Manoj K. Karmakar

A systematic review (meta-analysis) of the accuracy of the mallampati tests to predict the difficult airway

The original and modified Mallampati tests are commonly used to predict the difficult airway, but there is controversy regarding their accuracy. We searched MEDLINE and other databases for prospective studies of patients undergoing general anesthesia in which the results of a preoperative Mallampati test were compared with the subsequent rate of difficult airway (difficult laryngoscopy, difficult intubation, or difficult ventilation as reference tests). Forty-two studies enrolling 34,513 patients were included. The definitions of the reference tests varied widely. For predicting difficult laryngoscopy, both versions of the Mallampati test had good accuracy (area under the summary receiver operating characteristic (sROC) curve = 0.89 ± 0.05 and 0.78 ± 0.05, respectively). For predicting difficult intubation, the modified Mallampati test had good accuracy (area under the sROC curve = 0.83 ± 0.03) whereas the original Mallampati test was poor (area under the sROC curve = 0.58 ± 0.12). The Mallampati tests were poor at identifying difficult mask ventilation. Publication bias was not detected. Used alone, the Mallampati tests have limited accuracy for predicting the difficult airway and thus are not useful screening tests.

Placental transfer and fetal metabolic effects of phenylephrine and ephedrine during spinal anesthesia for cesarean delivery.

Background:Use of ephedrine in obstetric patients is associated with depression of fetal acid-base status. The authors hypothesized that the mechanism underlying this is transfer of ephedrine across the placenta and stimulation of metabolism in the fetus. Methods:A total of 104 women having elective Cesarean delivery under spinal anesthesia randomly received infusion of phenylephrine (100 &mgr;g/ml) or ephedrine (8 mg/ml) titrated to maintain systolic blood pressure near baseline. At delivery, maternal arterial, umbilical arterial, and umbilical venous blood samples were taken for measurement of blood gases and plasma concentrations of phenylephrine, ephedrine, lactate, glucose, epinephrine, and norepinephrine. Results:In the ephedrine group, umbilical arterial and umbilical venous pH and base excess were lower, whereas umbilical arterial and umbilical venous plasma concentrations of lactate, glucose, epinephrine, and norepinephrine were greater. Umbilical arterial Pco2 and umbilical venous Po2 were greater in the ephedrine group. Placental transfer was greater for ephedrine (median umbilical venous/maternal arterial plasma concentration ratio 1.13 vs. 0.17). The umbilical arterial/umbilical venous plasma concentration ratio was greater for ephedrine (median 0.83 vs. 0.71). Conclusions:Ephedrine crosses the placenta to a greater extent and undergoes less early metabolism and/or redistribution in the fetus compared with phenylephrine. The associated increased fetal concentrations of lactate, glucose, and catecholamines support the hypothesis that depression of fetal pH and base excess with ephedrine is related to metabolic effects secondary to stimulation of fetal &bgr;-adrenergic receptors. Despite historical evidence suggesting uteroplacental blood flow may be better maintained with ephedrine, the overall effect of the vasopressors on fetal oxygen supply and demand balance may favor phenylephrine.

Real-time ultrasound-guided paramedian epidural access: evaluation of a novel in-plane technique

BACKGROUND Current methods of locating the epidural space rely on surface anatomical landmarks and loss-of-resistance (LOR). We are not aware of any data describing real-time ultrasound (US)-guided epidural access in adults. METHODS We evaluated the feasibility of performing real-time US-guided paramedian epidural access with the epidural needle inserted in the plane of the US beam in 15 adults who were undergoing groin or lower limb surgery under an epidural or combined spinal-epidural anaesthesia. RESULTS The epidural space was successfully identified in 14 of 15 (93.3%) patients in 1 (1-3) attempt using the technique described. There was a failure to locate the epidural space in one elderly man. In 8 of 15 (53.3%) patients, studied neuraxial changes, that is, anterior displacement of the posterior dura and widening of the posterior epidural space, were seen immediately after entry of the Tuohy needle and expulsion of the pressurized saline from the LOR syringe into the epidural space at the level of needle insertion. Compression of the thecal sac was also seen in two of these patients. There were no inadvertent dural punctures or complications directly related to the technique described. Anaesthesia adequate for surgery developed in all patients after the initial spinal or epidural injection and recovery from the epidural or spinal anaesthesia was also uneventful. CONCLUSIONS We have demonstrated the successful use of real-time US guidance in combination with LOR to saline for paramedian epidural access with the epidural needle inserted in the plane of the US beam.

