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Choosing replacement and maintenance fluids

For daily maintenance requirements 500 ml of Hartmann's solution and 1500 ml of dextrose 5% is sufficient to supply electrolytes and fluid, but it should be noted that it only provides 600 cal.

If the operation was a relatively straightforward procedure in a fit patient not involving the gastrointestinal tract, and associated with little blood loss and a short general anaesthetic, for example hernia repair, cystoscopy or pinning of a fracture, intravenous fluids may not be required at all. The patient may be allowed to drink when fully conscious after the operation and be able to have a normal diet as soon as convenient.

Dangers of potassium infusion: It should be noted that Hartmann's solution and Haemaccel contain potassium, and these should be used sparingly, if at all, in a patient whose urine output is reduced. It is not necessary to replace potassium if the anticipated need for intravenous fluids is likely to last for 1-2 days as the body's store of potassium (3000 mmol) is more than sufficient.

POSTOPERATIVE COMPLICATIONS Haemorrhage

Haemorrhage is usually the result of a failure of technique but coagulation disorders may also play a role. Occult blood loss, for example postoperative haemoperitoneum, should be suspected when unexplained tachycardia, decreased blood pressure, decreased urine output and peripheral vasoconstriction occurs. A fall in the haematocrit is useful in making the diagnosis but this may not occur until quite late and consequently is of limited diagnostic help. The differential diagnosis of immediate postoperative hypotension includes MI, cardiac dysrhythmia, pulmonary embolism, pneumothorax, pericar-dial tamponade and severe allergic reaction. Infusions to expand the circulatory volume should be started as soon as other diseases have been ruled out. If hypotension persists, reoperation should be performed.

Respiratory complications

Postoperative respiratory complications (atelectasis and pneumonia) occur significantly more often than cardiac complications and are associated with significantly longer hospital stays. An accurate history and examination is central to the identification of patients at risk for respiratory complications. Approximately one-third of patients with respiratory complications will also have cardiac complications. Risk factors can be patient or procedure related:

• Patient-related risk factors:

- Chronic lung disease.

- Current cigarette smokers even in the absence of chronic lung disease.

- Morbid obesity.

• Procedure-related risk factors:

- Surgical procedures lasting longer than 3-4 h.

- General anaesthesia compared to regional anaesthesia.

- The rate of complications is inversely related to the distance of the incision from the diaphragm.

Routine preoperative spirometry does not accurately predict the risk of postoperative pulmonary complications in individual patients; however, one simple tool to assess capacity is stair climbing. In a prospective study of patients undergoing thoracotomy or laparotomy, the incidence of postoperative cardiopulmonary complications unable to climb one flight of stairs was 89%. No patient able to climb seven flights of stairs developed a postoperative complication.

Treatment

Cessation of smoking, weight reduction and prophylactic treatment of at-risk patients is helpful; oral and inhaled bron-chodilators, systemic steroids and antibiotics can decrease respiratory complications. Good postoperative analgesia, physiotherapy and provision of humidification to loosen secretions are vital; incentive spirometry can be helpful and chest physiotherapy is more effective if started preoperatively.

Cardiac complications

The normal physiological response to surgery is an increase in circulating catecholamines, which leads to an increase in heart rate, myocardial contractility and peripheral vascular resistance, all of which increase myocardial oxygen demand. Also, myocardial oxygen supply may be decreased by hypotension, tachycardia, anaemia and hypoxia. A patient with significant coronary artery disease may not be able to cope with this and may develop myocardial ischaemia. Most MI occur on the first postoperative night. Diagnosis of a perioperative MI can be difficult as the majority of postoperative myocardial ischaemic events are not associated with anginal pain. When present, features of perioperative MI include dysrhythmias, heart failure, hypotension and impaired mental status especially in the elderly.

In patients with significant ischaemic heart disease, coronary artery bypass grafting (CABG) prior to non-cardiac surgery is significantly protective against adverse cardiac events. The protection afforded by CABG appears to last for many years; however, the operative mortality of CABG is approximately 1%. Percutaneous transluminal angioplasty has also been advocated to alleviate myocardial ischaemia prior to non-cardiac surgery and also as an emergency intervention in perioperative patients with evolving acute MI in whom thrombolysis is clearly contraindicated.

Various interventions have been shown to reduce cardiac morbidity; a meta-analysis reported in 2001, showed that postoperative epidural analgesia, especially thoracic epidural analgesia, continued for more than 24 h reduces postoperative MI and maintenance of perioperative normothermia has also been shown to reduce cardiac morbidity in patients with known coronary artery disease undergoing major non-cardiac surgery.

