A Neuronal Mechanism of Propofol-Induced Central Respiratory Depression in Newborn Rats

Volatile anesthetics maintain tidal volume and minute ventilation to a greater degree than propofol under spontaneous respiration

Background

Although general anesthetics depress spontaneous respiration, the comprehensive effect of general anesthetics on respiratory function remains unclear. We aimed to investigate the effects of general anesthetics on spontaneous respiration in non-intubated mice with different types and doses of general anesthetic.

Methods

Adult C57BL/6 J mice were administered intravenous anesthetics, including propofol and etomidate, and inhalational anesthetics, including sevoflurane and isoflurane in vivo at doses of 0.5-, 1.0-, and 2.0-times the minimum alveolar concentration (MAC)/median effective dose (ED₅₀) to induce loss of the righting reflex (LORR). Whole-body plethysmography (WBP) was applied to measure parameters of respiration under unrestricted conditions without endotracheal intubation. The alteration in respiratory sensitivity to carbon dioxide (CO₂) under general anesthesia was also determined. The following respiratory parameters were continuously recorded during anesthesia or CO₂ exposure: respiratory frequency (FR), tidal volume (TV), minute ventilation (MV), expiratory time (TE), inspiratory time (TI), and inspiratory–expiratory time ratio (I/E), and peak inspiratory flow.

Results

Sub-anesthetic concentrations (0.5 MAC) of sevoflurane or isoflurane increased FR, TV, and MV. With isoflurane and sevoflurane exposure, the CO₂-evoked increases in FR, TV, and MV were decreased. Compared with inhalational anesthetics, propofol and etomidate induced respiratory suppression, affecting FR, TV, and MV. In 100% oxygen (O₂), FR in the group that received propofol 1.0-times the ED₅₀ was 69.63 ± 33.44 breaths/min compared with 155.68 ± 64.42 breaths/min in the etomidate-treated group. In the same groups, FR was 88.72 ± 34.51 breaths/min and 225.10 ± 59.82 breaths/min, respectively, in 3% CO₂ and 144.17 ± 63.25 breaths/min and 197.70 ± 41.93 breaths/min, respectively, in 5% CO₂. A higher CO₂ sensitivity was found in etomidate-treated mice compared with propofol-treated mice. In addition, propofol induced a greater decrease in FR, MV, and I/E ratio compared with etomidate, sevoflurane, and isoflurane at equivalent doses (all P < 0.05).

Conclusions

General anesthetics differentially modulate spontaneous breathing in vivo. Volatile anesthetics increase FR, TV, and MV at sub-anesthetic concentrations, while they decrease FR at higher concentrations. Propofol consistently depressed respiratory parameters to a greater degree than etomidate.

Sedative effects of acepromazine in combination with nalbuphine or butorphanol, intramuscularly or intravenously, in healthy cats: a randomized, blinded clinical trial

OBJECTIVES

The aim of this study was to compare the sedative effects in cats administered acepromazine-nalbuphine and acepromazine-butorphanol, intramuscularly (IM) and intravenously (IV), and the occurrence of adverse cardiorespiratory effects.

METHODS

Forty-six cats were randomly divided into four groups and administered acepromazine (0.05 mg/kg) combined with nalbuphine (0.5 mg/kg) or butorphanol (0.4 mg/kg), IV (ACP-NALIV and ACP-BUTIV groups, respectively) or IM (ACP-NALIM and ACP-BUTIM groups, respectively). Sedation scores, ease of intravenous catheter placement (simple descriptive scale [SDS] scores), physiologic variables, venous blood gases and the propofol dose required for anesthetic induction were recorded.

