Cardiovascular effects of intravenous midazolam after open heart surgery

Efficacy of Single-Bolus Administration of Remimazolam During Induction of Anesthesia in Patients Undergoing Cardiac Surgery: A Prospective, Single-Center, Randomized Controlled Study

BACKGROUND

Remimazolam is a recently marketed ultrashort-acting benzodiazepine. This drug is considered safe and effective during general anesthesia; however, limited information is available about its effects on patients undergoing cardiac surgery. Therefore, the present study was conducted to evaluate the efficacy and hemodynamic stability of a bolus administration of remimazolam during anesthesia induction in patients undergoing cardiac surgery.

METHODS

Patients undergoing elective cardiac surgery were randomly assigned to any 1 of the following 3 groups: anesthesia induction with a continuous infusion of remimazolam 6 mg/kg/h (continuous group), a single-bolus injection of remimazolam 0.1 mg/kg (bolus 0.1 group), or a single-bolus injection of remimazolam 0.2 mg/kg (bolus 0.2 group). Time to loss of responsiveness, defined as modified Observer's Assessment of Alertness/Sedation Scale <3, and changes in hemodynamic status during anesthetic induction were measured.

RESULTS

Times to loss of responsiveness were 137 ± 20, 71 ± 35, and 48 ± 9 seconds in the continuous, bolus 0.1, and bolus 0.2 groups, respectively. The greatest mean difference was observed between the continuous and bolus 0.2 groups (89.0, 95% confidence interval [CI], 79.1-98.9), followed by the continuous and bolus 0.1 groups (65.8, 95% CI, 46.9-84.7), and lastly between the bolus 0.2 and bolus 0.1 groups (23.2, 95% CI, 6.6-39.8). No significant differences were found in terms of arterial blood pressures and heart rates of the patients.

CONCLUSIONS

A single-bolus injection of remimazolam provided efficient anesthetic induction in patients undergoing cardiac surgery. A 0.2 mg/kg bolus injection of remimazolam resulted in the shortest time to loss of responsiveness among the 3 groups, without significantly altering the hemodynamic parameters. Therefore, this dosing can be considered a favorable anesthetic induction method for patients undergoing cardiac surgery.

Navigating the complex landscape of benzodiazepine- and Z-drug diversity: insights from comprehensive FDA adverse event reporting system analysis and beyond

Introduction

Medications which target benzodiazepine (BZD) binding sites of GABAA receptors (GABAARs) have been in widespread use since the nineteen-sixties. They carry labels as anxiolytics, hypnotics or antiepileptics. All benzodiazepines and several nonbenzodiazepine Z-drugs share high affinity binding sites on certain subtypes of GABAA receptors, from which they can be displaced by the clinically used antagonist flumazenil. Additional binding sites exist and overlap in part with sites used by some general anaesthetics and barbiturates. Despite substantial preclinical efforts, it remains unclear which receptor subtypes and ligand features mediate individual drug effects. There is a paucity of literature comparing clinically observed adverse effect liabilities across substances in methodologically coherent ways.

Methods

In order to examine heterogeneity in clinical outcome, we screened the publicly available U.S. FDA adverse event reporting system (FAERS) database for reports of individual compounds and analyzed them for each sex individually with the use of disproportionality analysis. The complementary use of physico-chemical descriptors provides a molecular basis for the analysis of clinical observations of wanted and unwanted drug effects.

Results and Discussion

We found a multifaceted FAERS picture, and suggest that more thorough clinical and pharmacoepidemiologic investigations of the heterogenous side effect profiles for benzodiazepines and Z-drugs are needed. This may lead to more differentiated safety profiles and prescription practice for particular compounds, which in turn could potentially ease side effect burden in everyday clinical practice considerably. From both preclinical literature and pharmacovigilance data, there is converging evidence that this very large class of psychoactive molecules displays a broad range of distinctive unwanted effect profiles - too broad to be explained by the four canonical, so-called "diazepam-sensitive high-affinity interaction sites". The substance-specific signatures of compound effects may partly be mediated by phenomena such as occupancy of additional binding sites, and/or synergistic interactions with endogenous substances like steroids and endocannabinoids. These in turn drive the wanted and unwanted effects and sex differences of individual compounds.

