The effect of the addition of epinephrine on early systemic absorption of epidural ropivacaine in humans

Pilot epinephrine dose-finding study to counter epidural-related blood pressure reduction

OBJECTIVE

An unwanted side effect associated with epidural analgesia is the reduction in blood pressure (BP) due to the sympathetic blockade. This study evaluated the hemodynamic effects of adding different epinephrine concentrations to epidurally injected local anesthetic solution to counteract sympathectomy. We hypothesized that epinephrine could mitigate the decrease in BP possibly caused by the local anesthetic, specifically decreasing the incidence of hypotension.

METHODS

Sixty-six patients were enrolled in a randomized, controlled, quadruple-blinded prospective study into three groups: epidural ropivacaine 0.2% without epinephrine (control) or with 2 µg/mL or 5 µg/mL epinephrine. Our primary outcome was the assessment of differences in hypotension between groups, defined as a >20% decrease in hypotension from baseline to the end of the intraoperative period.

RESULTS

Forty-seven patients completed the study, and 19 were withdrawn. Fifteen patients were in the control group, while 16 patients received 0.2% ropivacaine +2 µg/mL epinephrine, and 16 received 0.2% ropivacaine +5 µg/mL epinephrine. The overall rate of hypotension was 21.3% (10/47). There were no statistically significant differences in hypotension rates between the control group (33%) and groups receiving either +2 µg/mL (13%, p=0.165) or +5 µg/mL (19%, p=0.353) of epinephrine. In secondary analyses, respiratory rate showed greater decreases in control groups across the perioperative period compared with treatment groups (p=0.016) CONCLUSION: Adding epinephrine to the epidural local anesthetic did not significantly decrease the rate of hypotension. However, epinephrine mitigated decreases in respiratory rate across the perioperative period. Future studies will focus on increasing group size and higher epinephrine concentrations (10 µg/mL).

TRIAL REGISTRATION NUMBER

NCT02722746.

A Comparative Analysis of Pain Control Methods after Ankle Fracture Surgery with a Peripheral Nerve Block: A Single-Center Randomized Controlled Prospective Study

Background and Objectives: Patients experience severe pain after surgical correction of ankle fractures. Although their exact mechanism is unknown, dexamethasone and epinephrine increase the analgesic effect of anesthetics in peripheral nerve blocks. This study aimed to compare the postoperative pain control efficacy of peripheral nerve blocks with ropivacaine combined with dexamethasone/epinephrine and peripheral nerve blocks with only ropivacaine and added patient-controlled analgesia in patients with ankle fractures. Materials and Methods: This randomized, controlled prospective study included patients aged 18-70 years surgically treated for ankle fractures between December 2021 and September 2022. The patients were divided into group A (n = 30), wherein pain was controlled using patient-controlled analgesia after lower extremity peripheral nerve block, and group B (n = 30), wherein dexamethasone/epinephrine was combined with the anesthetic solution during peripheral nerve block. In both groups, ropivacaine was used as the anesthetic solution for peripheral nerve block, and this peripheral nerve block was performed just before ankle surgery for the purpose of anesthesia for surgery. Pain (visual analog scale), patient satisfaction, and side effects were assessed and compared between the two groups. Results: The patients' demographic data were similar between groups. Pain scores were significantly lower in group B than in group A postoperatively. Satisfaction scores were significantly higher in group B (p = 0.003). There were no anesthesia-related complications in either group. Conclusions: Dexamethasone and epinephrine as adjuvant anesthetic solutions can effectively control pain when performing surgery using peripheral nerve blocks for patients with ankle fractures.

Comparison of plasma concentrations of levobupivacaine with and without epinephrine for thoracic paravertebral block: A randomised trial

BACKGROUND

Thoracic paravertebral block (TPVB) is effective for analgesia for unilateral thoracic surgery. However, since the paravertebral space is highly vascular, injection of local anaesthetics into the paravertebral space may induce systemic local anaesthetic toxicity. We examined the effect of addition of epinephrine to paravertebral levobupivacaine on its plasma concentration.

