INFLUENCE OF AGE AND OTHER FACTORS ON HYPOXAEMIA IN THE POSTOPERATIVE PERIOD

Preoperative hypoxemia in conscious patients after subarachnoid hemorrhage

We retrospectively examined partial arterial pressure of oxygen (Pao₂) afer subarachnoid hemorrhage (SAH), adjusted for patient-related risk factors for hypoxemia in 51 adult patients with no disturbance of consciousness undergoing surgery for clipping of intracranial aneurysms. A control group of 174 patients undergoing other operations were used for comparison. Arterial blood gas analysis was performed while patients were spontaneously breathing room air in the supine position before induction of anesthesia. The Pao₂ in the SAH patients was significantly lower (p<0.0001) than that in the control group after adjustment for age, obesity, and smoking status. In three patients in the SAH group, Pao₂ was less than 60 mmHg. Close monitoring of arterial oxygenation with pulse oximetry is desirable, and supplemental oxygen should be considered during transfer from the patients' room to the operating suite, even for conscious patients of SAH without cardiopulmonary disease.

Preoperative and intraoperative factors associated with prolonged mechanical ventilation. A study in patients following major abdominal vascular surgery

A study of 51 patients undergoing elective major abdominal surgery was carried out to determine the incidence of postoperative respiratory failure requiring mechanical ventilation for more than 24 h and which preoperative and intraoperative factors are associated with this respiratory complication. Mechanical ventilation for more than 24 h was required in 12 of the 51 patients. These 12 patients had a significantly longer stay in the intensive care unit and in the hospital than the patients who were successfully extubated in the postoperative period. Also, there was a trend for a higher mortality in the ventilated group compared to the group of patients who did not require postoperative ventilation. Preoperative abnormalities in FEV1 did not identify which patients were destined to require postoperative ventilation. Significant differences for the ventilated versus the nonventilated patients included a longer history of cigarette smoking, a lower preoperative PaO2, and a large intraoperative blood loss.

Hypoxia in children following general anaesthesia

The oxygen saturations of 152 children were studied for the first 30 minutes following general anaesthesia with a pulse oximeter. Thirty-six patients (24%) recorded oxygen saturations of less than 90% while breathing room air and in all cases this occurred during the first ten minutes. Intubation (P less than 0.001), use of muscle relaxants (P less than 0.01), intravenous induction (P less than 0.01) and duration of anaesthesia of greater than one hour (P less than 0.02) were all associated with an increased incidence of hypoxaemia. There was no significant correlation with age, weight, procedure, time to wakening, or use of opiates. Clinical signs correlated poorly with hypoxaemia and it is recommended that all children should receive supplementary oxygen during transport to recovery wards and for at least the first ten minutes in recovery following general anaesthesia.

Local analgesia for surgical cure of prolapse in elderly or unfit women

Surgical correction of genital prolapse under local analgesia in elderly or unlit women is described. One hundred patients undergoing such surgery between 1972 and 1984 were reviewed. Eighty-five per cent were more than 60 years of age. Over 50 per cent had Fothergill repairs. Ninety-six per cent were assessed as having a good result. The incidence of postoperative complications was 20 per cent and there was no mortality. From our experience the technique seems to be a safe and worthwhile procedure.

