Bedside evaluation of respiratory distress

Cerebral cortex and respiratory muscles perfusion during spontaneous breathing attempts in ventilated patients and its relation to weaning outcomes: a protocol for a prospective observational study

INTRODUCTION

In addition to the well-documented factors that contribute to weaning failure, increased energy demands of the respiratory muscles during spontaneous breathing trials (SBTs) might not be met by sufficient increases in energy supplies. This discrepancy may deprive blood and oxygen of other tissues. In this context, restrictions in perfusion of splanchnic organs and non-working muscles during SBT have been associated with weaning failure. However, alterations in perfusion of the brain during the weaning process are less well understood.

OBJECTIVE AND HYPOTHESIS

To investigate whether cerebral cortex perfusion evolves differentially during the transition from mechanical ventilation (MV) to spontaneous breathing between patients failing or succeeding the SBT. We hypothesise that patients failing the SBT will exhibit reduced cerebral cortex perfusion during the transition from MV to spontaneous breathing as compared with patients succeeding the SBT.

METHODS AND ANALYSIS

This single-centre, prospective, observational study will be conducted in a medical Intensive Care unit of University Hospital Leuven, Belgium in ready to wean patients. Blood flow index in the cerebral cortex (prefrontal area), inspiratory (scalene) and expiratory muscle (upper rectus abdominis) and a non-working muscle (thenar eminence) will be simultaneously assessed by near-infrared spectroscopy (NIRS) using the tracer indocyanine green dye. Measurements will be performed on the same day during MV and during SBT. NIRS-derived tissue oxygenation index and cardiac output (by pulse contour analyses) will be recorded continuously. Twenty patients failing an SBT are estimated to be sufficient for detecting a significant difference in the change of cerebral cortex perfusion from MV to SBT (primary outcome) between SBT failure and success patients.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the local ethical committee (Ethische Commissie Onderzoek UZ/KU Leuven protocol ID: S60516). Results from this study will be presented at scientific meetings and congresses and published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT03240263; Pre-results.

DiapHRaGM: A mnemonic to describe the work of breathing in patients with respiratory failure

Background

The assessment of the work of breathing in the definitions of respiratory failure is vague and variable.

Objective

Identify a parsimonious set of signs to describe the work of breathing in hypoxemic, acutely ill patients.

Methods

We examined consecutive medical ICU patients receiving oxygen with a mask, non-invasive ventilation, or T-piece. A physician inspected each patient for 10 seconds, rated the level of respiratory distress, and then examined the patient for vital signs and 17 other physical signs. We used the rating of distress as a surrogate for measuring the work of breathing, constructed three multivariate models to identify the one with the smallest number of signs and largest explained variance, and validated it with bootstrap analysis.

Results

We performed 402 observations on 240 patients. Respiratory distress was absent in 78, mild in 157, moderate in 107, and severe in 60. Respiratory rate, hypoxia, heart rate, and frequency of most signs increased as distress increased. Respiratory rate and hypoxia explained 43% of the variance in respiratory distress. Diaphoresis, gasping, and contraction of the sternomastoid explained an additional 28%. Heart rate, blood pressure, alertness, agitation, body posture, nasal flaring, audible breathing, cyanosis, tracheal tug, retractions, paradox, scalene or abdominal muscles contraction did not increase the explained variance in respiratory distress.

Conclusion

Most of the variance is respiratory distress can be explained by five signs summarized by the mnemonic DiapHRaGM (diaphoresis, hypoxia, respiratory rate, gasping, accessory muscle). This set of signs may allow for efficient, standardized assessments of the work of breathing of hypoxic patients.

Approximate entropy of respiratory rate and tidal volume during weaning from mechanical ventilation

OBJECTIVE

To determine the effects of respiratory failure on respiratory rate pattern and tidal volume pattern.

DESIGN

Prospective, clinical study.

SETTING

Cardiovascular intensive care unit.

PATIENTS

Ten patients within 12 hrs of cardiac surgery, and 21 patients who required prolonged (>7 days) mechanical ventilation.

INTERVENTIONS

Patients were placed on spontaneous ventilation for weaning trials.

MEASUREMENTS AND MAIN RESULTS

During spontaneous ventilation, each breath's instantaneous respiratory rate and tidal volume were recorded for later analysis. Approximate entropy (ApEn) was calculated for respiratory rate and tidal volume series of the terminal 1000 breaths on each spontaneous ventilation trial in series of 100, 300, and 1000 breaths. Ten patients (controls) were studied and extubated within 12 hrs of cardiac surgery. The other 21 patients were studied during attempts to wean them from mechanical ventilation. These patients passed (Group V-Pass) 59 and failed (Group V-Fail) 14 weaning trials. Mean tidal volume did not vary between groups, but respiratory rate increased progressively from the control group to Group V-Pass to Group V-Fail (p < .017). Conversely, approximate entropy of respiratory rate (ApEn-RR) did not vary among the three groups at any time series length, but approximate entropy of tidal volume (ApEn-VT) increased from the control group to Group V-P (p< .017) to Group V-F (p< .017) at all time series lengths. ApEn-VT was very specific but only moderately sensitive at identifying respiratory failure.

