Cardiopulmonary Interactions.

OBJECTIVES: The objectives of this review are to discuss the mechanisms by which respiration impacts cardiovascular function and vice versa, with an emphasis on the impact of these interactions in pediatric cardiac critical care. DATA SOURCE: A search of MEDLINE was conducted using PubMed. CONCLUSIONS: In the presence of underlying cardiac and respiratory disease, the interplay between these two systems is significant and plays a pivotal role in the pathophysiology of acute and chronic phases of a wide spectrum of diseases. An understanding of these relationships is essential to optimizing the care of critically ill patients.

Multicenter randomized controlled trial of inhaled nitric oxide for pediatric acute respiratory distress syndrome.

OBJECTIVES: To test the hypothesis that inhaled nitric oxide (iNO) would lead to improved oxygenation and a decrease in duration of mechanical ventilation in pediatric patients with acute respiratory distress syndrome. STUDY DESIGN: A total of 55 children with acute respiratory distress syndrome were enrolled from 9 centers. Patients were randomized to iNO or placebo and remained on the study drug until death, they were free of ventilator support, or day 28 after the initiation of therapy. RESULTS: Mean baseline oxygenation indexes (OIs) were 22.0 ± 18.4 and 25.6 ± 14.9 (iNO and placebo groups, respectively, P = .27). There was a trend toward an improved OI in the iNO group compared with the placebo group at 4 hours that became significant at 12 hours. There was no difference in the OI between groups at 24 hours. Days alive and ventilator free at 28 days was greater in the iNO group, 14.2 ± 8.1 and 9.1 ± 9.5 days (iNO and placebo groups, respectively, P = .05). Although overall survival at 28 days failed to reach statistical significance, 92% (22 of 24) in the iNO group and 72% (21 of 29) in the placebo group (P = .07), the rate of extracorporeal membrane oxygenation-free survival was significantly greater in those randomized to iNO 92% (22 of 24) vs 52% (15 of 29) for those receiving placebo (P < .01). CONCLUSION: The use of iNO was associated with a significantly reduced duration of mechanical ventilation and significantly greater rate of extracorporeal membrane oxygenation-free survival.

Development of learning objectives and a validated testing tool for management of pediatric mechanical ventilation*.

OBJECTIVES: Graduate medical education is shifting toward an outcome-based paradigm, where physicians are evaluated for competency using well-defined criteria. Our aim was to learning objectives and a testing tool to assess competency in the management of mechanical ventilation for infants, children, and adolescents and to verify that the test was reliable and valid. DESIGN: Prospective reliability and validity study. SETTING: Large, university-affiliated academic hospital. SUBJECTS: Sixty-one total subjects from five different academic centers divided into three groups of varying experience. The groups were second- and third-year pediatric residents (Novice), second- and third-year pediatric critical care fellows (Advanced), and pediatric critical care faculty (Expert). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Ten learning objectives considered important for the management of pediatric mechanical ventilation were developed from expert opinion and current evidence. Based on these objectives, a 35-question multiple choice, knowledge- and case-based test was created. Content validity was achieved by consensus of three experts in pediatric critical care medicine evaluating whether the questions reflected the learning objectives and the responses were consistent with current practice and evidence-based medicine. The test was then administered to the three groups to establish construct validity. The "Novice" group scored a mean of 34.6% (95% CI, 28-41%), the "Advanced" group a mean of 59.4% (95% CI, 53-65%), and the "Expert" group a mean of 74.8% (95% CI, 69-80%), with p less than 0.01 for all comparisons. As determined by Hoyt's analysis, the reliability coefficient was 0.89, reflecting excellent reliability. CONCLUSIONS: This is the first description of specific learning objectives for management of pediatric mechanical ventilation and the first validated and reliable testing tool for assessing knowledge. This tool could be used by fellowship programs to assess fellow competency and identify knowledge gaps in this area prior to completion of training. Further work must be done to determine the criteria for determination of competency.

Usefulness of cerebral NIRS in detecting the effects of pediatric sleep apnea.

