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Biomedical subjects

Mark W Crawford

Publications and source records attributed to Mark W Crawford.

18 recordsLinked to original sources
PubMed2006

Preparation of the Dräger Primus anesthetic machine for malignant hyperthermia-susceptible patients.

PURPOSE: Preparation of anesthesia machines for patients who are susceptible to malignant hyperthermia includes flushing the machine with vapour-free fresh gas to washout residual anesthetic agents. To establish guidelines for the preparation of the Dräger Primus machine, we compared the washout profiles for isoflurane and sevoflurane in the Dräger Primus and Ohmeda Excel 210 anesthesia machines. TECHNICAL FEATURES: The machines were primed with 1.5% isoflurane or 2.5% sevoflurane. Fresh gas flow (FGF) was set at 10 L.min(-1) during the early washout phase, and subsequently reduced to 3 L.min(-1) during the late washout phase. A Miran ambient air analyzer measured the anesthetic concentration every minute during washout until a concentration of 5 ppm was achieved in the inspiratory limb of the circle circuit. We found that at a FGF of 10 L.min(-1), maximum washout times for isoflurane and sevoflurane in the Primus, 70 and 74 min, respectively, were approximately tenfold greater than for isoflurane in the Excel 210 (7.0 min). Increasing the FGF to 18 L.min(-1) decreased the washout time for isoflurane in the Primus, only moderately, to 52 min. We observed a threefold increase in anesthetic concentration in the Primus during the late washout phase. CONCLUSION: We conclude that the Primus must be flushed for at least 70 min to decrease the anesthetic concentration to 5 ppm when using a FGF of 10 L.min(-1). We recommend maintaining a FGF of 10 L.min(-1) for the duration of anesthesia in order to prevent the rebound increase in anesthetic concentration in the FGF.

Anesthesiology↗
PubMed2006

Effect of propofol anesthesia and continuous positive airway pressure on upper airway size and configuration in infants.

BACKGROUND: Infants are prone to obstruction of the upper airway during general anesthesia. Continuous positive airway pressure (CPAP) is often used to prevent or treat anesthesia-induced airway obstruction. The authors studied the interaction of propofol anesthesia and CPAP on airway caliber in infants using magnetic resonance imaging. METHODS: Nine infants undergoing elective magnetic resonance imaging of the brain were studied. Head position was standardized. Spin echo magnetic resonance images of the airway were acquired at the level of the soft palate, base of the tongue, and tip of the epiglottis. Four sets of images were acquired in sequence: (1) during light propofol anesthesia at an infusion rate of 80 microg . kg(-1) . min(-1), (2) after increasing the depth of propofol anesthesia by administering a bolus dose (2.0 mg/kg) and increasing the infusion rate to 240 microg . kg(-1) . min(-1), (3) during continued infusion of 240 microg . kg(-1). min propofol and application of 10 cm H2O CPAP, and (4) after removal of CPAP and continued infusion of 240 microg . kg(-1). min propofol. RESULTS: Increasing depth of propofol anesthesia decreased airway caliber at each anatomical level, predominantly due to anteroposterior narrowing. Application of CPAP completely reversed the propofol-induced decrease in airway caliber, primarily by increasing the transverse dimension. CONCLUSIONS: Airway narrowing with increasing depth of propofol anesthesia results predominantly from a reduction in anteroposterior dimension, whereas CPAP acts primarily to increase the transverse dimension. Although airway caliber during deep propofol anesthesia and application of CPAP was similar to that during light propofol anesthesia, there were significant configurational differences.

Anesthesia, Intravenous↗
PubMed2006

Extent and localization of changes in upper airway caliber with varying concentrations of sevoflurane in children.

BACKGROUND: Previous studies in humans suggest that inhibition of upper airway muscle activity is independent of the dose of inhalational anesthesia. Whether a dose-independent relation applies to changes in airway caliber is unknown. The authors sought to evaluate the configurational changes that lead to upper airway narrowing during inhalational anesthesia with sevoflurane and to determine whether these changes are dose dependent within a clinically relevant dose range. METHODS: Fifteen children undergoing elective magnetic resonance imaging of the brain were studied. Magnetic resonance images of the upper airway were acquired at sevoflurane concentrations of 0.5, 1.0, and 1.5 minimum alveolar concentration (MAC), administered in random sequence. At least 15 min was allowed for equilibration of inspired and alveolar partial pressures of sevoflurane. Images were acquired in early expiration at the level of the soft palate, base of the tongue, and tip of the epiglottis. Airway cross-sectional area (CSA), anteroposterior, and transverse dimension were determined using image-analysis software. RESULTS: At each anatomical level, pharyngeal CSA decreased progressively with increasing depth of sevoflurane anesthesia (P < 0.001). Increasing the sevoflurane concentration from 0.5 to 1.0 MAC reduced airway CSA by 13-18%, and a further increase to 1.5 MAC resulted in an overall 28-34% reduction in CSA. The reduction in CSA was predominantly due to a decrease in anteroposterior dimension. CONCLUSIONS: Increasing the depth of sevoflurane anesthesia resulted in a relatively uniform reduction in pharyngeal caliber at each anatomical level studied. The effect of sevoflurane on upper airway caliber is dose dependent.

