Benjamin Drenger

Systolic Pressure Variation Predicts the Response to Acute Blood Loss

STUDY OBJECTIVEnTo evaluate systolic pressure variation (SPV), defined as the difference between the maximum and minimum systolic blood pressure measured during a controlled mechanical respiratory cycle, as a predictor of the cardiac output (CO) response to an acute decrease in ventricular preload.nnnDESIGNnProspective study with each subject serving as his or her own control.nnnSETTINGnCardiac surgery operating rooms of a university medical center.nnnPATIENTSn15 adults with good ventricular function undergoing coronary artery bypass grafting.nnnINTERVENTIONnDuring stable anesthetic conditions and before surgical stimulation, 500 ml of blood was removed from each patient over 10 minutes.nnnMEASUREMENTS AND MAIN RESULTSnCO, central venous pressure (CVP), pulmonary artery diastolic pressure, and pulmonary artery occlusion pressure (PAOP), and SPV before and after phlebotomy were recorded. Phlebotomy was associated with significant decreases in CVP, PAOP, and CO, and an increase in SPV. Of these variables, SPV was the best predictor of the percent decrease in CO resulting from blood loss.nnnCONCLUSIONnSPV is a dynamic measurement, which, by revealing the response to small cyclical changes in left ventricular preload that occur during the controlled mechanical respiratory cycle, is a better predictor than central filling pressures of the response of CO to acute decreases in preload that occur as a result of acute blood loss.

Urinary function during epidural analgesia with methadone and morphine in post-cesarean section patients

&NA; Urinary function was assessed in 120 women after cesarean section under epidural anesthesia. Postoperative analgesia was obtained by means of epidurally administered methadone (40 patients) or morphine (40 patients). In the remaining 40 women, no narcotic drugs were given and postoperative pain was treated with intramuscular or oral non‐opiate analgesics and sedatives. Both methadone and morphine provided potent postoperative pain relief. Following epidural methadone, mean urine volumes of the first two postoperative voidings were increased (543 ± 38n ml and 571 ± 31 ml) as compared with those after epidural morphine (219 ± 25 ml and 218 ± 18 ml) and with those of patients receiving non‐opiate analgesics (319 ± 28ml and 414 ± 30 ml). The mean time interval between the end of surgery and first voiding following methadone analgesia was shorter (336 ± 27 min) than after morphine (582 ± 18 min) or after non‐opiate (448 ± 28 min) analgesic drugs. Difficulty in micturition and the need for bladder catheterization were also decreased in the group with epidural methadone (2.5%) in comparison with the groups receiving morphine (57.5%) or non‐opiate analgesic medicaments (12.5%). The use of epidural methadone for postoperative pain relief is advocated, both in view of its analgesic potency and of the low incidence of urinary disturbances.

Spinal cord stimulation evoked potentials during thoracoabdominal aortic aneurysm surgery

Although monitoring of somatosensory evoked potentials elicited from stimulation of lower extremity peripheral nerves has been suggested as a method for assessing neural function during thoracoabdominal aortic aneurysm surgery, this technique has been reported to yield a large number of false positives. It was believed that direct stimulation of the spinal cord would eliminate some of the problems associated with peripheral evoked potentials. The present study compared in 18 patients the use of scalp recorded evoked potential following stimulation of either the posterior tibial nerve via percutaneous needles or the spinal cord via an epidural electrode previously placed fluoroscopically. In 10 patients in whom distal bypass or shunt was not used, peripheral evoked potentials totally disappeared within 5-30 min of aortic clamping. Spinal cord stimulation evoked potentials disappeared permanently in 2 patients shortly after aortic cross-clamping; 1 died shortly after the procedure, and the other awoke densely paraplegic and died the next day. When distal perfusion was maintained by shunt or bypass, the disappearance of both peripheral and spinal evoked potentials accurately predicted the neurologic outcome of 1 paralyzed patient. Loss of spinal cord stimulation evoked potentials was found to be correlated with adverse neurologic outcome. Over the period of aortic clamping a gradual decrease in mean amplitude (50% at 45 min [P less than 0.05]) and a 20% increase in mean latency time were observed. Maintenance of adequate distal perfusion may permit the use of peripheral evoked potentials in the assessment of spinal cord ischemia during aortic cross-clamping.(ABSTRACT TRUNCATED AT 250 WORDS)

The action of intrathecal morphine and methadone on the lower urinary tract in the dog.

