Experimental Neurology 252 (2014) 12–17
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Isoflurane suppresses cortical spreading depolarizations compared to propofol — Implications for sedation of neurocritical care patients Masatoshi Takagaki a,b,1, Delphine Feuerstein a,⁎,1, Tetsuya Kumagai a,b, Markus Gramer a, Toshiki Yoshimine b, Rudolf Graf a a b
Max Planck Institute for Neurological Research, 50931 Cologne, Germany Department of Neurosurgery, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan
a r t i c l e
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Article history: Received 3 September 2013 Revised 24 October 2013 Accepted 4 November 2013 Available online 15 November 2013 Keywords: Isoflurane Propofol Stroke Cortical spreading depression Cerebral blood flow Intensive care unit
a b s t r a c t Sedatives in the neurointensive care unit can strongly influence patients' risks of developing secondary brain damage. In particular, isoflurane, a volatile anesthetic, has been recently re-introduced to the neurointensive care unit, and first clinical studies suggest beneficial effects due to elevation of cerebral blood flow and reduction of metabolism. In contrast, propofol is a commonly used intravenous sedative that reduces cerebral blood flow and intra-cranial pressure. We have here studied the influence of these two sedatives on the occurrence of cortical spreading depolarizations (CSDs), which have emerged over the last decade as a major mechanism of delayed brain injury in stroke and brain trauma, constituting a substantial vascular and metabolic threat to periinfarct tissue and being associated with poor patient outcome. Two experimental models were tested in Wistar rats anesthetized either with isoflurane or with propofol: KCl-evoked CSDs (n = 10) and spontaneous CSDs after occlusion of the middle cerebral artery (n = 14). Spatiotemporal patterns of CSD waves were observed by realtime laser speckle imaging of regional cerebral blood flow changes associated with the CSDs. During 30 min of cortical KCl application, 5.2 ± 0.7 CSDs were induced under isoflurane compared to 10.2 ± 1.8 CSDs under propofol (p b 0.001). After focal ischemia, 2.43 ± 1.0 CSDs/h emerged spontaneously under isoflurane versus 6.83 ± 2.5 CSDs/h under propofol (p b 0.001). Furthermore, baseline blood flow and glycemia were much higher under isoflurane compared to propofol, which may set the tissue in better metabolic conditions to recover from the occurrence of CSD waves. We conclude that isoflurane, in comparison to propofol, decreases the occurrence of CSDs and may improve recovery from these metabolically demanding waves. To reduce CSD induced secondary tissue damage, we suggest isoflurane to be favored over propofol to sedate acute stroke and trauma patients in the neurointensive care unit. © 2013 Elsevier Inc. All rights reserved.
Introduction Patients in the intensive care unit (ICU) are generally anesthetized to alleviate pain, agitation and facilitate tolerance of mechanical ventilation. For neurocritical care patients, the aims of sedation are additionally to prevent secondary brain damage, notably by sustaining an adequate cerebral blood flow (CBF), decreasing basal metabolism and maintaining low intracranial pressure. Recently, an additional mechanism for secondary injury has been put forward: cortical spreading depolarizations (CSDs — originally referred to as cortical spreading depressions) (Dreier, 2011; Lauritzen et al., 2011). These are mass depolarizations arising spontaneously and propagating around ischemic and traumatic Abbreviations: CSD, cortical spreading depression; ICU, intensive care unit; CBF, cerebral blood flow; MCAo, middle cerebral artery occlusion; DC, direct current; LSF, laser speckle flowmetry; ROI, region of interest. ⁎ Corresponding author at: Max Planck Institute for Neurological Research, Gleueler Strasse 50, 50931 Cologne, Germany. Fax: +49 221 4726 203. E-mail address: [email protected] (D. Feuerstein). 1 These authors contributed equally to the work. 0014-4886/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.expneurol.2013.11.003
lesions in the human brain (Dohmen et al., 2008; Hartings et al., 2011). Clinical studies suggest that frequent CSDs are associated with a worsening of vascular and metabolic conditions of the peri-infarct tissue (Bosche et al., 2010; Dreier et al., 2009; Feuerstein et al., 2010), secondary ischemic neurological deficits (Dreier et al., 2006) and poor patient outcome (Hartings et al., 2011). However, only few studies have examined the influence of anesthesia on CSDs in the context of the ICU (Hertle et al., 2012). We here compare the effects of isoflurane and propofol on the susceptibility to CSDs in two experimental models. Isoflurane is an inhalation anesthetic that has been recently re-introduced in the ICU via the Anesthetic Conserving Device (AnaConDa), a safe miniaturized vaporizer. First clinical applications in ischemic and hemorrhagic stroke patients seem promising, suggesting beneficial effects from increased CBF and reduced metabolism during isoflurane sedation (Bösel et al., 2012; Villa et al., 2012). In contrast, propofol is a potent intravenous hypnotic agent that has been widely used in neurointensive care patients, notably because it is easily titratable, with rapid onset and short duration of action and it decreases intra-cranial pressure while
M. Takagaki et al. / Experimental Neurology 252 (2014) 12–17
maintaining autoregulation (Villa et al., 2012). However, the effects of propofol on CSDs are largely unknown. Methods Surgical preparation All animal procedures were performed in accordance with the German regulations for animal protection. Male Wistar rats were anesthetized using isoflurane (5% for induction, 1.5–2% for maintenance) in 70%/30% nitrous oxide/oxygen during all surgical procedures. The animals breathed spontaneously and their rectal temperature was kept at 37 °C using a servo-controlled heating blanket. The left femoral artery was cannulated for continuous monitoring of arterial blood pressure and for hourly measurement of blood gases (arterial PaO2, PaCO2, pH). Frontal and parietal bones were exposed and thinned out to transparency using a dental drill. Drilling was performed under continuous saline irrigation to prevent heat injury. At the end of surgery, the thinned out skull surface was covered with warm paraffin oil and laser speckle images were continuously acquired during the whole duration