Study design: Retrospective study.
Objectives: The objective of this study was to compare the CO₂ response of acute tetraplegic cervical spinal cord injury (SCI) patients undergoing mechanical ventilation with a control group of critically ill patients ready for weaning of mechanical ventilation and successfully extubated.
Setting: This study was conducted at the intensive care unit of a University Hospital in Mallorca, Spain.
Methods: CO₂ response was studied in 12 acute tetraplegic cervical SCI patients at the C4-C7 level and 22 control patients. The control group patients were consecutively selected from a database of patients with mechanical ventilation and who were successfully extubated after a CO₂ response test. To increase the CO₂ , we used the method of re-inhalation of expired air, and we evaluated the hypercapnic ventilatory response, the change in minute ventilation induced by the increase of partial pressure of arterial carbon dioxide (PaCO₂ ), which measures the whole respiratory system (metabolic control, neuromuscular or ventilatory apparatus), and the hypercapnic drive response, the change in the airway occlusion pressure at 100 ms induced by the increase in PaCO2, which measures the chemosensitivity of the respiratory center.
Results: Cervical SCI patients were younger than the control group patients (26±7 and 62±12 years, respectively; P<0.001). Mean values of the hypercapnic ventilatory response in cervical SCI and control groups were 0.52±0.31 and 0.64±0.33 l min(-1) per mm Hg (P=0.40), respectively, and the hypercapnic drive response was 0.24±0.16 and 0.48±0.23 cm H₂O per mm Hg (P=0.001), respectively.
Conclusion: Acute tetraplegic cervical SCI patients had reduced hypercapnic drive response that may contribute to the difficult weaning, without reduction in hypercapnic ventilatory response.