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Biomedical subjects

Ira M Cheifetz

Publications and source records attributed to Ira M Cheifetz.

At least 19 recordsLinked to original sources
PubMed2007

Setting positive end-expiratory pressure during jet ventilation to replicate the mean airway pressure of oscillatory ventilation.

BACKGROUND: High-frequency ventilation can be delivered with either oscillatory ventilation (HFOV) or jet ventilation (HFJV). Traditional clinician biases may limit the range of function of these important ventilation modes. We hypothesized that (1) the jet ventilator can be an accurate monitor of mean airway pressure (P (aw)) during HFOV, and (2) a mathematical relationship can be used to determine the positive end-expiratory pressure (PEEP) setting required for HFJV to reproduce the P (aw) of HFOV. METHODS: In phase 1 of our experiment, we used a differential pressure pneumotachometer and a jet adapter in-line between an oscillator circuit and a pediatric lung model to measure P (aw), PEEP, and peak inspiratory pressure (PIP). Thirty-six HFOV setting combinations were studied, in random order. We analyzed the correlation between the pneumotachometer and HFJV measurements. In phase 2 we used the jet as the monitoring device during each of the same 36 combinations of HFOV settings, and recorded P (aw), PIP, and DeltaP. Then, for each combination of settings, the jet ventilator was placed in-line with a conventional ventilator and was set at the same rate and PIP as was monitored during HFOV. To determine the appropriate PEEP setting, we calculated the P (aw) contributed by the PIP, respiratory rate, and inspiratory time set for HFJV, and subtracted this from the goal P (aw). This value was the PEEP predicted for HFJV to match the HFOV P (aw). RESULTS: The correlation coefficient between the pneumotachometer and HFJV measurements was r = 0.99 (mean difference 0.62 +/- 0.30 cm H(2)O, p < 0.001). The predicted and actual PEEP required were highly correlated (r = 0.99, p < 0.001). The mean difference in these values is not statistically significantly different from zero (mean difference 0.25 +/- 1.02 cm H(2)O, p > 0.15). CONCLUSIONS: HFJV is an accurate monitor during HFOV. These measurements can be used to calculate the predicted PEEP necessary to match P (aw) on the 2 ventilators. Replicating the P (aw) with adequate PEEP on HFJV may help simplify transitioning between ventilators when clinically indicated.

Airway Resistance↗
PubMed2006

Extubation criteria in infants and children.

Predictors of extubation outcome attempt to provide objective data that may help to modify clinical decision making at the bedside. This article reviews the subjective and objective extubation readiness predictors tested in the pediatric medical literature. An understanding of the predictive capacity of the extubation criteria is vital for the critical care physician. No test is likely to predict the extubation outcome for an individual patient with absolute certainly. Therefore, weaning and extubation practices in the pediatric critical care setting remain variable, and teh development of standardized protocols for extubation remains controversial. Perhaps future well-designed, large-scale trials will provide more accurate predictors of extubation readiness to guide the safe and timely extubation of the pediatric patient.

Child↗
PubMed2006

Do all mechanically ventilated pediatric patients require continuous capnography?

With most patients in modern ICUs requiring mechanical ventilation, any technology that may lead to more optimal ventilatory strategies would be invaluable in the management of critically ill patients. The focus of most ventilator strategies is protecting the lung from the deleterious effects of mechanical ventilation. Every effort is made to minimize the duration of mechanical ventilation while optimizing the potential for successful extubation. A concise organized plan based on objective criteria that is adjusted to meet changes in patient status is clearly recommended. Continuous capnographic monitoring provides clinicians with clear, precise, objective data that may prove beneficial in the design and implementation of mechanical ventilatory strategies. There are no clear-cut methods for achieving the optimal ventilator strategy for a specific patient. Although guidelines and management theories exist throughout the medical literature, in practice, they often merely serve as loose guidelines. The dynamic properties of an acutely ill patient make the management of mechanical ventilation an ongoing process requiring clinical assessment and planning by multidisciplinary members of the patient care team. Comprehensive evaluation of ventilatory management strategies and patient responses must be made by a collaborative effort of physicians, respiratory care practitioners, and nurses. An objective, consistent approach to the overall management is essential. Although still controversial, it is the authors' opinion that volumetric capnograph provides the data necessary to establish adequate gas delivery, optimal PEEP, and effective ventilation with the least amount of mechanical assistance, regardless of clinician or institutional preferences.