BACKGROUND: Children with sleep apnea have increased morbidity if the sleep apnea is untreated. Polysomnography (PSG) is used to detect sleep apnea, but in children, there are technical difficulties that make the diagnosis more difficult. Cerebral near infrared spectroscopy (NIRS) has the ability to detect tissue hypoxia by measuring regional oxygen saturation (rSO2 ). We hypothesized that when used as an adjunct to PSG testing, cerebral NIRS would better detect the effects of sleep apnea in children than arterial pulse oximetry (SpO2 ). Specifically, we aimed to show that the apnea/hypopnea index (AHI) calculated with rSO2 from the NIRS would be greater than that calculated with SpO2 . METHODS: Forty-seven patients under 18 years of age who underwent PSG testing for sleep apnea were evaluated. Cerebral NIRS was utilized in addition to PSG. The AHI was calculated using SpO2 and compared to the AHI calculated using the rSO2 . A pediatric pulmonologist who was unaware of the NIRS data evaluated each patient for sleep apnea. Data are median (interquartile range). RESULTS: The median AHI(rSO2 ) was 2.4(1.2,5.1), significantly greater (P < 0.0001) than the AHI(SpO2 ) of 0.7(0.4,1.2). Four patients were diagnosed with sleep apnea; however, only one had an AHI(SpO2 ) ≥ 5, a typical threshold for the diagnosis of sleep apnea. All 4 subjects had an AHI(rSO2 ) ≥ 5 but 10 patients without sleep apnea had a value ≥5. The sensitivity and specificity for using the AHI(rSO2 ) to diagnose sleep apnea was 100% and 76.7%, respectively. CONCLUSION: Consistent with the ability of NIRS to detect tissue hypoxia, we found that the AHI calculated with rSO2 was greater than that using SpO2 . We conclude that NIRS has potential as a valuable adjunct to PSG in evaluating patients for sleep apnea and warrants further investigation for this purpose.

Cerebral and somatic oxygen saturations after repair of tetralogy of Fallot: effects of extubation on regional blood flow.

BACKGROUND: After repair of tetralogy of Fallot, some patients experience a low cardiac output state owing to right ventricular diastolic failure. Negative-pressure ventilation has been shown to improve cardiac output in these patients. What has not been evaluated is the effect of extubation and loading of the respiratory muscles on the distribution of cardiac output after repair of tetralogy of Fallot. METHODS: In 23 consecutive patients undergoing repair of tetralogy of Fallot, standard hemodynamic variables, central venous oxygen saturations, and near infrared spectroscopy of the brain, mesenteric, and renal circulations were monitored for 30 minutes before and after extubation. RESULTS: With extubation, the systolic blood pressure increased significantly from 96 ± 11 to 106 ± 15 mm Hg (p = 0.002) while the heart rate remained unchanged. With extubation, the central venous oxygen saturation increased significantly from 65% ± 7% to 70% ± 10% (p = 0.003). Cerebral oxygen saturations increased significantly from 67% ± 10% to 72% ± 9% (p = 0.0001), whereas mesenteric oxygenation fell significantly from 74% ± 15% to 72% ± 15% (p = 0.04). Renal oxygenation was unaffected by extubation. CONCLUSIONS: Cardiac output and cerebral oxygenation increased significantly during spontaneous respiration, the latter suggesting that the brain was in or approaching an oxygen supply-dependent state before extubation. Despite the increase in cardiac output, the presumed increase in respiratory pump perfusion, as well as the concurrent increase in cerebral perfusion, came at the expense of mesenteric perfusion. Renal oxygenation remained unchanged with extubation.

The impact of mechanical ventilation time before initiation of extracorporeal life support on survival in pediatric respiratory failure: a review of the Extracorporeal Life Support Registry.