METHODS

In a randomised single blind trial, twenty-four male patients who were scheduled to undergo elective unilateral pulmonary lobectomy or segmentectomy under general anaesthesia combined with TPVB were enrolled in this study. They were randomly divided into two groups: one group received a single bolus thoracic paravertebral injection of 1 mg/kg of 0.25% levobupivacaine with 5 μg/mL epinephrine and the other group received a single bolus thoracic paravertebral injection of 1 mg/kg of 0.25% levobupivacaine alone. Arterial blood samples were obtained for plasma levobupivacaine assay after injection. The peak plasma concentration (Cmax) and the time to peak plasma concentration (Tmax), for levobupivacaine were calculated.

RESULTS

There were no significant differences in patients' characteristics between the two groups. The mean arterial Cmax values of levobupivacaine were 0.48 ± 0.11 μg/mL with epinephrine and 0.71 ± 0.31 μg/mL without epinephrine (P = 0.041). The mean arterial Tmax values of levobupivacaine were 46.0 ± 35.6 min with epinephrine and 12.0 ± 7.2 min without epinephrine (P = 0.005).

CONCLUSION

The addition of 5-μg/mL epinephrine to a single bolus thoracic paravertebral injection of 1-mg/kg levobupivacaine significantly decreased Cmax and delayed Tmax of levobupivacaine. The addition of epinephrine to levobupivacaine may be a useful strategy to reduce systemic levobupivacaine toxicity.

CLINICAL TRIAL REGISTRATION NUMBER

UMIN 000021942.

A novel LC-MS/MS analytical method for detection of articaine and mepivacaine in blood and its application to a preliminary pharmacokinetic study

Local anaesthetics (LAs) are commonly used in surgery, especially in dentistry. They cause a transitory inhibition of nerve signal due to the blockade of the voltage-gated sodium channels. LAs are administrated alone or with vasoconstriction agents, such as adrenaline. Toxicity of LAs is associated to neurological and cardiovascular alterations. Tachycardia, arrhythmia, tremors, tonic-clonic seizure and respiratory depression (at high doses) are the main symptoms of intoxication by LAs. Lidocaine, articaine and mepivacaine are among the most used anaesthetics. This study aimed to fully validated a new method for the simultaneous detection of articaine and mepivacaine in whole blood. Sample treatment consisted in a liquid-liquid extraction with phosphate buffer (pH 8, 0.1 M) and ethyl-acetate. Analysis was performed by liquid chromatography-tandem mass spectrometry in multiple reaction monitoring mode (transitions: articaine, 285→8658 m/z; mepivacaine, 247→9870 m/z; lidocaine - internal standard -, 235→8658 m/z). The method proved to be highly sensitive with limit of quantifications for articaine and mepivacaine of 0.8 and 0.1 ng/mL, respectively. Accuracy and precision were always within the acceptance criteria. The new procedure was also successfully applied to a preliminary pharmacokinetics study.

Effect of premedication with subcutaneous adrenaline on the pharmacokinetics and immunogenicity of equine whole IgG antivenom in a rabbit model

Subcutaneous administration of a low dose of adrenaline is used to prevent the early adverse reactions (EARs) induced by snake antivenoms. We used a rabbit model to study the effect of premedication with adrenaline on the potential of antivenoms to exert therapeutic effects and to induce late adverse reactions. We found that premedication with adrenaline did not change the heart rate or blood pressure of normal rabbits, but reduced the rise in temperature in rabbits previously sensitized with antivenom. Pharmacokinetic studies suggest that premedication with adrenaline does not affect the ability of the antivenom to exert the initial control of envenomation nor the susceptibility of rabbits to develop recurrence of antigenemia and envenomation. Our results also indicate that it is unlikely that premedication with adrenaline decreases the incidence of late reactions induced by the antivenom administration, although it reduces the extent of early reactions.

The effects of adding epinephrine to ropivacaine for popliteal nerve block on the duration of postoperative analgesia: a randomized controlled trial

BACKGROUND

Duration of peripheral nerve blocks depends on multiple factors. Both technique and type of local anesthetic used, either with or without adjuncts, may result in different duration times of the block. The purpose of the present study was to compare the duration of postoperative analgesia of 30 mL ropivacaine 0.75 % with or without epinephrine for popliteal sciatic nerve block.

METHODS

Thirty-eight patients were included to receive ultrasound guided continuous popliteal nerve block with ropivacaine 0.75 % either without (ROPI) or with epinephrine 5 μg/mL (ROPI-EPI) for ankle fusion, subtalar fusion, or a combination of both. The primary outcome parameter was the duration of postoperative analgesia as reflected by the time to first request for postoperative analgesia (TTFR) through the popliteal nerve catheter. Secondary outcome measures included the onset of sensory and motor block and NRS score for pain at rest and during movement.