RESULTS

Mild sedation was observed in all groups approximately 30 mins after treatment administration (timepoint T1, prior to propofol administration). Sedation scores at T1 increased above baseline in all groups (P <0.05), but no significant difference was observed among groups. Dynamic interactive visual analogue scale sedation scores (range 0-100 mm) recorded at T1 were (median [interquartile range]): ACP-NALIM, 12 (10-12); ACP-NALIV, 11 (6-16); ACP-BUTIM, 11 (7-14); and ACP-BUTIV, 12 (7-19). Overall, SDS scores did not change from baseline at T1 and there was no significant difference among groups. The propofol dose did not differ among groups. Blood gases remained within the reference intervals for cats. Significant decreases from baseline were detected for all groups in systolic arterial pressure (SAP). Mean ± SD values at T1 were (mmHg): ACP-NALIM, 108 ± 13; ACP-NALIV, 102 ± 10; ACP-BUTIM, 97 ± 13; and ACP-BUTIV, 98 ± 21. Arterial hypotension (SAP <90 mmHg) was recorded at T1 in 0/11, 1/13, 4/11 and 5/11 cats in groups ACP-NALIM, ACP-NALIV, ACP-BUTIM and ACP-BUTIV, respectively, and was further exacerbated after the induction of anesthesia with propofol.

CONCLUSIONS AND RELEVANCE

In healthy cats administered acepromazine-nalbuphine and acepromazine-butorphanol, IM and IV, the degree of sedation was mild regardless of the protocol and the route of administration. The main adverse effect observed was a reduction in arterial blood pressure.

Optical imaging of propofol-induced central respiratory depression in medulla-spinal cord preparations from newborn rats

1. Propofol (2,6-diisopropylphenol) is an intravenous anaesthetic used for the induction and maintenance of general anaesthesia; it also potently and dose-dependently depresses respiration. The aim of the present study was to analyse propofol-induced changes in spatiotemporal patterns of inspiratory-related neural activity and to investigate the involvement of the GABAA receptor by using an optical imaging technique. 2. The brain stems and spinal cords of 0-1-day-old Wistar rats were isolated and stained using a fluorescent voltage-sensitive dye. Neuronal activity in the preparation was detected using an optical recording apparatus containing a charge-coupled device (CCD)-based camera. 3. Bath-applied propofol (7.5 μmol/L) decreased the C4 burst rate to 45.9% of baseline. Although optical signals corresponding to membrane depolarization during the pre-inspiratory phase in the parafacial region of the ventral medulla decreased to 28.7% of baseline following propofol application, those during the inspiratory phase in the caudal part of the rostral ventrolateral medulla did not. 4. The inhibitory effect of bath-applied propofol was reversed by 2 μmol/L bicuculline. 5. Changes in optical signals corresponding to the population activity of pre-inspiratory neurons were parallel to changes in the C4 burst rate. 6. The results suggest that propofol decreases the inspiratory burst rate by reducing the activity of pre-inspiratory neurons and that GABAA receptor activation plays a role in propofol-induced central respiratory depression. These results are consistent with those of previous electrophysiological studies.

Hemodynamic effects of dexmedetomidine during intra-operative electrocorticography for epilepsy surgery

Background:

Dexmedetomidine, a predominant alpha-2-adrenergic agonist has been used in anesthetic practice to provide good sedation. The drug is being recently used in neuroanesthesia during awake surgery for brain tumors and in functional neurosurgery.

Materials and Methods:

This prospective study analyzed the hemodynamic effects of dexmedetomidine infusion during electrocorticography in patients undergoing surgery for mesial temporal sclerosis. Dexmedetomidine infusion was administered during intra-operative electrocorticography recording, 15 minutes after the end tidal MAC of N₂O and isoflurane were decreased to zero. Anesthesia was maintained with O₂ : air mixture = 50:50, vecuronium and fentanyl. Heart rate (HR), mean arterial pressure (MAP) and end tidal carbon dioxide (ETCO₂) were recorded across at induction, 2 min prior to dexmedetomidine (PreDEX), 5 min during dexmedetomidine infusion (DEX; 1 μg/kg), 5 min after stopping dexmedetomidine and 10 minutes after stopping dexmedetomidine.

Results:

Forty patients with mesial temporal sclerosis (M: F = 27:13, mean age = 28.15 ± 10.9 years; duration of epilepsy = 12.0 ± 7.9 years) underwent anterior temporal lobe resection with amygdalohippocampectomy for drug-resistant epilepsy. Infusion of dexmedetomidine caused a transient fall in HR in 87.5% of patients and an increase in MAP in 62.5% of patients, which showed a tendency to revert back towards PreDEX values within 10 min after stopping the infusion. Sixty-five percent of the patients showed ≤25% reduction and 10% of them showed >25% reduction in HR. 47.5% of the patients showed ≤25% increase and 15% of them showed >25% increase in MAP. These changes were over a narrow range and within physiological limits.

