We present an ultra low power analogue adaptive sampler for extraction of features from an arterial blood pressure signal, prior to ADC operation or conversion. The architecture is implemented and simulated in UMC 180 nm technology. A worst case power consumption across process variation of 124.6 nW was achieved, with a process invariant key-point timing error of approximately 2.31 ms, corresponding to a sample error of magnitude less than 0.1 mmHg, simulated at body temperature of 37°C. This is significantly below the standard clinical recording accuracy of 1 mmHg for electronic measurement tools.