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THE EFFECT OF N₂O AND DESFLURANE ON CEREBRAL BLOOD FLOW IN CHILDREN

Department of Anaesthesia, Hospital for Sick Children, Toronto, Ontario M5G 1X8

INTRODUCTION

Nitrous oxide (N₂O) is commonly used in neurosurgical anesthesia in our institution. In adults desflurane has been shown to increase middle cerebral artery blood flow velocity (Vmca) similar to isoflurane (1). When added to desflurane, N₂O has been shown in adults to attenuate the systemic haemodynamic effects of desflurane but not the increase in Vmca (2). In children N₂O alone causes an increase in Vmca (3). This study aims to determine the effect of N₂O on Vmca in children anaesthetised with desflurane.

METHODS

After ethics board approval, 15 unpremedicated children aged 2 to 6 years scheduled for elective general, urological or orthopaedic surgery were enrolled. Anaesthesia was induced with sevoflurane in oxygen and tracheal intubation was performed following rocuronium 0.6mg/kg. Plain bupivacaine 1ml/kg was administered epidurally via the caudal route. IPPV was administered to achieve normocapnia. A TCD probe was used to measure Vmca in the M1 segment of the middle cerebral artery. Patients were randomised to receive a sequence of either Air/N₂O/Air (group 1) or N₂0/Air/N₂O (group 2) in oxygen with 1 age-adjusted MAC desflurane. Following changes in the gas concentration, 15 minutes were allowed to reach steady state, at which time three measurements were recorded each 30 seconds apart. Mean non invasive blood pressure(MAP), heart rate(HR), EtCO₂ and Vmca were recorded simultaneously. All data were recorded on computer and later analysed by an investigator unaware of the sequence. All parametric data are expressed as mean±SD. Student unpaired t-tests or ANOVA and Student-Newman-Keuls were used where appropriate. P<0.05 was accepted as significant.

RESULTS

6 patients have been studied to date. Mean HR, MAP and EtCO₂ remained stable (table 1). In both groups the administration of N₂O increased Vmca whereas air decreased Vmca. However, these changes did not reach statistical significance (figure 1).

View larger version (17K): [in this window] [in a new window]   Figure 1

This suggests that in children anaesthetised with 1 MAC desflurane, N₂0 might increase cerebral blood flow velocity in a similar way to that seen with other volatile agents (4).

REFERENCES

1 Anesth Analg 1992; 75: S32–7[Medline]

2 Eur J Anaesthesiol 1997; 14: 389–96[Medline]

3 Can J Anaesth 1992 Apr;39(4):409]. Can J Anaesth 1992; 38: 974–979

4 Acta Anaesth Scandinavia 1995; 39 (5): 653–8

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