OBJECTIVE: To evaluate the relationship between duration of mechanical ventilation before the initiation of extracorporeal life support and the survival rate in children with respiratory failure. Extracorporeal life support has been used as a rescue therapy for >30 yrs in children with severe respiratory failure. Previous studies suggest patients who received >7-10 days of mechanical ventilation were not acceptable extracorporeal life support candidates as a result of irreversible lung damage. DESIGN: A retrospective review encompassing the past 10 yrs of the International Extracorporeal Life Support Organization Registry (January 1, 1999, to December 31, 2008). SETTING: Extracorporeal Life Support Organization Registry database. PATIENTS: A total of 1325 children (≥ 30 days and ≤ 18 yrs) met inclusion criteria. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The following pre-extracorporeal life support variables were identified as independently and significantly related to the chance of survival: 1) >14 days of ventilation vs. 0-7 days was adverse (odds ratio, 0.32; p < .001); 2) the presence of a cardiac arrest was adverse (odds ratio, 0.56; p = .001); 3) pH per 0.1-unit increase was protective (odds ratio, 1.15; p < .001); 4) oxygenation index, per 10-unit increase was adverse (odds ratio, 0.95; p = .002); and 5) any diagnosis other than sepsis was related to a more favorable outcome. Patients requiring >7-10 or >10-14 days of pre-extracorporeal life support ventilation did not have a statistically significant decrease in survival as compared with patients who received 0-7 days. CONCLUSIONS: There was a clear relationship between the number of mechanical ventilation days before the initiation of extracorporeal life support and survival. However; there was no statistically significant decrease in survival until >14 days of pre-extracorporeal life support ventilation was reached regardless of underlying diagnosis. We found no evidence to suggest that prolonged mechanical ventilation should be considered as a contraindication to extracorporeal life support in children with respiratory failure before 14 days.

Hemodynamics and cerebral oxygenation following repair of tetralogy of Fallot: the effects of converting from positive pressure ventilation to spontaneous breathing.

PURPOSE: Following corrective surgery for tetralogy of Fallot (TOF), approximately one-third of these patients develop low cardiac output (CO) due to right ventricular (RV) diastolic heart failure. Extubation is beneficial in these patients because the fall in intrathoracic pressure that occurs with conversion from positive pressure breathing to spontaneous breathing improves venous return, RV filling and CO. We hypothesized that if CO were to increase but remain limited following extubation, the obligatory increase in perfusion to the respiratory pump that occurs with loading of the respiratory musculature may occur at the expense of other vital organs, including the brain. MATERIALS AND METHODS: We conducted a retrospective analysis of all patients undergoing repair of TOF and monitoring of cerebral oxygenation using near infrared spectroscopy. We evaluated the following parameters two hours prior to and following extubation: mean and systolic arterial blood pressure (MBP, SBP), right atrial pressure (RAP), heart rate (HR) and cerebral oxygenation. RESULTS: The study included 22 patients. With extubation, MBP and SBP increased significantly from 67.3 ± 6.5 to 71.1 ± 8.4 mm Hg (P= 0.004) and from 87.2 ± 8.6 to 95.9 ± 10.9 mm Hg (P= 0.001), respectively, while the HR remained unchanged (145 vs. 146 bpm). The RAP remained unchanged following extubation (11.9 vs. 12.0 mm Hg). Following extubation, cerebral oxygen saturations increased significantly from 68.5 ± 8.4 to 74.2 ± 7.9% (P < 0.0001). Cerebral oxygen saturations increased by ≥5% in 11 of 22 patients and by ≥10% in 5 of 22 patients. CONCLUSION: We conclude that converting from positive pressure ventilation to spontaneous negative pressure breathing following repair of TOF significantly improves arterial blood pressure and cerebral oxygenation.

Cardiopulmonary interaction.

