Highlights of the 2005 Greek Armed Forces Critical Care Meeting
Highlights of the 2005 Greek Armed Forces Critical Care Meeting
The issue of patient liberation from mechanical ventilation is surrounded by controversy. As there is a wide variety of factors causing respiratory failure, it is reasonable to anticipate that any single method would be inadequate. Clinical experience or predictive indices do not seem to suffice in isolation. Weaning failure does not simply indicate the need for reintubation and continued mechanical ventilation. Weaning failure per se may have an impact on morbidity and mortality. Reintubation may be traumatic and technically more challenging for the unstable patient in respiratory distress and with copious secretions. These patients may be prone to hemodynamic instability during reintubation or reinitiation of positive pressure ventilation. A failed weaning trial may delay future attempts, especially if complications have occurred. All these reasons underline the magnitude of the problem.
A distinction should be made between weaning and extubation failure: Weaning is the inability to tolerate spontaneous breathing without mechanical ventilatory support with the artificial airway in place. Extubation failure is the failure of spontaneous breathing after the removal of the artificial airway.
For the majority of critically ill patients, weaning and extubation are uneventful. In approximately 25% to 30% of mechanically ventilated patients, weaning difficulties are encountered.
Nevertheless, weaning comprises a large portion of the total time a patient spends on a ventilator. In a cross-sectional multicenter study in 47 medical-surgical ICUs in Spain, the overall duration of mechanical ventilation was found to be 27.1 ± 1.1 days, and weaning accounted for more than 40% of that time. Strategies or interventions that would expedite weaning would obviously have an impact on total amount of time spent on a ventilator.
Timing is a very important factor, as premature weaning will impose unnecessary stress on the respiratory systems. On the other hand, delayed weaning predisposes to complications related to mechanical ventilation and especially ventilator-acquired pneumonia (VAP).
Successful weaning is a complex process involving the lungs, the cardiovascular system (preload, afterload, and contractility), respiratory muscle and nerve function and integrity, chest wall characteristics (elastance, resistance), and ventilatory requirements (increased CO2 production and others).
The role of pressure support ventilation (PSV) in weaning was studied several years ago in a prospective study by Brochard and colleagues. In their study, 109 patients who satisfied weaning criteria were allocated to 3 different weaning modes: 35 received T piece trials, 43 received synchronized intermittent mandatory ventilation (SIMV), and 31 received PSV. Weaning failure results favored PSV as a method for weaning (23% for PSV, 43% for T piece, 42% for SIMV; P = 0.05).
Further prospective, randomized, multicenter studies have yielded different results. For example, in one trial, 546 patients requiring mechanical ventilation were randomly assigned to undergo SIMV, PSV, intermittent trials of spontaneous breathing, or a once-daily trail of spontaneous breathing. In this study, a once-daily trial of spontaneous breathing led to extubation about 3 times more quickly than SIMV and about twice as quickly as PSV. Multiple daily trials of spontaneous breathing were equally successful. Further studies have shown that pressure support and T-tube appear to be equally suitable methods for weaning trials.
The optimal duration of a weaning trial was also examined in a prospective, multicenter study in which 526 patients were allocated to 30- and 120-minute weaning trial groups. No differences were seen in ICU and hospital mortality rates and reintubation rates between the groups.
Also studied was the identification of patients who are candidates for weaning followed by daily weaning trials. This was shown to reduce the duration of mechanical ventilation and the cost of intensive care in a randomized, controlled trial of 300 patients receiving mechanical ventilation. Although there were no differences in the number of ICU and inhospital stays, there were fewer complications in the intervention group.
The impact of a protocol-driven weaning method as compared with the traditional physician-directed weaning was shown in a study by Kollef and colleagues. In the intervention group, the patients were evaluated by assigned nurses and respiratory therapists who were implementing a specific weaning protocol. There were no differences in mortality between the 2 groups, but in the intervention group the number of successful extubations were significantly higher compared with the control group (risk ratio 1.31; 95% confidence interval 1.15 to 1.50; P = .039). In another study, a ventilator management protocol was shown to decrease days of ventilatory support and VAP. More recent studies and reviews have confirmed the beneficial effect of a protocol-driven weaning approach, especially in chronic obstructive pulmonary disease (COPD) patients. Of note, the protocol-based approach was not shown to have any weaning benefit in a single-center prospective, controlled study. This study was conducted in a closed medical ICU fully staffed and with regular, system-based rounds.
