Document Detail

Arterial to end-tidal carbon dioxide gradient and physiological dead space monitoring during general anaesthesia: effects of patients' position.
MedLine Citation:
PMID:  9374078     Owner:  NLM     Status:  MEDLINE    
METHODS: One hundred and five ASA I-II patients, scheduled for elective surgical procedures were studied in order to evaluate the effect of different surgical postures on physiological pulmonary dead space (VDphys/ VT) and arterial to end-tidal carbon dioxide gradient [P(a-Et)CO2]. Patients were divided into four groups according to their position on the operating table: supine position (acting as control group, n = 33), 20 degree Trendelenburg position (n = 24), lateral position (n = 24) and prone position with convex saddle frame (n = 24). Physiologic dead space was measured using Enghoff modification of Bohr equation. Arterial CO2 partial pressure was measured by blood gas analysis and end tidal CO2 was measured by means of an infrared CO2 analyser. All measurements were performed 20 minutes after general anaesthesia induction, with patients mechanically ventilated by a constant inspiratory flow (TV = 8 ml kg-1, RR = 10-14, EIP = 10%) in order to reach a steady state end tidal CO2 ranging between 32 and 36 mmHg; afterwards surgery started. RESULTS: Arterial blood pressure showed a mean decrease of about 5-10% compared to baseline values, but no significant differences in arterial pressure decrease were found between the four groups. A significant VDphys/VT increase in postures other than supine was observed, unless it was statistically significant in lateral and prone position only; while P(a-Et)CO2 was higher in all postures compared to supine. Changes of intrapulmonary gas and blood distribution due to patients' posture are probably responsible for the observed physiologic dead space and CO2 gradient differences. CONCLUSIONS: In conclusion, the clinical practice of predicting PaCO2 from EtCO2 must be tempered by recognition of the potential magnitude of P(a-Et)CO2 gradient, which is higher than normal during general anaesthesia and further increased when positioning the patient other than supine.
A Casati; I Salvo; G Torri; E Calderini
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Minerva anestesiologica     Volume:  63     ISSN:  0375-9393     ISO Abbreviation:  Minerva Anestesiol     Publication Date:  1997 Jun 
Date Detail:
Created Date:  1997-12-22     Completed Date:  1997-12-22     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  0375272     Medline TA:  Minerva Anestesiol     Country:  ITALY    
Other Details:
Languages:  eng     Pagination:  177-82     Citation Subset:  IM    
Department of Anaesthesia and Intensive Care, IRCCS H S. Raffaele, University of Milan.
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MeSH Terms
Anesthesia, General*
Blood Pressure / physiology
Carbon Dioxide / blood*
Middle Aged
Partial Pressure
Posture / physiology*
Prospective Studies
Respiratory Dead Space / physiology*
Surgical Procedures, Elective
Reg. No./Substance:
124-38-9/Carbon Dioxide

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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