Postoperative Care
THE EARLY RECOVERY PERIOD
Most hospitals have a recovery ward (or postanaesthesia care unit, PACU) within, or in close proximity to, the operating theatre suite (see Ch 20). The Association of Anaesthetists of Great Britain and Ireland (AAGBI) recommends that fully staffed recovery facilities must be available at all times in hospitals with an emergency surgical service. Some locations where anaesthesia is provided (e.g. the X-ray department) may not have a recovery ward. This section describes common problems which occur in the immediate postoperative period and refers specifically to their management in a recovery ward; however, the same principles are applicable to recovery in other locations.
Staff, Equipment and Monitoring
The patient is nursed in a bed if available or if a prolonged stay is anticipated, but sometimes on a trolley (Fig. 40.1). All beds and trolleys must have the facility to be tipped head-down. Suction apparatus, including catheters, an oxygen supply with appropriate face mask, a self-inflating resuscitation bag and anaesthetic mask, a pulse oximeter and an automated non-invasive blood pressure monitor must be available for each patient. In addition, there should be a complete range of resuscitation equipment within the recovery area; this includes an anaesthetic machine, a range of laryngoscopes, tracheal tubes, bougies, intravenous (i.v.) cannulae, fluids, emergency drugs, electrocardiogram (ECG) monitor and defibrillator. Facilities for emergency airway management including surgical airways should also be available (see Ch 22).
FIGURE 40.1 Part of a recovery ward. Many patients are nursed on a trolley, but a bed is used if available, and particularly for those who have undergone major surgery and those who need to stay for several hours.
A wide range of drugs should be stored in the recovery area for the treatment of common complications and also emergency events (Table 40.1).
Consciousness has returned fully, a patent airway can be maintained and protective reflexes are present.
Ventilation and oxygenation are satisfactory.
The cardiovascular system is stable with no unexplained cardiac irregularity or persistent bleeding. Consecutive measurements of pulse rate and arterial pressure should approximate to the patient’s normal preoperative values or be at an acceptable level commensurate with the planned postoperative care. Peripheral perfusion should be adequate.
Pain and nausea are controlled.
CENTRAL NERVOUS SYSTEM
The drugs used. Recovery of consciousness may be delayed if the following agents have been used:
volatile anaesthetics with a high blood/gas solubility coefficient
barbiturates, particularly if large total doses have been given
opioids with a long duration of action, including large doses of fentanyl.
The timing of drug use. Delayed recovery may occur if a long-acting i.v. anaesthetic or analgesic drug has been given towards the end of the procedure, or if the more soluble volatile agents have been continued until the end of surgery.
Pain. The presence of pain speeds recovery of consciousness. Recovery may be delayed after minor procedures or if potent analgesia has been provided by administration of opioids or by regional anaesthesia.
hypoxaemia – in the presence of an adequate circulation, coma occurs only if profound hypoxaemia is present; agitation is a more common sign of hypoxia
hypercapnia – unconsciousness may occur if arterial carbon dioxide tension (PaCO2) exceeds 9–10 kPa
Hypoglycaemia
This occurs most commonly in diabetic patients treated with oral hypoglycaemic agents or insulin and an inadequate intake of glucose. The perioperative management of the diabetic patient is discussed in Chapter 18.
Cerebral Pathology
Consciousness may be impaired by functional or structural cerebral damage. Possible causes include:
episodes of cerebral ischaemia (e.g. carotid artery surgery, profound hypotension) or cerebral hypoxia during anaesthesia
intracranial haemorrhage, thrombosis or infarction – these may occur coincidentally or may have been associated with intraoperative hypertension, hypotension or arrhythmias
pre-existing cerebral lesions, e.g. tumour, trauma – anaesthetic techniques which increase intracranial pressure are likely to impair cerebral function
epilepsy – convulsions may have been masked by anaesthesia or neuromuscular blocking drugs
intracranial spread of local anaesthetic solution after subarachnoid injection – introduction into the subarachnoid space may be accidental, e.g. during epidural block or, rarely, interscalene brachial plexus block; unconsciousness is almost always accompanied by apnoea.
Confusion and Agitation
These occur occasionally during emergence from an otherwise uncomplicated anaesthetic.
Various drugs are associated with postoperative confusion, including:
RESPIRATORY SYSTEM
Common causes of hypoventilation in the immediate postoperative period are listed in Table 40.3. Hypoventilation results in an increase in PaCO2 (Fig. 40.2) and a decrease in alveolar oxygen tension (PAO2), and thus hypoxaemia, which may be corrected by increasing the inspired concentration of oxygen. The risk factors for developing hypoventilation include:
TABLE 40.3
Causes of Postoperative Hypoventilation
Factors Affecting Airway | Factors Affecting Ventilatory Drive | Peripheral Factors |
Upper airway obstruction | Respiratory depressant drugs | Muscle weakness |
Tongue | Preoperative CNS pathology | Residual neuromuscular block |
Laryngospasm | Intra- or postoperative cerebrovascular accident | Preoperative neuromuscular disease |
Oedema | Hypothermia | Electrolyte abnormalities |
Foreign body | Recent hyperventilation (PaCO2 low) | Pain |
Tumour | Abdominal distension | |
Bronchospasm | Obesity | |
Tight dressings | ||
Pneumo-/haemothorax |
CNS, central nervous system; PaCO2, arterial carbon dioxide tension.
