Preoxygenation during Pregnancy in the Head-up versus the Supine Position

Incidence and risk factors for maternal hypoxaemia during induction of general anaesthesia for non-elective Caesarean section: a prospective multicentre study

BACKGROUND

Pregnant women are at increased risk of hypoxaemia during general anaesthesia. Our aim was to determine the incidence and the risk factors that contribute to hypoxaemia in this setting.

METHODS

Every woman 18 yr or older who underwent a non-elective Caesarean section under general anaesthesia was eligible to participate in this multicentre observational study. The primary endpoint was the incidence of hypoxaemia defined as the SpO₂ ≤95%. The secondary endpoint was the incidence of difficult intubation defined as more than two attempts or failed intubation.

RESULTS

During the study period, 895 women were prospectively included in 17 maternity hospitals, accounting for 79% of women who had general anaesthesia for non-elective Caesarean section. Maternal hypoxaemia was observed in 172 women (19%; confidence interval [CI], 17-22%). Risk factors associated with hypoxaemia in the multivariate analysis were difficult or failed intubation (adjusted odds ratio [aOR]=19.1 [8.6-42.7], P<0.0001) and BMI >35 kg m^-2 (aOR=0.53 [0.28-0.998], P=0.0495). Intubation was difficult in 40 women (4.5%; CI, 3.3-6%) and failed intubation occurred in five women (0.56%; CI, 0.1-1%). In the multivariate analysis, use of a hypnotic drug other than propofol was associated with difficult or failed intubation (aOR=25 [2-391], P=0.02). A propensity score confirmed that propofol was associated with a significant decreased risk of difficulty or failure to intubate (P<0.001).

CONCLUSIONS

Hypoxaemia during Caesarean sections was observed in 19% of women and was significantly associated with difficult or failed intubation. The use of propofol may protect against the occurrence of difficult intubation.

[Effectiveness of preoxygenation using the head-up position and noninvasive ventilation to reduce hypoxaemia during intubation]

OBJECTIVE

The purpose of this article was to present an update of the preoxygenation management in morbidly obese adults, parturient women and hypoxemic critically-ill patients.

DATA SOURCES

All references obtained from the medical database Medline related to the area and more specifically during the last five years were reviewed.

DATA SYNTHESIS

Preoxygenation decreases the risk of hypoxia and should be optimized when the standard technique appears to be less effective as in morbidly obese adults, parturient women and critically-ill patients. The head-up position and noninvasive ventilation may be useful during preoxygenation probably because of the increase of ventilation and alveolar recruitment. The effectiveness of preoxygenation (when defined as the duration of the desaturation safety period) is enhanced in the head-up position as compared to supine position in the obese patient but not in parturient women. Noninvasive ventilation improves preoxygenation in the hypoxemic critically-ill patient but not in the obese patient. Neither the head-up position nor the noninvasive ventilation improve preoxygenation in parturient women.

CONCLUSION

Further studies are required to investigate other methods attempting to improve preoxygenation and prevent hypoxemia during intubation.