Cardiac Arrest

Resuscitation of cardiac arrest after cardiac surgery differs from conventional advanced life support (see Figure 8.1):

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  In shockable rhythms, up to three shocks should be administered in rapid succession before chest compressions

  
  
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  In asystole, epicardial pacing should be attempted before chest compressions

  
  
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  In pulseless electrical activity (PEA), pacing-induced VF should be excluded

  
  
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  Epinephrine administration may be deferred and doses reduced to reduce the risk of hypertension after return of spontaneous circulation

  
  
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  Chest reopening should be undertaken after two cycles

Figure 8.1 Algorithm for resuscitation after adult cardiac surgery. Six suggested modifications to the standard ALS algorithm are highlighted in the bright yellow boxes to the sides and below. Therapeutic hypothermia may be considered after successful resuscitation.

(Adapted from the Resuscitation Council (UK) 2010 ALS algorithm)

Initial Optimization

The response to increasing preload can be thought of in three distinct phases (Box 8.1).

Box 8.1 The three phases of the response to increasing preload

In health, preload optimization typically occurs with a PAWP of 10–15 mmHg. Many cardiac surgical patients have reduced LV compliance, which becomes further reduced by the effects of CPB and catecholamines. In these patients, a higher PAWP (i.e. >15 mmHg) is often required to maintain adequate SV.

Heart rate, rhythm and myocardial contractility are the major determinants of myocardial VO₂. Because of its 30% augmentation of end-diastolic volume (EDV), NSR is desirable whenever possible. Atrial or atrioventricular (A-V) pacing at 80–100 bpm can improve endocardial perfusion by shortening the diastolic filling time and reducing the EDV.

VF, and unstable ventricular and supraventricular tachydysrhythmias should be immediately converted by either electrical or chemical cardioversion. Maintenance of normal or supranormal [K⁺] (i.e. 4.5–5.5 mmol l^–1) and [Mg²⁺] reduces ventricular irritability.

Cardiodepressant antidysrhythmics should be used with caution in patients with impaired myocardial function.

Afterload can be viewed as the sum of external forces opposing ventricular ejection, of which the SVR is one component (Box 8.2). Laplace’s law states that the LV wall tension or stress is directly proportional to the intracavity pressure and cavity radius, and is inversely proportional to the LV wall thickness.

Considering the CO, MAP and PAWP in the patient with optimal preload simplifies haemodynamic management (Box 8.3).

Box 8.3 Simplified approach to haemodynamic management in the patient with optimal preload

LV Dysfunction

Ventricular function is commonly depressed for 8–24 hours following CPB. The ideal measure of LV performance, the slope of the end-systolic pressure–volume relationship (ESPVR), cannot easily be derived at the bedside. For this reason, surrogate measures of contractility (i.e. RA pressure, PAWP, MAP, PAP and CO) are used. Although echocardiography can be used to assess ventricular function, the findings are generally load-dependent (Figure 8.2).

Figure 8.2 LV pressure–volume loops illustrating (A) the normal ventricle, and (B) the decrease in slope of the ESPVR line with decreased contractility. This decrease in contractility can also be accompanied by a decrease in the SV, and an increase in the LVEDP.

Decreased contractility can be secondary to metabolic abnormalities, cardiodepressant agents, reperfusion injury and myocardial ischaemia (coronary vasospasm, thrombosis or occlusion). The incidence of perioperative MI (often clinically silent) is thought to be ~5%. The diagnosis of MI in the post-CABG patient may be challenging (Box 8.4).

Box 8.4 Diagnosis of perioperative MI

Before initiating inotropic therapy, all remediable factors (i.e. rate, rhythm, preload and afterload) should be addressed. Indications for use of the IABP and mechanical cardiac support are discussed in Chapters 6 and 16).

RV Dysfunction

RV failure can be difficult to manage because of the dependence of the LV filling on right-sided function. If the RV output falls, the LV filling and therefore the LV output are reduced. The RV is extremely sensitive to increases in afterload (i.e. PVR). Although more effective in LV failure, the IABP may reduce the RV afterload and improve coronary perfusion. Short-term use of an RV assist device may allow time for RV recovery.

