Injury and Liability Associated with Implantable Devices for Chronic Pain.

BACKGROUND: Due to an increase in implantable device-related anesthesia pain medicine claims, the authors investigated anesthesia liability associated with these devices. METHODS: After institutional review board approval, the authors identified 148 pain medicine device claims from 1990 or later in the Anesthesia Closed Claims Project Database. Device-related damaging events included medication administration events, infections, hematomas, retained catheter fragments, cerebrospinal fluid leaks, cord or cauda equina trauma, device placed at wrong level, stimulator incorrectly programmed, delay in recognition of granuloma formation, and other issues. RESULTS: The most common devices were implantable drug delivery systems (IDDS; 64%) and spinal cord stimulators (29%). Device-related care consisted of surgical device procedures (n = 107) and IDDS maintenance (n = 41). Severity of injury was greater in IDDS maintenance claims (56% death or severe permanent injury) than in surgical device procedures (26%, P < 0.001). Death and brain damage in IDDS maintenance claims resulted from medication administration errors (n = 13; 32%); spinal cord injury resulted from delayed recognition of granuloma formation (n = 9; 22%). The most common damaging events for surgical device procedures were infections, inadequate pain relief, cord trauma, retained catheter fragments, and subcutaneous hygroma. Care was more commonly assessed as less than appropriate (78%) and payments more common (63%) in IDDS maintenance than in surgical device procedure claims (P < 0.001). CONCLUSIONS: Half of IDDS maintenance claims were associated with death or permanent severe injury, most commonly from medication errors or failure to recognize progressive neurologic deterioration. Practitioners implanting or managing devices for chronic pain should exercise caution in these areas to minimize patient harm.

Trends in Pain Medicine Liability.

BACKGROUND: The authors examined changes in the frequency of pain medicine malpractice claims and associated treatment modalities and outcomes over time. METHODS: The authors analyzed trends in pain medicine claims from 1980 to 2012 in the Anesthesia Closed Claims Project database by binary logistic regression on year of event. Pain procedures in claims from 2000 to 2012 were compared with the proportion of pain procedures reported to the National Anesthesia Clinical Outcomes Registry in 2010-2014. RESULTS: Malpractice claims for pain medicine increased from 3% of 2,966 total malpractice claims in the Anesthesia Closed Claims Project database in 1980-1989 to 18% of 2,743 anesthesia claims in 2000-2012 (odds ratio [OR], 1.088 per year; 95% CI, 1.078 to 1.098; P < 0.001). Outcomes in pain claims became more severe over time, with increases in death and permanent disabling injury (OR, 1.094 per year; P < 0.001). Nonneurolytic cervical injections increased to 27% of pain claims in 2000-2012 (OR, 1.054; P < 0.001), whereas National Anesthesia Clinical Outcomes Registry demonstrates that lumbar injections are a more common procedure. Claims associated with medication management increased to 17% of pain claims in 2000-2012 (OR, 1.116 per year; P < 0.001). CONCLUSIONS: Pain medicine claims have increased over time and have increased in severity. Claims related to cervical procedures were out of proportion to the frequency with which they are performed. These liability findings suggest that pain specialists should aggressively continue the search for safer and more effective therapies.

Exogenously applied muscle metabolites synergistically evoke sensations of muscle fatigue and pain in human subjects.

NEW FINDINGS: What is the central question of this study? Can physiological concentrations of metabolite combinations evoke sensations of fatigue and pain when injected into skeletal muscle? If so, what sensations are evoked? What is the main finding and its importance? Low concentrations of protons, lactate and ATP evoked sensations related to fatigue. Higher concentrations of these metabolites evoked pain. Single metabolites evoked no sensations. This suggests that the combination of an ASIC receptor and a purinergic P2X receptor is required for signalling fatigue and pain. The results also suggest that two types of sensory neurons encode metabolites; one detects low concentrations of metabolites and signals sensations of fatigue, whereas the other detects higher levels of metabolites and signals ache and hot. The perception of fatigue is common in many disease states; however, the mechanisms of sensory muscle fatigue are not understood. In mice, rats and cats, muscle afferents signal metabolite production in skeletal muscle using a complex of ASIC, P2X and TRPV1 receptors. Endogenous muscle agonists for these receptors are combinations of protons, lactate and ATP. Here we applied physiological concentrations of these agonists to muscle interstitium in human subjects to determine whether this combination could activate sensations and, if so, to determine how the subjects described these sensations. Ten volunteers received infusions (0.2 ml over 30 s) containing protons, lactate and ATP under the fascia of a thumb muscle, abductor pollicis brevis. Infusion of individual metabolites at maximal amounts evoked no fatigue or pain. Metabolite combinations found in resting muscles (pH 7.4 + 300 nm ATP + 1 mm lactate) also evoked no sensation. The infusion of a metabolite combination found in muscle during moderate endurance exercise (pH 7.3 + 400 nm ATP + 5 mm lactate) produced significant fatigue sensations. Infusion of a metabolite combination associated with vigorous exercise (pH 7.2 + 500 nm ATP + 10 mm lactate) produced stronger sensations of fatigue and some ache. Higher levels of metabolites (as found with ischaemic exercise) caused more ache but no additional fatigue sensation. Thus, in a dose-dependent manner, intramuscular infusion of combinations of protons, lactate and ATP leads to fatigue sensation and eventually pain, probably through activation of ASIC, P2X and TRPV1 receptors. This is the first demonstration in humans that metabolites normally produced by exercise act in combination to activate sensory neurons that signal sensations of fatigue and muscle pain.

A single cocaine exposure enhances both opioid reward and aversion through a ventral tegmental area-dependent mechanism.

Repeated exposure to drugs of abuse produces forms of experience-dependent plasticity including behavioral sensitization. Although a single exposure to many addicting substances elicits locomotor sensitization, there is little information regarding the motivational effects of such single exposures. This study demonstrates that a single cocaine exposure enhances both rewarding and aversive forms of opioid place conditioning. Rats were given a single injection of cocaine (15 mg/kg i.p.) in their home cage at different times before conditioning. This treatment enhanced conditioned place preference (CPP) to morphine (2 x 10 mg/kg s.c.) if training began 1 or 5 but not 10 days after the cocaine injection. A single cocaine exposure also enhanced conditioned place aversion (CPA) to the kappa-opioid receptor agonist U69593 (2 x 0.16 mg/kg s.c.). Compared to morphine CPP, U69593 CPA was delayed and persistent. It was not observed at 1 day but appeared if the conditioning began 5 or 10 days after the cocaine injection. Although the cocaine-induced enhancements of both morphine CPP and U69593 CPA followed different time courses, suggesting different mechanisms, both effects were blocked by injection of the N-methyl-d-aspartate receptor antagonist MK-801 (0.5 nmol bilaterally) into the ventral tegmental area, immediately before the cocaine injection. Thus, through a circuit involving the ventral tegmental area, a single cocaine exposure enhanced both micro-opioid receptor reward and kappa-opioid receptor aversion.