Magnesium--essentials for anesthesiologists Herroeder, Susanne; Schönherr, Marianne E; De Hert, Stefan G ...
Anesthesiology,
04/2011, Letnik:
114, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Magnesium plays a fundamental role in many cellular functions, and thus there is increasing interest in its role in clinical medicine. Although numerous experimental studies indicate positive effects ...of magnesium in a variety of disease states, large clinical trials often give conflicting results. However, there is clear evidence for magnesium to benefit patients with eclampsia or torsades de pointes arrhythmias. In addition, magnesium seems to have antinociceptive and anesthetic as well as neuroprotective effects, yet well-designed large clinical trials are required to determine its actual efficacy in pain management or in the state of stroke or subarachnoid hemorrhage. The current review aims to provide an overview of current knowledge and available evidence with respect to physiologic aspects of magnesium and proposed indications and recommendations for its use in the clinical setting.
Preserving haemodynamics is expected to positively affect tissue oxygen saturation. We hypothesized that maintaining mean arterial blood pressure (MAP) (using phenylephrine (PE) or dobutamine (Dobu)) ...would equally affect regional cerebral and paravertebral tissue saturation (rS
c
O
2
and rS
pv
O
2
, respectively). Thirty-four patients were randomly assigned to receive either PE or Dobu, in order to keep MAP within 20% of the preoperative value. Their effect on haemodynamics, rS
c
O
2
and rS
pv
O
2
at thoracic level T
3
-T
4
, T
9
-T
10
and lumbar level L
1
-L
2
was calculated at different doses. Drug-induced haemodynamic effects differed between groups (∆MAP: -2%±21 and − 19%±17, ∆CI: -14.6%±14.6 and 24.1%±49.9, ∆HR: -21%±21 and 0%±16 for PE and Dobu, respectively). Both groups exhibited a significant decrease in rS
c
O
2
, with a more pronounced decline in the PE group (-14.1%±16.1) compared to the Dobu group (-5.9%±10.6). There were no significant changes at the paravertebral level in either group, but a slight but statistically significant difference was detected between the two groups at T
3
-T
4
and L
1
-L
2
. Current guidelines advocate maintaining adequate systemic blood pressures to prevent spinal cord ischaemia in specific procedures. However, it is still unknown which circulatory supportive drug is more beneficial for maintaining spinal cord perfusion. Our data indicates that, when used for maintenance of blood pressure within a 20% range of preoperative values, neither phenylephrine nor dobutamine affect paravertebral tissue saturation.
Experimental studies have related the cardioprotective effects of sevoflurane both to preconditioning properties and to beneficial effects during reperfusion. In clinical studies, the ...cardioprotective effects of volatile agents seem more important when administered throughout the procedure than when used only in the preconditioning period. The authors hypothesized that the cardioprotective effects of sevoflurane observed in patients undergoing coronary surgery with cardiopulmonary bypass are related to timing and duration of its administration.
Elective coronary surgery patients were randomly assigned to four different anesthetic protocols (n = 50 each). In a first group, patients received a propofol based intravenous regimen (propofol group). In a second group, propofol was replaced by sevoflurane from sternotomy until the start of cardiopulmonary bypass (SEVO pre group). In a third group, propofol was replaced by sevoflurane after completion of the coronary anastomoses (SEVO post group). In a fourth group, propofol was administered until sternotomy and then replaced by sevoflurane for the remaining of the operation (SEVO all group). Postoperative concentrations of cardiac troponin I were followed during 48 h. Cardiac function was assessed perioperatively and during 24 h postoperatively.
Postoperative troponin I concentrations in the SEVO all group were lower than in the propofol group. Stroke volume decreased transiently after cardiopulmonary bypass in the propofol group but remained unchanged throughout in the SEVO all group. In the SEVO pre and SEVO post groups, stroke volume also decreased after cardiopulmonary bypass but returned earlier to baseline values than in the propofol group. Duration of stay in the intensive care unit was lower in the SEVO all group than in the propofol group.
In patients undergoing coronary artery surgery with cardiopulmonary bypass, the cardioprotective effects of sevoflurane were clinically most apparent when it was administered throughout the operation.
The present study investigated the effects of propofol, desflurane, and sevoflurane on recovery of myocardial function in high-risk coronary surgery patients. High-risk patients were defined as those ...older than 70 yr with three-vessel disease and an ejection fraction less than 50% with impaired length-dependent regulation of myocardial function.
Coronary surgery patients (n = 45) were randomly assigned to receive either target-controlled infusion of propofol or inhalational anesthesia with desflurane or sevoflurane. Cardiac function was assessed perioperatively and during 24 h postoperatively using a Swan-Ganz catheter. Perioperatively, a high-fidelity pressure catheter was positioned in the left and right atrium and ventricle. Response to increased cardiac load, obtained by leg elevation, was assessed before and after cardiopulmonary bypass (CPB). Effects on contraction were evaluated by analysis of changes in dP/dt(max). Effects on relaxation were assessed by analysis of the load-dependence of myocardial relaxation. Postoperative levels of cardiac troponin I were followed for 36 h.
