Martin Allard

Cardiac Allotransplantation in Newborns as Therapy for Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome constitutes a spectrum of severe congenital cardiovascular anomalies dominated by underdevelopment or absence of the left ventricle, aortic valve, and mitral valve. ...

Who is at risk for postdischarge nausea and vomiting after ambulatory surgery

Background: About one in four patients suffers from postoperative nausea and vomiting. Fortunately, risk scores have been developed to better manage this outcome in hospitalized patients, but there is currently no risk score for postdischarge nausea and vomiting (PDNV) in ambulatory surgical patients. Methods: We conducted a prospective multicenter study of 2,170 adults undergoing general anesthesia at ambulatory surgery centers in the United States from 2007 to 2008. PDNV was assessed from discharge until the end of the second postoperative day. Logistic regression analysis was applied to a development dataset and the area under the receiver operating characteristic curve was calculated in a validation dataset. Results: The overall incidence of PDNV was 37%. Logistic regression analysis of the development dataset (n = 1,913) identified five independent predictors (odds ratio; 95% CI): female gender (1.54; 1.22 to 1.94), age less than 50 yr (2.17; 1.75 to 2.69), history of nausea and/or vomiting after previous anesthesia (1.50; 1.19 to 1.88), opioid administration in the postanesthesia care unit (1.93; 1.53 to 2.43), and nausea in the postanesthesia care unit (3.14; 2.44–4.04). In the validation dataset (n = 257), zero, one, two, three, four, and five of these factors were associated with a PDNV incidence of 7%, 20%, 28%, 53%, 60%, and 89%, respectively, and an area under the receiver operating characteristic curve of 0.72 (0.69 to 0.73). Conclusions: PDNV affects a substantial number of patients after ambulatory surgery. We developed and validated a simplified risk score to identify patients who would benefit from long-acting prophylactic antiemetics at discharge from the ambulatory care center.

The accuracy of noninvasive and continuous total hemoglobin measurement by pulse CO-Oximetry in human subjects undergoing hemodilution.

BACKGROUND: Total hemoglobin (tHb) is one the most frequently ordered laboratory measurements. Pulse CO-Oximetry™ (Masimo Corp., Irvine, CA) is a multi-wavelength spectrophotometric method for noninvasive and continuous hemoglobin monitoring (SpHb). In this study, we evaluated the accuracy of SpHb compared with laboratory CO-Oximeter measurement of tHb from arterial blood samples in 20 healthy volunteer subjects undergoing hemodilution. METHODS: After enrollment, approximately 500 mL of blood was drawn from subjects through an arterial or venous catheter. Each subject then rapidly received crystalloid IV fluid to compensate for the decrease in intravascular volume and reduce the hemoglobin concentration. Subjects received a maximum of 30 mL/kg IV fluid. SpHb was continuously monitored and recorded, and serial arterial blood samples were taken during the procedure. SpHb accuracy was analyzed by pairing SpHb and tHb measurements after the arterial blood draw with the resulting tHb test result. Bias, precision, and the average root-mean-square error were calculated. RESULTS: One hundred sixty-five tHb measurements were collected. The average decrease in tHb during the blood removal and hemodilution procedure was 2.4 ± 0.8 g/dL (mean ± SD). The average difference between 335 paired measurements of SpHb and tHb was −0.15 g/dL, 1 SD of the difference was 0.92 g/dL, and the average root-mean-square difference was 0.94 g/dL. The difference between SpHb and tHb was <2.0 g/dL for 97% of the measurements. The difference was <1.5 g/dL for 97% of the measurements when tHb was <10 g/dL. CONCLUSIONS: Pulse CO-Oximetry–based SpHb measurement is accurate within 1.0 g/dL (1 SD) compared with laboratory CO-Oximeter tHb measurement in subjects undergoing hemodilution.

The hemodynamically unstable patient in the intensive care unit: Hemodynamic vs. transesophageal echocardiographic monitoring

ObjectiveTransesophageal echocardiography is a diagnostic and monitoring modality. The objectives of our study were to compare the diagnoses obtained with continuous transesophageal echocardiography and hemodynamic monitoring in the intensive care unit, to determine interobserver variability of diagnosis obtained with both modalities, and to evaluate its impact. DesignProspective cohort study. SettingSurgical intensive care unit. PatientsConsecutive hemodynamically unstable patients after cardiac surgery. InterventionsAt admission, unstable patients were monitored during 4 hrs with transesophageal echocardiography and standard hemodynamic monitoring. The critical care physician evaluated the patients based on all information except the transesophageal echocardiography at 0, 2, and 4 hrs and formulated a hypothesis on the most likely cause of hemodynamic instability. Transesophageal echocardiography information was provided after each evaluation. To evaluate interobserver variability, all the hemodynamic and echocardiographic information was gathered, randomized, and evaluated by five clinicians for the hemodynamic data and five echocardiographers for the transesophageal echocardiography data. The evaluators were blinded to all other information. Kappa statistics were used to evaluate agreement. Impact of transesophageal echocardiography was assessed retrospectively by using the Deutsch scale. ResultsTwenty patients qualified for the study. The agreement between the hemodynamic and echocardiographic diagnosis showed a kappa at admission, 2 hrs, and 4 hrs of 0.33, 0.47, and 0.28. The interobserver agreement for the initial diagnosis (p = .014) and between all evaluators (p < .001) was significantly higher in the echocardiographic compared with the hemodynamic group. The transesophageal echocardiographic information was considered retrospectively to be essential in 34% and valuable in 34% of cases. ConclusionsThese observations support the belief that transesophageal echocardiographic monitoring in the intensive care unit is associated with higher interobserver agreement in diagnosing and excluding significant causes of hemodynamic instability for postoperative cardiac surgical patients.