of the experiments. Experimental groups Half the animals were maintained with 1.5–2% isoflurane, while the other half were switched to propofol. The breathing gas mixture was maintained at 70%/30% nitrous oxide/oxygen in all cases. In the propofol animals, propofol infusion was started at 38 mg/kg/h via tail vein and isoflurane weaned off over 15 min. Propofol concentration (33 to 53 mg/kg/h) was adjusted to keep breathing rate, similar to that observed under isoflurane, within 60–80 cycles/min and to abolish blood pressure response to tail pinch. Thirty minutes after isoflurane was completely off, systemic variables and CBF had stabilized to new levels (Table 1, Fig. 3). In our experience, this duration is sufficient to eliminate isoflurane from the system: isoflurane has indeed a low blood gas solubility and hence a rapid emergence and it has a short (about 5 min) context-sensitive half-time (Bailey, 1997). The depth of anesthesia was similar under both anesthetics (slightly more than 1 MAC in case of isoflurane and slightly more than 1 ED50 in case of propofol). It should be mentioned, however, that both PaO2 and PaCO2 were somewhat elevated under propofol compared to isoflurane (Table 1). In experimental group 1 (KCl group, n = 10), a cotton ball soaked and continuously infused with 3 M KCl at 10 μL/h for 30 min was placed over the dura in the frontal cortex to elicit CSDs under each respective anesthesia. In experimental group 2 (MCAo group, n = 14), focal ischemia was induced under each respective anesthesia by embolic occlusion of the middle cerebral artery (MCAo). After baseline imaging, a macrosphere (0.315 to 0.355 mm diameter; Brace, Alzenau, Germany) was advanced into the intra-carotid artery by injection of approximately 0.2 mL heparinized saline. This resulted in the occlusion of the MCA, causing spontaneous generation of CSDs that were observed for up to 3 h after macrosphere injection (Fig. 2). The position of the macrosphere in the neurovasculature was verified post-mortem by visual inspection of
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the brain base: only animals where the macrosphere was lodged at the bifurcation of the MCA and the anterior cerebral artery were included. Details about the macrosphere model are provided elsewhere (Gerriets et al., 2003; Kumagai et al., 2010). Note that during all procedures, systemic parameters were monitored (blood pressure, arterial blood gases) and maintained within physiological ranges in all animals included in this study, although propofol tended to induce a mild acidosis and a mild hypercapnia compared to isoflurane (Table 1). Laser speckle flowmetry (LSF) LSF measurement of CBF (CBFLSF) was implemented as previously described (Dunn et al., 2001; Kumagai et al., 2010; Nakamura et al., 2010). Regions of interest (ROI) were placed in areas devoid of major blood vessels and analyzed for CBFLSF (Figs. 1A and 2A). CBFLSF levels reported here are relative to baseline CBFLSF under isoflurane taken as 100%. The speed of CSD waves was calculated using two ROIs placed in the direction of wave propagation. Electrophysiological recordings CBFLSF measurements were combined with direct current (DC) and electrocorticogram recordings in two animals from the KCl group (Fig. 1A-B). A 3 μm tip glass micropipette, filled with 1 M sodium chloride, was implanted at 500 μm depth through a small burr-hole (Fig. 1A). Ag/AgCl reference and ground electrodes were placed subcutaneously in the neck. The electrophysiological signals were digitized at 250 Hz. A low-pass filter was applied at 0.1 Hz to yield the DC component. Artefactual high frequency noise and baseline drifts were filtered out using methods described earlier (Feuerstein et al., 2009). The mean value of the DC potentials over a 2 min period before CSD induction was taken as 0 mV and the amplitude of the DC shifts calculated relative to this value. The duration of the DC shift was given by the width at half maximum. Statistics All data are presented either as individual recordings or as mean value ± standard deviation. CSD characteristics between isoflurane and propofol were compared using unpaired t-tests within each experimental group and considered statistically significant at p b 0.05. Results Multiple CSDs induced by KCl application (KCl group) Following topical application of KCl, DC potential shifts linked to CSD were similar under the two anesthetics (−25.2 ± 5.3 mV for 22.5 ± 3.0 s under isoflurane versus −25.9 ± 7.8 mV for 24.5 ± 5.7 s under propofol). CBFLSF changes measured in one ROI near the DC electrode were temporally linked to the DC shift, confirming that CBFLSF is a suitable surrogate marker for CSD (Fig. 1B). CSD waves propagated at
Table 1 Systemic parameters. Data are given as average ± standard deviation across animals in each group. Arterial blood pressure data are the average of 1 h continuous recording in the KCl group and 3 h continuous recording after macrosphere injection in the MCAo group. MABP: mean arterial blood pressure; PaO2: arterial partial pressure in oxygen; PaCO2: arterial partial pressure in carbon dioxide; unpaired t-test within each group: *p b 0.05; **p b 0.01. Experimental group
Anesthesia
MABP (mm Hg)
PaO2 (mm Hg)
PaCO2 (mm Hg)
pH
KCl
Isoflurane (n = 5) Propofol (n = 5) Isoflurane (n = 7) Propofol (n = 7)
83.7 ± 4.8 104.3 ± 20.1 107.5 ± 16.6 124.5 ± 16.6
115.12 ± 36.8 143.4 ± 34.7 108.4 ± 28.0 142.8 ± 25.4*
40.5 48.7 38.4 47.0
7.42 7.34 7.40 7.36
MCAo
± ± ± ±
3.9 2.9** 7.0 5.2*
Blood sugar (mg/dL) ± ± ± ±
0.03 0.03** 0.04 0.04
128.6 ± 13.1 79.0 ± 5.7** 139.4 ± 28.9 94.6 ± 22.0**
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Fig. 1. Multiple CSDs induced by KCl application. A: Speckle contrast image of the left hemisphere and representative positions of the KCl cotton ball (frontal lobe), of the DC electrode and of two regions of interest (ROI) of 1 × 1 mm2 size for LSF analysis (parietal lobe). The arrow indicates the direction of propagation (frontal to caudal). B: DC potential shifts and CBFLSF changes for the ROI closest to the DC electrode (as per A) under isoflurane (top) and propofol (bottom). C: Effects of isoflurane (dark gray, n = 5) versus propofol (white, n = 5) on CSD propagation speed and frequency during 30 min KCl application. Bar height indicates the mean value and error bars the standard deviations. CSD propagation speeds were calculated between two ROIs shown in A for the first 5 waves in all animals. ***p b 0.001.
