Relationship between physiologic deadspace/tidal volume ratio and gas exchange in infants with acute bronchiolitis on invasive mechanical ventilation

A comparative study of early and late extubation following transoral odontoidectomy and posterior fixation

Background and Aims:

Elective ventilation is the usual practice after transoral odontoidectomy (TOO) and posterior fixation. This practice of elective ventilation is not based on any evidence. The primary objective of our study was to find out the difference in oxygenation and ventilation in patients extubated early compared to those extubated late after TOO and posterior fixation. The secondary objectives were to compare the length of Intensive Care Unit (ICU)/hospital stay and pulmonary complications between the two groups.

Material and Methods:

After TOO and posterior fixation, patients were either extubated in the operating room (Group E) or extubated next day (Group D). The oxygenation (PaO₂:FiO₂ ratio) and ventilation (PaCO₂) of the two groups before surgery, at 30 min and at 6/12/24 and 48 h after extubation were compared. Complications, durations of ICU and hospital stay were noted.

Results:

The base-line PaO₂:FiO₂ and PaCO₂ was comparable between the groups. No significant change in the PaO₂:FiO₂ was noted in the postoperative period in either group as compared to the preoperative values. Except for at 12 h after surgery, there was no significant difference between the two groups at various time intervals. No significant change in the PaCO₂ level was seen during the study period in either group. PaCO₂ measured at 30 min after surgery was more in Group E (37.5 ± 3.2 mmHg in Group E vs. 34.6 ± 2.9 mmHg in Group D), otherwise there was no significant difference between the two groups at various time intervals. One patient in Group E (7.1%) and two patients in Group D (13%) developed postoperative respiratory complication, but the difference was not statistically significant. The mean ICU stay (Group D = 42 ± 25 h vs. Group E = 25.1 ± 16.9 h) and mean hospital stay (Group D = 9.9 ± 4 days vs. Group E = 7.6 ± 2.2 days) were longer in Group D patients.

Conclusion:

Ventilation and oxygenation in the postoperative period in patients undergoing TOO and posterior fixation are not different between the two groups. However, the duration of ICU and hospital stay was prolonged in group D.

Higher Dead Space Is Associated With Increased Mortality in Critically Ill Children

OBJECTIVE

Elevated dead space has been consistently associated with increased mortality in adults with respiratory failure. In children, the evidence for this association is more limited. We sought to investigate the association between dead space and mortality in mechanically ventilated children.

DESIGN

Single-center retrospective review.

SETTING

Tertiary care pediatric critical care unit.

PATIENTS

Seven hundred twelve mechanically ventilated children with an arterial catheter.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The end-tidal alveolar dead space fraction ((PaCO2-PETCO2)/PaCO2), a dead space marker, was calculated with each arterial blood gas. The initial end-tidal alveolar dead space fraction (first arterial blood gas after intubation) (per 0.1 unit increase: odds ratio, 1.59; 95% CI, 1.40-1.81) and day 1 mean end-tidal alveolar dead space fraction (odds ratio, 1.95; 95% CI, 1.66-2.30) were associated with mortality. The relationship between both initial and day 1 mean end-tidal alveolar dead space fraction and mortality held in multivariate modeling after controlling for any of the following individually: PaO2/FIO2, oxygenation index, 24-hour maximal inotrope score, and Pediatric Risk of Mortality III (all p<0.01), although end-tidal alveolar dead space fraction was no longer significant after controlling for the combination of oxygenation index, 24-hour maximal inotrope score, and Pediatric Risk of Mortality III. In 217 children with acute hypoxemic respiratory failure, initial end-tidal alveolar dead space fraction (per 0.1 unit increase odds ratio, 1.38; 95% CI, 1.14-1.67) and day 1 mean end-tidal alveolar dead space fraction (per 0.1 unit increase odds ratio, 1.60; 95% CI, 1.27-2.0) were associated with mortality. Day 1 mean end-tidal alveolar dead space fraction remained associated with mortality after controlling individually for any of the following in multivariate models: PaO2/FIO2, oxygenation index, and 24-hour maximal inotrope score (p≤0.02), although end-tidal alveolar dead space fraction was no longer significant after controlling for the combination of oxygenation index, 24-hour maximal inotrope score, and Pediatric Risk of Mortality III.