RESULTS

Thirty patients, 15 in each group, were studied. Eight patients were withdrawn because of specific withdrawal criteria described in the protocol and replaced according to their group allocation. Median [interquartile range] TTFR was 463 [300-1197] min and 830 [397-1128] min for the ROPI vs ROPI-EPI group respectively. Hodges Lehman median difference between groups was 71 min (95 % CI -415 - 473 min). There was no difference in any clinical outcome measure between the groups.

CONCLUSION

The results of this study did not show any significant increase in the duration of postoperative analgesia by adding epinephrine to ropivacaine for popliteal nerve block. This may be due to the intrinsic vasoconstrictive properties of ropivacaine. The absence of a significant difference can also be the result of a type II error caused by a large variation in the individual TTFR.

TRIAL REGISTRATION

Trial register.nl identifier: NTR3330 , keyword TTFR.

Update on the clinical utility and practical use of ropivacaine in Chinese patients

We reviewed the Chinese and English literature for efficacy and tolerability data as well as pharmacological properties of ropivacaine in Chinese patients. Ropivacaine is a long-acting amide local anesthetic agent that elicits nerve block via reversible inhibition of sodium ion influx in nerve fibers. The available evidence in the literature on anesthesia practice indicates that ropivacaine produces equally surgical sensory block and postoperative and obstetrics analgesia with good maternal and fetal outcome to those of bupivacaine or levobupivacaine. It appears to be associated with comparable onset, quality, and duration of sensory block, but with a lower incidence or grade of motor block, compared to bupivacaine. The satisfaction of both patients and surgeons is high when ropivacaine is used. Thus, ropivacaine appears to be an important option for regional anesthesia and for the management of postoperative and labor pain, with its enhanced sensorimotor differentiation blockage at lower concentrations and enhanced safety at higher concentrations.

Pharmacokinetics of 450 mg ropivacaine with and without epinephrine for combined femoral and sciatic nerve block in lower extremity surgery. A pilot study

AIMS

No pharmacokinetic data exist on doses of ropivacaine larger than 300 mg for peripheral nerve block in man, although in clinical practice higher doses are frequently used. The purpose of the present study was to describe the pharmacokinetic profile in serum of 450 mg ropivacaine with and without epinephrine in patients undergoing anterior cruciate ligament reconstruction.

METHODS

Twelve patients were randomly allocated to receive a single shot combined sciatic/femoral nerve block with 60 ml of either ropivacaine 0.75% alone (group R, n = 6) or ropivacaine 0.75% plus epinephrine 5 μg ml(-1) (group RE, n = 6). Venous blood samples for total and free ropivacaine serum concentrations were obtained during 48 h following block placement. Pharmacokinetic parameters were calculated using a non-compartmental approach.

RESULTS

Results are given as mean (SD) for group R vs. group RE (95% CI of the difference). Total Cmax was 2.81 (0.94) μg ml(-1) vs. 2.16 (0.21) μg ml(-1) (95% CI -0.23, 1.53). tmax was 1.17 (0.30) h vs. 1.67 (0.94) h (95% CI -1.40, 0.40). The highest free ropivacaine concentration per patient was 0.16 (0.08) μg ml(-1) vs. 0.12 (0.04) μg ml(-1) (95% CI -0.04, 0.12). t(1/2) was 6.82 (2.26) h vs. 5.48 (1.69) h (95% CI -1.23, 3.91). AUC was 28.35 (5.92) μg ml(-1)  h vs. 29.12 (7.34) μg ml(-1)  h (95% CI -9.35, 7.81).

CONCLUSIONS

Free serum concentrations of ropivacaine with and without epinephrine remained well below the assumed threshold of 0.56 μg ml(-1) for systemic toxicity. Changes in pharmacokinetics with epinephrine co-administration did not reach statistical significance.

Absorption characteristics of epidural levobupivacaine with adrenaline and clonidine in children

AIM

To determine if the addition of adrenaline, clonidine, or their combination altered the pharmacokinetic profile of levobupivacaine administered via the caudal epidural route in children.

