$re = '/PV1\|(?:[^\|]*\|){18}1703000105\|(?:[^\|]*\|){31}CO/';
$str = 'MSH|^~\\&|SUNNY|SHSC|OACIS|SHSC|20210710161803||ORU^R01|SC20210710161803|P|2.3
PID|||7030389||Smith^John||20001010|M
PV1||I|||||||||||||||||1703000123|||||||||||||||||||||||||||||||
ORC|NW||||||||20210710161803
OBR|||SCVITALS-202107101618037402|SME^SunnyCare Manual Entry|||20210710010005|||~|||||||||||||||F
OBX|1|NM|0002-F828^SpRR||24|rpm|||||F|||20210710010005|||MANUAL
MSH|^~\\&|SUNNY|SHSC|OACIS|SHSC|20210710161803||ORU^R01|SC20210710161803|P|2.3
PID|||7030389||Smith^John||20001010|M
PV1||I|||||||||||||||||1703000105|||||||||||||||||||||||||||||||
ORC|CO||||||||20210710161803
OBR|||SCVITALS-202107101618037402|SME^SunnyCare Manual Entry|||20210710010005|||~|||||||||||||||F
OBX|1|NM|0002-F828^SpRR||24|rpm|||||F|||20210710010005|||MANUAL
MSH|^~\\&|SUNNY|SHSC|OACIS|SHSC|20210710161803||ORU^R01|SC20210710161803|P|2.3
PID|||7030389||Smith^John||20001010|M
PV1||I|||||||||||||||||1703000456|||||||||||||||||||||||||||||||
ORC|NW||||||||20210710161803
OBR|||SCVITALS-202107101618037402|SME^SunnyCare Manual Entry|||20210710010005|||~|||||||||||||||F
OBX|1|NM|0002-F828^SpRR||24|rpm|||||F|||20210710010005|||MANUAL
MSH|^~\\&|SUNNY|SHSC|OACIS|SHSC|20210710165010||ORU^R01|SC20210710165010|P|2.3
PID|||7030389||Smith^John||20001010|M
PV1||I|||||||||||||||||1703000105|||||||||||||||||||||||||||||||
ORC|NW||||||||20210710165010
OBR|||SCVITALS-202107101650108370|SME^SunnyCare Manual Entry|||20210710110005|||anpatel~anpatel|||||||||||||||F
OBX|1|NM|0002-F828^SpRR||34|rpm|||||F|||20210710110005|||MANUAL
MSH|^~\\&|SUNNY|SHSC|OACIS|SHSC|20210710165442||ORU^R01|SC20210710165442|P|2.3
PID|||7030389||Smith^John||20001010|M
PV1||I|||||||||||||||||1703000105|||||||||||||||||||||||||||||||
ORC|CO
OBR|||SCVITALS-202107101643353582|SME^SunnyCare Manual Entry|||20210710165442|||anpatel|||||||||||||||F
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php