Evaluation of routine postoperative chest X-rays in the management of the cardiac surgical patient

OBJECTIVES: To evaluate the role of routine chest X-rays in the management of patients post cardiac surgery. METHODS: 340 adult patients undergoing cardiac surgery were studied in three consecutive groups (A, B, C) of 100 patients each. Forty patients were excluded due to the intensive care stay greater than 36 h (n = 35), or early mortality within 36 h (n = 5). Routine chest X-rays were performed according to different protocols in Groups A and B. In group C there were no routine chest X-rays during the entire postoperative period [corrected]. In all three groups chest X-rays were performed where clinically indicated. Group A had three routine chest X-rays post-operation. Group B had one routine chest X-ray on day 4 post-operation. Group C had chest X-rays only when indicated. The X-rays were evaluated in terms of their assistance value and the resultant number of interventions. RESULTS: The three groups were similar preoperatively for age, sex, preoperative left ventricular function, presence of chronic obstructive airway disease and type of operation performed. The total number of chest X-rays in groups A, B and C were 304, 133 and 36, respectively. The number of chest X-rays leading to interventions were five, four and four in groups A, B and C, respectively. Chest X-rays that helped in management were 36, 28, and 28, respectively, in the same groups. There was no mortality or morbidity attributable to non-performance of routine chest X-ray. CONCLUSIONS: Routine chest X-rays post-cardiac surgery are of very little value and patients are adequately managed by performing chest X-rays only when clinically indicated. There was no increased mortality or morbidity attributed to lack of routine chest X-rays in any of these groups. We recommend performing chest X-rays only when clinically indicated in satisfactorily recovering adult cardiac surgical patients.     

Effect of sodium nitroprusside on compound action potential thresholds in the gerbil cochlea

OBJECTIVE: Trials that do not allow rejection of the null hypothesis of no treatment effect may have had an inappropriate design. Trials are virtually never assessed for correlation between responses to different treatment modalities. METHODS: Using a hypothetical example and several published studies we examine the influence of correlation levels between treatment modalities on the sensitivity of testing. RESULTS: The level of correlation between responses to different treatment modalities is a major determinant of the sensitivity both of crossover and parallel group clinical trials. CONCLUSIONS: It is very relevant to assess a priori correlation levels between responses to the different treatment modalities of a trial. If a negative correlation is anticipated, a crossover design is likely to lack sensitivity. If a positive correlation is anticipated a parallel-group design seems less appropriate, because it would lack the extra sensitivity of accounting for the positive correlation. Both designs would seem suitable for approximately zero correlations (e.g. comparison vs baseline or vs placebo under the assumption that the number of placebo responders is negligible.     

Ototoxicity of sodium nitroprusside

Nitric oxide (NO) not only has normal physiological roles like vasodilation and neurotransmission in the living organism, it could also have possible neurodestructive effects under certain pathological conditions. The present study aimed to determine whether direct exposure of guinea pig cochlea to a NO donor like sodium nitroprusside (SNP), or a nitric oxide synthase (NOS) inhibitor like N(G)-nitro-L-arginine methyl ester (L-NAME), would cause damage to the auditory hair cells. A piece of gelfoam was placed on the round window of the right ear of adult albino guinea pigs. It was then soaked with 0.1 ml of SNP (3.4 microM), 0.1 ml of L-NAME (9.3 microM or 18.5 microM) or 0.1 ml of injection water, the vehicle used to dissolve the above chemicals. Twelve animals receiving SNP were perfused 1 day, 2, 3 and 7 days later, with three animals being used for each survival period. Six animals receiving L-NAME were allowed to survive up to 7 days before perfusion. Eight animals receiving injection water or 0.45% saline were used as controls. With the scanning electron microscope, the inner and outer hair cells were counted over a 1 mm length of the basilar membrane in each turn of every cochlea. The results showed that, in animals treated with L-NAME at both concentrations stated, no significant loss of either inner or outer hair cells was noted in any part of the cochlea studied. However, as early as 1 day after SNP treatment, a striking loss of inner and outer hair cells was observed in the three lower turns of the cochlea. Damage to the outer hair cells was extended to the apical turn with increasing survival period, but no significant loss of inner hair cells was evident in the apical turn at any of the survival periods studied. To rule out the possibility that the effects were due to the presence of cyanide, a metabolite of SNP, hydroxycobalamin was introduced into the scala tympani of three animals through a cannula-osmotic pump device during SNP treatment. There was no significant difference in the results between the groups with and without hydroxycobalamin infusion 7 days after SNP treatment. The present study suggests that an excessive production of NO in the inner ear could lead to extensive loss of hair cells.     