Capnography↗
PubMed2006

Is permissive hypoxemia a beneficial strategy for pediatric acute lung injury?

The adverse effects of high oxygen levels have been widely reported, and clinicians have struggled for many years to find the ideal balance between inspired oxygen levels and acceptable arterial oxygen saturation. However, when asked "what is an acceptable oxygen saturation," one is hard pressed to find a definitive answer. Permissive hypoxemia is a concept similar to the well-described strategy of permissive hypercapnia. It is a strategy that allows the arterial oxygen saturation to be less than normal in an attempt to minimize the amount of artificial support provided to the lungs by mechanical ventilation. It must be noted that this concept is predominantly based on physiology, as data in the medical literature are very limited. Permissive hypoxemia as an approach to acute lung injury remains controversial in the clinical setting.

Blood Gas Analysis↗
PubMed2005

Heliox administration in the pediatric intensive care unit: an evidence-based review.

OBJECTIVE: To provide a comprehensive, evidence-based review of helium-oxygen gas mixtures (heliox) in the management of pediatric respiratory diseases. DATA SOURCE: A thorough, computerized bibliographic search of the preclinical and clinical literature regarding the properties of helium and its application in pediatric respiratory disease states. DATA SYNTHESIS: After an overview of the potential benefits and technical aspects of helium-oxygen gas mixtures, the role of heliox is addressed for asthma, aerosolized medication delivery, upper airway obstruction, postextubation stridor, croup, bronchiolitis, and high-frequency ventilation. The available data are objectively classified based on the value of the therapy or intervention as determined by the study design from which the data are obtained. CONCLUSIONS: Heliox administration is most effective during conditions involving density-dependent increases in airway resistance, especially when used early in an acute disease process. Any beneficial effect of heliox should become evident in a relatively short period of time. The medical literature supports the use of heliox to relieve respiratory distress, decrease the work of breathing, and improve gas exchange. No adverse effects of heliox have been reported. However, heliox must be administered with vigilance and continuous monitoring to avoid technical complications.

Administration, Inhalation↗
PubMed2005

Hemolytic characteristics of three commercially available centrifugal blood pumps.

OBJECTIVE: As compared with traditional extracorporeal roller-occlusion blood pumps, nonocclusive centrifugal pumps offer the benefits of requiring a smaller circuit surface area and, thus, a smaller prime volume. However, centrifugal blood pumps have been reported to generate unacceptable levels of hemolysis. We hypothesize that the newer generation centrifugal pumps have an incidence of hemolysis similar to the traditional roller head pumps and, thus, could be used for extracorporeal membrane oxygenation circuits. DESIGN: Randomized, prospective, bench study. SETTING: University research laboratory. INTERVENTIONS: Three centrifugal blood pumps (Cobe Revolution, Jostra Rotaflow, and Medtronic BioMedicus) were compared with a roller occlusion blood pump (Cobe Century). Hemolysis generation was examined during 6 hrs of continuous use. Two test runs per group were randomly performed on three consecutive days for a total of six test runs for each of the four pumps (n = 24). MEASUREMENTS AND MAIN RESULTS: Plasma free hemoglobin values were determined using a Spectra MaxPlus spectrophotometer. A normalized index of hemolysis was calculated to compare the individual trials. The Cobe Revolution and the Jostra Rotaflow compared favorably with the Cobe Century roller occlusion blood pump in the amount of hemolysis produced. CONCLUSIONS: These data are encouraging for the development of a low-prime, mobile neonatal extracorporeal membrane oxygenation circuit using centrifugal pump technology.

Animals↗
PubMed2005

Cumulative fluid intake minus output is not associated with ventilator weaning duration or extubation outcomes in children.