the same speed under isoflurane (3.80 ± 0.85 mm/min, n = 5) and propofol (3.98 ± 1.05 mm/min, n = 5). However, the number of CSDs that propagated during a 30 min application of KCl was double under propofol (10.2 ± 1.8) compared to isoflurane (5.2 ± 0.7) (Fig. 1C). Resting-state CBFLSF prior to induction of CSD under propofol was significantly lower than under isoflurane (58 ± 12.3%, t(8) = 7.6, p b 0.001, Fig. 3A). Glycemia was also very different: 128.6 ± 13.1 mg/dL under isoflurane vs. 79.0 ± 5.7 mg/dL under propofol (t(8) = 3.5, p = 0.008, Fig. 3B). Multiple CSDs spontaneously arising after MCAo (MCAo group) Immediately after macrosphere injection, a fast gradual decline in CBFLSF was observed generating an ischemic focus in the arterial territory of the MCA. Within the next 5 to 20 min, a primary CBFLSF wave, originating at the border of the ischemic territory, propagated across the entire exposed cortex. During the next 3 h, multiple subsequent secondary CBFLSF waves arose and propagated circumferentially around the ischemic core (Fig. 2B). The spatio-temporal patterns of the waves were similar in both anesthetics and comparable to previous studies (Kumagai et al., 2010; Nakamura et al., 2010). However, there were twice as many circumferential waves under propofol (6.83 ± 2.5 CSDs/h) as under isoflurane (2.43 ± 1.0 CSDs/h) despite identical propagation speeds (Fig. 2C). Resting-state CBFLSF prior to MCAo could not be accurately determined because the external carotid artery and the pterygopalatine branch of the internal carotid artery were ligated to enable macrosphere injection. This resulted in an immediate drop in CBFLSF and baseline
isoflurane blood flow could therefore not be measured. However, plasma glucose concentrations were again very different under both anesthetics: 139.4 ± 28.9 mg/dL under isoflurane vs. 94.6 ± 22.0 mg/dL under propofol (t(12) = −3.5, p = 0.004, Fig. 3C). Discussion CSD waves under propofol and isoflurane seem to share the same characteristics, with similar depolarization amplitude and duration, and similar waveform and propagation speed of associated CBFLSF waves. However, at doses comparable to those used in clinical intensive care settings (Bösel et al., 2012; Villa et al., 2012), the rate of CSD is halved by isoflurane in comparison to propofol, both when induced by KCl and when spontaneously propagating after focal ischemia. That CSD frequency is differently sensitive to anesthesia regimens than CSD propagation speed and duration has also been observed after KCl application by Kudo et al. (2008). We here detected CSD waves by LSF imaging and not DC recordings for two main reasons. First, LSF has been validated as a good method to track CSD waves against electrophysiological recordings (Ayata et al., 2004; Sukhotinsky et al., 2010) and membrane potential imaging (Obrenovitch et al., 2009). Second, since LSF is an imaging technique, CSD waves can be visualized in highly heterogeneous tissue, such as after focal ischemia (Kumagai et al., 2010; Luckl et al., 2009; Nakamura et al., 2010; Shin et al., 2006, 2007; Strong et al., 2006), as opposed to local DC measurements that could miss events if not placed on the path of a CSD wave. To our knowledge, this is the first study that investigates the impact of propofol on the susceptibility of CSD waves in the KCl and the MCAo
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Fig. 2. Multiple CSDs spontaneously arising after MCAo. A: Field of view and positions of three ROIs typically used for LSF analysis in this experimental group. Dashed line indicates the border of the ischemic core. The arrow indicates the direction of propagation of the circumferential CSD waves that are confined in the border zone of the ischemic core. B: CBFLSF in the three ROIs indicated in A (same gray shades) under isoflurane (top) and propofol (bottom). Note that the first CSD associated CBF wave propagates from the core to the periphery (black to light gray ROI), while the following waves are mostly found in the periphery of the ischemic core (gray ROIs). Note also that the first CBF wave is hypoemic in the core ROIs and hyperemic only in the periphery of the ischemic territory. C: Effects of isoflurane (dark gray, n = 7) versus propofol (white, n = 7) on the propagation speed and frequency of circumferential CSDs during the first hour after occlusion of the MCA. Bar heights indicate mean values and error bars standard deviations. ***p b 0.001.
models. We cannot undoubtedly conclude whether propofol leads to more SDs or isoflurane diminishes SDs but earlier studies observed a significant reduction in the number of transient DC shifts following both topical KCl application (Kitahara et al., 2001; Kudo et al., 2008)
A
KCl group 100
B
***
KCl group
Plasma glucose (mg/dL)
CBFLSF (%)
60
40
C
MCAo group
175 150
80
and MCAo when using isoflurane compared to other anesthetics (Patel et al., 1998). These findings can be explained by the mechanisms of action of isoflurane versus those of propofol. Although both anesthetics likely act on GABAA receptors (Campagna et al., 2003; Hara et al.,
**
***
125 100 75 50
20 25 0
0
isoflurane
propofol
isoflurane
propofol
isoflurane
propofol
Fig. 3. Baseline CBF and plasma glucose under isoflurane and propofol. A: Baseline CBFLSF prior to CSD propagation (KCl group) was significantly lower under propofol (n = 5) compared to isoflurane (n = 5). Baseline CBFLSF was calculated as the average CBFLSF over 5 min prior to the application of the KCl cotton ball. 100% CBFLSF was taken under isoflurane. Bar height indicates the mean value and error bars the standard deviations. B: Plasma glucose concentrations in the KCl group under isoflurane (n = 5) and under propofol (n = 5). Measurements were taken before and after KCl application. Bar height indicates the mean value and error bars the standard deviations. C: Plasma glucose concentrations in the MCAo group under isoflurane (n = 7) and under propofol (n = 7). Measurements were taken hourly just before and after MCAo. Bar height indicates the mean value and error bars the standard deviations.
