Intercurrent Disease and Anaesthesia
Intercurrent diseases may have a variety of effects on anaesthesia and surgery:
the course of the disease may be modified by anaesthesia and surgery
the disease may influence the effects of anaesthesia
concurrent drug therapy may influence the effects of anaesthesia
the choice of anaesthetic technique may be affected
the patient’s physiological reserve or functional capacity
the disease processes involved and whether they can be improved before surgery.
Physiological Reserve
It is increasingly recognized that physiological reserve is an important predictor of outcome from major surgery. Cardiopulmonary exercise (CPEX) testing is a useful tool to allow preoperative assessment of cardiovascular and respiratory reserve and the ability to withstand the stresses of major surgery. More simply, or where CPEX testing is unavailable, the capacity of the cardiorespiratory system to respond adequately to perioperative stress can be estimated in terms of metabolic equivalents (METs). If a patient has no major cardiac risk factors (see below) and can achieve more than 4 METs of activity without significant cardiorespiratory symptoms then the perioperative risk of an adverse cardiac event is low (Table 18.1). It may be possible to improve cardiorespiratory reserve before surgery in some patients. Knowledge of physiological reserve will guide the choice of anaesthetic technique, the level of monitoring used and the requirement for Level 2 or Level 3 care postoperatively.
TABLE 18.1
Metabolic Equivalent (MET) Levels for Readily Assessed Activity Levels
MET Score | Approximate Level of Activity |
1 | Dress, walk indoors |
2 | Light housework, slow walk |
4 | Climb one flight of stairs, run a short distance |
6 | Moderate sport, e.g. golf, doubles tennis or dancing |
10 | Strenuous sports or exercise |
One MET is approximately equivalent to an oxygen consumption of 3.5 mL kg−1 min−1.
Adapted from Fleisher LA, Beckman JA, Brown KA et al 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 50:1707–1732.
Extent of Surgery
This determines the level of physiological stress which the patient will experience. High-risk operations (cardiac morbidity > 5%) include aortic and other major vascular procedures; intermediate risk procedures include intraperitoneal, intrathoracic, major orthopaedic or urological surgeries, and also procedures anticipated to be prolonged and to involve significant fluid shifts and blood loss (Table 18.2). Following discussion with the patient and surgeon, it may be appropriate in some cases to consider alternatives to surgery or a less major operation if the patient is considered at too high a risk. In some cases the appropriate decision is not to undergo surgery.
TABLE 18.2
Cardiac Risk* Stratification for Non-Cardiac Surgical Procedures
Risk Stratification | Procedure Examples |
Vascular (reported cardiac risk often more than 5%) | Aortic and other major vascular surgery Peripheral vascular surgery |
Intermediate (reported cardiac risk generally 1% to 5%) | Intraperitoneal and intrathoracic surgery Carotid endarterectomy Head and neck surgery Orthopaedic surgery Prostate surgery |
Low † (reported cardiac risk generally less than 1%) | Endoscopic procedures Superficial procedures Cataract surgery Breast surgery Ambulatory surgery |
*Combined incidence of cardiac death and non-fatal myocardial infarction.
†These procedures do not generally require non-invasive testing.
Adapted from Fleisher LA, Beckman JA, Brown KA et al 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 50:1707–1732.
CARDIOVASCULAR DISEASE
Preoperative Assessment
The aims of preoperative assessment in this group are to:
define the fitness of the patient for the proposed anaesthetic and surgery
delineate the level of risk of the procedure
decide on the most appropriate anaesthetic technique
assess the requirement for preoperative therapy to be initiated, for example β-blockade or blood transfusion
assess the level of perioperative monitoring required
decide on the patient’s postoperative management, including where this should take place.
The Lee revised cardiac risk index for patients undergoing non-cardiac surgery identifies several intermediate risk factors (Table 18.3). The presence of two or more of these factors has been shown to identify patients with moderate (7%) and high (10%) risk of cardiac complications. There is evidence that this increased risk may continue for 6 months following surgery.
TABLE 18.3
Stratification of Risk Factors for Patients Undergoing Non-Cardiac Surgery
Active cardiac condition:
Unstable coronary syndrome (MI within 30 days, PCI within last 6 weeks)
Decompensated heart failure
Significant arrhythmias
Severe valvular disease
Intermediate Factors according to the Revised Cardiac Risk Index:
History of heart disease
History of compensated or prior heart failure
History of cerebrovascular disease
Diabetes mellitus*
Renal impairment
MI, myocardial infarction; PCI, percutaneous coronary intervention.
