Postoperative hypovolemia responding to fluid management
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.
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.
- 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.
- 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.
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
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.
- 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.
- 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.
- Flow parameters reduced
- After 3rd fluid challenge. Abdomen now closed
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.
|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|