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1994), isoflurane additionally inhibits NMDA receptors by binding at the glycine site (Dickinson et al., 2007). Clinically, sedatives with NMDA receptor antagonist capacities, such as ketamine, can abolish CSDs (Hertle et al., 2012; Sakowitz et al., 2009). Note that, in our study, we maintained 70% N2O in breathing gases for all animals, also including those anesthetized with propofol. N2O has been discussed as an inhibitor of NMDA receptors (Jevtović-Todorović et al., 1998) but did not seem to suppress CSD propagation under propofol. Additionally, isoflurane activates TREK-1 potassium “leak channels”, which clamp neurons to their resting potentials, making them more resistant to depolarization (Patel et al., 1999). Such properties have not been demonstrated for propofol. Decreasing the number of spontaneous CSD waves after brain injury may prove crucial for neurocritical care patients. The frequency of CSDs after focal ischemia has indeed been correlated to the extent of cortical injury in numerous experimental stroke models (Back et al., 1994; Busch et al., 1996; Koroleva and Bures, 1996; Patel et al., 1998; Takano et al., 1996). Clinically, recent evidence shows that the occurrence of CSDs is associated with secondary neurological deficits in subarachnoid hemorrhage patients (Dreier et al., 2006) and is an independent predictor of adverse clinical outcome in traumatic brain injury patients (Hartings et al., 2011). Our data therefore suggest that isoflurane should be favored over propofol, at least in patients affected by CSDs, which can be readily detected by electro-corticography in the intensive care unit (Dohmen et al., 2008; Dreier et al., 2009; Hartings et al., 2011; Hertle et al., 2012). Finally, sustaining adequate blood flow and supply of metabolic substrates to the injured brain is crucial, and particularly when CSD waves occur frequently. A prospective study in subarachnoid hemorrhage patients revealed that repetitive CSD waves exacerbate CBF deficiency in tissue at risk where a “cortical spreading ischemia” was observed (Dreier et al., 2009). Furthermore, recurrent CSD waves decrease oxygen (Bosche et al., 2010) and glucose (Feuerstein et al., 2010) availability in brain injury patients. We here measured significantly lower resting-state CBF under propofol compared to isoflurane (Fig. 3), as observed experimentally (Kaisti et al., 2003) and clinically (Bösel et al., 2012; Villa et al., 2012). Moreover, we found that propofol significantly lowered plasma glucose compared to isoflurane (Table 1), alike other studies (Zuurbier et al., 2008). Since lower plasma glucose is associated with lower brain extracellular glucose (Silver and Erecinska, 1994), propofol, as opposed to isoflurane, could intensify or accelerate the progressive depletion of brain glucose measured clinically after frequent CSDs (Feuerstein et al., 2010), and hence worsen patient outcome (Vespa et al., 2003). Insidiously, lower plasma glucose levels could even foster the recurrence of CSDs. Earlier studies indeed showed that the frequency of CSDs in peri-infarct tissue rises with decreasing blood glucose (Hopwood et al., 2005; Strong et al., 2000). From the latter study, it appears that the frequency of spontaneous CSDs begins to rise when plasma glucose first falls below some 135 mg/dL, i.e. in the range of propofol plasma glucose. Propofol could therefore not only reduce glucose availability necessary for the recovery of CSDs but may also promote the occurrence of CSDs in the infarcted brain. Altogether, this would argue for the use of isoflurane, at least instead of propofol, in brain injury patients. However, potential adverse effects of isoflurane in these patients should not be ignored (Maas and Stocchetti, 2012). We here measured a slight (non-significant) decrease in arterial pressure, which, together with an increase in CBF, and thereby in cerebral blood volume (Maekawa et al., 1986), could result in a reduction in cerebral perfusion pressure. We would therefore recommend the use of isoflurane during periods of high risk of occurrence of CSDs and under low or well-controlled intra-cranial pressure. Conclusions We here demonstrate that isoflurane, as opposed to propofol, protects against the occurrence of CSDs and could improve recovery from
these metabolically demanding events. This anesthetic could therefore limit the extent of secondary damage associated with repetitive CSDs in the human injured brain. Provided that cerebral perfusion pressure is stabilized in the normal range, we would advocate the use of isoflurane in acute ischemic and hemorrhagic stroke, and traumatic brain injury patients.
