Michael A Gentile

Deadspace to tidal volume ratio predicts successful extubation in infants and children

Objective Using a modification of the Bohr equation, single-breath carbon dioxide capnography is a noninvasive technology for calculating physiologic dead space (Vd/Vt). The objective of this study was to identify a minimal Vd/Vt value for predicting successful extubation from mechanical ventilation in pediatric patients. Design Prospective, blinded, clinical study. Setting Medical and surgical pediatric intensive care unit of a university hospital. Patients Intubated children ranging in age from 1 wk to 18 yrs. Interventions None. Measurements and Main Results Forty-five patients were identified by the pediatric intensive care unit clinical team as meeting criteria for extubation. Thirty minutes before the planned extubation, each patient was begun on pressure support ventilation set to deliver an exhaled tidal volume of 6 mL/kg. After 20 mins on pressure support ventilation, an arterial blood gas was obtained, Vd/Vt was calculated, and the patient was extubated. Over the next 48 hrs, the clinical team managed the patient without knowledge of the preextubation Vd/Vt value. Of the 45 patients studied, 25 had Vd/Vt ≤0.50. Of these patients, 24 of 25 (96%) were successfully extubated without needing additional ventilatory support. In an intermediate group of patients with Vd/Vt between 0.50 and 0.65, six of ten patients (60%) successfully extubated from mechanical ventilation. However, only two of ten patients (20%) with a Vd/Vt ≥0.65 were successfully extubated. Logistic regression analysis revealed a significant association between lower Vd/Vt and successful extubation. Conclusions A Vd/Vt ≤0.50 reliably predicts successful extubation, whereas a Vd/Vt >0.65 identifies patients at risk for respiratory failure following extubation. There appears to be an intermediate Vd/Vt range (0.51–0.65) that is less predictive of successful extubation. Routine Vd/Vt monitoring of pediatric patients may permit earlier extubation and reduce unexpected extubation failures.

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.

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

ObjectiveTo 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. DesignRandomized, crossover trial. SettingUniversity animal research laboratory. SubjectsTen swine (4.4–5.4 kg). InterventionsAcute 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 H2O) and frequency (10 Hz) were held constant. Oscillation amplitude (&Dgr;P) 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 ResultsGas exchange was assessed by arterial blood gas analysis after ventilation with each gas mixture. We demonstrated no significant difference in Paco2 or Pao2 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. ConclusionsWe 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.

Apnea Testing During Brain Death Assessment: A Review of Clinical Practice and Published Literature

The diagnosis of brain death is a complex process. Strong knowledge of neurophysiology and an understanding of brain death etiology must be used to confidently determine brain death. The key findings in brain death are unresponsiveness, and absence of brainstem reflexes in the setting of a devastating neurological injury. These findings are coupled with a series of confirmatory tests, and the diagnosis of brain death is established based on consensus recommendations. The drive to breathe in the setting of an intense ventilatory stimulus (ie, respiratory acidosis) is a critical marker of brainstem function. As a consequence, apnea testing is an important component of brain death assessment. This procedure requires close monitoring of a patient as all ventilator support is temporarily removed and Paco2 levels are allowed to rise. A “positive” test is defined by a total absence of respiratory efforts under these conditions. While apnea testing is not new, it still lacks consensus standardization regarding the actual procedure, monitored parameters, and evidence-based safety measures that may be used to prevent complications. The purpose of this report is to provide an overview of apnea testing and discuss issues related to the administration and safety of the procedure.

Inhaled Medical Gases: More to Breathe Than Oxygen

The mixture of oxygen and nitrogen is usually sufficient to achieve the therapeutic objective of supporting adequate gas exchange. Pediatric and neonatal patients have an assortment of physiologic conditions that may require adjunctive inhaled gases to treat the wide variety of diseases seen in this heterogeneous population. Inhaled nitric oxide, helium oxygen mixtures, inhaled anesthetics, hypercarbic mixtures, hypoxic mixtures, inhaled carbon monoxide, and hydrogen sulfide have been used to alter physiology in an attempt to improve patient outcomes. Balancing the therapeutic potential, possible adverse effects, and the complexity of the technical aspects of gas delivery, it is essential that clinicians thoroughly understand the application of medical gas therapy beyond the traditional nitrogen/oxygen mixture.

