title: Agreement between paired blood gas values in samples transported either by a pneumatic system or by human courier.
abstract: BACKGROUND
  Rapid accurate assessment of metabolic derangements is crucial in the critically ill. We evaluated if arterial blood gas (ABG) samples transported through a pneumatic tube system (PTS) agreed with values transported by a human courier.
  
  
  METHODS
  In this prospective study of 50-paired ABG samples, the couriered reference ABG was compared with those transported by PTS. Agreement was summarised by the mean difference with 95% limits of agreement (LOA) and Lin's concordance correlation (pc).
  
  
  RESULTS
  The mean (±SD) time from sampling to analysis was 35.7±23.2 (courier) and 38.6±22.1 (PTS) minutes. Agreement was good between courier and PTS for pH, PaCO(2), bicarbonate, oxygen saturation and PaO(2) values (pc>0.97). Although the mean difference in PaO(2) values between PTS and courier was small (-0.9 mm Hg) and the agreement was good, individual differences were clinically significant (95% LOA -40.8 to 39.0). For PaO(2) <160 mm Hg, analysis of PTS samples yielded erroneously high PaO(2) values and vice versa for PaO(2)>160 mm Hg compared to manual courier. This suggested exaggerated oxygen movement between the blood sample and air in the PTS.
  
  
  CONCLUSIONS
  In this study, analysis of samples transported through the PTS resulted in clinically unacceptable PaO(2) values. Delay in transport and analysis of ABG samples should be avoided and samples transported manually if they cannot be assessed on-site.
authors: Medical ICU, Christian Medical College and Hospital, Vellore, India.
authors: John
authors: J
authors: Victor Peter
authors: Department of Medicine, Christian Medical College and Hospital, Vellore, India.
authors: Shalom
authors: S
authors: Patole
authors: Department of Clinical Biochemistry, Christian Medical College and Hospital, Vellore, India.
authors: Jude
authors: J
authors: Joseph Fleming
authors: Department of Clinical Biochemistry, Christian Medical College and Hospital, Vellore, India.
authors: Ratnasamy
authors: R
authors: Selvakumar
authors: Department of Statistics, Macquarie University, Sydney, Australia.
authors: Petra L
authors: PL
authors: Graham