A scalpel, or lancet, is a small and extremely sharp bladed instrument used for surgery, anatomical dissection, and also for various arts and crafts (called a hobby knife). Scalpels may be single-use disposable or re-usable, and recently Safety Scalpels are the norm in the Operating Rooms. Re-usable scalpels can have permanently attached blades that can be sharpened or, more commonly, removable single-use blades. Disposable scalpels usually have a plastic handle with an extensible blade (like a utility knife) and are used once, then the entire instrument is discarded. Scalpel blades are usually individually packed in sterile pouches but are also offered non-sterile. Double-edged scalpels are referred to as “lancets”.
Scalpel blades are usually made of hardened and tempered steel, stainless steel, or high carbon steel; in addition, titanium, ceramic, diamond and even obsidian knives are not uncommon. For example, when performing surgery under MRI guidance, steel blades are unusable (the blades would be drawn to the magnets, or may cause image artifacts). Historically, the preferred material for surgical scalpels was silver, on account of its antimicrobial properties (although the mechanics were not understood at the time). Scalpel blades are also offered by select manufacturers with a zirconium nitride-coated edge to improve sharpness and edge retention. Others manufacture blades that are polymer-coated to enhance lubricity during a cut. Alternatives to scalpels in surgical applications include electrocautery and lasers.
Reusable handle (top) and disposable scalpels (bottom):
Surgical scalpels consist of two parts, a blade and a handle. The handles are often reusable, with the blades being replaceable. In medical applications, each blade is only used once (even if just for a single, small cut).
Types of Surgical Scalpel
Electrosurgery is the application of a high-frequency (radio frequency) alternating polarity, electrical current to biological tissue as a means to cut, coagulate, desiccate, or fulgurate tissue. Its benefits include the ability to make precise cuts with limited blood loss. Electrosurgical devices are frequently used during surgical operations helping to prevent blood loss in hospital operating rooms or in outpatient procedures.
In electrosurgical procedures, the tissue is heated by an electric current. Although electrical devices that create a heated probe may be used for the cauterization of tissue in some applications, electrosurgery is usually used to refer to a quite different method than electrocautery. Electrocautery uses heat conduction from a probe heated to a glowing temperature by a direct current (much in the manner of a soldering iron). This may be accomplished by direct current from dry-cells in a penlight-type device.
Electrosurgery, by contrast, uses radio frequency (RF) alternating current to heat the tissue by RF induced intracellular oscillation of ionized molecules that result in an elevation of intracellular temperature. When the intracellular temperature reaches 60 degrees C, instantaneous cell death occurs. If tissue is heated to 60-99 degrees C, the simultaneous processes of tissue desiccation (dehydration) and protein coagulation occur. If the intracellular temperature rapidly reaches 100 degrees C, the intracellular contents undergo a liquid to gas conversion, massive volumetric expansion, and resulting explosive vaporization.
Appropriately applied with electro surgical forceps, desiccation and coagulation result in the occlusion of blood vessels and halting of bleeding. While the process is technically a process of electrocoagulation, the term "electrocautery" is sometimes loosely, nontechnically and incorrectly used to describe it. The process of vaporization can be used to ablate tissue targets, or, by linear extension, used to transect or cut tissue. While the processes of vaporization/ cutting and desiccation/coagulation are best accomplished with relatively low voltage, continuous or near continuous waveforms, the process of fulguration is performed with relatively high voltage modulated waveforms. Fulguration is a superficial type of coagulation, typically created by arcing modulated high voltage current to tissue that is rapidly desiccated and coagulated. The continued application of current to this highly impedant tissue results in resistive heating and the achievement of very high temperatures - enough to cause breakdown of the organic molecules to sugars and even carbon, thus the dark textures from carbonization of tissue.
Diathermy is used by some as a synonym for electrosurgery but in other contexts diathermy means dielectric heating, produced by rotation of molecular dipoles in a high frequency electromagnetic field. This effect is most widely used in microwave ovens or some tissue ablative devices which operate at gigahertz frequencies. Lower frequencies, allowing for deeper penetration, are used in industrial processes.
RF Electrosurgery is commonly used in virtually all surgical disciplines including dermatological, gynecological, cardiac, plastic, ocular, spine, ENT, maxillofacial, orthopedic, urological, neuro- and general surgical procedures as well as certain dental procedures.