Conclusion:

The infusion of dexmedetomidine for a short period causes reduction of HR and increase in MAP in patients, however the variations are within acceptable range.

Dynamics of upper airways during the Müller maneuver in healthy subjects: a cine MRI study

The Müller maneuver has been widely applied to mimic the pathophysiological condition of obstructive sleep apnea (OSA) during wakefulness. We applied cine MRI to elucidate dynamics of the upper airway during the Müller maneuver in healthy subjects (n = 7). Three sets of images (during quiet nose breathing, quiet mouth breathing, and Müller maneuver) were recorded on sagittal midline plane together with impedance pneumography. The position of the tongue root changed during a respiratory cycle when subjects breathed quietly. At the early inspiratory phase the tongue root moved forward and upward, the retroglossal airway size increased toward the middle of inspiration, and the airway size became smaller again toward the end of inspiration. During expiration the airway size became further smaller. When the subject performed the Müller maneuver, the movement of the oropharynx and its narrowing were greater than those of the velopharynx. However, the airway was not completely obstructed. A relatively large morphological change was observed in the retropalatal and retroglossal regions with the backward and downward motion of the tongue root and flattening of the tongue shape during the Müller maneuver. Although patterns of upper airway narrowing and tongue shape alterations were variable among subjects, upper airway narrowing was commonly prominent in the retroglossal area. Cine MRI with the Müller maneuver enables to visualize the upper airway dynamics and could be easily applied to evaluate upper airway collapsibility during wakefulness.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Coadministration of the AMPAKINE CX717 with propofol reduces respiratory depression and fatal apneas

BACKGROUND

Propofol (2,6-diisopropylphenol) is used for the induction and maintenance of anesthesia in human and veterinary medicine. Propofol's disadvantages include the induction of respiratory depression and apnea. Here, the authors report a clinically feasible pharmacological solution for reducing propofol-induced respiratory depression via a mechanism that does not interfere with anesthesia. Specifically, they test the hypothesis that the AMPAKINE CX717, which has been proven metabolically stable and safe for human use, can prevent and rescue from propofol-induced severe apnea.

METHODS

The actions of propofol and the AMPAKINE CX717 were measured via (1) ventral root recordings from newborn rat brainstem-spinal cord preparations, (2) phrenic nerve recordings from an adult mouse in situ working heart-brainstem preparation, and (3) plethysmographic recordings from unrestrained newborn and adult rats.

RESULTS

In vitro, respiratory depression caused by propofol (2 μM, n = 11, mean ± SEM, 41 ± 5% of control frequency, 63 ± 5% of control duration) was alleviated by CX717 (n = 4, 50-150 μM). In situ, a decrease in respiratory frequency (44 ± 9% of control), phrenic burst duration (66 ± 7% of control), and amplitude (78 ± 5% of control) caused by propofol (2 μM, n = 5) was alleviated by coadministration of CX717 (50 μM, n = 5). In vivo, pre- or coadministration of CX717 (20-25mg/kg) with propofol markedly reduced propofol-induced respiratory depression (n = 7; 20mg/kg) and propofol-induced lethal apnea (n = 6; 30 mg/kg).

CONCLUSIONS

Administration of CX717 before or in conjunction with propofol provides an increased safety margin against profound apnea and death.

Isolated in vitro brainstem-spinal cord preparations remain important tools in respiratory neurobiology

Isolated in vitro brainstem-spinal cord preparations are used extensively in respiratory neurobiology because the respiratory network in the pons and medulla is intact, monosynaptic descending inputs to spinal motoneurons can be activated, brainstem and spinal cord tissue can be bathed with different solutions, and the responses of cervical, thoracic, and lumbar spinal motoneurons to experimental perturbations can be compared. The caveats and limitations of in vitro brainstem-spinal cord preparations are well-documented. However, isolated brainstem-spinal cords are still valuable experimental preparations that can be used to study neuronal connectivity within the brainstem, development of motor networks with lethal genetic mutations, deleterious effects of pathological drugs and conditions, respiratory spinal motor plasticity, and interactions with other motor behaviors. Our goal is to show how isolated brainstem-spinal cord preparations still have a lot to offer scientifically and experimentally to address questions within and outside the field of respiratory neurobiology.