A Pharmacokinetic-Pharmacodynamic Study of Intravenous Midazolam and Flumazenil in Adult New Zealand White-Californian Rabbits (Oryctolagus cuniculus)

Flumazenil, a competitive GABAA receptor antagonist, is commonly used in rabbits to shorten sedation or postanesthetic recovery after benzodiazepine administration. However, no combined pharmacokinetic (PK) and pharmacodynamic (PD) data are available to guide its administration in this species. In a prospective, randomized, blinded, crossover study design, the efficacy of IV flumazenil (FLU; 0.05 mg/kg) or saline control (SAL; equal volume) to reverse the loss of righting reflex (LORR) induced by IV midazolam (1.2 mg/kg) was investigated in 15 New Zealand white rabbits (2.73 to 4.65 kg, 1 y old). Rabbits were instrumented with arterial (central auricular artery) and venous (marginal auricular vein) catheters. After baseline blood sampling, IV midazolam was injected (T0). Flumazenil or saline (FLU/SAL) was injected 30 s after LORR. Arterial blood samples were collected at 1 and 3 min after midazolam injection, and at 1, 3, 6, 10, 15, 21, 28, 36, 45 and 60 min after injection with flumazenil. Plasma samples for midazolam, 1-OH-midazolam and flumazenil were analyzed using high performance liquid chromatography-high-resolution mass spectrometry and the time to return of righting reflex (ReRR) was compared between groups (Wilcoxon test). FLU terminal half-life, plasma clearance and volume of distribution were 26.3 min [95%CI: 23.3 to 29.3], 18.74 mL/min/kg [16.47 to 21.00] and 0.63 L/kg [0.55 to 0.71], respectively. ReRR was 25 times faster in rabbits treated with FLU (23 [8 to 44] s) compared with SAL (576 [130 to 1141] s; 95%CI [425 to 914 s]). Return of sedation (lateral recumbency) occurred in both groups (7/13 in FLU; 12/13 in SAL) with return of LORR in a few animals (4/13 in FLU; 7/13 in SAL) at 1540 [858 to 2328] s. In the population and anesthesia protocol studied, flumazenil quickly and reliably reversed sedation induced by midazolam injection. However, the potential return of sedation after flumazenil administration warrants careful monitoring in the recovery period.

Impact of Anesthetic and Ventilation Strategies on Invasive Hemodynamic Measurements in Pediatric Heart Transplant Recipients

BACKGROUND

Care of pediatric heart transplant recipients relies upon serial invasive hemodynamic evaluation, generally performed under the artificial conditions created by anesthesia and supportive ventilation.

OBJECTIVES

This study aimed to evaluate the hemodynamic impacts of different anesthetic and ventilatory strategies.

METHODS

We compared retrospectively the cardiac index, right- and left-sided filling pressures, and pulmonary and systemic vascular resistances of all clinically well and rejection-free heart transplant recipients catheterized from 2005 through 2017. Effects of spontaneous versus positive pressure ventilation and of sedation versus general anesthesia were tested with generalized linear mixed models for repeated measures using robust sandwich estimators of the covariance matrices. Least squared means showed adjusted mean outcome values, controlled for appropriate confounders.

RESULTS

720 catheterizations from 101 recipients met inclusion criteria. Adjusted cardiac index was 3.14 L/min/m² (95% CI 3.01-3.67) among spontaneously breathing and 2.71 L/min/m² (95% CI 2.56-2.86) among ventilated recipients (p < 0.0001). With spontaneous breathing, left filling pressures were lower (9.9 vs 11.0 mmHg, p = 0.030) and systemic vascular resistances were higher (24.0 vs 20.5 Woods units, p < 0.0001). After isolating sedated from anesthetized spontaneously breathing patients, the observed differences in filling pressures and resistances emerged as a function of sedation versus general anesthesia rather than of spontaneous versus positive pressure ventilation.

CONCLUSION

In pediatric heart transplant recipients, positive pressure ventilation reduces cardiac output but does not alter filling pressures or vascular resistances. Moderate sedation yields lower left filling pressures and higher systemic vascular resistances than does general anesthesia. Differences are quantitatively small.

Nasal midazolam vs ketamine for neonatal intubation in the delivery room: a randomised trial

OBJECTIVE

To compare the effectiveness of sedation by intranasal administration of midazolam (nMDZ) or ketamine (nKTM) for neonatal intubation.

DESIGN

A multicentre, prospective, randomised, double-blind study.

SETTING

Delivery rooms at four tertiary perinatal centres in France.

PATIENTS

Preterm neonates with respiratory distress requiring non-emergent endotracheal intubation for surfactant instillation.

