Evaluating the reliability of recorded fluid balance to approximate body weight change in patients undergoing cardiac surgery.

OBJECTIVES: The objective of this study was to investigate body weight change in adult patients undergoing cardiac surgery and to assess the accuracy of conventional recorded fluid balance charting methods to reflect this change in body weight.
DESIGN: This was a descriptive study.
SETTING: This study was conducted at the cardiac care unit and medical-surgical intensive care unit (ICU) of a private hospital in Melbourne, Australia.
SUBJECTS: The subjects were 32 adult patients who underwent cardiac surgical procedures. Twenty-six were male, and the mean age was 67 years (range 36-84 years). Twenty-three patients underwent coronary artery bypass graft surgery, and nine patients underwent heart valve repair or replacement+/-coronary artery bypass graft surgery between December 2003 and May 2004. OUTCOME MEASURES: The measures were recorded fluid balance for the perioperative period together with body weight measurements from the night before surgery and immediately on discharge from the ICU. An additional body weight measurement on the seventh postoperative day provided a trajectory of body weight gain or loss for the period of hospitalization after surgery. A retrospective medical history audit and an HV-CS digital chair scale (A&D Mercury Pty Ltd, Victoria, Australia) were used to collect the data.
RESULTS: Analysis revealed that 30 patients increased their body weight from the night before surgery until discharge from the ICU. The mean weight gain was 3.34 kg (standard deviation [SD] 1.17, 95% confidence interval 2.70-3.98, P<.001). The average preoperative body weight was 80.97 kg (SD 16.79), whereas the average ICU postoperative weight was 83.94 kg (SD 16.15). Twenty-six patients (81.25%) had returned to, or were below, their preoperative weight by their seventh postoperative day (M 2.96 kg, SD 2.24 kg, P<.05). The average recorded fluid balance during the perioperative period was +1.56 L (SD 2.59 L, P<.001) with a difference of 1.39 kg between the recorded fluid balance and measured body weight change. Three patients (9.75%) met the criteria for accurate recorded fluid balance, and eight patients (25%) experienced a net difference in the opposite direction between recorded fluid balance and body weight change during the perioperative period.
CONCLUSION: Body weight in patients who undergo cardiac surgery was found to fluctuate over the perioperative period. Use of recorded fluid balance to reflect change in body weight for patients undergoing cardiac surgery was deemed unreliable. Further investigation of body weight change and scrutiny of conventional recorded fluid balance charting methods for patients who undergo cardiac surgery is needed.