Fluids and body composition during anesthesia in children: a bioimpedance study

doi:10.21203/rs.3.rs-3150087/v1

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Fluids and body composition during anesthesia in children: a bioimpedance study

https://doi.org/10.21203/rs.3.rs-3150087/v1

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PURPOSE: The assessment of total body fluid volume, intracellular volume and extracellular volume before and after anesthesia may be useful to define a better intraoperative fluid administration.

METHODS: A bioimpedance spectroscopy device (BCM) was used to measure total body fluid volume, extracellular volume, intracellular volume. BCM-measurements were performed before and after general anesthesia in unselected healthy children and adolescents visiting the Pediatric Institute of Southern Switzerland for low-risk surgical procedures.

RESULTS: In 100 children and adolescents aged 7.0 [4.8 – 11] years (median and interquartile range), the average total body water (TBW) increased perioperatively with a delta value of 182 [0 – 383] mL/m² from pre- to postoperatively, as well as the extracellular water content (ECW), which had an equivalent increase with a delta value of 169 [19 – 307] mL/m². The changes in TBW and ECW significantly correlated with the amount of fluids administered.

CONCLUSIONS: This preliminary report shows that intraoperative fluid administration results in a significant fluid accumulation in low-risk schoolchildren during general anesthesia. Children without major health problems undergoing short procedures, do not need any perioperative intravenous fluid therapy, because they are allowed to take clear fluids up to 1 hour prior anesthesia. BCM-measurements could become useful for guiding intraoperative fluid therapy in future studies.

Children

Impedance

Total body water

Anesthesia

Most children who undergo common surgical interventions or investigations requiring anesthesia are nowadays hydrated at a rate of 1700 mL/m²/day with an isotonic solution.
The use bioimpedance spectroscopy for the assessment of fluid status in healthy children has already been successfully validated.
The bioimpedance spectroscopy is already currently widely used in various nephrological settings to calculate fluid overload and determine patient’s optimal fluid status.

What is new:

Routine intraoperative fluid administration results in a significant fluid accumulation during general anesthesia in low-risk surgical procedures.
Children and adolescents without major health problems undergoing short procedures (< 1 hour), do not need any perioperative intravenous fluid therapy, because they are allowed to take clear fluids up to 1 hour prior anesthesia.
BCM measurements could become useful to guide intraoperative fluid therapy and improve the postoperative volume status in future studies.

Hypotonic intravenous fluid maintenance therapy with 5%-dextrose at a rate of 1700 mL/m²/day (i.e.: 100 mL/kg/day for the first 10 kg of weight, 50 mL/kg/day for the next 10 kg of weight, and 20 mL/kg/day for weight over 20 kg) supplemented with sodium 3 mmol/kg/day has been routinely prescribed to children who undergo common surgical interventions or investigations requiring anesthesia. Some years ago, it was speculated that this traditional hydration practice, first proposed by Holliday and Segar in 1957, may result in hyponatremia and in an increased intracellular water content [1]. The suggestion was followed by a fascinating and often heated controversy. The debate has quieted in the meantime: well-designed trials comparing the use of hypotonic versus normal saline or lactated Ringer demonstrate that hypotonic fluids cause acute hyponatremia, whereas normal saline or lactated Ringer effectively prevents it. As a consequence, most children who undergo common surgical interventions or investigations requiring anesthesia are nowadays hydrated at the above-mentioned rate with an isotonic solution such as normal saline (0.9%) or lactated Ringer [2].

The amount of sodium administered using normal saline or lactated Ringer is about 3 times higher than that administered with the traditional Holliday-Segar method [3]. It is therefore tempting to assume that this strategy may sometimes be associated with an extracellular fluid volume expansion.

The body composition monitor (BCM, Fresenius Medical Care, Germany) is a novel, whole-body bioimpedance spectroscopy device, which is commonly used for the evaluation of body composition, total body fluid volume, intracellular volume and extracellular volume, both in adults and children [4–6]. The bioimpedance spectroscopy is already currently widely used in various nephrological settings to calculate fluid overload and determine patient’s optimal fluid status [7–10] and its use for the assessment of fluid status in healthy children has already been successfully validated [11].

The aim of the present study was to determine pre- to postoperative fluid distribution with a bioimpedance device in both children and adolescents undergoing low-risk surgical interventions requiring general anesthesia. The goal of this investigation is to better understand the water content, the body composition and the fluid status before and after anesthesia in order to define a better intraoperative fluid administration.

