Peri Operative Considerations

. Pulmonary complications A. Blood Gas:

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pO2 = 7(FiO2 where pO2 is the normal value for a given FiO2 is the percent spired oxygen and pCOs is the value taken from the test result. 

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Aa gradient = normal pO2 - test result pO2. 

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Percent physiologic shumt = Aa gradient /20.

B. Thromboembolism:

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common problem especially with hip procedures. 

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Risk factors: a history of thromboembolism, obesity, malignancy, age, congestive heart failure, birth control pill use, varicose veins, smoking, general anaesthetics, increased blood viscosity, immobilization, paralysis d pregnancy.

1. Deep venous thrombosis (DVT):

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venography: 97% accurate (70% for iliac veins). 

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125

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impedance plethysmography: sensitivity is poor. 

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duplex ultrasonography (B mode): sensitivity for DVT proximal to bifurcation is 90%. 

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Doppler imaging: bedside tool. 

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Prophylaxis such as heparin, coumadin (warfarin), aspirin, dextran, pneumatic compression,

l-labelled fibrinogen: false positive at operative site. 

enoxaparin are important in morbidity and mortality. Coumadin can be reversed with Vitamin K or fresh frozen plasma.

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Treatment is by heparin then followed by warfarin therapy for the next 3 months. All thigh DVTs need treatment, but those below popliteal fossa may not. Patients with preoperative finding of DVT require vena cava filter.

2. Pulmonary embolism (PE):

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suspected in postoperative patients with acute onset of pleuritic pain, tachypnoea (90%) and tachycardia (60%).

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ECG shows right bundle branch block, right axis deviation in 25%, may show ST depression or T wave inversioni lead III.

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Chest X ray will hardly show hyperlucency and ABGs may show normal PaOs but this does not exclude PE.

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V/Q scan may show the site of embolus but otherwise pulmonary angiography is the gold standard.

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Treatment with heparin (continuous IV infusion) and its efficacy is monitored with partial thromboplastin time (PTT) for 7-10 days then followed by oral warfarin for 3 months which is monitored using prothrombin time (PT).

 

3. Coagulation: a) intrinsic pathway: initiated by factor XII touching the exposed collagen in blood vessels. monitored by PTT. b) extrinsic pathway: initiated y presence of thromboplastin in the circulation due to cellular injury, monitored by PT>. c) platelet function is measured by bleeding time test. Fibrinolytic system is responsible in dissolving clot by converting plasminogen to plasmin and plasmin dissolves the clot. C. Adult Respiratory Distress Syndrome (ARDS):

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acute respiratory failure following pulmonary edema. Initiated by trauma, shock, infection etc. 

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Aetiologies: pulmonary infection, sepsis, fat embolism, microembolism, aspiration, fluid overload, atelectasis, oxygen toxicity, pulmonary contusion, head injury.

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manifested as tachypnoea, dyspnoea, hypoxemia, decreased lung compliance. Diagnosis can be made using ABGs following a long bone fracture.

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50% mortality rate. 

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Treatment is by ventilation with PEEP, but best avoided by early stabilization of long bone fractures.

D. Fat embolism: •

24-72 hrs after incidence of long bone fractures in 3-4% of patients.

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fatal in 10-15%. 

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manifested as tachypnoea, tachycardia, mental status changes and upper extremity petechiae.

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aetiologies: bone marrow fat (mechanical theory), chylomicron changes due to stress (metabolic theory).

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Ventilation-perfusion deficit resulted consistent with ARDS.

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Treatment is by ventilation with high levels of PEEP, but can be prevented by early stabilization of the fracture.

E. Pneumonia:

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aspiration pneumonia in patients with decreased mentation, supine position and decreased GI motility.

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Preventative measures: raising the bed’s head, use of antacids and metoclopramide

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Treatment by IV antibiotics and pulmonary toilet.

F. Pulmonary complications of orthopaedic disorders include scoliosis, Marfan syndrome. II. Non pulmonary complications A. Nutrition

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sufficient nutrition prior to elective surgery, otherwise complications such as wound dehiscence,

infection, pneumonia and sepsis can occur.

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indicators: arm muscle circumference size (best indicator), anergy panels, albumin levels, transferrin levels.

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atrophy of the intestinal mucosa can occur from lack of enteral feeding which then causes bacterial translocation. Early elemental feeding through a jejunostomi tube helps multiple trauma patients from complications.

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Full enteral or parenteral nutrition should be given since energy requirement is elevated during stress. Protein supplements are beneficial in patients at risk of developing multi organ failure.

B. Myocardial infarction (MI)

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identified by acute chest pain, radiation, EKG changes. Confirmed by elevated cardiac enzymes.

  Risk factors include age, smoking, increased cholesterol, hypertenson, aortic stenosis, history of coronary artery disease, diabetes, family histori of heart problems. C. GI complications

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ileus : treated with nasogastric suction and antacids. Common in diabetic with neuropathy.

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upper GI bleeding: risk factors include history of ulcers, NSAID use and smoking. Treated by lavage, ntacids and H2-blockers, vasopressin at left gastric artery may be required for more serious cases.

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Ogilvie syndrome: can follow total joint replacement surgery. Signified by caecum distention. If caecum > 10 cm on abdominal X-ray, decompression thru colonoscopy is required.

D. Decubitus ulcers

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risk factors include advanced age, critical illness and neurologic impairment.

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usually at sacrum, heels and buttocks.

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increase the risk of infections and morbidity. Once there, debridement and sometimes soft tissue flaps are required for healing.

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prevented by constant changing of position, special mattresses and treatment of systemic illness and malnutrition.

E. Urinary tract infections (UTI)

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most common nosocomial infections.

