Severe Hypercapnia After Low-Flow Oxygen Therapy in Patients With Neuromuscular Disease and Diaphragmatic Dysfunction

https://doi.org/10.4065/70.4.327Get rights and content

Objective

To increase the general awareness of the possible exacerbation of hypercapnia by the administration of low-flow oxygen in patients with neuromuscular disorders.

Design

We retrospectively reviewed the medical records of 118 consecutive adult patients with a diagnosis of neuromuscular disease who underwent phrenic nerve conduction studies during a 5-year period, and we analyzed pulmonary function data for 8 patients who underwent arterial blood gas studies before and after the administration of low-flow oxygen.

Material and Methods

In the eight patients with neuromuscular disease and diaphragmatic dysfunction (three with polymyositis, three with amyotrophic lateral sclerosis or nonspecific motor neuron disease, and one each with inflammatory motor neuropathy and chronic poliomyelitis), we analyzed the response of the arterial carbon dioxide tension (Paco2) after low-flow supplemental oxygen therapy (0.5 to 2 L/min). Linear analysis was used to attempt to find correlations between respiratory variables and the Paco2 response after oxygen therapy.

Results

For the overall study group, the mean Paco2 increased 28.2± 23.3 torr after low-flow oxygen treatment; in five patients, it increased by 27 torr or more. Four patients who were subsequently treated with nocturnal assisted ventilation were able to use supplemental oxygen during the day with less severe hypercapnia. Statistical analysis failed to reveal specific correlations between increased Paco2 values after oxygen therapy and any respiratory variables.

Conclusion

In patients with neuromuscular disease and diaphragmatic dysfunction, even low-flow supplemental oxygen should be administered with caution, and assisted ventilation should be strongly considered as an initial intervention.

Section snippets

PATIENTS AND METHODS

On review of the individual medical records of 118 consecutive adult patients, encountered during a 5-year period, who underwent phrenic nerve conduction studies and had a diagnosis of neuromuscular disease, we found 8 in whom results of the phrenic nerve conduction studies were abnormal and in whom repeated arterial blood gases (ABGs) were determined with the patient in the awake state before and after supplemental oxygen therapy. For these eight patients, demographic information, disease

RESULTS

A summary of the clinical and respiratory data for the study patients is shown in Table 1. The ABG responses before and after administration of supplemental oxygen and the time at which the tests were done are itemized in Table 2. The results of the phrenic nerve stimulation and diaphragmatic EMG response, the type of treatment, and the outcome of the study patients are summarized in Table 3. The mean age of the patients was 57 years, and the mean FVC, MVV, and Pimax were considerably decreased

DISCUSSION

Although this patient population had a variety of neuromuscular disorders, all patients had decreased or absent diaphragmatic EMG responses and moderate to severe reductions in the FVC. When admitted with the chief complaint of dyspnea, all patients were given low-flow oxygen therapy, and seven of the eight patients exhibited moderate to severe hypoxia and hypercapnia on initial ABG studies. Follow-up ABGs were determined primarily after changes in mental status and in three cases led to

CONCLUSION

Regardless of the underlying mechanisms for hypoventilation, data from the current study support the concept that, in patients with neuromuscular disease who have demonstrated diaphragmatic dysfunction and hypercapnia, supplemental oxygen therapy should be very closely monitored. Physicians should ideally repeat ABG studies after 60 minutes or less of supplemental oxygen therapy and be alert to the possibility of a substantial increase in the Paco2, level, especially if patients have

REFERENCES (20)

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1

Current address: The Mary Imogene Hospital, Cooperstown, New York.

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