Neuroprotective effect of volatile anesthetic agents: molecular mechanisms

Abstract Introduction: Intra-operative cerebral ischemia can be catastrophic, and volatile anesthetic agents have been recognized for their potential neuroprotective properties since the 1960s. In this review, we examine the neuroprotective effects of five volatile anesthetic agents in current or recent clinical use: isoflurane, sevoflurane, desflurane, halothane and enflurane. Methods: A review of publications in the National Library of Medicine and National Institutes of Health database from 1970 to 2007 was conducted. Results: Volatile anesthetic agents have been shown to be neuroprotective in multiple animal works of ischemic brain injury. Short-term neuroprotection (<1 week post-ischemia) in experimental cerebral ischemia has been reported in multiple works, although long-term neuroprotection (≥1 week post-ischemia) remains controversial. Comparison works have not demonstrated superiority of one specific volatile agent over another in experimental models of brain injury. Relatively few human works have examined the protective effects of volatile anesthetic agents and conclusive evidence of a neuroprotective effect has yet to emerge from human works. Conclusion: Proposed mechanisms related to the neuroprotective effect of volatile anesthetic agents include activation of ATP-dependent potassium channels, up-regulation of nitric oxide synthase, reduction of excitotoxic stressors and cerebral metabolic rate, augmentation of peri-ischemic cerebral blood flow and up-regulation of antiapoptotic factors including MAP kinases.

Venous carbon dioxide embolism in pigs: an evaluation of end-tidal carbon dioxide, transesophageal echocardiography, pulmonary artery pressure, and precordial auscultation as monitoring modalities.

We evaluated the effects of CO2 embolism on end-tidal carbon dioxide (ETCO2) and compared four methods for detection of gas embolism. Fourteen pigs were monitored for CO2 embolism with transesophageal echocardiography (TEE), changes in ETCO2, changes in mean pulmonary artery pressure (MPAP), and precordial auscultation (AUSC). Serial injections of CO2 (ranging from 0.05 to 5.0 mL/kg) were performed in seven pigs (Group 1). In the other seven pigs, CO2 was infused at rates between 0.01 and 0.4 mL.kg-1.min-1 (Group 2). Positive responses were defined as an acute change in heart sounds (AUSC), visualization of gas bubbles in the right cardiac chambers on TEE, an increase in MPAP > or = 3 mm Hg, and an acute change (increase or decrease) in ETCO2 > or = 3 mm Hg. In both groups, positive responses to CO2 embolism were represented by an initial decrease in ETCO2. The frequency with which positive responses were observed revealed that TEE was the most sensitive method (P < 0.05), whereas no differences were found among the other methods. In conclusion, in this model, positive response to CO2 embolism was represented by a decrease in ETCO2. TEE was the most sensitive method of detection of CO2 embolism, and ETCO2, MPAP, and AUSC were equally sensitive.

Evaluation of pulse cooximetry in patients undergoing abdominal or pelvic surgery.

Background: Intraoperative transfusion decisions generally are guided by blood loss estimation and periodic invasive hemoglobin measurement. Continuous hemoglobin measurement by pulse cooximetry (pulse hemoglobin; Rainbow® SET Pulse CO-Oximeter, Masimo Corporation, Irvine, CA) has good agreement with laboratory hemoglobin in healthy volunteers and could aid transfusion decision-making. Because intraoperative physiology may alter performance of this device, this study investigated pulse hemoglobin during surgery. Methods: Ninety-one adult patients undergoing abdominal or pelvic surgery in which large blood loss was likely were studied. Time-matched pulse hemoglobin measurements were recorded for each intraoperative arterial hemoglobin measurement obtained. Agreement between measurements was assessed by average difference (mean ± SD, g/dl), linear regression, and multiple measures Bland-Altman analysis. Results: The average difference between 360 time-matched measurements (bias) was 0.50 ± 1.44 g/dl, with wider limits of agreement (−2.3 to 3.3 g/dl) than reported in healthy volunteers. The average difference between 269 paired sequential pulse and arterial hemoglobin changes was 0.10 ± 1.11 g/dl, with half between −0.6 and 0.7 g/dl of each other. The bias was larger in patients with blood loss of more than 1,000 ml; hemoglobin less than 9.0 g/dl; any intraoperative transfusion; or intraoperative decrease in arterial hemoglobin at the time of sampling ≥2 g/dl (all P < 0.001). The range of bias was narrower at deeper anesthesia (P < 0.001). Conclusions: Evaluation of the sensor and software version tested suggests that although pulse cooximetry may perform well in ambulatory subjects, in patients undergoing surgery in which large blood loss is likely, an invasive measurement should be used in transfusion decision-making.