Dynamics of the blood pressure changes in sodium nitroprusside induced controlled arterial hypotension in neurosurgery

Dynamics of the arterial blood pressure changes under the influence of intravenous infusion of sodium nitroprusside (SN) were studied in 12 patients operated on for intracranial aneurysms. Adequate measures were undertaken to avoid blood pressure (BP) changes due to the anaesthetic procedure itself. It was found that the speed of BP lowering corresponded to the rate of infusion, and could easily reach 10 mm Hg/min. After stopping the infusion, the BP recovery rate averaged a mean speed of 8.5 mm Hg/min, varying from 3.8 to 12 mm Hg/min. High speeds of BP lowering and recovery achieved with the use of SN are the main advantages of this hypotensive agent in neurosurgical procedures.     

Effects of sodium nitroprusside and phenylephrine on blood flow in free musculocutaneous flaps during general anesthesia

BACKGROUND: Hypoperfusion and necrosis in free flaps used to correct tissue defects remain important clinical problems. The authors studied the effects of two vasoactive drugs, sodium nitroprusside and phenylephrine, which are used frequently in anesthetic practice, on total blood flow and microcirculatory flow in free musculocutaneous flaps during general anesthesia. METHODS: In a porcine model (n = 9) in which clinical conditions for anesthesia and microvascular surgery were simulated, latissimus dorsi free flaps were transferred to the lower extremity. Total blood flow in the flaps was measured using ultrasound flowmetry and microcirculatory flow was measured using laser Doppler flowmetry. The effects of sodium nitroprusside and phenylephrine were studied during local infusion through the feeding artery of the flap and during systemic administration. RESULTS: Systemic sodium nitroprusside caused a 30% decrease in mean arterial pressure, but cardiac output did not change. The total flow in the flap decreased by 40% (P < 0.01), and microcirculatory flow decreased by 23% in the skin (P < 0.01) and by 30% in the muscle (P < 0.01) of the flap. Sodium nitroprusside infused locally into the flap artery increased the total flap flow by 20% (P < 0.01). Systemic phenylephrine caused a 30% increase in mean arterial pressure, whereas heart rate, cardiac output, and flap blood flow did not change. Local phenylephrine caused a 30% decrease (P < 0.01) in the total flap flow. CONCLUSIONS: Systemic phenylephrine in a dose increasing the systemic vascular resistance and arterial pressure by 30% appears to have no adverse effects on blood flow in free musculocutaneous flaps. Sodium nitroprusside, however, in a dose causing a 30% decrease in systemic vascular resistance and arterial pressure, causes a severe reduction in free flap blood flow despite maintaining cardiac output.     

Effect of sodium nitroprusside on sperm motility, viability, and lipid peroxidation