Anesthesia, Inhalation↗
PubMed2006

Postoperative morphine consumption in children with sickle-cell disease.

BACKGROUND: Effective pain control is a primary goal in the perioperative management of patients with sickle-cell disease. To understand analgesic requirements better, the authors compared postoperative morphine consumption and pain scores in sickle and non-sickle children who had undergone laparoscopic cholecystectomy. METHODS: We reviewed the medical records of all sickle and non-sickle children referred to the Acute Pain Service of a tertiary care teaching hospital for patient-controlled analgesia (PCA) following laparoscopic cholecystectomy from 1996 to 2003. Data collected included postoperative morphine consumption, visual analogue pain scores, and perioperative outcome. RESULTS: Total postoperative morphine consumption in sickle children (n = 12) (1.58 +/- 0.78 mg.kg(-1)) was more than double when compared with non-sickle children (n = 10) (0.65 +/- 0.32 mg.kg(-1)) (P < 0.005). Duration of PCA use among sickle children (51 +/- 25 h) was more than double when compared with non-sickle children (21 +/- 11 h) (P < 0.005). Sickle patients had greater pain scores in the initial 24 h after surgery (P < 0.05) and used more adjuvant analgesics (P < 0.05). Duration of postoperative hospital stay was 3.4 +/- 1.6 days and 1.5 +/- 0.5 days for sickle and non-sickle children, respectively (P < 0.005). CONCLUSIONS: Sickle children self-administered more than double the amount of morphine, reported more intense pain, and remained hospitalized for more than twice as long as nonsickle children undergoing the same surgical procedure. These findings probably have a multifactorial origin, and might be attributable in part to alterations in pain perception, opioid pharmacokinetics, opioid tolerance, and psychosocial variables.

Adolescent↗
PubMed2006

A pilot study of the rectus sheath block for pain control after umbilical hernia repair.

BACKGROUND: Umbilical hernia repair, a common day surgery procedure in children, is associated with significant postoperative discomfort. The rectus sheath block may offer improved pain management following umbilical hernia repair. In this pilot study, we compared the efficacy of the rectus sheath block with that of our current standard practice--local anesthetic infiltration into the surgical wound--for pain control after umbilical hernia repair in children. METHODS: Fourteen children, aged 1-8 years, undergoing umbilical hernia repair were randomly assigned to receive either a rectus sheath block or local anesthetic infiltration into the surgical wound at completion of surgery. Anesthetic management was standardized. Each analgesic technique was performed using 0.8 ml x kg(-1) of 0.25% bupivacaine with epinephrine 1:200,000. Postoperatively, an investigator who was blinded to the analgesic technique recorded the Children's Hospital of Eastern Ontario Pain Scale (CHEOPS) scores and sedation scores every 10 min, and administered intravenous morphine 50 microg x kg(-1) for cases with CHEOPS scores > or = 8. Total morphine dose was recorded. Parents were telephoned the day after surgery to determine the overall satisfaction with pain control. RESULTS: Total postoperative morphine consumption did not differ significantly between groups, averaging 0.10 +/- 0.09 and 0.10 +/- 0.07 mg x kg(-1) for the local infiltration and rectus sheath groups, respectively. There were no significant differences in pain or sedation scores, and no complications related to either analgesic technique. DISCUSSION: Our results suggest that the rectus sheath block has no advantage over infiltration of local anesthetic into the surgical wound for postoperative pain management in children undergoing umbilical hernia repair.

Ambulatory Surgical Procedures↗
PubMed2006

Complete upper airway obstruction after induction of anesthesia in a child with undiagnosed lingual tonsil hypertrophy.

We present a case of a 9-year-old patient with previously undiagnosed lingual tonsil hypertrophy (LTH) that caused sudden and complete airway obstruction and inability to ventilate on induction of anesthesia. More frequently described in adults than in children, LTH can complicate mask ventilation, intubation or both, with the potential for catastrophic consequences.