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Patel, A.J., Honoré, E., Lesage, F., Fink, M., Romey, G., Lazdunski, M., 1999. Inhalational anesthetics activate two-pore-domain background K+ channels. Nat. Neurosci. 2, 422–426. Sakowitz, O.W., Kiening, K.L., Krajewski, K.L., Sarrafzadeh, A.S., Fabricius, M., Strong, A.J., Unterberg, A.W., Dreier, J.P., 2009. Preliminary evidence that ketamine inhibits spreading depolarizations in acute human brain injury. Stroke 40, e519–e522. Shin, H.K., Dunn, A.K., Jones, P.B., Boas, D.A., Moskowitz, M.A., Ayata, C., 2006. Vasoconstrictive neurovascular coupling during focal ischemic depolarizations. J. Cereb. Blood Flow Metab. 26, 1018–1030. Shin, H.K., Dunn, A.K., Jones, P.B., Boas, D.A., Lo, E.H., Moskowitz, M.A., Ayata, C., 2007. Normobaric hyperoxia improves cerebral blood flow and oxygenation, and inhibits peri-infarct depolarizations in experimental focal ischaemia. Brain 130, 1631–1642. Silver, I., Erecinska, M., 1994. Extracellular glucose concentration in mammalian brain: continuous monitoring of changes during increased neuronal activity and upon limitation in oxygen supply in normo-, hypo-, and hyperglycemic animals. J. Neurosci. 14, 5068–5076. Strong, A.J., Smith, S.E., Whittington, D.J., Meldrum, B.S., Parsons, A.A., Krupinski, J., Hunter, A.J., Patel, S., 2000. Factors influencing the frequency of fluorescence transients as markers of peri-infarct depolarizations in focal cerebral ischemia. 31, 214–222. Strong, A.J., Bezzina, E.L., Anderson, P.J.B., Boutelle, M.G., Hopwood, S.E., Dunn, A.K., 2006. Evaluation of laser speckle flowmetry for imaging cortical perfusion in experimental stroke studies: quantitation of perfusion and detection of peri-infarct depolarisations. J. Cereb. Blood Flow Metab. 26, 645–653. Sukhotinsky, I., Yaseen, M.A., Sakadzić, S., Ruvinskaya, S., Sims, J.R., Boas, D.A., Moskowitz, M.A., Ayata, C., 2010. Perfusion pressure-dependent recovery of cortical spreading depression is independent of tissue oxygenation over a wide physiologic range. J. Cereb. Blood Flow Metab. 30, 1168–1177. Takano, K., Latour, L.L., Formato, J.E., Carano, R.A., Helmer, K.G., Hasegawa, Y., Sotak, C.H., Fisher, M., 1996. The role of spreading depression in focal ischemia evaluated by diffusion mapping. Ann. Neurol. 39, 308–318. Vespa, P.M., McArthur, D., O'Phelan, K., Glenn, T., Etchepare, M., Kelly, D., Bergsneider, M., Martin, N.A., Hovda, D.A., 2003. Persistently low extracellular glucose correlates with poor outcome 6 months after human traumatic brain injury despite a lack of increased lactate: a microdialysis study. J. Cereb. Blood Flow Metab. 23, 865–877. Villa, F., Iacca, C., Molinari, A.F., Giussani, C., Aletti, G., Pesenti, A., Citerio, G., 2012. Inhalation versus endovenous sedation in subarachnoid hemorrhage patients: effects on regional cerebral blood flow. Crit. Care Med. 40, 2797–2804. Zuurbier, C.J., Keijzers, P.J.M., Koeman, A., Van Wezel, H.B., Hollmann, M.W., 2008. Anesthesia's effects on plasma glucose and insulin and cardiac hexokinase at similar hemodynamics and without major surgical stress in fed rats. Anesth. Analg. 106, 135–142.
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Experimental Neurology journal homepage: www.elsevier.com/locate/yexnr
Isoflurane suppresses cortical spreading depolarizations compared to propofol — Implications for sedation of neurocritical care patients Masatoshi Takagaki a,b,1, Delphine Feuerstein a,⁎,1, Tetsuya Kumagai a,b, Markus Gramer a, Toshiki Yoshimine b, Rudolf Graf a a b
Max Planck Institute for Neurological Research, 50931 Cologne, Germany Department of Neurosurgery, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan
a r t i c l e
i n f o
Article history: Received 3 September 2013 Revised 24 October 2013 Accepted 4 November 2013 Available online 15 November 2013 Keywords: Isoflurane Propofol Stroke Cortical spreading depression Cerebral blood flow Intensive care unit
a b s t r a c t Sedatives in the neurointensive care unit can strongly influence patients' risks of developing secondary brain damage. In particular, isoflurane, a volatile anesthetic, has been recently re-introduced to the neurointensive care unit, and first clinical studies suggest beneficial effects due to elevation of cerebral blood flow and reduction of metabolism. In contrast, propofol is a commonly used intravenous sedative that reduces cerebral blood flow and intra-cranial pressure. We have here studied the influence of these two sedatives on the occurrence of cortical spreading depolarizations (CSDs), which have emerged over the last decade as a major mechanism of delayed brain injury in stroke and brain trauma, constituting a substantial vascular and metabolic threat to periinfarct tissue and being associated with poor patient outcome. Two experimental models were tested in Wistar rats anesthetized either with isoflurane or with propofol: KCl-evoked CSDs (n = 10) and spontaneous CSDs after occlusion of the middle cerebral artery (n = 14). Spatiotemporal patterns of CSD waves were observed by realtime laser speckle imaging of regional cerebral blood flow changes associated with the CSDs. During 30 min of cortical KCl application, 5.2 ± 0.7 CSDs were induced under isoflurane compared to 10.2 ± 1.8 CSDs under propofol (p b 0.001). After focal ischemia, 2.43 ± 1.0 CSDs/h emerged spontaneously under isoflurane versus 6.83 ± 2.5 CSDs/h under propofol (p b 0.001). Furthermore, baseline blood flow and glycemia were much higher under isoflurane compared to propofol, which may set the tissue in better metabolic conditions to recover from the occurrence of CSD waves. We conclude that isoflurane, in comparison to propofol, decreases the occurrence of CSDs and may improve recovery from these metabolically demanding waves. To reduce CSD induced secondary tissue damage, we suggest isoflurane to be favored over propofol to sedate acute stroke and trauma patients in the neurointensive care unit. © 2013 Elsevier Inc. All rights reserved.
