Effective concentration of remifentanil for successful i-gel insertion during remimazolam induction.

BACKGROUND: Remifentanil can be used as adjuvants during remimazolam induction without neuromuscular blockade. We evaluated the 95% effective concentration (EC) of remifentanil effect-site concentration (Ce) for the successful insertion of an i-gel using the biased-coin up-and-down method in adult patients during remimazolam induction. METHODS: Forty 19-65 year-old patients scheduled to undergo surgery using i-gel were enrolled. Anesthesia was induced using remimazolam infusion (12 mg/kg/h). Simultaneously, remifentanil was infused at a predetermined Ce. After 5 min of anesthesia induction, the i-gel was inserted. The 95% EC (EC95) of remifentanil in each patient was determined using a biased-coin up-and-down method based on a successful insertion in a preceding patient. The step size of remifentanil Ce was 0.4 ng/ml. If the insertion failed, remifentanil Ce was increased in the next patient. Following successful insertions, the corresponding concentration decreased in subsequent patients with a probability of 1/19 or was maintained with a probability of 18/19. The time from remimazolam infusion initiation to a bispectral index (BIS) < 60 (time to BIS60) and hemodynamic variables were measured and recorded. RESULTS: The EC95 (95% CI) of Ce was 2.07 (1.94, 2.87) ng/ml. The overall time to BIS60 was 154.0 ± 39.9 s. No patient experienced significant hypotension or bradycardia during remimazolam induction. CONCLUSIONS: The EC95 of remifentanil Ce was 2.07 (1.94, 2.87) ng/ml for successful i-gel insertion during remimazolam induction at 12 mg/kg/h without hemodynamic instability in adult patients. Future studies should measure remifentanil Ce in elderly patients or using remimazolam at various infusion doses.

Effect of Erector Spinae Plane Block on Postoperative Pain after Laparoscopic Colorectal Surgery: A Randomized Controlled Study.

The erector spinae plane (ESP) block can be used to reduce pain and opioid requirements after abdominal surgery. We evaluated the effect of the ESP block on postoperative pain score, analgesic use, and quality of recovery (QoR) score in patients undergoing laparoscopy. Fifty-nine patients undergoing elective laparoscopic colorectal surgery were randomly assigned to control (n = 30) or ESPB (n = 29) groups after anesthesia induction. In the ESPB group, an ultrasound-guided ESP block was performed immediately after induction using 20 mL of 0.5% ropivacaine bilaterally. The primary outcome was the postoperative pain score, which was evaluated using the 11-point numeric rating scale (NRS) (0 = no pain, 10 = worst imaginable pain), in the recovery room. NRS "at rest" and "on cough" and total dose of fentanyl rescue (in the recovery room) as well as NRS "at rest" and the cumulative administered fentanyl dose of patient-controlled analgesia (24 h post-surgery) were significantly lower in the ESPB group than in the control group. The postoperative QoR score did not differ between the groups. Bilateral ESP block after induction reduced pain scores and opioid requirements for 24 h postoperatively but did not improve the QoR in patients undergoing laparoscopic colorectal surgery.

Trends in opioid prescribing practices in South Korea, 2009-2019: Are we safe from an opioid epidemic?

Opioid prescribing data can guide regulation policy by informing trends and types of opioids prescribed and geographic variations. In South Korea, the nationwide data on prescribing opioids remain unclear. We aimed to evaluate an 11-year trend of opioid prescription in South Korea, both nationally and by administrative districts. A population-based cross-sectional analysis of opioid prescriptions dispensed nationwide in outpatient departments between January 1, 2009, and December 31, 2019, was conducted for this study. Data were obtained from the Health Insurance Review & Assessment Service. The types of opioids prescribed were categorized into total, strong, and extended-release and long-acting formulation. Trends in the prescription rate per 1000 persons were examined over time nationally and across administrative districts. There are significant increasing trends for total, strong, and extended-release and long-acting opioid prescriptions (rate per 1000 persons in 2009 and 2019: total opioids, 347.5 and 531.3; strong opioids, 0.6 and 15.2; extended-release and long-acting opioids, 6.8 and 82.0). The pattern of dispensing opioids increased from 2009 to 2013 and slowed down from 2013 to 2019. The rate of opioid prescriptions issued between administrative districts nearly doubled for all types of opioids. Prescription opioid dispensing increased substantially over the study period. The increase in the prescription of total opioids was largely attributed to an increase in the prescription of weak opioids. However, the increase in prescriptions of extended-release and long-acting opioids could be a future concern. These data may inform government organizations to create regulations and interventions for prescribing opioids.

