Donald C. Finlayson

Vasodilator therapy after cardiac surgery: a review of the efficacy and toxicity of nitroglycerin and nitroprusside

Eight-five patients who required vasodilator therapy in the postoperative period after cardiac surgery were studied to compare the haemodynamic effects of nitroglycerin and nitroprusside, to evaluate local and systemic toxicity, and to develop long-range dosage recommendations. Ninety-one per cent of the patients received the vasodilators for postoperative hypertension, while nine per cent had low output syndromes. Both drugs significantly decreased blood pressure and central venous pressure, and increased heart rate. Nitroglycerin decreased both right and left ventricular filling pressures more than nitroprusside. No local toxicity or methaemoglobinaemia was found with either drug. Elevated thiocyanate levels were detected in 44 per cent of the nitroprusside group; however, none of the patients developed progressive metabolic acidosis. For prolonged infusions we found that nitroprusside at 1 μg·kg-1·min-1 and nitroglycerin at 0.5 μg·kg-1· min-1 were without significant toxicity.RésuméQuatre-vingt-cinq patients ayant requis des vasodilatateurs dans la période post-opératoire, après chirurgie cardiaque, ont fait ľobjet ďune étude prospective dont les buts étaient de comparer les effects hémodynamiques de la nitroglycérine et du nitroprussiate de sodium, ďévaluer la toxicité locale et systémique de ces agents et ďétablir des politiques sur leur usage. Leur emploi a été motivé par une hypertension artérielle post-opératoire dans 91 pour cent des cas et par un syndrome de bas débit dans les autres cas. Les deux agents ont diminué (de façon significative) la pression artérielle et la pression veineuse avec une accélération de la fréquence cardiaque. La nitroglycérine diminuait les pressions de remplissage gauches et droites de façon plus marquée que le nitroprussiate. On n’a relevé aucune toxicité locale ou de méthémoglobinémie avec ľun ou ľautre agent. Des taux élevés de thiocyanate ont été relevés chez 44 pour cent des patients ayant reçu du nitroprussiate; cependant, aucun de ceux-ci n’a présenté ďacidose métabolique progressive. Nous avons trouvé que le nitroprussiate de sodium, à raison de 1 μg · kg-1 · min-1 et la nitroglycérine, à raison de 0.5 μg·kg-1 · min-1, ne présentaient pas de toxicité significative en administration prolongée.

Incidence of Cell-Saver contamination during cardiopulmonary bypass

During regular bacteriological surveillance of cardiac surgical equipment and patients, the Cell Saver apparatus (CSA) was prospectively evaluated to determine if it represented an additional risk for infection. Nineteen patients were studied. After each operation, the effluent from the CSA was sterilely sealed for subsequent culture. A total of 42 aerobic and 42 anaerobic cultures were made. Postoperatively all patients were evaluated daily for four days and before discharge for clinical evidence of infection. Four patients had positive CSA cultures without evidence of postoperative clinical infection. Five patients in whom postoperative infectious complications developed had negative CSA cultures. Ten patients had negative CSA cultures and no evidence of postoperative infection. We conclude that the CSA does not appear to contribute to the risk of infection in cardiac surgical patients and that it is a safe adjunct to cardiac surgery.

The benefit of the Hemonetics® cell saver apparatus during cardiac surgery

This retrospective chart review of 155 patients having coronary artery bypass graft surgery (CABG) over a two-month period determined whether the use of a cell saver apparatus (CSA) (1) reduced or increased the requirements for homologous blood; (2) increased the incidence of postsurgical bleeding; (3) was costeffective. Two groups of patients were identified. Group 1 (n = 99) received both CSA processed red blood cells and homologous blood components. Requirement for homologous blood products was reduced in the first 24 hr after surgery (0.5 ± 1.0 vs 1.3 ± 1.8 units; P < 0.05) when compared with Group 2 (n = 56) in whom only homologous blood products were utilized. More patients in Group 1 had no transfusion requirements (45 vs 8; P < 0.05) and there was no increased risk of major haemorrhage. When the capital costs are included, utilization of the CSA was not costeffective. We conclude that utilisation of a CSA was safe, with no increased risk of bleeding, reduced requirements for homologous blood transfusions, but added to the cost of the procedure.RésuméCette revue rétrospective de 150 patients ayant eu des pontages aortocoronariens (CABG) détermine si l’utilisation du “cell saver” (CSA) 1) réduit ou augmente la nécessité d’une transfusion de sang homologue; 2) augmente l’incidence de saignement postopératoire; 3) est avantageuse considérant le coût. Deux groupes de patients ont été identifiés. Le Groupe 1 (n = 99) où les patients ont reçu des unités de sang hémoconcentrés par CSA et des dérivés de sang homologues. La demande pour des produits sanguins homologues a été réduite dans les premières 24 heures après la chirurgie (0,5 ± 1,0 vs 1,3 ± 1.8 unites; P < 0,05) comparativement au Groupe 2 (n = 56) chez qui uniquement des dérivés de sang homologue ont été utilisés. Plus de patients dans le Groupe 1 n’ont pas requis de transfusion (45 vs 8; P < 0.05) et il n’y avait pas d’augmentation du risque d’hémorragie majeure. En considérant le coût d’investissement, l’utilisationde la CSA ne présentait pas d’avantage économique. On conclut que l’utilisation de la CSA était sécuritaire, avec aucune augmentation du risque de saignement, diminuant la nécessité de transfusion de sang homologue, mais reprisénte un coût additionnel.

