Joanne Guay

Methemoglobinemia related to local anesthetics: a summary of 242 episodes.

BACKGROUND: The purpose of this article is to summarize all episodes of local anesthetic-related methemoglobinemia found in the medical literature. METHODS: I performed a search of the American National Library of Medicines PubMed with the following key words: “local anesthetic” and “methemoglobinemia.” RESULTS: Two-hundred-forty-two episodes (40.1% published in year 2000 or after) were found. Chocolate-colored blood suggests methemoglobinemia but other colors may be found. A discrepancy between the pulse oximeter saturation (≤90%) and the arterial oxygen partial pressure (≥70 mm Hg) was present in 91.8% of the episodes. The difference between oxygen saturation measured by pulse oximetry and co-oximetry varied from −6.2% to 44.7%. Plain prilocaine may induce clinically symptomatic methemoglobinemia in children older than 6 mo at doses exceeding 2.5 mg/kg. In adults, the dose of prilocaine should be kept lower than 5.0 mg/kg, which is reduced to 3.2 mg/kg in the presence of renal insufficiency and to 1.3 mg/kg if other oxidizing drugs are used concurrently. A single spray of benzocaine may induce methemoglobinemia. Clinical symptoms may be observed at relatively low methemoglobin values, including coma at 32.2 and 29.1% in children and adults, respectively. Rebound methemoglobinemia (benzocaine on mucous membranes) with methemoglobin values as high as 59.9% may occur up to 18 h after methylene blue administration. Complications of methemoglobinemia include hypoxic encephalopathy, myocardial infarction, and death. CONCLUSION: Benzocaine should no longer be used. Prilocaine should not be used in children younger than 6-mo-old, in pregnant women, or in patients taking other oxidizing drugs. The dose should be limited to 2.5 mg/kg.

Predicting blood loss in surgery for idiopathic scoliosis

The authors attempted to determine the relative importance of factors that influence bleeding during and after spinal fusion. Data from 30 ASA I patients with idiopathic scoliosis were prospectively collected and analyzed. Intraoperative bleeding was 1971 ± 831 ml (mean ± SD) (61.5 ± 27% of estimated blood volume (EBV) and correlated with the number of fused vertebrae (r = 0.66, P < 0.0001) and the duration of surgery (r = 0.46, P = 0.0105). There was no correlation between intraoperative bleeding and the Cobb curve angle (43 to 86°), the mean arterial blood pressure (MAP) (63 to 86 mmHg), the central venous pressure (CVP), the quantity of epinephrine infiltrated, muscle relaxants or opioids used, nor in the type of opioids used, the minimal body temperature or whether stored or autologous blood was used. Postoperative bleeding was 1383 ± 369 ml (43.1 ± 11.7% of EBV) and correlated with the length of time the Hemovac drain was in place (r = 0.40, P = 0.0285) and MAP (r = 0.40, P = 0.0285). There was no correlation between postoperative and intraoperative bleeding nor in the number of fused vertebrae. Six patients had greater postoperative than intraoperative bleeding. The total bleeding (intra-plus postoperative) was 3347 ± 920 ml (104.2 ± 30.6 of EBV) and correlated with the number of fused vertebrae (r = 0.63, P = 0.0001) and with the duration of surgery (r = 0.42, P = 0.0208). We conclude that the number of fused vertebrae is the key factor in predicting intraoperative and total bleeding. Postoperative bleeding is considerable (up to 76.9% of EBV). No other factors allow for adequate prediction of postoperative bleeding and these patients must be kept under strict surveillance after surgery.RésuméCette étude avait pour but de déterminer l’importance relative des facteurs qui influencent les pertes sanguines per et postopératoires au cours des arthrodèses vertébrales postérieures. Les données de 30 patients porteurs de scoliose idiopathique ont été recueillies prospectivement puis analysées. Le saignement intraopératoire était de 1971 ± 831 ml (moyenne ± DS) (61.5 ± 27% du volume sanguin estimé (VSE)) et était relié au nombre de vertèbres fusionnées (r = 0.66, P < 0.0001) et à la durée de la chirurgie (r = 0.46, P = 0.0105). Le saignement intraopératoire n’était pas relié au degré de courbure (43 à 86°), ni à la pression artérielle moyenne (PAM) (63 à 86 mmHg), à la pression veineuse centrale (PVC), à la quantité d’épinéphrine, de relaxants neuro- musculaires ou de morphiniques utilisés, ni à la sorte de morphinique utilisé, à la temperature corporelle minimale ou au type de sang administré. Le saignement post-opératoire était de 1383 ± 369 ml (43.1 ± 11.7% du VSE) et était relié à la durée du maintien d’un drain (r = 0.40, P = 0.0285) et à la PAM (r = 0.40, P = 0.0285). Le saignement post-opératoire n’était pas relié au saignement intra-opératoire ni au nombre de vertèbres fusionnées. Six patients ont eu un saignement post-opératoire supérieur au saignement intra-opératoire. Le saignement total (intra et postopératoire) était de 3347 ± 920 ml (104.2 ± 30.6% du VSE) et était relié au nombre de vertèbres fusionnées (r = 0.63, P = 0.0001) ainsi qu’à la durée de la chirurgie (r = 0.42, P = 0.0208). Nous concluons que le nombre de vertèbres fusionnées est le meilleur facteur pour prédire le saignement intraopératoire et le saignement total. Le saignement post-opératoire est élevé (jusqu’à 76.9% du VSE). Il n’y a pas d’autre facteur utile pouvant prédire le saignement post-opératoire et tous les patients doivent être surveillés étroitement en post-opératoire.