The effects of intrathecally administered morphine and methadone on lower urinary tract dynamics were investigated by cystometrograms and urethral pressure profiles in 16 anesthetized dogs. The examinations were performed before and 30, 60 and 90 minutes following intrathecal injection of 0.03 mg./kg. morphine or methadone. Intrathecal normal saline was used for control studies. Significant relaxation of the detrusor was noted after intrathecal morphine as expressed by a decrease in mean intravesical pressure (p less than 0.05) and by a rise in the calculated detrusor compliance. These effects were reversed by intravenously injected naloxone. As opposed to morphine, methadone caused an increase in detrusor tone. No appreciable effects were observed on the urethra after intrathecal morphine or methadone. Neither intravenous injection of the opiates nor intrathecal administration of saline caused alterations in bladder tone. The result may imply a spinal, albeit opposing, effect of the two opiates on bladder dynamics.

Volatile anesthetics depress calcium channel blocker binding to bovine cardiac sarcolemma

Volatile anesthetics produce their negative inotropic effect on the heart mainly by interference with calcium homeostasis in the myocardial cell. In order to elucidate the mechanism of the depression, we have evaluated the effect of the volatile anesthetics on the binding of the calcium channel blocker [3H]nitrendipine to purified bovine cardiac sarcolemma. The radioligand binding studies were carried out at 25 degrees C, with increasing concentrations of [3H]nitrendipine (0.01-1 nM), in the presence or absence of unlabeled nitrendipine to determine specific binding, and with or without 1.9% halothane, 2.3% isoflurane, and 4.8% enflurane. Separately, [3H]nitrendipine was measured in the presence of increasing doses of halothane (0.78, 1.33, 1.90, and 2.57%). Kinetic studies of association and dissociation rate were performed with 1.90% halothane and 1 nM [3H]nitrendipine at different time intervals. All three volatile anesthetics produced depression of [3H]nitrendipine binding to the isolated cardiac sarcolemma. Only halothane produced a significant depression in binding, ranging between 59 and 66% (P less than 0.05), depending on the concentration of [3H]nitrendipine used. Isoflurane produced 29-38% depression, and enflurane produced 5-22% depression. Halothane also produced a significant (P less than 0.01) dose-dependent decrease in [3H]nitrendipine-specific binding. The kinetic binding experiments demonstrated that the time course for halothanes effect on association and dissociation of [3H]nitrendipine was 5 min for the half-maximum effect; the maximal reduction in binding capacity was at 15-30 min (P less than 0.05). Scatchard analysis revealed that all three volatile anesthetics produced reduction in the maximal number of binding sites; however, they varied in their effect on binding affinity. Only halothane produced a homogenous increase in the dissociation constant, signifying reduced affinity of the Ca2+ blocker to the channel. We suggest that the volatile anesthetics produce conformational changes in these channels consistent with their ability to depress channel-mediated Ca2+ influx into myocytes.

Urodynamic Studies After Intrathecal Administration of Baclofen and Morphine in Dogs

The effects of intrathecally administered baclofen and morphine on the lower urinary tract dynamics of anesthetized dogs were investigated by means of cystometrogram and urethral pressure profile measurement. The experiments were performed prior to and 30, 60 and 90 minutes following intrathecal injection of either baclofen (0.03 mg./kg.), morphine (0.03 mg./kg.), or a mixture of the two (0.03 mg./kg. of each drug). Vesical pressure was significantly depressed after either baclofen (p less than 0.005) or morphine (p less than 0.005), while urethral pressure was decreased significantly only following baclofen (p less than 0.025). Administration of a baclofen/morphine admixture resulted in an additive reaction on the urethral pressure profile, compared with the changes brought about by each drug alone. Relaxation of the bladder and reduction in urethral resistance occurred 30 minutes post injection, increasing progressively after 60 and 90 minutes. The results demonstrated that baclofen, by its influence on cord neuron interaction, is capable of inhibiting the activity of the smooth muscle of the normal bladder and urethra, which in the case of the latter became more pronounced when both drugs were administered simultaneously by the intrathecal route.

Ischemic preconditioning decreases the reperfusion-related formation of hydroxyl radicals in a rabbit model of regional myocardial ischemia and reperfusion: The role of KATP channels

The objective of this study was to assess the effects of ischemic preconditioning (IP) on hydroxyl free radical production in an in vivo rabbit model of regional ischemia and reperfusion. Another goal was to determine whether KATP channels are involved in these effects. The hearts of anesthetized and mechanically ventilated New Zealand White rabbits were exposed through a left thoracotomy. After IV salicylate (100u2009mg/kg) administration, all animals underwent a 30-min stabilization period followed by 40u2009min of regional ischemia and 2u2009h of reperfusion. In the IP group, IP was elicited by 5u2009min of ischemia followed by 10u2009min of reperfusion (prior to the 40-min ischemia period). Glibenclamide, a KATP channel blocker, was administered prior to the preconditioning stimulus. Infarct size was measured by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. We quantified the hydroxyl-mediated conversion of salicylate to its 2,3 and 2,5-dihydroxybenzoate derivatives during reperfusion by high performance liquid chromatography coupled with electro-chemical detection. IP was evidenced by reduced infarct size compared to control animals: 22% vs. 58%, respectively. Glibenclamide inhibited this cardioprotective effect and infarct size was 53%. IP limited the increase in 2,3 and 2,5-dihydroxybenzoic acid to 24.3 and 23.8% above baseline, respectively. Glibenclamide abrogated this effect and the increase in 2,3 and 2,5-dihydroxybenzoic acid was 94.3 and 85% above baseline levels, respectively, similar to the increase in the control group. We demonstrated that IP decreased the formation of hydroxyl radicals during reperfusion. The fact that glibenclamide inhibited this effect, indicates that KATP channels play a key role in this cardioprotective effect of IP.

