Effect of continuous positive airway pressure on the rapid shallow breathing index in patients following cardiac surgery

Comparison of different methods of obtaining the rapid shallow breathing index

OBJECTIVE

To compare the Rapid Shallow Breathing Index (RSBI) obtained by the ventilometer and from mechanical ventilation parameters.

METHODS

Randomized crossover trial, including 33 intubated patients, on mechanical ventilation for at least 24 hours, undergoing spontaneous breathing test. Patients were submitted to the measurement of RSBI by four methods: disconnected from the ventilator through the ventilometer; in Pressure Support Ventilation (PSV) mode at a pressure of 7.ßcm H2O; in Continuous Positive Airway Pressure (CPAP) mode at a pressure of 5.ßcmH2O with flow trigger; in CPAP mode at a pressure of 5.ßcmH2O with pressure trigger.

RESULTS

No significant difference was detected between the RSBI obtained by the ventilometer and in the CPAP mode with flow and pressure triggers, however, in the PSV mode, the values were lower than in the other measurements (p.ß<.ß0.001). By selecting patients from the sample with higher RSBI (... 80 cycles.min-1.L-1), the value of the index obtained by the ventilometer was higher than that obtained in the three options of ventilation methods.

CONCLUSION

The RSBI obtained in the CPAP mode at a pressure of 5.ßcmH2O, in both triggers types, did not differ from that measured by the ventilometer; it is, therefore, an alternative when obtaining it from mechanical ventilation parameters is necessary. However, in the presence of borderline values, the RSBI measured by ventilometer is recommended, as in this method the values are significantly higher than in the three ventilation modalities investigated.

Identifying Novel Clusters of Patients With Prolonged Mechanical Ventilation Using Trajectories of Rapid Shallow Breathing Index

Objective

Patients with prolonged mechanical ventilation (PMV) are comprised of a heterogeneous population, creating great challenges for clinical management and study design. The study aimed to identify subclusters of PMV patients based on trajectories of rapid shallow breathing index (RSBI), and to develop a machine learning model to predict the cluster membership based on baseline variables.

Methods

This was a retrospective cohort study conducted in respiratory care center (RCC) at a tertiary academic medical center. The RCC referral criteria were patients with mechanical ventilation for at least 21 days with stable hemodynamic and oxygenation status. Patients admitted to the RCC from April 2009 to December 2020 were screened. Two-step clustering through linear regression modeling and k-means was employed to find clusters of the trajectories of RSBI. The number of clusters was chosen by statistical metrics and domain expertise. A gradient boosting machine (GBM) was trained, exploiting variables on RCC admission, to predict cluster membership.

Results

A total of 1371 subjects were included in the study. Four clusters were identified: cluster A showed persistently high RSBI; cluster B was characterized by a constant low RSBI over time; Cluster C was characterized by increasing RSBI; and cluster D showed a declining RSBI. Cluster A showed the highest mortality rate (72%), followed by cluster D (63%), C (62%) and B (61%; p = 0.005 for comparison between 4 clusters). GBM was able to predict cluster membership with an accuracy of &gt; 0.95 in ten-fold cross validation. Highly ranked variables for the prediction of clusters included thyroid-stimulating hormone (TSH), cortisol, platelet, free thyroxine (T4) and serum magnesium.

Conclusions

Patients with PMV are composed of a heterogeneous population that can be classified into four clusters by using trajectories of RSBI. These clusters can be easily predicted with baseline clinical variables.

Validation of rapid shallow breathing index displayed by the ventilator compared to the standard technique in patients with readiness for weaning

BACKGROUND

Rapid shallow breathing index (RSBI) is the most commonly used parameter for predicting weaning outcome. Measurement of RSBI by Wright spirometer (RSBI_standard) is the standard method in routine clinical practice. Data specific to the accuracy and reliability of the RSBI value displayed by the ventilator (RSBI_vent) are scarce. Accordingly, this study aimed to evaluate the association between the average value of RSBI_vent at different time points and RSBI_standard, and to assess the accuracy and reliability of these two RSBI measurement techniques.