We performed a prospective, observational, single center, cohort study in a pediatric population aged 0–16 years visiting the Pediatric Institute of Southern Switzerland, EOC, site of Ospedale San Giovanni in Bellinzona.

Patients

Bioimpedance measurements (BCM) were consecutively performed immediately before and after anesthesia in 100 unselected children and adolescents for both inpatient and outpatient surgery procedure. Patients with a limb amputation or a congenital malformation were not measured, as well as patients who had significant blood loss and therefore had received erythrocyte concentrates or colloid solution. All patients fasted overnight for more than 6 hours, but clear liquids (e.g. water, tee, sirup) were offered and suggested up to one hour before anesthesia (and first measurement). The type and duration of anesthesia as well as the type and amount of intravenous fluid therapy were prescribed according to standard clinical practice and the most recent guidelines [2].

The study was approved by the local ethics committee and fulfilled the last version of the Declaration of Helsinki [12]. The parents of all patients gave written informed consent.

BCM-measurements

According to the manufacturer's guidance, four non-recyclable electrode strips were taped to wrist, hand, ankle and foot, on the same side of the patient, lying in a supine position. Electrodes were connected to the BCM device using the cable provided by the manufacturer. Body weight, height, patient age, patient gender and the actual blood pressure measurement were entered into the BCM device. The bioimpedance measurement itself requires approximately 2 minutes, is non-invasive, safe, painless and is possible from the neonatal age. It measures at 50 frequencies over a range from 5 to 1000 kHz to determine the electrical resistances of the total body water and the extracellular water between electrodes. This allows for a simple, non-invasive, objective and accurate assessment of an individual patient’s fluid status (overhydration, total body water, extracellular and intracellular water) and an assessment of the body composition (lean tissue mass and adipose tissue mass) [5].

Other measurements and patient characteristics

Age, height, body weight, pre- and postoperative heart rate, blood pressure, respiratory rate, oxygen saturation measurements, fluid balance data and surgical data were documented in all patients. Body mass index (BMI) percentiles were calculated based on the CDC (Centre of Disease Control) reference intervals (overweight: 85-95th percentiles; obese: >95th percentile).

Sample size

Data were collected in a coded manner through a specific data collection form and reported in an electronic database. To have an 80% chance of detecting as significant (at p < 0.05) a variation in water content of 3% from pre to post anesthesia values, at least 90 patients were required.

Statistical analysis

Demographic data are presented as median and interquartile range. Changes in BCM-derived measurements from pre- to postoperatively (delta values) were obtained by subtracting the preoperative value from the postoperative value and expressed in ml/m². These changes were subsequently evaluated using the paired, two-sided, non-parametric Wilcoxon match paired test. Correlation analyses were performed using linear regression analysis. Comparison between different groups (i.e. obese and normal weight children) were performed using the Mann-Whitney test. Statistical significance was set at p < 0.05. Statistical analyses were performed with GraphPad Prism version 8.0.0, San Diego, California.

The study population comprised 100 infants and children, recruited from 03 February 2022 until 07 April 2022. Sixty-five were females and 35 males, aged 7 [4.2–11.0] years, with a body weight of 26.8 [18.1–42.7] kg and a height of 1.27 [1.10–1.54] m (Table 1). No patients had evidence of severe systemic disease, the ASA (American Society of Anesthesiology) physical status classification system being in all patients ≤ ASA II [13,14]. Almost all patients were premedicated prior anesthesia with oral midazolam (0.5 mg/kg, with a higher maximum dose of 10 mg, N = 93). At the discretion of the attending anesthesiologist, and depending on the past medical history of the patient, its characteristics and the surgical procedure, a total intravenous anesthesia (propofol) was given intraoperatively in 94% of cases, while in 6% of cases general anesthesia was provided by an inhalation anesthetic (desflurane or sevoflurane). The general anesthesia had a median duration of 63 [44–85] minutes. Ninety-six patients received anesthesia for a surgical intervention (pediatric surgery, N = 79; otolaryngology. N = 17; orthopedic surgery, N = 4) and 4 patients for an investigation (Magnetic Resonance Imaging).

