Haemodynamic monitoring benefits

Haemodynamic monitoring technology has made great strides in the last 20 years with the introduction of minimally invasive devices to measure stroke volume, cardiac output, depth of anaesthesia and tissue oxygenation. Such technologies are now capable of providing significant advances in the peri-operative management of the high-risk major surgery patient (Green and Paklet, 2010). Despite conventional intra-operative monitoring (pulse oximetry, invasive systemic blood pressure and central venous pressure, end tidal carbon dioxide and anaesthetic agent monitoring) there can be occult low levels of blood flow and oxygen delivery that lead to post-operative complications. Outcomes can be significantly improved with the use of protocols for pre-emptive intra-operative fluid and haemodynamic monitoring (Lees et al, 2010 and Hamilton et al, 2010). Moreover, when necessary, postoperative oxygen delivery targeting can also be provided in the ICU for those patients who have incurred an intraoperative oxygen deficit. Recent research has shown that high-risk surgery patients who have been haemodynamically (oxygen delivery) optimised without excessive fluid administration, have markedly reduced post-operative complication rates – down by 67% (Lobo et al, 2011). In the near future we will see progressive convergence of parameters into a single monitor and combined ‘intelligent’ graphical user interface. Multi-parameter haemodynamic monitors that display a ‘natural grouping’ of readings that allow the fine control of fluids, blood flow, oxygen delivery, tissue oxidation and anaesthetic drugs should become the 21st century norm. The number of ‘high-risk’ patients undergoing surgical interventions is increasing. There are around 250 million major surgical procedures performed worldwide annually, resulting in about 12.5 million patients with surgical complications. Monitoring of fluid and intravascular volume is notoriously difficult. Multiple studies and metaanalyses have failed to demonstrate the utility of traditional monitoring parameters to predict those patients who will respond to fluid therapy (Marik et al, 2009). Traditionally, monitored parameters such as central venous pressure, heart rate and arterial pressure and saturation are not useful measures of circulating blood volume and blood flow/oxygen delivery status. In marked contrast, advanced haemodynamic monitoring of the dynamic physiological parameters of stroke volume variation (fluid responsiveness status) and change in stroke volume, a marker of blood flow response, have been shown to both maintain adequate fluid status and ensure adequate tissue perfusion. Use of these parameters has significantly reduced operative mortality and complications (Lopes et al, 2007 and Giiglio et al, 2009).

Consistent care for high-risk patients

Advanced haemodynamic monitors greatly assist with therapeutic decision making and more accurately guide appropriate fluid and drug interventions. Through their use, anaesthetists and surgeons can provide greater consistency of care for the highest risk surgery patients. Given the mounting evidence base, it is surprising that haemodynamic monitoring of the high-risk surgery patient is not yet mainstream. There are 800,000 surgery patients a year in the UK who are applicable for such advanced monitoring, but less than 10% are currently monitored. Full adoption has been estimated as potentially saving the NHS up to £400 million per annum. However, exciting changes that are designed to promote adoption have recently been announced. In December 2011 the NHS Improvement and Efficiency Directorate published its report Innovation, Health and Wealth. This report sets out actions to drive full adoption by the NHS of such evidenced innovation. Advanced fluid/haemodynamic monitoring of elective surgery patients has been identified in the report as one of the three targets for a national adoption drive (from April 2011) throughout the NHS in England. Fluid therapy is required to preserve the normal intravascular blood volume and composition of the tissue and intra cellular fluids. It is aiming to achieve a delicate balance between maintenance needs (water is continuously lost through insensible and sensible losses) and more rapid repletion requirements that occur through haemorrhage. Anaesthetists and surgeons are increasingly aware of the importance of this fluid balance to ensure an adequate blood volume to assure positive oxygen balance in the perioperative period. However, the use of accurate haemodynamic monitors that detect central blood volume changes is still evolving. Research continues to further refine and quantify the most effective approaches/protocols for managing/ balancing fluids in high-risk surgery patients. There is a growing consensus that fluid therapy should be individually titrated to the patient’s condition and that generic, i.e. non individualised approaches are less effective and to be avoided if possible. The ambition is to achieve ‘the right amount of the right type of fluid at the right time’. However, even this ‘simple’ ambition is the subject of much discussion. In particular, there is growing debate regarding the necessity for some, or any, background maintenance crystalloid infusion during surgery. These so-called ‘maintenance’ fluid regimes are based on a presumed substantial loss of fluid during the operation and can require the infusion of high levels of fluids – as much as 12mL/kg/h. Putting this in perspective, a 80kg patient will have almost six litres of fluid infused over a six hour operation. This is unlikely to be required and is almost certainly an overkill that will likely lead to an excessive accumulation of fluid and salt. Such standardised fluid regimens are now potentially rendered obsolete by the new generation of haemodynamic monitors. A recent publication from Brazil has shed some light on this fluid balancing question. This looked at the effects of different maintenance fluids (restricted fluids or ‘normal’ i.e. higher levels) on outcome in two groups of patients. Both patient groups had controlled intravascular fluid volume and targeted levels of oxygen delivery.