Several empirical practical steps appear to be reasonable before considering a weaning trial. The important first step is the identification of the eligible patient. This patient should be hemodynamically stable and should require no vasoactive medications. Electrolytes and especially potassium should be normal. Thyroid function should be normal, and occult hypothyroidism should be especially considered and ruled out. Mental status should be adequate (usually Glasgow Coma Scale > 11). Oxygenation should be adequate, as reflected by a pO2 higher than 55 mm Hg or FiO2 less than 0.4 and PEEP less than 5 cm H2O. Most importantly, there should be resolution of the cause of the respiratory failure, and there should be no residual or occult infection, especially in cases of ARDS. Furthermore, other system contribution to respiratory failure, such as cardiac ischemia, intra-abdominal hypertension, or steroid-induced myopathy in a COPD patient, should be considered.
The patient should be carefully assessed for his/her ability to tolerate a weaning trial, and the duration of the trial should be predetermined. Subsequently, the patient should be very closely monitored during the trial and, if stable, extubation should be considered at the end.
Clinical acumen and experience do not appear to be particularly helpful. In a small study of 31 patients, of which 17 were successfully weaned, physicians' judgment showed poor positive and negative predictive value in predicting weaning outcome.
Despite extensive clinical research, the search for an objective bedside weaning index has not yielded satisfactory results. A helpful index identified more than 10 years ago is the rapid shallow index. It is defined as the ratio of the FiO2 to the tidal volume measured during spontaneous breathing. This index was the most accurate predictor of failure, and its absence the most accurate predictor of success in a small prospective study involving 64 patients. An interesting new index recently described is reported in the esophageal pressure swings during a spontaneous breathing trial. This index may provide additional information and assistance in weaning.
Noninvasive positive pressure ventilation (NIPPV) can be very helpful when weaning COPD patients. In a multicenter, randomized trial involving 50 patients, NIPPV following extubation was offered as an alternative to invasive pressure support in the interventional group when the patients failed a T-tube trial. At 60 days, more patients in the NIPPV group were weaned, and they had less mortality and shorter ICU stays. None developed VAP. NIPPV also appears to be a useful tool in helping prevent ventilation in the acutely hypoxemic patient.
Recently, the cuff-leak test was shown to be a sensitive and specific indicator in identifying patients at risk for postextubation stridor.
Finally, specialized weaning centers may assist in the weaning of difficult-to-wean patients.
The issue of patient liberation from mechanical ventilation is surrounded by controversy. As there is a wide variety of factors causing respiratory failure, it is reasonable to anticipate that any single method would be inadequate. Clinical experience or predictive indices do not seem to suffice in isolation. Weaning failure does not simply indicate the need for reintubation and continued mechanical ventilation. Weaning failure per se may have an impact on morbidity and mortality. Reintubation may be traumatic and technically more challenging for the unstable patient in respiratory distress and with copious secretions. These patients may be prone to hemodynamic instability during reintubation or reinitiation of positive pressure ventilation. A failed weaning trial may delay future attempts, especially if complications have occurred. All these reasons underline the magnitude of the problem.
A distinction should be made between weaning and extubation failure: Weaning is the inability to tolerate spontaneous breathing without mechanical ventilatory support with the artificial airway in place. Extubation failure is the failure of spontaneous breathing after the removal of the artificial airway.
For the majority of critically ill patients, weaning and extubation are uneventful. In approximately 25% to 30% of mechanically ventilated patients, weaning difficulties are encountered.
Nevertheless, weaning comprises a large portion of the total time a patient spends on a ventilator. In a cross-sectional multicenter study in 47 medical-surgical ICUs in Spain, the overall duration of mechanical ventilation was found to be 27.1 ± 1.1 days, and weaning accounted for more than 40% of that time. Strategies or interventions that would expedite weaning would obviously have an impact on total amount of time spent on a ventilator.
Timing is a very important factor, as premature weaning will impose unnecessary stress on the respiratory systems. On the other hand, delayed weaning predisposes to complications related to mechanical ventilation and especially ventilator-acquired pneumonia (VAP).
Successful weaning is a complex process involving the lungs, the cardiovascular system (preload, afterload, and contractility), respiratory muscle and nerve function and integrity, chest wall characteristics (elastance, resistance), and ventilatory requirements (increased CO2 production and others).
The role of pressure support ventilation (PSV) in weaning was studied several years ago in a prospective study by Brochard and colleagues. In their study, 109 patients who satisfied weaning criteria were allocated to 3 different weaning modes: 35 received T piece trials, 43 received synchronized intermittent mandatory ventilation (SIMV), and 31 received PSV. Weaning failure results favored PSV as a method for weaning (23% for PSV, 43% for T piece, 42% for SIMV; P = 0.05).