Nalbuphine antagonism of fentanyl-induced ventilatory depression: a randomized trial.

The authors anesthetized 18 patients with good pulmonary and ventricular function for coronary artery bypass grafting with high doses of fentanyl. When the patients were arousable and their vital signs stable in the intensive care unit, the authors administered nalbuphine or placebo (randomly and double-blinded) until extubation criteria were met, and subsequently gave nalbuphine for analgesia. In one of ten placebo patients, tracheal extubation was accomplished without nalbuphine. This patient then retained CO2 and required nalbuphine; the other nine placebo patients could not be extubated after placebo trials and were given nalbuphine. In all other patients in both groups, tracheal extubation was successful following nalbuphine (median dose 60 micrograms/kg, range 30-180 micrograms/kg). One patient became renarcotized 4 h after tracheal extubation without an increase in plasma fentanyl concentration; he received an additional dose of nalbuphine and recovered without further incident. Nine patients required treatment with vasoactive agents or beta-blockers for hypertension or tachycardia associated with the administration of nalbuphine. Eight of 18 patients were not satisfied with nalbuphine analgesia, and required morphine for relief of their pain. Recurrent elevations of fentanyl concentrations in plasma were observed and appeared to be related to increasing motor activity. Nalbuphine is an effective opioid antagonist after fentanyl anesthesia, but its use is associated with side effects, and analgesia for the post-sternotomy patient may be unsatisfactory unless the dose is carefully titrated to the minimum required to antagonize respiratory depression.

Paradoxical response of plasma lipoprotein(a) in patients undergoing cardiopulmonary bypass

Plasma lipid, lipoprotein and apolipoprotein levels are known to decrease after major surgery. Coronary artery bypass surgery additionally involves use of extracorporeal circulation by use of a cardiopulmonary bypass pump, which necessitates hemodilution due to saline dextrose infusion to prime the pump. To investigate changes in lipids, lipoproteins and apolipoproteins as well as changes in C-reactive protein and albumin we conducted a study on 22 patients undergoing cardiac surgery involving cardiopulmonary bypass. Timed arterial blood samples were taken before, during and after cardiopulmonary bypass. At the onset and during cardiopulmonary bypass a rapid and significant fall was observed in all lipids and lipoproteins except lipoprotein(a) with recovery to near basal levels by 72 h for cholesterol, triglycerides, high density lipoprotein cholesterol and albumin, while apolipoproteins AI and B remained below basal levels during the postoperative period up to 72 h. In contrast, lipoprotein(a) levels increased at the onset, doubled during cardiopulmonary bypass and remained elevated postoperatively. On the other hand, C-reactive protein levels fell at the onset and during cardiopulmonary bypass but they became markedly elevated postoperatively. When results were corrected for hemodilution, the response patterns remained unchanged. As lipoprotein(a) is both atherogenic and thrombogenic, its elevation during cardiopulmonary bypass may be clinically important.

Serum protein changes during cardiopulmonary bypass: implications for host defence:

A reduction in host defence capability, with increased risks of infection, occurs after open-heart surgery to a greater degree than after nonbypass surgery. Our costs for postoperative infections are large, about 15% of the total cost of open-heart surgery; better understanding of factors contributing to infection might allow reduction in these costs. Disturbance of the mechanisms involved in the handling of haemoglobin and iron may be among such factors, since free iron is a facultative requirement for the growth of all micro-organisms. We evaluated the change in serum proteins, particularly haptoglobin, during cardiopulmonary bypass. This study, in eight patients undergoing uncomplicated aortocoronary bypass employing a bubble oxygenator with haemodilution, and without clinical evidence of haemolysis, showed that free, unbound haptoglobin, evaluated by agarose gel electrophoresis, disappeared and was replaced by haemoglobin-bound haptoglobin within minutes of going on bypass. Such changes were not seen in three control patients who underwent comparably extensive surgery without bypass or in-bypass controls, in whom blood was evaluated after dilution with oxygenator prime. The disappearance of free haptoglobin and the possible disturbance of iron transport may have implications for host defences after bypass.

Gentamicin solution for mediastinal irrigation: Systemic absorption, bactericidal activity, and toxicity

Local irrigation with gentamicin sulfate represents a possible substitute for neomycin sulfate, used for many years but now no longer available for use as an irrigation fluid. In this investigation, mediastinal irrigation with gentamicin was used in 12 patients who had experienced problems after a heart operation. The regimen employed for mediastinal irrigation with gentamicin was equipotent with that using neomycin. We sought to determine the degree of absorption and risk of either inadequate or toxic blood levels that might follow gentamicin absorption. Irrigation periods were short, ranging from one to four days and determined by measurements of plasma gentamicin concentration using radioimmunoassay evaluation. Systemic gentamicin absorption occurred in all patients. Toxic levels of higher than 8.0 micrograms/mL occurred and were size related, ie, correlated with smaller body weight and surface area, and sex related, ie, female sex. Larger-sized patients often had inadequate levels. Despite the potential risk from toxic blood levels, major increases in serum creatinine levels were not seen. These findings suggest that monitoring of plasma gentamicin levels during mediastinal irrigation with gentamicin is mandatory to avoid both inadequate treatment and toxicity.