Correction to: Inert gas narcosis in scuba diving, different gases different reactions.

The original version of this article unfortunately contained a mistake.

Inert gas narcosis in scuba diving, different gases different reactions.

PURPOSE: Underwater divers face several potential neurological hazards when breathing compressed gas mixtures including nitrogen narcosis which can impact diver's safety. Various human studies have clearly demonstrated brain impairment due to nitrogen narcosis in divers at 4 ATA using critical flicker fusion frequency (CFFF) as a cortical performance indicator. However, recently some authors have proposed a probable adaptive phenomenon during repetitive exposure to high nitrogen pressure in rats, where they found a reversal effect on dopamine release. METHODS: Sixty experienced divers breathing Air, Trimix or Heliox, were studied during an open water dive to a depth of 6 ATA with a square profile testing CFFF measurement before (T0), during the dive upon arriving at the bottom (6 ATA) (T1), 20 min of bottom time (T2), and at 5 m (1.5 ATA) (T3). RESULTS: CFFF results showed a slight increase in alertness and arousal during the deep dive regardless of the gas mixture breathed. The percent change in CFFF values at T1 and T2 differed among the three groups being lower in the air group than in the other groups. All CFFF values returned to basal values 5 min before the final ascent at 5 m (T3), but the Trimix measurements were still slightly better than those at T0. CONCLUSIONS: Our results highlight that nitrogen and oxygen alone and in combination can produce neuronal excitability or depression in a dose-related response.

Cervical 10 kHz spinal cord stimulation in the management of chronic, medically refractory migraine: A prospective, open-label, exploratory study.

BACKGROUND: A significant minority of chronic migraine (CM) subjects fail conventional medical treatment (rCM), becoming highly disabled. Implantation of an occipital nerve stimulator is a therapeutic option for these subjects. Paresthesia-free cervical 10 kHz spinal cord stimulation (HF10 SCS) may provide an alternative. We report the results of a prospective, open-label, exploratory study assessing the long-term safety, tolerability and efficacy of cervical HF10 SCS in cohort of rCM subjects. METHODS: Included subjects were diagnosed with CM by an experienced headache specialist with the aid of an hourly headache diary. They were refractory to conventional medical treatments including onabotulinumtoxin-A injections. Medication overuse headache was not an exclusion criteria. Enrolled subjects underwent a 2- to 4-week tunnelled cervical HF10 SCS trial followed by a permanent system implant if a significant, subjective reduction in headache intensity/episodes was reported during the trial. Subjects were evaluated at baseline and 6 months after implantation with the aid of monthly diaries and headache-specific questionnaires. RESULTS: Seventeen subjects underwent a trial of cervical HF10 SCS; 14 were still implanted at 6 months (one trial failure, one trial infection, one implant site infection). Seven of the 14 subjects had >30% reduction in headache days. The average reduction in headache days was 6.9 for the overall population and 12.9 among the responders. Three subjects reported tenderness over the IPG/connection site, and one had a lead migration that required surgical revision. CONCLUSION: Paresthesia-free cervical HF10 SCS may be a safe and effective therapeutic option for chronic migraineurs refractory to conventional treatments.

Changes in cerebrospinal fluid magnesium levels in patients undergoing spinal anaesthesia for hip arthroplasty: does intravenous infusion of magnesium sulphate make any difference? A prospective, randomized, controlled study.