CONSORT the effect of a bolus dose of dexmedetomidine on postoperative pain, agitation, and quality of recovery after laparoscopic cholecystectomy.

BACKGROUND: The perioperative administration of dexmedetomidine may improve the quality of recovery (QoR) after major abdominal and spinal surgeries. We evaluated the effect of an intraoperative bolus of dexmedetomidine on postoperative pain, emergence agitation, and the QoR after laparoscopic cholecystectomy. METHODS: Patients undergoing elective laparoscopic cholecystectomy were randomized to receive dexmedetomidine 0.5 µg/kg 5 minutes after anesthesia induction (dexmedetomidine group, n = 45) or normal saline (control group, n = 45). The primary outcome was the QoR at the first postoperative day using a 40-item scoring system (QoR-40). Secondary outcomes included intraoperative hemodynamic parameters, postoperative agitation, pain, and nausea and vomiting. RESULTS: The heart rate and the mean blood pressure were significantly lower in the dexmedetomidine group than in the control group (P < .001 and .007, respectively). During extubation, emergence agitation was significantly lower in the dexmedetomidine group than in the control group (23% vs 64%, P < .001). The median pain scores in the post-anesthetic care unit were significantly lower in the dexmedetomidine group than in the control group (4 [2-7] vs 5 [4-7], P = .034). The incidence of postoperative agitation, pain, and nausea and vomiting was not different between the groups. On the first postoperative day, recovery profile was similar between the groups. However, the scores on the emotional state and physical comfort dimensions were significantly higher in the dexmedetomidine group than in the control group (P = .038 and .040, respectively). CONCLUSIONS: A bolus dose of dexmedetomidine after anesthesia induction may improve intraoperative hemodynamics, emergence agitation, and immediate postoperative analgesia. However, it does not affect overall QoR-40 score after laparoscopic cholecystectomy.

Laser-assisted endoscopic lumbar foraminotomy for failed back surgery syndrome in elderly patients.

Elderly patients with failed back surgery syndrome (FBSS) or post-laminectomy foraminal stenosis have a higher risk of perioperative morbidity with extensive revision surgery. Thus, there is a need for safer and less invasive surgical options, such as laser-assisted endoscopic lumbar foraminotomy (ELF). A pin-point laser beam can allow precise tissue ablation and dissection in fibrotic adhesion tissues while preventing normal tissue injury. The present study aimed to describe the surgical technique of laser-assisted ELF and to evaluate the clinical outcomes of elderly patients with FBSS. Two-year follow-up data were collected from 26 consecutive patients aged 65 years or older who were treated with laser-assisted ELF for FBSS. Full-endoscopic foraminal decompression was performed using a side-firing laser and mechanical instruments. The average age of the patients was 70.2 years (range, 65-83 years). The mean visual analog pain score for leg pain improved from 8.58 at baseline to 3.35 at 6 weeks, 2.19 at 1 year, and 2.35 at 2 years after ELF (P < 0.001). The mean Oswestry disability index improved from 65.93 at baseline to 31.41 at 6 weeks, 21.77 at 1 year, and 20.64 at 2 years after ELF (P < 0.001). Based on the modified Macnab criteria, excellent or good results were obtained in 84.6% patients and symptomatic improvements were obtained in 92.3%. Extensive revision surgery in elderly patients might cause significant surgical morbidities. Laser-assisted ELF under local anesthesia could be a safe and effective surgical alternative for such patients at risk.

Effects of ventilatory strategy on arterial oxygenation and respiratory mechanics in overweight and obese patients undergoing posterior spine surgery.