Reducing the RV afterload can improve the RV systolic performance and the right heart CO. Drug therapy includes inhaled milrinone, NO (5–10 ppm) and epoprostenol (PGI₂); IV PGI₂ (2–5 ng kg^–1 min^–1); and oral agents, such as sildenafil and bosentan.

Pericardial Tamponade

Pericardial tamponade is characterized by hypotension, tachycardia and an elevated CVP. Although it typically occurs acutely within 24 hours of cardiac surgery, it can develop chronically over several days. In tamponade, the decrease in the LV filling during inspiration is accentuated. The fall in the SV produces a reflex increase in HR and myocardial contractility. Diagnostic clues include those described in Box 8.5.

In addition to detecting an obvious extracardiac collection, the most common TOE manifestation is the collapse of the right-sided chambers when their intracavity pressures are at their lowest – i.e. the RV in early diastole and the RA in early systole. Management consists of resuscitation (Box 8.6) and prompt surgical drainage.

Postoperative AF

AF and atrial flutter are the most common postoperative supraventricular tachydysrhythmias following cardiac surgery. New-onset AF occurs within 24–72 hours of surgery in up to 30% patients. Independent predictors of AF include age >65 years, hypertension, male sex, a previous history of AF and valve surgery.

In the absence of contraindications, all patients who develop AF should be anticoagulated within 24–48 hours. If AF has persisted for >48 hours and therapeutic anticoagulation has not been maintained, TOE should be performed to exclude the presence of LA thrombus.

Electrical or chemical cardioversion to NSR is preferred, especially when patients are haemodynamically unstable, symptomatic or unable to receive anticoagulation. Pharmacological ventricular rate control may be acceptable in some cases.

Respiratory Failure

Acute respiratory failure is the inability to perform adequate intrapulmonary gas exchange causing hypoxia with or without hypercarbia. The accepted quantitative criteria for the diagnosis are PaO₂ <8.0 kPa (60 mmHg) on air and PaCO₂ >6.5 kPa (49 mmHg) in the absence of primary metabolic alkalosis.

Atelectasis affects dependent areas of lung – particularly the left lower lobe following internal mammary artery harvest. The combined effects of anaesthesia, mechanical ventilation and sternotomy reduce functional residual capacity, vital capacity and tidal volume (Vt). These effects may be compounded by diaphragmatic dysfunction caused by direct or thermal (cold) injury to the phrenic nerve. Recruitment manoeuvres, such as PEEP and full lung expansion prior to chest closure, may reverse some of the atelectasis that inevitably occurs during surgery. Postoperative atelectasis is best managed by adequate analgesia, physiotherapy, recruitment manoeuvres, incentive spirometry and forced coughing.

ALI and ARDS

Hypoxia with bilateral pulmonary infiltrates and low LA pressure following cardiac surgery used to be known as ‘pump lung’. The clinical features, which resemble those of sepsis with severe hypoxaemia, include increased PVR, increased vascular permeability and an elevated alveolar–arterial O₂ gradient. This ALI usually resolves within 48 hours or progresses to ARDS (Table 8.1).

The incidence of ARDS following CPB is reported to be as high as 2.5% in some series. Predisposing factors include redo cardiac surgery, hypotension, sepsis and massive transfusion. The aetiology and subsequent complications, rather than respiratory failure itself, dictate mortality from ARDS. Death is usually due to multiple organ dysfunction. The avoidance of CPB does not eliminate the risk of ALI or ARDS. The management of ARDS following cardiac surgery is summarized in Box 8.8.

Box 8.8 General principles of the early management of ARDS following cardiac surgery

Definitions

Nowadays, the term ARF has been replaced by the term acute kidney injury (AKI). The RIFLE classification (Risk of renal dysfunction, Injury to the kidney, Failure of kidney function, Loss of kidney function and End-stage kidney disease) defines AKI according to changes in serum creatinine concentration and urine output (Figure 8.3).

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Related

Related posts:

Chapter 3 – Diagnostic Techniques Chapter 6 – Weaning from Cardiopulmonary Bypass Chapter 14 – Surgery for Cardiomyopathy and Pericardial Disease Chapter 22 – Postoperative Paediatric Care Chapter 21 – Common Congenital Heart Lesions and Procedures Chapter 35 – TOE for Miscellaneous Conditions

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