OBJECTIVE: The effect of fluid balance on respiratory outcomes for critically ill children has not been evaluated. The only indicator of fluid balance routinely recorded across our intensive care units was estimated fluid intake and output. We sought to determine whether cumulative intake minus output (I-O) at the start of weaning predicted weaning duration and whether cumulative I-O at extubation predicted extubation failure. DESIGN: Prospective observational study. SETTING: Ten pediatric intensive care units. PATIENTS: Cumulative I-O was recorded daily for 301 mechanically ventilated children (<18 yrs of age) from November 1999 through April 2001. INTERVENTIONS: Cumulative I-O was recorded during a study of weaning strategies and extubation failure in which mechanical ventilation of the majority of patients during weaning and extubation was managed according to a protocol that did not include fluid balance indicators. Outcomes were the time to successful removal of ventilatory support and the rate of initial extubation failure. MEASUREMENTS AND MAIN RESULTS: Relationships between cumulative I-O and outcomes were assessed by means of proportional hazards and logistic regression. The mean cumulative I-O per kilogram of ideal body weight at the start of weaning was 101 mL (sd, 180). Cumulative I-O at the time weaning was initiated did not predict duration of mechanical ventilator weaning. The mean cumulative I-O per kilogram of ideal body weight at extubation was 136 mL (sd, 237). Cumulative I-O at extubation did not predict extubation outcome. There was an association between cumulative I-O at extubation and the duration of weaning in cases not managed by a protocol. CONCLUSION: Although routinely recorded, cumulative fluid I-O does not appear to have clinical utility in cases managed according to a mechanical ventilator protocol in which tidal volume and oxygenation on minimal levels of ventilator support are systematically tested.

Adolescent↗
PubMed2005

Neonatal thyrotoxicosis and persistent pulmonary hypertension necessitating extracorporeal life support.

We report a case of neonatal Graves' disease involving an infant with severe persistent pulmonary hypertension (PPHN) associated with neonatal thyrotoxicosis that necessitated extracorporeal membrane oxygenation. Hyperthyroidism, although uncommon in the newborn period, has been associated with pulmonary hypertension among adults. The exact mechanisms responsible for this effect on pulmonary vascular pressure are not well understood. Recent studies have provided evidence that thyrotoxicosis has direct and indirect effects on pulmonary vascular maturation, metabolism of endogenous pulmonary vasodilators, oxygen economy, vascular smooth muscle reactivity, and surfactant production, all of which may contribute to the pathophysiologic development of PPHN. Therefore, because PPHN is a significant clinical entity among term newborns and the symptoms of hyperthyroidism may be confused initially with those of other underlying disorders associated with PPHN (eg, sepsis), it would be prudent to perform screening for hyperthyroidism among affected newborns.

Adolescent↗
PubMed2005

Carbon dioxide elimination and gas displacement vary with piston position during high-frequency oscillatory ventilation.

INTRODUCTION: Alterations in gas displacement in pediatric patients ventilated with the SensorMedics 3100A high-frequency oscillator are most commonly manipulated by adjusting the amplitude, frequency, and percent inspiratory time. The piston-position-and-displacement indicator is commonly centered and subsequently not adjusted. That practice may limit the clinician's ability to optimize carbon dioxide elimination. We hypothesized that varying the piston position would alter gas displacement and carbon dioxide elimination. METHODS: We conducted an observational study in a tertiary pediatric intensive care unit and a correlated bench study. In the clinical study, 24 patients were ventilated with a SensorMedics 3100A high-frequency oscillator. Transcutaneously measured carbon dioxide ((tCO(2))) values were documented with the piston-position-and-displacement indicator in left, center, and right positions. In the bench study the oscillator was set and maintained at: mean airway pressure 15 cm H(2)O, inspiratory time 33% of respiratory-cycle time, bias flow 20 L/min. A pneumotachometer attached to a respiratory mechanics monitor was placed between the ventilator circuit and a test lung. Data were collected with the piston-position-and-displacement indicator at the left, center, and right positions with frequencies of 4-14 Hz and amplitudes of 25-55 cm H(2)O. Data were collected over a 3-minute time period for each combination of frequency, amplitude, and piston-position-and-displacement-indicator position. We compared the data with repeated-measures analysis of variance. Pairwise comparisons were performed with a 2-tailed Student's test with Bonferroni correction. RESULTS: Among the 24 patients (tCO(2)) was significantly associated with the position of the piston (p < 0.007). In the bench study, gas displacement was higher when the piston-position-and-displacement indicator was positioned to the left (than when at the center position) 91.7% of the time (p < 0.0001). When the piston-position-and-displacement indicator was positioned to the right (as compared to the center position), gas displacement was lower 75% of the time (p < 0.0001). CONCLUSION: Adjusting the oscillator piston alters the volume of gas displaced and provides an additional means for titrating carbon dioxide elimination. .

