title: Transient decrease in PaCO(2) and asymmetric chest wall dynamics in early progressing pneumothorax.
abstract: OBJECTIVE
  Diagnosis of pneumothorax (PTX) in newborn infants has been reported as late. To explore diagnostic indices for early detection of progressing PTX, and offer explanations for delayed diagnoses.
  
  
  METHODS
  Progressing PTX was created in rabbits (2.3 ± 0.5 kg, n = 7) by injecting 1 ml/min of air into the pleural space. Hemodynamic parameters, tidal volume, EtCO(2), SpO(2), blood gas analyses and chest wall tidal displacements (TDi) on both sides of the chest were recorded.
  
  
  RESULTS
  (Mean ± SD): A decrease in SpO(2) below 90 % was detected only after 46.6 ± 11.3 min in six experiments. In contrary to the expected gradual increase of CO(2), there was a prolonged transient decrease of 14.2 ± 4.5 % in EtCO(2) (p < 0.01), and a similar decrease in PaCO(2) (p < 0.025). EtCO(2) returned back to baseline only after 55.2 ± 24.7 min, and continued to rise thereafter. The decrease in CO(2) was a mirror image of the 14.6 ± 5.3 % increase in tidal volume. The analysis of endotracheal flow and pressure dynamics revealed a paradoxical transient increase in the apparent compliance. Significant decrease in mean arterial blood pressure was observed after 46.2 ± 40.1 min. TDi provided the most sensitive and earliest sign of PTX, decreasing on the PTX side after 16.1 ± 7.2 min. The TDi progressively decreased faster and lower on the PTX side, thus enabling detection of asymmetric ventilation.
  
  
  CONCLUSIONS
  The counterintuitive transient prolonged decrease in CO(2) without changes in SpO(2) may explain the delay in diagnosis of PTX encountered in the clinical environment. An earlier indication of asymmetrically decreased ventilation on the affected side was achieved by monitoring the TDi.
authors.affiliation: Department of Neonatology, Faculty of Medicine, Carmel Medical Center, 7 Michal St, 34632, Haifa, Israel. dwaisman@netvision.net.il
authors.forename: Dan
authors.initials: D
authors.lastname: Waisman
authors.forename: Anna
authors.initials: A
authors.lastname: Faingersh
authors.forename: Carmit
authors.initials: C
authors.lastname: Levy
authors.forename: Ifat
authors.initials: I
authors.lastname: Colman-Klotzman
authors.forename: Avi
authors.initials: A
authors.lastname: Rotschild
authors.forename: Oscar
authors.initials: O
authors.lastname: Lichtenstein
authors.forename: Amir
authors.initials: A
authors.lastname: Landesberg
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000032:analysis*; D008297:Male; D010100:Oxygen / Q000032:analysis; D010313:Partial Pressure; D011030:Pneumothorax / Q000097:blood / Q000175:diagnosis / Q000503:physiopathology*; D011817:Rabbits; D035441:Thoracic Wall / Q000503:physiopathology*; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen