1.1.3 Cardiac anesthesia

From the earliest days of cardiac surgery, anaesthetists have played a major role in the outcome of operations. As early as 1946, Potts said: "Expert anaesthesia is essential in this type of operation" [22]. However, anaesthetic techniques have evolved considerably over the last half century.

For the first ductus arteriosus ligation by Robert Gross (Boston 1938), the anaesthetist was a nurse, Mrs Betty Lank; she used cyclopropane by mask; her main monitoring was a finger on the child's temporal artery [8]. Most of the children who subsequently underwent surgery (ductus arteriosus ligation, Blalock-Taussig shunt, aorto-pulmonary anastomosis) were cyanotic, hypodynamic and sometimes moribund. The technique consisted of premedication with morphine-scopolamine, intubation with controlled ventilation and cyclopropane anaesthesia; a cannula in the saphenous vein was used for fluid perfusion. Intracardiac surgery began with a closed mitral commissurotomy (Charles Bailey, Philadelphia 1948); in this case K.K. Keown performed anaesthesia with a mixture of oxygen and N₂O (50/50 to 30/70); the patient was intubated under local anaesthesia and ventilated manually. Analgesia was provided by intravenous injections of 0.2% procaine and unconsciousness was maintained by thiopenthal. Monitoring consisted of pressure cuff and ECG on an oscilloscope. The patient was extubated on the operating table [11]. This technique, accompanied by morphine supplements and intercostal procaine infiltrations, became widely used.

The first valve replacements were performed in patients with massive aortic insufficiency. They were intubated awake with local anaesthetic, then put to sleep with low doses of thiopental and maintained with a mixture of O₂ /N₂O supplemented with ether and morphine; in some centres, tubocurarine was used. Monitoring was always pressure cuff and ECG [18]. The operative mortality was 20%. AW. Conn, in Toronto, introduced halothane in 1959; he was also the first to describe radial artery catheterisation for invasive pressure measurement [5]. It should be noted that this catheterisation was performed by open dissection and not by percutaneous puncture (which was introduced in 1970).

For the next decade or so, anaesthesia for bypass surgery was based on the same basic technique described above; monitoring was already well codified: 3 lead ECG, arterial and central venous catheterisation, rectal and oesophageal temperatures, frequent monitoring of arterial and venous gas levels [20]. In 1967, Earl Wynands (Royal Victoria Hospital, Montreal) defined the requirements of anaesthesia for coronary surgery: generous premedication, deep anaesthesia, invasive monitoring, frequent blood gas and potassium checks, maintenance of baseline blood pressure (neosynephrine), postoperative ventilatory support for 4-24 hours in the intensive care unit [30]. The operative mortality was reduced to 1.3%. In 1969, Lowenstein (Massachusetts General Hospital, Boston) proposed the administration of high doses of morphine (0.5 - 3 mg/kg iv) to improve haemodynamic stability and suppress harmful sympathetic stimulation [15]; the administration of high doses of narcotics and curare thus became the hallmark of so-called "cardiac" anaesthesia. Subsequently, high doses of fentanyl (50-100 mcg/kg) were preferred because they reduced arterial resistance less than morphine [27]. In Europe, neuroleptanesthesia (fentanyl - droperidol - curare and ventilation with a 30/70 mixture of O₂ /N₂O) became very popular and was commonly used for bypass surgery. In 1976, Joel Kaplan introduced the intraoperative infusion of nitroglycerin during coronary artery bypass grafting and recommended the use of V5 lead to diagnose ischaemic episodes [9,10]. During the same period, the Swan-Ganz catheter became widely used for more detailed assessment of haemodynamics [28].

Since the early 1980s, various hypnotic agents have been combined: isoflurane, flunitrazepam, midazolam, etomidate, propofol and sevoflurane. New morphinomimetics have been introduced (alfentanil, sufentanil, remifentanil) with the aim of obtaining a greater hypnotic effect and shortening the post-operative phase; the pharmacokinetics of these new substances have made it possible to use continuous infusions and maintain a high degree of stability in relation with the desired effects. Loco-regional anaesthesia appeared in the hope of reducing the physiological response to stress (stress-free anaesthesia) by cardiac sympathicolysis and finding a better balance between the depth of analgesia and the possibility of accelerated recovery [3,14]. However, epidurals have never become the norm in cardiac surgery. These changes have reduced morbidity in certain circumstances, but have not significantly altered patient outcomes.

Regarding the impact of anaesthesia in cardiac surgery, Slogoff and Keats (Texas Heart Institute, Houston) demonstrated in 1985 that the incidence of intraoperative ischaemia leading to infarction in coronary artery bypass grafting was not correlated with the anaesthetic technique itself, but with the performance of the individual anaesthetist [25]. The article is famous for the excess mortality associated with anaesthetist number 7 in the study! Three subsequent publications, each involving more than 1,000 patients, confirmed that the choice of technique had little effect on patient outcome; it was the quality of the anaesthetist that mattered [17,26,29]. Thirty years later, two new studies came to completely different conclusions. The first found that only high-risk patients suffered from the anaesthetist's performance when the anaesthetist was in the bottom quartile of a performance scale [7]. The second showed that 95% of the variability in heart surgery outcomes was due to the patient's own risks, 4% to the surgeon's performance and only 1% to the anaesthetist's performance [19]. What has happened to explain such dissonance over a quarter of a century? Five possible explanations have been suggested [6].

Our understanding of haemodynamics and cardiology has advanced by leaps and bounds.

• The pharmacopoeia has provided a wide range of drugs with specific properties, some of which improve patient outcomes, such as halogenated drugs, β blockers and levosimendan for ischaemic patients [2,12,13,21]. Technology has developed new management systems (sophisticated ventilators, ultrasound puncture, etc.) and monitoring systems (cerebral oxygen saturation,BIS,transesophageal echocardiography, etc.) that improve patient safety [13].
• The training of cardiovascular anaesthetists has improved considerably, particularly with the introduction of echocardiography, which has provided them with huge cardiological, haemodynamic and pathophysiological knowledge that has influenced their entire practice.
• Numerous protocols and recommendations (guidelines), based on acquired evidence and written by experts, have defined the best strategy in difficult situations.
• Standardisation of practice has introduced reliable routines that limit improvisation and impose well-codified procedures.

A major factor in perfecting cardiac anaesthesia was the introduction of transesophageal echocardiography (TEE). The first application of TEE for intraoperative monitoring of ventricular function was by M. Matsumoto (Albert Einstein College of Medicine, New York 1980), although it was only an M-mode function, which was difficult to use [16]. The first two-dimensional TEE images were obtained by Schlutter and Hanrath in 1982 [24]. In the same year, TEE was tested in patients in the operating room by Michael Cahalan and Michael Roizen of UCSF (San Francisco) with the aim of continuously assessing blood volume, function and ischaemia [1,23]. Their presentation to the ASA was a real revolution, especially since some of the leading figures of that time considered this innovation to be "pretentious and hopeless"! The technique was later complemented by colour Doppler and proved to be more sensitive than the ECG for the diagnosis of ischaemia during coronary artery bypass grafting, as demonstrated by F. Clements and N. DeBruijn at Duke University [4]. TEE is now part of routine monitoring in cardiac surgery, and manufacturers have made numerous improvements to the instrumentation over the last decade (tissue Doppler, three-dimensional images, miniaturisation of devices and probes, portable devices, etc).

© PG Chassot  April 2007, last update September 2019

References

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