Goal-directed fluid therapy algorithm

--- title: Fluids & Nutrition description: Fluid therapy, crystalloids vs colloids, goal-directed fluid therapy, enteral and parenteral nutrition — topic notes for MS and DNB General Surgery. group: Perioperative Care subtopics: 9 sources: - NICE Clinical Guideline CG174 — Intravenous fluid therapy in adults in hospital - Surviving Sepsis Campaign Guidelines 2021 - OPTIMISE trial (goal-directed fluid therapy) - SAFE trial, NEJM 2004 (albumin vs saline) - Standard surgical references (Bailey & Love, Sabiston) for general principles ---

Balanced Crystalloids vs Normal Saline

Definition & Classification

Normal Saline (NS): 154 mEq/L Na&spplus; and Cl&supminus;; hyperchloremic, slightly hyperosmolar (~308 mOsm/L), pH ~5.5.
Balanced Crystalloids (BC): Ringer’s Lactate, Plasma-Lyte — electrolyte composition closer to plasma; chloride partially replaced by bicarbonate or metabolizable buffers (lactate, acetate).

Pathophysiology & Rationale

NS risks:

Hyperchloremic metabolic acidosis from high chloride load; dilutional bicarbonate loss.
Possible renal vasoconstriction, reduced GFR; increased AKI risk in some settings.

BC theoretical advantages:

Mitigate acid–base disturbances; less acidosis.
Electrolyte profile closer to physiology → improved homeostasis.

Caveat BC may be relatively hypotonic in TBI → risk of cerebral oedema; NS is sometimes preferred in neurocritical care.

Setting	BC Advantage	Caution / No Benefit
Critically ill (general)	Possibly lower composite mortality & AKI	Data mixed, inconclusive overall
Adult sepsis	Reduced 28/30-day mortality, lower AKI	Low-quality evidence, needs more RCTs
TBI	—	Potential harm: increased mortality with BC — prefer NS
Pediatric sepsis	Lower mortality, AKI, hyperchloremia, shorter stay	Slightly longer LOS in some studies
DKA (adults)	Faster metabolic resolution, faster insulin weaning	Strong support for BC use

Parameter	Balanced Crystalloids	Normal Saline	Plasma
Na&spplus; (mmol/L)	130–140	154	140
Cl&supminus; (mmol/L)	98–110	154	103
Buffer	Lactate (RL), acetate/gluconate (Plasma-Lyte)	None	Bicarbonate
pH	~6.5–7.4	~5.5	7.4
Osmolarity (mOsm/L)	273–294	308	295
Distribution	25% intravascular, 75% interstitial	Same	100% intravascular
Duration of effect	30–60 min	30–60 min	2–6 hours
Cost	Low	Low	High
Indications	Resuscitation, perioperative maintenance	Hypovolemia (if no balanced fluid)	Major blood loss, coagulopathy, plasma exchange
Contraindications	Severe liver failure (RL — lactate metabolism)	Hyperchloremia, renal impairment	Allergy, volume overload risk

Practical Recommendations — Exam Answer Style

Choice of fluid should be individualized, context-specific.
Balanced crystalloids generally preferred in: adult sepsis (weak recommendation, SSC 2021), pediatric sepsis, DKA management (faster resolution).
Normal Saline may remain appropriate in: TBI (cerebral oedema risk with BC), alkalosis/hypochloremia needing chloride load, hyperkalemia/hypercalcemia where fluid content affects electrolytes.
Further large RCTs needed to clarify benefit across subpopulations.

Key take-home Balanced crystalloids = more physiologic composition, reduce hyperchloremic acidosis risk. Evidence supports improved outcomes in sepsis, pediatric septic shock, and DKA. NS still indicated in TBI or specific electrolyte/acid–base derangements. SSC 2021 gives a weak recommendation for BC in adult sepsis.

Colloids vs Crystalloids

Definition

Crystalloids — solutions of small molecules (electrolytes ± buffers) that pass easily through semipermeable membranes.

Balanced: Ringer’s Lactate, Plasma-Lyte
Unbalanced: 0.9% Normal Saline

Colloids — solutions of large-molecular-weight substances (proteins or polysaccharides) that stay in the intravascular space longer by exerting oncotic pressure.