BACKGROUND: Most investigators have attributed the reduced postoperative pain or anaesthetic drug requirements in patients receiving i.v. magnesium sulphate (MgSO(4)) infusion during spinal or general anaesthesia to central N-methyl-d-aspartate (NMDA) receptor magnesium (Mg) activity. In this study, we investigated how cerebrospinal fluid (CSF) Mg concentrations change after spinal anaesthesia, and whether peripherally infusing MgSO(4) influences central Mg levels. METHODS: Forty-five patients undergoing continuous spinal anaesthesia for hip arthroplasty were randomly assigned to receive either i.v. MgSO(4) at a dose of 50 mg kg(-1) diluted in 100 ml 0.9% saline solution followed by 15 mg kg(-1) h(-1) for 6 h or saline at the same volume [mean (sd) 64 (10) ml]. The changes in CSF and serum total and ionized Mg concentrations were assessed at six time points before and after spinal anaesthesia. Secondary outcome variables included serum and CSF electrolytes and proteins. RESULTS: Thirty-five patients completed the study. We found that spinal anaesthesia reduced total and ionized Mg concentrations in CSF by about 10%. Increasing serum Mg concentration over 80% of the baseline value left CSF Mg levels unchanged. CONCLUSIONS: Spinal anaesthesia unexpectedly reduced CSF total and ionized Mg concentrations in patients undergoing hip arthroplasty, although the mechanism is unclear. The dose used for peripheral MgSO(4) infusion in this study had no influence on central Mg concentrations in neurologically healthy patients undergoing spinal anaesthesia. If CSF Mg concentration is a reliable marker of Mg brain bioavailability, peripherally infused MgSO(4) during spinal anaesthesia is unlikely to influence central NMDA receptor activity.

In vivo effects on human skeletal muscle oxygen delivery and metabolism of cardiopulmonary bypass and perioperative hemodilution.

PURPOSE: To investigate the in vivo effects of cardiopulmonary bypass (CPB) and perioperative hemodilution on human skeletal muscle oxygen delivery and metabolism and to determine the dilution state at which these effects arise. METHODS: We conducted this observational study in adult patients undergoing CPB surgery. Microcirculatory data were obtained by near-infrared spectroscopy from the brachioradial muscle in 20 consecutive patients undergoing hemodilution for CPB. Outcome variables included tissue oxy- and deoxyhemoglobin concentration ([HbO(2)], [HHb]), oxygen content, blood flow, oxygen delivery, and oxygen consumption. RESULTS: Although CPB left tissue blood flow and oxygen delivery unchanged, both microcirculatory variables correlated significantly and inversely with hematocrit (Hct) (r = -0.39, p < 0.001; r = -0.50, p < 0.001). CPB also left muscle oxygen consumption (mVO(2)) unchanged and this variable correlated with the tissue hemoglobin concentration and tissue oxygen delivery (r = 0.40, p = 0.001; r = 0.35, p = 0.005). During CPB most of the systemic cardiovascular variables remained unchanged. Conversely at Hct lower than 30%, mean arterial pressure and pH decreased and lactate values increased twofold, whereas microvascular blood volume and oxygen delivery increased. At Hct lower than 20% blood flow and oxygen delivery increased, whereas hemoglobin and oxygen content variables decreased. CONCLUSIONS: CPB leaves skeletal muscle oxygen delivery and metabolism as measured by near-infrared spectroscopy unchanged. The only factor that correlates directly with the oxygen content variables and inversely with blood flow, and induces significant changes in tissue hemoglobin content and oxygen delivery, is hemodilution.

Tetraplegia following parathyroidectomy in two long-term haemodialysis patients.

We report two cases of postoperative iatrogenic tetraparesis, which occurred in different hospitals after surgery for parathyroidectomy. Both patients were on long-term haemodialysis. The prolonged neck extension usually required by this procedure was probably the main factor involved in the genesis of the spinal cord injury. Spinal abnormalities associated with chronic renal failure may have made these patients more vulnerable. In our opinion, it is advisable to investigate thoroughly any sign of spinal stenosis in patients who undergo any procedure requiring significant neck extension, particularly if on long-term haemodialysis.

Ropivacaine and levobupivacaine for bilateral selective ankle block in patients undergoing hallux valgus repair.

