Rahim Behnia

Effects of hyperosmotic mannitol infusion on hemodynamics of dog kidney.

This study evaluated the effect of systemic infusion of hypertonic mannitol on renal hemodynamics (aortic pressure [P]-renal blood flow [RBF] relationship, glomerular filtration rate [GFR], and effective renal plasma flow [ERPF]) during 50% reduction of left kidney blood flow. Conditioned mongrel dogs anesthetized with halothane were hydrated by continuous infusion of lactated Ringers solution containing creatinine to measure GFR and p-aminohippurate (PAH), to measure ERPF. The left kidney was exposed and two hydraulic occluders were placed, one around the aorta just above the renal arteries and the other around the left renal artery. Experimental design consisted of measuring P near the left renal artery, RBF by electromagnetic flowmeter, and ERPF and GFR by clearance methods in both kidneys in response to stepwise reduction in the aortic pressure by aortic occlusion before and after 50% reduction in the left kidney blood flow. The P-RBF relationship, GFR, and ERPF thus obtained were compared with those obtained during systemic intravenous infusion of 20% mannitol for a period of 1 h. We found that 1) a transient increase occurred in RBF with step reduction of P from 80 to 60 mm Hg under control conditions; 2) reducing the RBF by 50% changed the shape of the P-RBF relationship from a convex to the P axis to a linear form with a marked shift toward the P axis; 3) infusion of mannitol, during reduced RBF, caused a significant shift of the P-RBF curve toward the RBF axis and returned the linear P-RBF relationship toward normal, but had no effect on altered yield pressure; and 4) infusion of hypertonic mannitol had slightly increased GFR and ERPF in the right (unconstricted) kidney. However, hypertonic mannitol significantly increased GFR and ERPF values in the left (constricted) kidney suggesting a beneficial effect of mannitol on ischemic kidney. The results are consistent with the hypothesis that infusion of hypertonic mannitol to ischemic kidney increases RBF, presumably by decreasing the intrarenal vascular resistance. We speculate that this compensatory response may be mediated either 1) by stimulating the release of a vasodilator substance (e.g., prostaglandins), or 2) by washing out interstitial sodium, thereby reducing the sensitivity of the renal vasculature to ischemia-induced stimulation of renin-angiotensin system. (Anesth Analg 1996;82:902-8)

Systemic effects of absolute alcohol embolization in a patient with a congenital arteriovenous malformation of the lower extremity

C ongenital arteriovenous malformations (AVMs) are abnormal connections of the arterial and venous systems. AVMs occur most often in the extremities and may involve skin, ‘subcutaneous tissues, muscle, and bone. AVMs can result in disfigurement, gangrene, and bleeding (1). Large AVMs can cause a dramatic decrease in total peripheral resistance and an increase in cardiac output (2). Multiple surgical and radiologic procedures have been used for the treatment of AVMs with minimal success. Materials such as avitene, polyvinyl alcohol foam, silk, gelfoam, and anhydrous ethanol (absolute alcohol) have been used to embolize the AVMs. (3-7) Embolization of the AVMs can result in lifethreatening hemorrhage (6) and severe hemodynamic alteration (7). This case report describes the hemodynamic and physiologic changes that occurred after absolute alcohol embolization in one patient.

Hemodynamic responses associated with lithotripsy.

Because ESWL produces a painful stimulus, general or regional anesthesia is required to prevent not only pain but also movement by the patient that might alter the position of a stone targeted on the image intensifier screen (3). Extracorporeal shock wave lithotripsy requires that the anesthetized patient be immersed in water in a semisitting position while high energy shock waves are delivered to the kidney to crush the stone (4). Anesthesia, immersion in water, and ESWL itself may significantly affect the cardiovascular system and the kidney (3-7), but the cardiovascular responses have not been quantitated in detail. We therefore undertook the present study in ll patients of hemodynamic changes associated with general anesthesia and ESWL, as measured by a transesophageal Doppler ultrasonic cardiac output monitor, other methods for measuring hemodynamic function being difficult in patients almost totally immersed in water. cost (1,2).

