title: Corrections of Enghoff's dead space formula for shunt effects still overestimate Bohr's dead space.
abstract: Dead space ratio is determined using Enghoff's modification (VD(B-E)/VT) of Bohr's formula (VD(Bohr)/VT) in which arterial is used as a surrogate of alveolar PCO₂. In presence of intrapulmonary shunt Enghoff's approach overestimates dead space. In 40 lung-lavaged pigs we evaluated the Kuwabara's and Niklason's algorithms to correct for shunt effects and hypothesized that corrected VD(B-E)/VT should provide similar values as VD(Bohr)/VT. We analyzed 396 volumetric capnograms and arterial and mixed-venous blood samples to calculate VD(Bohr)/VT and VD(B-E)/VT. Thereafter, we corrected the latter for shunt effects using Kuwabara's (K) VD(B-E)/VT and Niklason's (N) VD(B-E)/VT algorithms. Uncorrected VD(B-E)/VT (mean ± SD of 0.70 ± 0.10) overestimated VD(Bohr)/VT (0.59 ± 0.12) (p < 0.05), over the entire range of shunts. Mean (K) VD(B-E)/VT was significantly higher than VD(Bohr)/VT (0.67 ± 0.08, bias -0.085, limits of agreement -0.232 to 0.085; p < 0.05) whereas (N)VD(B-E)/VT showed a better correction for shunt effects (0.64 ± 0.09, bias 0.048, limits of agreement -0.168 to 0.072; p < 0.05). Neither Kuwabara's nor Niklason's algorithms were able to correct Enghoff's dead space formula for shunt effects.
authors.affiliation: Department of Surgical Sciences, Section of Anesthesiology & Critical Care, Uppsala University, Uppsala, Sweden; Instituto de Investigación Sanitaria, Fundación Jiménez Díaz, IIS-FJD, Madrid, Spain; CIBERES, Spain. Electronic address: fsuarez.sipmann@surgsci.uu.se.
authors.forename: Fernando
authors.initials: F
authors.lastname: Suarez-Sipmann
authors.forename: Arnoldo
authors.initials: A
authors.lastname: Santos
authors.forename: Stephan H
authors.initials: SH
authors.lastname: Böhm
authors.forename: Joao Batista
authors.initials: JB
authors.lastname: Borges
authors.forename: Göran
authors.initials: G
authors.lastname: Hedenstierna
authors.forename: Gerardo
authors.initials: G
authors.lastname: Tusman
mesh_terms: D000465:Algorithms; D000818:Animals; D019296:Capnography; D002245:Carbon Dioxide / Q000097:blood; D012126:Respiratory Dead Space / Q000502:physiology*; D034421:Sus scrofa; D013552:Swine; D013990:Tidal Volume / Q000502:physiology
chemical_list: D002245:Carbon Dioxide
keywords: Acute lung injury; Bohr's formula; Dead space; PEEP; Shunt; Vd/Vt