An Analysis of Secondary Outcomes for the Study: Ultrasound Guided Fascia Iliaca Block Versus Spinal Opioid for Analgesia After Total Hip Arthroplasty

Introduction: We performed a randomised, controlled, double blind, non-inferiority study comparing ultrasound guided fascia iliaca block with spinal morphine for analgesia after total hip arthroplasty (THA). We hypothesised that if an ultrasound guided fascia ilaca block was non-inferior in this respect, that it may actually be advantageous if it reduced the incidence of side effects commonly associated with spinal morphine. These include: nausea and vomiting, pruritus, urinary retention, sedation and most seriously, respiratory depression. Such adverse effects may be uncomfortable for the patient and delay mobilisation and rehabilitation (1). Methods: Necessary IRB approvals were granted. Study methodology including a priori statistical analysis was published prior to commencement (2). The trial was registered with clinicaltrials.gov (NCT01217294). 108 patients aged between 18 and 85 years and weighing between 50-110kg were recruited from May 2011 to April 2014. The primary outcome was 24 hour morphine consumption. Secondary outcomes included: pain scores (VAS out of 10), morphine consumption, nausea, pruritus, urinary retention, sedation, respiratory depression, mobilisation and patient satisfaction. Statistical analysis was performed using Z tests of 2 proportions, students t tests and wilcoxon rank sum tests as appropriate (R studio Version 0.98.953 - © 2009-2013). Secondary outcomes were analysed on an ‘as treated’ basis. Any serious adverse events were recorded and reported. Results: There were no statistically significant differences between the study groups for: ultrasound guided fascia iliaca block or spinal performance and associated adverse events, duration of surgery, blood loss during surgery, administration of pre-operative paracetamol, administration of intra-operative anti-emetic, time to first administration of morphine, VAS pain scores at rest at 3, 24, 36 and 48 hours, VAS pain scores on movement at 3, 24, 36 and 48 hours, respiratory depression, hypotension, sedation, nausea, vomiting, urinary retention, pruritus, mobilisation at first attempt, power grade before mobilisation, patient satisfaction or adverse events. Outcomes reaching statistical significance (p < 0.05) in favour of spinal morphine were: morphine consumption at all time points (3, 6, 12, 24, 36, and 48 hours), pain scores (VAS) at rest and movement at 6 and 12 hours and time to first mobilisation. Full results are tabulated in Table 1. Conclusions: This study has clear implications for practice and supports the use of 0.1mg spinal morphine as providing adequate analgesia after total hip arthroplasty. Ultrasound guided fascia iliaca block is not only inferior in the provision of analgesia after THA but confers no advantage in reducing the side-effect profile. We do not recommend replacing spinal morphine with ultrasound guided fascia iliaca block for THA.