Myocardial Metabolism Altered by Ischemic Preconditioning and Enflurane in Off-Pump Coronary Artery Surgery

OBJECTIVEnDuring off-pump coronary artery bypass (OPCAB) surgery, the heart is subjected to ischemia and reperfusion. The authors hypothesized that the volatile anesthetics are as effective as ischemic preconditioning (IPC) in preserving myocardial function during off-pump cardiac surgery, and this effect is because of multiple mechanisms of action. Therefore, the effects of enflurane with its calcium inhibition and antioxidative properties were compared with mechanical IPC in preserving myocardial cellular markers.nnnDESIGNnA prospective, randomized, controlled, and partly blinded study.nnnSETTINGnA tertiary care university hospital.nnnPARTICIPANTSnTwenty-five patients undergoing elective single-graft OPCAB surgery.nnnINTERVENTIONSnPatients were randomized into 3 groups: (1) control (n = 8), (2) a single 5-minute ischemia/reperfusion interval of IPC before coronary occlusion (n = 9), and (3) 1.6% enflurane anesthesia 15 minutes before and during graft attachment (n = 8). Arterial and coronary sinus venous blood were analyzed for biochemical indices of ischemia and hydroxyl radical generation.nnnMEASUREMENTS AND MAIN RESULTSnAlthough the hemodynamic changes were small, myocardial lactate production in the control group increased by 120%, whereas in the enflurane group it decreased significantly (p < 0.01) compared with the control and IPC groups. Oxygen utilization in the control group was 44% higher (p < 0.03), and there was also a larger release of the hydroxyl radical-dependent adduct 2,3-dihydroxybenzoic acid (225% increase, p < 0.05) compared with both study groups. During reperfusion, initial anterior wall hypokinesis by TEE was observed, with slow recovery during reperfusion compared with early recovery in both study groups.nnnCONCLUSIONSnCoronary occlusion during OPCAB surgery results in increased production of ischemia-related metabolic products. The application of methods such as IPC or volatile anesthesia appears to reduce the metabolic deficit, free-radical production, and physiologic changes.

Patient data management systems in anaesthesia: an emerging technology

The purpose of this review is to define the expectations of an on-line automatic patient data management system (PDMS) into anaesthesia work-stations in and around the operating room suite. These expectations are based on review of available information in the medical literature, and trials of several systems that are available commercially, three of them in a more detailed fashion (i.e. Informatics®, Datex® and North American Drager®). The ideal PDMS should:- communicate with and capture the information from different monitors, anaesthesia machines and electronic gadgets (e.g., infusion pumps) used in the operating room (OR), while presenting selected relevant values and trends on a screen.- inform the anaesthetist of deviations from preselected limits of physiological and technical values. In the future, the system will hopefully be upgraded to include an algorithm-based decision support system.- communicate with the hospital mainframe computer, and automatically transfer demographic data, laboratory and imaging results, and records obtained during preoperative consultations.- at the end of each anaesthetic procedure, create an anaesthetic record with relevant data automatically collected by the system, as well as that which was entered manually by the physician during the procedure. A copy of this anaesthesia file must be kept on a computerized archive system. None of the systems so far evaluated fulfilled all our expectations. We have therefore adopted an approach for the gradual introduction of such a system into our OR environment over the next two to five years, during which expected improvements may be incorporated to upgrade the system.RésuméCette présentation vise à déterminer s’il est possible de recueiller avec un seul ordinateur et de rassembler automatiquement toutes les données médicales fournies par les systèmes accessibles à notre poste de travail du bloc opératoire (système de gestion des données médicales: SGDM). Notre approche est basée sur des informations extraites de la littérature médicale à partir de plusieurs systèmes déjà commercialisés. Trois d’entre eux ont été plus particulièrement étudiés (Informatics®, Datex® et North American Drager®). Le SGDM devrait:- capter et communiquer les renseignements obtenus de moniteurs et appareils utilisés en salle d’opération pour l’anesthésie, tout en affichant les chiffres et tendances sur un écran.- avertir l’anesthésiste de toute donnée anormale. A l’avenir, on devrait être en mesure à partir des données recueillies et d’un algorithme de créer un système qui permettra à l’anesthésiste de prendre des décisions.- pouvoir communiquer avec l’ordinateur central de l’hôpital et transmettre automatiquement les données démographiques, les résultats de laboratoires et les dossiers de la visite préopératoires.- A la fin de chaque opération, constituer un dossier comprenant les paramètres spécifiques à l’anesthésie recueillies automatiquement par le système ainsi que ceux que le médecin a introduits pendant l’intervention; une copie de ce dossier serait conservée dans des archives informatisées. Aucun des systèmes évalués ne remplit les conditions de notre SGDM. Les auteurs annoncent leur décision d’introduire ce système graduellement dans nos blocs opératoires en deux à cinq ans.