Natural: Albumin
Synthetic: Gelatins, Dextrans, Hydroxyethyl Starch (HES)

Classification

Crystalloids

Isotonic: 0.9% NS, RL
Hypotonic: 0.45% NS, D5W
Hypertonic: 3% NS, 7.5% NS

Colloids

Natural: Albumin (4%, 5%, 20%), Fresh Frozen Plasma
Synthetic: Gelatins (Haemaccel, Gelofusine), Dextrans (Dextran-40, -70), HES (withdrawn/restricted in many settings due to renal risk)

Feature	Crystalloids	Colloids
Composition	Small molecules, electrolytes ± buffers	Large molecules (protein, starch, gelatin)
Oncotic pressure	Low	High
Volume expansion	Short-lived (~⅓ remains intravascular at 1 h)	More sustained (up to 24h for albumin)
Capillary leak	Rapid redistribution if leaky	Leaks into interstitium in sepsis/ARDS
Cost	Low	High (esp. albumin)
Storage	Easy	More complex, sometimes cold chain

Pharmacokinetics & Volume Effect

Crystalloids: 1 L expands plasma volume by ~250–300 mL (rest goes interstitial).
Colloids: 1 L expands plasma volume by ~800–1000 mL (if endothelium intact).
In capillary leak states (sepsis, burns), colloids may escape into interstitium — reduced advantage, can worsen oedema.

Clinical Evidence & Newer Concepts

Critically ill (SAFE trial, NEJM 2004): 4% albumin vs NS in ~7,000 ICU patients — no significant overall mortality difference. Subgroup: TBI — albumin associated with increased mortality.
Synthetic colloids: HES linked to increased AKI, increased need for RRT, possible increased mortality (VISEP, 6S, CHEST trials) — use now restricted. Gelatins/dextrans carry anaphylaxis risk and coagulopathy, limited benefit over crystalloids.
Perioperative fluid therapy: modern ERAS protocols emphasize goal-directed therapy, usually starting with crystalloids, adding albumin only for persistent hypoalbuminemia or refractory volume deficit.
Cost and availability: crystalloids universally available and cheaper; BC preferred over NS for most resuscitation except TBI, severe alkalosis.

Advantages & Disadvantages

Crystalloids	Colloids
+ Cheap, widely available, easy storage + No allergy risk − Large volumes → interstitial oedema, dilutional coagulopathy − Short intravascular half-life	+ More sustained plasma volume expansion (if capillary intact) + Smaller volume needed for resuscitation − Expensive − Allergy/anaphylaxis risk (esp. gelatins, dextrans) − Coagulopathy (esp. dextrans, HES) − Renal injury with HES − Ineffective in leaky capillary states

Current Practical Recommendations

Per Surviving Sepsis Campaign 2021, ERAS, and surgical guidelines

First-line: balanced crystalloids for initial resuscitation in most surgical/ICU patients.
Normal Saline: use in TBI, hyponatremia, metabolic alkalosis.
Albumin: consider as adjunct in sepsis with hypoalbuminemia, after crystalloids.
Synthetic colloids (HES, dextran, gelatin): avoid in sepsis, burns, renal dysfunction.
Goal: avoid both under- and over-resuscitation; use dynamic preload assessment (PPV, SVV, passive leg raise).

Key exam take-home No strong mortality benefit of colloids over crystalloids in most settings. Synthetic colloids (esp. HES) largely abandoned in critical care due to renal injury and coagulopathy. Balanced crystalloids preferred over NS for most patients. Albumin has a niche role — mainly sepsis with hypoalbuminemia, or cirrhosis with large-volume paracentesis.

Goal-Directed Fluid Therapy (GDFT) in the Perioperative Period

Definition

An individualized, dynamic approach to perioperative fluid administration guided by specific physiological targets (haemodynamic and perfusion parameters), aiming to optimize tissue oxygen delivery while avoiding both hypovolemia and fluid overload.

Rationale

Traditional fluid therapy uses fixed formulas (body weight, fasting deficit, maintenance + surgical losses).
This can cause under-resuscitation (hypoperfusion, AKI) or overload (pulmonary oedema, impaired wound healing).
GDFT uses real-time monitoring to titrate fluids to the patient’s physiological response.

Goals of Perioperative Fluid Therapy

Maintain adequate intravascular volume.
Optimize cardiac output and tissue perfusion.
Maintain oxygen delivery (DO₂).
Prevent complications of fluid overload (ARDS, oedema, impaired healing).