Introduction Patients in the intensive care unit (ICU) are generally anesthetized to alleviate pain, agitation and facilitate tolerance of mechanical ventilation. For neurocritical care patients, the aims of sedation are additionally to prevent secondary brain damage, notably by sustaining an adequate cerebral blood flow (CBF), decreasing basal metabolism and maintaining low intracranial pressure. Recently, an additional mechanism for secondary injury has been put forward: cortical spreading depolarizations (CSDs — originally referred to as cortical spreading depressions) (Dreier, 2011; Lauritzen et al., 2011). These are mass depolarizations arising spontaneously and propagating around ischemic and traumatic Abbreviations: CSD, cortical spreading depression; ICU, intensive care unit; CBF, cerebral blood flow; MCAo, middle cerebral artery occlusion; DC, direct current; LSF, laser speckle flowmetry; ROI, region of interest. ⁎ Corresponding author at: Max Planck Institute for Neurological Research, Gleueler Strasse 50, 50931 Cologne, Germany. Fax: +49 221 4726 203. E-mail address: [email protected] (D. Feuerstein). 1 These authors contributed equally to the work. 0014-4886/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.expneurol.2013.11.003
lesions in the human brain (Dohmen et al., 2008; Hartings et al., 2011). Clinical studies suggest that frequent CSDs are associated with a worsening of vascular and metabolic conditions of the peri-infarct tissue (Bosche et al., 2010; Dreier et al., 2009; Feuerstein et al., 2010), secondary ischemic neurological deficits (Dreier et al., 2006) and poor patient outcome (Hartings et al., 2011). However, only few studies have examined the influence of anesthesia on CSDs in the context of the ICU (Hertle et al., 2012). We here compare the effects of isoflurane and propofol on the susceptibility to CSDs in two experimental models. Isoflurane is an inhalation anesthetic that has been recently re-introduced in the ICU via the Anesthetic Conserving Device (AnaConDa), a safe miniaturized vaporizer. First clinical applications in ischemic and hemorrhagic stroke patients seem promising, suggesting beneficial effects from increased CBF and reduced metabolism during isoflurane sedation (Bösel et al., 2012; Villa et al., 2012). In contrast, propofol is a potent intravenous hypnotic agent that has been widely used in neurointensive care patients, notably because it is easily titratable, with rapid onset and short duration of action and it decreases intra-cranial pressure while
M. Takagaki et al. / Experimental Neurology 252 (2014) 12–17
maintaining autoregulation (Villa et al., 2012). However, the effects of propofol on CSDs are largely unknown. Methods Surgical preparation All animal procedures were performed in accordance with the German regulations for animal protection. Male Wistar rats were anesthetized using isoflurane (5% for induction, 1.5–2% for maintenance) in 70%/30% nitrous oxide/oxygen during all surgical procedures. The animals breathed spontaneously and their rectal temperature was kept at 37 °C using a servo-controlled heating blanket. The left femoral artery was cannulated for continuous monitoring of arterial blood pressure and for hourly measurement of blood gases (arterial PaO2, PaCO2, pH). Frontal and parietal bones were exposed and thinned out to transparency using a dental drill. Drilling was performed under continuous saline irrigation to prevent heat injury. At the end of surgery, the thinned out skull surface was covered with warm paraffin oil and laser speckle images were continuously acquired during the whole duration of the experiments. Experimental groups Half the animals were maintained with 1.5–2% isoflurane, while the other half were switched to propofol. The breathing gas mixture was maintained at 70%/30% nitrous oxide/oxygen in all cases. In the propofol animals, propofol infusion was started at 38 mg/kg/h via tail vein and isoflurane weaned off over 15 min. Propofol concentration (33 to 53 mg/kg/h) was adjusted to keep breathing rate, similar to that observed under isoflurane, within 60–80 cycles/min and to abolish blood pressure response to tail pinch. Thirty minutes after isoflurane was completely off, systemic variables and CBF had stabilized to new levels (Table 1, Fig. 3). In our experience, this duration is sufficient to eliminate isoflurane from the system: isoflurane has indeed a low blood gas solubility and hence a rapid emergence and it has a short (about 5 min) context-sensitive half-time (Bailey, 1997). The depth of anesthesia was similar under both anesthetics (slightly more than 1 MAC in case of isoflurane and slightly more than 1 ED50 in case of propofol). It should be mentioned, however, that both PaO2 and PaCO2 were somewhat elevated under propofol compared to isoflurane (Table 1). In experimental group 1 (KCl group, n = 10), a cotton ball soaked and continuously infused with 3 M KCl at 10 μL/h for 30 min was placed over the dura in the frontal cortex to elicit CSDs under each respective anesthesia. In experimental group 2 (MCAo group, n = 14), focal ischemia was induced under each respective anesthesia by embolic occlusion of the middle cerebral artery (MCAo). After baseline imaging, a macrosphere (0.315 to 0.355 mm diameter; Brace, Alzenau, Germany) was advanced into the intra-carotid artery by injection of approximately 0.2 mL heparinized saline. This resulted in the occlusion of the MCA, causing spontaneous generation of CSDs that were observed for up to 3 h after macrosphere injection (Fig. 2). The position of the macrosphere in the neurovasculature was verified post-mortem by visual inspection of
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the brain base: only animals where the macrosphere was lodged at the bifurcation of the MCA and the anterior cerebral artery were included. Details about the macrosphere model are provided elsewhere (Gerriets et al., 2003; Kumagai et al., 2010). Note that during all procedures, systemic parameters were monitored (blood pressure, arterial blood gases) and maintained within physiological ranges in all animals included in this study, although propofol tended to induce a mild acidosis and a mild hypercapnia compared to isoflurane (Table 1). Laser speckle flowmetry (LSF) LSF measurement of CBF (CBFLSF) was implemented as previously described (Dunn et al., 2001; Kumagai et al., 2010; Nakamura et al., 2010). Regions of interest (ROI) were placed in areas devoid of major blood vessels and analyzed for CBFLSF (Figs. 1A and 2A). CBFLSF levels reported here are relative to baseline CBFLSF under isoflurane taken as 100%. The speed of CSD waves was calculated using two ROIs placed in the direction of wave propagation. Electrophysiological recordings CBFLSF measurements were combined with direct current (DC) and electrocorticogram recordings in two animals from the KCl group (Fig. 1A-B). A 3 μm tip glass micropipette, filled with 1 M sodium chloride, was implanted at 500 μm depth through a small burr-hole (Fig. 1A). Ag/AgCl reference and ground electrodes were placed subcutaneously in the neck. The electrophysiological signals were digitized at 250 Hz. A low-pass filter was applied at 0.1 Hz to yield the DC component. Artefactual high frequency noise and baseline drifts were filtered out using methods described earlier (Feuerstein et al., 2009). The mean value of the DC potentials over a 2 min period before CSD induction was taken as 0 mV and the amplitude of the DC shifts calculated relative to this value. The duration of the DC shift was given by the width at half maximum. Statistics All data are presented either as individual recordings or as mean value ± standard deviation. CSD characteristics between isoflurane and propofol were compared using unpaired t-tests within each experimental group and considered statistically significant at p b 0.05. Results Multiple CSDs induced by KCl application (KCl group) Following topical application of KCl, DC potential shifts linked to CSD were similar under the two anesthetics (−25.2 ± 5.3 mV for 22.5 ± 3.0 s under isoflurane versus −25.9 ± 7.8 mV for 24.5 ± 5.7 s under propofol). CBFLSF changes measured in one ROI near the DC electrode were temporally linked to the DC shift, confirming that CBFLSF is a suitable surrogate marker for CSD (Fig. 1B). CSD waves propagated at
