Does stroke volume increase after a fluid challenge? A study on the management of patients undergoing major head and neck free flap surgery: preliminary data

Introduction

Major head and neck surgery involving reconstructive free flaps for oropharyngeal cancers are complex and prolonged operations during which appropriate fluid management can become difficult. Potential adverse effects of fluid mismanagement in this group of patients include flap hypoperfusion related to hypovolaemia or flap oedema and deterioration in alveolar-arterial gradients related to excessive fluid administration. This study looked at ongoing standard practice, to determine whether the use of a cardiac output monitor could improve fluid management in this subset of patients.

Methods

Single-blinded, prospective observational study conducted on consecutive adult patients undergoing major head and neck reconstructive free flap surgery. All patients were anaesthetised by the same individual, using a standardised technique. Volume-controlled positive pressure ventilation was initiated in all patients. Patients received maintenance crystalloid fluids at a rate of 5 ml/kg/hour. Additional fluid challenges (250 ml crystalloid boluses given over 5 minutes) were administered at the discretion of the anaesthetist. A priori criterion of fluid responsiveness was defined as an increase in stroke volume (SV) >10% as measured with the LiDCOrapid after a fluid challenge. The anaesthetist was blinded to the LiDCOrapid data and observations were made by an independent investigator. Data were collected on: heart rate (HR), mean arterial pressure (mAP) and central venous pressure (CVP).

Results

Forty-seven fluid boluses were assessed. The median age of the patients was 72 years (range 68 to 81 years) and their median weight was 71.2 kg (range 63 to 88 kg). The ventilatory set-up used a median tidal volume of 7 ml/kg (range 450 to 600 ml). Fifteen out of 47 (32%) of the fluid challenges were positive when assessed against the change in stroke volume. When comparing the fluid responders with the nonresponders, there were no differences in HR (62 ± 10 bpm vs 62 ± 10 bpm), mAP (63 ± 6 mmHg vs 63 ± 7 mmHg) or CVP (8 ± 3 mmHg vs 10 ± 3 mmHg).

Conclusions

This preliminary report suggests that only 32% of fluid challenges given in theatre were effective in increasing the SV >10% and potentially two-thirds of the fluid challenges may have been detrimental. This can be seen only if SV is monitored continuously. If further data confirm this, LiDCOrapid may be useful to guide fluid administration in order to optimise the SV, thereby minimizing the risk of fluid overload.