in children with lung injury, who have historically benefited from increased PEEP levels without over-distention.

Pressure-rate product and phase angle as measures of acute inspiratory upper airway obstruction in rhesus monkeys

RATIONALE

There are limited validated, objective, and minimally invasive techniques for the bedside evaluation of upper airway obstruction (UAO) in sick infants, despite its frequency in pediatric medicine. Prior techniques include pressure-rate product (PRP), a product of esophageal pressure and respiratory rate and phase angles (PAs), a measure of asynchrony between ribcage and abdominal respiratory movements in infants with UAO. The purpose of this study is to validate the PRP and compare it to a previously validated PA in rhesus monkeys.

METHODS

Calibrated resistors were applied to the inspiratory limb of 10 anesthetized, intubated, and spontaneously breathing rhesus monkeys (weight 8.7 +/- 2.5 kg). Airway pressure, respiratory rate, PAs, heart rate, and oxygen saturation were recorded. Obstruction was applied in random order as 0, 5, 20, 200, 500, and 1,000 cmH(2)O/L/sec for 2-min periods, the last 15 sec (10-20 breaths) were analyzed for each timeframe.

RESULTS

PA increased significantly at the 200 cmH(2)O/L/sec level but it reached a plateau above 500 cmH(2)O/L/sec. PRP rose progressively and was significantly different at all levels of obstruction. Esophageal pressure change was progressively and statistically significantly different from baseline and each other at 200, 500, and 1,000 cmH(2)O/L/sec (P < 0.001).

CONCLUSIONS

In this model of UAO, PRP tracks increasing inspiratory load better than PA. PRP continued to be linear up through the highest inspiratory resistance where the change in PA reached a plateau before the highest load. The assessment of esophageal pressure changes may offer the simplest objective measure of UAO.

S-nitrosylation of endothelial nitric oxide synthase is associated with monomerization and decreased enzyme activity

Endothelial nitric oxide synthase (eNOS) is active only as a homodimer. Recent data has demonstrated that exogenous NO can act as an inhibitor of eNOS activity both in intact animals and vascular endothelial cells. However, the exact mechanism by which NO exerts its inhibitory action is unclear. Our initial experiments in bovine aortic endothelial cells indicated that exogenous NO decreased NOS activity with an associated decrease in eNOS dimer levels. We then undertook a series of studies to investigate the mechanism of dimer disruption. Exposure of purified human eNOS protein to NO donors or calcium-mediated activation of the enzyme resulted in a shift in eNOS from a predominantly dimeric to a predominantly monomeric enzyme. Further studies indicated that endogenous NOS activity or NO exposure caused S-nitrosylation of eNOS and that the presence of the thioredoxin and thioredoxin reductase system could significantly protect eNOS dimer levels and prevent the resultant monomerization and loss of activity. Further, exogenous NO treatment caused zinc tetrathiolate cluster destruction at the dimer interface. To further determine whether S-nitrosylation within this region could explain the effect of NO on eNOS, we purified a C99A eNOS mutant enzyme lacking the tetrathiolate cluster and analyzed its oligomeric state. This enzyme was predominantly monomeric, implicating a role for the tetrathiolate cluster in dimer maintenance and stability. Therefore, this study links the inhibitory action of NO with the destruction of zinc tetrathiolate cluster at the dimeric interface through S-nitrosylation of the cysteine residues.

Inhaled nitric oxide increases surfactant protein gene expression in the intact lamb

Inhaled nitric oxide (iNO) is used to treat a number of disease processes. Although in vitro data suggest that nitric oxide (NO) alters surfactant protein gene expression, the effects in vivo have not been studied. The objective of this study was to evaluate the effects of iNO on surfactant protein (SP)-A, -B, and -C gene expression in the intact lamb. Thirteen 4-wk-old lambs were mechanically ventilated with 21% oxygen and received iNO at 40 ppm (n = 7) or vehicle gas (n = 6) for 24 h. Peripheral lung biopsies were obtained at 0, 12, and 24 h and analyzed for surfactant mRNA, protein, and total DNA content. Inhaled NO increased SP-A and SP-B mRNA content by 80% from 0 to 12 h and by 78 and 71%, respectively, from 0 to 24 h. There was an increase in SP-A and SP-B protein content by 45% from 0 to 12 h, and a decrease by 70 and 65%, respectively, from 0 to 24 h. DNA content was unchanged. The mechanisms and physiological effects of these findings warrant further investigation.

Comparison of patients with central sleep apnea. With and without Cheyne-Stokes respiration

This study was designed to determine the impact of central sleep apnea with or without Cheyne-Stokes respiration (CSR) on morbidity and mortality. Central sleep apnea was found in 77 male general medical ward in-patients. Cheyne-Stokes respiration was found in 49 of the 77 men; in 15 men, CSR was severe, ie, > or = 25 percent of the night spent in CSR, in 34 men CSR was mild (1 to 25 percent CSR). Twenty-eight men had central sleep apnea but no CSR. An additional 31 patients had no sleep apnea and no CSR. The patients with severe CSR had more central apneas, more, but shorter desaturations, more awakenings and more wake time during the night, but spent more time in bed than those with no CSR or no apnea. Radiographic evidence was consistent with an association of CSR and heart failure. In addition, patients with severe CSR were at almost twice the risk of dying compared with those with no apnea and had a shorter survival time. Nevertheless, we could not confirm that CSR was an independent predictor of elevated mortality risk, implying that some other factors specific to severe CSR predispose these patients to shorter survival time.

