Towards pain-free blood gases

Blood gas analysis is unique among blood tests in its requirement for arterial blood; all others are performed on venous, or more rarely, capillary blood samples. Sampling arterial blood is a technically difficult procedure to perform, and painful for the patient: significantly more painful than sampling either venous or capillary blood. 

A recent study evaluating a needle-free device that jet propels a dose of the analgesic lidocaine through skin suggests the possibility of less painful arterial blood gas sampling. The study population comprised 42 emergency department patients who required arterial blood gases. Each was randomly allocated to one of two procedures prior to having arterial blood sampled. 

The first (control) group comprised 21 patients who received 1 mL of lidocaine gel (2 %) applied topically to the proposed site of arterial puncture 5 minutes prior to arterial blood sampling. The remaining 21 patients received lidocaine (2 %) delivered to the proposed arterial puncture site via the jet injector from around 2 cm above the skin, also 5 minutes prior to blood sampling. 

Both doctors collecting the blood samples and study patients were blinded to the intervention applied. Immediately after blood had been sampled, patients were asked to score the pain of the procedure using a visual analogue scale (VAS) 0-10; 0 being ”no pain” and 10 being “worst imaginable pain”. 

The mean (± SD) VAS score of those 21 patients treated conventionally with topically applied gel was significantly higher than that for the 21 patients treated with the jet injector (4.19 ± 1.43 versus 1.29 ± 0.9). 

Doctors found the procedure significantly easier if the patients had been pretreated with the jet injector; on average it required 1.29 tries to get a satisfactory sample in this group compared with 2.10 tries per patient among the conventionally treated group. The authors of this study conclude that “...jet injection of lidocaine provides beneficial and rapid anesthesia, which results in less pain and fewer procedural failures.”