How can I put information in the cck fields differents to title and body?

Hi.
I am creating CCK nodes through the SOAP using the node.save service. When I send the fields, the fields title is created succesfully, but my CCK fields wasn't create. Anybody can help me?

This is the envelope that I use to send the message:

?xml version="1.0" encoding="utf-16"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<soap:Body>
  <node.save xmlns="http://192.192.192.4:90/intranet/services/soap/">
    <node xsi:type="xsd:struct">
            <type xsi:type="xsd:string">estudio</type>
            <title xsi:type="xsd:string">John Doe</title> 
	    <field_institution_id xsi:type="xsd:Array">
		<value xsi:type="xsd:string">
		     Health center
		</value>
            </field_institution>
        </node>
  </node.save>
</soap:Body>
</soap:Envelope>

Thanks in advance!