Factors influencing the respiratory capacity after upper abdominal surgery

The analgesic requirement and some factors influencing the respiratory capacity after upper abdominal surgery were studied during the first 2 days postoperatively in 417 patients, aged 17 to 84 years, undergoing surgery in the upper part of the abdomen. The operations were cholecystectomy or choledocholithotomy through a subcostal incision, partial gastric resection, repair of a diaphragmatic hernia or vagotomy through a midline incision. Pain relief was achieved in a random order either by intercostal block (i.c.b.) and centrally acting analgesics on demand, or by centrally acting analgesics alone. The analgesic demand was recorded, and the respiratory capacity was monitored by the peak expiratory flow rate (PEF). A smaller analgesic requirement and a smaller change in PEF were found after cholecystectomy than after any other kind of surgery. The demand for analgesics was age-dependent, and patients under 60 years of age demanded more than those aged 60 years and older. Bilateral i.c.b. given after surgery through a midline incision had few advantages, but unilateral i.c.b. following cholecystectomy and choledocholithotomy with a subcostal incision had positive effects. Thus it decreased the demand for centrally acting analgesics and resulted in higher PEF values than without i.c.b. for cholecystectomy during the period of effective nerve block and for choledocholithotomy for 2 whole days postoperatively. Smokers seemed to benefit from i.c.b. for 2 postoperative days. The reduction of PEF after cholecystectomy also seemed to be related to the duration of treatment with centrally acting analgesics.

Pulmonary atelectasis after anaesthesia: pathophysiology and management

The pathophysiological basis of pulmonary atelectasis is reviewed and risk factors that enhance lung collapse are discussed. Management strategies to reduce or eliminate risk factors and to prevent collapse are discussed and the rational bases of these strategies are identified. Instability of lung alveoli is a consequence of surface tension and regional differences in alveolar size. The inherent tendency of alveoli to collapse is enhanced by the following risk factors; low lung volume, high closing volume, oxygen therapy, a rapid shallow ventilatory pattern, chronic lung disease, smoking, obesity, postoperative pain following abdominal or thoracic surgery, narcotic induced ventilatory depression, and neurological, neuromuscular, muscular and musculoskeletal diseases associated with mechanical impairment of respiratory function. The primary goal of perioperative respiratory management is prevention of atelectasis. Appropriate management strategies include physiotherapy and delay of elective surgery if substantial improvement in respiratory status can be achieved by specific treatments such as antibiotics, bronchodilators, steroids, and reduction of tobacco use and caloric intake. In selected cases, elective postoperative controlled ventilation may be indicated.

Postoperative hypophosphataemia

The possible mechanisms of postoperative hypophosphataemia were studied in women undergoing uncomplicated cholecystectomy. Six patients were allocated to each of three groups. Group I received no intravenous fluids, group II received dextrose/saline solution alone and group III received dextrose/saline solution with phosphorus supplementation. The serum concentration of inorganic phosphorus fell in all three groups, the greatest fall being in the group receiving dextrose/saline solution. However, the lowest level reached (0.82 mmol/l) was within the normal range for our laboratory. Concentrations of red blood cell adenosine triphosphate and 2,3-diphosphoglycerate showed similar changes. The operations were not associated with a large catabolic response nor with an increase in urinary phosphorus excretion. The postoperative reduction in serum concentration of inorganic phosphorus appeared to be due mainly to haemodilution. There is no indication for routine phosphorus supplementation following uncomplicated elective surgery.

Hypoxaemia in elderly patients suffering from fractured neck of femur

The purpose of this study was to assess the degree and frequency of hypoxaemia in elderly patients with fractured neck of femur and to note the effect of manipulation and internal fixation on these measurements. Twenty-seven patients aged between 44 and 93 were studied for 5 days after the fracture and for 5 days after surgery. The fractures were treated by internal fixation under either general anaesthesia or spinal analgesia. The arterial oxygen tension following the fracture but before surgery was low relative to the ages of the patients, and the arterial carbon dioxide tension was low in twenty-five out of twenty-seven patients. There was also a significant increase in the dead space/tidal volume ratio (VD/VT) and the alveolar-arterial oxygen tension difference, (A--a)DO2 in eight out of nine patients in the first 5 days following the fracture. The mean arterial oxygen tension was still reduced up to 5 days postoperatively. The VD/VT ratio returned to normal postoperatively although the (A-a)DO2 remained elevated. The haemoglobin and platelet levels following the fracture and before surgery were low, although not remarkably so, and there was no significant change post-operatively. There were no significant changes in the electrocardiograph or the chest radiographs. These results and their implications are discussed.