After CPB, cardiac index and dP/dt(max) were significantly lower in patients under propofol anesthesia. Post-CPB, leg elevation resulted in a significantly greater decrease in dP/dt(max) in the propofol group, whereas the responses in the desflurane and sevoflurane groups were comparable with the responses before CPB. After CPB, load dependence of left ventricular pressure drop was significantly higher in the propofol group than in the desflurane and sevoflurane group. Troponin I levels were significantly higher in the propofol group.
Sevoflurane and desflurane but not propofol preserved left ventricular function after CPB in high-risk coronary surgery patients with less evidence of myocardial damage postoperatively.
The molecular background of the Ca(2+)-sensitizing effect of levosimendan relates to its specific interaction with the Ca(2+)-sensor troponin C molecule in the cardiac myofilaments. Over the years, ...significant preclinical and clinical evidence has accumulated and revealed a variety of beneficial pleiotropic effects of levosimendan and of its long-lived metabolite, OR-1896. First of all, activation of ATP-sensitive sarcolemmal K(+) channels of smooth muscle cells appears as a powerful vasodilator mechanism. Additionally, activation of ATP-sensitive K(+) channels in the mitochondria potentially extends the range of cellular actions towards the modulation of mitochondrial ATP production and implicates a pharmacological mechanism for cardioprotection. Finally, it has become evident, that levosimendan possesses an isoform-selective phosphodiesterase-inhibitory effect. Interpretation of the complex mechanism of levosimendan action requires that all potential pharmacological interactions are analyzed carefully in the framework of the currently available evidence. These data indicate that the cardiovascular effects of levosimendan are exerted via more than an isolated drug-receptor interaction, and involve favorable energetic and neurohormonal changes that are unique in comparison to other types of inodilators.
While the effects of phenylephrine (PE) and ephedrine (E) on cerebral oxygen saturation (rS
c
O
2
) already has been studied, the effect on paraspinal oxygen saturation (rS
ps
O
2
) is still ...unexplored. This study aims to assess the effect of PE and E on rS
c
O
2
and rS
ps
O
2
, measured with near-infrared spectroscopy. A randomized 4-treatment cross-over trial was designed in 28 patients under BIS-titrated anaesthesia with sevoflurane. If MAP decreased more than 20% from baseline, incremental doses of PE and/or E were given according to the randomization (group I: E–PE–E, group II: PE–E–PE, group III: E–E–E, group IV: PE–PE–PE). rS
c
O
2
and rS
ps
O
2
on T
3
–T
4
, T
9
–T
10
and L
1
–L
2
were recorded. Differences in rSO
2
(post-pretreatment) within each group were analyzed with paired Student’s
t
test. Differences in effects of PE and E on rS
c
O
2
and rS
ps
O
2
were analyzed with linear mixed-modelling. Following PE administration, rS
c
O
2
decreased significantly (– 2.7% ± 3.5), while it remained stable following E (– 0.6% ± 3.6). Contrastingly, rS
ps
O
2
at T
3
–T
4
, T
9
–T
10
and L
1
–L
2
slightly increased following PE (0.4% ± 2.5, 0.7% ± 2.0 and – 0.1% ± 1.4, respectively), while it decreased after E administration (– 1.3% ± 3.4%, – 0.7% ± 2.6% and – 1.3% ± 2.7%, respectively). Compared to E, PE administration was associated with a significant decrease in rS
c
O
2
(– 2.1%, 95% CI – 3.1%, – 1.2%, p < 0.001). In contrast, compared to PE, E was associated with a significant decrease in rS
ps
O
2
at T
3
–T
4
, T
9
–T
10
and L
1
–L
2
(– 2.0%, 95% CI – 2.8, – 1.1, p < 0.001; – 1.4%, 95% CI – 2.4%, – 0.4%, p = 0.006; and – 1.5%, 95% CI – 2.3%, – 0.8%, p < 0.001, respectively). An opposite effect on rS
c
O
2
and rS
ps
O
2
was observed after bolus administration of PE and E.
Sevoflurane has been shown to protect against myocardial ischemia and reperfusion injury in animals. The present study investigated whether these effects were clinically relevant and would protect ...left ventricular (LV) function during coronary surgery.