OBJECTIVE: To analyze the effect of sodium nitroprusside, a nitric oxide releaser, on sperm motion and lipid peroxidation-induced membrane damage in cryopreserved human sperm. DESIGN: Post-thaw, cryopreserved, human sperm samples were washed and divided into three aliquots. Each aliquot was incubated with either 0, 50, or 100 nM sodium nitroprusside. INTERVENTIONS: Samples were analyzed for lipid peroxidation (measured by malonaldehyde-thiobarbituric acid reactivity) at 3 hours post-thaw. MAIN OUTCOME MEASURES: Percent viability and motion parameters were assessed at 0, 10, and 30 minutes and 2, 3, 5, and 6 hours post-thaw. RESULTS: All results represent a mean +/- SEM, n = 10. Lipid peroxidation in samples incubated with 50 nM sodium nitroprusside (15.1 +/- 2.1 nM malonaldehyde/10(8) sperm) or 100 nM sodium nitroprusside (13.2 +/- 2.1 nM malonaldehyde/10(8) sperm) was significantly lower than in controls (22.7 +/- 3.1 nM malonaldehyde/10(8) sperm). Percent viability was significantly reduced from 0 minutes (60.6% +/- 3.5%) to 6 hours post-thaw in controls (38.0% +/- 5.1%) but not in 50 nM (46.8% +/- 10.4%) or 100 nM (48.8% +/- 6.5%) sodium nitroprusside-treated samples. Compared with controls (18.3% +/- 3.4%), maintenance of percent motility at 3 hours post-thaw was significantly improved in 50 nM (24.5% +/- 2.9%) and in 100 nM (26.3% +/- 3.2%) sodium nitroprusside-treated samples. Straight line velocity maintenance was significantly improved in 50 nM (37.3 +/- 1.3) and in 100 nM (37.0 +/- 1) sodium nitroprusside-treated samples as compared with controls (30.5 +/- 1.7). Significant improvements in curvilinear velocity maintenance compared with controls (56.3 +/- 2.9) also were observed in 50 nM (65.9 +/- 2.1) and 100 nM (72.1 +/- 4.1) sodium nitroprusside-treated samples. Significant differences in the motion parameters of sodium nitroprusside-treated samples were maintained at 5 and 6 hours post-thaw in comparison to controls. CONCLUSION: These results suggest that sodium nitroprusside is beneficial to the maintenance of post-thaw sperm motion and viability for up to 6 hours and that reduction of lipid peroxidative damage to sperm membranes may be the mechanism for these benefits.     

A comparison of prostacyclin and sodium nitroprusside for the treatment of heart failure after cardiac surgery

OBJECTIVE: To study the effects of the two vasodilators, prostacyclin and sodium nitroprusside, on central hemodynamics in heart failure after cardiac surgery. DESIGN: Randomized cross-over study. SETTING: Multi-institutional university hospital. PARTICIPANTS: Ten patients. Inclusion criteria: cardiac index less than 2.5 L/min/m2; pulmonary capillary wedge pressure greater than 15 mmHg, systemic vascular resistance index greater than 2,500 dynes.s.cm-5/m2, and treatment with inotropic support. Five patients were treated with intra-aortic balloon counterpulsation. INTERVENTIONS: After control measurements, mean arterial pressure was decreased by 10% to 20% with each vasodilator in each patient. MEASUREMENTS AND RESULTS: Sodium nitroprusside induced decreases in mean pulmonary arterial pressure (-21%), pulmonary capillary wedge pressure (-29%), central venous pressure (-17%), and systemic vascular resistance (-25%), and increases in cardiac output (+7%) and stroke volume (+6%) compared with control. Prostacyclin decreased mean pulmonary arterial pressure (-14%), pulmonary capillary wedge pressure (-19%), central venous pressure (-7%), and systemic (-40%) and pulmonary (-25%) vascular resistances, whereas cardiac output (+25%) and stroke volume (+22%) increased compared with control. Prostacyclin, compared with sodium nitroprusside, induced a more pronounced increase in cardiac output and stroke volume, associated with less pronounced decreases in cardiac filling pressures and more profound decreases in systemic and pulmonary vascular resistances. CONCLUSION: Prostacyclin appears to be a useful agent, superior to sodium nitroprusside, in the treatment of postoperative heart failure in patients with normal or mildly elevated cardiac filling pressures, where vasodilator treatment is indicated.     

Effects of sodium nitroprusside on hemodialysis-induced platelet activation

Plasminogen activator inhibitor-2 (PAI-2), a member of the serpin gene family, is thought to serve as a primary regulator of plasminogen activation in the extravascular compartment. High levels of PAI-2 are found in keratinocytes, monocytes, and the human trophoblast, the latter suggesting a role in placental maintenance or embryo development. The primarily intracellular distribution of PAI-2 also may indicate a unique regulatory role in a protease-dependent cellular process such as apoptosis. To examine the potential functions of PAI-2 in vivo, we generated PAI-2-deficient mice by gene targeting in embryonic stem cells. Homozygous PAI-2-deficient mice exhibited normal development, survival, and fertility and were also indistinguishable from normal controls in response to a bacterial infectious challenge or endotoxin infusion. No differences in monocyte recruitment into the peritoneum were observed after thioglycollate injection. Epidermal wound healing was equivalent among PAI-2 -/- null and control mice. Finally, crossing PAI-2 -/- with PAI-1 -/- mice to generate animals deficient in both plasminogen activator inhibitors failed to uncover an overlap in function between these two related proteins.     