CONCLUSION

Respiratory failure causes tidal volume patterns to become increasingly irregular, but increasing respiratory rate has no effect on respiratory rate pattern.

Weaning and extubation in the intensive care unit. Clinical or index-driven approach?

OBJECTIVE

To assess the outcome of a clinical judgement-based approach to weaning and extubation and to adduce the predictive accuracy of various mechanical respiratory indices measured in parallel.

DESIGN

Prospective study.

SETTING

Multidisciplinary intensive care unit at a university teaching hospital.

PATIENTS

163 consecutive mechanically ventilated patients, excluding tracheotomy, for weaning trial and extubation.

INTERVENTIONS

Using bedside clinical assessment, aided by arterial gas analysis, patients were weaned from mechanical ventilation to spontaneous ventilation via to continuous positive airway pressure (CPAP) circuit (with pressure support) of a microprocessor-controlled ventilator. Extubation occurred from the CPAP circuit at 7 cmH2O pressure support, fractional inspired oxygen (FIO2) < or = 0.5 and CPAP level of < or = 5 cmH2O, such that the partial pressure of oxygen in arterial blood (PaO2) was > or = 65 mmHg. Before extubation, observation for a 1-h (T0 and T60) trial period allowed measurement of vital capacity (VC), expired minute volume (VE), respiratory rate/tidal volume (f/VT) and maximal inspiratory pressure (MIP) using a one-way valve technique over 25 s.

MEASUREMENTS AND MAIN RESULTS

Over 7 months, 163 patients (62 females and 101 males; mean (SD) age 64(15) years) were considered. There were 91 surgical (18 with chronic obstructive pulmonary disease; COPD) and 72 medical (28 with COPD) patients. Ventilation was for > or = 1 day (median 5 days, range 1-31) in 115 [group I; APACHE II score 23(8)] and < or = 1 day in 48 [Group II; APACHE II score 17(6)]. Three patients (all Group I: 2 surgical, 1 medical) were reintubated within 24 h, an overall extubation failure rate of 1.8%. In group I, at T0, PaO2/FIO2 was 238(65), f/VT 50(26), MIP 44(21) cmH2O, VE 10.6(3.7) l/min, VC 13(5) ml/kg. Cardiorespiratory variables did not change significantly in either group, T0 to T60. For prediction of reintubation (n = 163), only VE (threshold > 10 l/min) and f/VT (threshold > 100) demonstrated moderate sensitivity and specificity at T60: 67 and 52% and 33 and 94%, respectively.

CONCLUSIONS

Bedside clinical judgement of weaning and extubation produces satisfactory outcomes. As a routine, mechanical predictive indices have limited utility.

Respiratory rate predicts cardiopulmonary arrest for internal medicine inpatients

OBJECTIVE

To assess whether vital sign measurements could identify internal medicine patients at risk for cardiopulmonary arrest.

DESIGN

Retrospective case-control study comparing 72 hours of pre-arrest vital sign measurements with 72 hours of vital sign measurements for patients from the same units who did not experience cardiopulmonary arrest.

SETTING

Twelve non-intensive care internal medicine units at a large midwestern academic medical center.

PATIENTS

Cases included all 59 inpatients who had experienced cardiopulmonary arrest between May 1989 and December 1990; patients who were designated do-not-resuscitate (DNR) or had less than 72 hours of vital sign recordings were excluded. Controls included 91 inpatients without cardiopulmonary arrest who were matched for units and who had 72 hours of vital sign recordings.

RESULTS

The occurrence of one or more respiratory rates > 27 breaths per minute over a 72-hour period had a sensitivity of 0.54 and a specificity of 0.83 (odds ratio = 5.56, 95% CL = 2.67-11.49) in predicting cardiopulmonary arrest. Other respiratory rate thresholds were also predictive of arrest. The ability of respiratory rate to predict arrest was stronger in units with high incidences of arrest relative to units with low incidences, for example, in units for the management of gastrointestinal disease (sensitivity = 1.00, specificity = 0.86) and renal disease (sensitivity = 0.69, specificity = 0.87). Respiratory rate remained a significant predictor (p < 0.001) after controlling for patient age and gender. Pulse rate and blood pressure were not predictive of cardiopulmonary arrest.

CONCLUSIONS

Using elevated respiratory rates as a signal for focused diagnostic studies and therapeutic interventions in internal medicine patients may be useful in reducing the incidence of subsequent cardiopulmonary arrest, and lowering associated morbidity and mortality.

Latent dystrophic myopathy revealed by unsuccessful weaning from mechanical ventilation

We report a patient who had difficulty in weaning from mechanical ventilation which was due to an unsuspected latent dystrophic myopathy. The association of latent dystrophic myopathy and unsuccessful weaning has not been previously reported.