The benefits of adding epidural analgesia to general anesthesia : a metaanalysis

The purpose of this metaanalysis was to determine the benefits of postoperative epidural analgesia in patients operated on under general anesthesia. By searching the American National Library of Medicines Pubmed database from 1966 to July 10, 2004, 70 studies were identified. These included 5402 patients, of which 2660 had had epidural analgesia. Epidural analgesia reduces the incidence of arrhythmia, odds ratio (OR) = 0.59 (95%CI = 0.42, 0.81, P = 0.001); time to tracheal extubation, OR = −3.90 h (95%CI = −6.37, −1.42, P = 0.002); intensive care unit stay, OR = −2.94 h (95%CI = −5.66, −0.22, P = 0.03); visual analogical pain (VAS) scores at rest, OR = −0.78 (95%CI = −0.99, −0.57, P < 0.00001) and during movement, OR = −1.28 (95%CI = −1.81, −0.75, P < 0.00001); maximal blood epinephrine, OR = −165.70 pg·ml−1 (95%CI = −252.18, −79.23, P = 0.0002); norepinephrine, OR = −134.24 pg·ml−1 (95%CI = −247.92, −20.57, P = 0.02); cortisol, OR = −55.81 nmol·l−1 (95%CI = −79.28, −32.34, P < 0.00001); and glucose concentrations achieved, OR = −0.87 nmol·l−1 (95%CI = −1.37, −0.37, P = 0.0006). It also reduces the first 24-h morphine consumption, OR = −13.62 mg (95%CI = −22.70, −4.54, P = 0.003), and improves the forced vital capacity (FVC), OR = 0.23 l (95%CI = 0.09, 0.37, P = 0.001) at 24 h. A thoracic epidural containing a local anesthetic reduces the incidence of renal failure: OR = 0.34 (95%CI = 0.14, 0.81, P = 0.01). Epidural analgesia may thus offer many advantages over other modes of postoperative analgesia.

A trial of desmopressin to reduce blood loss in patients undergoing spinal fusion for idiopathic scoliosis.

