Postural effects on pulmonary gas exchange abnormalities in severe obesity before and after bariatric surgery

Eva Rivas, Ebymar Arismendi, Alvar Agustí, Concepción Gistau, Peter Wagner, Roberto Rodriguez-Roisin*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


BACKGROUND: We hypothesized that in morbid obesity, pulmonary gas exchange abnormalities will worsen when supine and that bariatric surgery (BS) will mitigate this effect. METHODS: Gas exchange was investigated in 19 morbidly obese and 8 non-obese, age-matched control females, spontaneously breathing ambient air, both upright and supine, before and one year after BS. RESULTS: In control non-obese individuals, no postural changes in arterial blood gases (ABGs) were observed. While obese subjects had more altered PaO2, SaO2 and AaPO2 values than controls (P<0.05 each) when upright, the values unexpectedly remained unchanged when supine. This was also the case in the subset of 6 normoxemic obese but the remaining 13 hypoxemic individuals actually improved ABGs when supine: PaO2 (by +2.7±1.3 mmHg, P=0.06), SaO2 (by +1.5±0.6%), pH (by +0.01±0.01) and AaPO2 (by-3.4±1.4 mmHg); and cardiac output increased (by +0.4±0.2 Lmin-1) (P<0.05 each). After BS, PaO2 (from 75.5±2.4 to 89.4±2.4 mmHg), AaPO2 (from 27.0±2.0 to 15.4±2.1 mmHg) (P<0.05 each), and pulmonary gas exchange were improved compared to before BSwhen upright, but ABGs worsened when supine (PaO2, by-4.6±1.7 mmHg; AaPO2, by +4.2±1.6 mmHg) (P<0.05 each). CONCLUSIONS: Before BS, ABGs are not altered in normoxemic obese subjects moving from upright to supine, even improving in those with hypoxemia when supine. After successful BS, pulmonary gas exchange improved when upright in all subjects but ABGs deteriorated when supine. However, the important clinical observation is the lack of gas exchange deterioration when supine, which may have implications for critical care and anesthesia settings.

Original languageEnglish
Pages (from-to)403-410
Number of pages8
JournalMinerva Anestesiologica
Issue number4
Early online date9 Jun 2015
Publication statusPublished - Apr 2016
Externally publishedYes


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