Adolescent↗
PubMed2004

Inhaled nitric oxide results in deteriorating hemodynamics when administered during cardiopulmonary bypass in neonatal swine.

OBJECTIVE: To evaluate if inhaled nitric oxide (iNO) has a lung-protective effect when it is delivered during the ischemic phase of neonatal cardiopulmonary bypass (CPB). DESIGN: Prospective, randomized, controlled study. SETTING: Surgical research laboratory in a university hospital. SUBJECTS: Thirty-five neonatal swine. INTERVENTIONS: One-week-old swine (2.1-3.4 kg) were exposed to cool, low-flow CPB bypass designed to mimic the bypass used during neonatal congenital heart repair. Animals were randomized to four groups: a) CPB without exposure to iNO (n = 9); b) iNO delivery only during CPB with discontinuation of iNO at the start of reperfusion (n = 7); c) iNO delivery both during CPB and during the 90-min post-CPB observation period (n = 7); and d) iNO delivery only after separation from CPB (n = 7). Each animal was placed on nonpulsatile CPB and cooled to a nasopharyngeal temperature of 18 degrees C (64 degrees F). Low-flow CPB (35 mL.kg(-1).min(-1)) was instituted for 90 mins. The blood flow then was returned to 100 mL.kg(-1).min(-1), and the animals were warmed to 36 degrees C (96.8 degrees F) before separation from CPB. Animals were followed 90 mins post-CPB. Lung tissue was harvested and evaluated for myeloperoxidase activity, wet/dry weight, and lung pathology. Five animals underwent sham protocol, receiving instrumentation but not exposure to CPB or iNO. MEASUREMENTS AND MAIN RESULTS: We measured pulmonary vascular resistance, right ventricular output, and pulmonary artery pressure in all animals at 30, 60, and 90 mins following separation from CPB. Study animals that received iNO during the ischemic period of CPB were not protected against CPB-induced lung injury. Those animals treated with iNO both during and after CPB trended worse than those receiving iNO only after CPB. Inhaled nitric oxide delivered only after separation from CPB improved the hemodynamic variables compared with all other groups. Differences in lung wet/dry weight, myeloperoxidase, and pathology were not significantly different among groups. CONCLUSIONS: The delivery of iNO during the ischemic period of CPB does not protect against CPB-induced lung injury in a neonatal piglet CPB model. Delivery of iNO during this phase of CPB may, in fact, worsen the post-CPB hemodynamic condition. Inhaled nitric oxide should be used with caution during periods of low pulmonary blood flow CPB. Inhaled nitric oxide remains effective for reducing pulmonary vascular resistance after CPB.

Administration, Inhalation↗
PubMed2004

Successful treatment of acute chest syndrome with high-frequency oscillatory ventilation in pediatric patients.