METHODS

Children aged <18 years old scheduled to undergo sub-umbilical surgery were administered caudal levobupivacaine plain 2.5 mg · ml(-1) or with adjuvants adrenaline 5 mcg · ml(-1) or clonidine 2 mcg · ml(-1) or their combination. Covariate analysis included weight and postnatal age (PNA). Time-concentration profile analysis was undertaken using nonlinear mixed effects models. A one-compartment linear disposition model with first-order input and first-order elimination was used to describe the data. The effect of either clonidine or adrenaline on absorption was investigated using a scaling parameter (Fabs(CLON), Fabs(ADR)) applied to the absorption half-life (Tabs).

RESULTS

There were 240 children (median weight 11.0, range 1.9-56.1 kg; median postnatal age 16.7, range 0.6-167.6 months). Absorption of levobupivacaine was faster when mixed with clonidine (Fabs(CLON) 0.60; 95%CI 0.44, 0.83) but slower when mixed with adrenaline (Fabs(ADR) 2.12; 95%CI 1.45, 3.08). The addition of adrenaline to levobupivacaine resulted in a bifid absorption pattern. While initial absorption was unchanged (Tabs 0.15 h 95%CI 0.12, 0.18 h), there was a late absorption peak characterized by a Tabs(LATE) 2.34 h (95%CI 1.44, 4.97 h). The additional use of clonidine with adrenaline had minimal effect on the bifid absorption profile observed with adrenaline alone. Neither clonidine nor adrenaline had any effect on clearance. The population parameter estimate for volume of distribution was 157 l 70 kg(-1). Clearance was 6.5 l · h(-1) 70 kg(-1) at 1-month PNA and increased with a maturation half-time of 1.6 months to reach 90% of the mature value (18.5 l · h(-1) 70 kg(-1)) by 5 months PNA.

CONCLUSIONS

The addition of adrenaline decreases the rate of levobupivacaine systemic absorption, reducing peak concentration by half. Levobupivacaine concentrations with adrenaline adjuvant were reduced compared to plain levobupivacaine for up to 3.5 hours. Clonidine as an adjuvant results in faster systemic absorption of levobupivacaine and similar concentration time profile to levobupivacaine alone. Adding adrenaline with clonidine does not alter the concentration profile observed with adrenaline alone.

Systemic Levels of Local Anaesthetic after Intra-Peritoneal Application – a Systematic Review

There is a lack of cohesive reports on the systemic levels of local anaesthetic after intraperitoneal application. A comprehensive systematic review with no language restriction was conducted. Eighteen suitable articles were identified. Data were compiled and presented according to local anaesthetic agent. Intraperitoneal local anaesthetic has been studied in many different procedures, including open and laparoscopic surgery. A total of 415 patients were included for analysis. There were no cases of clinical toxicity. There were 11 (2.7%) cases with a systemic level above or close to a safe threshold (as determined by the report authors) in three trials utilising intraperitoneal local anaesthetic after laparoscopic cholecystectomy. Intraperitoneal lignocaine doses varied from 100 to 1000 mg, mean Cmax ranged from 1.01 to 4.32 μg/ml and mean Tmax ranged from 15 to 40 minutes. Intraperitoneal bupivacaine doses varied from 50 to 150 mg (weight based doses also reported), mean Cmax ranged from 0.29 to 1.14 μg/ml and mean Tmax ranged from 15 to 60 minutes. Intraperitoneal ropivacaine doses varied from 100 to 300 mg, mean Cmax ranged from 0.66 to 3.76 μg/ml and mean Tmax ranged from 15 to 35 minutes. The addition of adrenaline to intraperitoneal local anaesthetic almost halves systemic levels and prolongs Tmax. Intraperitoneal local anaesthetic results in detectable systemic levels in the perioperative setting. Despite a lack of clinical toxicity, careful attention to dose is still required to prevent potential systemic toxic levels. Clinicians should also consider the addition of adrenaline to intraperitoneal local anaesthetic solutions to further add to the systemic safety profile.

Effect of epinephrine on epidural, intrathecal, and plasma pharmacokinetics of ropivacaine and bupivacaine in sheep

BACKGROUND

Local vasoconstriction induced by epinephrine added to epidural local anaesthetics has been shown to improve their quality and duration of action in several clinical reports. There are several assumptions on the mechanisms. This study was designed to evaluate the influence of epinephrine on transmeningeal uptake of epidurally administered ropivacaine and bupivacaine by measuring local anaesthetic concentrations in the epidural and intrathecal spaces and in plasma.