Prolonged inspiratory to expiratory (I:E) ratio ventilation may improve arterial oxygenation or gas exchange and respiratory mechanics in patients with obesity. We performed a randomised study to compare the effects of the conventional ratio ventilation (CRV) of 1:2 and the equal ratio ventilation (ERV) of 1:1 on arterial oxygenation and respiratory mechanics during spine surgery in overweight and obese patients. Fifty adult patients with a body mass index of ≥25 kg/m2 were randomly allocated to receive an I:E ratio either l:2 (CRV; n = 25) or 1:1 (ERV; n = 25). Arterial oxygenation and respiratory mechanics were recorded in the supine position, and at 30 minutes and 90 minutes after placement in the prone position. The changes in partial arterial oxygen pressure (PaO2) over time did not differ between the groups. The changes in partial arterial carbon dioxide pressure over time were significantly different between the two groups (P = 0.040). The changes in mean airway pressure (Pmean) over time were significantly different between the two groups (P = 0.044). Although ERV provided a significantly higher Pmean than CRV during surgery, the changes in PaO2 did not differ between the two groups.

Remifentanil-Sparing Effect of Pectoral Nerve Block Type II in Breast Surgery under Surgical Pleth Index-Guided Analgesia during Total Intravenous Anesthesia.

The pectoral nerve block type II (Pecs II block) can provide adequate perioperative analgesia in breast surgery. The surgical pleth index (SPI) is used to monitor the nociception balance using pulse oximetry. We investigated the remifentanil-sparing effect of Pecs II block under SPI guided analgesia during total intravenous anesthesia (TIVA). Thirty-nine patients undergoing breast surgery under remifentanil-propofol anesthesia were randomly assigned to the intervention (Pecs group, n = 20) or control group (n = 19). Remifentanil and propofol concentrations were adjusted to maintain an SPI of 20-50 and a bispectral index of 40-60, respectively. The Pecs group received an ultrasound-guided Pecs II block preoperatively using 30 mL of 0.5% ropivacaine. Total infused remifentanil during the surgery was significantly less in the Pecs group than in the control group (6.8 ± 2.2 µg/kg/h vs. 10.1 ± 3.7 µg/kg/h, p = 0.001). Pain scores on arrival at the postanesthetic care unit (PACU) (3 (2-5) vs. 5 (4-7)) and the rescue analgesic requirement in the PACU (9 vs. 2) was significantly lower in the Pecs group than in the control group. In conclusion, Pecs II block was able to reduce the intraoperative remifentanil consumption by approximately 30% and improve the postoperative pain in PACU in patients undergoing breast surgery under SPI-guided analgesia during TIVA.

Sonographic Guidance for Supraclavicular Brachial Plexus Blocks: Single vs. Double Injection Cluster Approach.

BACKGROUND: The cluster approach for supraclavicular brachial plexus block (SC-BPB) can be easily performed but may result in asymmetric local anesthetic (LA) spread. The authors hypothesized that the use of a cluster approach in each of the 2 planes would achieve better 3-dimensional LA distribution than the traditional single cluster approach. OBJECTIVES: The purpose of the present study was to compare a double injection (DI) in 2 planes (one injection in each plane) with the traditional single injection (SI) cluster approach for ultrasound-guided SC-BPB. STUDY DESIGN: A randomized, controlled trial. SETTING: Department of Anesthesiology and Pain Medicine, Gachon University Gil Medical Center. METHODS: In the SI group (n = 18), 30 mL of LA was injected into the main neural cluster after penetrating the brachial plexus sheath laterally. In the DI group (n = 18), the needle penetrated the sheath in a downward direction at the first skin puncture, and 15 mL of LA was injected, and at the second skin puncture (behind the initial puncture site), the needle penetrated the sheath in an upward direction, and 15 mL was again injected. Ultrasound-guided SC-BPB was evaluated from immediately after the block every 5 minutes to 30 minutes by sensory and motor testing. The main outcome variables were procedural time; onset time (time for complete sensory and motor block of the median, radial, ulnar, and musculocutaneous nerves); and rate of blockage of all 4 nerves. RESULTS: Procedure times (medians [interquartile range]) were similar in the DI and SI groups (5.5 [4.75 - 8] vs. 5 [4 - 7] minutes, respectively; P = 0.137). Block onset time in the DI group was not significantly different from that in the SI group (10 [5 - 17.5] vs. 20 [6.25 - 30] minutes, P = 0.142). However, the rate of blockage of all 4 nerves was significantly higher in the DI group (94% vs. 67%, P = 0.035). LIMITATIONS: Although the results of this study indicate LA distribution in the DI group was more evenly spread within brachial plexus sheaths than in the SI group, this was not confirmed by ultrasonography or contrast radiography. CONCLUSION: The DI approach can be performed easily as single cluster approach and increases the consistency of ultrasound-guided SC-BPB over the SI approach in terms of the rate of blocking of all 4 nerves. Key words: Brachial plexus block, corner pocket approach, cluster approach, multiple injection, supraclavicular block, ultrasound.

