7/30/2019 Beach Chair Position May Decrease Cerebral Perfusion

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NEWSLETTERVolume 22, No. 2, 25-40 Circulation 81,489 Summer 20

www.apsf.org The Official Journal of the Anesthesia Patient Safety Foundatio

Inside:

Review of Maternal Arrest Cases ............................ .................................. ..........................Page 28

Cardiology Perspective on Stents................................... ................................. ....................Page 32

Dear SIRS: Alarm Requires Selection of Heart Rate Source ................................ ........Page 34

Donor List..................................................................................................................................Page 35

Case Report: Wrap Delays Detection of Disconnect ............................... .........................Page 36

Q&A: Pipeline Pressure Primer...................... ................................. ................................. ....Page 38

by David J. Cullen, MD, and Robert R. Kirby, MD

Case Presentation

A 47-year-old, healthy female underwent generalanesthesia for shoulder arthroscopy. Preoperativeblood pressure (BP) was 125/83 mmHg. After pre-medication with 50 mg of meperidine, 40 mg hydrox-

yzine, and 0.2 mg glycopyrrolate intramuscularly,anesthesia was induced with 200 mg propofol, 100mg succinylcholine, and 30 mg lidocaine. Becauseshe was hypertensive, just prior to induction, 50 mgof labetalol was given intravenously. Anesthesia wasmaintained with 2% isoflurane, 60% nitrous oxide,and oxygen. The patient was placed in the barber-shop position for the surgery. Twenty minutes intothe case, blood pressure decreased to 100/60 mmHgand then remained in the 80-90 mmHg systolic rangefor the remainder of the case. Oxygen saturation was100% and end tidal CO2 values were in the 30sthroughout the case. Upon arrival in the post-anes-thesia care unit (PACU), her blood pressure was113/60 mmHg but she did not awaken. Naloxone

0.1 mg was given intravenously, but she remainedunresponsive and did not move her extremities.Another 0.1 mg of naloxone was given 35 min afterarrival in the PACU followed by 3 more doses ofnaloxone and 2 doses of physostigmine. During thistime, her trachea remained intubated and she waswell oxygenated. Neurologic evaluation suggested adiencephalic syndrome, possibly brain infarction.She was unresponsive to voice commands or painfulstimuli, and reflexes were decreased bilaterally. Acomputer axial tomography (CAT) scan of the headwas normal initially, but 5 days later suggested brainswelling and obliteration of the cistern. Magnetic res-

resistance increase. Under nonanesthetized contions, these effects are compensated for by an increin systemic vascular resistance by up to 50-80%. Hoever, this autonomic response is blocked by vasodiing anesthetics, which further exacerbate acompromise cardiac output. Blood pressure remaunchanged or increases slightly in nonanesthetiz

patients in the sitting position but decreases in anesthetized state. Cerebral perfusion pressure (Cdecreases by approximately 15% in the sitting positin non-anesthetized patients and could furtdecrease under anesthesia because of vasodilatand impaired venous return. Venous return fromcerebral circulation is usually increased by inspiratsubatmospheric pressure during spontaneous velation, but this mechanism is nullified by positpressure ventilation. Obstruction of the interjugular veins in the sitting position may also impcerebral venous drainage, especially with unfavorapositions of the head and neck, such as flexion of head. Pohl and Cullen reported a series of case2005 that documented blood pressure decreases raing from 28-42%; consequently, hypotension wthought to be a likely cause of ischemic brain injuGiven the potential for peripheral vasodilatation amyocardial depression that can occur in patients ware anesthetized with potent intravenous and inhational drugs, the effects of the upright position aanesthesia synergize.

Cerebral autoregulation has been thoughtmaintain cerebral blood flow (CBF) constbetween MAP of 50-150 mmHg. However, it mbe remembered that in poorly controlled hypertsive patients, autoregulation of CBF is shifted to right, requiring higher CPP/MAP to ensure aquate cerebral perfusion. In recent years, Drummoand others have emphasized that the quoted value

50 mmHg for the lower limit of autoregulation (LLshould be modified upward to reflect a rangevalues from 70-93 mmHg with a mean value of 80mmHg rather than the specific number of 50 mmHSome orthopedic surgeons request deliberhypotension for shoulder surgery. With the acqucence of the anesthesiologist or the nurse anesthetdeliberate hypotension to mean arterial pressure50-60 mmHg eliminates any margin for error in cblood pressure falls further. In addition, neither surgeon nor the anesthesiologist nor the CRNA tycally seems to consider the added effect of the beachair position on cerebral perfusion.

See Perfusion, Page

onance imaging (MRI) 1 week later showed changesin both cerebral hemispheres suggesting corticalinfarcts, involvement of the anterior and medial tem-poral lobe bilaterally, no significant edema, and nosignificant herniation. At no time was there any evi-dence of an intracranial bleed. After 2 weeks, herGlasgow coma scale was 3; her fundi were clear and

crisp. She had corneal reflexes, a positive gag, andnegative dolls eyes; she was hyperreflexive withincreased tone and was unresponsive to noxiousstimuli in all 4 extremities. She is expected to remainin a persistent vegetative state.