Scanning acoustic microscopy of neoplastic and inflammatory cutaneous tissue specimens

Acoustic microscopy utilizes high frequency ultrasound to generate microscopic images. The current study was designed to examine representative disorders of the skin by use of a reflective scanning acoustic microscope (R-SAM), and to determine whether the obtainable resolution was sufficient to render a microscopic diagnosis. An Olympus UH3 Scanning Acoustic Microscope was utilized with lenses producing burst wave frequencies at 600 and 800 MHz (600 and 800 million cylces/sec). Cutaneous tissue specimens representing 12 different neoplastic and inflammatory disorders were examined. Acoustic images of unstained sections were compared with conventional light microscopic study of sections stained with hematoxylin-eosin. In most neoplasms examined, it was possible to make a specific diagnosis primarily from low magnification pattern analysis. Although individual cells could be visualized, cytologic atypia was poorly defined. In the inflammatory disorders, a specific diagnosis was possible in all but bullous pemphigoid and lichen planus, because the composition of the inflammatory infiltrate was difficult to determine. The advantages of the R-SAM include the capability of producing an acoustic profile of the tissue and the future possibility of in situ diagnosis.

Neurologic complications of the epidermal nevus syndrome

The epidermal nevus syndrome is a neurocutaneous disorder characterized by distinctive skin lesions and often serious somatic and central nervous system (CNS) abnormalities. We observed four cases of this disorder with epidermal nevi and neurologic manifestations, including mental retardation, seizures, ophthalmologic abnormalities, intracranial aneurysm, and porencephalic cyst. A review of 60 reported cases of the epidermal syndrome and our experience suggest that CNS complications are more likely to be associated with epidermal nevi on the head and that the CNS abnormalities are most often ipsilateral to the skin lesion.

Loss of epidermal Langerhans' cells and endothelial cell HLA-DR antigens in the skin in progressive systemic sclerosis

Skin biopsies from the volar aspect of the forearm were studied in 26 patients with progressive systemic sclerosis (PSS) (16 diffuse, 10 CREST) and 4 controls using monoclonal antibodies against Langerhans' cells, T lymphocytes, macrophages, B lymphocytes, NK/K cells and HLA-DR antigen(s). Langerhans' cells were reduced or absent (anti-T6, anti-HLA-DR) in 19 of 20 clinically involved and in all 6 uninvolved PSS skin biopsies. Electron microscopic studies of 3 PSS patients indicated a reduction in the number of Langerhans' cells, with normal morphology of the remaining. HLA-DR antigen(s) on dermal endothelial cells were absent or reduced in 8 of 20 involved and 5 of 6 uninvolved PSS skin biopsies, but were present on the surface of dermal mononuclear cells presumably representing activated T lymphocytes. Increased numbers of dermal macrophages were found in 19% of PSS biopsies compared with controls. Absence of Langerhans' cells appears to represent the most widespread immunopathological feature of PSS. It is also associated with absent endothelial HLA DR surface antigens and activated T lymphocytes within the dermis.

Cell kinetic basis for pathophysiology of psoriasis

Studies on the cell proliferation kinetics of psoriatic epidermal cells are presented and the results compared to similar studies for normal epidermis. The short 36-h duration of the psoriatic cell cycle (Tc) is confirmed with the first double-peaked fraction of labeled mitoses (FLM) curve in human subjects. The growth fraction of psoriasis using two experimental techniques approximates 100% within 36 h, confirming the rapid Tc found by the FLM method. The cell kinetic basis for the pathophysiology of psoriasis consists of at least 3 proliferative abnormalities in comparison to normal epidermis. By far the largest alteration is the shortening of the Tc from 311 to 36 h. There is also a doubling of the proliferative cell population in psoriasis from 27,000 to 52,000 cells/mm and an increase in the growth fraction from 60% to 100%. As a consequence of these abnormalities the psoriatic epidermis produces 35,000 cells/day from a proliferative compartment of 52,000 cells/mm2 surface area. This is a 28-fold greater production of cells than the 1,246 cells/day produced in normal epidermis. The biochemical or control factors leading to these kinetic differences continue to remain elusive.

Stimulation of WI-38 cell cycle transit: effect of serum concentration and cell density

Flow microfluorometry has been used to characterize the effects of serum concentration and cell density on the initiation of cell cycle transit of stationary phase (G0) human diploid fibroblasts (strain WI-38). The concentration of serum used to stimulate these cultures had no effect on the time cells began appearing in S (the DNA synthetic period), nor on the synchrony with which they moved around the cell cycle. However, as the serum concentration increased, the fraction of the stationary phase population released from G0 increased. Cell density modulated the ability of serum to stimulate cell cycle traverse. For example, at a cell density of 1.81 X 10(4) cells/cm2, 78% of the population was sensitive to serum stimulation; whereas, when the density was increased to 7.25 X 10(4) cells/cm2, only 27% of the population could be stimulated. This effect of cell density on the serum response is not simply the result of changing the ratio of serum concentration to cell density, but appears to reflect a true modulation of the population's sensitivity to serum stimulation. These results are consistent with the interpretation that the primary action of serum is to determine the transition of cells from a non-cycling G0 state to a cycling state and that cell density determines the proportion of the population capable of undergoing this transition.