Lesson 2 ppt notes.docx

Pt positioning is a team responsibility Cardiovascular changes Venous return compromised by paralysis, neuraxial blockage, PPV, and general anesthesia Sitting, reverse Trendelenburg, anything feet down head up – blood pressure decrease and preload decreases Trendelenburg – increase in preload and B...

Pt positioning is a team responsibility Cardiovascular changes Venous return compromised by paralysis, neuraxial blockage, PPV, and general anesthesia Sitting, reverse Trendelenburg, anything feet down head up – blood pressure decrease and preload decreases Trendelenburg – increase in preload and BP, increase ICP, venous pooling and congestion of vessels in head FRC decreases from standing to supine VQ mismatch in lateral position Supine (dorsal decubitus) Most common and least harmful for pt FRC decreased and venous return improved Pressure points in supine position Arms out (less than 90 degrees), supinated or tucked Brachial plexus can be compressed if not Elbow should be padded to protect ulnar nerve Frog leg position Hips and knees are flexed and hips externally rotated Access to groin, rectum, and inner thigh Keep knees supported to reduce injury Trendelenburg and reverse Trendelenburg Used to expose intraabdominal and pelvic contents during laparoscopic or robotic surgery Avoid shoulder braces to prevent brachial plexus injuries Trendelenburg Increased venous return Increased intraabdominal pressure Cephalad displacement of diaphragm Decrease FRC Increased work of breathing and PAP – insufflation will add to increase increased ICP and IOP Stomach above airway – put NG/OG Limit fluids Long times in Trendelenburg can cause swelling in face and airway Robot surgery Watch face for people leaning or hitting Need to pad the face Usually performed with pts in steep Trendelenburg Airway swelling Most common in Trendelenburg and prone, surgical cases around neck Limit fluids after positioning Leak test – deflate cuff and listen to air around cuff before extubation Reverse Trendelenburg Increased FRC Decrease preload and BP and brain perfusion Insufflation on preload Introduction of gas (usually CO2) into cavity Pressure can occlude vena cava and impair preload Always want to check hemodynamics prior to insufflation Insufflation happens and pt is bradycardic and hypotensive Stop insufflation Give anticholinergic/antimuscarinic e.g. Glycopyrrolate (preferred) or atropine Strap and platform Complications Pressure alopecia – prevent pressure on parts of head Lordosis is lost when pt paralyzed – back pain common Ulnar nerve injury is the most common nerve injury Lithotomy Hips flexed and legs out held by stirrups Types of stirrups Allen stirrups Candy cane – cause peroneal nerve injuries Knee cradles Avoid bucking in stirrups Complications Legs up = increased preload – increased CO, CVP, and ICP Increased abdominal pressure increased – decreased FRC, TV Caution for finger damage Compartment syndrome Peroneal nerve injury most common, femoral nerve, obturator nerve, saphenous nerve Compartment syndrome Lateral decubitus For lungs, hip, kidney, colonoscopy Head must be neutral to prevent brachial pressure Ear flat and in hole of pillow Watch pressure on face on down side Axillary roll to keep pressure off shoulder but not in axilla Put pulse ox on down arm, BP cuff opposite of IV arm, pulse ox opposite of BP cuff Hip pressure can lead to rhabdomyolysis VQ mismatch that happens when in the lateral position Ventilation better in upper lung, perfusion better in down lung One lung ventilation complicates matters – HPV = hypoxic pulmonary vasoconstriction Kidney rest Pt must be in right position or the IVC can be compressed Park bench Semi-prone position where pt looks like they’re trying to look at the floor Posterior fossa surgical access Rhabdomyolysis Risk factors = prolonged surgical time, hypotension, obesity, downward pressure from strap Bean bag Can be used to position lateral or Trendelenburg pts Bag is molded and attached to suction Prevents pts from sliding or tilting Prone (ventral decubitus) Surgical access to structures on posterior Cardiac function similar to supine Pulmonary function may be better if intraabdominal position is reduced Eyes free from pressure with q 15 min checks Arms in superman position i.e. in front of pt Flipping Lines, foley, intubation before