Further prospective, randomized, multicenter studies have yielded different results. For example, in one trial, 546 patients requiring mechanical ventilation were randomly assigned to undergo SIMV, PSV, intermittent trials of spontaneous breathing, or a once-daily trail of spontaneous breathing. In this study, a once-daily trial of spontaneous breathing led to extubation about 3 times more quickly than SIMV and about twice as quickly as PSV. Multiple daily trials of spontaneous breathing were equally successful. Further studies have shown that pressure support and T-tube appear to be equally suitable methods for weaning trials.
The optimal duration of a weaning trial was also examined in a prospective, multicenter study in which 526 patients were allocated to 30- and 120-minute weaning trial groups. No differences were seen in ICU and hospital mortality rates and reintubation rates between the groups.
Also studied was the identification of patients who are candidates for weaning followed by daily weaning trials. This was shown to reduce the duration of mechanical ventilation and the cost of intensive care in a randomized, controlled trial of 300 patients receiving mechanical ventilation. Although there were no differences in the number of ICU and inhospital stays, there were fewer complications in the intervention group.
The impact of a protocol-driven weaning method as compared with the traditional physician-directed weaning was shown in a study by Kollef and colleagues. In the intervention group, the patients were evaluated by assigned nurses and respiratory therapists who were implementing a specific weaning protocol. There were no differences in mortality between the 2 groups, but in the intervention group the number of successful extubations were significantly higher compared with the control group (risk ratio 1.31; 95% confidence interval 1.15 to 1.50; P = .039). In another study, a ventilator management protocol was shown to decrease days of ventilatory support and VAP. More recent studies and reviews have confirmed the beneficial effect of a protocol-driven weaning approach, especially in chronic obstructive pulmonary disease (COPD) patients. Of note, the protocol-based approach was not shown to have any weaning benefit in a single-center prospective, controlled study. This study was conducted in a closed medical ICU fully staffed and with regular, system-based rounds.
Several empirical practical steps appear to be reasonable before considering a weaning trial. The important first step is the identification of the eligible patient. This patient should be hemodynamically stable and should require no vasoactive medications. Electrolytes and especially potassium should be normal. Thyroid function should be normal, and occult hypothyroidism should be especially considered and ruled out. Mental status should be adequate (usually Glasgow Coma Scale > 11). Oxygenation should be adequate, as reflected by a pO2 higher than 55 mm Hg or FiO2 less than 0.4 and PEEP less than 5 cm H2O. Most importantly, there should be resolution of the cause of the respiratory failure, and there should be no residual or occult infection, especially in cases of ARDS. Furthermore, other system contribution to respiratory failure, such as cardiac ischemia, intra-abdominal hypertension, or steroid-induced myopathy in a COPD patient, should be considered.
The patient should be carefully assessed for his/her ability to tolerate a weaning trial, and the duration of the trial should be predetermined. Subsequently, the patient should be very closely monitored during the trial and, if stable, extubation should be considered at the end.
Clinical acumen and experience do not appear to be particularly helpful. In a small study of 31 patients, of which 17 were successfully weaned, physicians' judgment showed poor positive and negative predictive value in predicting weaning outcome.
Despite extensive clinical research, the search for an objective bedside weaning index has not yielded satisfactory results. A helpful index identified more than 10 years ago is the rapid shallow index. It is defined as the ratio of the FiO2 to the tidal volume measured during spontaneous breathing. This index was the most accurate predictor of failure, and its absence the most accurate predictor of success in a small prospective study involving 64 patients. An interesting new index recently described is reported in the esophageal pressure swings during a spontaneous breathing trial. This index may provide additional information and assistance in weaning.
Noninvasive positive pressure ventilation (NIPPV) can be very helpful when weaning COPD patients. In a multicenter, randomized trial involving 50 patients, NIPPV following extubation was offered as an alternative to invasive pressure support in the interventional group when the patients failed a T-tube trial. At 60 days, more patients in the NIPPV group were weaned, and they had less mortality and shorter ICU stays. None developed VAP. NIPPV also appears to be a useful tool in helping prevent ventilation in the acutely hypoxemic patient.
Recently, the cuff-leak test was shown to be a sensitive and specific indicator in identifying patients at risk for postextubation stridor.
Finally, specialized weaning centers may assist in the weaning of difficult-to-wean patients.
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