Effect of nitroprusside on smooth muscle and adrenergic nerve terminals in isolated blood vessels

Experiments were designed to assess the mode of action of nitroprusside on isolated blood vessels and its relative potency on venous and arterial smooth muscle. Strips from dog blood vessels were mounted in an organ bath for isometric tension recording. Sodium nitroprusside (10(-5) M) depressed the contraction of saphenous vein strips caused by electric stimulation, tyramine, K+, Ba++, norepinephrine and acetylcholine. The depression of the norepinephrine-induced contractions also occurred in a Ca++- free medium and when Ca++ influx was inhibited by verapamil. Nitroprusside reduced the frequency of the spontaneous contractions of strips of portal-mesenteric veins. It depressed the contraction caused by norepinephrine in tibial artery strips more than in saphenous vein strips. Saphenous vein strips were incubated with (3H)norepinephrine and mounted for superfusion and isometric tension recording. Sodium nitroprusside (10(-5) M) had no effect on the basal efflux of 3H compounds. During electric stimulation, it did not change the output of (3H)norepinephrine but increased the outflow of deaminated and O-methylated metabolites. Thus sodium nitroprusside 1) has a direct effect on the smooth muscle cells which is independent of Ca++ influx, 2) depresses contractions of different types of vascular smooth muscle and 3) does not inhibit the release of norepinephrine from the nerve endings.     

Neurotoxic effects of sodium nitroprusside in rat hippocampal slices

The effect of a permanent transection on myelin gene expression in a regenerating sciatic nerve and in an adult sciatic nerve was compared to establish the degree of axonal control exerted upon Schwann cells in each population. First, the adult sciatic nerve was crushed, and the distal segment allowed to regenerate. At 12 days post-crush, the sciatic nerve was transected distal to the site of crush to disrupt the Schwann cell-axonal contacts that had reformed. Messenger RNA (mRNA) levels coding for five myelin proteins were assayed in the distal segment of the crush-transected nerve after 9 days and were compared to corresponding levels in the distal segments of sciatic nerves at 21 days post-crush and 21 days post-transection using Northern blot and slot-blot analysis. Levels of mRNAs found in the distal segment of the transected and crush-transected nerve suggested that Schwann cells in the regenerating nerve and in the mature adult nerve are equally responsive to axonal influences. The crush-transected model allowed the genes that were studied to be classified according to their response to Schwann cell-axonal contact. The levels of mRNAs were 1) down-regulated to basal levels (P0 and MBP mRNAs), 2) down-regulated to undetectable levels (myelin-associated glycoprotein mRNAs), 3) upregulated (mRNAs encoding 2'3'-cyclic nucleotide phosphodiesterase and beta-actin), or 4) not stringently controlled by the removal of Schwann cell-axonal contact (proteolipid protein mRNAs). This novel experimental model has thus provided evidence that the expression of some of the important myelin genes during peripheral nerve regeneration is dependent on continuous signals from the ingrowing axons.     

How to control the blood glucose level in the surgical diabetic patient

Plasma activities of lactic dehydrogenase (LDH), creatine phosphokinase (CPK), glutamic pyruvic transaminase (GPT), and alkaline phosphatase (ALP) were studied, along with hematological changes, in rats suffering from various degrees of experimental decompression sickness (DS). By 1 h after decompression, LDH and CPK activities were elevated in moderate and severe DS whereas GOT and GPT were elevated only in severe DS. ALP was reduced in all decompressed rats. Hematological changes indicated hemoconcentration, the degree of which paralleled the severity of DS. By 24 h after decompression, all enzyme activities were approaching control levels with the exception of GOT, which was further elevated from the 1-h value. The observed lung damage in rats with severe DS in conjunction with the hematologic and enzyme data suggested that hypoxemic-hypoxia, incident to bubble embolization of pulmonary vasculature, was a major factor in altering the blood enzyme pattern in DS. Serum enzyme data from two inadequately decompressed divers are also reported.     