Discordant lumbar epidural hematoma after caudal steroid injection: A case report (CARE-compliant).

RATIONALE: Caudal epidural injection is one of the conventional treatments of chronic back pain. Even though spinal epidural hematoma after caudal epidural injection is rare but it can cause serious neurologic complication. PATIENT CONCERNS: An 83-year-old woman taking cilostazol received caudal epidural steroid injection because of her chronic back pain. Six hours later, she experienced an acute hip pain which worsened with time. DIAGNOSIS: Magnetic resonance image showed acute cord compression due to a spinal epidural hematoma at L2-S1 level with concomitant central canal compromise at L2/3, L3/4 level. INTERVENTIONS: Emergency decompressive laminectomy and evacuation of the lumbar epidural hematoma were performed. OUTCOMES: All of her symptoms were resolved over the 72 hours following surgery. LESSONS: Continuous vigilance after caudal epidural injection is important to prevent catastrophic neurologic deterioration with early detection and early treatment.

Agreement of New Automated Matched Alternation Flicker using Undilated Fundus Photography for the Detection of Glaucomatous Structural Change.

PURPOSE: To determine the agreement among glaucoma experts and general ophthalmologists regarding detection of glaucomatous structural changes using a new automated matched alternation flicker (AMAF) method with fundus photographs (FPs) of undilated eyes. METHODS: Sixty-six pairs of FPs of normal tension glaucoma patients were collected. FPs were taken at intervals of more than 12 months. Alternating flicker images were created using a new AMAF application. In a blinded manner, two glaucoma experts and two general ophthalmologists compared the presence of glaucomatous structural changes using either the AMAF method or the side-by-side comparison method. The interobserver and intraobserver agreements were compared using the Bland and Altman plot analysis. RESULTS: The glaucoma experts detected more glaucoma progression using the AMAF method (average, 50.7%) compared with the side-by-side method (average, 32.5%). General ophthalmologists detected more glaucomatous progression with the AMAF method (average, 40.9%) than with the side-by-side method (average, 25.0%). The AMAF method showed fair to substantial interreader agreement (k = 0.511-0.724) and fair to perfect intrareader agreement (k = 0.631-0.943). Interreader and intrareader agreements using the AMAF method were better for the glaucoma experts compared with the general ophthalmologists. CONCLUSIONS: The AMAF method showed more changes in FPs than the classical side-by-side comparison method. Regarding inter- and intrareader agreements, agreement for the glaucoma experts was best using the AMAF method, but for the general ophthalmologists agreement was best using the side-by-side comparison method.

Prediction of in-hospital mortality and morbidity using high-sensitivity C-reactive protein after burr hole craniostomy.

BACKGROUND: The purpose of this study was to assess whether preanesthetic laboratory values can predict in-hospital mortality and morbidity in patients who have undergone burr hole craniostomy due to chronic subdural hematoma. METHODS: From January 2007 to February 2016, the records of 502 consecutive patients who underwent burr hole craniotomy were analyzed. All cases of burr hole craniostomy were fitted with a drain, as required by our institutional protocol. RESULTS: Patients' demographic data and preoperative laboratory values were subjected to logistic regression analysis to predict in-hospital mortality and morbidity after burr hole craniostomy. Hemoglobin, prothrombin time, activated partial thromboplastin time, serum glucose, and high-sensitivity C-reactive protein (hsCRP) were found to be significantly associated with in-hospital mortality and morbidity by univariate regression analysis, but of these, only hsCRP (hazard ratio 1.210, 95 % confidence interval 1.089-1.345, P < 0.001) was found to significantly predict in-hospital mortality and morbidity by multivariate regression analysis. Areas under the curve for predicting in-hospital mortality and morbidity were 0.765 (95 % confidence interval 0.624-0.906, P = 0.002) and 0.646 (0.559-0.733, P = 0.001), respectively. CONCLUSIONS: Preoperative hsCRP was found to be an independent predictor of in-hospital mortality and morbidity after burr hole craniostomy due to chronic subdural hematoma.

Anesthetic experience of an adult male with citrullinemia type II: a case report.