CONCLUSIONS

Increased dead space is associated with higher mortality in critically ill children, although it is no longer independently associated with mortality after controlling for severity of oxygenation defect, inotrope use, and severity of illness. However, because end-tidal alveolar dead space fraction is easy to calculate at the bedside, it may be useful for risk stratification and severity-of-illness scores.

Bronchiolitis

Everyone on the planet is exposed to respiratory syncytial virus (RSV) infection by the age of 2 years. Most infants admitted to the pediatric intensive care unit (PICU) for respiratory support during this infection are previously healthy, but their principal risk for needing PICU treatment is young age. That is, if you are born in October/November in the northern hemisphere, then your first winter exposure to RSV is likely to be when you are less than 4 months of age and vulnerable because of poor respiratory mechanical reserve (Alonso et al. 2007). However, if you are born in May/June, then you will be 7–8 months during your first winter exposure to RSV, much bigger and stronger and have more efficient thoracic and diaphragmatic mechanics. In the PICU, the main predictors of severe outcome in previously well infants appear to be young age, presence of apnea, and pulmonary consolidation on admission chest radiograph (Tasker et al. 2000; Lopez Guinea et al. 2007). Taken together, we can say that more severe RSV bronchiolitis in PICU practice is typically a problem of pulmonary consolidation, poor respiratory mechanics, and poor reserve, in the younger infant.

Non invasive monitoring in mechanically ventilated pediatric patients

Cardiopulmonary monitoring is a key component in the evaluation and management of critically ill patients. Clinicians typically rely on a combination of invasive and non-invasive monitoring to assess cardiac output and adequacy of ventilation. Recent technological advances have led to the introduction: of continuous non-invasive monitors that allow for data to be obtained at the bedside of critically ill patients. These advances help to identify hemodynamic changes and allow for interventions before complications occur. In this manuscript, we highlight several important methods of non-invasive cardiopulmonary monitoring, including capnography, transcutaneous monitoring, pulse oximetry, and near infrared spectroscopy.

Neurally triggered breaths reduce trigger delay and improve ventilator response times in ventilated infants with bronchiolitis

PURPOSE

Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation designed to improve patient-ventilator interaction by interpreting a neural signal from the diaphragm to trigger a supported breath. We hypothesized that neurally triggered breaths would reduce trigger delay, ventilator response times, and work of breathing in pediatric patients with bronchiolitis.

METHODS

Subjects with a clinical diagnosis of bronchiolitis were studied in volume support (pneumatic trigger) and NAVA (pneumatic and neural trigger) in a crossover design. Airway flow and pressure waveforms were obtained with a pneumotachograph and computerized digital recorder and were recorded for 120 s for each experiment.

RESULTS

Neurally triggered breaths had less trigger delay (ms) (40 ± 27 vs. 98 ± 34; p < 0.001) and reduced ventilator response times (ms) (15 ± 7 vs. 36 ± 25; p < 0.001) compared with pneumatically triggered breaths. Neurally triggered breaths had reduced pressure-time product (PTP) area A (cmH(2)O * s), the area of the pressure curve from initiation of breath to start of ventilator pressurization (0.013 ± 0.010; p < 0.001), and reduced PTP area B (cmH(2)O * s), the area of the pressure curve from start of ventilator pressurization to return of baseline pressure (0.008 ± 0.006 vs. 0.023 ± 0.009; p = 0.003). Reduced PTP may indicate decreased work of breathing.

CONCLUSION

Neurally triggered breaths reduce trigger delay, improve ventilator response times, and may decrease work of breathing in children with bronchiolitis. Further analysis is required to determine if neurally triggered breaths will improve patient-ventilator synchrony.