Severe acute chest syndrome afflicts patients with sickle cell disease and can cause hypoxemia refractory to conventional treatments. Obstructive mucus plugging and the development of acute respiratory distress syndrome may underlie the pathophysiology of refractory hypoxemia in acute chest syndrome. Although high-frequency oscillatory ventilation (HFOV) is well established in the treatment of pediatric acute respiratory distress syndrome, there is no support in the literature for its role in managing hypoxemia in acute chest syndrome. In disease processes with high airways resistance and obstructive mucus plugging, HFOV may predispose to air-trapping and increased morbidity secondary to air leak syndromes. We report the first successful HFOV management of pediatric patients suffering from severe acute chest syndrome and hypoxic respiratory failure. These cases suggest that HFOV should be strongly considered for patients with severe acute chest syndrome that is refractory to conventional mechanical ventilation.

Anemia, Sickle Cell↗
PubMed2004

Heliox administration during high-frequency jet ventilation augments carbon dioxide clearance.

We report the combined use of heliox and high-frequency jet ventilation to augment carbon dioxide clearance, with a focus on the important technical considerations. Our case is a 5-month old infant with acute respiratory failure associated with gas trapping, hypercarbia, respiratory acidosis, and air leak. Despite maximal conventional ventilation, bronchodilator therapy, corticosteroids, and sedation, the infant continued to demonstrate worsening gas exchange necessitating an escalation of support to high-frequency oscillatory ventilation. After the development of an air leak and continued difficulties with carbon dioxide clearance, the patient was transitioned to high-frequency jet ventilation. Persistent hypercarbia resulted in the addition of heliox to facilitate ventilation. Improvements in gas exchange occurred rapidly. The combination of heliox and high frequency jet ventilation resulted in improved carbon dioxide clearance, respiratory stabilization, and the ability to wean ventilator settings.

Acute Disease↗
PubMed2003

The feasibility of conducting clinical trials in infants and children with acute respiratory failure.

Designing robust clinical trials in critically ill, mechanically ventilated children requires an understanding of the epidemiology and course of pediatric respiratory failure. As part of a clinical trial, we screened all mechanically ventilated children in nine large pediatric intensive care units (ICUs) across North America for 6 consecutive months. Of 6,403 total ICU admissions, 1,096 (17.1%) required mechanical ventilator support for a minimum of 24 hours. Of these, 701 (64%) met one or more exclusion criteria for trial enrollment. Common reasons for exclusion were upper airway obstruction (13.5%) and cyanotic congenital heart disease (11.5%). Life support interventions were restricted for 9.7% of patients, and 5.5% were chronically ventilator dependent. In the patients who were eligible for respiratory failure studies, 62.4% had an acute primary diagnosis of pulmonary disease, 14.2% neurologic disease, and 8.9% cardiac disease. Chronic underlying conditions were present in 43.2% of the patients. The most common acute diagnosis was bronchiolitis in infants (43.6%) and pneumonia in children 1 year old and older (24.5%). Mortality was rare (1.6%), and the median duration of ventilation was 7 days. The design of clinical trials in critically ill children is feasible but must account for the diverse population, infrequent mortality, and short duration of mechanical ventilation.

Acute Disease↗
PubMed2003

Heliox does not affect gas exchange during high-frequency oscillatory ventilation if tidal volume is held constant.