Table 1

Demographic and baseline characteristics of 100 children and adolescents undergoing common surgical interventions requiring anesthesia.
N		100
Males : Females, N		35 : 65
Age, years		7.0 [4.2–11.0]
Body weight, kg		26.8 [18.1–42.7]
Height, m		1.27 [1.10–1.54]
Body surface area, m²		0.95 [0.75–1.32]
Body mass index, kg/m²		16.9 [15.2–19.9]
	Overweight, N	14
	Obese, N	12
Heart rate, bpm		90 [75–102]
Systolic blood pressure, mmHg		103 [93–108]
Diastolic blood pressure, mmHg		48 [41–61]
Duration of surgical procedure, min		49 [30–66]
	< 60 min, N	64
	60–120 min, N	26
	≥ 120 min, N	10
Duration of anesthesia, min		63 [44–85]
Type of anesthesia
	Intravenous anesthetics, N	94
	Inhalation anesthetics, N	6
Perioperative IV fluids administered, mL/m²		256 [178–382]
	Ringer-infusion, N	42
	Ringer-infusion and NaCl 0.9%, N	28
	NaCl 0.9%, N	26
	None, N	4
Continuous variables are reported as median and interquartile range; categorical variables are presented as counts.

A prophylaxis to prevent postoperative nausea and vomiting was given in 94 cases, usually with ondansetron and dexamethasone. The median duration of the surgical procedure was 49 [30–66] minutes. In the 79 pediatric surgery patients blood loss was irrelevant; and in the other 21 (otolaryngology and orthopedic surgery) the estimated blood loss was about 50 ml.

There were no perioperatively respiratory and cardiac complications. The median perioperative fluid therapy amounted to 225 [200–400] mL, equivalent to 256 [178–382] mL/m² when adjusted to the body surface area, with four patients receiving no fluid therapy at all. Nearly half of the patients was hydrated with an isotonic solution (lactated Ringer, 42%), 26% received a normal saline solution (NaCl 0.9%) while 28% received a combination of both normal saline and lactated Ringer fluid-therapy. The urinary output was always checked in young children at the end of all surgical procedures in the diapers and no relevant amount of urine output was observed during the procedure.

All the main vital signs routinely monitored were lower immediately after anesthesia than before, as expected by the anesthetic medications used, but always in normal reference ranges.

As shown in Table 2, the average total body water (TBW) increased perioperatively with a delta value of 182 [0–383] mL/m² from pre- to postoperatively. The extracellular water content (ECW) had an equivalent increase with a delta value of 169 [19–307] mL/m². Nevertheless, the intracellular water content (ICW) did not significantly change (delta value of 0 [-125–158] mL/m²). No differences were observed between the group of patients with no relevant blood loss (N = 79) and the group of patients (N = 21) with somewhat of blood loss.

Table 2

Volume status of 100 children and adolescents before and after anesthesia.
	before [L]	delta [mL/m²]	p-value
Total Body Water	16.4 [11.9–25.3]	182 [0–383]	P < 0.0001
Extracellular Water	6.9 [5.1–10.6]	169 [19–307]	P < 0.0001
Intracellular Water	9.5 [6.7–14.7]	0 [-125–158]	P = 0.77182
Continuous variables are reported as median and interquartile range.
Delta values were calculated by subtracting preoperative value from the postoperative value.
Significance between pre- and postoperative was determined by Wilcoxon matched paired t-test (p < 0.05).

Linear regression analyses evaluating the relationship between perioperative fluid administration and changes in pre- to postoperative fluid status, show that the changes in TBW (r² = 0.05, p = 0.02) and ECW (r² = 0.20, p < 0.0001) correlates with the amount of fluids administered (Fig. 1). However, variations in ICW was not significantly associated with the fluids given.

Body composition, as assessed by the BCM device (fat tissue index and lean tissue index) did not show any correlation with TBW, ECW or ICW variations. Nevertheless, comparing the group of lean children (N = 74) with the group of obese children (N = 12), lean children showed a higher perioperative increase in ECW compared to obese children (p = 0.03; Fig. 2) by similar administered fluids (as expressed in ml/m²).

Most children who undergo anesthesia are nowadays hydrated with an isotonic solution such as normal saline (0.9%) or lactated Ringer at a rate of 1700 ml/m²/day.² Nevertheless, the amount of sodium administered with these infusions is important and one can speculate that this strategy might be associated with an extracellular fluid volume expansion.

The main results of this preliminary study confirm this hypothesis: routine intraoperative fluid administration as mentioned above results in a significant increase in the total body water and extracellular water content as assessed by the bioimpedance technique. The intracellular water content did not show relevant changes.