INTERVENTIONS

Treatment was randomly allocated, with each neonate receiving a bolus of 0.1 mL/kg in each nostril, corresponding to 0.2 mg/kg for nMDZ and 2 mg/kg for nKTM. The drug was repeated once 7 min later at the same dose if adequate sedation was not obtained.

MAIN OUTCOME MEASURES

Success was defined by adequate sedation before intubation and adequate comfort during the procedure. Intubation features, respiratory and cardiovascular events were recorded.

RESULTS

Sixty newborns, with mean (SD) gestational age and birth weight of 28 (3) weeks and 1100 (350) g, were included within the first 20 min of life. nMDZ was associated with a higher success rate (89% vs 58%; RR: 1.54, 95% CI 1.12 to 2.12, p<0.01) and shorter delays between the first dose and intubation (10 (6) vs 16 (8) min, p<0.01).Number of attempts, time to intubation, mean arterial blood pressure measures over the first 12 hours after birth and length of invasive ventilation were not different.

CONCLUSIONS

nMDZ was more efficient than nKTM to adequately sedate neonates requiring intubation in the delivery room. The haemodynamic and respiratory effects of both drugs were comparable.

CLINICAL TRIAL

This clinical trial was recorded on the National Library of Medicine registry (NCT01517828).

Implementation of a Nurse-Driven Sedation Protocol in a PICU Decreases Daily Doses of Midazolam

OBJECTIVES

To evaluate the impact of a nurse-driven sedation protocol on the length of mechanical ventilation, total daily doses of sedatives, and complications of sedation.

DESIGN

A single-center prospective before and after study was conducted from October 2010 to December 2013.

SETTING

Twelve-bed surgical and medical PICU of the university-affiliated hospital in Nantes, France.

PATIENTS

A total of 235 patients, between 28 days and 18 years old, requiring mechanical ventilation for at least 24 hours were included in the study; data from 194 patients were analyzed.

INTERVENTIONS

During the first study phase, no protocol was used. During the second phase, patients were sedated according to a nurse-driven protocol.

MEASUREMENTS AND MAIN RESULTS

In the whole population, the length of mechanical ventilation did not differ between protocol and control groups (protocol, 4 [3-8] vs control, 5 [3-7.5]; p = 0.44). Analyzing age subgroups, the length of mechanical ventilation was significantly shorter in the protocol group than in the control group in children older than 12 months (4 [3-8] vs 5 [2.75-11.25] d; p = 0.04). Daily dose of midazolam decreased during the protocol phase compared with the control phase (1 [0.56-1.8] and 1.2 [0.85-2.4] mg/kg/d, respectively; p = 0.02). No differences were shown regarding other daily dose of drugs. In the control group, 68% of children had more than 20% of COMFORT-behavior scale assessment under the target (oversedation) versus 59% in the protocol group (p = 0.139).

CONCLUSIONS

Implementation of a nurse-driven sedation protocol in a PICU is feasible and safe, allowed a decrease in daily dose of benzodiazepines, and decreased the duration of mechanical ventilation in older patients.

A Comparative Analysis of Preemptive Versus Targeted Sedation on Cardiovascular Stability After High-Risk Cardiac Surgery in Infants

OBJECTIVE

To compare the effect of two sedation practices on cardiovascular stability during the early postoperative period in young infants following cardiac surgery: the routine early use of midazolam infusion (preemptive sedation) and the discretionary use of sedatives tailored to the patient's clinical condition (targeted sedation).

DESIGN

Retrospective cohort study with matched controls.

SETTING

A 15-bedded pediatric cardiac ICU.

PATIENTS

Sedation strategies were compared by matching patients before and after the introduction of a targeted sedation guideline, replacing the existing practice of preemptive sedation. Inclusion criteria were age less than 6 months and cardiopulmonary bypass time greater than 150 minutes. Matching criteria were surgical procedure, age, and duration of cardiopulmonary bypass and cross-clamp. The main outcome was cardiovascular instability, defined by the presence of one of the following criteria in the first 12 hours after PICU admission: 1) simultaneous administration of greater than or equal to two inotropic or vasopressor drugs; 2) administration of greater than 60 mL/kg fluid boluses. Secondary outcomes were: 1) markers of cardiac output adequacy (heart rate, blood pressure, vasoactive inotropic score, urine output, volume of fluid boluses, central venous oxygen saturation, lactate); 2) occurrence of adverse events (cardiac arrest, extracorporeal membrane oxygenation, death); 3) sedatives administered and depth of sedation.

