Oxygen supplementation during Caesarean delivery

Editor—It was interesting to read the article by Khaw and colleagues.1 Oxygen is used during spinal anaesthesia in obstetric practice as a part of the management of tissue hypoxia secondary to postspinal hypotension. Spinal anaesthesia is associated with an inevitable decrease in maternal blood pressure and thus possible tissue hypoxia, affecting both mother and fetus. The incidence and severity of maternal hypotension is variable and mainly depends upon the degree of sympathetic block (i.e. decrease in systemic vascular resistance), and effective intravascular volume status (i.e. venous return). The detrimental effects of hypotension in this situation cannot be underestimated.2 In addition, there is no fool-proof way to prevent this hypotension. Well-established methods are volume expansion along with vasopressors, appropriate patient positioning, and supplementary oxygen therapy.3 By using conventional monitors (e.g. non-invasive blood pressure and pulse oximetry), there is a time lag between the occurrence of hypotension (and thus hypoxia), its detection, and institution of effective therapy. Thus, these patients will invariably be exposed to a period of hypoxia that can adversely affect the fetus. Using supplementary oxygen will not prevent the problem but will help to improve oxygen delivery,4 and may benefit the fetus during this critical time. It is sensible to continue the current practice of using oxygen until we have a treatment method that is 100% effective to prevent post spinal hypotension. The decision to use oxygen should not be based on the incision-to-delivery (U–D) interval, whether it is prolonged or not. It would also be interesting to know why the authors1 allowed the oxygen saturation to drop to 95% before starting oxygen therapy. It should be more appropriate to maintain oxygen saturation at least at the baseline level until the fetus is delivered.

N. G. Mandal and A. Gulati

Peterborough, UK


 
Editor—Drs Mandal and Gulati advocate the continued use of supplementary maternal oxygen during spinal anaesthesia for Caesarean section, with the rationale that this may improve fetal and maternal tissue hypoxia secondary to postspinal hypotension. We thank them for their interest in our paper.1 However, we believe they are confusing the issues and disagree with a number of their comments.

It is a common misconception amongst anaesthetists who continue to administer supplementary oxygen to mothers during regional anaesthesia, that it does no harm but might possibly do some good.5 However, evidence to support this practice is lacking. Drs Mandal and Gulati have highlighted the potential detrimental effects that hypotension may have on fetal well-being. Surely the correct approach to this is to improve our management of hypotension,2 and we have provided some clues on how this may be achieved.6 Specifically, we showed that, in patients who received neither supplementary oxygen nor volume expansion, maternal and fetal hypoxia did not occur to any important degree when maternal blood pressure was maintained using a liberal infusion of phenylephrine.6

In our previous work, we found that administration of high-concentration oxygen during elective Caesarean section resulted in maternal and fetal lipid peroxidation, but achieved only a marginal increase in umbilical venous that was not clinically important.4 As a result, we discontinued the practice of giving oxygen to uncomplicated cases. Nevertheless, there remained a concern that this overlooked the potential benefit of oxygen in the event that the uterine incision-to-delivery (U–D) interval is prolonged. Our current study1 shows that this concern is unfounded: despite earlier work that showed that a prolonged U–D interval was associated with fetal acidosis,7 8 we found no benefit from administration of oxygen 60% to the mother when the U–D interval was >180 s.

We believe that clinical practice should be evidence-based. In the absence of data to support any benefit from maternal oxygen—and the possibility that there may even be potential harm from increased free radical activity4—we stand by our recommendation that routine administration of supplementary oxygen during uncomplicated elective Caesarean section under regional anaesthesia is not necessary.

K. S. Khaw and W. Ngan Kee

Hong Kong, China

References

1 Khaw KS, Ngan Kee WD, Lee A, et al. Supplemtary oxygen therapy for elective Caesarean section under spinal anaesthesia: useful in prolonged uterine incision-to-delivery interval. Br J Anaesth 2004; 92: 518–22[Abstract/Free Full Text]

2 Riley ET. Spinal anaesthesia for Caesarean delivery: keep the pressure up and don't spare the vasoconstrictors. Br J Anaesth 2004; 92: 459–61[Free Full Text]

3 Shnider S, Levinson G. Anesthesia for Cesarean section. In: Shnider S, Levinson G, eds. Anesthesia for Obstetrics, 3rd Edn. Williams and Wilkins: Philadelphia, 1993; 217

4 Khaw KS, Wang CC, Ngan Kee WD, Pang CP, Rogers MS. Effects of high inspired oxygen fraction during elective caesarean section under spinal anaesthesia on maternal and fetal oxygenation and lipid peroxidation. Br J Anaesth 2002; 88: 4–5[Free Full Text]

5 Backe SK, Lyons G. Oxygen and elective Caesarean section. Br J Anaesth 2002; 88: 4–5[Free Full Text]

6 Ngan Kee WD, Khaw KS, Ng FF, Lee BB. Prophylactic phenylephrine infusion for preventing hypotension during spinal anesthesia for cesarean delivery. Anesth Analg 2004; 98: 815–21[Abstract/Free Full Text]

7 Bader AM, Datta S, Arthur GR, Benvenuti E, Courtney M, Hauch M. Maternal and fetal catecholamines and uterine incision-to-delivery interval during elective Cesarean. Obstet Gynecol 1990; 75: 600–3[Abstract]

8 Datta S, Ostheimer GW, Weiss JB, Brown WU, Jr, Alper MH. Neonatal effect of prolonged anesthetic induction for Cesarean section. Obstet Gynecol 1981; 58: 331–5[Abstract]





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