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Re: The value of ABGs

Dear Editor

We write in response to the paper by Cross et al. on the use of NIV.[1] We are encouraged to see research into such an important and under investigated area of emergency medicine.

We do however have concerns regarding the study design, in particular the criteria on which NIV was initiated. The benefits of NIV have mainly been demonstrated in patients with a respiratory acidosis rather than those with symptoms of respiratory distress and/or hypoxia alone as in this trial. Current widely accepted guidelines from the British Thoracic Society recommend initiation of NIV for a respiratory acidosis (pH <7.35).[2] Thus knowledge of arterial blood tensions is critical to its application. We would challenge the usefulness of the authors’ definition of acute respiratory failure without arterial blood gas analysis.

In addition, NIV was initiated prior to a trial of accepted medical therapy for acute respiratory failure, such as nebulized or intravenous bronchodilators or vasodilators. Patients with acute hypercapnic respiratory failure often improve rapidly with this initial treatment and thus will not go on to require NIV. Furthermore the omission of arterial blood gas analysis, prior to the initiation of NIV means that it is difficult to gain an objective assessment of response to treatment.

In conclusion, further trials using more objective methods of patient assessment, are required to guide future management of acute respiratory failure in the emergency department.

References

1. Cross A M, Cameron P, Kierce M, Ragg M, and Kelly A-M. Non- invasive ventilation in acute respiratory failure: a randomised comparison of continuous positive airways pressure ands bi-level positive airway pressure. Emerg Med J 2003; 20:531–534.

2. British Thoracic Society Guidelines on the use of NIV. Thorax 2002; 57:192–211.