Parameters Used in GDFT

Clinical: urine output ≥0.5 mL/kg/hr; capillary refill, skin turgor, HR, BP (limited sensitivity).

Laboratory: BUN:Creatinine ratio — >20 suggests hypovolemia, <10 suggests fluid overload; serum lactate (raised → inadequate perfusion).

Oxygenation: PaO₂:FiO₂ ratio (normal ~500, <300 suggests pulmonary fluid overload/ARDS); ScvO₂ target >70%; SvO₂.

Haemodynamic/dynamic indices: stroke volume variation (SVV >13% → fluid responsive); pulse pressure variation (PPV >12% suggests responsiveness); fluid bolus challenge (250 mL over 5–10 min); cardiac output monitoring (oesophageal Doppler, LiDCO, PiCCO, FloTrac).

Principles of GDFT

Give fluid bolus (200–250 mL crystalloid/colloid).
Assess response via SV, CO, SVV, PPV.
If stroke volume rises ≥10% → fluid responsive → continue.
If no significant change → stop further fluids, consider inotropes/vasopressors.

GDFT decision algorithm — original diagram

Parameter	Target	Interpretation
Urine output	≥0.5 mL/kg/hr	Adequate renal perfusion
MAP	≥65 mmHg	Ensures organ perfusion
CVP	8–12 cmH₂O	Trend monitoring only, not reliable alone
SVV	<10–12% after optimization	>13% → fluid responsive
PPV	<12%	>12% suggests preload responsiveness
Stroke volume	Optimize to plateau	No further rise after bolus = target met
Cardiac index	>2.2 L/min/m²	Ensures adequate flow
ScvO₂	>70%	Reflects DO₂/VO₂ balance
SvO₂	>65%	More accurate with PA catheter
Serum lactate	<2 mmol/L	Elevated → tissue hypoperfusion
BUN:Cr ratio	10–20 normal	>20 hypovolemia, <10 overload
PaO₂:FiO₂	>300	<300 suggests pulmonary overload/ARDS

Mnemonic — GDFT targets “U-MaSS COLaB-Pa” — Urine output ≥0.5 · MAP ≥65 · SVV <12% · SV optimized · CO >2.2 · ScvO₂ >70% · Lactate <2 · BUN:Cr 10–20 · PaO₂/FiO₂ >300

Evidence

Multiple RCTs/meta-analyses (e.g. OPTIMISE trial) show GDFT reduces postoperative renal/pulmonary complications and hospital stay; effect on mortality less clear.
Recommended by ERAS protocols.

Exam writing tip Start with definition, emphasize rationale, explain monitoring parameters, include an algorithm/flowchart, and conclude with evidence and the ERAS recommendation.

Intravenous Fluid Therapy in Adults (NICE CG174)

Introduction

IV fluid therapy = administering fluids to maintain or restore fluid & electrolyte balance when the oral/enteral route is inadequate.
Mismanagement → dehydration, overload, electrolyte imbalance, morbidity/mortality.
Applies to adults ≥16 yr in hospital (excludes pregnancy, severe renal/liver disease, diabetes, burns, ICU).

Principles — the “5 R’s”

Resuscitation — restore intravascular volume.
Routine maintenance — meet daily basic needs.
Replacement — correct existing deficits.
Redistribution — manage abnormal shifts.
Reassessment — continuous monitoring and adjustment.

Assessment & Monitoring

Initial assessment: history (intake, losses, comorbidities, refeeding risk); examination (pulse, BP, JVP, capillary refill, oedema, postural hypotension); clinical monitoring (NEWS, fluid chart, weight); labs (FBC, urea, creatinine, electrolytes).

Indicators for resuscitation: SBP <100 mmHg, HR >90/min, cap refill >2s, RR >20/min, NEWS ≥5, positive passive leg raise.

Reassessment: ABCDE approach; continuous monitoring if resuscitating, daily otherwise; check serum chloride daily if 0.9% NaCl used; reassess on transfer or clinical change.

Fluid type	Na&spplus; (mmol/L)	Cl&supminus; (mmol/L)	Notes
0.9% NaCl	154	154	Risk: hyperchloremic acidosis
Hartmann’s / Ringer’s lactate	131	111	Balanced, preferred for resuscitation
5% Dextrose	0	0	Free water, no electrolytes
4% Dextrose in 0.18% NaCl	30	30	Maintenance use

Management by Category

Resuscitation: crystalloid (Na&spplus; 130–154 mmol/L); 500 mL bolus over <15 min, reassess; avoid tetrastarch; albumin 4–5% only in severe sepsis.