RF Electrosurgery is performed using a RF electrosurgical generator (also referred to as an electrosurgical unit or ESU) and a handpiece including one or two electrodes - a monopolar or bipolar instrument. All RF electrosurgery is bipolar so the difference between monopolar and bipolar instruments is that monopolar instruments comprise only one electrode while bipolar instruments include both electrodes in their design.
The monopolar instrument called an "active electrode" when energized, requires the application of another monopolar instrument called a "dispersive electrode" elsewhere on the patient's body that functions to 'defocus' or disperse the RF current thereby preventing thermal injury to the underlying tissue. This dispersive electrode is frequently and mistakenly called a "ground pad" or "neutral electrode". However virtually all currently available RF electrosurgical systems are designed to function with isolated circuits - the dispersive electrode is directly attached to the ESU, not to "ground". The same electrical current is transmitted across both the dispersive electrode and the active electrode, so it is not "neutral". The term "return electrode" is also technically incorrect since alternating electrical currents refer to alternating polarity, a circumstance that results in bidirectional flow across both electrodes in the circuit.
Bipolar instruments generally are designed with two "active" electrodes, such as a forceps for sealing blood vessels. However, the bipolar instrument can be designed such that one electrode is dispersive. The main advantage of bipolar instruments is that the only part of the patient included in the circuit is that which is between the two electrodes, a circumstance that eliminates the risk of current diversion and related adverse events. However, except for those devices designed to function in fluid, it is difficult to vaporize or cut tissue with bipolar instruments.
Neural and muscle cells are electrically-excitable, i.e. they can be stimulated by electric current. In human patients such stimulation may cause acute pain, muscle spasms, and even cardiac arrest. Sensitivity of the nerve and muscle cells to electric field is due to the voltage-gated ion channels present in their cell membranes. Stimulation threshold does not vary much at low frequencies (so called rheobase-constant level). However, the threshold starts increasing with decreasing duration of a pulse (or a cycle) when it drops below a characteristic minimum (so called chronaxie). Typically, chronaxie of neural cells is in the range of 0.1–10 ms, so the sensitivity to electrical stimulation (inverse of the stimulation threshold) decreases with increasing frequency in the kHz range and above. (Note that frequency of the alternating electric current is an inverse of the duration of a single cycle). To minimize the effects of muscle and neural stimulation, electrosurgical equipment typically operates in the radio frequency (RF) range of 100 kHz to 5 MHz.
Operation at higher frequencies also helps minimizing the amount of hydrogen and oxygen generated by electrolysis of water. This is especially important consideration for applications in liquid medium in closed compartments, where generation of gas bubbles may interfere with the procedure. For example, bubbles produced during an operation inside an eye may obscure a field of view.
There are several commonly used electrode configurations or circuit topologies:
With "bipolar" instruments the current is applied to the patient using a pair of similarly-sized electrodes. For example, special forceps, with one tine connected to one pole of the RF generator and the other tine connected to the other pole of the generator. When a piece of tissue is held by the forceps, the RF alternating polarity electrical current oscillates between the two forceps tines, heating the intervening tissue by the previously described synchronous oscillation of intracellular ions.
In monopolar configuration the patient is attached to the dispersive electrode, a relatively large metal plate or a flexible metalized plastic pad which is connected to the RF generator or electrosurgical unit (ESU). The surgeon uses a pointed or blade shaped electrode called the "active electrode" to make contact with the tissue and exert a tissue effect...vaporization, and it's linear propagation called electrosurgical cutting, or the combination of desiccation and protein coagulation used to seal blood vessels for the purpose of Hemostasis. The electric current oscillates between the active electrode and the dispersive electrode with the entire patient interposed between the two. Since the concentration of the RF current reduces with distance from the active electrode the current density rapidly (quadratically) decreases. Since the rate of tissue heating is proportional to the square of current density, the heating occurs in a very localized region, only near the portion of the electrode, usually the tip, near to or in contact with the target tissue.
On an extremity such as a finger, there is limited cross-sectional area to disperse the current, a circumstance which might result in higher current density and some heating throughout the volume of the extremity.
Another bipolar instrument is characterized with both electrodes on the same design, but the dispersive electrode is much larger than the active one. Since current density is higher in front of the smaller electrode, the heating and associated tissue effects take place only (or primarily) in front of the active electrode, and exact position of the dispersive electrode on tissue is not critical.