Insensible Fluid Loss


Article Author:
Janelle McNeil-Masuka


Article Editor:
Tanna Boyer


Editors In Chief:
Stephen Leslie
Karim Hamawy


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Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
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Hussain Sajjad
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Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
7/10/2019 12:42:52 AM

Definition/Introduction

Water is essential for the maintenance of life. As the major element of fluid compartments in the body, water makes up approximately 60% of body weight. Gender, age, physical activity, and adiposity are pertinent factors that may alter this percentage.[1] In the body, water subdivides between extracellular (33%) and intracellular (67%) spaces. Thirst and hormonal mechanisms are both responsible for maintaining total body water within a tight range. A decrease in plasma volume, increase in plasma osmolality, or decrease in blood pressure all stimulate a patient’s thirst drive. The hormone vasopressin is responsible for controlling daily water balance, and hyperosmolality stimulates its release.

The body uses water for a variety of mechanisms from transporting nutrients to excreting wastes and tissue structure viability. Water balance occurs by matching the daily water input/output to and from the body. The primary means of water intake is by consumption of food and fluids. Daily fluid maintenance requirements for adults are approximately 1.5 to 2.5L of water.[1] The majority of fluid loss occurs in urine, stool, and sweat but is not limited to those avenues. Insensible fluid loss is the amount of body fluid lost daily that is not easily measured, from the respiratory system, skin, and water in the excreted stool. The exact amount is unmeasurable but is estimated to be between 40 to 800mL/day in the average adult without comorbidities.[2] A total loss of approximately 600 to 800mL/day characterizes 30 to 50% of all water loss, contingent on the level of water consumed. Thus insensible water loss is a significant component of water balance and needs to be routinely monitored.

During the perioperative period, the goals of fluid management are to provide a suitable volume of parenteral fluid to support cardiac preload, intravascular volume, oxygen carrying capacity, and electrolyte balance. Additionally, parenteral fluid replenishment focuses on equipping the body with enough fluid to meet both insensible and sensible physiologic losses. Maintenance fluid rate replacement is calculated by using the “4-2-1” rule, which came from the 1950s work published in Pediatrics.[3] For the first 10kg of the patient, fluid replacement is at a rate is 4mL/kg/h. For the next 10kg, the rate is 2mL/kg/h, and for each kg, after 20kg the rate is 1mL/kg/h. Preoperative fasting causes a fluid deficit leading to a slight decrease in the extracellular fluid while maintaining intravascular volume. Without any fluid intake overnight, a patient’s fluid deficit is proportionate to the duration of the fast. This deficit is estimated by multiplying the normal maintenance rate by the length of the fast.[4] Fluid replacement during surgery centers on the type/extent of surgery as well as a patient's hourly needs.

Issues of Concern

Intravenous fluid therapy typically consists of using colloids, crystalloids, or a combination of both. Crystalloids such as normal saline contain usually contain salts with or without glucose. When crystalloids are given, they precipitously equilibrate with and disperse throughout the whole extracellular fluid space. In initial fluid resuscitation, crystalloids are classically the first line fluid used in most patients.[5] Colloids can be an option if the hemodynamic response is insufficient. When choosing a solution, the type of fluid loss is a consideration.[6] Losses primarily associated with water are replaced with a hypotonic solution. Losses involving both electrolytes and water are replaced with isotonic solutions. Glucose can be adding to either solution depending on the patient’s medical condition or needs. Overall in the operating room, isotonic solutions tend to be preferentially used because intraoperative fluid losses are isotonic. The two most frequently used solutions are normal saline and lactated ringers.[7]

Colloid solutions such as albumin typically contain proteins or large glucose polymers. When a colloid solution is given, the high protein content the solution keeps the solution intravascular for a more extended period. Secondarily, this type of solution works to support the intravascular plasma oncotic pressure. Colloids cost substantially more than crystalloids and are associated with more complications, both of which tend to limit their use.[6] Primary indications for colloids include fluid resuscitation in patients with significant intravascular fluid loss. Conditions associated with substantial protein loss, for example, are burn patients and patients with severe hypoalbuminemia.[8] Overall, the guidance of the choice of fluid administered intravenously is a function of the cardiovascular state, patient’s volume status, renal function, comorbidities, serum osmolarity, and any electrolyte imbalances.[8]

Clinical Significance

Evaluation of intravascular volume and clinical assessment are critical because fluid compartment volumes cannot easily be measured. Intravascular volume may undergo assessment by using laboratory/physical exams, and hemodynamic monitoring means.  Frequent evaluations are necessary despite the method used to confirm the initial impression to best manage fluid replacement. The physical examination is most reliable when assessing a patient’s baseline fluid status.[9]  Clues to hypovolemia include hydration of mucous membranes, skin turgor, resting heart rate, and intensity of peripheral pulses. Additionally, blood pressure particularly orthostatic changes and urinary output, are also important indicators of fluid status gleaned from a physical examination. Perioperatively, physiologic manipulation from surgical stress and anesthesia alter these signs (due to increased antidiuretic hormone secretion) rendering them unreliable.[9]

Insensible fluid loss is routinely a cause of concern when evaluating patients. Patients may exhibit nonspecific and specific signs on exams such as dry mucous membranes, poor skin turgor, poor capillary refill, tachycardia, and dyspnea. The cause of insensible fluid loss may be due to many diagnoses, including surgery, respiratory loss, dehydration, burns, metabolic, and vascular etiologies. While the physical exam findings may point to hypovolemia, the cause is difficult to know without proper laboratory and imaging studies.[10] [Level I/II]  Fortunately, the majority of patients will tolerate a fluid bolus challenge with quick re-examination after to assess for positive versus no change in their clinical status.  There has also recently been an explosion in the ability to noninvasively measure functions of fluid status (cardiac output, etc.) with medical devices that make estimates of these measurements. 