Cycling of the Mechanical Ventilator Breath

Patient-ventilator interaction is a key element in optimizing mechanical ventilation. The change from inspiration to expiration is a crucial point in the mechanically ventilated breath, and is termed “cycling.” Patient-ventilator asynchrony may occur if the flow at which the ventilator cycles to exhalation does not coincide with the termination of neural inspiration. Ideally, the ventilator terminates inspiratory flow in synchrony with the patients neural timing, but frequently the ventilator terminates inspiration either early or late. Most current mechanical ventilators include adjustable cycling features that, when used in conjunction with waveform graphics, can enhance patient-ventilator synchrony.

Orienting new respiratory therapists into the neonatal/pediatric environment: a survey of educators and managers.

BACKGROUND: Neonatal/pediatric respiratory care is recognized as a unique and complex area of clinical practice. Despite the substantial effort and costs associated with orienting neonatal/pediatric practitioners, few data exist related to the process of training respiratory therapists (RTs) in the acute neonatal/pediatric environment. To gain insight into the adequacy of preparation of RTs entering the neonatal/pediatric environment, the length of orientation necessary to achieve a base level of competency, and the methods used to train new neonatal/pediatric practitioners, we surveyed neonatal/pediatric respiratory care educators and managers. METHODS: The invitation to participate in the survey was distributed via e-mail to 1,259 members of the AARC education specialty section and 1,828 members of the AARC managers specialty section. The survey included 15 questions (not including the demographics questions), scored on 5-point Likert scale, and asked about: what type of degree program (associates degree or bachelors degree) better prepares new RTs for the neonatal/pediatric environment; experience requirements for orientation of neonatal/pediatric RTs; the role of simulation in training neonatal/pediatric RTs; and whether the neonatal/pediatric specialty credentialing exam should be used as a method of competency testing. There were 4 questions regarding simulation (the use of interactive full-body manikins in a realistic patient care environment), orientation times based on experience, and where the majority of the orientation time was spent. RESULTS: We received 251 responses (response rate 8%). The majority of respondents were either affiliated with or worked for urban, not-for-profit, non-government organizations. Sixty-three percent disagreed that an associates degree respiratory therapy program, and 42% disagreed that a bachelors degree program adequately prepares a new RT to work in the neonatal/pediatric critical care environment immediately after graduation. Seventy-one percent strongly agreed that childrens hospital respiratory care departments should have a dedicated respiratory therapy educator. Seventy-six percent agreed that simulation is an effective tool for training RTs for neonatal/pediatric critical care. Sixty-five percent agreed that RTs should be required to take an exam at the end of the orientation period to verify competency. Fifty-nine percent strongly agreed that neonatal/pediatric RTs should have the National Board for Respiratory Care Registered Respiratory Therapist (RRT) credential. CONCLUSIONS: There appears to be a discrepancy in the educational preparation expected prior to entering the acute-care neonatal/pediatric environment and what training methods are most appropriate and cost-effective for orienting new RTs to this specialized environment. A dedicated respiratory therapy educator is valued. Simulation is considered an effective tool for training RTs and provides training opportunities that otherwise would not be available. The neonatal/pediatric specialty certification exam appears to be recognized as a valid method of determining mastery and verifying competence.

Analysis of Radial Artery Catheter Placement by Respiratory Therapists Using Ultrasound Guidance