METHODS

This prospective cohort study included mechanically ventilated patients who were ready to wean. At the beginning of spontaneous breathing trial using the flow-by method, RSBI was measured by two different techniques at the same time, including: (1) Wright spirometer (breathing frequency/average tidal volume in 1 min) (RSBI_standard), and (2) the values displayed on the ventilator at 0, 15, 30, 45, and 60 s (RSBI_vent).

RESULTS

Forty-seven patients were enrolled. The RSBI_vent value was significantly higher than the RSBI_standard value for every comparison. According to Spearman's correlation coefficient (r) and intraclass correlation coefficient (ICC), the average value of RSBI from 5 time points (0, 15, 30, 45, and 60 s) showed the best correlation with the standard technique (r = 0.76 [P < 0.001], and ICC = 0.79 [95% CI 0.61-0.88], respectively). Bland-Altman plot also showed the best agreement between RSBI_standard and the RSBI_vent value averaged among 5 time points (mean difference - 17.1 breaths/min/L).

CONCLUSIONS

We found that the ventilator significantly overestimates the RSBI value compared to the standard technique by Wright spirometer. The average RSBI_vent value among 5 time points (0, 15, 30, 45, and 60 s) was found to best correlate with RSBI_standard.

Dynamic inhomogeneity of aeration along the vertical axis of the lung may predict weaning failure regardless of diaphragm dysfunction

PURPOSE

This study aimed to investigate dynamic changes of lung aeration during a spontaneous breathing trial (SBT) in patients with diaphragm dysfunction (DD) and to predict weaning failure using electrical impedance tomography (EIT).

MATERIALS AND METHODS

We enrolled 40 adult patients who received mechanical ventilation over 48 h and were eligible for SBT with a T-piece. All patients were screened for DD using ultrasonography before SBT. EIT data, including global inhomogeneity index (an off-site parameter), and temporal skew of aeration (TSA) (an on-site parameter) were collected.

RESULTS

Sixteen (40%) patients had DD. During SBT, the tidal impedance variation decreased by 32% from baseline in patients with DD and by 14% in those without DD (p = 0.001). The global inhomogeneity index in the SBT failure group (n = 9) was 0.92 (median), and that of the SBT success group was 0.65 (p = 0.004). The TSA along the vertical axis of the lung was 12.0% and 2.0%, respectively (p = 0.001). With a vertical TSA cutoff of ≥4.35%, SBT failure was predicted with a sensitivity of 88.9% and specificity of 96.9% (area under the curve: 0.955).

CONCLUSION

Dynamic inhomogeneity of aeration along the vertical axis of the lung as assessed using TSA predicts SBT failure regardless of DD.

TRIAL REGISTRATION

This trial was retrospectively registered at cris.nih.go.kr (identifier: KCT003567; release date February 27, 2019).

Pulmonary Ultrasound: A New Era in Critical Care Medicine

Pulmonary ultrasonography is a complementary study that is easy to perform at the patient bedside with no need to transfer the patient to special areas. The technique provides information with high sensitivity and specificity for different pathologies. Pulmonary ultrasonography is a very important diagnostic tool in the assessment of lung, pleural, and chest wall diseases. Pulmonary ultrasound provides low-cost analysis, easy real-time reproduction, and safety, all of which have made it a beneficial tool in the diagnostic arsenal available to medical personnel. The purpose of this review was to describe the usefulness of pulmonary ultrasound in critical areas.

An Open Label Randomized Controlled Trial to Compare Low Level Pressure Support and T-piece as Strategies for Discontinuation of Mechanical Ventilation in a General Surgical Intensive Care Unit

Objective

The purpose of this study was to compare the efficacy of continuous low pressure support (PSV) and T-piece as strategies for discontinuation of mechanical ventilation and extubation in a surgical ICU.

Patients and Methods

This was a prospective open label randomized control study in surgical ICU patients who were intubated, mechanically ventilated, and who met criteria for a spontaneous breathing trial. Eligible, enrolled patients were randomized to receive low-level pressure supportup to 7 cmH2O (PSV) or T-piece as the mode of their spontaneous breathing trial.