flip You should be at the head Put pt at FiO2 100% to increase FRC Disconnect lines and monitors as appropriate After positioning, reassess position of ETT and vital signs Increased abdominal pressure will increase intrathoracic pressure – decreased FRC, decreased pulmonary compliance, increased PAP Compress vena cava and impede venous return – decreased BP Can lubricate eyes in prone cases Complications Increased airway edema – cuff leak test Blindness Skin can tear when edematous Facial swelling Pressure injuries Albumin can be used to decreased third spacing Most common eye injury is corneal abrasion Postoperative blindness can be caused by ischemic optic neuropathy or central retinal artery occlusion Ischemic optic neuropathy Rare Decreased perfusion so less blood flow to eyeball Retinal artery occlusion From direct pressure (external) or embolus (internal) Mayfield tongs = head holder via pins screwed to skull Used in neurosurgery and posterior cervical surgery Pt will have a hemodynamic response – must be properly anesthetized What happens if pt moves? Subdural tear and dural bleed When you can’t paralyze pt, can use opioids instead Jackknife position Used for rectal or anal surgeries Knee pressure is increased – pad the knees Knee chest pt Used for lumbar laminectomies or sigmoidoscopies Rarely used Severe hypotension from pooling in legs Sitting position Posterior cervical spine and posterior fossa surgery Arms must be positioned to slightly elevate the shoulders Venous air embolism Mill wheel murmur Decreased ETCO2 Increased in RA and PA pressures Increase in end-tidal N2 Sudden attempts to breath i.e. gasp reflex Detection = TEE (Gold standard but most invasive), esophageal stethoscope, precordial stethoscope, ETCO2 Treatment Surgeon floods the surgical field and occlude air entry site Aspirate air via right atrial catheter Discontinue N2O if using Place pt in lateral left position Beach chair Used for shoulder surgeries Complications = neurologic injury, hypotension, bradycardia, cervical flexion if head not secured Excessive cervical flexion impedes venous and arterial flow Keep 2 finger breaths between mandible and sternum ETT obstruction and tongue swelling Can get diffuse cerebral edema secondary to ischemia in sitting or beach chair position MAP is about 10-15 lower at head Zero art line at tragus Positioning Types of injuries / resulting deficits Pressure injuries = pt unable to sense pressure or reposition Compartment syndrome: damage to neural and vascular structures as a result of increased pressures and decreased tissue perfusion in muscles with tight, fascial borders More common in lower extremities but can occur in upper extremities or abdomen (tight wound closures) In lithotomy position, legs should be lowered every 2-3 hour Nerve injuries Occurs when peripheral nerves are subjected to compression, stretch, ischemia, metabolic derangement, and trauma during surgery All ultimately due to some type of ischemia Ulnar nerve is most commonly injured and causes a claw hand Brachial nerve is second most common Root cause is ischemia secondary to stretching, compression, or vessel occlusion Compression e.g. failure to use axillary roll, injury from frequent BP checks, use of shoulder braces Stretch e.g. femoral nerve kinked under inguinal ligament in exaggerated lithotomy position, brachial plexus after arm falls off armboard Transection e.g. surgeon inadvertently cuts nerve Damage to peroneal nerve can cause foot drop Factors associated with postoperative nerve injury = muscular physique, smoking, preexisting neuropathy, length of procedure, intraoperative hypotension Eye injuries Corneal abrasions most common due to decreased reflexes and tear production Postoperative vision loss as a result of increased intraocular pressure and decrease in ocular perfusion pressure Ischemic optic neuropathy (ION) is caused by ischemia to part of optic nerve Most common cause of postoperative vision loss in the prone spine surgery pt Central retinal artery occlusion (CRAO) caused by decreased blood supply to entire retina Improper head position that results in external pressure to eye Emboli that migrate to central retinal artery VAE occurrence, identification, treatment Venous air embolism – occurs when air or other gases enter the venous circulation and travel to the right side of