Routine maintenance — initial prescription: water 25–30 mL/kg/day; Na&spplus;/K&spplus;/Cl&supminus; ~1 mmol/kg/day each; glucose 50–100 g/day (prevents ketosis).

Obese → use ideal body weight, max ~3 L/day.
Elderly, cardiac/renal disease, refeeding risk → 20–25 mL/kg/day.
Typical day-1 fluid: 0.18% NaCl + 4% dextrose + 27 mmol/L K&spplus;, ≤2.5 L/day.
Deliver preferably in daytime to improve sleep.
Never add K&spplus; directly to bag.

Replacement & redistribution: modify maintenance for deficits (dehydration, bleeding), ongoing losses (vomiting, drains, diarrhoea), redistribution (sepsis, oedema, postoperative state). Seek expert help if: severe sepsis, hypo/hypernatremia, major organ dysfunction, malnutrition/refeeding issues.

Complication	Definition	Time frame
Hypovolaemia	Clinical dehydration, low urine, ↑urea/Cr	During therapy
Pulmonary oedema	Breathlessness, X-ray findings	During/≤6h post-IVF
Hyponatraemia	Na&spplus; <130 mmol/L	≤24h post-IVF
Hypernatraemia	Na&spplus; ≥155 mmol/L	≤24h post-IVF
Hyper/hypokalaemia	K&spplus; >5.5 / <3.0 mmol/L	≤24h post-IVF
Peripheral oedema	Pitting oedema, no cardiac/renal cause	≤24h post-IVF

Maintenance prescription rule “30 : 1 : 100” — 30 mL/kg H₂O : 1 mmol/kg Na/K/Cl : 100 g glucose

Artificial Nutritional Support

Introduction

Adequate nutrition is vital for postoperative recovery and wound healing.
Indicated when oral intake is inadequate for >5 days, or earlier in malnourished patients.
Commonly required in major head, neck, or GI surgeries (oesophagectomy, gastrectomy, pancreaticoduodenectomy).
Preoperative planning: consider IV access, nasojejunal tube, or feeding jejunostomy intraoperatively.

Indications

Inability to meet caloric needs orally: dysphagia (stroke, head & neck malignancy, stricture), severe trauma/burns, neurological impairment.
GI tract non-functional or inaccessible: prolonged ileus, bowel obstruction, severe pancreatitis, short bowel syndrome, high-output fistula.
Severe catabolic states: sepsis, major trauma, extensive surgery.
Pre- and post-operative support in malnourished patients.

Route	Advantages	Disadvantages
Enteral	Maintains gut mucosal integrity & immune function; fewer septic complications; cheaper, physiologic	Not feasible in GI obstruction, ileus, severe malabsorption; diarrhoea, aspiration risk
Parenteral	Useful when gut cannot be used; precise nutrient control	Expensive, technically demanding; catheter sepsis, metabolic complications; loss of gut mucosal barrier

Key points Enteral nutrition preferred whenever possible. Start feeding early (within 5 days) if oral intake inadequate. Prevent refeeding syndrome with slow initiation and electrolyte monitoring. Central venous access preferred for PN >14 days. Regular multidisciplinary input (dietician, surgeon, physician) essential.

Enteral Nutrition

Definition

Delivery of nutrients directly into the GI tract through oral, gastric, or post-pyloric routes, when normal oral intake is inadequate but the gut is functional.

Types — by Route

Oral supplementation (nutrient-dense polymeric/elemental/modular feeds)
Tube feeding: nasogastric (NG), nasoduodenal/nasojejunal, gastrostomy (PEG — endoscopic, surgical, radiological), jejunostomy (PEJ, surgical)

Types — by Nutrient Composition

Polymeric: intact protein, polysaccharides, long-chain triglycerides — needs normal digestion/absorption.
Elemental/monomeric: amino acids, monosaccharides, MCT — for malabsorption, short bowel, pancreatitis.
Oligomeric/semi-elemental: peptides, oligosaccharides, MCT — intermediate.
Modular: single nutrient modules for tailoring.
Disease-specific: renal (low protein), hepatic (BCAA-enriched), pulmonary (high fat/low carb), diabetic (low GI, fibre-added).