Results

A total of 520 patients were randomized (260 in PSV group and 260 in T-piece group). There were no differences between the groups in baseline characteristics except duration of MV before trial was longer in PSV group. There were also no differences in hemodynamic and respiratory measures between groups. The PSV had a significant higher number of SBT attempt before success and extubation. After extubation, the re-intubation within 48 hours had a lower trend in PSV group (PSV vs. T-piece: 10% vs. 14.6%; p=0.11). The pneumonia occurrence, hospital mortality, hospital and ICU length of stay were not significant different between groups. In multivariable analysis, PSV was associated with a lower risk of success at the first SBT (adjusted relative risk, RR 0.79 [95% confidence interval, CI, 0.70 - 0.88]; p<0.001], and a lower risk of re-intubation within 48 hours after extubation (adjusted RR 0.62 [95%CI 0.40 - 0.98]; p=0.04). There were no differences between groups in pneumonia after extubation and in hospital mortality rate.

Conclusion

Although PSV needs a higher number of SBT trial before success and extubation, the re-intubation within 48 hours is lower than T piece. However, there were no differences between the groups in term of pneumonia after extubation, hospital mortality as well as ICU and hospital length of stay.

The use of Rapid Shallow Breathing Index shortens time to extubation in patients undergoing coronary artery bypass grafting

Background

This study aims to investigate the effects of the use of the Rapid Shallow Breathing Index on extubation success and time to extubation in patients undergoing elective isolated coronary artery bypass grafting.

Methods

This prospective, randomized-controlled study included a total of 72 patients (55 males, 19 females; mean age 60.3±9.3 years; range 45 to 76 years) who underwent isolated coronary artery bypass grafting between February 2016 and November 2016. The patients were divided into two groups as the RSBI group (n=36) and the control group (n=36). The control group was extubated by conventional criteria that were routinely applied in our clinic, while the RSBI group was extubated, when the index scores became below 77 breaths per min/L, following ensuring hemodynamic stability and weaning procedure from mechanical ventilation.

Results

The mean time to wean from mechanical ventilation was 5.8±1.0 hours in the RSBI group and 8.1±2.0 hours in the control group (p=0.03). Extubation protocol performed through the use of the index was found to provide 26% earlier extubation compared to the conventional extubation criteria. There was no significant difference in the postoperative follow-up parameters or clinical conditions.

Conclusion

Our study results show that a practical tool such as the Rapid Shallow Breathing Index can be reliably used for making a decision in favor of extubation in patients undergoing coronary artery bypass grafting. A shortened time to extubation by the use of this index may provide substantial benefits in terms of prevention of infections, mechanical ventilation-induced lung injuries, and potential pulmonary complications.

The rapid shallow breathing index as a predictor of successful mechanical ventilation weaning: clinical utility when calculated from ventilator data

OBJECTIVE:

The use of the rapid shallow breathing index (RSBI) is recommended in ICUs, where it is used as a predictor of mechanical ventilation (MV) weaning success. The aim of this study was to compare the performance of the RSBI calculated by the traditional method (described in 1991) with that of the RSBI calculated directly from MV parameters.

METHODS:

This was a prospective observational study involving patients who had been on MV for more than 24 h and were candidates for weaning. The RSBI was obtained by the same examiner using the two different methods (employing a spirometer and the parameters from the ventilator display) at random. In comparing the values obtained with the two methods, we used the Mann-Whitney test, Pearson's linear correlation test, and Bland-Altman plots. The performance of the methods was compared by evaluation of the areas under the ROC curves.

RESULTS:

Of the 109 selected patients (60 males; mean age, 62 ± 20 years), 65 were successfully weaned, and 36 died. There were statistically significant differences between the two methods for respiratory rate, tidal volume, and RSBI (p < 0.001 for all). However, when the two methods were compared, the concordance and the intra-observer variation coefficient were 0.94 (0.92-0.96) and 11.16%, respectively. The area under the ROC curve was similar for both methods (0.81 ± 0.04 vs. 0.82 ± 0.04; p = 0.935), which is relevant in the context of this study.

CONCLUSIONS:

The satisfactory performance of the RSBI as a predictor of weaning success, regardless of the method employed, demonstrates the utility of the method using the mechanical ventilator.

