Simple, Difficult, or Prolonged Weaning: The Most Important Factor Is the Success or Failure of the First Weaning Trial

A recent international consensus conference¹ published in 2007 proposed to categorize ventilated patients into 3 groups, based on the difficulty and duration of the weaning process: “simple weaning” (group 1) includes patients who succeed the first weaning trial and are extubated without difficulty, “difficult weaning” (group 2) includes patients who fail the first weaning trial and require up to 3 spontaneous breathing trials or 7 days to achieve successful weaning, and “prolonged weaning” (group 3) includes patients who require more than 7 days of weaning after the first weaning trial. According to the literature,^2–4 the proportion of patients in each group was estimated at 70% for simple weaning, 15% for difficult weaning, and 15% for prolonged weaning. The conference emphasized that the first weaning trial must be performed as soon as the patient meets the following criteria: resolution of disease for which the patient was intubated; cardiovascular stability with no or minimal vasopressors; no continuous sedation; and adequate oxygenation, defined as P_aO2/F_IO2 ≥ 150 mm Hg and PEEP ≤ 8 cm H₂O.

This last point is crucial and could explain the differences in failure rates of the first weaning trial reported in this issue of Respiratory Care by Tonnelier et al.⁵ In earlier studies,^2–4 a weaning trial was performed when F_IO2 was ≤ 40%, PEEP ≤ 5 cm H₂O, P_aO2/F_IO2 > 200 mm Hg, and after the success of respiratory physiology criteria, with a rapid shallow breathing index < 105 breaths/min/L, and maximum inspiratory pressure > −20 cm H₂O. In more recent studies,^6,7 patients were screened earlier to pass a weaning trial (F_IO2 ≤ 50% with PEEP up to 8 cm H₂O) and could be extubated with a P_aO2/F_IO2 < 200 mm Hg without added respiratory physiology criteria that are unnecessary and may in fact delay extubation.⁸ In earlier studies the failure rate of the first weaning trial was not 30%, as expected, but 40–50% of patients.^6,7 Tonnelier et al⁵ report their experience over a 1-year period with an early weaning strategy modeled on the recent recommendations.¹ The first-weaning-trial failure rate was 46%, but over 70% of the patients were ventilated more than 48 hours.⁵ Another fundamental result is that mortality was higher in the patients with prolonged weaning, but not in the patients with difficult weaning, as compared to the simple weaning patients.

The success or failure of the first weaning trial distinguishes the simple weaning group from the difficult and prolonged weaning groups. After failure of the first weaning trial the main goal is to hasten weaning to prevent difficult weaning from becoming prolonged weaning. The success obviously depends on the patient, and most patients in the prolonged weaning group have neuromuscular or chronic respiratory disease, but success also depends on the treatment. In 1988, Lemaire et al clearly demonstrated the occurrence of cardiopulmonary edema as the cause of respiratory distress shortly after the beginning of a spontaneous breathing trial.⁹ The cardiac origin is probably one of the most common causes of weaning failure, due to systolic or diastolic left-ventricular dysfunction or to an ischemic mitral regurgitation. It should be diagnosed by all means, because it can be effectively treated with diuretics and/or vasodilators, and sometimes even by coronary angioplasty in cardiac ischemia. Recently, several studies found benefit from brain natriuretic peptide^10–12 or echocardiography^13,14 to unmask the cardiac origin of weaning failure.

However, the increase in left-ventricular filling pressure during the transition from mechanical ventilation to spontaneous ventilation depends on the type of weaning trial. The weaning trial is generally performed either with a T-piece and simply disconnecting the patient from the ventilator, or with a low level of pressure support, but in all cases the trial must be done without PEEP, which could mask cardiac dysfunction.¹⁵ The main objective of the weaning process in simple weaning is to detect weaning readiness as early as possible, which is best achieved with a systematic approach. A pressure-support trial is easy to implement into a protocol because it is not necessary to disconnect the patient from the ventilator, and respiratory rate and tidal volume are continuously monitored by the ventilator. In addition, the failure rate is lower with pressure support than with T-piece,^15–17 due to lower respiratory muscle effort during pressure support,¹⁵ which may hasten weaning. However, the mortality of patients who fail extubation is particularly high (40–50%),¹⁸ and the more difficult T-piece test may reduce the re-intubation rate. Tonnelier et al found a higher rate of extubation failure in the difficult and prolonged weaning patients than in the simple weaning patients,⁵ and that result should encourage a prolonged T-piece trial, in order to avoid re-intubation in difficult-to-wean patients.

After failure of the first weaning trial, most patients are ventilated with pressure-support ventilation.¹⁹ Frequent patient-ventilator asynchrony is a risk in prolonged mechanical ventilation,²⁰ and altered sleep quality by numerous central apneas²¹ and ineffective efforts.²² An excessive ventilation delivering large tidal volume and long insufflation time is the main contributing factor to these asynchronies.²³ A key objective is to optimize ventilator settings that could improve sleep quality and maybe shorten weaning duration.

The study by Tonnelier et al⁵ is important because it allows us to update the data on weaning since the international conference.¹ Using a protocol of early weaning, the failure rate of the first weaning trial is nearly 50% of the ventilated patients in the intensive care unit (excluding drug intoxication and uncomplicated postoperative patients), and more than two thirds of the patients were ventilated more than 2 days. Tonnelier et al found a high risk of re-intubation in difficult-to-wean patients, and high mortality when weaning duration exceeded one week. This study highlights that failure of the first weaning trial is a warning signal, and it is necessary to initiate new research to determine the optimal treatment.

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