Commentaries on Viewpoint: Why do some patients stop breathing after taking narcotics? Ventilatory chemosensitivity as a predictor of opioid-induced respiratory depression

Neurobiology of the carotid body

The carotid body (CB) is a bilateral arterial chemoreceptor located in the carotid artery bifurcation with an essential role in cardiorespiratory homeostasis. It is composed of highly perfused cell clusters, or glomeruli, innervated by sensory fibers. Glomus cells, the most abundant in each glomerulus, are neuron-like multimodal sensory elements able to detect and integrate changes in several physical and chemical parameters of the blood, in particular O₂ tension, CO₂ and pH, as well as glucose, lactate, or blood flow. Activation of glomus cells (e.g., during hypoxia or hypercapnia) stimulates the afferent fibers which impinge on brainstem neurons to elicit rapid compensatory responses (hyperventilation and sympathetic activation). This chapter presents an updated view of the structural organization of the CB and the mechanisms underlying the chemosensory responses of glomus cells, with special emphasis on the molecular processes responsible for acute O₂ sensing. The properties of the glomus cell-sensory fiber synapse as well as the organization of CB output are discussed. The chapter includes the description of recently discovered CB stem cells and progenitor cells, and their role in CB growth during acclimatization to hypoxemia. Finally, the participation of the CB in the mechanisms of disease is briefly discussed.

Neuronal mechanisms underlying opioid-induced respiratory depression: our current understanding

Opioid-induced respiratory depression (OIRD) represents the primary cause of death associated with therapeutic and recreational opioid use. Within the United States, the rate of death from opioid abuse since the early 1990s has grown disproportionally, prompting the classification as a nationwide "epidemic." Since this time, we have begun to unravel many fundamental cellular and systems-level mechanisms associated with opioid-related death. However, factors such as individual vulnerability, neuromodulatory compensation, and redundancy of opioid effects across central and peripheral nervous systems have created a barrier to a concise, integrative view of OIRD. Within this review, we bring together multiple perspectives in the field of OIRD to create an overarching viewpoint of what we know, and where we view this essential topic of research going forward into the future.

A methodology to explore ventilatory chemosensitivity and opioid-induced respiratory depression risk

Our new and noteworthy methodology allows for exploration of preoperative ventilatory chemosensitivity, measured as the hypercapnic ventilatory response (HCVR), as a risk factor for postoperative opioid-induced respiratory depression (OIRD). This feasible and reliable methodology produced preliminary data that showed highly variable depression of HCVR by remifentanil, predominance of OIRD during light sleep, and potentially negative correlation between OIRD frequency generally and HCVR measurements when measured in the presence of remifentanil. Although the results are preliminary in nature, this novel methodology may guide future studies that can one day lead to effective clinical screening tools.

Regulatory Effects of Propofol on High-Dose Remifentanil-Induced Hyperalgesia

We aimed to evaluate the regulatory effects of propofol on high-dose remifentanil-induced hyperalgesia. A total of 180 patients receiving laparoscopic cholecystectomy were randomly divided into sevoflurane + high-dose remifentanil (SH) group, sevoflurane + low-dose remifentanil (SL) group and propofol + high-dose remifentanil group (PH) group (n=60). After intravenous administration of midazolam, SH and SL groups were induced with sevoflurane and remifentanil, and PH group was induced with propofol and remifentanil. During anesthesia maintenance, SH and SL groups were given 0.3 μg/kg/min and 0.1 μg/kg/min sevoflurane and remifentanil respectively, and PH group was given 0.3 μg/kg/min propofol and remifentanil. The three groups had significantly different awakening time, extubation time and total dose of remifentanil (P<0.001). Compared with SL group, periumbilical mechanical pain thresholds 6 h and 24 h after surgery significantly decreased in SH group (P<0.05), and the visual analog scale (VAS) scores significantly increased 30 min, 2 h and 6 h after surgery (P<0.05). Compared with SH group, periumbilical mechanical thresholds 6 h and 24 h after surgery were significantly higher in PH group (P<0.05), and VAS scores 30 min, 2 h and 6 h after surgery were significantly lower (P<0.05). PH group first used patient-controlled intravenous analgesia pump significantly later than SL group did (P<0.05). The total consumptions of sufentanil in PH and SL groups were significantly lower than that of SH group (P<0.05). The incidence rates of bradycardia and postoperative chill in PH and SH groups were significantly higher than those of SL group (P<0.05). Anesthesia by infusion of high-dose remifentanil plus sevoflurane caused postoperative hyperalgesia which was relieved through intravenous anesthesia with propofol.

Physiology of the Carotid Body: From Molecules to Disease

The carotid body (CB) is an arterial chemoreceptor organ located in the carotid bifurcation and has a well-recognized role in cardiorespiratory regulation. The CB contains neurosecretory sensory cells (glomus cells), which release transmitters in response to hypoxia, hypercapnia, and acidemia to activate afferent sensory fibers terminating in the respiratory and autonomic brainstem centers. Knowledge of the physiology of the CB has progressed enormously in recent years. Herein we review advances concerning the organization and function of the cellular elements of the CB, with emphasis on the molecular mechanisms of acute oxygen sensing by glomus cells. We introduce the modern view of the CB as a multimodal integrated metabolic sensor and describe the properties of the CB stem cell niche, which support CB growth during acclimatization to chronic hypoxia. Finally, we discuss the increasing medical relevance of CB dysfunction and its potential impact on the mechanisms of disease.

Cardiovascular and respiratory activity of PK20, opioid and neurotensin hybrid peptide in anesthetized and awake rats

AIM

Chimeric compound - PK20 despite its therapeutic activity on nociceptive and inflammatory processes may affect respiration and blood pressure. Our objective was to evaluate influence of the hybrid composed of endomorphin-2 and neurotensin fragments on ventilation, heart rate and blood pressure in anesthetized and awake rats.

METHODS

The effects of PK20 (1mg/kg) were studied either after its intravenous administration in anesthetized rats or intraperitoneal injection in awake state. Tidal volume and the timing components of the breathing pattern, arterial blood pressure, and heart rate were recorded.

RESULTS

Intravenous administration of PK20 in the neurally intact rats evoked a dose-dependent apnoea followed by a transient insignificant increase in tidal volume and breathing rate. The blood pressure changes were biphasic: transient increase was replaced by prolonged hypotension. Midcervical vagotomy abrogated all post-PK20 respiratory effects. Hypotension was eliminated after blockade of neurotensin NTS₁ receptor, while respiratory changes were reduced by blockade of both: NTS₁ and μ opioid receptors. After PK20 intraperitoneal injection awake rats did not show any significant changes in ventilation and blood pressure.

CONCLUSION

This chimeric peptide should be used with care via intravenous administration in anesthetized animals since PK20 may evoke respiratory apnoea and hypotension. Nevertheless, applied intraperitoneally in the same dose in conscious rats induced no adverse effects.

Journal of Clinical Monitoring and Computing 2015 end of year summary: respiration

This paper reviews 17 papers or commentaries published in Journal of Clinical Monitoring and Computing in 2015, within the field of respiration. Papers were published covering monitoring and training of breathing, monitoring of gas exchange, hypoxemia and acid-base, and CO2 monitoring.