Indications

Inability to maintain adequate oral intake with intact GI tract: neurologic (stroke, head injury, coma, dementia); oropharyngeal/oesophageal pathology (severe dysphagia, stricture, malignancy); postoperative (major head–neck/GI surgery, unsafe oral intake); critically ill (burns, sepsis, trauma if gut usable); preoperative malnutrition build-up.
Contraindication to parenteral nutrition when gut is functional.

Route	Access	Duration	Indication
Oral supplements	By mouth	Short–long term	Mild undernutrition
Nasogastric (NG)	Nose → stomach	≤4–6 weeks	Short-term, intact gag reflex
Nasojejunal (NJ)	Nose → jejunum	≤4–6 weeks	High aspiration risk, pancreatitis
PEG (gastrostomy)	Endoscopic/surgical/radiologic	>4–6 weeks	Long-term, intact gastric emptying
Jejunostomy (PEJ/surgical)	Endoscopic/surgical	Long-term	Gastroparesis, gastric outlet obstruction, high aspiration risk

Gastrostomy Techniques

PEG (Percutaneous Endoscopic Gastrostomy): endoscopic placement, avoids GA; internal bumper apposes stomach to abdominal wall.
RIG (Radiologically Inserted Gastrostomy): under fluoroscopy, balloon/pigtail fixation; used if endoscopy not feasible.
Surgical gastrostomy: for distorted anatomy or failed PEG/RIG; laparotomy/laparoscopic placement, stomach fixed to abdominal wall.

Complications: early — perforation, bleeding, peritonitis, local sepsis; late — tube blockage/displacement, persistent gastric fistula.

Jejunostomy

Usually placed intraoperatively (e.g. oesophagectomy); can also be placed radiologically. Tube fixed to abdominal wall.

Complications: early — leakage, peritonitis, bleeding, displacement; late — granulation tissue, local sepsis.

Advantages of Enteral Nutrition

Physiological: preserves gut mucosal integrity, prevents atrophy; maintains GALT (gut-associated lymphoid tissue) — decreases bacterial translocation and septic complications; stimulates bile flow and pancreatic secretions.

Clinical: lower infection incidence vs PN; better glycaemic control than PN; early EN reduces postoperative ileus and improves wound healing.

Practical: easier and safer administration than PN; cheaper; fewer metabolic complications (hyperglycaemia, liver dysfunction).

Disadvantages

Mechanical/access-related: tube malposition, kinking, blockage, dislodgement; nasal/oesophageal ulceration, sinusitis, otitis (NG/NJ); aspiration pneumonia if gastric emptying impaired.

GI: nausea, vomiting, abdominal distension; diarrhoea (osmotic, rapid infusion, contamination); constipation; GI bleeding, ulceration, perforation (rare).

Metabolic: electrolyte disturbances (esp. critically ill); refeeding syndrome risk; less precise nutrient control than PN.

Category	Complications
Mechanical	Malposition, kinking, knotting; nasal/oesophageal ulceration, sinusitis, pressure necrosis; blockage/displacement; aspiration pneumonia
Gastrointestinal	Nausea, vomiting, distension; diarrhoea; constipation; GI bleeding, ulceration
Metabolic	Electrolyte imbalance (hypo/hypernatremia, hypokalemia, hypophosphatemia); hyperglycaemia; refeeding syndrome; dehydration or fluid overload
Infective	Sinusitis, otitis (nasal tubes); peristomal infection (PEG/jejunostomy site); peritonitis (surgical jejunostomy leak)

Limitations

Contraindicated in severe gut dysfunction (ileus, obstruction, severe ischaemia).
Not always feasible in haemodynamically unstable patients.

Contraindications

Absolute: intestinal obstruction (mechanical or paralytic ileus); severe intestinal ischaemia/mesenteric infarction; peritonitis or intra-abdominal sepsis where gut use is unsafe; severe GI haemorrhage; inability to access GI tract safely.

Relative: severe diarrhoea uncontrolled by feed adjustment; high aspiration risk (unprotected airway, uncontrolled reflux); haemodynamic instability (shock, high-dose vasopressors — bowel ischaemia risk); severe pancreatitis (NJ feeding often still feasible); severe malabsorption unresponsive to elemental feeds.

Parenteral Nutrition

Definition

Administration of nutrients intravenously, bypassing the GI tract, to provide substrates for energy, growth, and tissue repair.