Airway Obstruction↗
PubMed2006

Development of acute opioid tolerance during infusion of remifentanil for pediatric scoliosis surgery.

We tested the hypothesis that continuous intraoperative infusion of remifentanil is associated with the development of clinically relevant acute opioid tolerance in adolescents undergoing scoliosis surgery. Thirty adolescents were randomly assigned to receive an intraoperative analgesic regimen consisting of continuous remifentanil infusion or intermittent morphine alone. Postoperative analgesic consumption was assessed with a patient-controlled analgesia device that was used to self-administer morphine. Cumulative postoperative morphine consumption, pain scores, and sedation scores were recorded by a blinded investigator every hour for the first 4 h postoperatively and then every 4 h for a total of 24 h. Cumulative morphine consumption in the remifentanil group was significantly more than that in the morphine group at each time point in the initial 24 h after surgery (P < 0.0001). At 24 h after surgery, cumulative morphine consumption was 30% greater in the remifentanil group (1.65 +/- 0.41 mg/kg) than in the morphine group (1.27 +/- 0.32 mg/kg) (95% confidence interval for the difference, 0.11 to 0.65 mg/kg). Differences in pain and sedation scores were not statistically significant. These data suggest that intraoperative infusion of remifentanil is associated with the development of clinically relevant acute opioid tolerance in adolescents undergoing scoliosis surgery.

Adolescent↗
PubMed2005

Preoperative screening for sickle cell disease in children: clinical implications.

PURPOSE: Preoperative screening of at-risk patients for sickle cell disease (SCD) is recommended as a method to decrease perioperative morbidity. However, the effectiveness of pre-operative screening in accomplishing this goal has never been demonstrated. We undertook a retrospective study to determine the prevalence of positive test results among those screened preoperatively at our institution and to determine whether amendments to present screening guidelines can be recommended. METHODS: The hematology laboratory database of a university teaching hospital was searched to identify all patients who underwent preoperative screening for SCD from October 1999 to October 2003. The medical records of those patients testing positive were reviewed. RESULTS: Of 1,906 children screened preoperatively, 79 (4.1%) were diagnosed as having sickle cell trait and three (0.16%) as having some form of SCD: one had homozygous hemoglobin S and two had sickle-hemoglobin C disease. Two of the three had a family history for SCD and none had a preoperative hemoglobin concentration < 10 g.dL(-1). No patient developed perioperative sickle-related complications. CONCLUSION: Preoperative screening of 1,906 children identified only one asymptomatic child with undiagnosed SCD and a negative family history, suggesting that routine preoperative screening for SCD is rarely of significant clinical value in our population. Had preoperative screening not been performed, no child requiring preoperative transfusion would have been missed, representing a long-run probability of at least 99.84% that no at-risk child would require transfusion. We recommend that preoperative screening for SCD be undertaken selectively, giving consideration to the risks and benefits of screening to the individual patient.

Adolescent↗
PubMed2005

Anterior ischemic optic neuropathy complicating cranial vault reconstruction for sagittal synostosis in a child.

The authors report a case of postoperative visual loss in a pediatric patient who underwent an uneventful cranial vault reconstruction. A 5-year-old boy underwent total cranial vault reconstruction for nonsyndromic sagittal synostosis. He was positioned prone for 6 hours and then supine for the final 2 hours of surgery. Controlled hypotension was used to maintain the systolic arterial pressure at 80 mmHg to 90 mmHg. The intraoperative hematocrit was 23% to 31%. In the immediate postoperative period, both pupils were noted to be reactive to light. After an uneventful night in the intensive care unit, he was transferred to the ward. The eyelids were edematous on postoperative day 1, and visual examination was no longer possible. He was discharged home on postoperative day 4, and readmitted 2 days later with bilateral blindness. The pupils were nonreactive, and the optic discs were pale and edematous. Computed tomography and magnetic resonance imaging of the head revealed no abnormality. Intravenous steroid therapy was initiated, and the patient was taken to the operating room for re-exploration; the intracranial pressure was found to be normal. The presumed diagnosis was bilateral infarctions of the anterior optic nerves. Visual acuity 14 months after surgery was less than 3/200 in the right eye and 20/20-2 in the left, indicating significant recovery. Pediatric patients undergoing cranial vault reconstruction are at risk for postoperative visual loss because of ischemic optic nerve injury. Prolonged duration in the prone position and significant blood loss may be risk factors.

Blindness↗
PubMed2005

The upper airway in Weaver syndrome.

