Reply to Dr. Cramer
1
Respiratory Medicine (2006) 100, 1669 LETTER TO THE EDITOR Reply to Dr. Cramer I read with interest the comments in the letter by Derek Cramer and would like to thank him for some very interesting points. It is true that agreement decreases between measurements of PO 2 in arterial and capillary blood as the PO 2 value increases. This is illustrated in Fig. 4 of our study, which plots capillary PO 2 against arterial PO 2 . It can be seen that for smaller values of PO 2 , around 10 kPa, the measurements converge and for higher values the measurements diverge. This is consistent with previous reports. 1,2 This implies that, as suggested, capillary PO 2 measurements may agree well enough with arterial PO 2 to be used in situations where the PO 2 is likely to be low e.g. patients with chronic lung disease who are being assessed for long term oxygen therapy. In patients with acute exacerbations of COPD, however, I believe that continuous pulse oximetry is a better way to detect clinically important hyper- oxia and hypoxia. The issue of blood flow after capillary puncture is also important. Patients with acute exacerbations of COPD who attend the Emergency Department can have poor peripheral perfusion and obtaining a capillary sample can be more difficult than when they are well. At the same time it is important to get a reasonably quick estimate of their blood gas values. It was felt that any sampling technique should be robust enough to guarantee an adequate sample in the vast majority of these cases. This is why a combination of a vasodilating paste, a needle and squeezing the ear was used. When the results were analysed this technique appeared to work very well. One capillary sample was successfully ob- tained in all patients and a second sample was taken in all but five of them. Although there are some reports that say squeezing the ear may result in contamination with venous blood, lymph and fatty tissue, it is unclear if this is actually true. 3 In our study there was good agreement between measurements of PCO 2 ,H + and HCO 3 despite this. The use of a small scalpel to make a slightly bigger incision is worth considering. However, as one of the aims of capillary sampling is to improve patient comfort, using a needle and squeezing is something most patients may prefer! References 1. Pitkin AD, Roberts CM, Wedzicha JA. Arterialised earlobe blood gas analysis: an underused technique. Thorax 1994; 49:364–6. 2. Sauty A, Uldry C, Debetaz LF, et al. Differences in PO 2 and PCO 2 between arterial and arterialised earlobe samples. Eur Respir J 1996;9:186–9. 3. AARC Clinical Practice Guideline. Respir Care 1994;39(12): 1180–3. Ross Murphy The Royal Infirmary of Edinburgh, Department of Accident and Emergency Medicine, Edinburg, UK E-mail address: [email protected] ARTICLE IN PRESS 0954-6111/$ - see front matter & 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.rmed.2006.05.001
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Transcript of Reply to Dr. Cramer
ARTICLE IN PRESS
Respiratory Medicine (2006) 100, 1669
0954-6111/$ - sdoi:10.1016/j.r
LETTER TO THE EDITOR
Reply to Dr. Cramer
I read with interest the comments in the letter byDerek Cramer and would like to thank him for somevery interesting points.
It is true that agreement decreases betweenmeasurements of PO2 in arterial and capillary bloodas the PO2 value increases. This is illustrated in Fig.4 of our study, which plots capillary PO2 againstarterial PO2. It can be seen that for smaller valuesof PO2, around 10 kPa, the measurements convergeand for higher values the measurements diverge.This is consistent with previous reports.1,2
This implies that, as suggested, capillary PO2
measurements may agree well enough with arterialPO2 to be used in situations where the PO2 is likely tobe low e.g. patients with chronic lung disease whoare being assessed for long term oxygen therapy.
In patients with acute exacerbations of COPD,however, I believe that continuous pulse oximetry isa better way to detect clinically important hyper-oxia and hypoxia.
The issue of blood flow after capillary puncture isalso important. Patients with acute exacerbationsof COPD who attend the Emergency Departmentcan have poor peripheral perfusion and obtaining acapillary sample can be more difficult than whenthey are well. At the same time it is important toget a reasonably quick estimate of their blood gasvalues.
It was felt that any sampling technique should berobust enough to guarantee an adequate sample inthe vast majority of these cases. This is why acombination of a vasodilating paste, a needle and
ee front matter & 2006 Elsevier Ltd. All rights reservmed.2006.05.001
squeezing the ear was used. When the results wereanalysed this technique appeared to work verywell. One capillary sample was successfully ob-tained in all patients and a second sample wastaken in all but five of them.
Although there are some reports that saysqueezing the ear may result in contamination withvenous blood, lymph and fatty tissue, it is unclear ifthis is actually true.3 In our study there was goodagreement between measurements of PCO2, H
+ andHCO3� despite this.
The use of a small scalpel to make a slightlybigger incision is worth considering. However, asone of the aims of capillary sampling is to improvepatient comfort, using a needle and squeezing issomething most patients may prefer!
References
1. Pitkin AD, Roberts CM, Wedzicha JA. Arterialised earlobeblood gas analysis: an underused technique. Thorax 1994;49:364–6.
2. Sauty A, Uldry C, Debetaz LF, et al. Differences in PO2 andPCO2 between arterial and arterialised earlobe samples. EurRespir J 1996;9:186–9.
3. AARC Clinical Practice Guideline. Respir Care 1994;39(12):1180–3.
Ross MurphyThe Royal Infirmary of Edinburgh,
Department of Accident and Emergency Medicine,Edinburg, UK
E-mail address: [email protected]
ed.
