Limitations of the inotrope score use as a measure of primary graft dysfunction

Allograft dysfunction is the major cause of early morbidity and mortality following cardiac transplantation. Poor graft function can be secondary to transplant complications or, when no identifiable cause is present, primary graft dysfunction (PGD). To standardize the definition of PGD, a consensus conference was convened which produced a document that defines severity categories and criteria for assessing left and right ventricular dysfunction. A critical sub-criterion in the consensus definition of PGD is a score intended to reflect the need for inotropic support after transplant. However, during the Australian and New Zealand trial of Hypothermic Oxygenated Perfusion preservation of donor hearts, we realized that the consensus inotrope score was inflated by the disproportionate impact of norepinephrine (NE), upcoding PGD grades from mild to moderate. A review of 50 heart transplant patients at The Alfred Hospital showed that in 38% of the instances when the inotropic score exceeded the consensus cutoff value due to NE, there was no identifiable PGD or vasoplegia and in 16% of instances, the cutoff was exceeded due to vasoplegia without PGD. Given the importance of accurate PGD classification in an era when static cold storage preservation is being replaced by machine perfusion and temperature controlled static storage, we contend that NE should be removed from the inotrope score equation to prevent up coding of mild to moderate PGD. Furthermore, we think that PGD classification should incorporate sensitive load- independent cardiac performance measures in the context of given levels of pharmacological and mechanical cardiac support.