*The original Lee Revised Cardiac Risk Index included only diabetes treated with insulin, though it is now thought that Type II diabetes is also an intermediate risk factor.
Adapted from Fleisher LA, Beckman JA, Brown KA et al 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 50:1707–1732.
high-risk surgery (defined as intraperitoneal, intrathoracic or suprainguinal vascular surgery)
ischaemic heart disease diagnosed either from the history or investigation
insulin-dependent diabetes mellitus
History: Symptoms of cardiovascular disease include chest pain, dyspnoea, palpitations, ankle swelling and intermittent claudication. Past medical history and medical records usually reveal the nature and severity of disease, as many patients with cardiovascular symptoms will already have undergone relevant investigations.
Examination: Preoperative cardiovascular examination should include measurement of heart rate, arterial pressure and assessment of peripheral pulses and perfusion. Signs of heart failure should be sought, including a third heart sound, elevated jugular venous pressure and fine basal crepitations on auscultation of the lung fields. The heart should be auscultated for murmurs indicative of valvular disease. In particular, it is vital to make the diagnosis of aortic stenosis pre-operatively.
Risk Stratification: Assessment of the patient’s risk of a perioperative cardiac event provides prognostic information. These issues may be discussed with the patient and appropriate written information provided. Adequate provision of information and the opportunity to ask questions has been shown to allay preoperative anxiety. Assessment also guides perioperative investigation and management.
In patients with an active cardiac condition defined as unstable coronary syndrome, decompensated heart failure, significant arrhythmias or severe valvular disease (Table 18.3), only emergency procedures should be considered. Elective procedures should be postponed for evaluation, testing and optimization of the patient’s active cardiac condition to minimize perioperative risk. The need for evaluation and further testing depends on the risks associated with a particular surgical procedure, the patient’s physiological reserve or functional capacity, and whether testing would change management. Patients undergoing low-risk surgery, or those with proven good functional capacity undergoing intermediate or higher risk surgery, can usually proceed to surgery. They will only require further invasive cardiac investigations if it would change management (i.e. they would require medical optimization or be a candidate for coronary revascularization) (Fig. 18.1).
FIGURE 18.1 Cardiac evaluation and care algorithm for noncardiac surgery based on active clinical conditions, known cardiovascular disease, or cardiac risk factors for patients 50 years of age or greater. *See Table 18.3 for active cardiac conditions. † See Table 18.1 for estimated MET level equivalent. ‡ Clinical risk factors include ischaemic heart disease, compensated or prior heart failure, diabetes mellitus, renal insufficiency, and cerebrovascular disease (Table 18.3). §Consider perioperative beta blockade for populations in which this has been shown to reduce cardiac morbidity/mortality. ACC/AHA indicates American College of Cardiology/American Heart Association. HR, heart rate; LOE, level of evidence; and MET, metabolic equivalent. (Adapted from Fleisher LA, Beckman JA, Brown KA et al 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 50:1707–1732.)
For example, patients who have sustained a myocardial infarction (MI) within the 30 days before proposed surgery are a high-risk group. As a result of increased sympathetic stimulation and the coagulation activation secondary to surgery, such patients have a very high risk (up to 28%) of perioperative MI, which carries a high (10–15%) mortality. A history of uncomplicated MI more than 30 days before surgery is no longer considered an absolute contraindication to elective surgery, provided that the patient is symptom-free and has a good exercise capacity (see Table 18.1).
Increasing numbers of patients now present for non-cardiac surgery having undergone percutaneous coronary interventions (PCI), particularly intracoronary stenting (ICS). Guidelines for the optimal perioperative management of these patients have been produced (Fig. 18.2). There are a number of important points. Firstly, it is beneficial to discuss the patient’s management with an experienced cardiologist. The risk of non-cardiac surgery in patients with intracoronary stents depends on the timing of surgery related to insertion of the stent and the type of stent used. Bare metal stents have been largely superseded by drug-eluting stents, which contain a cytotoxic agent. This is slowly released from the ICS to limit endothelialization, which reduces the incidence of thrombosis and stenosis within the stent itself. However, more prolonged and intensive antiplatelet therapy is required for drug-eluting stents because they are at increased risk of thrombosis until re-endothelialization has occurred. Following insertion of any ICS, there is an initial requirement for dual antiplatelet therapy (e.g. aspirin and clopidogrel). Non-cardiac surgery should be avoided during this time if possible. If antiplatelet therapy is stopped, the risk of stent thrombosis (which carries a 7% mortality) is high, while continuing therapy increases the risk of perioperative bleeding. The duration of dual antiplatelet therapy should be a minimum of one month after bare metal stents and up to 12 months for drug-eluting stents. It is recommended that even urgent surgery should be postponed for at least 4–6 weeks after ICS insertion, and elective surgery deferred for 3 months after bare metal stent, and for 12 months after drug-eluting stent insertion. If possible, even beyond these times, aspirin should be continued throughout the perioperative period, particularly because abrupt cessation of aspirin increases thrombogenicity. In the future, the possibility of bridging therapy with short-acting glycoprotein IIb/IIa inhibitors such as tirofiban may be considered.