BACKGROUND: Citrullinemia type II is an autosomal recessive urea cycle disorder and a subtype of citrin deficiency. However, the management of recurrent hyperammonemia with neurologic symptoms in patients with citrullinemia type II is quite different from the management of other types of urea cycle disorders. In pats with citrullinemia type II, regional anesthesia might be a good choice for the early detection of hyperammonemic symptoms and addressing psychic stress. CASE PRESENTATION: A 48-year-old male with adult onset citrullinemia type II was scheduled for urethral scrotal fistula repair. During the first operation, spinal anesthesia with conscious sedation using dexmedetomidine was used, a second operation was performed after confirmation of infection control and a stable neurologic condition. In this patient, dietary planning with close monitoring of serum ammonia level and close observation of neurologic conditions might lead to successful perioperative care. CONCLUSION: For anesthesia of patients with adult onset citrullinemia type II, close monitoring of neurologic signs and serum ammonia are important to reduce neurologic complications induced by hyperammonemia. Regional anesthesia with a proper dietary plan might reduce patient stress and prevent metabolic tragedy.

Preoperative serum lactate cannot predict in-hospital mortality after decompressive craniectomy in traumatic brain injury.

PURPOSE: Despite the utility of serum lactate for predicting clinical courses, little information is available on the topic after decompressive craniectomy. This study was conducted to determine the ability of perioperative serum lactate levels to predict in-hospital mortality in traumatic brain-injury patients who received emergency or urgent decompressive craniectomy. METHODS: The medical records of 586 consecutive patients who underwent emergency or urgent decompressive craniectomy due to traumatic brain injuries from January 2007 to December 2014 were retrospectively analyzed. Pre- and intraoperative serum lactate levels and base deficits were obtained from arterial blood gas analysis results. RESULTS: The overall mortality rate after decompressive craniectomy was 26.1 %. Mean preoperative serum lactate was significantly higher in the non-survivors (P = 0.034) than the survivors but had no significance for predicting in-hospital mortality in the multivariate regression analysis (P = 0.386). Rather, preoperative Glasgow Coma Score was a significant predictor for in-hospital mortality (hazard ratio 0.796, 95 % confidence interval 0.755-0.836, P < 0.001). CONCLUSION: Preoperative lactate level is not an independent predictor of in-hospital mortality after decompressive craniectomy in traumatic brain-injury patients.

Male patients require higher optimal effect-site concentrations of propofol during i-gel insertion with dexmedetomidine 0.5 µg/kg.

BACKGROUND: The pharmacokinetics and pharmacodynamics of an anesthetic drug may be influenced by gender. The purpose of this study was to compare effect-site half maximal effective concentrations (EC50) of propofol in male and female patients during i-gel insertion with dexmedetomidine 0.5 µg/kg without muscle relaxants. METHODS: Forty patients, aged 20-46 years of ASA physical status I or II, were allocated to one of two groups by gender (20 patients per group). After the infusion of dexmedetomidine 0.5 µg/kg over 2 min, anesthesia was induced with a pre-determined effect-site concentration of propofol by target controlled infusion. Effect-site EC50 values of propofol for successful i-gel insertion were determined using the modified Dixon's up-and-down method. RESULTS: Mean effect-site EC50 ± SD of propofol for successful i-gel insertion was significantly higher for men than women (5.46 ± 0.26 µg/ml vs. 3.82 ± 0.34 µg/ml, p < 0.01). The EC50 of propofol in men was approximately 40% higher than in women. Using isotonic regression with a bootstrapping approach, the estimated EC50 (95% confidence interval) of propofol was also higher in men [5.32 (4.45-6.20) µg/ml vs. 3.75 (3.05-4.43) µg/ml]. The estimated EC95 (95% confidence interval) of propofol in men and women were 5.93 (4.72-6.88) µg/ml and 4.52 (3.02-5.70) µg/ml, respectively. CONCLUSIONS: During i-gel insertion with dexmedetomidine 0.5 µg/kg without muscle relaxant, male patients had higher effect-site EC50 for propofol using Schnider's model. Based on the results of this study, patient gender should be considered when determining the optimal dose of propofol during supraglottic airway insertion. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02268656. Registered August 26, 2014.

Perioperative Concerns for Profound Metabolic Alkalosis During Kidney Transplantation: A Case Report.