INTERVENTIONS

Introduction of a guideline of targeted sedation.

MEASUREMENTS AND MAIN RESULTS

Thirty-three patients with preemptive sedation were matched to 33 patients with targeted sedation. Targeted sedation resulted in less frequent oversedation, without compromising cardiovascular stability, as indicated by similar occurrence of cardiovascular instability (68.8% with preemptive sedation vs 62.5% with targeted sedation; p = 0.53) and adverse events, and similar markers of cardiac output adequacy. Although all preemptively sedated patients received an infusion of midazolam in the first 12 hours after surgery, only 19.4% of patients in the targeted sedation group received a sedative infusion (p < 0.001).

CONCLUSIONS

Our data suggest that after high-risk cardiac surgery in young infants, routine sedation with midazolam may not prevent low cardiac output syndrome. When accompanied by a careful assessment of level of sedation, routine sedation of infants after high-risk cardiac surgery can be avoided without compromising hemodynamic stability or patient safety. The potential benefit of this approach is reduced exposure to sedative.

Sedation in Critically Ill Children with Respiratory Failure

This article discusses the rationale of sedation in respiratory failure, sedation goals, how to assess the need for sedation as well as effectiveness of interventions in critically ill children, with validated observational sedation scales. The drugs and non-pharmacological approaches used for optimal sedation in ventilated children are reviewed, and specifically the rationale for drug selection, including short- and long-term efficacy and safety aspects of the selected drugs. The specific pharmacokinetic and pharmacodynamic aspects of sedative drugs in the critically ill child and consequences for dosing are presented. Furthermore, we discuss different sedation strategies and their adverse events, such as iatrogenic withdrawal syndrome and delirium. These principles can guide clinicians in the choice of sedative drugs in pediatric respiratory failure.

Intubation in the delivery room: experience with nasal midazolam

BACKGROUND

Neonates are often intubated in the delivery room (DR) without anesthesia because vascular access is impossible.

AIMS

To assess neonatal comfort and adverse events after use of nasal midazolam (nMDZ) for intubation in the DR.

STUDY DESIGN

Prospective data collection over 6months on the intubation of neonates with respiratory distress requiring tracheal instillation of surfactant.

SUBJECTS

Twenty-seven neonates with median (Q25-75) gestational age and birthweight of, respectively, 29 (27-33)weeks and 1270 (817-1942)g received a 0.1mg/kg dose of nMDZ, and intubation was performed at the onset of tonus resolution or apnea.

OUTCOME MEASURES

Comfort was assessed with a scale of hetero-pain assessment and electrical skin conductance monitoring. Continuous pulse oximetry was recorded in the first postnatal hour, with oscillometric blood pressure measurement every 10min.

RESULTS

Seventy percent of the patients required a single dose, with intubation performed 4.8 (3-9)min after administration. Combined electro-clinical assessment found adequate comfort during the procedure in 68% of neonates. Mean blood pressure decreased from 39 (34-44)mmHg before to 31 (25-33)mmHg 1h following nMDZ (p=0.011).

CONCLUSION

nMDZ provided rapid and effective sedation to intubate neonates in the DR but potentially exposed them to hypotension, thus requiring close hemodynamic monitoring.

Premedication for neonatal intubation: Current practice in Saudi Arabia

BACKGROUND

Despite strong evidence of the benefits of rapid sequence intubation in neonates, it is still infrequently utilized in neonatal intensive care units (NICU), contributing to avoidable pain and secondary procedure-related physiological disturbances.

OBJECTIVES

The primary objective of this cross-sectional survey was to assess the practice of premedication and regimens commonly used before elective endotracheal intubation in NICUs in Saudi Arabia. The secondary aim was to explore neonatal physicians' attitudes regarding this intervention in institutions across Saudi Arabia.

METHODS

A web-based, structured questionnaire was distributed by the Department of Pediatrics, Umm Al Qura University, Mecca, to neonatal physicians and consultants of 10 NICUs across the country by E-mail. Responses were tabulated and descriptive statistics were conducted on the variables extracted.

RESULTS

85% responded to the survey. Although 70% believed it was essential to routinely use premedication for all elective intubations, only 41% implemented this strategy. 60% cited fear of potential side effects for avoiding premedication and 40% indicated that the procedure could be executed more rapidly without drug therapy. Treatment regimens varied widely among respondents.