the heart or pulmonary vessels Etiology Entrainment of air into an open flowing vein or dural sinus Infusion of air or other gas under pressure into a vein Typical Situations Surgical procedures in which the operative site is above the level of the heart (e.g., sitting craniotomy, cesarean section during externalization of the uterus, shoulder arthroscopy, hip arthroplasty) Surgical procedures requiring insufflation of gas (e.g., laparoscopic surgery) Invasive procedures that expose an open vein to atmosphere during spontaneous ventilation (e.g., CVP placement or disconnection) Any invasive procedure in which the patient is connected to a high-pressure gas source Prevention Avoid positioning the patient such that the surgical field or CVP cannulation site is above the level of the heart if possible Mechanically ventilate the patient when the surgical field must be above the level of the heart Place the patient in Trendelenburg during placement or removal of a CVP Maintain occlusive pressure on CVP decannulation sites for 5 minutes after bleeding has stopped, then place an occlusive dressing over the site Remove all air from IV solution bags and lines (e.g., CPB cannulae, rapid infuser systems) prior to pressurized infusion When there is a risk of VGE, maintain a high CVP with increased administration of IV fluids Avoid administering N2O to patients at risk of VGE Consider placement of multiorifice CVP catheter in patients at high risk of VGE Manifestations The manifestations are determined by the volume of gas embolized in relation to the size of the patient, the rate at which embolization occurs, and the rate at which the gas dissolves in the blood. Detection depends on the monitors in place at the time of the embolic event. In the awake patient: Coughing, dyspnea, bronchospasm, hypotension, altered mental status, and circulatory collapse In the awake or anesthetized patient, manifestations will depend on the monitoring in place at the time of the event ECG changes: Tachyarrhythmias are common, Right heart strain pattern, ST-T wave changes Hemodynamic changes: Systemic hypotension secondary to decreased CO, Increase in CVP due to mechanical obstruction and right heart failure, Increase in PA pressure due to release of vasoactive inflammatory mediators A loud, coarse, continuous “mill wheel” murmur on auscultation Pulmonary signs and symptoms: Crackles (rales) and wheezing, Decreased ET CO2, Increased ET N2; rarely measured (requires mass spectrometer or Raman scattering techniques) Decreased arterial O2 saturation Central nervous system EEG changes may be caused by different mechanisms Cerebral hypoperfusion due to decreased CO Paradoxical embolism to the cerebral circulation through a patent foramen ovale (PFO) TEE: Presence of air in cardiac chambers; Detects as little as 0.02 mL/kg air in right heart; Allows detection of intracardiac paradoxical embolism (most commonly due to a PFO) Precordial Doppler ultrasound: VGE changes character and intensity of emitted sound; Detects as little as 0.05 mL/kg of air in right heart Presence of gas bubble in the aspirate from a multiorifice CVP catheter More than one means of detection should be used in cases at high risk for VGE Management FART = flood, aspirate, remove nitrous, turn to lower site below heart and turn to left side Notify the surgeon immediately of a possible VGE The surgeon should check for possible entry sites in the wound/ flood the wound with saline or pack with wet gauze to stop further air entrapment Attempt to aspirate gas from multiorifice CVP catheter Administer 100% O2 Provide Valsalva maneuver by manual ventilation to prevent further air from entering the heart and to reveal the vascular entry site to the surgeon Infuse IV fluid rapidly Use vasopressors and inotropes as needed to support the circulation (see Event 9, Hypotension) Reposition the patient, if feasible First, tilt the operating table to lower the surgical site below the level of the heart If possible, place patient in left-side-down position Consider applying 5 cm H2O PEEP Perform CPR if cardiac arrest occurs Direct aspiration of air from the heart or great vessels via a thoracotomy may be necessary Internal cardiac massage may be required If VGE to cranial arterial system is suspected, consider emergency MRI and consider hyperbaric O2 therapy if available