Desmopressin (DDAVP) has been reported to reduce bleeding in patients undergoing spinal fusion. To evaluate its efficacy in normal patients, 30 healthy young patients (ASA physical status I or II) undergoing spinal fusion for idiopathic scoliosis were randomly allocated to receive either 100 mL of physiologic saline solution (placebo group) or DDAVP (10 μg/m2 of body surface area) (DDAVP group) in a prospective, double-blind trial. Intraoperative blood loss was measured by weighing sponges and suction drainage and postoperative bleeding by wound drainage. The amount of blood loss expressed as a percent of the estimated blood volume was similar in both groups during the intraoperative period (67.0% ± 28.8% [mean ± SD] placebo group vs 57.4% ± 26.5% DDAVP group), the postoperative period up to 24 h (32.5% ± 6.4% placebo group vs 31.1% ± 10.6% DDAVP group), and both periods (94.3% ± 29.4% placebo group vs 88.2% ± 30.7% DDAVP group). With the dose used in our study, we conclude that DDAVP does not reduce surgical bleeding in patients undergoing spinal fusion for idiopathic scoliosis.

Theophylline poisoning. Pharmacological considerations and clinical management.

SummaryThe recent marketing of slow release preparations of theophylline and new indications for the use of the drug have resulted in a marked increase in the sale of theophylline products. This phenomenon combined with the drug’s highly variable pharmacokinetics has led to an increase in the number of theophylline intoxications.The morbidity and mortality rates associated with theophylline intoxication are significant. Therefore it is essential that clinicians are aware of the pathophysiology, clinical presentation and treatment of this poisoning. Theophylline intoxication mainly affects the gastrointestinal, cardiovascular and central nervous systems. Signs and symptoms range from mild gastrointestinal upset to serious central nervous system manifestations such as seizures, a symptom often associated with a bad prognosis.Theophylline serum concentrations are very useful for making decisions regarding treatment. However, their interpretation should take into account several factors such as the age of the patient and the type of intoxication (acute versus chronic).Prevention of gastrointestinal absorption should be the principal objective of treatment of an oral theophylline poisoning. The repetitive administration of activated charcoal not only prevents theophylline absorption but also increases its rate of elimination. Once absorbed, external methods such as haemodialysis and haemoperfusion can significantly accelerate the elimination of the drug from the body. Finally, the rapid suppression of seizures and cardiac arrhythmias are essential to prevent severe neurological sequelae and death.Since theophylline intoxication can be potentially life-threatening, its administration should be monitored with regular measurements of the serum theophylline concentration, especially in the very young and the very old.

The Epidural Test Dose: A Review

This review systematically examines the literature on the ability of the classical epidural test dose and other strategies to detect intravascular, intrathecal, or subdural epidural needle/catheter misplacement. For detection of simulated intravascular misplacements, a sensitivity (S) and a positive predictive value (PPV) ≥80 demonstrated by at least two randomized controlled trials coming from two different centers were determined for the following tests and patient populations: Nonpregnant adult patients = increase in systolic blood pressure (SBP) ≥15 mm Hg (S = 80–100 and 93–100; PPV = 80–100 and 83–100) or either an increase in SBP ≥15 mm Hg or an increase in heart rate ≥10 bpm after the injection of 10 (S = 100; PPV = 83–100) or 15 μg of epinephrine (S = 100; PPV = 83–100); pregnant patients = sedation, drowsiness, or dizziness within 5 min after the injection of 100 μg of fentanyl (S = 92–100; PPV = 91–95); and children = increase in SBP ≥15 mm Hg after the injection of 0.5 μg/kg of epinephrine (S = 81–100; PPV = 100). Conversely, more studies are required to determine the best strategies to detect intrathecal and subdural epidural needle/catheter misplacements in these three patient populations.