Considerations When Using theBeach Chair Position

The beach chair (barbershop) position wasdeveloped in the 1980s for orthopedic shoulderarthroscopy procedures. Patients are sat up atangles varying from 30-90 above the horizontalplane with appropriate padding and with the headsecured in a headrest. Injuries to the brachialplexus are reduced compared to the lateral decubi-tus position, and the surgeon has excellent access tothe shoulder. The position helps the surgeonbecause the weight of the arm distracts the shoul-der joint while avoiding distortion of the intra-articular anatomy.

However, significant changes can develop whenpatients are moved to the upright position. Mean arte-rial pressure (MAP), central venous pressure (CVP),pulmonary artery occlusion pressure (PAOP), strokevolume, cardiac output, and PaO2 all decrease whilethe alveolar-arterial oxygen gradient (PAO2-PaO2),pulmonary vascular resistance, and total peripheral

Beach Chair Position May Decrease Cerebral PerfusionCatastrophic Outcomes Have Occurred

7/30/2019 Beach Chair Position May Decrease Cerebral Perfusion

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APSF NEWSLETTER Summer 2007 PAGE

pressure. If the beach chair position is combined withthe use of deliberate hypotension, cerebral perfusionwill be severely compromised. An even more exag-gerated occurrence may develop when the BP cuff

must be placed on the leg because the contralateralarm is not available for BP measurement, e.g., in apatient with prior lymph node dissection for breastcancer. In the beach chair position, the legs are consid-erably lower than the trunk, therefore the BP differ-ence between the BP cuff measured on the leg and theBP in the brain will be even greater than the gradientbetween the arm and the brain.

The following case illustrates this point. A 54-year-old woman underwent left shoulder replace-ment surgery in the beach chair position. The patienthad no history of hypertension or myocardial infarc-tion. Preoperative electrocardiogram, echocardio-gram, thallium scan, and exercise tolerance test werenormal. The patient received an interscalene block

with 40 ml of 0.5% bupivacaine with epinephrine(1:200,000). Because of a previous mastectomy, a 20-gauge intravenous catheter was placed in the rightfoot and a noninvasive BP cuff was placed on the calf.There was no documentation that the calf BP was val-idated to the left arm BP before the patient was anes-thetized and the left arm became unavailable. Noarterial catheter was placed although deliberatehypotension was used. Anesthesia was induced with100 mg propofol, 250 mg sodium pentothal, 50 mgrocuronium, and 250 mcg fentanyl. Anesthesia wasmaintained with 3.5% sevoflurane and 67% nitrousoxide in oxygen. Nitroglycerin, 50 mcg times 3 doses,and labetalol, 5 mg times 4 doses, were used to pro-duce deliberate hypotension. One hour after induc-tion, her systolic BP was between 85-100 mmHg. Twohours later, her BP was 70/40 mmHg and thenremained around 90/60 mmHg for the next 40 min,when it decreased to 50/25 and was treated withphenylephrine. Electrocardiography showed sinusrhythm throughout, oxygen saturations were alwayshigh, and end-tidal CO2 was in the high 20s for most ofthe case. In the PACU, emergence was delayed, andshe did not breathe spontaneously. A radial arterycatheter was finally placed while she was in thePACU, and BPs were normal. Apnea persisted and herpupils were fixed and dilated. Blood gas analysis oncontrolled ventilation showed a PaO2 of 236 mmHg,PaCO2 of 35 mmHg, and pH of 7.4, with glucose of 92mg/dl. Neurologic evaluation revealed brain deathwith no CBF, flat electroencephalogram, no reflexes,

no response to pain, and no lesions on the CAT scan.At autopsy the upper spinal cord and medulla wereinfarcted. The anesthesia equipment tested normal. Inthis case, not only was deliberate hypotension used tovery low values, but BP was measured in the leg whilethe patient was in the sitting position. One can onlyimagine how low the BP was in the brain when BP inthe leg was 70/40 or 90/60.

In addition to avoiding deliberate hypotension,one must be extremely vigilant and treat aggressivelythe unexpected hypotension that often occurs duringanesthesia in the beach chair position for the reasonsenumerated above. These treatments are well knownto all anesthesia providers and include careful controlof the inhalation anesthetic concentration, adequate

and timely fluid administration, and vasopressor infu-

sion, as needed during the time of the procedure whthe patient is upright and at risk.

Head position is also important because so

degree of head manipulation is required when potioning the patient in the seated position. Most sgeons use a headrest to immobilize the head. Sevestudies suggest that CBF can be compromisedmechanical obstruction and injury to major veinsarteries. Blood flow reduction in the vertebral artcaused by extension and rotation or tilt of the hemay result in posterior brain circulation infarcts.

Finally, hypotension and generalized circulatinstability can result from gas embolism. This rcomplication has been reported with both air acarbon dioxide distension of the joint capsule flowed by pressurized injection of irrigation fluThus, anesthesiologists and CRNAs should keep possibility of venous gas embolism in mind durishoulder arthroscopy in the sitting position if suddcardiovascular collapse occurs.

SummaryDespite its low incidence, intraoperative stro

associated with shoulder surgery, particularlyhealthy patients at no risk for stroke, is a totally unpected and devastating complication. Patients in beach chair position are at risk for an intraoperatstroke if borderline low BPs, as measured in the arare used without appreciating the effect on CPP aCBF. Because of the specific physiologic changes asciated with the sitting position, great care shouldapplied when using and interpreting BP cuff msurements in the nonoperative arm or, even moreif leg measurements of BP must be used. Blood prsure values