CONCLUSION

Rates of premedication use prior to non-emergent neonatal intubation are suboptimal. Flawed information and lack of unified unit policies hampered effective implementation. Evidence-based guidelines may influence country-wide adoption of this practice.

The role of systematic reviews in pharmacovigilance planning and Clinical Trials Authorisation application: example from the SLEEPS trial

BACKGROUND

Adequate sedation is crucial to the management of children requiring assisted ventilation on Paediatric Intensive Care Units (PICU). The evidence-base of randomised controlled trials (RCTs) in this area is small and a trial was planned to compare midazolam and clonidine, two sedatives widely used within PICUs neither of which being licensed for that use. The application to obtain a Clinical Trials Authorisation from the Medicines and Healthcare products Regulatory Agency (MHRA) required a dossier summarising the safety profiles of each drug and the pharmacovigilance plan for the trial needed to be determined by this information. A systematic review was undertaken to identify reports relating to the safety of each drug.

METHODOLOGY/PRINCIPAL FINDINGS

The Summary of Product Characteristics (SmPC) were obtained for each sedative. The MHRA were requested to provide reports relating to the use of each drug as a sedative in children under the age of 16. Medline was searched to identify RCTs, controlled clinical trials, observational studies, case reports and series. 288 abstracts were identified for midazolam and 16 for clonidine with full texts obtained for 80 and 6 articles respectively. Thirty-three studies provided data for midazolam and two for clonidine. The majority of data has come from observational studies and case reports. The MHRA provided details of 10 and 3 reports of suspected adverse drug reactions.

CONCLUSIONS/SIGNIFICANCE

No adverse reactions were identified in addition to those specified within the SmPC for the licensed use of the drugs. Based on this information and the wide spread use of both sedatives in routine practice the pharmacovigilance plan was restricted to adverse reactions. The Clinical Trials Authorisation was granted based on the data presented in the SmPC and the pharmacovigilance plan within the clinical trial protocol restricting collection and reporting to adverse reactions.

Premedication for endotracheal intubation in the newborn infant

Endotracheal intubation, a common procedure in newborn care, is associated with pain and cardiorespiratory instability. The use of premedication reduces the adverse physiological responses of bradycardia, systemic hypertension, intracranial hypertension and hypoxia. Perhaps more importantly, premedication decreases the pain and discomfort associated with the procedure. All newborn infants, therefore, should receive analgesic premedication for endotracheal intubation except in emergency situations. Based on current evidence, an optimal protocol for premedication is to administer a vagolytic (intravenous [IV] atropine 20 μg/kg), a rapid-acting analgesic (IV fentanyl 3 μg/kg to 5 μg/kg; slow infusion) and a short-duration muscle relaxant (IV succinylcholine 2 mg/kg). Intubations should be performed or supervised by trained staff, with close monitoring of the infant throughout.

Premedication for nonemergency endotracheal intubation in the neonate

Endotracheal intubation is a common procedure in newborn care. The purpose of this clinical report is to review currently available evidence on use of premedication for intubation, identify gaps in knowledge, and provide guidance for making decisions about the use of premedication.

Cardiovascular manifestations of sedatives and analgesics in the critical care unit

There are numerous sedatives and analgesics used in critical care medicine today; these medications are used on critically ill patients, many of whom have heart disease, including coronary artery disease or congestive heart failure. The purpose of this review is to recognize the effects of these medications on the heart. Studies that evaluated the effects of sedatives and analgesics on normal individuals or on those with heart disease were reviewed. Current choices for sustained sedation in the critically ill include the benzodiazepines, morphine, propofol, and etomidate. Each of these medications has their particular advantages and disadvantages. Benzodiazepines provide the greatest amnesia and cardiovascular safety but they can cause significant hypotension in the hemodynamically unstable patient. Morphine provides analgesia and cardioprotective activity after ischemia, although the large observational study CRUSADE showed increased mortality rate in those patients with non-ST segment elevation myocardial infarction who received morphine. Propofol is the most easily titratable drug with cardioprotective features, but its use must be accompanied with great attention to possible development of propofol infusion syndrome, which is a deadly disease, especially in patients with head injury and those with septic shock receiving vasopressors. Etomidate has a rapid onset effect and short period of action with great hemodynamic stability even in patients with shock and hypovolemia, but the incidence of adrenal insufficiency during infusion, not bolus doses, may cause deterioration in the circulatory stability. In conclusion, the sedatives and analgesics mentioned here have characteristics that give them a cardiovascular safety profile useful in critically ill patients. However, use of these drugs on an individual basis is dependent on each agent's safety and efficacy.