Pharmacokinetics and clinical efficacy of intrarectal solution of acetaminophen

Acetaminophen is frequently administered orally to children for its analgesic properties, although its potency has never been clearly evaluated in this population. In certain situations (patients vomiting or unconscious), acetaminophen has to be given rectally. However, the rectal absorption of suppositories is frequently erratic. We undertook this study first, to measure the absorption of an aqueous solution of acetaminophen administered rectally. Secondly, we evaluated acetaminophen’s postoperative analgesic effects in children aged 1 to 8 years old undergoing adenoidectomy and/or tonsillectomy and compared its efficacy to meperidine. Twenty children received 20 mg·kg-1 of acetaminophen at the time of induction of anaesthesia while 20 others received 1 mg·kg-1 of meperidine intramuscularly. Thirty-two patients required meperidine in the Recovery Room. There was no statistical difference between the patients who received acetaminophen (18), and those who received meperidine (14). The absorption of acetaminophen was incomplete (peak serum concentration: 70.8 µnol·L1) and delayed. We conclude that the rectal administration of acetaminophen at the induction of anesthesia results in incomplete and delayed absorption and does not prevent the occurrence of immediate postoperative pain in children undergoing adeno-tonsillectomy.RésuméĽacétaminophène est un médicament fréquemment utilisé en pédiatrie pour ses propriétés analgésiques quoique son efficacité n’est pas été bien étudié dans cette population. Dans certaines situations cliniques, telles les vomissements et ľinconscience, les médicaments doivent être administrés par voie rectale. Toutefois il est bien connnu que ľabsorption des suppositoires est souvent erratique. C’est pourquoi nous avons étudié ľabsorption rectale ďune solution aqueuse ďacétaminophène. De plus, nous avons comparé son effet analgésique à celui de la mépéridine chez 40 enfants agés de un à huit ans admis pour adéno-amygdalectomie. Au moment de ľinduction anesthésique, 20 patients ont reçu 20 mg·kg-1 ďacétaminophène intrarectal alors que les autres ont reçu 1 mg·kg1 de mépéridine intra-musculaire. čanalgésie post-opératoire s’est avérée insuffisante chez 32 patients (acétaminophène: 18, mépéridine: 14). čabsorption de ľacétaminophène a été incomplète (concentration sérique maximale: 70.8 µmol·L1) et retardée. En conclusion, ľadministration intra-rectale ďacétaminophène au moment de ľinduction anesthésique ne procure pas une analgésie post-opératoire adéquate et entraine une absorption incomplète et retardée.

Benzodiazepine poisoning. Clinical and pharmacological considerations and treatment.

SummaryBenzodiazepines are among the most frequently prescribed drugs worldwide. This popularity is based not only on their efficacy but also on their remarkable safety. Pure benzodiazepine overdoses usually induce a mild to moderate central nervous system depression; deep coma requiring assisted ventilation is rare, and should prompt a search for other toxic substances. The severity of the CNS depression is influenced by the dose, the age of the patient and his or her clinical status prior to the ingestion, and the coingestion of other CNS depressants. In severe overdoses, benzodiazepines can occasionally induce cardiovascular and pulmonary toxicity, but deaths resulting from pure benzodiazepine overdoses are rare.Quantitative determinations of benzodiazepines are not useful in the clinical management of intoxicated patients since there is no correlation between serum concentrations and pharmacological and toxicological effects.Benzodiazepine overdoses occurring during pregnancy rarely induce serious morbidity in mothers or fetuses, although large doses administered near delivery can induce respiratory depression in neonates. The teratogenic potential of benzodiazepines remains controversial, but is probably small if it exists at all.There is clear evidence that the prolonged use of even therapeutic doses of benzodiazepines will lead to dependence. The risk of developing significant withdrawal symptoms is related to dosage and duration of treatment.Prevention of gastrointestinal absorption should be initiated in all intentional benzodiazepine overdoses. Forced diuresis and dialysis techniques are not indicated since they will not significantly accelerate the elimination of these agents. Intravenous administration of flumazenil, a pure benzodiazepine antagonist, effectively reverses benzodiazepine-induced CNS depression.

