Some further points on this thread:
1 I discourage my SHOs from doing ABGs early in the acutely breathless
patient. A clinical diagnosis of LVF/bronchospasm/pneumonia should be
obvious and treatment should be commenced before any investigations are
ordered. For example, an early blood gas in LVF often reveals marked
hypercarbia, with pCO2 of 12 to 15 KPa, and juniors wrongly interpret this
to mean the patient in oxygen sensitive. Of course these patients are
profoundly hypoxic and acutely hypercarbic, confirmed by a normal
bicarbonate level. They need high concentration oxygen and their CO2 levels
fall rapidly with appropriate treatment. The early blood gas does not help
their treatment, and often only serves to confuse the unwary.
2 Tachypnoeic patients for whatever reason need oxygen. In the the rare
case of an oxygen sensitive patient, they will gradually become hypopnoeic
and narcotised with hypercarbia. This is very obvious clinically. As long as
the patient is tachypnoeic and vaguely alert, then they are excreting CO2,
and their oxygen therapy is clearly not causing respiratory depression. In
other words treat the patient and not the ABG results!
3 Charles Brault (see below) speaks of dangerous elevations of CO2 in
asthmatics who are treated with high concentrations of oxygen. But this is
in relation to patients who were hypocarbic! Surely a rise in CO2 is a good
thing in such patients? Don't understand what he's on about there, but I
haven't seen the original paper he has quoted.
I suppose the foregoing is obvious to most of us in A&E; wish the junior
physicians could learn this...
Adrian Fogarty
A&E Consultant
Royal Free Hospital
----- Original Message -----
From: Charles Brault <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 11, 2000 8:21 PM
Subject: Re: Oxygen administration in COPD
>Chest marCH 2000;117:728-733.
(Liberally re-translated from French)
Deleterious effect of high concentration oxygen on acutely exacerbated
asthmatics
Researchers from the University Hospitals of Cleveland testing a group of
37 admissible patients (32 women; 43±2,7 yo) FEV1 of 49,1±3,6% of
theoretical values. Patients were hypocapnic & hypoxic (PaCO2/O2 from
36,8±1,1/70,2±2,5 mm Hg).
They received100% oxygen via NRM for 20 minutes.
A repeat ABG & pulmonary function test was repeated at the end of the 20
minutes
A statistically significant increase in the PaCO2 in 25 patients (67,6%).
No significant physiological changes were observed on 15 of the Pts (40,5%
of Pt total),
With a PaCO2 pressure gradient of 5,9mmHg (p<0,0001).
The PaCO2 was more significant on the more compromised Pts
showing a reverse relation between FEV1 :& PaCO2
Administration of 100% O2 to Pt with Severe airway obstruction would bring
on clinicaly significant negative effects to asthmatic in respiratory
distress.
This phenomena as not been observed on stable Pt with moderate obstructions
Chest mars 2000;117:728-733.
Charles Brault EMT-P
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