Effect of pain produced by direct arterial puncture on arterial pH, PaO2 and PaCO2

A prospective double-blind, randomised study was conducted on 48 patients of either gender in the age group of 15 to 75 years belonging to ASA physical status I or II to study the effect of pain on arterial pH, arterial oxygen tension (PaO₂) and arterial carbon dioxide tension (PaCO₂). After performing moditied Alien's test, the radial artery was cannulated with a 20 Jelco(TM) cannula under local anaesthesia. An arterial sample was then drawn from the cannula after 10 minutes. Immediately following this the patient was informed of the pain that would be caused by an arterial puncture on the other hand and another sample was drawn from the contralateral radial artery using a 24 SWG hypodermic needle. After the second sample was taken, the patient was told to hyperventilate for one minute before drawing a third sample from the arterial cannula. There was no statistically significant difference in arterial blood gases (ABG) between the pain group and the cannula group. There was significant difference in ABG between the pain group and hyperventilation group (p < 0.001) and between cannula group and hyperventilation group (p < 0.001). It was concluded that arterial puncture performed with a 24 SWG hypodermic needle in unanaesthetised skin does not alter arterial blood gases.