OBJECTIVE: To compare gas exchange with heliox and oxygen-enriched air during high-frequency oscillatory ventilation, while controlling for tidal volume, in a pediatric swine model of acute lung injury. We hypothesized that when tidal volume delivery is held constant, heliox does not alter gas exchange. DESIGN: Randomized, crossover trial. SETTING: University animal research laboratory. SUBJECTS: Ten swine (4.4-5.4 kg). INTERVENTIONS: Acute lung injury (A-a gradient of >300 mm Hg) was created using repeated saline lavage during conventional mechanical ventilation. The animals were then administered high-frequency oscillatory ventilation and ventilated with 60% oxygen/40% helium and 60% oxygen/40% nitrogen in a randomized, crossover trial. When changing gas mixtures within each animal, mean airway pressure (Paw = 16.8 +/- 0.3 cm H(2)O) and frequency (10 Hz) were held constant. Oscillation amplitude (DeltaP) was adjusted to maintain constant tidal volume delivery as measured by respiratory inductive plethysmography. Next, the animals were ventilated with 40% oxygen/60% helium and 40% oxygen/60% nitrogen in a randomized crossover trial, again controlling for tidal volume. MEASUREMENTS AND MAIN RESULTS: Gas exchange was assessed by arterial blood gas analysis after ventilation with each gas mixture. We demonstrated no significant difference in Paco(2) or Pao(2) between the heliox and oxygen-enriched air with either the 40% or 60% oxygen mixtures. The oscillation amplitude required to achieve the same tidal volume delivery was significantly less with heliox. CONCLUSIONS: We conclude that if tidal volume delivery is maintained constant, heliox does not alter gas exchange when compared with oxygen-enriched air. However, to achieve the same tidal volume delivery, a lower oscillation amplitude is required with heliox. The clinical benefit of heliox administration during high-frequency oscillatory ventilation has yet to be determined. Possible advantages of heliox include improved ventilation of larger patients when approaching the power limitations of the Sensormedics 3100A oscillator and a potential reduction in the oscillation amplitude delivered to the more proximal gas exchange units.

Animals↗
PubMed2003

Mechanically ventilated pediatric stem cell transplant recipients: effect of cord blood transplant and organ dysfunction on outcome.

OBJECTIVES: To compare survival of pediatric umbilical cord blood and bone marrow transplant recipients requiring admission to a pediatric intensive care unit for mechanical ventilation and to determine the effect of organ dysfunction on outcome. DESIGN: Retrospective chart review. SETTING: Tertiary care referral center for pediatric stem cell transplants. PATIENTS: All children 0-18 yrs old admitted to the pediatric intensive care unit for mechanical ventilation after receiving a stem cell transplant. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Data were collected from medical records of 86 patients who received a stem cell transplant and were subsequently admitted to the pediatric intensive care unit for mechanical ventilation. Demographic data were collected at the time of intubation, and physiologic data were collected at 6 hrs and 96 hrs after intubation. The pediatric intensive care unit, hospital, and 2-yr survival rates for umbilical cord blood transplant recipients were 37%, 25%, and 19%, respectively. The survival rates for bone marrow transplant recipients were 47%, 32%, and 21% for the same time periods. Umbilical cord blood and bone marrow transplant recipients with hepatic dysfunction had a significantly worse outcome, as did patients admitted for respiratory failure or sepsis. CONCLUSIONS: Pediatric recipients of an umbilical cord blood transplant who subsequently required mechanical ventilation had lower pediatric intensive care unit and hospital survival rates compared with patients receiving bone marrow transplantation. Survival at 2 yrs for umbilical cord blood transplant and bone marrow transplant patients was similar. Predictors of outcome for all stem cell transplant recipients requiring mechanical ventilation included pediatric intensive care unit diagnosis requiring intubation and hepatic function. Predictors of outcome can be identified shortly after intubation in pediatric stem cell transplant recipients and may aid in therapeutic decision making and family counseling.

Bone Marrow Transplantation↗
PubMed2003

Invasive and noninvasive pediatric mechanical ventilation.

Both invasive and noninvasive mechanical ventilation techniques are inherent to the care of most patients admitted to intensive care units. Despite the everyday use of mechanical ventilation for thousands of patients and the availability of thousands of reports in the medical literature, there are no clear and consistent guidelines for the use of mechanical ventilation for pediatric patients. In many areas data are lacking, and in other areas data are extrapolated from studies performed with adult subjects. Despite the variability in views about mechanical ventilation, 2 themes are consistent. First, modern pediatric respiratory care requires a substantial institutional commitment for state-of-the-art management of the mechanically ventilated patient. Second, a team approach involving physicians, nurses, and respiratory therapists is essential. This review highlights some of the major issues affecting the pediatric patient who requires invasive or noninvasive mechanical ventilation. These issues are pertinent to critical care clinicians because one of the most common reasons for admission to an intensive care unit is the need for mechanical ventilation. Furthermore, the duration of mechanical ventilation is one of the major determinants of the duration and cost of an intensive care unit stay.

Child↗