Rapid shallow breathing index

Predicting successful liberation of patients from mechanical ventilation has been a focus of interest to clinicians practicing in intensive care. Various weaning indices have been investigated to identify an optimal weaning window. Among them, the rapid shallow breathing index (RSBI) has gained wide use due to its simple technique and avoidance of calculation of complex pulmonary mechanics. Since its first description, several modifications have been suggested, such as the serial measurements and the rate of change of RSBI, to further improve its predictive value. The objective of this paper is to review the utility of RSBI in predicting weaning success. In addition, the use of RSBI in specific patient populations and the reported modifications of RSBI technique that attempt to improve the utility of RSBI are also reviewed.

Seated and semi-recumbent positioning of the ventilated intensive care patient - effect on gas exchange, respiratory mechanics and hemodynamics

OBJECTIVES

To compare the effect of semi-recumbent and sitting positions on gas exchange, respiratory mechanics and hemodynamics in patients weaning from mechanical ventilation.

BACKGROUND

Upright positions are encouraged during rehabilitation of the critically ill but there effects have not been well described.

METHODS

A prospective, randomized, cross-over trial was conducted. Subjects were passively mobilized from supine into a seated position (out of bed) and from supine to a semi-recumbent position (>45° backrest elevation in bed). Arterial blood gas (PaO2/FiO2, PaO2, SaO2, PaCO2 and A-a gradient), respiratory mechanics (VE,VT, RR, Cdyn, RR/VT) and hemodynamic measurements (HR, MABP) were collected in supine and at 5 min and 30 min after re-positioning.

RESULTS

Thirty-four intubated and ventilated subjects were enrolled. The angle of backrest inclination in sitting (67 ± 5°) was greater than gained with semi-recumbent positioning (50 ± 5°, p < 0.001). There were no clinically important changes in arterial blood gas, respiratory mechanic or hemodynamic values due to either position.

CONCLUSIONS

Neither position resulted in significant changes in respiratory and hemodynamic parameters. Both positions can be applied safely in patients being weaned from ventilation.

The effect of flow trigger on rapid shallow breathing index measured through the ventilator

BACKGROUND

The rapid shallow breathing index (RSBI) has the best predictive value to assess readiness for weaning from mechanical ventilation. At many institutions, this index is conveniently measured without disconnecting the patient from the ventilator, but this method may be inaccurate. Because modern ventilators have a base flow in the flow trigger mode that may provide a substantial help to the patient, we hypothesized that the RSBI is significantly decreased when measured through the ventilator with flow trigger even without continuous positive airway pressure (CPAP) and pressure support (PS).

METHODS

The RSBI was calculated using the values of minute ventilation and respiratory rate obtained either through the digital display of the ventilator or from a digital ventilometer. The RSBI was measured using 3 different methods: method 1, CPAP and PS both 0 cm H2O with flow trigger; method 2, CPAP and PS both 0 cm H2O without flow trigger; and method 3, using digital ventilometer.

RESULTS

A total of 165 measurements per method were obtained in 80 adult patients in the medical intensive care unit (MICU). The RSBI (breaths/min/L) values were 70.2 ± 26.5 with method 1, 85.4 ± 30.3 with method 2, and 80.1 ± 30.3 with method 3. The RSBI was significantly decreased using mechanical ventilation with flow trigger as compared with mechanical ventilation without flow trigger (P < .0001) or digital ventilometer (P < .0001). When method 1 was compared with methods 2 and 3, the RSBI decreased by 17% and 12%, respectively.

CONCLUSIONS

The RSBI measurement is significantly decreased by the base flow delivered through modern ventilators in the flow trigger mode. If RSBI is measured through the ventilator in the flow trigger mode, the difference should be considered when using RSBI to assess readiness for weaning from mechanical ventilation.

Weaning from mechanical ventilation

PURPOSE OF REVIEW

Liberation from mechanical ventilation is a defining moment for intubated patients, and thus a critical clinical decision. Extubating the patient too early exposes the patient to extubation failure and reintubation. Waiting too long increases the complications of prolonged intubation. Tools to help the physician with this critical decision and to test readiness have been available for decades, and are continuously being improved. New methods to improve extubation outcomes are also being developed. This review covers the latest studies in order to help physicians take advantage of the latest developments in a rapidly evolving field.