Twenty coronary surgery patients were randomly assigned to receive either target-controlled infusion of propofol or inhalational anesthesia with sevoflurane. Except for this, anesthetic and surgical management was the same in all patients. A high-fidelity pressure catheter was positioned in the left ventricle and the left atrium. LV response to increased cardiac load, obtained by leg elevation, was assessed before and after cardiopulmonary bypass (CPB). Effects on contraction were evaluated by analysis of changes in dP/dt(max). Effects on relaxation were assessed by analysis of the load dependence of myocardial relaxation (R = slope of the relation between time constant tau of isovolumic relaxation and end-systolic pressure). Postoperative concentrations of cardiac troponin I were followed during 36 h.
Before CPB, leg elevation slightly increased dP/dt(max) in the sevoflurane group (5 +/- 3%), whereas it remained unchanged in the propofol group (1 +/- 6%). After CPB, leg elevation resulted in a decrease in dP/dt(max) in the propofol group (-5 +/- 4%), whereas the response in the sevoflurane group was comparable to the response before CPB (5 +/- 4%). Load dependence of LV pressure fall (R) was similar in both groups before CPB. After CPB, R was increased in the propofol group but not in the sevoflurane group. Troponin I concentrations were significantly lower in the sevoflurane than in the propofol group.
Sevoflurane preserved LV function after CPB with less evidence of myocardial damage in the first 36 h postoperatively. These data suggest a cardioprotective effect of sevoflurane during coronary artery surgery.
Previous work has demonstrated paradoxical increases in cerebral oxygen saturation (ScO2) as blood pressure decreases and paradoxical decreases in ScO2 as blood pressure increases. It has been ...suggested that these paradoxical responses indicate a functional cerebral autoregulation mechanism. Accordingly, the authors hypothesized that if this suggestion is correct, paradoxical responses will occur exclusively in patients with intact cerebral autoregulation.
Thirty-four patients undergoing elective cardiac surgery were included. Cerebral autoregulation was assessed with the near-infrared spectroscopy-derived cerebral oximetry index (COx), computed by calculating the Spearman correlation coefficient between mean arterial pressure and ScO2. COx less than 0.30 was previously defined as functional autoregulation. During cardiopulmonary bypass, 20% change in blood pressure was accomplished with the use of nitroprusside for decreasing pressure and phenylephrine for increasing pressure. Effects on COx were assessed. Data were analyzed using two-way ANOVA, Kruskal-Wallis test, and Wilcoxon and Mann-Whitney U test.
Sixty-five percent of patients had a baseline COx less than 0.30, indicating functional baseline autoregulation. In 50% of these patients (n = 10), COx became highly negative after vasoactive drug administration (from -0.04 -0.25 to 0.16 to -0.63 -0.83 to -0.26 after administration of phenylephrine, and from -0.05 -0.19 to 0.17 to -0.55 -0.94 to -0.35 after administration of nitroprusside). A negative COx implies a decrease in ScO2 with increase in pressure and, conversely, an increase in ScO2 with decrease in pressure.
In this study, paradoxical changes in ScO2 after pharmacological-induced pressure changes occurred exclusively in patients with intact cerebral autoregulation, corroborating the hypothesis that these paradoxical responses might be attributable to a functional cerebral autoregulation.
We assessed extracranial contamination of the near-infrared spectroscopy (NIRS) signal during administration of phenylephrine. The study was performed with NIRO 200NX which employs both the Modified ...Beer-Lambert (MBL) method to measure total hemoglobin (tHb, expressed in µM), and Spatially Resolved Spectroscopy (SRS) to measure total hemoglobin content (nTHI, expressed in arbitrary units (a.u.)). SRS tends to not be affected by extracranial blood flow. As vasoconstriction with phenylephrine mainly occurs in the extracranial area, we hypothesized that if NIRS measurements are indeed prone to extracranial contamination, tHb will be more affected by the administration of phenylephrine than nTHI. After ethical committee approval, 20 consenting cardiac surgery patients were included. Phenylephrine was administered whenever clinically indicated and its effect on nTHI and tHb was evaluated. To adjust for the difference in raw scale units, Z-scores were calculated. Data were analyzed with Wilcoxon Signed Ranks Test and the Hodges-Lehmann method. A total of 191 data sets were obtained in 20 patients (10 male, 65 ± 15 years, 77 ± 16 kg, 166 ± 11 cm). The median difference before and after administration of phenylephrine was − 0.006 a.u. 95%CI − 0.010 to − 0.002 (p < 0.001) and − 0.415 µM 95%CI − 0.665 to − 0.205 (p < 0.001) for nTHI and tHb, respectively. The median difference between the Z-scores of nTHI and tHb was − 0.02 95%CI − 0.04 to − 0.003 (p = 0.03), with a higher variability in the Z-scores of tHb. Phenylephrine induced significant larger changes in MBL values compared to SRS values, indicating that the MBL method might be more prone to extracranial contamination. Trial and clinical registry: Trial registration number: B670201939459, ethical committee number: 2019/0265, date of approval: March 19, 2019.
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