The effect-site concentration of propofol producing respiratory depression during spinal anesthesia

BACKGROUND

Propofol is used worldwide for its sedative effective; nonetheless, has the serious side effect of respiratory depression. An increased blood concentration of propofol is well known to be associated with increased respiratory depression. However, there are no studies of the effect site concentration inducing respiratory depression. The purpose of this study was to determine the effect site concentration inducing respiratory depression of propofol when sedating a patient after spinal anesthesia.

METHODS

This study included thirty seven males who received operations with spinal anesthesia, which was performed on L3-4 and L4-5. All patients were monitored with the bispectral index and were continuously infused with propofol using target controlled infusion. Respiratory depression was diagnosed when one of the following was evident without upper respiratory obstructive signs: a greater than 20% increase of end tidal carbon dioxide from baseline pressure or pulse oximetry oxygen saturation lower than 95%. We obtained the EC(5), EC(10), and EC(50) of the effect site propofol for respiratory depression.

RESULTS

The EC(5) of propofol for respiratory depression was 3.09 mcg/ml (95% CI, 2.60-3.58). The EC(10) of propofol for respiratory depression was 3.18 mcg/ml (95% CI, 2.57-3.80). The EC(50) of propofol for respiratory depression was 3.99 mcg/ml (95% CI, 2.36-5.61).

CONCLUSIONS

The EC(5), EC(10), and EC(50) of effect site propofol for respiratory depression during spinal anesthesia were 3.09 mcg/ml ,3.18 mcg/ml, and 3.99 mcg/ml, respectively.

Propofol abolished the phrenic long-term facilitation in rats

The aim was to investigate the effect of propofol anesthesia on the phrenic long-term facilitation (pLTF) in rats. We hypothesized that pLTF would be abolished during propofol-compared with urethane anesthesia. Fourteen adult, male, anesthetized, vagotomized, paralyzed, and mechanically ventilated Sprague-Dawley rats (seven per group), were exposed to the acute intermittent hypoxia (AIH) protocol. Peak phrenic nerve activity (PNA), burst frequency (f), and breathing rhythm parameters (Ti, Te, Ttot) were analyzed during the first hypoxia (TH1), as well as at 15 (T15), 30 (T30), and 60min (T60) after the final hypoxic episode, and compared to the baseline values. In propofol-anesthetized rats no significant changes of PNA were recorded after the last hypoxic episode, i.e. no pLTF was induced. There was a significant increase of PNA (59.4+/-6.6%, P<0.001) in urethane-anesthetized group at T60. AIH did not elicit significant changes in f, Ti, Te, Ttot in either group at T15, T30, and T60. The pLTF, elicited by AIH, was induced in the urethane-anesthetized rats. On the contrary, pLTF was abolished in the propofol-anesthetized rats.

Connectivity of the primate superior colliculus mapped by concurrent microstimulation and event-related FMRI

Background

Neuroanatomical studies investigating the connectivity of brain areas have heretofore employed procedures in which chemical or viral tracers are injected into an area of interest, and connected areas are subsequently identified using histological techniques. Such experiments require the sacrifice of the animals and do not allow for subsequent electrophysiological studies in the same subjects, rendering a direct investigation of the functional properties of anatomically identified areas impossible.

Methodology/Principal Findings

Here, we used a combination of microstimulation and fMRI in an anesthetized monkey preparation to study the connectivity of the superior colliculus (SC). Microstimulation of the SC resulted in changes in the blood oxygenation level-dependent (BOLD) signals in the SC and in several cortical and subcortical areas consistent with the known connectivity of the SC in primates.

Conclusions/Significance

These findings demonstrates that the concurrent use of microstimulation and fMRI can be used to identify brain networks for further electrophysiological or fMRI investigation.