METHODS

Ropivacaine (50 mg) and bupivacaine (30 mg) were administered epidurally in sheep with and without epinephrine (75 microg). A microdialysis technique was used to simultaneously measure epidural and intrathecal drug concentrations. Resulting dialysate and plasma concentrations were used to calculate pharmacokinetic parameters for ropivacaine and bupivacaine.

RESULTS

Co-administration of epinephrine decreased epidural clearance for ropivacaine [0.6 (sd 0.1) vs 0.4 (0.1) ml min(-1)] but not significantly for bupivacaine [1.2 (0.4) vs 0.8 (0.3) ml min(-1)]. The resultant increase in epidural area under the concentration-time curves (31% for ropivacaine and 52% for bupivacaine) was also observed in the intrathecal space (21% increase for ropivacaine and 37% for bupivacaine). There was no significant influence of epinephrine on ropivacaine plasma pharmacokinetics. Plasma Cmax for bupivacaine was decreased.

CONCLUSIONS

These results show that epinephrine decreases the clearance and distribution processes involved in epidural disposition of ropivacaine and bupivacaine, leading to an increased uptake into the intrathecal space with an apparent more pronounced effect for bupivacaine.

Clinically useful adjuvants in regional anaesthesia

PURPOSE OF REVIEW

In this review, emphasis is placed on adjuvant drugs that are already in clinical use. The list of adjuvants studied during the review period includes adrenaline, clonidine, ketamine, neostigmine, nondepolarizing muscle relaxants, and nonsteroidal antiinflammatory drugs. Some future aspects are considered in a couple of experimental studies on slow-release local anaesthetic formulations.

RECENT FINDINGS

Adrenaline not only acts as a vasoconstrictor, it may also produce analgesia through an alpha2-adrenergic mechanism. Adrenaline may facilitate the uptake of the local anaesthetic into nerves. The addition of adrenaline to a mixture of ropivacaine and fentanyl clearly improves thoracic epidural analgesia. Several recent studies have shown a synergism of clonidine with local anaesthetics in various types of blocks, as well as with spinal opioids. Bradycardia and hypotension may be associated with the use of clonidine. Neostigmine may cause antinociception both in the spinal cord and in peripheral nerves. Neostigmine has been found to potentiate the effect of spinal opioids, but gastrointestinal side effects are frequent. Biodegradable microcapsules containing bupivacaine and dexamethasone have been tested in humans and found to produce analgesia for several days (intercostal block). Local inflammatory reactions and paraesthesias, however, were observed in 30% of cases.

SUMMARY

Adrenaline and opioids may be regarded as the best investigated and most important adjuvants in regional anaesthesia. Other drugs, such as clonidine and neostigmine, may prolong analgesia in various regional anaesthetic techniques, but possible side effects may limit their clinical application. Further development is needed concerning extra-long acting analgesic formulations.

Ropivacaine: a pharmacological review

Ropivacaine (Naropin, AstraZeneca) a new long-acting amide local anaesthetic agent, is a pure S-enantiomer, with a high pKa and relatively low-lipid solubility. Since its clinical introduction in 1996, it has been the focus of intense interest because of its increased CNS and cardiovascular safety compared with bupivacaine. This article reviews the pharmacology of ropivacaine with particular emphasis placed on toxicological issues. Compared with bupivacaine (the drug of choice for many years), ropivacaine is equally effective for subcutaneous infiltration, epidural, intrathecal and peripheral nerve block surgery, and obstetrics and postoperative analgesia. Ropivacaine is virtually identical to bupivacaine in terms of onset, quality and duration of sensory block, but seems to produce less motor block. The lesser toxicity of ropivacaine compared with bupivacaine has been confirmed in numerous animal experiments as well as human studies, including studies considering the presumed lower potency of ropivacaine. In fact, the reduced cardiovascular toxicity compared with bupivacaine may be a distinct feature of ropivacaine. So far, the increased cost of ropivacaine compared with bupivacaine has limited its wider clinical use -- in spite of the improved safety profile. During the last few years, cost differences between bupivacaine and ropivacaine have been minimized, thus making pharmacoeconomical speculations a much lesser concern when choosing a local anaesthetic drug. In conclusion, ropivacaine appears to be a safer local anaesthetic agent than bupivacaine. It seems particularly indicated for major peripheral nerve blocks and obstetrics. Ropivacaine should be considered when regional blocks are used in neonates and young infants. With the current trend in the cost development, ropivacaine will most likely be used increasingly in the future.

