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Case Studies

Postoperative hypovolemia responding to fluid management

Background

Sussex, UK

70 year old man, weight 87 kg, height 178 cm, BSA 2.06m2.

Postoperative cardiac surgery in cardiac recovery unit.

Patient remained ventilated and sedated.

BP adequate, patient warming up, urine output adequate, CVP 4mmHg.

Baseline Readings

CO/CI low.   HR not necessarily compensating CO/CI at this stage.

Baseline readings

SV low. Possible relative hypovolemia due to vasodilating with warming/sedation.

FTc low. Possible relative hypovolemia due to vasodilating with warming/sedation.

PV reduced. For a healthy individual at age 70, PV should be approximately 50-80cm/s.

The clinician suspected hypovolemia and a rapid 200ml fluid challenge was given.

Following a 200ml fluid challenge

Using the Frank-Starling mechanism and following a rapid fluid challenge, SV is expected to rise by 10% or more in a fluid responsive patient.

No increase in SV. CO, BP and HR unchanged. FTc increased slightly. The clinician believed that there was a sustained relative hypovolaemia because the patient was continuing to warm and therefore decided to give further fluid.

1st 200ml fluid challenge

Following a 2nd 200ml fluid challenge

SV now increased by more than 10% from 59ml to 76ml. Other ODM parameters also increasing. FTc increase is consistent with a reduction in the vasoconstriction associated with compensation therefore reducing afterload. The clinician believed that PV is increasing to match the increased preload. HR and BP are essentially unchanged. Since the SV has now increased appropriately, a further 200ml was given.

2nd 200ml fluid challenge

Following a 3rd 200ml fluid challenge

SV increased by more than 10% indicating the heart was still fluid responsive.

FTc, CO and PV also continue to increase. BP increased slightly. CVP increased to 8mmHg.

Following a 4th fluid challenge, the SV did not increase by 10% and since the flow parameters, BP and HR were all now acceptable; the clinician decided not to give further fluid and reassess within 15 minutes.

3rd Fluid Challenge

Summary

Despite no changes after the first challenge, a decision to try further fluid resulted in the appropriate response. This will depend on the clinical situation as to whether to give a second bolus or not. In this case scenario, the patient was dilating due to postoperative warming. This caused a relative hypovolemia where the circulating volume was inadequate. BP, CVP, HR and urine output did not indicate a hypovolemic situation and responded slower to the fluid. Without this type of monitoring, the appropriate resuscitation for covert hypovolemia would have been missed.

Effects of vasodilation, useful ectopics

Background

Montreux, Switzerland

83 year old man, Wt 66kg. Ht 177 cm, BSA 1.82 m2. Intraoperative closure of colostomy. No cardiac history

Baseline at start of surgery

CO, SV and FTc may be acceptable for a healthy resting individual. CI and PV are on the lower end of normal A normal PV for this age is approximately 50-80cm/s. Although these parameters appear normal, vasodilation and therefore low resistance/afterload is usually expected with anaesthesia, but since FTc is ‘normal’, the vasodilation could be masked by a relatively low preload.

Baseline at start of surgery

After epidural top up

Before a fluid challenge was considered, a bolus of the epidural was given. This is likely to cause further dilation. SV, SVI and PV have reduced, which may indicate that preload may not be sufficient. CO/CI is similar, FTc has increased slightly. The clinician surmised that there may be relative hypovolemia present due to vasodilation, and two 200ml rapid fluid challenges were given to fill the dilated vascular space.

After epidural top up

Useful ectopic

All parameters have increased following the fluid and in particular the SV has increased by >10% indicating fluid responsiveness. Subsequently, isolated atrial ectopics were seen on the ECG. This can be useful when using EDM monitoring to determine fluid responsiveness. If the waveform after the ectopic is larger than a normal waveform, this indicates that the compensatory pause allows more filling and this larger waveform indicates fluid responsiveness.

Useful ectopic

Flow parameters reduced

Despite these indications of a possible reduction in circulating blood volume, no further fluid was given and 10 minutes later, SV and other parameters reduced. The clinician then gave three fluid challenges as per algorithm with good SV increases.

Flow parameters reduced

After 3rd fluid challenge. Abdomen now closed

SV increased by >10 %. Other flow parameters increased. These indicate good responses to fluid.

After 3rd fluid challenge, abdomen now closed

Summary

This case scenario describes how relative hypovolaemia can be missed. Since FTc is inversely related to resistance/afterload, it can be assumed that when the patient is dilated, that FTc should rise, however if the vascular space remains under filled (relative hypovolemia), the flow numbers may reduce initially until filling commences. It also describes how the presence of isolated ectopics could have helped the clinician to diagnose fluid responsiveness earlier. Both of these issues can be observed and corrected using the EDM monitors.

Abbreviations:

FTC – Flow Time corrected ECG – Electrocardiograph
CO – Cardiac Output/CI – Cardiac Index Wt – Weight
SV – Stroke Volume/SVI – Stroke Volume Index Ht – Height
PV – Peak Velocity BSA – Body Surface Area

 

BP – Blood Pressure CVP – Central Venous Pressure
CO – Cardiac Output HR – Heart Rate
SV – Stroke Volume Wt – Weight
FTc – Flow Time corrected Ht – Height
PV – Peak Velocity BSA – Body Surface Area