OBJECTIVE: To highlight and review the physiology and pathophysiology of cardiopulmonary interaction in the critically ill pediatric patient. DATA SOURCE: A MEDLINE-based literature source. OUTLINE OF REVIEW: This review is divided into two sections: 1) The physiologic basis of cardiopulmonary interaction, and 2) critical clinical conditions in which cardiac and/or pulmonary dysfunction impact each other in the provision of adequate oxygen delivery. The physiology section focuses on the original research identifying fundamental volume-pressure and pressure-flow relationships and then proceeds to discuss how changes in intrathoracic pressure and lung volume affect ventricular loading conditions. The clinical section chooses several common scenarios in which this normal physiology is altered and an understanding of the impact of these physiologic aberrations on cardiac and/or pulmonary function is required to make sound management decisions. CONCLUSIONS: Improving oxygen transport balance is the primary goal in the management of children with life-threatening disorders. To optimize the opportunity for a successful outcome, the intensivist must understand the complex relationship between the cardiac and pulmonary systems in the effort to provide sufficient oxygen to meet the body's metabolic demands. Furthermore, the application of therapies separately designed to support the function of the heart and the function of the lungs may be synergistic or antagonistic, further complicating the management scheme. We conclude that this review will encourage the reader to pursue further literature or perhaps engage in further research related to this often underappreciated but vital interplay between cardiac and pulmonary functions.

Fontan patient with plastic bronchitis treated successfully using aerosolized tissue plasminogen activator: a case report and review of the literature.

Plastic bronchitis is an uncommon condition characterized by the production of large pale bronchial casts that obstruct the tracheobronchial tree. The cellular content, cohesiveness, and often rubber-like consistency distinguish bronchial casts from the usual mucus plugs found with such disease states as asthma. Plastic bronchitis can be found secondary to many conditions, and a simplified classification scheme organizes it into two groups: an inflammatory type consisting of casts with an eosinophilic inflammatory infiltrate and an acellular type with a predominance of fibrin distinguished by its relative lack of cellular infiltrate, its mucin predominance, and its appearance only in children with congenital cyanotic heart disease. This report describes a 5-year-old girl who experienced plastic bronchitis 3 months after a Fontan procedure for hypoplastic left heart syndrome that was treated successfully with aerosolized tissue plasminogen activator.

Interactive effects of high-frequency oscillatory ventilation and inhaled nitric oxide in acute hypoxemic respiratory failure in pediatrics.

OBJECTIVE: High-frequency oscillatory ventilation (HFOV) and inhaled nitric oxide (iNO) have been reported to improve oxygenation in children with acute hypoxemic respiratory failure (AHRF), but their roles in the treatment of AHRF remains unknown. The use of HFOV improves oxygenation by increasing lung recruitment. iNO can improve oxygenation in AHRF, but it may have limited efficacy in patients with poor lung inflation. Based on these findings, we hypothesized that the combined treatment of HFOV and inhalation of low-dose NO would improve oxygenation and survival in children with severe AHRF compared with children treated with conventional mechanical ventilation (CMV) or either treatment alone. SETTING: Tertiary pediatric intensive care units at seven academic centers. DESIGN: Post hoc analysis of data from children enrolled in a multicenter, randomized, masked study of the use of iNO in the treatment of AHRF. PATIENTS: A total of 108 pediatric patients with AHRF defined as an oxygenation index of >15 twice within 6 hrs. Mode of ventilation (HFOV or CMV) was determined by the patient's physician based on guidelines to maximize oxygenation. The patient was then randomized to treatment with or without iNO. Comparisons were made between patients who were treated with HFOV plus iNO (n = 14), HFOV alone (n = 12), CMV plus iNO (n = 35), and CMV alone (n = 38). INTERVENTIONS: Ventilation with CMV or HFOV with or without iNO. MEASUREMENTS AND MAIN RESULTS: We found that the change in Pao /Fio ratio was greatest in the HFOV plus iNO group compared with the other treatment groups at 4 hrs (p =.02) and 12 hrs (p =.01). After 24 hrs of treatment, both HFOV plus iNO and HFOV alone resulted in greater improvement in Pao2/Fio2 ratio than either CMV alone or CMV plus iNO (p =.005). After 72 hrs, treatment with HFOV alone resulted in a greater improvement in Pao2/Fio2 ratio than either CMV alone or CMV plus iNO (p =.03). There was no difference in predefined treatment failures between treatment groups. CONCLUSIONS: We conclude that the combination of HFOV with iNO causes a greater improvement in oxygenation than either treatment strategy alone in children with severe AHRF. We speculate that the enhanced lung recruitment by HFOV enhances the effects of low dose iNO on gas exchange.