A Randomized Double-Blinded Comparison of Phenylephrine and Ephedrine Infusion Combinations to Maintain Blood Pressure During Spinal Anesthesia for Cesarean Delivery: The Effects on Fetal Acid-Base Status and Hemodynamic Control

BACKGROUND: Phenylephrine and ephedrine are both used to maintain arterial blood pressure during spinal anesthesia for cesarean delivery. Usually, either drug is given alone but several previous studies have described combining the drugs. However, the effect of varying the proportion of vasopressors in such combinations has not been reported. METHODS: One-hundred-twenty-five parturients having spinal anesthesia for elective cesarean delivery were randomized to receive an IV infusion of phenylephrine and ephedrine combined in one of five different concentration ratios. Assuming phenylephrine 100 μg to be approximately equipotent to ephedrine 8 mg, the groups contained the proportional potency equivalent of 100%, 75%, 50%, 25% or 0% of phenylephrine and 0%, 25%, 50%, 75% or 100%, respectively, of ephedrine. The infusions were adjusted to maintain systolic blood pressure (SBP) near baseline until uterine incision. Hemodynamic changes and umbilical cord blood gases were compared. RESULTS: As the proportion of phenylephrine decreased and proportion of ephedrine increased among the groups, the following significant trends were detected: the incidences of hypotension and nausea/vomiting increased, the median magnitude of deviations of SBP above or below baseline and the bias for SBP to be above baseline increased, maternal heart rate was faster, fetal pH and base excess decreased, umbilical arterial oxygen content decreased and umbilical venous Po2 increased. CONCLUSIONS: When varying combinations of phenylephrine and ephedrine were given by infusion to maintain arterial blood pressure during spinal anesthesia for cesarean delivery, as the proportion of phenylephrine decreased and the proportion of ephedrine increased, hemodynamic control was reduced and fetal acid-base status was less favorable. Combinations of phenylephrine and ephedrine appear to have no advantage compared with phenylephrine alone when administered by infusion for the prevention of hypotension associated with spinal anesthesia for cesarean delivery.

Postthoracotomy pain syndrome.

Postthoracotomy pain syndrome is relatively common and is seen in approximately 50% of patients after thoracotomy. It is a chronic condition, and about 30% of patients might still experience pain 4 to 5 years after surgery. In the majority of patients pain is usually mild and only slightly or moderately interferes with normal daily living. In a small subset of patients pain can be severe and can be described as a true disability to the extent that these patients are incapacitated. The exact mechanism for the pathogenesis of PTPS is still not clear, but cumulative evidence suggests that it is a combination of neuropathic and nonneuropathic (myofascial) pain. Trauma to the intercostal nerve during thoracotomy is the most likely cause. Because pain does not cause disability in the majority of patients, management is usually conservative. If pain is causing disability then multidisciplinary pain management involving the pain specialist, social worker, physical therapist, and a psychologist is required. It is mandatory to exclude recurrence of disease or malignancy as a cause for the pain prior to initiating treatment. As with most forms of neuropathic pain, treatment of PTPS is also difficult and patients might require more than one form of therapy to control pain and reduce disability. Based on current evidence, it is not possible to draw any firm conclusion regarding whether any form of analgesic or surgical technique can influence the generation of PTPS. Preemptive analgesia initiated prior to surgery shows promise and might help reduce the incidence of PTPS. Scientific evidence is steadily growing but there is still a need for large, prospective, randomized trials evaluating PTPS. Until more is known about this condition and how to prevent the central and peripheral nervous system changes that produce long-term pain after thoracotomy, patients must be warned preoperatively about the possibility of developing PTPS and how it might affect their quality of life after surgery. In addition, measures such as selecting the least traumatic and painful surgical approach, avoiding intercostal nerve trauma, and adopting an aggressive multimodal perioperative pain management regimen commenced before the surgical incision should be performed to prevent postthoracotomy pain syndrome.