FIGURE 18.2 Recommended timing of noncardiac surgery following percutaneous coronary intervention (PCI) depends on whether a stent was placed and the type of stent used. (Adapted from Fleisher LA, Beckman JA, Brown KA et al 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery. J Am Coll Cardiol 50:1707–1732.)
Investigations: Standard investigations including haematology, biochemistry, an ECG and chest X-ray are necessary in all patients with proven or suspected cardiovascular disease. A coagulation screen may be indicated.
Subsequent investigations depend on the assessed risk for the patient and the clinical findings.
Between these two extremes lies a group of patients at increased risk of perioperative cardiovascular events in whom further assessment is indicated because perioperative care is influenced by the results. Moreover, accurate determination of risk to the patient may help decision-making with regard to the need for surgery and/or the type of operation and anaesthetic (Fig. 18.1).
Patients who should be considered for further pre-operative testing include:
patients with poor or unknown functional capacity
patients with clinical risk factors undergoing intermediate or high-risk surgery
patients with diabetes mellitus
Preoperative Therapy
Pre-Existing Cardiovascular Disease: Ischaemic heart disease. Medical therapy should be reviewed and optimized if symptoms are poorly controlled.
Antihypertensive therapy should be continued as far as possible throughout the perioperative period.
Treatment and Additional Interventions: β-Blockers. Established β-blocker therapy should be maintained throughout the perioperative period either orally or intravenously if necessary. Sudden preoperative cessation may be associated with rebound effects such as angina, myocardial infarction, arrhythmias and hypertension. The dose of β-blocker may be reduced if there is undue bradycardia preoperatively (< 50 beat min−1). Intraoperative bradycardia usually responds to intravenous atropine or glycopyrrolate. Some studies have shown that institution of perioperative β-blockade reduces short and long term cardiovascular morbidity and mortality in patients with definite evidence of ischaemic heart disease undergoing high-risk surgery.
Premedication: Anxiety is a cause of sympathetic nervous system activation which may be detrimental in patients with cardiovascular disease. While not all patients require anxiolytic premedication, there should be a low threshold for use in these patients. A benzodiazepine such as temazepam is usually satisfactory. In patients with low or fixed cardiac output states, e.g. mitral or aortic stenosis, constrictive pericarditis or congestive cardiac failure, and other high-risk patients, it is important to avoid hypotension or excessive sedation, respiratory depression and hypoxaemia which could result from premedication, and in these situations it may be preferable to omit sedative premedication.
Anaesthesia: General Principles
Anaesthesia should comprise a balanced technique aimed at maintaining cardiovascular stability. A variety of options may be suitable, including both general and regional anaesthesia or a combination.
Tachycardia should be avoided and an adequate arterial pressure maintained (there should not be a sustained reduction in arterial pressure of more than 20% of the patient’s normal pressure). Coronary perfusion and myocardial oxygen delivery are thus maintained without increasing myocardial work and oxygen requirements.
For patients identified as high risk, consideration should be given to stress reduction. Measures to achieve this are dictated by the patient and operative factors. These include the following:
Use of neuraxial blockade. This has been associated with reduced perioperative myocardial ischaemia and infarction. However, this must be balanced against the sympathetic block and associated hypotension. This may be pronounced, particularly with a high spinal block. Early judicious use of vasopressors coupled with maintenance of intravascular volume should limit this problem. However, neuraxial blockade, particularly spinal block, is relatively contraindicated if there is severely limited cardiovascular reserve and if maintenance of adequate arterial pressure is critical, e.g. severe aortic stenosis (see below).
The level of intraoperative monitoring should be dictated by risk assessment. The following should be considered in addition to standard monitoring.
