We aimed to assess the pharmacokinetics of vancomycin in critically ill infants, and to evaluate the standard recommended dose oJ 10 mglkg 6 hourly. All infanfs admitted to the Baragwanath Hospital fCU who had arterial lines in situ, and for whom vancomycin 10 mg/kg 6 hourly was prescrib"ed for an infectiVe insult and who had parental consent, were included in the study. Vancomycin was infused over 60 minutes. Serum samples were taken immediately before the dose and at 30, 60, 120 and 300 minutes after the end of the vancomycin infusion, on days 2 and 8 of therapy. Extrapolated peak concentration (Cmax), trough concentration (Cm in), apparent volume of distribution (Vd), elimination half-life (tOe!) and clearance (CL) were determined for each patient. Day 2 values were compared with those of day 8. Day 2 serum concentrations were assayed on 20 patients and day 8 concentrations in 15. The mean vancomycin Vd on day 2 (0.81I1kg) was significantly (P=0.007) larger than that on day 8 (0.44 IIkg). The change in Vd resulted in a significant change in mean Cmax (29.1 vs 35.5 p.g/ml) (P=0.02) and mean tOe! (5.3 vs 3.4h) (P=O.OI) over the treatment period. Critically ill infants displayed a large initial volume of distribution which probably resulted from aggressive fluid resuscitation. This also results in a large variation in other pharmacokinetic parameters, namely Cmax and tOe!' Although the routine monitoring of vancomycin serum concentrations remain controversial, we feel that in view of these large pharmacokinetic variations, the critically ill infant is a specific group where monitoring of vancomycin serum levels is indicated.
The PRISM score needs to be recalibrated or recalculated for our patient population in view of the high discrepancy and poor discriminatory function shown. Part of the inaccuracy may derive from different demographic characteristics of our ICU population and a different pattern of diseases. It appears that PRISM is not population independent.
SummaryA prospective study was conducted to compare simultaneous intrathoracic and intra-abdominal central venous pressures in 10 critically ill, ventilatedpaediatric intensive care patients. Central venous pressures were measured using the water column technique over a 6 h study period. There was excellent correlation between intrathoracic and intra-abdominal vena caval pressure measurements (r = 0 . 9 7 4 ,~ < 0.001). The difference between pairedmeasurements didnot exceed the limits of agreement (+ 2SD, -2.36 to 4.42 cm HzO). The mean (SD) dixerence between readings was small (1.03 + 1.69 cmH20) and was within clinically tolerable limits. These data suggest a clinically useful, close relationship between intra-abdominal and conventional intrathoracic central venous pressure measurement in this group of patients.
Key wordsAnaesthesia; paediatric.Monitoring central venous pressure (CVP) can be a valuable adjunct to the management of critically ill children. It has been generally accepted that CVP should be measured intrathoracically from the superior vena cava [ 1-41. However, placement of a central venous catheter within the chest, via the subclavian or internaljugular vein, carries a risk of potentially life threatening complications such as pneumothorax, haemothorax and cardiac arrhythmias [5-81. In addition, as recommended by the US Food and Drug Administration [9], the position of the intrathoracic central venous catheter must be carefully ascertained and shown to be within the superior vena cava and not intracardiac. This requirement of accurate placement in children of differing sizes can create practical problems, such as repeated positioning and frequent radiographs with the attendant radiation exposure. Although radiographic confirmation of the catheter position is equally important with intra-abdominal catheters, malposition is less likely [lo]. This would reduce the need for repeated radiographs.In order to avoid the serious complications of intrathoracic central venous catheter placement, the femoral vein has become an increasingly common site for central venous access in children [1&12]. However, there is insufficient clinical evidence as to the accuracy of CVP measurements in this site. Recent studies which showed excellent correlation between CVP measurements from the superior and inferior vena cava were performed in dogs [ 131 and in children undergoing cardiac catheterisation [14] and cardiac surgery [ 151. A direct simultaneous comparison of intrathoracic and intra-abdominal CVP has hitherto not been reported in mechanically ventilated patients with lung pathology. We therefore evaluated the relationship between intrathoracic and intra-abdominal CVP measurement in this group of paediatric patients.
MethodsAfter institutional approval, mechanically ventilated children in the ICU requiringrepeat central venouscatheter placement were considered for study. It is our unit policy to change the site of a central venous catheter every 5 days. Patients were enrolled after informed parental consent wa...
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