The Effect of Age on the Systemic Absorption and Systemic Disposition of Ropivacaine after Epidural Administration

Knowledge about the systemic absorption and disposition of ropivacaine after epidural administration is important in regard to its clinical profile and the risk of systemic toxicity. We investigated the influence of age on the pharmacokinetics of ropivacaine 1.0% after epidural administration, using a stable-isotope method. Twenty-four patients were enrolled in 1 of 3 groups according to age (group 1: 18-40 yr; group 2: 41-60 yr; group 3: > or =61 yr). Patients received 150 mg ropivacaine hydrochloride epidurally. After 25 min, patients received 50 mL 0.44 mg/mL deuterium-labeled ropivacaine (D3-ropivacaine) IV. Arterial blood samples were collected up to 24 h after epidural administration. Total plasma concentrations of ropivacaine and D3-ropivacaine were determined using liquid chromatography mass spectrometry. In the oldest patients, elimination half-life was significantly longer (ratio of the geometric means 0.60; 95% confidence interval, 0.37-0.99) and clearance was significantly decreased (mean difference, 194 mL/min; 95% confidence interval, 18-370 mL/min) compared with the youngest patients. The systemic absorption was biphasic. Absorption kinetics for ropivacaine (fractions absorbed: (F1, F2) and half-lives: (t(1/2),a1), t(1/2),a2) during the fast and slow absorption process: 0.27 +/- 0.08 and 0.77 +/- 0.12, respectively; 10.7 +/- 5.2 min and 248 +/- 64 min, respectively) were in the same range as for other long-acting local anesthetics. F1 was on average 0.11 (95% confidence interval, 0.002-0.22) higher in the youngest compared with the middle age group. Observed age-dependent pharmacokinetic differences do not likely influence the risk of systemic toxicity in the elderly after a single epidural dose of ropivacaine.

Advantages and disadvantages of adrenaline in regional anaesthesia

Adrenaline has been added to local anaesthetic solutions for more than a century. The aim has been to delay the absorption of the local anaesthetic drug and to prolong and enhance its anaesthetic effect, both in peripheral and central neuraxial blockades. The intention in this chapter has been to give up-to-date knowledge about adrenaline as an adjuvant to local anaesthetics and/or opioids in clinical peripheral and central blockades. My own research has focused on optimizing postoperative epidural analgesia by adding adrenaline and/or fentanyl to an epidural mixture with dilute bupivacaine or ropivacaine. The main part of this chapter will therefore focus on the advantages and disadvantages of adrenaline in epidural analgesia. However, recent knowledge about adrenaline in peripheral blockade will also be covered, together with some pharmaceutical comments on the shelf-life of local anaesthetic mixtures containing adrenaline.

Epidural Ropivacaine Anesthesia Decreases the Bispectral Index During the Awake Phase and Sevoflurane General Anesthesia

The sedative effects of epidural anesthesia without volatile and IV anesthetics and quantification of the degree of epidural anesthesia-induced sedation have not been investigated. In the current study we evaluated the effects of epidural anesthesia on the bispectral index (BIS) during the awake phase and during general anesthesia. After placing the epidural catheter, the patients were randomly allocated to 2 groups receiving either 5 mL of epidural saline (group S) or the same volume of 0.75% ropivacaine (group R). The BIS measurements during the awake phase were performed at 7, 12, 13, 14, 22, and 23 min after the epidural injection. General anesthesia was then induced with propofol and vecuronium and maintained with 0.75% sevoflurane. From approximately 10 min after tracheal intubation, the BIS measurements were made at 1-min intervals for 10 min. The BIS during the awake phase was significantly lower in group R than in group S (P < 0.05). The BIS during general anesthesia was significantly lower in group R than in group S (P < 0.0001). Epidural anesthesia decreased the BIS during the awake phase and during general anesthesia. The decrease of the BIS associated with epidural anesthesia was more prominent during general anesthesia than during the awake phase.