In a randomized, double-blind, placebo-controlled trial comparing atenolol with placebo on overall survival and cardiovascular morbidity in patients with or at risk for coronary artery disease who were undergoing non-cardiac surgery, overall mortality after discharge from the hospital was significantly lower among the atenolol-treated patients than among those who were given placebo.

Heart failure

Heart failure is a syndrome where the cardiac output is insufficient for the body's needs. The best predictor for the development of postoperative heart failure is symptoms and signs of its existence preoperatively. However, heart failure can be precipitated by an increase in demand for cardiac output, such as anaemia, hypoxia and sepsis or through deterioration in pump function through MI, perioperative volume overload, pulmonary embolus or cardiac dysrhyth-mia. Treatment is directed at the primary cause and provision of medical therapy directed at normalizing intravascular volume and cardiac output.

Cardiac dysrhythmias

Cardiac dysrhythmias are common in the perioperative period; transient dysrhythmias are said to occur in approximately 80% of patients if continuous electrocardiographical (ECG) monitoring is employed, but only 5% are significant. Atrial fibrillation is the commonest rhythm disturbance seen in patients undergoing non-cardiac surgery, occurring in 10% of patients admitted to a surgical ICU.

The guiding principle in the treatment of perioperative cardiac dysrhythmias and conduction disturbances is that

Table 3.3. Analysis of infection rates related to wound types.

Wound type Total number Number infected %

Clean 47 054 732 1.5

Clean contaminated 9370 720 7.7

Contaminated 442 676 15.2

Dirty 2093 832 40

Overall 62 939 2960 4.7

Note: From Cruse PJ, Foord R. The epidemiology of wound infection. A 10-year prospective study of 62 939 wounds. Surg Clin North Am 1980; 60: 27-40.

the cause of the dysrhythmia should be identified and reversed if possible. Common causes include electrolyte disturbance, acid-base imbalance, acute volume depletion and alterations in autonomic tone.

Wound complications

Haematoma

Wound haematoma is almost always caused by imperfect haemostasis. Haematoma produces elevation and discolouration of wound edges, discomfort and swelling. At times, blood leaks through skin sutures. Small haematomas resolve but increase the incidence of wound infection. Treatment consists of gentle evacuation of clots under sterile conditions. Neck haematomas following operations on the thyroid and parathyroid may compress the trachea and need urgent evacuation.

Seroma

This is a serous fluid collection beneath the wound. Seromas often follow operations that involve elevation of skin flaps. Seroma delays wound healing and increases the risk of wound infection. A seroma may be gently expressed or evacuated by needle aspiration.

Infection

Wound infection has undergone a change in nomenclature and the term surgical site infection (SSI) is now used. SSI can be classified as (a) incisional or (b) organ space. Incisional SSI are further classified as superficial or deep.

Risks of SSI can be considered as patient or procedure related. The most important factor during the procedure is the degree of contamination (see Table 3.3). Patient-related factors that increase risk of SSI include:

• malnutrition or obesity,

Prophylactic antibiotics effectively reduce the rate of postoperative infection. One pre-incisional dose is usually sufficient, although a second dose is advised during surgery lasting more than 3-4 h. Prolonged antibiotic therapy should be avoided because of the cost and the increased likelihood of colonization and infection with antibiotic resistant bacteria.

Dehiscence and incisional hernia

Dehiscence of the wound is most often seen in abdominal surgical procedures. Systemic risk factors are old age, diabetes mellitus, uraemia, immunosuppression, jaundice, hypoalbu-minaemia, cancer and obesity. Local risk factors are poor surgical technique of wound closure, raised intra-abdominal pressure due to obstructive airway disease and infection.

Wound dehiscence is commonly seen between the fifth and eighth postoperative day. The discharge of serosan-guinous fluid is often the first warning of a disruption. In some cases, sudden dehiscence may occur on coughing or straining. Patients with wound dehiscence are returned to the theatre and the wound repaired.

Incisional hernia occurs in approximately 10% of lapar-otomy incisions; one important risk factor is the individual surgeon's technique and attention to detail; studies have shown no differences in the complication rate between different suture materials or between continuous and interrupted closure techniques but marked individual differences in wound complication rates between surgeons. A continuous big-bite closure (resulting in a 4:1, suture length: wound length ratio) with slowly absorbable monofilament suture has been found to be the optimal technique (see Chapter 6).