Pressure-Heart Rate Relationship in Intact and After Stepwise Elimination of Three Major Baroreflex loops in Dogs

Systemic arterial blood pressure (BP)-heart rate (HR) relationship (the pressor test) is often used as an index of baroreflex. We evaluated this index by simultaneously comparing BP-HR, right carotid sinus pressure (CSP)-nerve action potentials (NAP), and NAP-HR relationships in dogs anesthetized with pentobarbital. BP was increased or decreased stepwise by intravenous (IV) infusions of phenylephrine or sodium nitroprusside, respectively. In nine dogs BP-HR and CSP-NAP relationships were measured and NAP-HR relationship was constructed before and after sequential and stepwise sectioning of the left aortic depressor nerve (LADN), the right aortic depressor nerve (RADN), and blockade of the left carotid sinus nerve (BLK) with 1% lidocaine. We found that HR was a negative sigmoidal function of BP in intact dogs. Linear slope of this relationship was significantly reduced after sectioning of LADN and RADN, but returned toward baseline after BLK. NAP was a positive sigmoidal function of CSP in intact dogs. Linear slope of this relationship was significantly depressed after sectioning of LADN and RADN. However, after BLK, the slope surpassed control, suggesting the existence of a central communication between the two carotid sinuses. HR was a negative function of NAP in intact dogs. However, as the other baroreflex feedback loops were eliminated, the slope of the NAP-HR relationship approached zero indicating that a closed integrated parallel feedback system is required for reflex regulation of HR. Our findings suggest that under normal conditions the pressor test is a valid index for baroreceptor function, but its use may not be warranted in chronic pathological states, such as atherosclerosis and hypertension. However, in contrast to the present acute experimental model, chronic pathological processes may not develop in sequence, and baroreceptor function on the affected site may not be completely eliminated from the baroreceptor loop such as performed in this study. (Anesth Analg 1996;83:965-74)

Local versus central effect of halothane on carotid sinus baroreceptor function.

Depressive effect of halothane on carotid sinus baroreceptor function may be due to direct local action, action in the CNS, or both. Paris of dogs were anesthetized with pentobarbital and ventilated with oxygen. The carotid sinus of the recipient dog was isolated and perfused with blood from the common carotid artery of the donor dog. Blood from the recipient sinus was returned through its external carotid to the donor common carotid. Thus, both carotid sinuses of the donor and the contralateral carotid sinus of the recipient dog received uninterrupted circulation. Carotid sinus nerve action potentials and lingual artery pressure of the isolated recipient sinus were recorded before and during steady state end-tidal halothane concentrations of 0, 0.5, 1.0, 1.5, 2.0, and 2.5% in oxygen, given randomly first to the donor dog (to evaluate direct local effect) and then to the recipient dog (to determine central effect). The dog not given halothane received pentobarbital. Plots of normalized nerve activity versus halothane concentrations showed approximately zero slope when the donor was given halothane but showed significant decrease in nerve activity when the recipient was given halothane. Halothane appears to have no direct local effect but causes depression of baroreceptor nerve activity, possibly via CNS inhibition of sympathetic efferents to the carotid sinus.

Hemodynamic and catecholamine responses associated with extracorporeal shock wave lithotripsy

Patients undergoing extracorporeal shock wave lithotripsy (ESWL) for nephrolithiasis are anesthetized and immersed in water in a semisitting position. Hypertension and tachycardia have been reported to accompany ESWL, and it was hypothesized that those problems were a result of adrenal medullary release of epinephrine or norepinephrine. Therefore, the effects of ESWL on cardiovascular variables and circulating epinephrine and norepinephrine levels in nine patients anesthetized with 1.1% isoflurane in 50% nitrous oxide and oxygen were studied. End-tidal carbon dioxide (CO2) was maintained at 34 +/- 2 mmHg. Cardiac output (CO) and mean arterial pressure (MAP) were measured, and total peripheral resistance (TPR) was calculated at the following time points: (1) after immersion prior to shock wave therapy (control); (2) after 300 shocks; (3) after 800 shocks; and (4) 5 minutes after the completion of ESWL with the patient still immersed. Circulating epinephrine and norepinephrine concentrations were determined at the above times as well as before and after induction of anesthesia but prior to immersion. There was a statistically significant (p less than 0.05) decrease in CO and an increase (p less than 0.05) in MAP and TPR with ESWL treatment. These values returned to baseline levels when treatment was stopped. Plasma epinephrine and norepinephrine values did not change significantly throughout the study period. It was concluded that these ESWL-associated hemodynamic changes were probably not mediated via epinephrine or norepinephrine.

