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.

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.

Levobupivacaine vs. racemic bupivacaine in peribulbar anaesthesia: a randomized double blind study in ophthalmic surgery.

AIMS: The Authors examine the employement of a new anaesthetic agent, levobupivacaine 0.50% (S - enantiomer of racemic mixture of bupivacaine), for peribulbar anaesthesia in a randomized double blind study vs. racemic bupivacaine 0.50% alone or in association with hyaluronidase 10 IU x ml(-1). MATERIALS AND METHODS: 120 patients were divided into four groups of 30 each: group L (levobupivacaine 0.50%), group B (racemic bupivacaine 0.50%), group LH (levobupivacaine-hyaluronidase 10 IU x ml(-1)), group BH (racemic bupivacaine-hyaluronidase 10 IU x ml(-1)). RESULTS: The onset-time (14 +/- 3.2 min vs. 13 +/- 4.8 min) and the duration of anaesthesia (195 +/- 34.2 vs. 204 +/- 37.6) were similar. The ocular akinesia was evaluated with an 8 point system: it was considered sufficient for surgery with values of less than 5 points. The association with hyaluronidase increased the spread of local anaesthetics (76.6% of group LH, 73.3% of group BH) with local anaesthetics alone (60% of group L, 56.6% of group B). Moderate hypotension (<30% baseline) was reported in 3 patients (10%) of group L, 2 (6.6%) of group B, 1 (3.3%) of group LH and 2 (6.6%) of group BH. Statistical analysis (Student-Newman-Keuls test) was significant between group L vs. BH, B vs. BH and LH vs. BH as regards onset-time of anaesthesia; between group B vs. LH, B vs. BH and L vs. LH for the duration of anaesthesia. Chi square test for the general akinesia score showed significant results in group L vs. LH (p=0.043) and B vs. LH 8P =0.018); as regards the score 0, test reported significant values between groups B vs. LH (p=0.004) and B vs. BH (p=0.017). CONCLUSIONS: In conclusion levobupivacaine, a longlasting local anaesthetic with limited cardio and neurotoxicity, might be useful for vitreoretinal surgery in elderly patients, compared with general anaesthesia.

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.

Effects of remifentanil-based general anaesthesia with propofol or sevoflurane on muscle microcirculation as assessed by near-infrared spectroscopy.

BACKGROUND: Although anaesthetics are known to alter microcirculation no study has, to our knowledge, documented changes in human skeletal microcirculatory function during general anaesthesia. METHODS: Forty-four patients undergoing maxillofacial surgery at a university hospital were prospectively randomized to receive general anaesthesia with remifentanil combined with propofol or sevoflurane. Muscle microcirculation was investigated with near-infrared spectroscopy (NIRS) before general anaesthesia was induced and 30 min later. An NIRS device (NIMO, Nirox) was used to quantify calf deoxyhaemoglobin [HHb], oxyhaemoglobin [HbO2], and total haemoglobin [HbT] concentrations, coupled to a series of venous and arterial occlusions to measure calf blood flow, muscle oxygen consumption, calf vascular resistance, microvascular compliance, and haemoglobin resaturation rate (RR). RESULTS: In both the groups, general anaesthesia induced marked changes in muscle microcirculation: the tissue blood volume increased (+33% in remifentanil-sevoflurane and +45% with remifentanil-propofol groups), microvascular resistance decreased (-31% and -38%, respectively), and the post-ischaemic haemoglobin RR decreased (-48% and -36%, respectively). In the remifentanil-propofol group, the muscle blood flow increased (P<0.001), whereas in the remifentanil-sevoflurane group microvascular compliance and muscle oxygen consumption decreased (P<0.01). CONCLUSIONS: Remifentanil-based general anaesthesia with propofol or sevoflurane altered the muscle microcirculation in different ways. Quantitative NIRS, a technique that takes into account the optical tissue properties of the individual subject, can effectively measure these changes non-invasively.

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.

Evaluation of neutrophil CD64 expression and procalcitonin as useful markers in early diagnosis of sepsis.

