A. The first point to make is that approximately 20% of patients who are acidotic at the time of arrival in the emergency room will correct their pH completely into the normal range just with standard medical therapy including, most importantly, properly controlled oxygen therapy . This applies even to patients with very severe acidosis. In most patients, therefore, NIV should not be started until an hour or two has elapsed. At that stage arterial blood gas tensions should be measured and if the pH is less than 7.35 and the patient is hypercapnic, NIV should be initiated . It is important to note that in the pH range 7.30–7.35, 80% of patients will get better without NIV, but only 10 patients need to receive NIV to avoid one intubation . If a patient is tolerating NIV poorly and does not want to use it, it is reasonable not to push it, but to continue to monitor the patient carefully. Once the pH is less than 7.30 the outcome without NIV is much worse and these patients should be encouraged very strongly to continue, even if they don't like it very much.
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