Adverse events associated with intravenous regional anesthesia (Bier block): a systematic review of complications

STUDY OBJECTIVE To characterize the complications reported with intravenous regional anesthesia (IVRA). DESIGN Literature search. SETTING University-affiliated hospital. MEASUREMENTS A search was done in the American National Library of Medicines PUBMED, EMBASE (1980-2007, wk 11), and Medline (from 1950) in March 2007. All complications associated with IVRA were reviewed. MAIN RESULTS The lowest dose of local anesthetic associated with a seizure was 1.4 mg/kg for lidocaine; 4 mg/kg for prilocaine, and 1.3 mg/kg for bupivacaine. Cardiac arrests and deaths were reported with lidocaine and bupivacaine only. The lowest dose associated with a cardiac arrest was 2.5 mg/kg for lidocaine and 1.6 mg/kg for bupivacaine. Local anesthetic toxicity occurring during tourniquet inflation has been reported, with tourniquet pressure exceeding initial systolic arterial blood pressure by 150 mmHg. Seizures occurring after tourniquet deflation have been reported with a tourniquet time as long as 60 minutes. Ten cases of compartment syndrome are reported. CONCLUSION Seizures have been reported with lidocaine at its lowest effective dose (1.5 mg/kg).

Neuraxial anesthesia for the prevention of postoperative mortality and major morbidity: an overview of cochrane systematic reviews.

BACKGROUND:This analysis summarized Cochrane reviews that assess the effects of neuraxial anesthesia on perioperative rates of death, chest infections, and myocardial infarction. METHODS:A search was performed in the Cochrane Database of Systematic Reviews on July 13, 2012. We have included all Cochrane systematic reviews that examined subjects of any age undergoing any type of surgical (open or endoscopic) procedure, compared neuraxial anesthesia to general anesthesia alone for the surgical anesthesia, or neuraxial anesthesia plus general anesthesia to general anesthesia alone for the surgical anesthesia, and included death, chest infections, myocardial infarction, and/or serious adverse events as outcomes. Studies included in these reviews were selected on the same criteria. RESULTS:Nine Cochrane reviews were selected for this overview. Their scores on the Overview Quality Assessment Questionnaire varied from 4 to 6 of a maximal possible score of 7. Compared with general anesthesia, neuraxial anesthesia reduced the 0- to-30-day mortality (risk ratio [RR] 0.71; 95% confidence interval [CI], 0.53–0.94; I2 = 0%) based on 20 studies that included 3006 participants. Neuraxial anesthesia also decreased the risk of pneumonia (RR 0.45; 95% CI, 0.26–0.79; I2 = 0%) based on 5 studies that included 400 participants. No difference was detected in the risk of myocardial infarction between the 2 techniques (RR 1.17; 95% CI, 0.57–2.37; I2 = 0%) based on 6 studies with 849 participants. Compared with general anesthesia alone, adding neuraxial anesthesia to general anesthesia did not affect the 0- to-30-day mortality (RR 1.07; 95% CI, 0.76–1.51; I2 = 0%) based on 18 studies with 3228 participants. No difference was detected in the risk of myocardial infarction between combined neuraxial anesthesia–general anesthesia and general anesthesia alone (RR 0.69; 95% CI, 0.44–1.09; I2 = 0%) based on 8 studies that included 1580 participants. Adding a neuraxial anesthesia to general anesthesia reduced the risk of pneumonia (RR 0.69; 95% CI, 0.49–0.98; I2 = 9%) after adjustment for publication bias and based on 9 studies that included 2433 participants. The quality of the evidence was judged as moderate for all 6 comparisons. The quality of the reporting score of complications related to neuraxial blocks was 9 (4 to 12 [median {range}]) for a possible maximum score of 14. CONCLUSIONS:Compared with general anesthesia, neuraxial anesthesia may reduce the 0-to-30-day mortality for patients undergoing a surgery with an intermediate-to-high cardiac risk (level of evidence moderate). Large randomized controlled trials on the difference in death and major outcomes between regional and general anesthesia are required.