RECENT FINDINGS

This review highlights the recent advances in assessing and testing for readiness of weaning and liberation from mechanical ventilation, the cause of weaning failure, the value of weaning protocols, and the role of noninvasive positive pressure ventilation in liberating patients from invasive mechanical ventilation.

SUMMARY

Recent findings are shedding more light on this topic, and transforming 'the artistic' aspect of weaning and liberation from mechanical ventilation into a more 'scientific' approach that will expedite liberation from mechanical ventilation yet without encountering high failure rates, and without exposing patients to unnecessary risks.

New insights into weaning from mechanical ventilation: left ventricular diastolic dysfunction is a key player

PURPOSE

To investigate the diagnostic performance of Doppler echocardiography (DE) in predicting the outcome of weaning from mechanical ventilation in patients without overt cardiac disease.

METHODS

Fifty critical care noncardiac patients who fulfilled predetermined criteria for weaning underwent DE before and at the end of spontaneous breathing trial (pre-SBT/end-SBT, respectively). "Conventional" mitral inflow analysis and "advanced" DE parameters [tissue Doppler imaging (TDI)-derived mitral/tricuspid annular velocities and color M-mode Doppler velocity of propagation (V p)] were used to assess left ventricular (LV) diastolic function/filling pressures. Weaning was considered successful if patients had been extubated after successful SBT and sustained spontaneous breathing for more than 48 h.

RESULTS

Twenty-eight patients (56%) failed weaning: 23 patients failed SBT and 5 required reintubation within 48 h. Weaning failure was associated with the degree of LV diastolic dysfunction at pre-SBT (P = 0.01). Patients who failed weaning presented evidence of increased LV filling pressures at pre-SBT, by demonstrating increased E/E m and E/V p ratios compared with patients with successful outcome (P ≤ 0.004); pre-SBT values of lateral E/E m greater than 7.8 and E/V p greater than 1.51 predicted weaning failure with an area under the curve, sensitivity (%), and specificity (%) of 0.86, 79, and 100, and 0.74, 75, and 73, respectively. Lateral E/E m was the only factor independently associated with weaning failure before SBT; OR (95% CI) 5.62 (1.17-26.96), P = 0.03.

CONCLUSIONS

Our findings suggest that LV diastolic dysfunction is significantly associated with weaning outcome in critically ill patients with preserved LV systolic function. An E/E m ratio greater than 7.8 may identify patients at high risk of weaning failure.

Comparison of 3 different methods used to measure the rapid shallow breathing index

PURPOSE

Rapid shallow breathing index (RSBI) is conveniently measured through the ventilator. If continuous positive airway pressure (CPAP) is used, it may change the RSBI value. We measured the RSBI with a handheld spirometer and through the ventilator, with and without CPAP, to assess differences.

MATERIALS AND METHODS

Rapid shallow breathing index was measured in 3 ways: (1) CPAP 0 cm H(2)O and fraction of inspired oxygen (Fio(2)) 0.4, (2) CPAP 5 cm H(2)O and Fio(2) 0.4, and (3) ventilator disconnected and Fio(2) 0.21. Tidal volume and respiratory frequency were recorded from ventilator monitor values in methods 1 and 2, and from a handheld spirometer and observed respiratory frequency, in method 3.

RESULTS

A total of 170 measurements, each using all 3 methods, were obtained from 80 patients admitted to a medical intensive care unit. The mean RSBI values for methods 1, 2, and 3 were 98.1 ± 58.7, 87.6 ± 51.2, and 108.3 ± 65.3, respectively (P < .001). The RSBI decreased by 9.4% when using CPAP 0 cm H(2)O and by 19.1% when using CPAP 5 cm H(2)O.

CONCLUSIONS

The RSBI values measured through the ventilator with CPAP 5 cm H(2)O are much lower than the values measured with a handheld spirometer. Even the RSBI values measured with CPAP 0 cm H(2)O are significantly lower. This is attributable to the base flow delivered by some ventilators. The difference must be taken into account during weaning assessment.