Table 1 Systemic parameters. Data are given as average ± standard deviation across animals in each group. Arterial blood pressure data are the average of 1 h continuous recording in the KCl group and 3 h continuous recording after macrosphere injection in the MCAo group. MABP: mean arterial blood pressure; PaO2: arterial partial pressure in oxygen; PaCO2: arterial partial pressure in carbon dioxide; unpaired t-test within each group: *p b 0.05; **p b 0.01. Experimental group
Anesthesia
MABP (mm Hg)
PaO2 (mm Hg)
PaCO2 (mm Hg)
pH
KCl
Isoflurane (n = 5) Propofol (n = 5) Isoflurane (n = 7) Propofol (n = 7)
83.7 ± 4.8 104.3 ± 20.1 107.5 ± 16.6 124.5 ± 16.6
115.12 ± 36.8 143.4 ± 34.7 108.4 ± 28.0 142.8 ± 25.4*
40.5 48.7 38.4 47.0
7.42 7.34 7.40 7.36
MCAo
± ± ± ±
3.9 2.9** 7.0 5.2*
Blood sugar (mg/dL) ± ± ± ±
0.03 0.03** 0.04 0.04
128.6 ± 13.1 79.0 ± 5.7** 139.4 ± 28.9 94.6 ± 22.0**
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Fig. 1. Multiple CSDs induced by KCl application. A: Speckle contrast image of the left hemisphere and representative positions of the KCl cotton ball (frontal lobe), of the DC electrode and of two regions of interest (ROI) of 1 × 1 mm2 size for LSF analysis (parietal lobe). The arrow indicates the direction of propagation (frontal to caudal). B: DC potential shifts and CBFLSF changes for the ROI closest to the DC electrode (as per A) under isoflurane (top) and propofol (bottom). C: Effects of isoflurane (dark gray, n = 5) versus propofol (white, n = 5) on CSD propagation speed and frequency during 30 min KCl application. Bar height indicates the mean value and error bars the standard deviations. CSD propagation speeds were calculated between two ROIs shown in A for the first 5 waves in all animals. ***p b 0.001.
the same speed under isoflurane (3.80 ± 0.85 mm/min, n = 5) and propofol (3.98 ± 1.05 mm/min, n = 5). However, the number of CSDs that propagated during a 30 min application of KCl was double under propofol (10.2 ± 1.8) compared to isoflurane (5.2 ± 0.7) (Fig. 1C). Resting-state CBFLSF prior to induction of CSD under propofol was significantly lower than under isoflurane (58 ± 12.3%, t(8) = 7.6, p b 0.001, Fig. 3A). Glycemia was also very different: 128.6 ± 13.1 mg/dL under isoflurane vs. 79.0 ± 5.7 mg/dL under propofol (t(8) = 3.5, p = 0.008, Fig. 3B). Multiple CSDs spontaneously arising after MCAo (MCAo group) Immediately after macrosphere injection, a fast gradual decline in CBFLSF was observed generating an ischemic focus in the arterial territory of the MCA. Within the next 5 to 20 min, a primary CBFLSF wave, originating at the border of the ischemic territory, propagated across the entire exposed cortex. During the next 3 h, multiple subsequent secondary CBFLSF waves arose and propagated circumferentially around the ischemic core (Fig. 2B). The spatio-temporal patterns of the waves were similar in both anesthetics and comparable to previous studies (Kumagai et al., 2010; Nakamura et al., 2010). However, there were twice as many circumferential waves under propofol (6.83 ± 2.5 CSDs/h) as under isoflurane (2.43 ± 1.0 CSDs/h) despite identical propagation speeds (Fig. 2C). Resting-state CBFLSF prior to MCAo could not be accurately determined because the external carotid artery and the pterygopalatine branch of the internal carotid artery were ligated to enable macrosphere injection. This resulted in an immediate drop in CBFLSF and baseline
isoflurane blood flow could therefore not be measured. However, plasma glucose concentrations were again very different under both anesthetics: 139.4 ± 28.9 mg/dL under isoflurane vs. 94.6 ± 22.0 mg/dL under propofol (t(12) = −3.5, p = 0.004, Fig. 3C). Discussion CSD waves under propofol and isoflurane seem to share the same characteristics, with similar depolarization amplitude and duration, and similar waveform and propagation speed of associated CBFLSF waves. However, at doses comparable to those used in clinical intensive care settings (Bösel et al., 2012; Villa et al., 2012), the rate of CSD is halved by isoflurane in comparison to propofol, both when induced by KCl and when spontaneously propagating after focal ischemia. That CSD frequency is differently sensitive to anesthesia regimens than CSD propagation speed and duration has also been observed after KCl application by Kudo et al. (2008). We here detected CSD waves by LSF imaging and not DC recordings for two main reasons. First, LSF has been validated as a good method to track CSD waves against electrophysiological recordings (Ayata et al., 2004; Sukhotinsky et al., 2010) and membrane potential imaging (Obrenovitch et al., 2009). Second, since LSF is an imaging technique, CSD waves can be visualized in highly heterogeneous tissue, such as after focal ischemia (Kumagai et al., 2010; Luckl et al., 2009; Nakamura et al., 2010; Shin et al., 2006, 2007; Strong et al., 2006), as opposed to local DC measurements that could miss events if not placed on the path of a CSD wave. To our knowledge, this is the first study that investigates the impact of propofol on the susceptibility of CSD waves in the KCl and the MCAo
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Fig. 2. Multiple CSDs spontaneously arising after MCAo. A: Field of view and positions of three ROIs typically used for LSF analysis in this experimental group. Dashed line indicates the border of the ischemic core. The arrow indicates the direction of propagation of the circumferential CSD waves that are confined in the border zone of the ischemic core. B: CBFLSF in the three ROIs indicated in A (same gray shades) under isoflurane (top) and propofol (bottom). Note that the first CSD associated CBF wave propagates from the core to the periphery (black to light gray ROI), while the following waves are mostly found in the periphery of the ischemic core (gray ROIs). Note also that the first CBF wave is hypoemic in the core ROIs and hyperemic only in the periphery of the ischemic territory. C: Effects of isoflurane (dark gray, n = 7) versus propofol (white, n = 7) on the propagation speed and frequency of circumferential CSDs during the first hour after occlusion of the MCA. Bar heights indicate mean values and error bars standard deviations. ***p b 0.001.
