Opioid sensitivity in treated and untreated obstructive sleep apnoea: a prospective cohort study

BACKGROUND

Opioid administration to patients with obstructive sleep apnoea (OSA) is controversial because they are believed to be more sensitive to opioids. However, objective data on opioid effects in OSA are lacking. We tested the hypothesis that subjects with untreated OSA have increased sensitivity to opioids compared with subjects without OSA, or with OSA treated with continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BIPAP).

METHODS

This was a single-centre, prospective cohort study in subjects without OSA (n=20), with untreated OSA (n=33), or with treated OSA (n=21). OSA diagnosis was verified using type III (in-home) polysomnography. Subjects received a stepped-dose remifentanil infusion (target effect-site concentrations of 0.5, 1, 2, 3, 4 ng ml-1). Primary outcome was miosis (pupil area fractional change), the most sensitive opioid effect. Secondary outcomes were ventilatory rate, end-expired CO2, sedation, and thermal analgesia.

RESULTS

There were no differences in miosis between untreated OSA subjects (mean=0.51, 95% confidence interval [CI] 0.41-0.61) and subjects without OSA (mean=0.49, 95% CI 0.36-0.62) (mean difference=0.02, 95% CI -0.18 to 0.22); between treated OSA subjects (mean=0.56, 95% CI 0.43-0.68) and subjects without OSA (difference=0.07, 95% CI -0.16 to 0.29); or between untreated OSA and treated OSA (difference=-0.05, 95% CI -0.25 to 0.16). There were no significant differences between subjects without OSA, untreated OSA, and treated OSA in ventilatory rate, end-expired CO2, sedation, or thermal analgesia responses to remifentanil. There was no relationship between OSA severity and magnitude of opioid effects.

CONCLUSIONS

Neither obstructive sleep apnoea nor obstructive sleep apnoea treatment affected sensitivity to the miotic, sedative, analgesic, or respiratory depressant effects of the opioid remifentanil in awake adults. These results challenge conventional notions of opioid effects in obstructive sleep apnoea.

CLINICAL TRIAL REGISTRATION

NCT02898792 (clinicaltrials.gov).

Intravenous Magnesium - Lidocaine - Ketorolac Cocktail for Postoperative Opioid Resistant Pain: A Case Series of Novel Rescue Therapy

BACKGROUND

Severe postoperative pain is principally managed by opioids. While effective, opioids do not provide adequate relief in many patients and cause many side effects, including antinociceptive tolerance and opioid-induced hyperalgesia. To evaluate if a combination of intravenous Magnesium, Lidocaine, Ketorolac (MLK cocktail) is a useful rescue therapy through synergistic pharmacological mechanisms for acute pain relief. We present the intravenous combination of magnesium, lidocaine, and ketorolac (MLK cocktail) as a possible rescue for opioid insensitive severe post-operative pain.

MATERIALS AND METHODS

The principal settings were the post-operative care unit (PACU) and the surgical ward. We retrospectively analyzed the electronic medical record and anesthesia documents of 14 patients experiencing severe postoperative pain, >7/10 visual-analogue pain score (VAS), despite receiving at least 8 mg of intravenous morphine milligram equivalents (MME) after arrival in the LAC+USC Medical Center PACU between September 2012 and January 2013. The data reviewed included patients' demographics, disease etiology, surgical procedure, opioids received perioperatively, and visual-analogue pain scores before and after each analgesic received, and after the MLK cocktail. The a priori primary outcome and a posteriori secondary outcome of this study are mean visual-analogue pain score and morphine milligram equivalent dose administered per hour, respectively. The main tool evaluated has been VAS score.

RESULTS

In patients who failed to respond to opioid analgesics, administration of the MLK cocktail improved the VAS pain scores immediately from 9.4 ± 1.0 to 3.6 ± 3.5. The MLK cocktail also decreased the MME doses/hour in the immediate 12 hours postoperative period from 12.4 ± 5.6 to 1.1 ± 0.9.

CONCLUSION

In patients experiencing opioid-resistant severe postoperative pain, the magnesium, lidocaine, and ketorolac combination may be an effective nonopioid rescue therapy. Additionally, magnesium, lidocaine, and ketorolac may be utilized in cases complicated by either antinociceptive tolerance or opioid-induced hyperalgesia and can restore opioid responsiveness.

Early Life Stress and Risks for Opioid Misuse: Review of Data Supporting Neurobiological Underpinnings

A robust body of research has shown that traumatic experiences occurring during critical developmental periods of childhood when neuronal plasticity is high increase risks for a spectrum of physical and mental health problems in adulthood, including substance use disorders. However, until recently, relatively few studies had specifically examined the relationships between early life stress (ELS) and opioid use disorder (OUD). Associations with opioid use initiation, injection drug use, overdose, and poor treatment outcome have now been demonstrated. In rodents, ELS has also been shown to increase the euphoric and decrease antinociceptive effects of opioids, but little is known about these processes in humans or about the neurobiological mechanisms that may underlie these relationships. This review aims to establish a theoretical model that highlights the mechanisms by which ELS may alter opioid sensitivity, thereby contributing to future risks for OUD. Alterations induced by ELS in mesocorticolimbic brain circuits, and endogenous opioid and dopamine neurotransmitter systems are described. The limited but provocative evidence linking these alterations with opioid sensitivity and risks for OUD is presented. Overall, the findings suggest that better understanding of these mechanisms holds promise for reducing vulnerability, improving prevention strategies, and prescribing guidelines for high-risk individuals.

Behavioral meaningful opioidergic stimulation activates kappa receptor gene expression

The periaqueductal gray (PAG) has been reported to be a location for opioid regulation of pain and a potential site for behavioral selection in females. Opioid-mediated behavioral and physiological responses differ according to the activity of opioid receptor subtypes. The present study investigated the effects of the peripheral injection of the kappa-opioid receptor agonist U69593 into the dorsal subcutaneous region of animals on maternal behavior and on Oprk1 gene activity in the PAG of female rats. Female Wistar rats weighing 200-250 g at the beginning of the study were randomly divided into 2 groups for maternal behavior and gene expression experiments. On day 5, pups were removed at 7:00 am and placed in another home cage that was distant from their mother. Thirty minutes after removing the pups, the dams were treated with U69593 (0.15 mg/kg, sc) or 0.9% saline (up to 1 mL/kg) and after 30 min were evaluated in the maternal behavior test. Latencies in seconds for pup retrieval, grouping, crouching, and full maternal behavior were scored. The results showed that U69593 administration inhibited maternal behavior (P < 0.05) because a lower percentage of kappa group dams showed retrieval of first pup, retrieving all pups, grouping, crouching and displaying full maternal behavior compared to the saline group. Opioid gene expression was evaluated using real-time reverse-transcription polymerase chain reaction (RT-PCR). A single injection of U69593 increased Oprk1 PAG expression in both virgin (P < 0.05) and lactating female rats (P < 0.01), with no significant effect on Oprm1 or Oprd1 gene activity. Thus, the expression of kappa-opioid receptors in the PAG may be modulated by single opioid receptor stimulation and behavioral meaningful opioidergic transmission in the adult female might occur simultaneously to specific changes in gene expression of kappa-opioid receptor subtype. This is yet another alert for the complex role of the opioid system in female reproduction.