3% Hypertonic saline following subarachnoid hemorrhage in rats

BACKGROUND Hypertonic saline (HTS) has been proposed as a treatment after aneurysmal subarachnoid hemorrhage (SAH) to minimize ischemic brain injury due to its osmotic and rheologic properties. Although the benefits of 7.2% HTS use in brain injury have been studied, there is a paucity of data on the use of 3%HTS. METHODS We investigated whether 3%HTS can reduce brain water content and improve neurologic function after SAH in the rodent model compared to 0.9% saline solution (NS). Neurologic testing was conducted at 24 hours post-SAH prior to sacrificing animals for brain water content evaluation. FINDINGS There was significant potentiation of brain water content in the right hemisphere between 3%HTS and NS groups. The modified Garcia score was not significantly different between the two groups; however, the vibrissae-stimulated forelimb placement test showed significantly lower scores in the HTS group. 3%HTS does not decrease brain edema or improve neurologic deficits as compared to NS. In fact, our study showed 3%HTS potentiated brain edema and worsened neurologic deficits in the rat SAH model. CONCLUSIONS Given the potential adverse effects of HTS therapies, including hyperchloremic acidosis, and the lack of benefit found in our study, more investigation is required to evaluate the clinical use of 3%HTS in the setting of SAH.

Simvastatin treatment in surgically induced brain injury in rats

BACKGROUND HMG-CoA reductase inhibitors (Statins) have been shown to reduce blood brain barrier (BBB) disruption and improve neurologic outcome in cerebrovascular disorders. Brain injury due to neurosurgical procedures can lead to post-operative complications such as brain edema and altered neurologic function. The objective of this study was to evaluate whether simvastatin reduces brain edema by preventing BBB disruption and improves neurologic status after surgically-induced brain injury (SBI). METHODS Animals were pretreated for seven days with vehicle or simvastatin i.p. daily, after which they underwent SBI. Neurologic evaluation was assessed at 24 hours post-SBI and the animals were sacrificed for brain water content calculation and BBB evaluation. FINDINGS Brain water content was significantly increased in the right frontal lobe in all SBI groups as compared to the left frontal lobe. There was no significant difference in brain water content in the right frontal lobe between simvastatin and vehicle treated groups. Evans blue testing did not show a significant difference in disruption of the BBB between groups. Neurologic scores were not significantly different. CONCLUSIONS Simvastatin did not reduce brain water content, protect the BBB, or improve neurologic scores after SBI.

103 A PROSPECTIVE STUDY TO EVALUATE THE INCIDENCE OF HIGH LEVELS OF METHEMOGLOBIN IN PATIENTS USING A NEW PULSE CO-OXIMETER.

Methemoglobin is hemoglobin with iron in a ferric state instead of a ferrous state, thus unable to carry oxygen causing cyanosis and a left shift of the oxyhemoglobin dissociation curve. Methemoglobinemia, either congenital or acquired, is a rare clinical occurrence and can be life threatening for individuals with levels greater than 20%. Acquired methemoglobinemia has multiple etiologies and is commonly caused by topical anesthetic drugs such as benzocaine, prilocaine, and lidocaine. Nitrates, both topical and intravenous, can also precipitate clinically significant levels. The inherited form of methemoglobinemia is rare and generally presents early in life. Until recently, the only method for measuring methemoglobin levels was to send a blood sample for co-oximetry analysis. Conventional dual-wavelength pulse oximetry does not detect methemoglobin levels and its mearsurement of oxygen saturation becomes unreliable in the setting of even small levels of methemoglobin in the blood. Recently, a new mutiwavelength pulse co-oximeter was developed that enables the detection of methemoglobin and carboxyhemoglobin (Masimo RAD 57 pulse co-oximeter, Irvine, CA). After institutional review board approval, we performed a prospective study to determine the incidence of elevated methemoglobin levels in 500 patients on medications known to cause elevations in methemoglobin levels. All patients were screened using the new pulse co-oximeter to determine the methemoglobin levels. Patients with clinically significant elevations in methemoglobin levels were referred to clinicians for further evaluation and treatment. Of the patients screened, 498 patients had clinically insignificant methemoglobin levels. Two patients exposed to benzocaine, a topical anesthetic, were found to have serious elevations in methemoglobin levels. One patient with benzocaine toxicity was found to have initial methemoglobin levels of 38.9 to 45.8% using the pulse co-oximeter. This level was confirmed with co-oximetry analysis. The second patient was discovered just after the initiation of methylene blue therapy for a methemoglobin level of 24%. The results of this study demonstrate the need to monitor patients exposed to triggering medications. Both patients with elevated methemoglobin levels were successfully treated. Of these patients with benzocaine toxicity only one of them was recognized by clinicians prior to diagnosis using the pulse co-oximeter. The pulse co-oximeter is portable and small; it provides an opprtunity for early noninvasive diagnosis of high methemoglobin level at a low cost.