Types — by Composition

Partial PN (PPN): supplies part of daily requirements; usually peripheral, short-term; lower osmolarity (<900 mOsm/L); glucose, amino acids, electrolytes, vitamins.
Total PN (TPN): full caloric/nutritional requirements; requires central venous access (high osmolarity); dextrose, amino acids, lipids, electrolytes, vitamins, trace elements.

By duration: short-term (<2 weeks) — peripheral PN; long-term (>2 weeks) — central PN.

By route: central TPN (subclavian, internal jugular, PICC); peripheral PN (limited osmolarity).

Indications

When enteral feeding is not possible, contraindicated, or insufficient.

GI dysfunction: intestinal obstruction, severe short bowel syndrome, high-output enterocutaneous fistulae, severe pancreatitis (if EN not tolerated), intractable vomiting/diarrhoea.
Perioperative: preoperative in severe malnutrition; postoperative in major GI surgery when prolonged NPO is expected.
Critical illness: severe trauma, burns, sepsis where EN isn’t feasible.
Oncology: malignant bowel obstruction, radiation enteritis.

Routes of Administration

Route	Duration	Comment
Central Venous Catheter (CVC)	Long-term	Preferred; reduces thrombophlebitis
PICC line	Weeks–months	Inserted via basilic/cephalic vein
Peripheral line	<14 days	Low-osmolar feeds only
Hickman / Port	Long-term (>3 months)	Implanted subcutaneous device

Confirm line tip in SVC/right atrium (chest X-ray).
Protect PN bag from light (vitamin degradation).
Include PN volume in fluid balance chart.
Withdraw PN gradually once enteral/oral feeding is adequate.

Advantages

Nutritional delivery when gut not usable (obstruction, ileus, high-output fistula).
Precise control over nutrient composition and fluid-electrolyte balance.
Immediate support without need for digestion/absorption.
Useful in severe catabolic states (burns, trauma, sepsis).
Tailorable to individual requirements.
Bypasses GI complications (bleeding, obstruction, severe diarrhoea).

Disadvantages

Invasive — requires central line for long-term PN.
High infection risk: catheter-related sepsis, fungal infection.
Metabolic complications: hyper/hypoglycaemia, electrolyte derangement, refeeding syndrome.
Hepatic complications: steatosis, cholestasis, hepatic fibrosis (long-term TPN).
Metabolic bone disease: osteoporosis/osteomalacia.
Expensive, requires trained personnel.
Doesn’t maintain gut mucosal integrity or microbiota — bacterial translocation, immune compromise.

Contraindications

Absolute: functioning, accessible GI tract (enteral always preferred if feasible); haemodynamic instability with poor perfusion (ischaemia, poor utilization risk); inability to secure venous access safely.

Relative: severe uncorrected metabolic derangement; advanced irreversible terminal illness where care goals are palliative; lack of facilities/expertise to monitor PN safely.

Complications of Parenteral Nutrition

Type	Examples
Insertion	Pneumothorax, misplacement
Line	Sepsis, thrombosis, blockage
Metabolic	Refeeding syndrome, glucose derangement, liver dysfunction, metabolic bone disease, vitamin deficiency

Insertion complications: pneumothorax (0.5–1%, esp. subclavian — manage with chest drain); misplacement (tip should lie in lower SVC or atriocaval junction).

Line complications: sepsis (up to 15% — take paired cultures, line + peripheral, remove line if positive); thrombosis (may cause SVC occlusion/PE — anticoagulation ± thrombolysis); blockage (prevent with regular flushing, dedicated lumen, heparin/thrombolytic lock).

Refeeding syndrome Occurs in severely malnourished patients after rapid feeding. Pathophysiology: hypophosphataemia → fluid & electrolyte shifts. Symptoms: arrhythmias, weakness, cardiac failure, seizures. Labs: ↓phosphate, K&spplus;, Mg²&spplus;, Ca²&spplus;; lactic acidosis.

Risk factors: BMI <16 or weight loss >15% in 3–6 months; no intake >10 days; low baseline K&spplus;/Mg²&spplus;/PO₄³&supminus;; alcoholism, insulin, chemotherapy, antacids, diuretics.

Prevention: start at 10 kcal/kg/day, increase slowly over 4–7 days, supplement thiamine/vitamins/trace elements.

Blood glucose derangement: hyperglycaemia common — use variable insulin infusion; adjust insulin when PN interrupted to avoid hypoglycaemia.

