Conservative fluid strategy during cardiac surgery does not reduce ICU stay

In patients undergoing cardiac surgery, a conservative fluid management strategy reduced the amount of bolus fluid administered but did not reduce ICU length of stay compared with usual care.

The Fluids After Bypass Study evaluated a protocol-guided strategy that utilized stroke volume variation to guide administration of bolus fluid and compared it with usual care fluid administration until desedation or up to 24 hours in patients in the ICU after cardiac surgery.

“IV fluid therapy is commonplace in patients following cardiac surgery, with reports of up to 93% of patients receiving at least one fluid bolus in the postoperative period. Although IV fluids are administered with the intention of correcting hippophilia and improving cardiac output, this may result in a positive fluid balance that has also been associated with adverse outcomes in other surgical populations,” Rachael L. Parke, PhD, RN, MHSc, associate professor and nurse senior research fellow in the Cardiothoracic and Vascular ICU at Auckland City Hospital and School of Nursing at the University of Auckland in New Zealand, said during a presentation during the virtual Society of Critical Care Medicine’s Critical Care Congress. “Studies of a restrictive fluid strategy in other patient populations have shown mixed results. However, no such evidence existed within the cardiac surgical population.”

The investigator-initiated, prospective, multicenter, parallel-group, open-label, randomized controlled superiority trial enrolled 715 participants aged at least 16 years undergoing elective cardiac surgery with planned use of cardiopulmonary bypass with a preoperative EuroSCORE II of at least 0.9. Procedures were performed at five cardiac surgical centers in New Zealand from November 2016 to December 2018.

Participants were randomly assigned to the intervention arm (n = 358; median age, 70 years; 28.5% women) or the usual care arm (n = 357; median age, 68 years; 24.4% women). The intervention arm utilized stroke volume variation to guide bolus fluid administration. Per the protocol, clinicians administered first bolus fluid if participants had inadequate cardiac output before receiving fluid; if so, they then used stroke volume variation to assess the likelihood of the participant being volume responsive. The aim was to administer fluid only to those who were objectively determined to have an inadequate cardiac output and who were likely to respond to IV fluids, according to Parke. In the usual care arm, participants received IV bolus fluid as determined by local protocols and the bedside clinician. Treatment was administered from the time of ICU admission until time that routine postoperative sedation was stopped or for a period of 24 hours, whichever occurred first.

The primary outcome was length of stay in the ICU to day 28 after enrollment. Secondary outcomes included processes of care, physiological and safety measures, mortality, quality of life and disability-free survival to 180 days postoperatively.

Most participants underwent isolated coronary bypass surgery or single-valve surgery (mean time, 118 minutes).

Bolus fluid was administered in 93.1% of participants. Those in the intervention arm received less bolus fluid (1,506 mL vs. 2,190 mL; P < .0001) and had a lower overall fluid balance (1,687 mL vs. 1,821 mL; P = .33) compared with the usual care arm, according to the results.

The researchers reported no difference between the groups in requirement for vasopressor therapy.

Overall, 12,399 reasons were recorded for bolus administration, as Parke said multiple reasons could be chosen by a patient’s bedside clinician administering their fluid bolus. Hypertension (33%) was the most commonly reported reason, followed by low central venous pressure (14%) and stroke volume variation (13%).

Researchers did not observe significant differences in ICU length of stay measured as actual length of stay from ICU admission to actual discharge in the intervention arm and the usual care arm (27.9 hours vs. 25.6 hours; P = .95). There were also no significant differences in ICU length of stay measured from time to ICU admission to time judged fit for discharge in the intervention arm and the usual care arm (21 hours for both; P = .94).

In both the intervention and usual care arms, the researchers reported no difference in use of renal replacement therapy in the ICU (2.3% vs. 1.4%; P = .4) or development of renal dysfunction, or quality of life or disability-free survival at hospital discharge (51.1% vs. 45.9%; P = .19), at 3 months (91.4% vs. 90.7%; P = .76) and at 6 months (92.2% vs. 92.1%; P = .96).

Mortality was higher in the intervention arm at 3 months (3.7% vs. 1.4%; P = .06) and 6 months (5.3% vs. 2.8%; P = .09), likely due to higher mortality before ICU discharge (3.9% vs. 1.4%; P = .04), Parke said.

According to Parke, limitations of this study include limiting bedside clinicians to only access stroke volume variation to guide patient management and not cardiac output, only being able to deliver the protocol guiding fluid administration when the patient was sedated and ventilation, not having a blinded intervention and not attempting to control or measure fluid balance in patients before their operation and ICU admission.

Reference:

Parke RL, et al. Crit Care Med. 2021;doi:10.1097/CCM.0000000000004883.