Nursing Actions and Interventions

Assessment of fluid status is taught in nursing school, medical school, and physician assistant school.  Knowledge of fluid status and insensible fluid losses is paramount in the care of critically ill patients.  There must be free-flowing information and communication regarding fluid status from bedside nurses to the other medical professionals that are part of the patient's care team.  Physicians across the United States are more commonly turning to point of care ultrasound (POCUS) to provide quick, accurate information on the fluid status of their patients by looking at the inferior vena cava and heart using transthoracic echocardiograms.  As this becomes more common, the healthcare team will be able to accurately assess and treat fluid status and monitor for insensible fluid losses.  Interestingly, there is level I/II evidence that radiologists can provide the healthcare team with pertinent imaging findings that may help to elude the cause of hypovolemia,[10] which point to a positive future for continued POCUS growth. 


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Insensible Fluid Loss - Questions

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A 68-year-old female with colon cancer is being prepped to undergo a hemicolectomy with general anesthesia and an epidural for postoperative pain management. She did a bowel prep the day prior and only had clear liquids, and has been NPO since 8 pm. Her weight is 50 kg. She has an 18 G peripheral IV cannula in place. Her incision will be medium-sized, from her belly button to her pubic symphysis. Her case starts at 8 am. Once she is has been put under general anesthesia, how much crystalloid would she need per hour to account for insensible fluid losses?



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A 92-year-old female patient is admitted to the nursing home after a short hospital stay for a fractured right hip. She has been taking clindamycin for an infected right heel pressure ulcer and has now developed watery diarrhea. Her blood pressure is 83/52 mmHg and the heart rate is 115/min. Her family is concerned that she has not been eating and drinking well. What is the most likely cause of this patient's current condition?



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A 56-year-old female who had a total abdominal hysterectomy via laparoscopy for fibroids and heavy vaginal bleeding is being evaluated on the second post-op day. Her pain is well-controlled, and she is eating a normal diet. Her major complaint is bilateral ankle swelling, stating, "my socks are too tight." What is the most likely cause of this symptom?



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An intubated patient is being evaluated in the intensive care unit (ICU). The ventilator is not connected to a humidifier. The bedside nurses are carefully monitoring the patient's fluid status by measuring fluid in (IV fluids, no PO intake) and fluid out (urine, nasogastric tube output). They have consistently been measuring the patient as having a net neutral fluid balance for the last three days. However, the patient appears dehydrated every morning, tachycardic and hypotensive, and dry mucous membranes. Which of the following is most likely to explain this finding?



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Insensible Fluid Loss - References

References

HOLLIDAY MA,SEGAR WE, The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957 May;     [PubMed]
Winata AS,Jen WY,Teng ML,Hing WC,Iyer SG,Ma V,Chua HR, Intravenous maintenance fluid tonicity and hyponatremia after major surgery- a cohort study. International journal of surgery (London, England). 2019 May 8;     [PubMed]
Doherty M,Buggy DJ, Intraoperative fluids: how much is too much? British journal of anaesthesia. 2012 Jul;     [PubMed]
Rich K, Review of article: Effects of fluid resuscitation with colloids versus crystalloids on mortality in critically ill patients presenting with hypovolemic shock the CRISTAL randomized trial by Djillali Annane, Shidasp Siami, Samir Jaber, et al (JAMA 2013;310:1809-17). Journal of vascular nursing : official publication of the Society for Peripheral Vascular Nursing. 2014 Jun;     [PubMed]
Vermeulen LC Jr,Ratko TA,Erstad BL,Brecher ME,Matuszewski KA, A paradigm for consensus. The University Hospital Consortium guidelines for the use of albumin, nonprotein colloid, and crystalloid solutions. Archives of internal medicine. 1995 Feb 27;     [PubMed]
Liamis G,Filippatos TD,Elisaf MS, Correction of hypovolemia with crystalloid fluids: Individualizing infusion therapy. Postgraduate medicine. 2015 May;     [PubMed]
Finfer S,Bellomo R,Boyce N,French J,Myburgh J,Norton R, A comparison of albumin and saline for fluid resuscitation in the intensive care unit. The New England journal of medicine. 2004 May 27;     [PubMed]
Heming N,Lamothe L,Jaber S,Trouillet JL,Martin C,Chevret S,Annane D, Morbidity and Mortality of Crystalloids Compared to Colloids in Critically Ill Surgical Patients: A Subgroup Analysis of a Randomized Trial. Anesthesiology. 2018 Dec;     [PubMed]
Bampoe S,Odor PM,Dushianthan A,Bennett-Guerrero E,Cro S,Gan TJ,Grocott MP,James MF,Mythen MG,O'Malley CM,Roche AM,Rowan K,Burdett E, Perioperative administration of buffered versus non-buffered crystalloid intravenous fluid to improve outcomes following adult surgical procedures. The Cochrane database of systematic reviews. 2017 Sep 21;     [PubMed]
Boldt J, New light on intravascular volume replacement regimens: what did we learn from the past three years? Anesthesia and analgesia. 2003 Dec;     [PubMed]

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