Prevalence of survivor bias in observational studies on fresh frozen plasma: erythrocyte ratios in trauma requiring massive transfusion

Observational studies on transfusion in trauma comparing high versus low plasma:erythrocyte ratio were prone to survivor bias because plasma administration typically started later than erythrocytes. Therefore, early deaths were categorized in the low plasma:erythrocyte group, whereas early survivors had a higher chance of receiving a higher ratio. When early deaths were excluded, however, a bias against higher ratio can be created. Survivor bias could be reduced by performing before-and-after studies or treating the plasma:erythrocyte ratio as a time-dependent covariate. We reviewed 26 studies on blood ratios in trauma. Fifteen of the studies were survivor bias-unlikely or biased against higher ratio; among them, 10 showed an association between higher ratio and improved survival, and five did not. Eleven studies that were judged survivor bias-prone favoring higher ratio suggested that a higher ratio was superior. Without randomized controlled trials controlling for survivor bias, the current available evidence supporting higher plasma:erythrocyte resuscitation is inconclusive.

Ultrasonography of the Adult Thoracic and Lumbar Spine for Central Neuraxial Blockade

The role of ultrasound in central neuraxial blockade has been underappreciated, partly because of the relative efficacy of the landmark-guided technique and partly because of the perceived difficulty in imaging through the narrow acoustic windows produced by the bony framework of the spine. However, this also is the basis for the utility of ultrasound: an interlaminar window that permits passage of sound waves into the vertebral canal also will permit passage of a needle. In addition, ultrasound aids in identification of intervertebral levels, estimation of the depth to epidural and intrathecal spaces, and location of important landmarks, including the midline and interlaminar spaces. This can facilitate neuraxial blockade, particularly in patients with difficult surface anatomic landmarks. In this review article, the authors summarize the current literature, describe the key ultrasonographic views, and propose a systematic approach to ultrasound imaging for the performance of spinal and epidural anesthesia in the adult patient.

Ultrasound-guided lumbar plexus block through the acoustic window of the lumbar ultrasound trident

Lumbar plexus block (LPB) is frequently used in combination with an ipsilateral sacral plexus or sciatic nerve block for lower limb surgery. This is traditionally performed using surface anatomical landmarks, and the site for local anaesthetic injection is confirmed by observing quadriceps muscle contraction to peripheral nerve stimulation. In this report, we describe a technique of ultrasound-guided LPB that was successfully used, in conjunction with a sciatic nerve block, for anaesthesia during emergency lower limb surgery. The anatomy, sonographic features, technique of identifying the lumbar plexus, and the potential benefits of using this approach are discussed.

Ultrasound-Guided Regional Anesthesia

Abstract Peripheral nerve blocks are frequently performed in children to provide anesthesia or analgesia during the perioperative period. Success depends on the ability to accurately place the needle—and thereby the local anesthetic—close to the target nerve without causing injury to the nerve or adjacent structures. In the past, clinicians relied on anatomic landmarks, fascial clicks, loss of resistance, or nerve stimulation to position the needle in the vicinity of the nerve. Anatomic landmarks provide valuable clues to the position of the nerve, but they are surrogate markers, lack precision, vary among children of different ages, and may be difficult to locate in obese children. Even nerve stimulation, which has been recommended as the gold standard for nerve localization, may not always elicit a motor response and its use does not guarantee success or preclude complications. Moreover, the accuracy of needle placement cannot be predicted with any of these methods, which may lead to multiple attempts to place the needle that may result in pain and possibly an incomplete or failed nerve block. The use of ultrasound (US) to guide peripheral and central neuraxial blocks has improved both accuracy and safety in both adults and children. In this chapter, the basic principles of US imaging and the techniques of US-guided regional anesthesia (USGRA) in children are described and reviewed.

Acute pain management of patients with multiple fractured ribs: a focus on regional techniques.

Purpose of reviewThoracic trauma leading to multiple fractured ribs (MFR) remains very common. Good analgesia may help to improve a patients respiratory mechanics and to avoid intubation of the trachea for ventilatory support and therefore may dramatically alter the course of recovery. We herein review the analgesia options for patients with MFR. Recent findingsFor healthy patients with one to two fractured ribs, systemic analgesics may suffice. For more than three to four fractured ribs, studies and experience have reaffirmed the superior analgesia made possible with thoracic epidural, thoracic paravertebral, and intercostal blocks. From experience, interpleural block has significant drawbacks. Catheterization allows the continuation of analgesia for 2 or more days with just one block. Use of the landmark technique is usually satisfactory for accurate block placement but ultrasound and nerve stimulation are showing promise in further improving needle and catheter placement accuracy, especially in the presence of difficult anatomy. SummaryThoracic epidural, thoracic paravertebral, and intercostal blocks are the top choices for patients with MFR and they are of equivalent efficacy. Each has unique advantages and disadvantages. Our preference tends to be the thoracic paravertebral approach.