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resulting in increased risk of infections at joint following TJA.

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Preoperatively, should be treated sufficiently. Preoperative catherisation may reduce the rate of postoperative UTI. Catheter is removed 24 hrs postoperatively.

F. Prostatic hyperplasia

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results in urinary retention and increased risk of UTI.

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Should be sought before the surgery based on history, physical examination especially PR and

urine flow studies < 17 ml/s peak flow rate. G. Acute tubular necrosis

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results in renal failure in trauma patients.

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Early treatment includes alkalisation of urine.

H. Genitourinary injury

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Retorgrade urethrogram is used to find lower urinary tract injury.

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Risks increased with the use of NSAID. Should be suspected in patients with displaced anterior pelvic fractures.

I. Shock

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insufficient perfusion to vital tissues and organs.

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Hypovolaemic shock: due to volume loss - resulting in decreased cardiac output (CO), increased peripheral vascular resistance (PVR) and venous construction. Treated by Ringer’s lactate fluid, then blood transfusion. Massive blood replacement requires fresh frozen plasma and platelets. Urine output shows the adequacy of fluid resuscitation. Insufficient fluid resuscitation can result in metabolic acidosis.

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Cardiogenic shock: due to ineffective pumping - resulting in decreased CO, increased PVR, venous dilation.

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Vasogenic shock: due to PE or pericadial tamponade - arteriolar constriction, venous dialtion.

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Neurogenic shock/ septic shock: due to blood pooling- arteriolar, capillary and venous dilation.

J. Compartment syndrome covered in Chapter 10,Trauma. III. Intraoperative consideration A. Anaesthesia

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local anaesthesia may allow quicker recovery, decreased blood loss and fewer postoperative complications.

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reduced blood loss with controlled hypotension during surgery - by nitroprussode, nitroglycerine, isoflurane.

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Patients with neuromuscular disorders (Duchenne’s muscular dystrophy, arthrogryposis, osteogenesis imperfecta) should be suspected for malignant hyperthermia (autosomal dominant, hypermetabolic disorder of skeletal muscles) following the use of anaesthetics especially halothatne and succinylcholine. Disease is marked by muscle rigidity, hypermetabolism, masseter muscle spasm, increased temperature and acidosis due to defect of cell membrane affecting calcium transport. For defintivie diagnosis, muscle biopsy is required. Treated by dantrolene, electrolytes balance, increased urinary output, respoiratory support and cooling.

B. Spinal cord monitoring

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usually testing the posterior column.

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Somatosensory cortical evoked potentials (SCEP) monitors spinal cord by evoking response from stimulation of peripheral areas.

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Somatosensory spinal evoked potentials (SSEP) are more invasive but more sensitive. Preoperative recordings are compared to the ones measured at critical times durnig surgery.

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The wake up test is the standard, done by patients responds in moving the peripheral parts according to commands upon lightening of anaesthesia.

C. Torniquet

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can result to injury of nerve and muscle underneath it.

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prevented by careful application, wide cuffs, lower pressure (200 mmHg in upper extremity and 250 mmHg or 100-150 mmHg above systolic in lower extremity), double cuffs.

IV. Other problems A. Pain control

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acute implies the presence of potential tissue damage whereas chronic (3-6 months) does not.

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Postoperative control of pain can be mediated at the nociceptors, decrease transduction of the nerve A and C fibers, dorsal column, spinothalamic tract, thalamus (local prostaglandin inhibitors, long acting local anaesthetics); increase modulation of brain stem centres or production of endogenous opiates (perispinal and sstemic opiates).

B. Transfusion •

transfusion reactions

* allergic reaction: most common, occurs at the end of transfusion. Chills, pruritus, erythema and urticaria results but usually resolved spontaneously. Pretreated by diphenhydramine/Benadryl and hydrocortisone in patients with history of allergy. * febrile reaction: occurs after the initial 100-300cc of packed RBCs transfusion. Chills and fevers due to antibody reactoin to foreing WBCs. Treatment is as allergy. * hemolytic reaction: occurs early in the transfusion. Signified by chills, fever, tachycardia, chest tightness, flank pain. Treated by stopping the transfusion, IV fluids, appropriate lab studies and monitoring in intensive care. •

transfusion risks

* hepatitis, cytomegalovirus, HTLV-1 and HIV. * donors deferral of high risk individuals and more effective screening methods decrease the prevalence. •

alternative to homologous blood transfusion

* autologous deposition: At least Hb=11 and Hematocrit of 33%. Iron supplement during donation is routine. Storage of several units of blood prior to elective surgery with anticipated blood loss. Need adequate times between the donation and surgery.

* cell saver- intraoperative autotransfusion: 400 ml blood loss to recover 250 ml. Can be used for only 4 hours at one time. * autotransfusion: postoperative drain recuperation is used. * acute preoperative normovolemic hemodilution: storage of autologous blood (replaced by crystalloids) preoperatively for immediate use of intra/postoperatively. * pharmacologic intervention: desmopression (ADH) analogue to increase level of factor VIII, recombinant erythropoietin to increase erythropoiesis and synthetic erythrocyte substitutes. * judicious use of blood products: platelet transfusion in massve bleeding or coagulopathies. Fresh frozen plasma for patients with massive bleeding and abnormal coagulation tests. Cryoprecipitate for haemophilia and for consumptive coagulopathis as a source of fibrinogen. C. Heterotopic ossification

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seen after THA, in head injured patients and in elbow injuries patients.

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Prophylaxis during THA: indomethacin. Diphosphonate does not prevent formation of osteoid matrix since the matrix calcifies after discontinuation of medication. Etidronate sodium prevents bone resorption at low dose and bone mineralisation at high dose.