BACKGROUND: A selective ankle block, blocking the tibial, deep and superficial peroneal nerves, can be used successfully for great toe surgery. No comparative information is available on selective ankle block using ropivacaine and levobupivacaine. METHODS: We compared the onset time and success rate of a selective ankle block using low volumes (12 ml) of ropivacaine 10 mg/ml and levobupivacaine 7.5 mg/ml in 40 patients undergoing elective repair of bilateral hallux valgus. Each patient received an ankle block induced in one foot with ropivacaine and in the contralateral foot with levobupivacaine. RESULTS: The success rate was higher [90% vs. 75%, hazard ratio (95% CI) 0.39 (0.23-0.64)] and anesthesia onset time was shorter (median, 10 vs. 20 min) after ropivacaine than after levobupivacaine. In successful ankle blocks, post-operative pain was similar in the two groups. CONCLUSION: In this study, ropivacaine 10 mg/ml had a shorter anesthesia onset time and a higher success rate than levobupivacaine 7.5 mg/ml for selective ankle block.

Effects of sternotomy on heart-lung interaction in patients undergoing cardiac surgery receiving pressure-controlled mechanical ventilation.

BACKGROUND: The key concept underlying the dynamic indexes of preload dependence is the physiological heart-lung interaction. During sternotomy this interaction undergoes various changes, some of which remain unclear. Our primary aim was to investigate how the interaction changes during sternotomy by evaluating pulse pressure variations (PPV) with the chest closed and after sternotomy in patients ventilated using the pressure-controlled mode. METHODS: We prospectively studied 25 patients undergoing coronary artery bypass grafting (CABG) receiving pressure-controlled ventilation. Standard hemodynamic data, PPV and tidal volume delivered were recorded before and after sternotomy, and, with the chest open, before and after positive end-expiratory pressure (PEEP) was applied and inspiratory pressure was increased. RESULTS: Sternotomy left all variables statistically unchanged from values before thoracotomy although in the subgroup of patients with a PPV > 8% (56%) sternotomy significantly reduced PPV (from 14.4 +/- 5.2% to 8.9 +/- 4.5%). With the chest open, when PEEP was applied at 5 cm H(2)O, tidal volume decreased (from 643 +/- 83 to 587 +/- 104 ml) and stroke volume decreased (from 77 +/- 17 to 72 +/- 15 ml) but PPV remained unchanged. When PEEP was discontinued and inspiratory pressure was increased by 5 cm H(2)O, tidal volume increased (from 643 +/- 83 to 814 +/- 89 ml) and PPV increased (from 8.2 +/- 3.9% to 12.3 +/- 6.8%) but stroke volume remained unchanged. CONCLUSIONS: In patients ventilated in the pressure-controlled mode, except those with a pre-sternotomy PPV > 8% (fluid responders), sternotomy leaves standard hemodynamic data and PPV unchanged. When the chest wall is open, cyclic changes (tidal volume) but not continuous changes (PEEP) in intrathoracic pressure directly influence PPV.

Combined intrathecal and epidural magnesium sulfate supplementation of spinal anesthesia to reduce post-operative analgesic requirements: a prospective, randomized, double-blind, controlled trial in patients undergoing major orthopedic surgery.

