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38: Hyperoxygenation in pregnancy exerts a more profound effect on hemodynamics than in a non-pregnant state

      Objective

      The hemodynamic effects of oxygen therapy are under recognized and the impact of hyperoxygenation (HO) on maternal hemodynamics is currently unknown. Using transthoracic bioreactance (NICOM), we sought to examine the effect of brief hyperoxygenation on cardiac index (CI), systemic vascular resistance (SVR), blood pressure (BP), stroke volume (SV) and heart rate (HR) in pregnant mothers during the third trimester as compared to those observed in a non-pregnant population subjected to the same period of hyperoxygenation.

      Study Design

      Hemodynamic monitoring was performed in a continuous manner over a 30-minute period using NICOM. HO (O2 100% v/v inhalational gas) was carried out at a rate of 12L/min via a partial non-rebreather mask for 10-minutes. CI, SVR, SV, HR, and BP were recorded prior to HO (Time 1), at the end of HO (Time 2), and 10 minutes following the cessation of HO (Time 3). Data were presented as means ±SD or medians [IQR]. Two-way ANOVA with repeated measures was used to assess the change in hemodynamic indices over time, and the differences between the two groups.

      Results

      Forty six pregnant and twenty non-pregnant females were prospectively recruited with a median age of 33[26 – 38] and 32 [28-37] years respectively (p=0.82). The median gestation was 35 [33 – 37] weeks. Baseline hemodynamic measurements are seen in Table 1 (mean ±SD). In the pregnant group there was a fall in CI over the study period coupled with a rise in SVR with no recovery by time 3 (Figure 1). HR decreased in Time 2, returning to baseline levels by 10 minutes post-cessation of HO. There was a decrease in SV over the study period. There was no change in systolic or diastolic BP over the study period. In the non pregnant group there was no significant change in the CI, TPR, SV, HR, systolic or diastolic BP over the study period.

      Conclusion

      Hyperoxygenation during the third trimester is associated with a fall in CI, mediated by a decrease in HR, and a rise in SVR without recovery to baseline levels at 10 minutes following cessation of HO. Similar hemodynamic changes have been documented in other patient populations in response to hyperoxia and counteract any proposed increase in oxygen delivery, limiting the benefit of oxygen therapy in the absence of hypoxia. In light of these cardiovascular effects, the role of hyperoxygenation in obstetric patients, especially those with cardiovascular disease, requires further investigation.
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