Quantitation of neutrophil CD64 expression and procalcitonin (PCT) levels in blood samples have been recently proposed as useful tools for early detection of sepsis. To determine the usefulness of these tests, we analyzed blood samples of 112 patients, admitted to an intensive care unit (ICU), presenting clinical symptoms of sepsis, as well as of 50 healthy controls. At the end of the study, a retrospective analysis showed that only 52 of the 112 ICU-patients presented a real sepsis (positive blood culture). The results obtained indicated that of the 52 patients with sepsis, 50 and 49 presented levels of neutrophil CD64 expression >or= 2398 molecules per cell (cut-off determined by receiver operator characteristic analysis) and PCT levels >0.5 ng/ml (cut-off suggested by the manufacturer), respectively. However, the neutrophil CD64 test showed higher specificity in detecting sepsis since 5 out of the 60 ICU-patients without sepsis (negative blood culture), presented CD64 expression levels >or= 2398 molecules per cell, PCT levels >or= 0.5 ng/ml were shown in 27 patients. Moreover, while none of the 50 healthy controls presented a neutrophil CD64 level higher than the cut-off value, 5 patients presented PCT levels >or= 0.5 ng/ml. In conclusion, our data seem to indicate that the quantitation of CD64 expression could be taken into consideration as a sensitive and specific test for early diagnosis of sepsis.

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.

Anatomy and imaging of lumbar plexus.

Sensory and motor innervation of the whole lower limb is due to lumbo-sacral-plexus that arises from the spinal roots L1-S3. The whole lower limb can be blocked from its origin to the foot for surgical procedures or for postoperative analgesia. Single or continuous lumbar plexus blockade can be an alternative to general anesthesia and central block in elective and traumatic hip or femur repair, for knee surgery and for postoperative analgesia. To understand the relative plexus depth and the relationship between the plexus and the closer structure in order to avoid complicance, the aid of imaging technique such as CT-scan, MRI and ultrasounds can be considered.

A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure.

BACKGROUND AND METHODS: The role of noninvasive positive-pressure ventilation delivered through a face mask in patients with acute respiratory failure is uncertain. We conducted a prospective, randomized trial of noninvasive positive-pressure ventilation as compared with endotracheal intubation with conventional mechanical ventilation in 64 patients with hypoxemic acute respiratory failure who required mechanical ventilation. RESULTS: Within the first hour of ventilation, 20 of 32 patients (62 percent) in the noninvasive-ventilation group and 15 of 32 (47 percent) in the conventional-ventilation group had an improved ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2:FiO2) (P=0.21). Ten patients in the noninvasive-ventilation group subsequently required endotracheal intubation. Seventeen patients in the conventional-ventilation group (53 percent) and 23 in the noninvasive-ventilation group (72 percent) survived their stay in the intensive care unit (odds ratio, 0.4; 95 percent confidence interval, 0.1 to 1.4; P=0.19); 16 patients in the conventional-ventilation group and 22 patients in the noninvasive-ventilation group were discharged from the hospital. More patients in the conventional-ventilation group had serious complications (66 percent vs. 38 percent, P=0.02) and had pneumonia or sinusitis related to the endotracheal tube (31 percent vs. 3 percent, P=0.003). Among the survivors, patients in the noninvasive-ventilation group had shorter periods of ventilation (P=0.006) and shorter stays in the intensive care unit (P=0.002). CONCLUSIONS: In patients with acute respiratory failure, noninvasive ventilation was as effective as conventional ventilation in improving gas exchange and was associated with fewer serious complications and shorter stays in the intensive care unit.

O2 consumption-O2 delivery relationship and arteriolar resistance in the forearm of critically ill patients measured by near infrared spectroscopy.

Eight patients with severe sepsis, four with septic shock, and eight without sepsis were studied to investigate whether skeletal muscle influences the whole body O2 consumption (VO2)-O2 delivery relationship and hemodynamics. A forearm VO2-O2 delivery dependency was observed only in nonseptic patients, in whom no whole body VO2-O2 delivery dependency appeared. No forearm VO2-O2 delivery relationship was observed in septic and shock patients, in whom whole body VO2-O2 delivery dependency was found. In shock patients the lack of forearm VO2-O2 delivery dependency was associated with low forearm arteriolar resistance (FAR) even at a relatively low forearm blood flow (FBF). Neither a relationship between forearm VO2 and whole body VO2 nor between FAR and SVR was found in any groups of patients. Septic shock was associated with low FAR that was not affected by the FBF decrease, indicating that in this condition, hemodynamics could be influenced by skeletal muscle resistance.