Preconditioning abolishion by midazolam in isolated hearts of rats

PURPOSE

To study the effects of benzodiazepine midazolam in the coronary flow (Cflo), cardiac frequency (CF) and myocardial contractility in isolated hearts of rats subjected to ischemic preconditioning (IPC).

METHODS

30 Wistar rats were used, undistinguished by gender. After anesthesia with ethyl ether, the hearts were put into perfusion (Krebs-Henseleit solution, 95% O2 and 5% CO2, 37 degrees C, 110-120mmHg), in disposable Langendorff type system. Five groups of six animals were constituted: GI- Control; GII- Ischemia; GIII- IPC; GIV- Ischemia + 100mcg of midazolam; GV- IPC + 100mcg of midazolam. After stabilization (t0), and on times t5, t10, t15, t20 and t25, CF, Cflo, systolic pressure (SP) and diastolic pressure (DP) and dP/dt were recorded. DP was maintained at 5 +/- 2 mmHg. The statistical method ANOVA and Tukey Test were employed for p < or = 0.05.

RESULTS

No significant variations have occurred between Cflo and CF. On Pd/td, differences have occurred (p<0.05) between groups I and II (respectively 94.7+/-23.0 and 62.3+/-12.1%). The preconditioning (GIII), improved significantly the results in the group II (respectively 62.3+/-12.1 and 87.1+/-12.4 %). The decrease in dP/dt in group II was not prevented by midazolam (GIV) (62.3+/-12,1 and 60.5+/-15.8 %). In group III, dP/dt was 87.1+/-12.4%, whereas in group V, only 55.5+/-17.2% (p<0.05)

CONCLUSION

Midazolam, when administered before the ischemia, was unable to prevent the ischemic deterioration of the myocardium. When administered before the preconditioning, it has abolished its protective effect.

Pädiatrische Intensivmedizin

Dieses Kapitel soll einen verständlichen Überblick geben über Besonderheiten der intensivmedizinischen Betreuung des Kindes, insbesondere des Kleinkindes, im Vergleich zur Intensivmedizin beim Erwachsenen. Es werden deshalb nicht alle Aspekte der pädiatrischen Intensivmedizin im Sinne eines eigenständigen Lehrbuchs beleuchtet. In einem ersten Teil (·Kap. 84.2-84.4) werden allgemeine Themen und Aspekte inklusive die kardiopulmonale Reanimation behandelt, in einem zweiten Teil (·Kap. 84.5) werden spezifische pädiatrische Krankheitsbilder und ihre Therapie diskutiert.

The influence of diazepam and midazolam on adenosine-induced forearm vasodilation in humans

Adenosine is an endogenous purine with vasodilating and cardioprotective properties. Animal experiments have shown that some benzodiazepine-induced effects can be explained by potentiation of adenosine effects, via inhibition of the nucleoside transport system. The objective of this study was to determine whether the frequently used benzodiazepines diazepam and midazolam increase adenosine-induced vasodilation in the human forearm vascular bed, measured by venous occlusion plethysmography. Adenosine (0.6, 6, 20, and 60 nmol/min/dl ForeArm Volume) was infused into the brachial artery with and without concomitant separate infusion of diazepam (21 nmol/min/dl, n = 9) and midazolam (23 nmol/min/dl, n = 8). Plasma concentrations of diazepam resp. midazolam at the end of the infusion protocol averaged 0.5 +/- 0.2 microg/ml plasma (1.6 microM) for diazepam versus 1.2 +/- 0.4 microg/ml plasma (3 microM) for midazolam. Intra-arterial infusion of the benzodiazepines did not alter baseline vascular tone, and had no significant influence on the forearm vasodilator response to adenosine. The adenosine-induced relative change in Forearm Vascular Resistance (FVR) was -3 +/- 7, -48 +/- 8, -75 +/- 6, and -85 +/- 3% in the absence and 3.5 +/- 11, -54 +/- 5, -74 +/- 5, and -82 +/- 3% resp. in the presence of diazepam (P > 0.1, repeated measures ANOVA, n = 9). Likewise, in the absence resp. presence of midazolam, FVR fell by 1 +/- 6, 55 +/- 5, 74 +/- 3, and 84 +/- 2% resp. 11 +/- 11, 59 +/- 2, 80 +/- 3, and 87 +/- 2% (P > 0.1, n = 7). Intra-brachial infusion of diazepam and midazolam resulting in forearm concentrations in the high therapeutic range does not augment adenosine-induced forearm vasodilation. A possible interaction at supra-therapeutic levels of the benzodiazepines can not be excluded from the present study, but lacks clinical significance.

