Tracheal occlusion pressure: a simple index to monitor respiratory muscle fatigue during acute respiratory failure in patients with chronic obstructive pulmonary disease.

STUDY OBJECTIVE

To assess respiratory muscle fatigue in acute respiratory failure in patients with chronic obstructive pulmonary disease and evaluate its influence on weaning patients from mechanical ventilation.

DESIGN AND PATIENTS

We studied the time course of tracheal occlusion pressure (P0.1) and high-to-low ratio of the diaphragmatic electromyogram in 16 patients in acute respiratory failure with chronic obstructive pulmonary disease.

METHODS

All patients were intubated and studied during a 15-minute weaning period from ventilation. Minute ventilation (VE), arterial blood gases, P0.1 and high-to-low ratio of the diaphragm were measured every day from the onset to the end of acute failure (before extubation) at 5 and 15 minutes into the weaning period. The diaphragmatic electromyogram was recorded with an esophageal electrode and the high-to-low ratio of the electrical signal analyzed to assess diaphragmatic fatigue.

MEASUREMENTS AND MAIN RESULTS

In all patients P0.1 was markedly increased (7.1 +/- 2.4 cm H2O, mean +/- SE) on the first day of acute failure and did not change during weaning. In 11 patients, P0.1 had decreased to 4.7 +/- 1.8 cm H2O (P less than or equal to 0.002) before extubation (which was done after 5 to 9 days). In these patients, the high-to-low ratio of the diaphragm decreased rapidly-during the first minutes of weaning on the first day of acute failure and remained low throughout weaning, whereas before extubation no decrease in high-to-low ratio was seen during weaning. In 5 patients, P0.1 did not change significantly from the onset of acute failure and the high-to-low ratio remained low before extubation. These 5 patients had to be reintubated within 2 to 6 days. In both groups of patients, VE did not change significantly from the first to last day of acute failure (10.3 +/- 3 compared with 10.7 +/- 2.1 min-1), whereas blood gases during room air breathing improved significantly from the first to last day of acute failure, respectively, in each group (arterial oxygen pressure [PaO2], 33.5 +/- 1.5 compared with 44 +/- 9 mm Hg (P less than or equal to 0.05) and PaO2 56 +/- 2.3 compared with 49 +/- 2 mm Hg (P less than 0.005).

CONCLUSIONS

Extubation should not be done in patients with respiratory muscle fatigue despite improvement in arterial blood gases and clinical status; and P0.1 provides a valid and simple index to assess the likelihood of respiratory muscle fatigue.