FIGURE 40.2 Gas exchange during hypoventilation. Note the relatively rapid increase in alveolar partial pressure of carbon dioxide (PCO2) compared with the slow decrease in arterial oxygen saturation. PO2, partial pressure of oxygen.
Airway Obstruction
Airway obstruction caused by the tongue, by indrawing of the pharyngeal muscles or by blood or secretions in the pharynx may be ameliorated by placing the patient in the lateral or recovery position (see Fig. 21.7). This position should be used for all unconscious patients who have undergone oral or ear, nose and throat surgery, and for patients at risk of gastric aspiration.
Ventilatory Drive
There are several possible causes of reduced ventilatory drive during recovery from anaesthesia (see Table 40.3). The presence of intracranial pathology, e.g. tumour, trauma or haemorrhage, may affect ventilatory drive in the postoperative period. Ventilation is reduced in the presence of hypothermia, although it is usually appropriate for the metabolic needs of the body. Hypoventilation occurs in the hypocapnic patient, e.g. after a period of hyperventilation until PaCO2 is restored to normal, and in the presence of primary metabolic alkalosis.
Reduced ventilatory drive is easy to diagnose if the ventilatory rate or tidal volume is clearly reduced. However, lesser degrees of hypoventilation may be difficult to detect, and the signs of moderate hypercapnia, e.g. hypertension and tachycardia, may be masked by the residual effects of anaesthetic agents, or misdiagnosed as pain-induced (see Table 40.2).
Peripheral Factors
The commonest peripheral factor associated with hypoventilation is residual neuromuscular blockade. This may be exaggerated by disease of the neuromuscular junction, e.g. myasthenia gravis, or by electrolyte disturbances. Inadequate reversal of neuromuscular blockade is usually associated with uncoordinated, jerky movements, although these may occur occasionally during recovery of consciousness in patients with normal neuromuscular function. Measurement of tidal volume is not a reliable guide to adequacy of reversal of neuromuscular blockade; a normal tidal volume may be achieved with only 20% return of diaphragmatic power, but the ability to cough remains severely impaired. Traditional clinical signs of adequacy of reversal of neuromuscular blockade (such as if the patient is able to lift the head from the trolley for 5 s or maintain a good hand grip) correlate poorly with objective signs of neuromuscular function. Some more objective means of assessment are listed in Table 40.4, but these require the cooperation of the patient. In the unconscious or uncooperative patient, nerve stimulation (see Ch 6) provides the best means of assessing neuromuscular function, although there are differences among the non-depolarizing relaxants in the relationship between their actions in the forearm and diaphragm.
TABLE 40.4
Clinical Assessment of the Adequacy of Antagonism of Neuromuscular Block
Subjective
Grip strength
Adequate cough
Objective
Ability to sustain head lift for at least 5 s
Ability to produce vital capacity of at least 10 mL kg−1
Hypoxaemia
A functional classification of causes of hypoxaemia in the early recovery period is shown in Table 40.5. An inspired oxygen concentration of less than 21% should never occur, although PaO2 is decreased when air is breathed at high altitudes.
TABLE 40.5
Functional Classification of the Causes of Hypoxaemia in the Postoperative Period
Reduced inspired oxygen concentration
Ventilation–perfusion abnormalities
Shunting
Hypoventilation
Diffusion deficits
Diffusion hypoxia after nitrous oxide anaesthesia
Hypoventilation
This has been discussed in detail above. Moderate hypoventilation, with some elevation of PaCO2, leads to a modest reduction in PaO2 (Fig. 40.2). Obstructive sleep apnoea may produce profound transient but repeated decreases in arterial oxygenation. SaO2 may decrease to less than 75%, corresponding to a PaO2 of less than 5 kPa (40 mmHg). These repeated episodes of hypoxaemia cause temporary, and possibly permanent, defects in cognitive function in elderly patients and may contribute to perioperative myocardial infarction. Obstructive sleep apnoea is exacerbated by opioid analgesics, and patients who are known to suffer from this condition should be monitored carefully in the postoperative period, preferably in a high-dependency unit. Patients who normally use a continuous positive airways pressure (CPAP) mask to reduce obstructive sleep apnoeic episodes should use the mask at night throughout the postoperative period.