Trimethaphan-induced hypotension: effect on renal function

This study was designed to evaluate the effects of trimethaphan-induced hypotension on renal function in healthy young patients undergoing maxillofacial surgery. Anaesthesia was induced with thiopentone and was maintained with halothane 1.5-2.0 per cent in oxygen. Each patient served as his own control, and data were analyzed using the paired t-test. Trimethaphan was infused at a rate of 45-52 [xg-kg-lmin-1 for an average hypotensive period of 53 ± 4 (mean ± SEM) minutes to reduce the mean arterial pressure (MAP) to 49 ± 2 torr. Endogenous creatinine clearance, urinary Po2, sodium reabsorption rate (TNa), and serum and urine osmolalities were determined before, during and after arterial hypotension with trimethaphan. Urine flow averaged 2.9 ± 1 ml/min during the period of hypotension. Endogenous creatinine clearance and TNa were significantly decreased (p < 0.05) in the hypotensive period. These values returned to normal levels within one hour upon discontinuation of trimethaphan and restoration of blood pressure. We found no statistical difference in urine Po2, and serum and urine osmolalities during control, hypotensive and recovery periods. These results suggest that medullary renal tissue oxygenation, an index of tissue viability, may have remained adequate despite a significant reduction in endogenous creatinine clearance during the hypotensive period. Furthermore, it appears that the effect of trimethaphan-induced hypotension on renal function is similar to the sodium nitro-prusside-induced hypotension in man which we have reported previously.RésuméCette étude aé6lé entreprise dans le but d’évaluer le retentissement de l’hypotension produite par le trimetaphan (TMP) sur la fonction résale de jeunes adultes en bon état subissant une intervention maxillo-faciale. L’anesthésie a été induite au thiopentone et maintenue à l’halothane 1.5-2.0 pour cent dans l’oxygène. Chaque patient était son propre contrôle et les données ont été analysées avec le test de Student. Le TMP a été perfusé#x00E9; à la vitesse de 45-52ing-kg--min-1 pour une durée moyenne d’hypotension de 53 ± 4 (moyenne ± SEM) minutes de façbaisser la pression artérielle moyenne à 49 ± 2 torr. La clairance de Iacréatinine endogène, la Po2 urinaire, la vitesse de réabsorbtion au sodium (TNa) et l’osmolalité urinaire et sérique ont été déterminées avant, pendant et après l’hypotension au TMP. Le débit urinaire était en moyenne de 2.9 ± 1 ml/min pendant la période d’hypotension. La clairance de la créatinine endogène et laT Na se sont abaissées de facçon significative (P < 0.05) pendant la péiiode hypotensive. II n’y a eu de différence significative dans la P02 urinaire et les osmolalités sérique et urinaire pendant la période de contrôle, d’hypotension et de recouvrement. Ces résultats suggèrent que l’index de viabilité du tissus rénal qu’est I’oxygénation médullaire pourrait être adéquat malgré une baisse significative de la clairance de la créatinine endogène pendant la période hypotensive. De plus, il semble que le retentissement de l’hypotension produite par le TMP sur la fonction résale est identique à celle produite chez 1’homme par le nitroprussiate de soude.

A Comparison of General Versus Local Anesthesia During Inguinal Herniorraphy

The current study was done to compare the hemodynamic changes, recovery events and economic impact of elective inguinal herniorrhaphy performed with general anesthesia (GA) or regional field block (RB) in 20 patients (American Society of Anesthesiology class I). In the GA group, anesthesia was induced with thiopental and the trachea was intubated after intravenous administration of 0.08 milligrams per kilogram of vecuronium. GA was maintained with 1.2 +/- 0.25 per cent enflurane in 50 per cent nitrous oxide and oxygen, and ventilation was controlled to keep PECO2 at 36 +/- 2 millimeters of mercury. Anesthesia in the RB group was accomplished by local injection of 3.5 +/- 0.5 milligrams per kilogram of 0.5 per cent bupivacaine. In each patient, a suprasternal ultrasonic Doppler probe was used to measure cardiac output before induction of anesthesia, during and after operation. Total peripheral resistance was calculated from mean arterial pressure and cardiac output. There were no statistically significant differences between cardiac output, mean arterial pressure, total peripheral resistance and heart rate in the two groups at any time period during the study. Patients in the RB group did not require parenteral medication for relief of postoperative pain, whereas all those in the GA group did. Significant cost benefits were realized by the RB group because of elimination of general anesthetic and reduction of recovery room fees.