Five-lead ECG. The usual ECG configuration for anaesthetic monitoring is standard limb lead II. Whilst this is useful for identifying arrhythmias, myocardial ischaemia occurs most commonly in the left ventricle and is detected more sensitively with a CM5 configuration (see Fig. 16.2).
Direct arterial pressure recording.
CVP monitoring with or without central venous oxygen saturations.
Oesophageal Doppler, providing a measurement of cardiac output and intravascular filling.
Other minimally invasive cardiac output monitors are now available and may prove useful as intraoperative monitors. Examples include devices which derive cardiac output and other variables from the arterial pressure waveform using internal algorithms. Some devices (FloTrac/Vigileo or LiDCO) use a standard arterial catheter whereas others (PiCCO) require a dedicated thermistor tipped catheter in a proximal (femoral or axillary artery).
Pulmonary artery flotation catheter with continuous cardiac output and mixed venous oxygen saturation monitoring.
Patients should be well oxygenated and normocapnic.
Close attention to fluid balance is mandatory. This begins preoperatively when fluid depletion secondary to factors such as excessive fasting times and bowel preparation should be corrected. As far as possible, normovolaemia should be maintained. Intravascular volume depletion is known to compromise organ perfusion and oxygen delivery but there is increasing evidence that postoperative recovery is also compromised by excessive volume and sodium loading in the immediate perioperative period.
Patients at high risk from cardiovascular disease do not tolerate anaemia. The optimal level of haemoglobin is the subject of much discussion but is probably around 10 g L−1.
Patients should be actively warmed to avoid hypothermia, which activates the stress response, predisposes to arrhythmias and increases oxygen consumption postoperatively as a result of shivering.
Effective perioperative analgesia is essential. Pain is a potent stimulator of the stress response and uncontrolled sympathetic activation increases myocardial work and oxygen demand, predisposing to myocardial ischaemia or infarction.
Before embarking on anaesthesia and surgery, consideration needs to be given to the patient’s management and destination postoperatively, e.g. would benefit be derived from a period of artificial ventilation or continued close monitoring in a high dependency or intensive care area postoperatively?
Good communication between all of the relevant carers, including cardiology, critical care and the surgical team, is important.
Anaesthetic Agents: Most intravenous anaesthetic induction agents are cardiovascular depressants, causing both vasodilatation and myocardial depression. This is exaggerated in patients with low fixed cardiac output states and by concurrent hypovolaemia. Of the agents in regular use, etomidate is the least cardiac depressant. Care with dosing and rate of administration limits the hypotension caused by drugs such as propofol or thiopental. Co-induction with more than one agent may be beneficial in reducing the dose requirements of each and limiting hypotension. Concurrent administration of midazolam and a short-acting opioid (alfentanil or fentanyl) is often used. Remifentanil may be useful in these patients, in a low-dose infusion of 0.1–0.2 μg kg−1 min−1. It limits the dose of induction agent required and blunts the cardiovascular response to laryngoscopy and tracheal intubation. However, used in high doses, it may induce respiratory muscle stiffness and make bag and mask ventilation difficult before the onset of neuromuscular blockade.
Of the neuromuscular blocking agents, rocuronium and vecuronium are the most cardiostable.
Arrhythmias
Antiarrhythmic therapy should continue throughout the perioperative period.
Indications for preoperative temporary pacing include:
bradyarrhythmia unresponsive to atropine if associated with syncope, hypotension or ventricular arrhythmias
second-degree heart block (Mobitz 2)
first-degree heart block associated with bifascicular block
Intraoperative Arrhythmias: Arrhythmias are common in the perioperative period and are often self-limiting and require no specific treatment. However, precipitants of these arrhythmias should be sought and corrected if possible as they are more likely to occur and cause cardiovascular compromise in patients with underlying heart disease.
Factors predisposing to intraoperative arrhythmias include the following.
vagal stimulation, e.g. anal or cervical dilatation, traction on mesentery, traction on extraocular muscles
laryngoscopy and tracheal intubation
laparascope insertion or intra-abdominal insufflation of gas with peritoneal stretching during laparascopic procedures.
Management: This depends on the nature of the arrhythmia, likely causes and the degree of haemodynamic compromise.
The precipitant should be removed if possible. Reflex arrhythmias tend to occur more commonly during light anaesthesia and may often be prevented by deepening anaesthesia.