BACKGROUND: The use of ultrasound (US) guidance for radial artery cannulation has been shown to improve first attempt success rate, reduce time to successful cannulation, and reduce complications. We sought to determine whether properly trained respiratory therapists (RTs) could utilize US guidance for the placement of radial artery catheters. Primary outcome measurements were successful cannulation and first attempt success rate. Secondary outcomes included the effect of systolic blood pressure, prior attempts, palpable pulse strength, and gender in relation to US-guided radial artery cannulation success rates. METHODS: RTs certified in arterial catheter insertion were trained in radial artery catheterization using US by emergency medicine physicians. Subjects were enrolled based on the need for an arterial catheter placement. The catheters and US devices used were standardized. Data recorded included pulse strength, systolic and diastolic blood pressure, number of attempts, and successful/unsuccessful artery cannulation. All catheterization attempts were performed according to institutional policy and procedure. RESULTS: One hundred twenty-two radial artery catheter insertion attempts were made between December of 2008 and October of 2011, in patients in whom the treating physician requested RT radial artery cannulation. The overall success rate was 86.1%, whereas the first attempt success rate was 63.1%. There was no difference found between the overall mean success rate for weak or absent pulses, age, systolic blood pressure, gender, or prior attempts. Conclusion: RTs can effectively utilize US technology to place radial artery catheters. Systolic blood pressure, prior attempts, and gender are not reliable predictors of success for US-guided radial artery cannulation. Training on the use of US should be strongly encouraged for all practitioners who place radial artery catheters.

Ventilator Advisory System Employing Load and Tolerance Strategy Recommends Appropriate Pressure Support Ventilation Settings: Multisite Validation Study

BACKGROUND Loads on the respiratory muscles, reflected by noninvasive measurement of the real-time power of breathing (POBn), and tolerance of these loads, reflected by spontaneous breathing frequency (f) and tidal volume (Vt), should be considered when evaluating patients with respiratory failure. Pressure support ventilation (PSV) should be applied so that muscle loads are not too high or too low. We propose a computerized, ventilator advisory system employing a load (POBn) and tolerance (f and Vt) strategy in a fuzzy logic algorithm to provide guidance for setting PSV. To validate these recommendations, we performed a multisite study comparing the advisory system recommendations to experienced physician decisions. METHODS Data were obtained from adults who were receiving PSV (n = 87) at three university sites via a combined pressure/flow sensor, which was positioned between the endotracheal tube and the Y-piece of the ventilator breathing circuit and was directed to the advisory system. Recommendations from the advisory system for increasing, maintaining, or decreasing PSV were compared at specific time points to decisions made by physician intensivists at the bedside. RESULTS There were no significant differences in the recommendations by the advisory system (n = 210) compared to those of the physician intensivists to increase, maintain, or decrease PSV (p > 0.05). Physician intensivists agreed with 90.5% of all recommendations. The advisory system was very good at predicting intensivist decisions (r(2) = 0.90; p < 0.05) in setting PSV. CONCLUSIONS The novel load-and-tolerance strategy of the advisory system provided automatic and valid recommendations for setting PSV to appropriately unload the respiratory muscles that were as good as the clinical judgment of physician intensivists.

Clinical Management Strategies for Airway Pressure Release Ventilation: A Survey of Clinical Practice

BACKGROUND: Airway pressure release ventilation (APRV) is a commonly used mode of ventilation designed to increase mean airway pressure and thus oxygenation. Different strategies for clinical management have been described in the literature but are largely based on physiologic concepts, animal data, and small clinical trials. The purpose of this study was to determine how APRV is currently managed by surveying practicing respiratory therapists with experience using APRV. METHODS: A 15-item survey was developed by the authors and posted on the AARConnect online media platform in January 2016 after being declared exempt by our institutions institutional review board. Survey questions were derived from a literature review of recommended APRV settings. Responses were limited to one per institution. RESULTS: The survey was completed by 60 respondents who used APRV. Of the 4 key initial APRV settings (P high, P low, T high, and T low), there was good agreement among survey responders and published guidelines for setting initial T high (4–6 s) and initial P low (0 cm H2O). There was some disagreement regarding initial P high, with 48% of responders matching P high to conventional ventilation plateau pressures but another 31% using conventional ventilation mean airway pressure plus 2–5 cm H2O. The most disagreement was with the T low setting, with only 47% of survey responders agreeing with published guidelines about using the expiratory flow signal to set T low. There was good agreement among survey responders and published guidelines for what changes to make when gas exchange was outside of the targeted range. A substantial number of respondents accepted P high and APRV release volumes that may exceed lung-protective limits. CONCLUSIONS: There is only limited consensus among practitioners for initial APRV settings, probably reflecting the paucity of good clinical outcome data and confusion surrounding the physiology of this mode.