Effect of sulfhydryl oxidoreduction on permeability of cardiac tetrodotoxin-insensitive sodium channel

Effects of sulfhydryl oxidizing and reducing agents on permeability of the tetrodotoxin (TTX)-insensitive Na-channel were investigated in guinea-pig ventricular myocytes using the whole-cell patch-clamp technique. Mercury chloride (HgCl2) at 1-100 microM irreversibly blocked Na+ currents with no significant changes in the gating kinetics. In contrast, the hydrophilic sulfhydryl oxidizing agent, thimerosal at 50-100 microM little affected Na+ permeation through the Na-channel. The Hg2+-induced block of Na+ current could be readily reversed by 1,4-dithiothreitol (DTT), an agent that reduces disulfide bonds. These results indicate that the formation of sulfur-Hg-sulfur bridge is essential for Hg2+ block. Pretreatment with DTT prevented the Hg2+ block of Na+ current, whereas Zn2+ and Cd2+ retained their abilities to block Na+ current after DTT treatment. An application of Zn2+ or Cd2+ resulted in the restoration of Hg2+ sensitivity of the DTT-treated channel. A conformational model for the Na-channel with multiple free sulfhydryl groups and native disulfide bonds could account for our experimental data regarding the effects of sulfhydryl modifying agents on the channel permeability. We conclude that the cardiac TTX-insensitive Na-channel contains functionally important free sulfhydryl groups and disulfide bonds which are accessible from the extracellular side by an aqueous pathway. These sulfhydryls would be capable of modulating the Na-channel permeability by affecting the conformation of channel pore region.     

Some aspects of sodium nitroprusside reaction with human erythrocytes

Sodium nitroprusside is an excellent agent for lowering blood pressure in hypertensive emergencies, for producing controlled hypotension during anesthesia, and for treating acute myocardial infarction and chronic heart failure. Toxic effects of this drug have been reported and above-normal cyanide and thiocyanate concentrations have been observed in the blood of a small proportion of subjects receiving nitroprusside. Nitrite, syanide, and thiocyanate are major decomposition products of nitroprusside, resulting from an in vitro reaction with human blood. On the basis of the conversion mechanism, we suggest that, in the cyanide/thiocyanate cycle, only cyanide is directly responsible for any acute toxicity attributed to sodium nitroprusside. In this work, the extent of cyanide production by erythrocytes in vitro was studied. The rate of detoxification of cyanide by human liver in vitro was experimentally determined and data from a search for a possible inhibitor of the nitroprusside/hemoglobin reaction are presented. Also, the possible mechanism of the nitroprusside/hemoglobin reaction is discussed.     

Fenoldopam mesylate versus sodium nitroprusside in the acute management of severe systemic hypertension

Thirty-three patients with severe systemic hypertension defined as a diastolic blood pressure (DBP) > or = 120 mm Hg were randomized in a single-blind fashion to be treated with either intravenous fenoldopam mesylate (FNP) or sodium nitroprusside (NTP). Fenoldopam mesylate and NTP infusion rates began at 0.1 microgram/kg/minute and 0.5 microgram/kg/minute, respectively and were titrated to achieve a goal DBP of between 95 and 110 mm Hg; or a reduction of at least 40 mm Hg if the baseline DBP was > 150 mm Hg. Fenoldopam mesylate (n = 15) reduced blood pressure from 217/145 +/- 6/5 to 187/112 +/- 6/3 mm Hg (P < .001) at an average infusion rate of 0.5 +/- 0.1 microgram/kg/minute. The average time to achieve goal DBP with FNP was 1.5 +/- 1.4 hours. Nitroprusside (n = 18) reduced blood pressure from 210/136 +/- 5/2 to 172/103 +/- 6/2 mm Hg (P < .001) at an average infusion rate of 1.2 +/- .24 micrograms/kg/minute. Nitroprusside response time averaged 2 +/- 2.5 hours. There was no significant difference between the magnitude of effect seen with either FNP or NTP; nor was there any difference observed in the adverse effect rates of the two agents. Fenoldopam mesylate and NTP demonstrate similar overall efficacy in the treatment of severe systemic hypertension.