Chest
Volume 101, Issue 6, June 1992, Pages 1639-1643
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Clinical Investigations in Critical Care
Effects of Doxapram on Hypercapnic Response during Weaning from Mechanical Ventilation in COPD Patients

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Failure of weaning from mechanical ventilation in COPD patients is often related to diaphragmatic fatigue. Whether there is a central respiratory drive fatigue and a reserve of excitability is still debated. The purpose of this study was to analyze the following in 13 COPD patients weaned from mechanical ventilation: (1) ventilatory ( V˙e/PetCO2) and neuromuscular (P0.1/PetCO2) response to hypercapnia; (2) the maximum reserve capacity measured through changes in the V˙e/PetCO2 and P0.1/PetCO2 slopes after doxapram (DXP) infusion, which, given during the test, allows measurement of the maximum response capacity to overstimulation; and (3) analyze the influence of these changes on the outcome of weaning. The results show a variable P0.1/PetCO2 response and a low V˙e/PetCO2. DXP infusion does not change the slopes of these relations but increases the end-expiratory volume (ΔFRCd); (p<0.02). Since there was no change in the V˙e/PetCO2, P0.1/PetCO2, and ΔFRC values with or without DXP, there was no excitability reserve in patients who were successfully weaned. When weaning failed, DXP did not change V˙e/PetCO2 and P0.1/ PetCO2 slope, but ΔFRCd was greater the ΔFRC (p<0.001). The excitability reserve in these patients leads to an increase in end-expiratory volume, probably worsening the diaphragm dysfunction.

Section snippets

Patients

Thirteen patients (seven men, six women) aged 58 to 74 years (67.5 ± 6.5 years), with COPD gave their informed consent. All had a long history of chronic bronchitis and were regularly treated in the unit. Functional tests performed within four months before or after decompensation confirmed the acute obstructive syndrome. Current hospitalization was due to a bacterial infection requiring mechanical ventilation. All patients had long-term tracheostomies. Medication included feeding through a

Results

During the study, no patient showed cardiovascular or neurologic change and none of them required reinstitution of mechanical ventilation.

Results are shown in Tables 1 and 2. In a baseline state, ie, before rebreathing tests, breathing ambient air (15 min), patients were hypoxic (PaO2 = 40 ± 7.2 mm Hg; ext: 24 to 50) with variable hypercapnia (PaCO2 = 46.9 ± 6.3 mm Hg; ext = 38-64; P0.1 average was high but with strong intraindividual variations (7.9 ± 3.1 cm H2O, ext: 2.3 to 14.4; VC = 0.39).

Discussion

The results of this study bring out the following findings: (1) Response to hypercapnia is generally weak in COPD patients weaned from mechanical ventilation but there are strong individual differences.

(2) The respiratory centers can still be stimulated, as shown by the increase in P0.1d/PETCO2 in some patients, but this “overstimulation” causes an increase in the end-expiratory volume. (3) The neuromuscular and ventilatory response to hypercapnia with and without DXP does not allow prediction

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  • Cited by (0)

    Manuscript received September 23; revision accepted January 22.

    Professor of Anesthesiology.

    Research Engineer, Staff Anesthesiologist.

    §

    Associate Professor of Physiology.

    Staff Anesthesiologist.

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