Cardiovascular changes during mild therapeutic hypothermia and rewarming in infants with hypoxic-ischemic encephalopathy

BACKGROUND

Clinical trials of mild cooling to 35 degrees C or below in infants with early hypoxic-ischemic encephalopathy are under way. The objective of this study was to systematically document cardiovascular changes associated with mild therapeutic hypothermia and rewarming in such infants.

PATIENTS AND METHODS

Nine infants with gestational ages of 36 to 42 weeks, with 10-minute Apgar scores of 5 or less, clinical encephalopathy, and an abnormal electroencephalogram before 6 hours were cooled by surface cooling the trunk (n = 3) or by applying a cap perfused with cooled water (n = 6) for a median of 72 hours. The target core temperature was 34.0 degrees C to 35.0 degrees C for head-cooled infants and 33.0 degrees C to 34.0 degrees C for surface-cooled infants. Maintenance heating and rewarming were provided by an overhead heater.

RESULTS

Mean arterial blood pressure increased by a median of 10 mm Hg during cooling and fell by a median of 8 mm Hg on rewarming. Heart rate decreased by a median of 34 beats/minute on cooling and increased by a median of 32 beats/minute on rewarming. A large increase in the output of the overhead heater decreased mean arterial blood pressure in 5 infants. Anticonvulsant drugs, sedatives, or intercurrent hypoxemia also produced falls in temperature. The inspired oxygen fraction had to be increased by a median of.14 to maintain oxygenation during cooling with 2 infants requiring 100% oxygen, an effect probably attributable to pulmonary hypertension, which was reversible with rewarming.

CONCLUSIONS

Therapeutic cooling produces changes in heart rate and blood pressure that are not hazardous, but the combination of inadvertent overcooling and inappropriately rapid rewarming, together with sedative drugs that can impair normal thermoregulatory vasoconstriction, can cause hypotension in posthypoxic newborn infants. Infants who already require 50% oxygen should be cooled cautiously because pulmonary hypertension may develop. Knowledge of these cardiovascular changes, careful monitoring, anticipation, and correction should help to avoid potential adverse effects in the upcoming clinical trials.

L-arginine and substance P reverse the pulmonary endothelial dysfunction caused by congenital heart surgery

BACKGROUND

The increase in pulmonary vascular resistance (PVR) seen in children after cardiopulmonary bypass has been attributed to transient pulmonary endothelial dysfunction (PED). We therefore examined PED in children with congenital heart disease by assessing the L-arginine-nitric oxide (NO) pathway in terms of substrate supplementation (L-arginine [L-Arg]), stimulation of endogenous NO release (substance P [Sub-P]), and end-product provision (inhaled NO) before and after open heart surgery.

METHODS AND RESULTS

Ten patients (aged 0.62+/-0.27 years) with pulmonary hypertension undergoing cardiac catheterization who had not had surgery and 10 patients (aged 0.65+/-0.73 years) who had recently undergone cardiopulmonary bypass were examined. All were sedated and paralyzed and received positive-pressure ventilation. Blood samples and pressure measurements were taken from catheters in the pulmonary artery and the pulmonary vein or left atrium. Respiratory mass spectrometry was used to measure oxygen uptake, and cardiac output was determined by the direct Fick method. PVR was calculated during steady state at ventilation with room air, during FIO(2) of 0.65, then during additional intravenous infusion of L-Arg (15 mg. kg(-1). min(-1)) and Sub-P (1 pmol. kg(-1). min(-1)), and finally during inhalation of NO (20 ppm). In preoperative patients, the lack of an additional significant change of PVR with L-Arg, Sub-P, and inhaled NO suggests little preexisting PED. Postoperative PVR was higher, with an additional pulmonary endothelial contribution that was restorable with L-Arg and Sub-P.

CONCLUSIONS

Postoperatively, the rise in PVR suggested PED, which was restorable by L-Arg and Sub-P, with no additional effect of inhaled NO. These results may indicate important new treatment strategies for these patients.