Liver dysfunction (IFALD): ~25% incidence; fatty liver → fibrosis → cirrhosis (esp. children); risk factors — short bowel, lack of colonic continuity, high-fat PN, minimal enteral intake; management — alternate lipid-free PN, promote enteral feeds.

Metabolic bone disease: osteoporosis/osteomalacia → fractures, renal calculi; supplement Ca²&spplus;, phosphate, Vit D, ± bisphosphonates.

Vitamin/trace element deficiency: long-term PN → anaemia, neuropathy, alopecia; prevent with regular micronutrient monitoring.

Enteral vs Parenteral — Summary

Feature	Enteral Nutrition	Parenteral Nutrition
Route	GI tract	Intravenous (peripheral/central)
Physiological effect	Maintains gut integrity, prevents atrophy	Bypasses gut, mucosal atrophy risk
Infection risk	Lower	Higher (catheter-related)
Cost	Cheaper	Expensive
Indication	When gut works	When gut unusable or contraindicated
Complications	Aspiration, diarrhoea	Metabolic, hepatic, catheter-related

Caloric & Protein Requirements in the Post-Operative Period

Introduction

Post-operative nutrition is vital for wound healing, immune function, and recovery. Surgery induces a catabolic stress response, increasing energy and protein requirements via elevated metabolic rate and nitrogen loss.

Energy Metabolism After Surgery

Phase	Duration	Metabolic state	Features
Ebb phase	0–24 hrs post-op	↓ Metabolism	↓O₂ consumption, ↓energy expenditure, ↓body temperature
Flow phase	2–10 days	↑ Catabolism	↑cortisol, ↑catecholamines, ↑gluconeogenesis, ↑protein breakdown
Anabolic/recovery phase	After 7–10 days	↑ Protein synthesis	Tissue repair, positive nitrogen balance

Caloric Requirements

1. Basal Energy Expenditure (BEE) — calculated via the Harris–Benedict equation.

2. Total Energy Requirement (TER) = BEE × (stress factor + activity factor). Combined stress + activity factors range from 1.2 to over 2.

Condition	Stress factor	Approx. requirement (kcal/kg/day)
Post-op elective surgery	1.1–1.2	25–30
Moderate infection/trauma	1.3–1.5	30–35
Sepsis, major burns, multiple trauma	1.5–2.0	35–45
Severe burns (>40%)	2.0–2.5	up to 50

Average post-op requirement: 30–35 kcal/kg/day

Protein Requirement

Condition	Protein requirement (g/kg/day)
Normal adult	0.8–1.0
Post-operative (mild stress)	1.0–1.2
Moderate stress (infection, trauma)	1.3–1.5
Severe stress, burns, sepsis	1.5–2.0
Protein-losing conditions	up to 2.5

Goal: achieve positive nitrogen balance (nitrogen intake > nitrogen loss). Nitrogen intake (g) = Protein intake (g) ÷ 6.25.

Carbohydrate & Fat Requirement

Macronutrient	Requirement	Remarks
Carbohydrates	3–5 g/kg/day (~50–60% of calories)	Prevents ketosis, spares protein
Fat	1–2 g/kg/day (~30–40% of calories)	Essential fatty acids, energy-dense

Fluid & Electrolyte Requirement

Component	Requirement
Water	30–35 mL/kg/day
Sodium	1–2 mmol/kg/day
Potassium	1 mmol/kg/day
Glucose	100–150 g/day minimum to prevent ketosis

Summary Table

Parameter	Normal	Post-op mild stress	Severe stress/sepsis
Calories	25 kcal/kg	30–35 kcal/kg	40–50 kcal/kg
Protein	1 g/kg	1.2–1.5 g/kg	2 g/kg
Carbohydrates	3–4 g/kg	4–5 g/kg	5–6 g/kg
Fat	1 g/kg	1–2 g/kg	2 g/kg
Water	30–35 mL/kg	30–40 mL/kg	40–50 mL/kg

Key points for exam Energy needs rise with surgical stress severity. Protein catabolism is a major cause of post-op weight loss and delayed healing. Early enteral feeding (within 24–48 hrs) is preferred to maintain gut integrity and immune function. Indirect calorimetry is the gold standard if available. Overfeeding → hyperglycaemia, CO₂ retention, fatty liver. Underfeeding → poor wound healing, infection, muscle wasting.

