Validation of cardiac echocardiography for measuring cardiac output to be applied for the multiple inert gas elimination technique.

The multiple inert gas elimination technique (MIGET) is being increasingly used in respiratory physiology and pathophysiology. Six inert gases are given as an intravenous infusion then measured in samples of expired air and mixed arterial and venous blood. This requires right-sided catheterization, a procedure that is sometimes ethically inappropriate. The present article reports a method in which inert gas levels in mixed venous blood were calculated, rather than measured, using Fick's law. Echocardiography was used to measure arterial inert gas levels and cardiac output. The method was validated in 11 men scheduled to undergo coronary bypass surgery. Cardiac output was either calculated based on biometrical (C) data or measured using four different methods in random order, namely Fick's law with oxygen (FiO2) or the inert gases (FiIG) as the tracers, thermodilution (TH), and echocardiography (E). Cardiac output values in L.min-1 (mean +/- SD) were as follows: C, 4.99 +/- 0.39; FiO2, 5.44 +/- 0.86; FiIG, 5.55 +/- 0.92; TH, 5.77 +/- 0.88; and E, 5.53 +/- 0.64. No significant differences were found among the four measured cardiac output values, of which the mean was 5.57 +/- 0.70 L/min, a value that was significantly higher than the calculated value. This difference is probably ascribable to the use of dopamine, dobutamine, or epinephrine in six of the 11 patients. A 1 L/min-1 cardiac output error, in either direction, was found to have a marked influence on the distribution of alveolar perfusion at various VA/Q ratios. Conversely, as expected, ventilation distribution was not influenced by cardiac output. In conclusion, echocardiography provides satisfactory cardiac output estimations using the MIGET except in patients with septal hypertrophy, subaortic membranes, a mitral valve prosthesis, or a mitral valve ring.

Nasal continuous positive airway pressure in the perioperative management of patients with obstructive sleep apnea submitted to surgery.

Anesthetic, sedative, and analgesic drugs have been shown in animals and humans to selectively impair upper airway muscle activity. In patients with an already compromised upper airway, these drugs may further jeopardize upper airway patency, especially during sleep. Thus, patients with obstructive sleep apnea syndrome (OSAS) are at high risk for surgery because of the use of the aforementioned drugs in the perioperative period. It has been recommended that such drugs should be avoided or used with extreme caution in patients with OSAS submitted to surgery. We report herein on 16 adult patients with documented OSAS undergoing various types of surgical procedures, including coronary artery bypass surgery. Anesthesia was carried on with the usual type of drugs for each type of surgery. Postoperative opioid analgesia and sedation were not restricted. The first patient, whose OSAS was diagnosed but not treated, died after various complications, including a respiratory arrest in the ward. The second patient experienced serious postoperative complications until a treatment for OSAS with nasal continuous positive airway pressure (N-CPAP) was instituted, and thereafter he made an uneventful recovery. The 14 following patients were started on N-CPAP before surgery, were put on N-CPAP as soon as extubated, on a near-continuous basis, for 24 to 48 h and thereafter for all sleep periods. None of them had major complications. The intensive care unit and hospital stays were the normal ones for each type of surgery in our institution. We conclude that N-CPAP started before surgery and resumed immediately after extubation allowed us to safely manage a variety of surgical procedures in patients with OSAS, and to freely use sedative, analgesic, and anesthetic drugs without major complications. Every effort should be made to identify patients with OSAS and institute N-CPAP therapy before surgery.

Liver transplantation and pulmonary gas exchanges in hypoxemic children.

Hypoxemia in cirrhotic patients is well documented. One of the possible causes of this association seems to be the presence of functional intrapulmonary shunts. The extent of the ventilation/perfusion ratio (VA/Q) abnormalities and their regression after orthotopic liver transplantation has been previously studied in adults by the multiple inert gas elimination technique. We report here a similar study in three children where the hypoxemia was the main indication for early liver grafting, although the liver function was still preserved at that time. Their hypoxemia was almost exclusively caused by a right to left shunt (VA/Q = 0) with a minimal amount of poorly ventilated but well perfused areas (Low VA/Q). This association may explain the poor response of the arterial oxygen pressure to an increased inspired oxygen concentration. Despite these very large VA/Q mismatches, the children underwent successful liver transplantations, resulting in a regression of the intrapulmonary shunt, as demonstrated by multiple inert gas elimination technique, and compatible with a normal life.

[Myocardial revascularization with internal mammary artery graft: analysis of early and late post-operative respiratory morbidity]. / Revascularisation myocardique avec greffon mammaire: analyse de la morbidité respiratoire post-opératoire immédiate et tardive.