Evolution of pattern of breathing during a spontaneous breathing trial predicts successful extubation

PURPOSE

Rapid shallow breathing may occur at any time during spontaneous breathing trials (SBT), questioning the utility of a single determination of the rapid shallow breathing index (RSBI). We hypothesize that change in RSBI during SBT may more accurately predict successful extubation than a single determination.

METHODS

Prospective observational study. Seventy-two subjects were extubated. At 24 h, 63/72 remained extubated (Extubation Success), and 9 were re-intubated (Extubation Failure). Respiratory rate (RR), tidal volume (VT) and RSBI were measured every 30 min during 2-h T-piece SBT. Change in respiratory parameters was assessed as percent change from baseline.

RESULTS

Initial RSBI was similar in Extubation Success and Extubation Failure groups (77.0 +/- 4.8, 77.0 +/- 4.8, p = ns). Nevertheless, RSBI tended to remain unchanged or decreased in the Extubation Success group; in contrast RSBI tended to increase in the Extubation Failure group because of either increased RR and/or decreased VT (p < 0.001 for mean percent change RSBI over time), indicating worsening of the respiratory pattern. Quantitatively, only 7/63 subjects of the Extubation Success group demonstrated increased RSBI >or=20% at any time during the SBT. In contrast, in the Extubation Failure group, RSBI increased in all subjects during the SBT, and eight of nine subjects demonstrated an increase greater than 20%. Thus, with a 2-h SBT the optimal threshold was a 20% increase (sensitivity = 89%, specificity = 89%). Similar results were obtained at 30 min (threshold = 5% increase). Percent change of RSBI predicted successful extubation even when initial values were >or=105.

CONCLUSION

Percent change of RSBI during an SBT is a better predictor of successful extubation than a single determination of RSBI.

Clinical review: liberation from mechanical ventilation

Mechanical ventilation is the defining event of intensive care unit (ICU) management. Although it is a life saving intervention in patients with acute respiratory failure and other disease entities, a major goal of critical care clinicians should be to liberate patients from mechanical ventilation as early as possible to avoid the multitude of complications and risks associated with prolonged unnecessary mechanical ventilation, including ventilator induced lung injury, ventilator associated pneumonia, increased length of ICU and hospital stay, and increased cost of care delivery. This review highlights the recent developments in assessing and testing for readiness of liberation from mechanical ventilation, the etiology of weaning failure, the value of weaning protocols, and a simple practical approach for liberation from mechanical ventilation.

Predictive value of rapid shallow breathing index measured at initiation and termination of a 2-hour spontaneous breathing trial for weaning outcome in ICU patients

BACKGROUND/PURPOSE

The rapid shallow breathing index (RSBI) is a weaning parameter usually measured at the start of a spontaneous breathing trial (SBT). This study investigated the value of RSBI measured at the beginning and termination of SBT as a predictor of weaning outcome.

METHODS

RSBI was measured during the initial 1 minute (RSBI1) and at termination (RSBI2) of an SBT in 172 patients recovering from acute respiratory failure.

RESULTS

Weaning was successful in 106 patients and failed in 66 patients. Among the 66 patients with weaning failure, 12 required reintubation within 48 hours (extubation failure), and the remaining 54 patients could not be extubated after SBT (trial failure). There were no differences between RSBI1 in the three groups (69.4 +/- 27.5, 81.7 +/- 24.4 and 75.5 +/- 26.5, respectively), but RSBI2 was significantly higher in patients with extubation failure (95.9 +/- 20.6) and trial failure (98.0 +/- 50.0) than in patients with weaning success (64.6 +/- 26.3) (both p < 0.001). Logistic regression revealed that RSBI2 was superior to RSBI1 and various physiologic indices in predicting weaning outcome. For the 118 extubated patients, the mean area under the receiver operating characteristic curve for RSBI2 and RSBI1 was 0.83 and 0.63, respectively. Using a threshold value of 105, the sensitivity, specificity, accuracy and likelihood ratio for weaning outcome were 0.91, 0.25, 0.85 and 1.38 for RSBI2 and 0.89, 0.16, 0.60 and 1.06 for RSBI1, respectively.

CONCLUSION

This study found that RSBI measured at the completion of SBT was superior to that measured at the start in predicting weaning outcome in critically ill patients.