models. We cannot undoubtedly conclude whether propofol leads to more SDs or isoflurane diminishes SDs but earlier studies observed a significant reduction in the number of transient DC shifts following both topical KCl application (Kitahara et al., 2001; Kudo et al., 2008)
A
KCl group 100
B
***
KCl group
Plasma glucose (mg/dL)
CBFLSF (%)
60
40
C
MCAo group
175 150
80
and MCAo when using isoflurane compared to other anesthetics (Patel et al., 1998). These findings can be explained by the mechanisms of action of isoflurane versus those of propofol. Although both anesthetics likely act on GABAA receptors (Campagna et al., 2003; Hara et al.,
**
***
125 100 75 50
20 25 0
0
isoflurane
propofol
isoflurane
propofol
isoflurane
propofol
Fig. 3. Baseline CBF and plasma glucose under isoflurane and propofol. A: Baseline CBFLSF prior to CSD propagation (KCl group) was significantly lower under propofol (n = 5) compared to isoflurane (n = 5). Baseline CBFLSF was calculated as the average CBFLSF over 5 min prior to the application of the KCl cotton ball. 100% CBFLSF was taken under isoflurane. Bar height indicates the mean value and error bars the standard deviations. B: Plasma glucose concentrations in the KCl group under isoflurane (n = 5) and under propofol (n = 5). Measurements were taken before and after KCl application. Bar height indicates the mean value and error bars the standard deviations. C: Plasma glucose concentrations in the MCAo group under isoflurane (n = 7) and under propofol (n = 7). Measurements were taken hourly just before and after MCAo. Bar height indicates the mean value and error bars the standard deviations.
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1994), isoflurane additionally inhibits NMDA receptors by binding at the glycine site (Dickinson et al., 2007). Clinically, sedatives with NMDA receptor antagonist capacities, such as ketamine, can abolish CSDs (Hertle et al., 2012; Sakowitz et al., 2009). Note that, in our study, we maintained 70% N2O in breathing gases for all animals, also including those anesthetized with propofol. N2O has been discussed as an inhibitor of NMDA receptors (Jevtović-Todorović et al., 1998) but did not seem to suppress CSD propagation under propofol. Additionally, isoflurane activates TREK-1 potassium “leak channels”, which clamp neurons to their resting potentials, making them more resistant to depolarization (Patel et al., 1999). Such properties have not been demonstrated for propofol. Decreasing the number of spontaneous CSD waves after brain injury may prove crucial for neurocritical care patients. The frequency of CSDs after focal ischemia has indeed been correlated to the extent of cortical injury in numerous experimental stroke models (Back et al., 1994; Busch et al., 1996; Koroleva and Bures, 1996; Patel et al., 1998; Takano et al., 1996). Clinically, recent evidence shows that the occurrence of CSDs is associated with secondary neurological deficits in subarachnoid hemorrhage patients (Dreier et al., 2006) and is an independent predictor of adverse clinical outcome in traumatic brain injury patients (Hartings et al., 2011). Our data therefore suggest that isoflurane should be favored over propofol, at least in patients affected by CSDs, which can be readily detected by electro-corticography in the intensive care unit (Dohmen et al., 2008; Dreier et al., 2009; Hartings et al., 2011; Hertle et al., 2012). Finally, sustaining adequate blood flow and supply of metabolic substrates to the injured brain is crucial, and particularly when CSD waves occur frequently. A prospective study in subarachnoid hemorrhage patients revealed that repetitive CSD waves exacerbate CBF deficiency in tissue at risk where a “cortical spreading ischemia” was observed (Dreier et al., 2009). Furthermore, recurrent CSD waves decrease oxygen (Bosche et al., 2010) and glucose (Feuerstein et al., 2010) availability in brain injury patients. We here measured significantly lower resting-state CBF under propofol compared to isoflurane (Fig. 3), as observed experimentally (Kaisti et al., 2003) and clinically (Bösel et al., 2012; Villa et al., 2012). Moreover, we found that propofol significantly lowered plasma glucose compared to isoflurane (Table 1), alike other studies (Zuurbier et al., 2008). Since lower plasma glucose is associated with lower brain extracellular glucose (Silver and Erecinska, 1994), propofol, as opposed to isoflurane, could intensify or accelerate the progressive depletion of brain glucose measured clinically after frequent CSDs (Feuerstein et al., 2010), and hence worsen patient outcome (Vespa et al., 2003). Insidiously, lower plasma glucose levels could even foster the recurrence of CSDs. Earlier studies indeed showed that the frequency of CSDs in peri-infarct tissue rises with decreasing blood glucose (Hopwood et al., 2005; Strong et al., 2000). From the latter study, it appears that the frequency of spontaneous CSDs begins to rise when plasma glucose first falls below some 135 mg/dL, i.e. in the range of propofol plasma glucose. Propofol could therefore not only reduce glucose availability necessary for the recovery of CSDs but may also promote the occurrence of CSDs in the infarcted brain. Altogether, this would argue for the use of isoflurane, at least instead of propofol, in brain injury patients. However, potential adverse effects of isoflurane in these patients should not be ignored (Maas and Stocchetti, 2012). We here measured a slight (non-significant) decrease in arterial pressure, which, together with an increase in CBF, and thereby in cerebral blood volume (Maekawa et al., 1986), could result in a reduction in cerebral perfusion pressure. We would therefore recommend the use of isoflurane during periods of high risk of occurrence of CSDs and under low or well-controlled intra-cranial pressure. Conclusions We here demonstrate that isoflurane, as opposed to propofol, protects against the occurrence of CSDs and could improve recovery from
these metabolically demanding events. This anesthetic could therefore limit the extent of secondary damage associated with repetitive CSDs in the human injured brain. Provided that cerebral perfusion pressure is stabilized in the normal range, we would advocate the use of isoflurane in acute ischemic and hemorrhagic stroke, and traumatic brain injury patients.
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