Weaver syndrome is a rare disorder of unknown etiology characterized by skeletal overgrowth, distinctive craniofacial and digital abnormalities, and advanced bone age. The prime anesthetic problem reported in children with Weaver syndrome is difficulty with tracheal intubation, resulting in part from relative micrognathia, short neck, and an anterior and cephalad position of the larynx. In this report, the authors describe their experience with two children diagnosed with Weaver syndrome who presented for dental surgery. Contrary to previous reports, tracheal intubation was accomplished with relative ease, suggesting that difficulty in intubation in Weaver syndrome may be age-related, diminishing with advancing age and growth of the mandible, as has been reported for other micrognathic syndromes such as Pierre Robin sequence.

Anesthesia, General↗
PubMed2005

Dose-response of remifentanil for tracheal intubation in infants.

To compare the dose-response of remifentanil for tracheal intubation in infants and children, 32 healthy full-term infants and 32 children were anesthetized with 10 mug/kg glycopyrrolate and 4.0 mg/kg propofol and administered 1 of 4 doses of remifentanil (1.25, 1.50, 1.75, or 2.00 microg/kg) to facilitate tracheal intubation. We determined the effective doses of remifentanil in 50% (ED50) and 98% (ED98) of patients by using logistic regression analysis. We found that logistic regression curves were similar for infants and children (P = 0.38). ED50 and ED98 values for remifentanil were 1.70 +/- 0.1 microg/kg and 2.88 +/- 0.5 microg/kg, respectively. In a second double-blind study, 24 infants were anesthetized with propofol and randomized to receive either 3.0 microg/kg remifentanil or 2.0 mg/kg succinylcholine to facilitate tracheal intubation. The duration of apnea, tracheal intubating conditions and hemodynamic changes were determined. We found that the duration of apnea and intubating conditions after propofol/remifentanil were similar to those after propofol/succinylcholine. Bradycardia, hypotension, and chest wall rigidity did not occur. We conclude that the dose-response of remifentanil for tracheal intubation is similar in infants and children. Propofol/remifentanil provides clinically acceptable intubating conditions, stable hemodynamics, and a duration of apnea comparable to that with propofol/succinylcholine in infants.

Aging↗
PubMed2005

Near-miss injection of an anesthetic agent into a cerebrospinal fluid external ventricular drain: special report.

OBJECTIVE AND IMPORTANCE: Human error has been increasingly recognized as a cause of patient morbidity and mortality. One method of error prevention is the reporting of a near-miss event. We report that intravenous anesthetic agents were nearly injected into the external ventricular drainage (EVD) of a patient during an emergency shunt procedure. CLINICAL PRESENTATION: A 3-year-old male patient with multiple cerebrospinal fluid shunts and shunt infection had an external ventricular drain catheter tunneled to exit just inferior to the left clavicle during a previous procedure. The exit site was covered by an occlusive dressing. This particular system, the Codman external drainage system II collection bag and tubing set (Codman & Shurtleff, Inc., Raynham, MA), contains two access ports (a three-way stoppered port and an angled rubber stoppered injection port). At induction of anesthesia, the EVD system was mistaken for a central venous line and was nearly injected with propofol and rocuronium. Fortunately, the error was quickly recognized and the patient came to no harm. INTERVENTION AND TECHNIQUE: A modified EVD system has recently been released that does not include the three-way port, and features an embedded bright green stripe in the tubing to distinguish it from intravenous tubing. CONCLUSION: We recommend using caution when tunneling EVDs to sites that might be confused with central venous access sites. EVD system tubing should be designed so it can be easily distinguished from intravenous tubing, and it should be clearly labeled as an EVD line.

Anesthetics↗
PubMed2004

Magnesium deficiency alters the threshold for epinephrine-induced arrhythmias during halothane or sevoflurane anesthesia in the rat.