Fever

Fever is common in the postoperative period and it has diverse causes. Tissue trauma during surgery, with systemic release of pyrogenic substances, may be a major cause of early postoperative fever. Other non-infectious causes of early postoperative fever include drug hypersensitivity (including anaesthetic agents) and transfusion reactions.

Fever within 48 h after surgery is usually caused by atelectasis. Lung re-expansion causes the body temperature to return to normal. When fever appears after the second postoperative day, the differential diagnosis includes venous access site phlebitis, pneumonia and urinary tract infection.

Patients without an infection are rarely febrile after the fifth postoperative day. The onset of fever this late would suggest a wound infection, or less often, anastomotic breakdown and intra-abdominal abscess. Bacterial pneumonias are often precipitated by perioperative aspiration or early postoperative atelectasis and consequently tend to occur within the first week of surgery.

Urinary tract infections may appear at any time. They occur almost exclusively in patients with bladder catheteri-zation or a previous history of urinary tract manipulation. Thrombophlebitis and pulmonary embolism are important causes of postoperative fever, which may occur either early or late.

Urinary retention

Urinary retention is common, especially after pelvic or peri-neal operations or operations under spinal/epidural anaesthesia and may require temporary catheterization. In a male patient if a catheter cannot be passed, a suprapubic cystotomy may be needed.

Postoperative delerium and cognitive impairment

Delerium, or acute confusional state, is a clinical syndrome characterized by acute disruption of attention and cognition, and it is associated with increased morbidity and mortality, longer hospital stays, higher costs, poor functional recovery and frequently leads to increases in dependency on carers after discharge.

Hypoxia must be excluded either by oximetry or blood gas estimation. A review of the anaesthetic chart or recovery room notes may reveal the cause. In most cases, of course, no cause is found. Management involves:

• the correction of metabolic disturbances;

• elimination or reduction of all non-essential medication;

• the presence of family members to provide emotional support;

• hypnotics, for example chloral hydrate (250-1000 mg orally at bed time) if sleep disturbance is severe or a short course of low-dose neuroleptic (oral or intramuscular haloperidol).

Lesser degrees of postoperative cognitive dysfunction, characterized by impairment of memory and concentration are common after major surgery in the elderly and symptoms may persist for months or years.

Venous thromboembolism

The pathophysiology of venous thromboembolism (VTE) involves three factors (Virchow's triad):

1. damage to the vessel wall,

2. slowing down of blood flow,

3. an increase in coagulability.

Clinical risk factors include the following: increasing age; prolonged immobility, stroke or paralysis; previous throm-botic disease; cancer and its treatment; major surgery (particularly operations involving the abdomen, pelvis and lower extremities); trauma (especially fractures of the pelvis, hip or leg); obesity; varicose veins; cardiac dysfunction; indwelling central venous catheters; inflammatory bowel disease; nephrotic syndrome and pregnancy or oestrogen use. For surgical patients, the incidence ofVTE is affected by the preexisting factors just listed and by factors related to the procedure itself, including the site, technique and duration of the procedure, the type of anaesthetic, the presence of infection and the degree of postoperative immobilization.

Graded compression elastic stockings (ES) reduce the incidence of leg deep venous thrombosis (DVT). Intermittent

Figure 3.1. Factors contributing to postoperative morbidity. (From Wilmore DW, Kehlet H. Management of patients in fast track surgery. Br Med J 2001; 322(7284): 473-476. Reproduced with permission from the BMJ Publishing Group.)

pneumatic compression (IPC) is an attractive method of prophylaxis because there is no risk of haemorrhagic complications. In trials comparing IPC with prophylactic heparin, both agents produced similar reductions in DVT.

All surgical patients should be assessed for risk ofVTE and appropriate prophylaxis established.

Postoperative nausea and vomiting, and ileus

Fear of postoperative nausea and vomiting (PONV) is a leading concern for patients about to undergo surgery. PONV is unpleasant and increases the risk of aspiration pneumonia; it is the leading cause of unexpected admission following planned day surgery. Several factors contribute to the aetiology of PONV:

• individual susceptibility;

• use of opioids in the perioperative period;

• gastrointestinal procedures;

• duration of surgery;

• intra- or postoperative hypoxaemia.

The incidence of postoperative vomiting may be reduced by preoperative administration of ondansetron, a 5-hydrox-ytryptamine 3 (5-HT3) receptor antagonist.

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