BACKGROUND: New ways of decreasing post-operative analgesic drug requirements are of special interest after major surgery. Magnesium sulfate (MgSO(4)) alters pain processing and reduces the induction and maintenance of central sensitization by blocking the N-methyl-D-aspartate (NMDA) receptor in the spinal cord. We investigated whether supplementation of spinal anesthesia with combined intrathecally and epidurally infused MgSO(4) reduced patients' post-operative analgesia requirements. METHODS: In a randomized, prospective, double-blind, placebo-controlled trial, we enrolled 120 consecutive patients undergoing orthopedic surgery during spinal anesthesia (levobupivacaine and sufentanil). Patients were randomly assigned to receive intrathecal MgSO(4) (94.5 mg, 6.3%), epidural MgSO(4) (2%, 100 mg/h), intrathecal and epidural MgSO(4) combined or spinal anesthesia alone (controls). Post-operative morphine consumption was assessed in all groups by patient-controlled analgesia (PCA). RESULTS: Of the 120 patients enrolled, 103 (86%) completed the study. Morphine consumption at 36 h after surgery was 38% lower in patients receiving spinal anesthesia plus epidural MgSO(4) [- 14.963 mg; 95% confidence interval (CI), - 1.44 to - 28.49 mg], 49% lower in those receiving spinal anesthesia plus intrathecal MgSO(4) (- 18.963 mg; 95% CI, - 5.27 to - 32.65 mg) and 69% lower in the intrathecal-epidural combined group (- 26.963 mg; 95% CI, - 13.73 to - 40.19 mg) relative to control patients receiving spinal anesthesia alone. No complications developed during the post-operative course or at 1 month after surgery. CONCLUSION: In patients undergoing orthopedic surgery, supplementation of spinal anesthesia with combined intrathecal and epidural MgSO(4) significantly reduces patients' post-operative analgesic requirements.

Lateral popliteal sciatic nerve block: a single injection targeting the tibial branch of the sciatic nerve is as effective as a double-injection technique.

BACKGROUND: Evidence indicating that single- and double-injection techniques for inducing a sciatic nerve block via a posterior subgluteal approach yield a similar success rate prompted us to investigate whether the two anesthetic techniques yield a similar success rate via a lateral approach. We also hypothesized that, owing to the peculiar anatomic features of the sciatic nerve at the popliteal level, a single injection via the lateral approach might induce effective anesthesia by targeting the tibial nerve only. METHODS: Ninety-six patients undergoing popliteal sciatic nerve block via a lateral popliteal approach for foot surgery were randomized to receive a single 30-ml injection of ropivacaine 7.5 mg/ml to block the tibial nerve (TN group, n= 32) or the common peroneal nerve (CPN group, n= 32), or two separate 15-ml injections (TN + CPN group, n= 32), after stimulation to evoke motor responses from the target nerves. RESULTS: The mean time to obtain a complete sensory blockade (surgical anesthesia) was shorter in the TN group than in the CPN and TN + CPN groups (14 +/- 7 min vs. 23 +/- 17 and 21 +/- 14 min, respectively; P < 0.05). The success rate was similar in the TN and TN + CPN groups (94%) and, 25 min after the initial injection, was already better in these groups than in the CPN group (94% vs. 75%; P < 0.05). CONCLUSIONS: A lateral popliteal sciatic nerve block obtained with a single 30-ml injection of ropivacaine 7.5 mg/ml after electrostimulation to locate the tibial nerve is as effective as multiple TN + CPN stimulation and injection, and local anesthesia has a significantly shorter onset time.

[Stewart's approach]. / L'approccio quantitativo di Stewart all'equilibrio acido-base.

The concentration of H + in blood plasma is one of the most finely regulated variables of the human physiology; acute changes of this concentration result in serious cellular and general consequences. An advanced understanding of the acid-base physiology is essential to the management of "acute" patients, and is as important as the exact understanding of the cardiac and pulmonary physiology. Stewart's approach to acid-base balance has come to the identification of three independent variables that regulate pH in blood plasma: carbon dioxide, relative concentration of strong ions, and total weak acid concentrations. All changes in blood pH occur through changes in these three variables.

Postpartum cerebral ischaemia after accidental dural puncture and epidural blood patch.

Puerperal women are reported to have a rate of cerebral infarction 13 times greater than non-pregnant females. We report a case of cerebral ischaemia in a 30-yr-old healthy parturient after epidural analgesia for labour, complicated by dural puncture treated with two epidural blood patches. Investigations showed the development of cerebral ischaemia on postpartum day 14. A transcranial Doppler ultrasonography showed vasospasm of the left middle cerebral artery still present at 3-month follow-up. At 1-yr follow-up, the patient had homonymous hemianopsia. We discuss the possible causative mechanism of the cerebral ischaemia in relation to the dural puncture and epidural blood patch.