OBJECTIVE: To determine the effect of chronic magnesium (Mg2+) deficiency on the relative arrhythmogenicity of halothane and sevoflurane in the rat. DESIGN: Prospective, randomized, nonblinded study. SETTING: University laboratory. PARTICIPANTS: Male Sprague-Dawley rats (n = 48). INTERVENTIONS: Rats were maintained on a Mg2+-deficient or control diet for 14 days, at which time they were anesthetized with halothane or sevoflurane, a tracheostomy was performed, and the lungs were ventilated to maintain normocapnia. Catheters were inserted into a femoral vein and carotid artery. Lead II of the electrocardiogram was monitored to determine the threshold for epinephrine-induced arrhythmias. MEASUREMENTS AND MAIN RESULTS: Chronic Mg2+ deficiency significantly decreased the dose of epinephrine required for arrhythmias (ADE). The reduction in the ADE was approximately one third during halothane anesthesia (p < 0.05) and one fifth during sevoflurane anesthesia (p < 0.001). Infusion of magnesium sulphate completely reversed the reduction in ADE. In normomagnesemic rats, the halothane ADE was significantly less than the sevoflurane ADE (mean difference = 6.0 microg/kg, 95% confidence interval of the difference = 3.6 to 8.4 microg/kg) (p < 0.005). Mg2+ deficiency significantly attenuated the difference between the halothane ADE and the sevoflurane ADE (mean difference in the Mg2+-deficient group = 0.6 microg/kg, 95% confidence interval of the difference = -0.2 to 1.5 microg/kg). CONCLUSION: Chronic Mg2+ deficiency decreased the threshold for epinephrine-induced arrhythmias and attenuated differences between the arrhythmogenic potential of halothane and sevoflurane, suggesting that arrhythmias are as likely to develop with sevoflurane as with halothane in the presence of coexisting magnesium deficiency and elevated catecholamines.

Anesthesia, Inhalation↗
PubMed2003

Effect of increasing depth of propofol anesthesia on upper airway configuration in children.

BACKGROUND: The upper airway tends to be obstructed during anesthesia in spontaneously breathing patients. The purpose of the current study was to determine the effect of increasing depth of propofol anesthesia on airway size and configuration in children. METHODS: Magnetic resonance images of the upper airway were obtained in 15 children, aged 2-6 yr. Cross-sectional area, anteroposterior dimension, and transverse dimension were measured at the level of the soft palate, dorsum of the tongue, and tip of the epiglottis. Images were obtained during infusion of propofol at a rate of 50-80 microg.kg-1.min-1 and after increasing the depth of anesthesia by administering a bolus dose of propofol and increasing the infusion rate to 240 microg.kg-1.min-1. RESULTS: Overall, the cross-sectional area of the entire pharyngeal airway decreased with increasing depth of anesthesia. The reduction in cross-sectional area was greatest at the level of the epiglottis (24.5 mm2, 95% confidence interval = 16.9-32.2 mm2; P < 0.0001), intermediate at the level of the tongue (19.3 mm2, 95% confidence interval = 9.2-29.3 mm2; P < 0.0001), and least at the level of the soft palate (12.6 mm2, 95% confidence interval = 2.7-22.6 mm2; P < 0.005) in expiration and resulted predominantly from a reduction in anteroposterior dimension. The airway cross-sectional area decreased further in inspiration at the level of the epiglottis. The narrowest portion of the airway resided at the level of the soft palate or epiglottis in the majority of children. CONCLUSION: Increasing depth of propofol anesthesia in children is associated with upper airway narrowing that occurs throughout the entire upper airway and is most pronounced in the hypopharynx at the level of the epiglottis.

Anesthesia, Intravenous↗
PubMedDate not supplied

Acute chest syndrome shows a predilection for basal lung regions on the side of upper abdominal surgery.

PURPOSE: Upper abdominal surgery for cholecystectomy or splenectomy is the most frequently performed surgical procedure in patients with sickle cell disease (SCD). The acute chest syndrome (ACS) is the most common sickle-related postoperative complication. The objective of the study was to characterize the clinical and radiological presentation of ACS complicating cholecystectomy and splenectomy. METHODS: The medical records of all children with SCD undergoing cholecystectomy or splenectomy during the 15-year period from January 1988 through December 2002 were reviewed. Patients who experienced ACS within 14 days after surgery were identified. Data collected included demographics, perioperative management, clinical and radiological findings, and outcome. RESULTS: The overall incidence of postoperative ACS was 16%, occurring in nine of 51 patients having cholecystectomy and in seven of 48 patients having splenectomy. Mean time to onset of symptoms was 49 hr after surgery (range, 24-96 hr). Cough, fever, and an abnormal chest examination were documented for all patients at presentation. Radiologically, ACS involved the basal lobes in all cases and was multi-lobar in 25%. Patients were more likely to have new infiltrates involving the lung on the side of the surgery or bilateral infiltrates than isolated contralateral infiltrates at presentation (P < 0.0001). Isolated upper or middle lobe involvement did not occur. Fifty percent of cases demonstrated evidence of a pleural effusion. CONCLUSION: ACS complicating cholecystectomy or splenectomy shows a predilection for basal lung regions and for the lung on the side of surgery. These results have implications for the pathogenesis and prevention of postoperative ACS.

Acute Disease↗