Pre‐oxygenation in pregnancy: an investigation using physiological modelling

Hypoxaemia during anaesthetic induction in obstetrics is hazardous for mother and baby, but the onset of desaturation can be delayed by pre‐oxygenation. This study investigated pre‐oxygenation during pregnancy using computer simulation. The Nottingham Physiology Simulator was configured to replicate normal pregnant physiology. Three pregnant and three non‐pregnant subjects were created, representing population variation according to published physiological values. They underwent pre‐oxygenation by tidal and vital capacity breathing of 100% oxygen. Pre‐oxygenation during tidal breathing proceeded more rapidly in pregnancy, the median [range] time to achieve 95% of the maximum change in PÉo2 being 1 min 37 s [1:23–1:52] in pregnant subjects, compared to 2 min 51 s [2:28–3:15] in non‐pregnant subjects. Vital capacity pre‐oxygenation required seven breaths [5–10] in pregnant subjects, compared to six breaths [4–9] in non‐pregnant subjects, to achieve the same PÉo2 as after 95% complete tidal pre‐oxygenation. We recommend 2 min of tidal breathing for pre‐oxygenation in pregnancy.

[1]  M. C. Morris,et al.  Preoxygenation for Cesarean Section: A Comparison of Two Techniques , 1985 .

[2]  J. Moodley,et al.  Echocardiographic Assessment of Cardiovascular Hemodynamics in Normal Pregnancy , 2004, Obstetrics and gynecology.

[3]  H. Knuttgen,et al.  Physiological response to pregnancy at rest and during exercise. , 1974, Journal of applied physiology.

[4]  Jonathan G. Hardman,et al.  Apnoea in pregnancy: an investigation using physiological modelling , 2008, Anaesthesia.

[5]  N. Butte,et al.  Adjustments in energy expenditure and substrate utilization during late pregnancy and lactation. , 1999, The American journal of clinical nutrition.

[6]  J G Hardman,et al.  A physiology simulator: validation of its respiratory components and its ability to predict the patient's response to changes in mechanical ventilation. , 1998, British journal of anaesthesia.

[7]  F. Plaat,et al.  Why Mothers Die — Report on Confidential Enquiries into Maternal Deaths in the United Kingdom 1994–96 , 1999, Anaesthesia.

[8]  M. Reade,et al.  Temporary epicardial pacing after cardiac surgery: a practical review , 2007, Anaesthesia.

[9]  J G Hardman,et al.  Estimating venous admixture using a physiological simulator. , 1999, British journal of anaesthesia.

[10]  M. Norris,et al.  Preoxygenation for cesarean section: a comparison of two techniques. , 1984, Anesthesiology.

[11]  A. Hildreth,et al.  A prospective, randomised controlled trial comparing the efficacy of pre‐oxygenation in the 20° head‐up vs supine position * , 2005, Anaesthesia.

[12]  J G Hardman,et al.  Modelling: a core technique in anaesthesia and critical care research. , 2006, British journal of anaesthesia.

[13]  A. Skinner,et al.  Preoxygenation--the importance of a good face mask seal. , 1995, British journal of anaesthesia.

[14]  N. Bedforth,et al.  Predicting patients' responses to changes in mechanical ventilation: a comparison between physicians and a physiological simulator , 1999, Intensive Care Medicine.

[15]  J G Hardman,et al.  Investigating Hypoxemia during Apnea: Validation of a Set of Physiological Models , 2000, Anesthesia and analgesia.

[16]  F. García-Río,et al.  Comparison of helium dilution and plethysmographic lung volumes in pregnant women. , 1997, The European respiratory journal.

[17]  S. Snowdon,et al.  Pre‐oxygenation and the parturient patient , 1987, Anaesthesia.

[18]  D. Levy.  Emergency Caesarean section: best practice * , 2006 .

[19]  M. Goldberg,et al.  Denitrogenation in pregnancy , 1989, Canadian journal of anaesthesia = Journal canadien d'anesthesie.

[20]  A. Baraka,et al.  Preoxygenation of pregnant and nonpregnant women in the head-up versus supine position. , 1992, Anesthesia and analgesia.

[21]  G. R. Kelman,et al.  Maternal blood-gases, PAo2--Pao2), hysiological shunt and VD/VT in normal pregnancy. , 1976, British journal of anaesthesia.

[22]  J G Hardman,et al.  Fighting for breath: apnoea vs the anaesthetist , 2007, Anaesthesia.

[23]  J. Pittet,et al.  Standard preoxygenation technique versus two rapid techniques in pregnant patients. , 2004, International journal of obstetric anesthesia.

[24]  S. Clark,et al.  The Effects of Maternal Position and Cardiac Output on Intrapulmonary Shunt in Normal Third‐Trimester Pregnancy , 1996, Obstetrics and gynecology.

[25]  Y. Mallédant,et al.  Préoxygénation avant induction pour césarienne , 1994 .