During anesthesia and perioperative circumstances, the main goals are to avoid fluid deficits, ensure electrolytes homeostasis and achieve stability of vital parameters.

The use of normal saline (or lactated Ringer) infusions does not increase the intracellular volume (and does not cause hyponatremia anymore), yet provide an extracellular fluid volume expansion. This tendency is more pronounced in lean compared to obese children.

This analysis shows that the extracellular fluid expansion is directly correlated to the amount of fluid administered.

A general vasodilatation and increased secretion of proinflammatory mediators and stress hormones during surgery can be mentioned as possible explanations for this increase in total body water content. General anesthesia causes peripheral vasodilatation resulting in a redistribution and accumulation of fluids [15]. Moreover, surgery represents a traumatic insult and initiates an acute stress response leading to secretion of proinflammatory mediators and stress hormones, which control the sympathoadrenal system and the hypothalamic-pituitary-adrenal axis. Increased levels of adrenocorticotrophic hormone, antidiuretic hormone, cortisol, aldosterone and catecholamines result in increased catabolism, reduced urinary secretion, disturbed microcirculation and increased vascular permeability leading to salt and fluid retention [16]. An explanation for the more pronounced fluid accumulation in lean compared to obese children could be the fact that lean children have a more pronounced stress response to surgery compared to obese children, who, at the contrary, have already at rest a high basal sympathetic activity [17].

The present results have relevant clinical consequences: In otherwise healthy schoolchildren (ASA ≤ 2) undergoing minor surgical interventions or investigations requiring anesthesia, a more prudent and economical fluid administration is warranted in order to avoid fluid accumulation (unless blood pressure and heart rate remain stable during anesthesia). One can also speculate that this category of low-risk schoolchildren do not necessitate in any case fluid administration during anesthesia.

Some limitations need to be mentioned: The preoperative as well as the postoperative measurements were not taken in the awake child. Nevertheless, the time delay would be potentially too long with the consequences of relevant changes during the postoperative time. Secondly, the approved study protocol did not plan to perform laboratory tests, such as measurements of electrolytes, hemoglobin, serum creatinine, albumin or inflammatory markers, which could give us more information about the pathophysiological changes behind fluid accumulation.

Strengths of this analysis are the easy to perform, well accepted, painless, not invasive and validated technique used to assess body composition and fluid content in children and the standardized measurement protocol, which allows precise and reproducible results.

In conclusion, this study demonstrates that fluid accumulation occurs in low-risk schoolchildren during general anesthesia. The results of this preliminary study suggest that children and adolescents without major health problems (ASA ≤ 2) undergoing short procedures (< 1 hour), could not require any perioperative intravenous fluid therapy, unless vital parameters remain stable. Perioperative fluid prescription could be advised only in the management of critically ill children and/or long procedures, but further studies are needed. Moreover, BCM-measurements yielded plausible results in children and adolescents undergoing general anesthesia and could become useful for guiding intraoperative fluid therapy in future studies.

ASA

American Society of Anesthesiology

BCM

body composition monitor

BMI

Body mass index

CDC

Centre of Disease Control

ECW

extracellular water content

ICW

intracellular water content

TBW

total body water

FUNDING

Dr Betti was supported by an internal funding from Ente Ospedaliero Cantonale for junior researchers (AFRI).

COMPETING INTERESTS

The authors have no relevant financial or non-financial interests to disclose.

AUTHOR CONTRIBUTIONS

Substantial contributions to conception and design (G.D.S, C.B.), acquisition of data (C.B., C.C., I.B.), analysis (C.B.; G.D.S) and interpretation of data (G.D.S, C.B.).

Drafting the article or revising it critically for important intellectual content: all authors

Final approval of the version to be published: all authors

ETHICS APPROVAL

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of the Cantone Ticino authority.

CONSENT TO PARTICIPATE

All parents gave written informed consent for the patients’ participation in the study.

DATA AVAILABILITY

The dataset generated and analyzed during the current study is available from the corresponding author on reasonable request.

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No competing interests reported.

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Fluids and body composition during anesthesia in children: a bioimpedance study

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Abstract

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What is Known

INTRODUCTION

METHODS

Patients

BCM-measurements

Other measurements and patient characteristics

Sample size

Statistical analysis

RESULTS

DISCUSSION

Abbreviations

Declarations

References

Additional Declarations

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