ORGANISATION

The convergence of large numbers of patients with very similar problems in the cardiac ICU provides an ideal environment for the standardisation of care based on protocols and clinical pathways. One of the traps of postoperative cardiac care is that the sameness of the patients tends to obscure their particularity. Individual patient assessment must carefully address the multisystemic manifestations of cardiovascular and degenerative diseases.

Cardiac surgery involves a continuum of care from presentation to postdischarge management and rehabilitation. The intensive care specialist must be involved in this continuum, not functioning in isolation from surgeons, anaesthetists, cardiologists and family practitioners.

The postoperative stage is largely set by the preoperative and operative phases of management. A component of postoperative management is active participation both in principle and in particular in patient selection and preparation as well as in the conduct of anaesthesia and surgery. Relevant aspects include suitability and preparation for surgery, advanced care planning and more technical issues such as temperature management, invasive monitoring, haemodynamic management and transport. Movement from the operating theatre to the ICU and later to the ward will only appear seamless if the management systems have been well coordinated in advance.

CARDIOVASCULAR MANAGEMENT

The first step in the intensive care management of the newly arrived patient who has undergone cardiac surgery involves a simple transfer of ventilation, monitoring and drug administration from transport to ICU systems. This should be structured to minimise disruption.

Management is conveniently dictated by standardised protocols, which should cover investigations, fluid and electrolyte management, vasoactive and other drug administration and mechanical ventilation. Standardisation is probably more important than the particulars of the protocol, which might vary considerably among institutions. Optimal cardiovascular management requires a sound knowledge of normal and abnormal cardiovascular physiology. It also requires an understanding of the haemodynamic changes usually seen in the postoperative patient (Figure 22.1).¹

Figure 22.1 Haemodynamic changes following cardiac surgery. Systemic vascular resistance index (SVRI).

HYPERTENSION

Complications associated with hypertension include:

Significant postoperative hypertension is more common in patients having a history of hypertension and with cessation of β-blockade, but is reasonably common in the early postoperative period. Both absolute pressure and dp/dt are important factors in vascular injury. Vascular resistance declines over the first few hours (see Figure 22.1), so that therapy during this period is best undertaken with agents with a short duration of action. Nitroglycerine is theoretically more appropriate than nitroprusside because of the possibility of coronary steal with the latter agent.⁶ In practice, this is almost never apparent and nitroprusside appears to be more effective. Simple measures such as the provision of adequate analgesia and sedation should also be considered.

The target blood pressure varies with the indication. Excessive reduction of blood pressure risks reducing myocardial oxygen supply more than demand. Under most circumstances, a mean arterial pressure between 90 and 100 mmHg (12.0 and 13.5 kPa) seems optimal.⁷ Much lower target pressures may be applicable for the management of heart failure or in the presence of a vulnerable aorta, such as occurs with aortic trauma, dissection or aneurysm. Reduction of dp/dt with beta-blockade is more important than absolute blood pressure control in the management of aortic dissection.

LOW CARDIAC OUTPUT

The aetiology of a low cardiac output following heart surgery is diverse (see Table 22.1). The most common causes include:

Transient, reversible myocardial depression may follow an episode of acute ischaemia (preoperative or intraoperative) and is especially problematic where intraoperative myocardial protection has been difficult or suboptimal. Recognition of a low-output state in the absence of invasive monitoring may be difficult. Many of the usual signs of low output are also consequences of anaesthesia and surgery. Tachycardia may be obscured by drugs, hypothermia and heart disease, and even lactic acidosis may be an unreliable marker in this patient group.¹

In the early postoperative period, a relatively low cardiac output may not warrant intervention, providing tissue oxygen delivery is adequate. Since beta-blockade is beneficial in the postoperative cardiac patient, beta-agonists should not be used unquestioningly. Nevertheless, optimisation of cardiac function does confer some benefit⁸ and intervention is clearly required when tissue oxygen delivery is inadequate.

Low cardiac output is associated with increased gastrointestinal, renal and neurological complications.