The Dept of Anaesthesia & Intensive Care, CUHK
First posted June 2006
The term "high risk surgical patient" is poorly defined. In this context it should be taken to refer to the group of patients, who were considered to be at high risk of post operative death, and were included in studies of pre-operative "optimization" to a pre-determined oxygen delivery (table 1).
Unfortunately, the entry criteria for inclusion in this group were never systematically investigated nor clearly defined so that it is difficult to determine with certainty whether an individual patient meets the criteria. This difficulty in defining the "high risk" group may underlie the markedly different baseline mortalities in different studies.
A number of studies have examined the effect of increasing oxygen delivery in "high risk" patients with the aim of reducing morbidity and mortality. This is based on data showing that those patients with an oxygen delivery >600 ml/min.m2 have a lower mortality. It was postulated that patients with a lower oxygen delivery may have covert tissue hypoxia.
Two single centre studies have demonstrated an impressive reduction in mortality associated with a treatment strategy aimed at pre-operative "optimization" by increasing oxygen delivery to >600 ml/min.m2. However a multi-centred study, albeit using different criteria for high risk, failed to demonstrate any benefit from this approach. More recently a study has shown that increasing oxygen delivery post-operatively reduces hospital length of stay in high risk patients.
Lobo et al studied 37 patients with two or more of the following criteria:
Patients in both groups were treated to standard resuscitation end-points. In addition patients were treated with fluids, inotrope and vasoactive agents to maintain oxygen delivery between 520-600 ml/min.m2 (control group) and >600 ml/min.m2 (protocol group). The study was stopped early because of lower mortality in the protocol group. Note that the mortality in the control group was surprisingly high.
Table 1. 28 day mortality in control and protocol groups (Lobo et al)
Wilson et al studied 138 elective patients at risk of post-op complications because of :
Patients in protocol group received fluids and either adrenaline or dopexamine to increase oxygen delivery to >600 ml/min.m2. All protocol patients but only some control patients were admitted to the ICU.
Mortality was significantly lower in the protocol group (table 2). Fewer patients in the dopexamine group developed complications compared with the adrenaline group. Again, the mortality in the control group was surprisingly high.
Table 2. Hospital mortality in control and protocol groups (Wilson et al).
Sandham et al randomized 1994 patients >60 years old with ASA class III or IV risk, scheduled for urgent or elective major abdominal, thoracic, vascular or hip fracture surgery to a protocol and control groups. In the protocol group patients were managed with a pulmonary artery catheter and their oxygen delivery was increased to 550-600 ml/min.m2 with fluids, inotropes, vasoactive drugs and blood.
There was no difference in mortality between control and protocol groups with 7.7% hospital mortality in the control group and a 7.8% hospital mortality in the intervention group. It could, however, be argued that the target oxygen delivery was not high enough in the protocol group.
More recently Pearse et al studied the effect of increasing oxygen delivery to >600 ml/min.m2 post operatively and demonstrated a reduction in the number of patients developing complications, the number of complications per patient and duration of hospital stay. However there was no significant difference in 28-day mortality (11.3% versus 15%).
© Charles Gomersall June 2006
April, 2014 unless
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