To evaluate the respiratory morbidity resulting from myocardial revascularization with internal mammary artery (IMA) graft, we reviewed 153 patients operated on between April and November 1988. There were 124 men with a mean age of 61 years. A bilateral IMA graft was used in 30 patients (20%). During the harvesting of the mammary graft, the homolateral pleura was systematically opened. Acute respiratory failure was more frequent in patients with bilateral IMA (13%) than in patients with unilateral IMA graft (3%) (p less than 0.05). Consequently, the mean duration of mechanical ventilation was longer in patients with bilateral IMA graft: 56 versus 23 hours (p less than 0.05). Lung volume measurements were altered according to a restrictive pattern. On the 9th post-operative day, forced vital capacity was reduced to 59.6% of the pre-operative value in patients with unilateral IMA and to 47.1% in patients with bilateral IMA graft (p less than 0.001). Late results were obtained in 111 patients. After a mean follow-up of 7 months, forced vital capacity was still reduced to 86.8% of the pre-operative value in patients with single IMA and to 78.1% in patients with bilateral IMA graft (p less than 0.001). In conclusion, respiratory morbidity is not negligible. Bilateral IMA grafting should generally be reserved to young patients (less than 65 years) with normal pre-operative pulmonary function tests.

Effects of two inotropic drugs, dopamine and dobutamine, on pulmonary gas exchange in artificially ventilated patients.

The inotropic agents, dopamine (DP) and dobutamine (DB), both decrease PaO2, probably by a redistribution of the VA/Q ratio. The aim of this study was to assess the effect of both drugs on the VA/Q ratio, using the multiple inert gas elimination method. Ten artificially ventilated patients (eight males), aged 45-74 years were investigated. Blood gases, cardiac output and concentrations of inert gases were measured before and 30 min after infusion of DB or DP. DP and DB were administered alternatively at a rate of 5 micrograms.k-1 min-1. The decrease in PaO2 was significantly greater with DP (12 +/- 9 torr) than with DB (7 +/- 9 torr) (P less than 0.01). Both drugs similarly increased cardiac output: +2.61.min-1 +/- 1.4 for DP and 2.21.min-1 +/- 1.5 for DB. Both DP and DB significantly (P less than 0.01) increased the perfusion of alveoli with VA/Q = 0 (+4 +/- 7% for DP and +3 +/- 7% for DB) and 0 less than VA/Q less than 0.1 (+11 +/- 8.5% for DP and +5.5 +/- 10.5% for DB) (no significant difference between the drugs). When shunt and "shunt-like" effect are considered together, there was a significantly greater increase in the amount of blood going to alveoli with a low VA/Q ratio with DP compared to DB. Both drugs decreased the perfusion of alveoli with 0.1 less than VA/Q less than 10, but the decrease was significantly less for DB than for DP (-15 +/- 6.5% for DP and -8.5 +/- 7% for DB, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

[Surgical plasty of the left main coronary artery]. / La plastie chirurgicale du tronc commun de l'artère coronaire gauche.

Critical stenosis of left main coronary artery (LMCA) is usually treated by conventional bypass surgery. However, this approach consumes an appreciable length of conduit, leads to occlusion of LMCA, and restores only a retrograde perfusion of a rather extensive myocardial area. As from June 1985, we performed 13 LMCA patch plasties in 12 patients. LMCA was approached either posteriorly via a curved aortotomy (9 cases), or anteriorly (4 cases) after retraction, partial or complete division of the main pulmonary artery. In 1 patient, a posterior LMCA plasty failed and a conventional double by-pass graft was needed. This patient underwent, 8 months later, a successful repeat patch plasty using a transpulmonary anterior approach. There was no perioperative myocardial infarction. There was no mortality. All of the patients underwent a 6 months postoperative angiographic control, with an excellent result in 12 cases: a significant restenosis of LMCA was successfully treated by percutaneous coronary angioplasty in 1 asymptomatic patient having concomitantly received a sequential mammary graft. All of the 4 patients are asymptomatic. A direct surgical approach to critical stenosis of LMCA is a valuable alternative treatment for this condition.

Should amiodarone be discontinued before cardiac surgery?

Between October 1985 and October 1986, 37 patients, chronically treated with amiodarone, underwent general anesthesia for cardiac, thoracic or vascular surgery. Among them, the 8 non-cardiac surgery patients showed neither intra-, nor postoperative complications. The 29 cardiac surgery patients, had various complications ranging from dysrhythmias (52%), sometimes necessitating a pacemaker (24%), to marked and even fatal vasoplegia. We describe the only fatal case and compare our complication rate with that described in the available literature. Most complications could be symptomatically treated. In addition, amiodarone has a very long elimination half-life: therefore withdrawal before surgery implies delaying operations by several weeks, and puts patients at increased risk of malignant dysrhythmias. However, fatal vasoplegia does occur, and its real incidence should be assessed by a broader survey.