Ambulatory anesthesia for foot surgery.

Ambulatory surgery has developed extensively over the past few years in most Western countries. The absence of specific legislation in Italy creates a lack of trust in patients and interferes with the development of this discipline. The authors describe their experience in the organisation of an outpatient foot surgery centre over the past thirteen years, which is in constant expansion and currently performs about 300 operations every year. They report the criteria used to select patients, the organisation of the operating theatre, pre- and postoperative treatment and the anesthetic techniques used. Among the latter, they describe a new approach used to block the popliteal sciatic nerve. The results obtained show a high approval rate from the majority of patients treated. The authors attribute this success to a series of factors, including patient selection and surgical procedures, the maintenance of constant standards of quality similar to those in hospitals and the experience of outpatient anesthesia.

Prolonged mivacurium-induced neuromuscular block. Case report.

A 38-year-old white male patient was admitted to the hospital for elective surgery. General anesthesia was performed with propofol, alfentanil, nitrous oxide and mivacurium as neuromuscular blocker. Seven months before he had the same surgery without anesthetic problems (he received: propofol, vecuronium bromide, fentanil, nitrous oxide). Neuromuscular monitoring was carried out because the patient was included in a study assessing the clinical effect of mivacurium in microlaryngoscopy surgery. After mivacurium administration the first signs of recovery from neuromuscular block were observed after 255 min. The tracheal tube was withdrawn after 410 min from mivacurium administration, at this time the T1 was 80% of the control values and 7 min later the T1 reached 98%.

High-dose aprotinin with gentamicin-vancomycin antibiotic prophylaxis increases blood concentrations of creatinine and cystatin C in patients undergoing coronary artery bypass grafting.

Both aprotinin and gentamicin-vancomycin antibiotic prophylaxis have been used widely in cardiac surgery to prevent bleeding and infections, respectively. As the drugs are excreted almost entirely by glomerular filtration, we investigated their action on renal function when administered either separately or together. To increase consistency, we measured serum concentrations of creatinine and cystatin C, a new marker of glomerular filtration rate, that many recent studies have shown to be more sensitive than serum creatinine. One hundred patients undergoing coronary artery bypass surgery were allocated randomly to one of four groups: group A received antibiotic prophylaxis with cefamandole and no aprotinin; group B received cefamandole and high-dose aprotinin; group C received antibiotic prophylaxis with gentamicin and vancomycin, but no aprotinin; and group D received both high-dose aprotinin and gentamicin-vancomycin antibiotic prophylaxis. Data from 84 patients, for whom data collection was complete, were analysed. In the first week after operation, mean serum concentrations of cystatin C and creatinine either remained constant or decreased slowly in all groups, except for group D. In group D, both markers increased gradually from postoperative day 2 onwards. The increase in cystatin C was significant on postoperative day 5 (from mean 1.02 (SD 0.11) mg litre-1 before operation to 1.35 (0.32) mg litre-1; P < 0.05), reaching a peak on postoperative day 7 (1.45 (0.35) mg litre-1; P < 0.05), while the increase in creatinine concentration was significant on postoperative day 6 (from 1.05 (0.16) mg dl-1 before operation to 1.29 (0.34) mg dl-1; P < 0.05). We conclude that simultaneous administration of high-dose aprotinin and prophylactic use of gentamicin with vancomycin increased serum concentrations of cystatin C and creatinine in the first postoperative week in patients undergoing cardiac surgery.

Paramedian diencephalic syndrome.

The clinical characteristics of paramedian diencephalic syndrome (PDS) are described on the basis of two recently observed cases: one with paramedian thalamic infarct, the other with paramedian thalamopeduncular infarct. Analysis of the clinical symptoms and the results of CBF study show that PDS is a complex neurological syndrome characterized by symptoms due to both anatomical lesions and functional disconnections.