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Prediction of the Physiological Dead Space /Tidal Volume Ratio during Anaesthesia/IPPV from Simple Pre‐operative Tests
Author(s) -
Fletcher R.,
Jonson B.
Publication year - 1981
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1981.tb01606.x
Subject(s) - medicine , anesthesia , spirometry , hyperventilation , tidal volume , pco2 , general anaesthesia , surgery , respiratory system , asthma
It can be shown that the assumption of an arbitrary value for V D phys/V T during IPPV can lead to unacceptable degrees of hypo‐ or hyperventilation. We investigated 33 adult patients scheduled for major non‐thoracic surgery, to see if any simple tests could be used to predict V D phys/V T during anaesthesia/IPPV. Fifteen were smokers and 18 non‐ or ex‐smokers. The tests were spirometry, and the single breath tests for CO 2 and for N 2 (SBT‐CO 2 : SBT‐N 2 ). Patients were ventilated during anaesthesia with a Servo Ventilator 900 B, and SBT‐CO 2 was recorded from a CO 2 Analyzer 930. During anaesthesia/IPPV, smokers had significantly greater V D phys/V T (0.40±0.10 vs. 0.31 ±0.07 [ P <0.01]), and they had more steeply sloping phase IIIs of SBT‐CO 2 ( P <0.01) than non‐ and ex‐smokers. For smokers, V D phys/V T was correlated to age (r = 0.75, P <0.01), to the slope of phase III of both SBT‐CO 2 and SBT‐N 2 , and to the ratio of FEV% to its predicted value. For non‐ and ex‐smokers, only one variable, efficiency, describing the shape of SBT‐CO 2 , was correlated to V D phys/V T (r = 0.53, P <0.05). Pre‐operative prediction of V D phys/V T based on age, smoking history, and SBT‐CO 2 can reduce the uncertainty in estimating V D phys/V T and therefore ventilatory requirements. It appears to offer the greatest benefits amongst smokers, who show a large variation in V D phys/V T .