Physiological abnormalities should be corrected, as specific antiarrhythmic therapy may be ineffective in the presence of uncorrected hypoxaemia, hypovolaemia or electrolyte abnormalities. Treatment of these should be concurrent with specific management of the arrhythmia.
Intraoperative Bradyarrhythmias: Bradyarrhythmias may often be prevented and may be treated using an intravenous anticholinergic, e.g. atropine or glycopyrrolate.
Intraoperative Tachyarrhythmias: These are either supraventricular or ventricular in origin. Generally, but not exclusively, supraventricular arrhythmias are narrow-complex, in distinction to broad-complex ventricular arrhythmias.
If the patient is not severely compromised, management depends on the individual arrhythmia:
Atrial fibrillation. This is the commonest supraventricular arrhythmia seen intraoperatively. Often, a return to sinus rhythm cannot be achieved until the underlying precipitants are resolved. Improvements in oxygenation, volume status and analgesia may all improve the situation. However, ventricular rate control may also require treatment with either amiodarone or digoxin. Beta blockers or verapamil may also be used to slow ventricular rate. When surgery is complete, anticoagulation should be considered to avoid the embolic complications of atrial fibrillation.
Atrial flutter. This should be managed in the same way as atrial fibrillation if it occurs intraoperatively.
AV node/AV re-entry tachycardia and atrial tachycardia. Vagal manoeuvres, e.g. carotid sinus massage, may be tried, as can intravenous adenosine. Adenosine transiently slows AV conduction and may convert supraventricular tachycardia (SVT) to sinus rhythm. Alternatively, it may aid diagnosis by revealing flutter or fibrillation waves. A rapid i.v. bolus of 6 mg is given, followed by 12 mg a maximum of three times at 2-min intervals. Adenosine is contraindicated in patients with asthma, second- or third-degree heart block, patients receiving carbamazepine or dipyridamole and patients with a denervated heart, e.g. after cardiac transplant. Care must be taken with its use if the patient has Wolff-Parkinson-White syndrome. Verapamil, β-blockers and amiodarone may control the ventricular rate. Intravenous verapamil should never be given to a β-blocked patient.
Ventricular tachycardia. Synchronized DC cardioversion is the treatment of choice. Alternatively, amiodarone (300 mg i.v. over 20-60 min, followed by an infusion of 900 mg over 24 h) may be given if the arrhythmia is well tolerated. Lidocaine 1 mg kg− 1 may be used as an alternative if amiodarone is not available, but should not be given if amiodarone has been given already.
Permanent Pacemakers: Many patients with these devices have underlying heart disease which should be managed accordingly.
Permanent pacemakers are inserted in an increasing number of patients and are becoming increasingly complex. Pacemakers are classified by a series of 5 letters relating to the functions they possess (Table 18.4).
Specific Issues in Anaesthetic Management:
Preoperative assessment: the pacemaker clinic should be contacted to find out the indication for pacemaker insertion, its history and mode of action noted, and any evidence of malfunction sought. The underlying rhythm and rate should be determined and the consequences in case of pacemaker malfunction failure known to determine the need for backup support.
The main intraoperative hazards are electromagnetic interference, which may reprogramme the pacemaker, cause inappropriate inhibition or trigger a defibrillator discharge, or damage the pacemaker circuitry.
Routine investigations should include ECG, chest X-ray and electrolytes.
The pacemaker should have been checked within 3 months of elective surgery. The battery life should be known; consider replacing any device near its elective replacement time.
Due to the complexity of programming available, it is no longer acceptable practice to use a magnet to return the pacemaker to a fixed rate mode. Magnets should not be used, as they have an unpredictable effect on programming.
Some pacemakers have a rate modulation facility. This implies that they can vary the rate of pacing with the patient’s activity detected usually by muscle activity or respiratory activity so that heart rate may be increased with exercise. In general, rate modulation features should be inactivated before anaesthesia and surgery as shivering and muscle fasciculation may be misinterpreted and lead to inappropriate increases in heart rate.
Central venous or pulmonary artery catheters may dislodge pacing leads, particularly if the pacemaker has only recently been inserted. Consideration should be given to use of the femoral vein for central venous access and to alternative monitors of cardiac output.
Alternative pacing should be available in the event of pacemaker failure; external pacing is a rapid and effective back-up.
Pacemakers should be routinely checked postoperatively either before discharge or via an early appointment at the pacemaker clinic. Electromagnetic interference may unpredictably reprogramme the pacemaker or cause damage to it.