Cerebral protection using retrograde cerebral perfusion during hypothermic circulatory arrest

BackgroundRetrograde cerebral perfusion through the superior vena cava (SVC) has been proposed to protect the brain from ischaemic injury during profound hypothemnic circulatory arrest (PHCA). Its contribution to cerebral protection is unclear. Furthermore, the addition of anaesthetic or vasodilating agents to the SVC perfusate to enhance brain protection, has never been described.MethodsIn three patients undergoing repair of the ascending aorta utilizing PHCA, the upper body was retrogradely perfused with cold (16°C) blood through the SVC by the cardiopulmonary bypass pump. Electroencephalographic activity was monitored using a computenzed electroencephalographic monitor (Cerebro Trac 2500, SRD). Perfusion pressure was measured at a port in the cannula connector. Etomidate or thiopentone was injected into the SVC perfusate to arrest reappearing electroencephalographic activity. Nitroglycerin or nitroprusside was injected into the perfusate to increase retrograde flow and maintain a constant perfusion pressure.ResultsDuring PHCA penods of up to 61 min, recurrent electroencephalographic activity was abolished by the retrograde administration of small boluses of etomidate (total 50 mg) or thiopentone (total 500 mg). Nitroprusside (100 μg) and nitroglycerin (2 μg · kg−1 · min−1) increased retrograde flow from 220 to 550 and 660 ml · min−1, respectively, while maintaining perfusion pressure (25–26 mmHg). Recovery from anaesthesia and surgery was uneventful, with no adverse neurological sequelae.ConclusionInjection of anaesthetic agents into the retrograde SVC perfusate during PHCA, can suppress reoccumng electroencephalographic activity and retrograde injection of vasodilators can facilitate an increase in perfusion. It is suggested that both may augment brain protection.RésuméObjectifLa perfusion cérébrale rétrograde par la veine cave supérieure (VCS) pourrait protéger le cerveau de l’ischémie pendant l’arrêt circulatoire en hypothermie profonde (ACHP) mais cette hypothèse n’est pas prouvée. En outre, on n’a jamais rapporté non plus que les agents anesthésiques ou vasodilatateurs ajoutés au liquide de perfusion de la VCS amplifiaient la protection cérébrale.MéthodesAu cours d’une réparation de l’aorte ascendante sous ACHP, on a perfusé la partie supérieure du corps de trois patients par voie rétrograde avec du sang froid (16C) par la VCS à l’aide d’une pompe de circulation extracorponelle. Un moniteur informatisé (Cenebro Trac 2500, SRD) a servi a monrtorer l’activité électroencéphalographique. La pression de perfusion était mesurée par un orifice situé sur la canule. L’activité électroencéphalographique était interrompue par l’injection dans le liquide de perfusion de la VCS d’étomidate et de thiopental. Le nitroprussiate et la nitroglycénne étaient ajoutés au perfusat afin d’augmenter le flux rétrograde et maintenir constante la pression de perfusion.RésultatsL’admmistration rétrograde de petits bolus d’étomidate (total 50 mg) ou de thiopental (total 500 mg) a aboli la reprise de l’activité électroencéphalographique pendant 61 min d’ACPH ou moins. Le nitroprussiate (100 μg) et la nitroglycérine (2 μg · kg−1 · min−1) ont accru le flux rétrograde de 220 à 550 et à 660 ml · min−1 respectivement, tout en maintenant la pression de perfusion constante (25–26 mmHg). La récupération anesthésique et chirurgicale s’est deroulee sans problèmes ni séquelles neurologiques.ConclusionLinjection d’agents anesthésiques dans le liquide de perfusion rétrograde de la VCS pendant l’ACPH peut suppnmer la repnse de l’activité électroencéphalographique. L’injection rétrograde de vasodilatateurs peut favoriser l’augmentation de la perfusion. Ces deux interventions pourraient accroître la protection cérébrale.