Minitutorial preoptimisation of the high risk surgical patient

High risk surgical patients are those with poor preoperative status or who are about to undergo a major procedure or one involving heavy blood loss. In 1979, Shoemaker et al. defined the criteria for high surgical risk:

• patient history: age > 70 years with major limitations of physiological function, previous severe cardiopulmonary or vascular disease, severe nutritional disorders

• critical factors: severe multiple trauma, massive acute blood loss, shock, severe sepsis, respiratory failure, acute abdominal catastrophe, acute intestinal or renal failure

• surgical procedure: extensive surgery for cancer or prolonged surgery.

Shoemaker's group observed a mortality of 25% in their own high risk surgical patients. Outcome was dramatically influenced by the ability of the patient's cardiopulmonary system to adapt. Values for CO, DO2, and oxygen uptake were significantly higher in survivors than in non-survivors. It was postulated that the observed increase in CO and DO2 were circulatory responses owing to increased postoperative oxygen demand. However, subsequent trials which aimed for "supranormal" values in CO and DO2 were associated with adverse outcomes.

In high risk surgical patients, reduced cardiac output may compromise perfusion in organs such as the gastrointestinal tract and kidney, leading to ischaemia and reperfusion injury. The subsequent release of reactive oxygen species and inflammatory mediators leads to activation of immune cells and distant organ injury (for example, lung and liver) leading to MODS. Early detection of gastrointestinal hypoperfusion could provide advance warning of this - it is associated with more severe organ dysfunction, longer ICU stay, and greater mortality in surgical and trauma patients. Gastrointestinal hypoperfusion as detected by gastric pH measurements (tonometry) in postoperative cardiac surgery patients has been shown to be an early indicator of circulatory failure and increased morbidity.

In one randomised trial, Boyd et al. used dopexamine to increase perioperative DO2 in high risk surgical patients. The mean dose of dopexamine infused was 1-2 |ig kg-1 per minute preoperatively and 1-3 |ig kg-1 per minute postoperatively. Mortality at 28 days was 5-7% in the dopexamine group and 22-2% in the controls. A few years later, Wilson et al. randomised high risk patients into three groups. Controls received routine perioperative care and two groups were preoptimised. Optimisation consisted of invasive haemodynamic monitoring, fluid loading to achieve a PAOP of 12 mmHg, blood transfusion to achieve an Hb of > 11 g dl-1, oxygen therapy to achieve saturations of > 94%, and either adrenaline or dopexamine to increase DO2 to > 600 ml O2 per minute. Inotropic support was continued during surgery and for at least 12 hours afterwards; 70% of patients had more than two Shoemaker entry criteria. Mortality was reduced in both the adrenaline and dopexamine groups (2% and 4%) compared with the controls (17%). This was statistically significant. Dopexamine also significantly reduced postoperative morbidity when compared with both the adrenaline and the control groups.

Dopexamine has anti-inflammatory properties as well as improving regional blood flow and renal function in rat models of sepsis to a greater extent than either dopamine or dobutamine. Its various anti-inflammatory effects have yet to be proved in clinical practice.

In most of these outcome studies, PA catheters were used to monitor cardiac output and calculate oxygen transport. Research has concentrated on developing and evaluating less invasive methods for assessing the adequacy of resuscitation. Intramucosal pH (pHi) has been shown to be of greater value in monitoring trauma patients than oxygen transport measurements. In elderly patients with proximal femur fractures, using oesophageal Doppler monitoring to guide volume replacement, led to more fluid administration to the treatment group and a significant reduction in hospital stay. There was no impact on hospital mortality, possibly because of the small numbers studied. In elective cardiac surgical patients with ejection fractions > 50%, patients who received volume expansion to maximum stroke volume had a significantly reduced morbidity and hospital stay. These studies support the concept that adequate fluid resuscitation is of vital importance in high risk surgical patients.

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