Diathermy: bipolar diathermy should be used if possible. If unipolar diathermy is used, the diathermy and ground plate should be as far from the pacemaker as possible and the current pathway should be placed at right angles to the pacing wire(s).
Lithotripsy: the lithotriptor should be at least 12 cm away from the pacemaker and rate modulation should be deactivated.
Peripheral nerve stimulators and transcutaneous electrical nerve stimulators (TENS) should be kept at least 12 cm from the pacemaker.
Defibrillator paddles should be 12 cm away from the pacemaker.
Implantable Cardioverter Defibrillators (ICDs): Increasingly, these devices are used for the management of patients with recurrent life-threatening episodes of VF and VT. ICDs may also have a pacemaker function. As with permanent pacemakers, they may be subject to electromagnetic interference and the same precautions apply.
Valvular Heart Disease
General Principles
The patient’s functional reserve is a good indicator of the severity of a valve lesion
Routine antibiotic prophylaxis is no longer recommended for all patients with valvular heart disease
Patients with valvular heart disease may be receiving anticoagulants; perioperative heparinization is necessary
No specific anaesthetic technique is preferred for valvular heart disease. The aim is to maintain cardiovascular stability. In severe disease, this is often best achieved using a general anaesthetic technique with opioids and controlled ventilation
Mitral Stenosis
Patients with mitral stenosis who present for surgery are frequently receiving digoxin, diuretics and anticoagulants. Preoperative control of atrial fibrillation, treatment of pulmonary oedema and management of anticoagulant therapy (see Ch 13) are necessary. During anaesthesia, control of heart rate is important. Tachycardia reduces diastolic ventricular filling and thus cardiac output, while bradycardia also results in decreased cardiac output because stroke output is limited. As with aortic stenosis, drugs which produce vasodilatation may cause severe hypotension. As a result of pre-existing pulmonary hypertension, patients are particularly vulnerable to hypoxaemia. Both hypoxaemia and acidosis are potent pulmonary vasoconstrictors and may produce acute right ventricular failure. Thus, opioid analgesics should be prescribed cautiously, and airway obstruction avoided.
Hypertrophic Cardiomyopathy
Diagnosis is confirmed by echocardiography.
Acute changes in volume status cause severe haemodynamic consequences and hypovolaemia should be avoided
Outflow obstruction is exacerbated by catecholamines so that inotropic agents should be avoided
Patients are usually receiving a β-blocker which should be continued perioperatively
Patients with previous malignant ventricular arrhythmias are likely to have an ICD in situ.
RESPIRATORY DISEASE
Assessment
Investigations
Chest X-ray: The preoperative chest X-ray is a poor indicator of functional impairment but may be indicated in certain situations:
ECG: This may indicate right atrial enlargement or right ventricular hypertrophy (P pulmonale in II; dominant R wave in III, V1–3). Associated ischaemic heart disease is common, and ECG abnormalities may confirm this (Fig. 18.1).
Haematology: Polycythaemia occurs secondary to chronic hypoxaemia, while anaemia aggravates tissue hypoxia. Leucocytosis may indicate active infection.
Sputum Culture: Sputum culture is essential in patients with chronic lung disease or suspected acute infection.
Pulmonary Function Tests: Peak expiratory flow rate, forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) can be measured easily at the bedside. The FEV1:FVC ratio is decreased in obstructive lung disease and normal in restrictive disease. In the presence of obstructive disease, the test should be repeated 5–10 min after administration of a bronchodilator aerosol to provide an indication of reversibility. An FVC < 1–1.5 L is indicative of limited ability to take large sigh breaths, expand lung bases and clear secretions by coughing.
Blood Gas Measurement: Arterial blood gas measurement is indicated in patients with chronic respiratory disease scheduled to undergo significant surgery and also if there is suspected acute hypoxaemia. It is also advisable when pulmonary function tests are markedly abnormal, e.g. in obstructive disease where the FEV1 is less than 1.5 L. A raised PaCO2 with normal pH indicates chronic hypercapnia with renal compensation; a combined raised PaCO2 and acidosis indicates an acute event. Hypercapnia, particularly if acute, associated with acidosis, is likely to be associated with postoperative pulmonary complications. With a PaCO2 of 6.7 kPa (50 mmHg) or greater, elective controlled ventilation may be required after major surgery. The combination of a low preoperative arterial oxygen tension (PaO2) and dyspnoea at rest is also associated with a high likelihood of the need for planned ventilation after abdominal surgery.