Macronutrient Requirements & Nutritional Assessment

Total Energy Requirement

Harris–Benedict equation (BMR):

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

In illness: hypermetabolism up to 120% of predicted. Stable/mild stress: 20–30 kcal/kg IBW/day. Severe stress: up to 30 kcal/kg IBW/day.

Note Use ideal body weight (IBW), not actual body weight, in obese patients.

Refeeding risk: start ≤50% of requirement, advance over 24–48 hrs per tolerance. If refeeding syndrome risk: ≤50% for first 48 hrs, then titrate up if stable.

Macronutrients

Macronutrient	Requirement	Function / Notes
Carbohydrates	45–65% of calories, ~2 g/kg/day glucose	Main CNS substrate, provides energy
Protein	1.5 g/kg IBW/day (~20% energy)	Meets increased nitrogen demand (0.25 g N/kg/day), reduces catabolism
Fat	20–35% of calories; essential FAs: linoleic & linolenic acid	Energy-dense, prevents EFA deficiency, used as triglyceride emulsions in PN

Parenteral nutrition: glucose 100–200 g/day; fat 100–200 g/week. Combination reduces CO₂ production and fluid overload, improves substrate use.

Micronutrients & Trace Elements

Category	Key points
Vitamins B & C	Increased demand post-op for collagen synthesis & wound healing; Vitamin C 60–80 mg/day
Vitamin B12	Supplement especially after gastric surgery or alcoholism
Fat-soluble vitamins (A, D, E, K)	Malabsorption risk in biliary/pancreatic obstruction
Electrolytes (Na&spplus;, K&spplus;, PO₄³&supminus;)	Losses in diarrhoea — replace and monitor
Trace elements (Mg, Zn, Fe)	Cofactors in metabolism; replace to prevent refeeding syndrome

Nutritional Assessment — the ABCD Approach

A — Anthropometry

Parameter	Formula / Normal
BMI	weight (kg) / height² (m²)
MUAC	Mid-upper arm circumference
TSF	Triceps skinfold thickness
MAMC	MUAC − (3.14 × TSF)

Indicators for nutrition support: BMI <18.5 kg/m² with >10% weight loss (3–6 mo); BMI <20 kg/m² with >5% weight loss (3–6 mo).

Caveat Anthropometry is altered by fluid shifts in critically ill patients.

B — Biochemistry

Test	Significance
Albumin	Falls in malnutrition/inflammation; not reliable acutely
CRP, WBC	Markers of inflammation
Hb / HbA1c	Nutritional anaemia / diabetes control
Electrolytes (Na&spplus;, urea, Ca²&spplus;, PO₄³&supminus;)	Assess renal function, refeeding risk

C — Clinical evaluation: symptoms (nausea, vomiting, early satiety, dysphagia, reflux, diarrhoea, constipation); past history (malignancy, IBD, liver disease, stroke, Parkinson’s, dementia); malabsorptive states (short bowel, high-output stoma, enterocutaneous fistula, pancreatic insufficiency).

D — Dietary assessment: estimate intake using diet diary; compare to energy requirement (25–35 kcal/kg lean body weight); consider recent/anticipated decreased intake (>5 days) → initiate nutritional support.

MUST Tool (Malnutrition Universal Screening Tool)

Parameter	Score 0	Score 1	Score 2
BMI (kg/m²)	≥20	18.5–20	<18.5
Weight loss (3–6 mo)	≤5%	5–10%	>10%
Acute disease	–	–	Add 2 if likely no intake ≥5 days

Total score	Risk	Action
0	Low	Routine care
1	Medium	Observe, document intake for 3 days
≥2	High	Dietician referral, nutritional support

Follow-up: hospital — weekly; care homes — monthly; community — yearly (>75 yrs).

If height/weight unavailable: use recalled/measured surrogate (e.g. knee height), clinical impression (thin/average/obese), or clues like loose clothes, decreased appetite, dysphagia, disease causing weight loss.

Key takeaways Energy: 25–30 kcal/kg IBW/day (max 30 in severe stress) · Protein: 1.5 g/kg IBW/day · Carbohydrate: 45–65% calories · Fat: 20–35% calories (100–200 g/week in PN) · Caution — refeeding: start ≤50% of needs · Screening: MUST tool is standard for malnutrition risk · Assessment: ABCD — Anthropometry, Biochemistry, Clinical, Dietary