INTRODUCTION: Profound metabolic alkalosis is an uncommon consideration for the anesthetic management of kidney transplantation. Serum total carbon dioxide content and complex electrolyte abnormalities might be important diagnostic clues for the presence of metabolic alkalosis in the absence of arterial blood gas analysis. CASE PRESENTATION: A 34-year-old female visited Gachon University Gil Medical Center, Incheon, South Korea during year 2015. She experienced aggravated renal function due to chronic hypokalemia and severe hypochloremic metabolic alkalosis, induced by laxative abuse, and underwent ABO incompatible kidney transplantation. Serum total carbon dioxide content remained high (about 60 mEq/L) over eight months of monthly follow-up prior to kidney transplantation. CONCLUSIONS: The authors described their anesthetic experience of profound metabolic alkalosis with complex electrolyte abnormalities and provided a review of relevant literature.

Preanesthetic mortality prediction in diabetics undergoing major lower limb amputation at a tertiary referral hospital: Implications of preoperative echocardiographic and laboratory values.

PURPOSE: Cardiac comorbidities in patients undergoing amputation due to diabetic foot ulcer are associated with high mortality rates. The authors investigated whether preanesthetic echocardiographic and laboratory values can predict inhospital mortality in type II diabetes patients undergoing major lower limb amputation under spinal anesthesia. METHODS: The archived medical records of 215 patients were retrospectively reviewed. Demographic data and preoperative laboratory and transthoracic echocardiographic values were analyzed by multivariate logistic regression for factors independently associated with inhospital mortality. RESULTS: Of the 215 patients, 12 died in hospital after amputation. Preoperative hemoglobin level (hazard ratio, 0.082; 95% confidence interval, 0.013-0.509; P = .007) and left ventricular ejection fraction (hazard ratio, 0.874; 95% confidence interval, 0.779- 0.981; P = .023) were found to be significant predictors of inhospital mortality. CONCLUSIONS: Preoperative hemoglobin level and left ventricular ejection fraction are highly correlated with inhospital mortality in type II diabetes patients undergoing major lower extremity amputation under spinal anesthesia.

Anesthetic management of a patient with pulmonary arteriovenous malformation under total intravenous anesthesia : A case report.

A 23-year-old woman with pulmonary arteriovenous malformation was scheduled for open reduction and internal fixation due to her mandible fracture. Total intravenous anesthesia using propofol and remifentanil was selected as the anesthetic method in order to avoid the inhibition of hypoxic pulmonary vasoconstriction and the exacerbation of intrapulmonary shunting. After the standard monitoring devices were applied, anesthesia was then induced and maintained with a target controlled infusion of propofol and remifentanil in the range of 2.5-3.0 microg/ml and 2-3 ng/ml, respectively. Anesthesia was performed uneventfully and the patient was discharged without complication.

Stewart's physicochemical approach in neurosurgical patients with hyperchloremic metabolic acidosis during propofol anesthesia.

There is both in vitro and clinical evidence that high-dose propofol can inhibit mitochondrial respiration, resulting in metabolic acidosis. The purpose of this study was to evaluate the effects of propofol anesthesia on the acid-base status in neurosurgical patients with large amount of normal saline administration. Thirty patients undergoing clipping of cerebral aneurysm were randomly assigned to receive propofol (n=15) or isoflurane (n=15). Propofol dose (mean+/-standard error) infused for maintenance was 5.7+/-0.2 mg/kg/h in propofol group. Acid-base parameters such as PaCO2, pH, serum bicarbonate concentration, standard base excess, serum electrolyte concentration, total protein, albumin, lactate, and phosphate were measured before and 4 hours after the induction of anesthesia, and after surgery. The apparent strong ion difference (SIDa), the effective SID (SIDe), and the amount of weak plasma acid were calculated using the Stewart equation. There were no significant differences in pH, PaCO2, bicarbonate, and lactate between 2 groups throughout the whole investigation period. After surgery, standard base excess significantly decreased in both groups without intergroup difference. SIDa and SIDe significantly decreased in both groups, and lactate and strong ion gap significantly increased after surgery in propofol group, but there were no significant differences between 2 groups. Both propofol and isoflurane were associated with hyperchloremic metabolic acidosis in neurosurgical patients with large amount of normal saline administration. The acid-base balance between the 2 anesthetics was similar using Stewart's physicochemical approach.