Dose of local anesthetics for peripheral nerve block is decreased in patients with hypovolemia shock because-

In hypovolemia shock there is preferential perfusion of vital organs so whatever drug is intravascularly absorbed goes to vital organs CNS and CVS end cause systemic toxicity. Decreasing systemic absorption of local anesthetics increase their safety margin in clinical uses. The rate and extent of systemic absorption depends on the site of injection, the dose, the drugs intrinsic Pharmacokinetic propeies and the addition and cytochrome P450 enzymes. Severe liver disease may slow the clearance of amino amide local anesthetics and significant drug levels may therefore accumulate.